// TODO: @cleanup, rigorous cleanup of dead code and silly object-oriented
//  trait impls where I deem them unfit.

use std::fmt;
use std::fmt::{Debug, Display, Formatter};
use std::ops::{Index, IndexMut};

use super::arena::{Arena, Id};
use crate::collections::StringRef;
use crate::protocol::inputsource::*;
use crate::protocol::input_source2::{InputPosition2, InputSpan};

/// Helper macro that defines a type alias for a AST element ID. In this case 
/// only used to alias the `Id<T>` types.
macro_rules! define_aliased_ast_id {
    // Variant where we just defined the alias, without any indexing
    ($name:ident, $parent:ty) => {
        pub type $name = $parent;
    };
    // Variant where we define the type, and the Index and IndexMut traits
    (
        $name:ident, $parent:ty, 
        index($indexed_type:ty, $indexed_arena:ident)
    ) => {
        define_aliased_ast_id!($name, $parent);
        impl Index<$name> for Heap {
            type Output = $indexed_type;
            fn index(&self, index: $name) -> &Self::Output {
                &self.$indexed_arena[index]
            }
        }

        impl IndexMut<$name> for Heap {
            fn index_mut(&mut self, index: $name) -> &mut Self::Output {
                &mut self.$indexed_arena[index]
            }
        }
    };
    // Variant where we define type, Index(Mut) traits and an allocation function
    (
        $name:ident, $parent:ty,
        index($indexed_type:ty, $indexed_arena:ident),
        alloc($fn_name:ident)
    ) => {
        define_aliased_ast_id!($name, $parent, index($indexed_type, $indexed_arena));
        impl Heap {
            pub fn $fn_name(&mut self, f: impl FnOnce($name) -> $indexed_type) -> $name {
                self.$indexed_arena.alloc_with_id(|id| f(id))
            }
        }
    };
}

/// Helper macro that defines a wrapper type for a particular variant of an AST
/// element ID. Only used to define single-wrapping IDs.
macro_rules! define_new_ast_id {
    // Variant where we just defined the new type, without any indexing
    ($name:ident, $parent:ty) => {
        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
        pub struct $name (pub(crate) $parent);

        impl $name {
            pub(crate) fn new_invalid() -> Self     { Self($parent::new_invalid()) }
            pub(crate) fn is_invalid(&self) -> bool { self.0.is_invalid() }
            pub fn upcast(self) -> $parent          { self.0 }
        }
    };
    // Variant where we define the type, and the Index and IndexMut traits
    (
        $name:ident, $parent:ty, 
        index($indexed_type:ty, $wrapper_type:path, $indexed_arena:ident)
    ) => {
        define_new_ast_id!($name, $parent);
        impl Index<$name> for Heap {
            type Output = $indexed_type;
            fn index(&self, index: $name) -> &Self::Output {
                if let $wrapper_type(v) = &self.$indexed_arena[index.0] {
                    v
                } else {
                    unreachable!()
                }
            }
        }

        impl IndexMut<$name> for Heap {
            fn index_mut(&mut self, index: $name) -> &mut Self::Output {
                if let $wrapper_type(v) = &mut self.$indexed_arena[index.0] {
                    v
                } else {
                    unreachable!()
                }
            }
        }
    };
    // Variant where we define the type, the Index and IndexMut traits, and an allocation function
    (
        $name:ident, $parent:ty, 
        index($indexed_type:ty, $wrapper_type:path, $indexed_arena:ident),
        alloc($fn_name:ident)
    ) => {
        define_new_ast_id!($name, $parent, index($indexed_type, $wrapper_type, $indexed_arena));
        impl Heap {
            pub fn $fn_name(&mut self, f: impl FnOnce($name) -> $indexed_type) -> $name {
                $name(
                    self.$indexed_arena.alloc_with_id(|id| {
                        $wrapper_type(f($name(id)))
                    })
                )
            }
        }
    }
}

define_aliased_ast_id!(RootId, Id<Root>, index(Root, protocol_descriptions), alloc(alloc_protocol_description));
define_aliased_ast_id!(PragmaId, Id<Pragma>, index(Pragma, pragmas), alloc(alloc_pragma));
define_aliased_ast_id!(ImportId, Id<Import>, index(Import, imports), alloc(alloc_import));
define_aliased_ast_id!(ParserTypeId, Id<ParserType>, index(ParserType, parser_types), alloc(alloc_parser_type));

define_aliased_ast_id!(VariableId, Id<Variable>, index(Variable, variables));
define_new_ast_id!(ParameterId, VariableId, index(Parameter, Variable::Parameter, variables), alloc(alloc_parameter));
define_new_ast_id!(LocalId, VariableId, index(Local, Variable::Local, variables), alloc(alloc_local));

define_aliased_ast_id!(DefinitionId, Id<Definition>, index(Definition, definitions));
define_new_ast_id!(StructDefinitionId, DefinitionId, index(StructDefinition, Definition::Struct, definitions), alloc(alloc_struct_definition));
define_new_ast_id!(EnumDefinitionId, DefinitionId, index(EnumDefinition, Definition::Enum, definitions), alloc(alloc_enum_definition));
define_new_ast_id!(UnionDefinitionId, DefinitionId, index(UnionDefinition, Definition::Union, definitions), alloc(alloc_union_definition));
define_new_ast_id!(ComponentDefinitionId, DefinitionId, index(ComponentDefinition, Definition::Component, definitions), alloc(alloc_component_definition));
define_new_ast_id!(FunctionDefinitionId, DefinitionId, index(FunctionDefinition, Definition::Function, definitions), alloc(alloc_function_definition));

define_aliased_ast_id!(StatementId, Id<Statement>, index(Statement, statements));
define_new_ast_id!(BlockStatementId, StatementId, index(BlockStatement, Statement::Block, statements), alloc(alloc_block_statement));
define_new_ast_id!(LocalStatementId, StatementId, index(LocalStatement, Statement::Local, statements), alloc(alloc_local_statement));
define_new_ast_id!(MemoryStatementId, LocalStatementId);
define_new_ast_id!(ChannelStatementId, LocalStatementId);
define_new_ast_id!(LabeledStatementId, StatementId, index(LabeledStatement, Statement::Labeled, statements), alloc(alloc_labeled_statement));
define_new_ast_id!(IfStatementId, StatementId, index(IfStatement, Statement::If, statements), alloc(alloc_if_statement));
define_new_ast_id!(EndIfStatementId, StatementId, index(EndIfStatement, Statement::EndIf, statements), alloc(alloc_end_if_statement));
define_new_ast_id!(WhileStatementId, StatementId, index(WhileStatement, Statement::While, statements), alloc(alloc_while_statement));
define_new_ast_id!(EndWhileStatementId, StatementId, index(EndWhileStatement, Statement::EndWhile, statements), alloc(alloc_end_while_statement));
define_new_ast_id!(BreakStatementId, StatementId, index(BreakStatement, Statement::Break, statements), alloc(alloc_break_statement));
define_new_ast_id!(ContinueStatementId, StatementId, index(ContinueStatement, Statement::Continue, statements), alloc(alloc_continue_statement));
define_new_ast_id!(SynchronousStatementId, StatementId, index(SynchronousStatement, Statement::Synchronous, statements), alloc(alloc_synchronous_statement));
define_new_ast_id!(EndSynchronousStatementId, StatementId, index(EndSynchronousStatement, Statement::EndSynchronous, statements), alloc(alloc_end_synchronous_statement));
define_new_ast_id!(ReturnStatementId, StatementId, index(ReturnStatement, Statement::Return, statements), alloc(alloc_return_statement));
define_new_ast_id!(GotoStatementId, StatementId, index(GotoStatement, Statement::Goto, statements), alloc(alloc_goto_statement));
define_new_ast_id!(NewStatementId, StatementId, index(NewStatement, Statement::New, statements), alloc(alloc_new_statement));
define_new_ast_id!(ExpressionStatementId, StatementId, index(ExpressionStatement, Statement::Expression, statements), alloc(alloc_expression_statement));

define_aliased_ast_id!(ExpressionId, Id<Expression>, index(Expression, expressions));
define_new_ast_id!(AssignmentExpressionId, ExpressionId, index(AssignmentExpression, Expression::Assignment, expressions), alloc(alloc_assignment_expression));
define_new_ast_id!(BindingExpressionId, ExpressionId, index(BindingExpression, Expression::Binding, expressions), alloc(alloc_binding_expression));
define_new_ast_id!(ConditionalExpressionId, ExpressionId, index(ConditionalExpression, Expression::Conditional, expressions), alloc(alloc_conditional_expression));
define_new_ast_id!(BinaryExpressionId, ExpressionId, index(BinaryExpression, Expression::Binary, expressions), alloc(alloc_binary_expression));
define_new_ast_id!(UnaryExpressionId, ExpressionId, index(UnaryExpression, Expression::Unary, expressions), alloc(alloc_unary_expression));
define_new_ast_id!(IndexingExpressionId, ExpressionId, index(IndexingExpression, Expression::Indexing, expressions), alloc(alloc_indexing_expression));
define_new_ast_id!(SlicingExpressionId, ExpressionId, index(SlicingExpression, Expression::Slicing, expressions), alloc(alloc_slicing_expression));
define_new_ast_id!(SelectExpressionId, ExpressionId, index(SelectExpression, Expression::Select, expressions), alloc(alloc_select_expression));
define_new_ast_id!(LiteralExpressionId, ExpressionId, index(LiteralExpression, Expression::Literal, expressions), alloc(alloc_literal_expression));
define_new_ast_id!(CallExpressionId, ExpressionId, index(CallExpression, Expression::Call, expressions), alloc(alloc_call_expression));
define_new_ast_id!(VariableExpressionId, ExpressionId, index(VariableExpression, Expression::Variable, expressions), alloc(alloc_variable_expression));

// TODO: @cleanup - pub qualifiers can be removed once done
#[derive(Debug)]
pub struct Heap {
    // Root arena, contains the entry point for different modules. Each root
    // contains lists of IDs that correspond to the other arenas.
    pub(crate) protocol_descriptions: Arena<Root>,
    // Contents of a file, these are the elements the `Root` elements refer to
    pragmas: Arena<Pragma>,
    pub(crate) imports: Arena<Import>,
    pub(crate) parser_types: Arena<ParserType>,
    pub(crate) variables: Arena<Variable>,
    pub(crate) definitions: Arena<Definition>,
    pub(crate) statements: Arena<Statement>,
    pub(crate) expressions: Arena<Expression>,
}

impl Heap {
    pub fn new() -> Heap {
        Heap {
            // string_alloc: StringAllocator::new(),
            protocol_descriptions: Arena::new(),
            pragmas: Arena::new(),
            imports: Arena::new(),
            parser_types: Arena::new(),
            variables: Arena::new(),
            definitions: Arena::new(),
            statements: Arena::new(),
            expressions: Arena::new(),
        }
    }
    pub fn alloc_memory_statement(
        &mut self,
        f: impl FnOnce(MemoryStatementId) -> MemoryStatement,
    ) -> MemoryStatementId {
        MemoryStatementId(LocalStatementId(self.statements.alloc_with_id(|id| {
            Statement::Local(LocalStatement::Memory(
                f(MemoryStatementId(LocalStatementId(id)))
            ))
        })))
    }
    pub fn alloc_channel_statement(
        &mut self,
        f: impl FnOnce(ChannelStatementId) -> ChannelStatement,
    ) -> ChannelStatementId {
        ChannelStatementId(LocalStatementId(self.statements.alloc_with_id(|id| {
            Statement::Local(LocalStatement::Channel(
                f(ChannelStatementId(LocalStatementId(id)))
            ))
        })))
    }
}

impl Index<MemoryStatementId> for Heap {
    type Output = MemoryStatement;
    fn index(&self, index: MemoryStatementId) -> &Self::Output {
        &self.statements[index.0.0].as_memory()
    }
}

impl Index<ChannelStatementId> for Heap {
    type Output = ChannelStatement;
    fn index(&self, index: ChannelStatementId) -> &Self::Output {
        &self.statements[index.0.0].as_channel()
    }
}

#[derive(Debug, Clone)]
pub struct Root {
    pub this: RootId,
    // Phase 1: parser
    // pub position: InputPosition,
    pub pragmas: Vec<PragmaId>,
    pub imports: Vec<ImportId>,
    pub definitions: Vec<DefinitionId>,
}

impl Root {
    // TODO: @Cleanup
    pub fn get_definition_ident(&self, h: &Heap, id: &[u8]) -> Option<DefinitionId> {
        for &def in self.definitions.iter() {
            if h[def].identifier().value.as_bytes() == id {
                return Some(def);
            }
        }
        None
    }
}

#[derive(Debug, Clone)]
pub enum Pragma {
    Version(PragmaVersion),
    Module(PragmaModule),
}

impl Pragma {
    pub(crate) fn as_module(&self) -> &PragmaModule {
        match self {
            Pragma::Module(pragma) => pragma,
            _ => unreachable!("Tried to obtain {:?} as PragmaModule", self),
        }
    }
}

#[derive(Debug, Clone)]
pub struct PragmaVersion {
    pub this: PragmaId,
    // Phase 1: parser
    pub span: InputSpan, // of full pragma
    pub version: u64,
}

#[derive(Debug, Clone)]
pub struct PragmaModule {
    pub this: PragmaId,
    // Phase 1: parser
    pub span: InputSpan, // of full pragma
    pub value: Identifier,
}

#[derive(Debug, Clone)]
pub enum Import {
    Module(ImportModule),
    Symbols(ImportSymbols)
}

impl Import {
    pub(crate) fn span(&self) -> InputSpan {
        match self {
            Import::Module(v) => v.span,
            Import::Symbols(v) => v.span,
        }
    }

    pub(crate) fn as_module(&self) -> &ImportModule {
        match self {
            Import::Module(m) => m,
            _ => unreachable!("Unable to cast 'Import' to 'ImportModule'")
        }
    }
    pub(crate) fn as_symbols(&self) -> &ImportSymbols {
        match self {
            Import::Symbols(m) => m,
            _ => unreachable!("Unable to cast 'Import' to 'ImportSymbols'")
        }
    }
    pub(crate) fn as_symbols_mut(&mut self) -> &mut ImportSymbols {
        match self {
            Import::Symbols(m) => m,
            _ => unreachable!("Unable to cast 'Import' to 'ImportSymbols'")
        }
    }
}

#[derive(Debug, Clone)]
pub struct ImportModule {
    pub this: ImportId,
    // Phase 1: parser
    pub span: InputSpan,
    pub module: Identifier,
    pub alias: Identifier,
    pub module_id: RootId,
}

#[derive(Debug, Clone)]
pub struct AliasedSymbol {
    pub name: Identifier,
    pub alias: Option<Identifier>,
    pub definition_id: DefinitionId,
}

#[derive(Debug, Clone)]
pub struct ImportSymbols {
    pub this: ImportId,
    // Phase 1: parser
    pub span: InputSpan,
    pub module: Identifier,
    pub module_id: RootId,
    pub symbols: Vec<AliasedSymbol>,
}

#[derive(Debug, Clone)]
pub struct Identifier {
    pub span: InputSpan,
    pub value: StringRef<'static>,
}

impl PartialEq for Identifier {
    fn eq(&self, other: &Self) -> bool {
        return self.value == other.value
    }
}

impl Display for Identifier {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.value.as_str())
    }
}

#[derive(Debug, Clone, PartialOrd, Ord)]
pub enum ParserTypeVariant {
    // Basic builtin
    Message,
    Bool,
    UInt8, UInt16, UInt32, UInt64,
    SInt8, SInt16, SInt32, SInt64,
    Character, String,
    // Literals (need to get concrete builtin type during typechecking)
    IntegerLiteral,
    // Marker for inference
    Inferred,
    // Builtins expecting one subsequent type
    Array,
    Input,
    Output,
    // User-defined types
    PolymorphicArgument(DefinitionId, usize), // usize = index into polymorphic variables
    Definition(DefinitionId, usize), // usize = number of following subtypes
}

impl ParserTypeVariant {
    pub(crate) fn num_embedded(&self) -> usize {
        match self {
            x if *x <= ParserTypeVariant::Inferred => 0,
            x if *x <= ParserTypeVariant::Output => 1,
            ParserTypeVariant::PolymorphicArgument(_, _) => 0,
            ParserTypeVariant::Definition(_, num) => num,
            _ => { debug_assert!(false); 0 },
        }
    }
}

pub struct ParserTypeElement {
    // TODO: @cleanup, do we ever need the span of a user-defined type after
    //  constructing it?
    pub full_span: InputSpan, // full span of type, including any polymorphic arguments
    pub variant: ParserTypeVariant,
}

/// ParserType is a specification of a type during the parsing phase and initial
/// linker/validator phase of the compilation process. These types may be
/// (partially) inferred or represent literals (e.g. a integer whose bytesize is
/// not yet determined).
#[derive(Debug, Clone)]
pub struct ParserType {
    pub elements: Vec<ParserTypeElement>
}

/// Specifies whether the symbolic type points to an actual user-defined type,
/// or whether it points to a polymorphic argument within the definition (e.g.
/// a defined variable `T var` within a function `int func<T>()`
#[derive(Debug, Clone)]
pub enum SymbolicParserTypeVariant {
    Definition(DefinitionId),
    // TODO: figure out if I need the DefinitionId here
    PolyArg(DefinitionId, usize), // index of polyarg in the definition
}

/// ConcreteType is the representation of a type after resolving symbolic types
/// and performing type inference
#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub enum ConcreteTypePart {
    // Markers for the use of polymorphic types within a procedure's body that
    // refer to polymorphic variables on the procedure's definition. Different
    // from markers in the `InferenceType`, these will not contain nested types.
    Marker(usize),
    // Special types (cannot be explicitly constructed by the programmer)
    Void,
    // Builtin types without nested types
    Message,
    Bool,
    Byte,
    Short,
    Int,
    Long,
    String,
    // Builtin types with one nested type
    Array,
    Slice,
    Input,
    Output,
    // User defined type with any number of nested types
    Instance(DefinitionId, usize),
}

#[derive(Debug, Clone, Eq, PartialEq)]
pub struct ConcreteType {
    pub(crate) parts: Vec<ConcreteTypePart>
}

impl Default for ConcreteType {
    fn default() -> Self {
        Self{ parts: Vec::new() }
    }
}

impl ConcreteType {
    pub(crate) fn has_marker(&self) -> bool {
        self.parts
            .iter()
            .any(|p| {
                if let ConcreteTypePart::Marker(_) = p { true } else { false }
            })
    }
}

// TODO: Remove at some point
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum PrimitiveType {
    Unassigned,
    Input,
    Output,
    Message,
    Boolean,
    Byte,
    Short,
    Int,
    Long,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Type {
    pub primitive: PrimitiveType,
    pub array: bool,
}

#[allow(dead_code)]
impl Type {
    pub const UNASSIGNED: Type = Type { primitive: PrimitiveType::Unassigned, array: false };

    pub const INPUT: Type = Type { primitive: PrimitiveType::Input, array: false };
    pub const OUTPUT: Type = Type { primitive: PrimitiveType::Output, array: false };
    pub const MESSAGE: Type = Type { primitive: PrimitiveType::Message, array: false };
    pub const BOOLEAN: Type = Type { primitive: PrimitiveType::Boolean, array: false };
    pub const BYTE: Type = Type { primitive: PrimitiveType::Byte, array: false };
    pub const SHORT: Type = Type { primitive: PrimitiveType::Short, array: false };
    pub const INT: Type = Type { primitive: PrimitiveType::Int, array: false };
    pub const LONG: Type = Type { primitive: PrimitiveType::Long, array: false };

    pub const INPUT_ARRAY: Type = Type { primitive: PrimitiveType::Input, array: true };
    pub const OUTPUT_ARRAY: Type = Type { primitive: PrimitiveType::Output, array: true };
    pub const MESSAGE_ARRAY: Type = Type { primitive: PrimitiveType::Message, array: true };
    pub const BOOLEAN_ARRAY: Type = Type { primitive: PrimitiveType::Boolean, array: true };
    pub const BYTE_ARRAY: Type = Type { primitive: PrimitiveType::Byte, array: true };
    pub const SHORT_ARRAY: Type = Type { primitive: PrimitiveType::Short, array: true };
    pub const INT_ARRAY: Type = Type { primitive: PrimitiveType::Int, array: true };
    pub const LONG_ARRAY: Type = Type { primitive: PrimitiveType::Long, array: true };
}

impl Display for Type {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        match &self.primitive {
            PrimitiveType::Unassigned => {
                write!(f, "unassigned")?;
            }
            PrimitiveType::Input => {
                write!(f, "in")?;
            }
            PrimitiveType::Output => {
                write!(f, "out")?;
            }
            PrimitiveType::Message => {
                write!(f, "msg")?;
            }
            PrimitiveType::Boolean => {
                write!(f, "boolean")?;
            }
            PrimitiveType::Byte => {
                write!(f, "byte")?;
            }
            PrimitiveType::Short => {
                write!(f, "short")?;
            }
            PrimitiveType::Int => {
                write!(f, "int")?;
            }
            PrimitiveType::Long => {
                write!(f, "long")?;
            }
        }
        if self.array {
            write!(f, "[]")
        } else {
            Ok(())
        }
    }
}

#[derive(Debug, Clone)]
pub enum Field {
    Length,
    Symbolic(FieldSymbolic),
}
impl Field {
    pub fn is_length(&self) -> bool {
        match self {
            Field::Length => true,
            _ => false,
        }
    }

    pub fn as_symbolic(&self) -> &FieldSymbolic {
        match self {
            Field::Symbolic(v) => v,
            _ => unreachable!("attempted to get Field::Symbolic from {:?}", self)
        }
    }
}

#[derive(Debug, Clone)]
pub struct FieldSymbolic {
    // Phase 1: Parser
    pub(crate) identifier: Identifier,
    // Phase 3: Typing
    pub(crate) definition: Option<DefinitionId>,
    pub(crate) field_idx: usize,
}

#[derive(Debug, Clone, Copy)]
pub enum Scope {
    Definition(DefinitionId),
    Regular(BlockStatementId),
    Synchronous((SynchronousStatementId, BlockStatementId)),
}

impl Scope {
    pub fn is_block(&self) -> bool {
        match &self {
            Scope::Definition(_) => false,
            Scope::Regular(_) => true,
            Scope::Synchronous(_) => true,
        }
    }
    pub fn to_block(&self) -> BlockStatementId {
        match &self {
            Scope::Regular(id) => *id,
            Scope::Synchronous((_, id)) => *id,
            _ => panic!("unable to get BlockStatement from Scope")
        }
    }
}

#[derive(Debug, Clone)]
pub enum Variable {
    Parameter(Parameter),
    Local(Local),
}

impl Variable {
    pub fn identifier(&self) -> &Identifier {
        match self {
            Variable::Parameter(var) => &var.identifier,
            Variable::Local(var) => &var.identifier,
        }
    }
    pub fn is_parameter(&self) -> bool {
        match self {
            Variable::Parameter(_) => true,
            _ => false,
        }
    }
    pub fn as_parameter(&self) -> &Parameter {
        match self {
            Variable::Parameter(result) => result,
            _ => panic!("Unable to cast `Variable` to `Parameter`"),
        }
    }
    pub fn as_local(&self) -> &Local {
        match self {
            Variable::Local(result) => result,
            _ => panic!("Unable to cast `Variable` to `Local`"),
        }
    }
    pub fn as_local_mut(&mut self) -> &mut Local {
        match self {
            Variable::Local(result) => result,
            _ => panic!("Unable to cast 'Variable' to 'Local'"),
        }
    }
}

/// TODO: Remove distinction between parameter/local and add an enum to indicate
///     the distinction between the two
#[derive(Debug, Clone)]
pub struct Parameter {
    pub this: ParameterId,
    // Phase 2: parser
    pub span: InputSpan,
    pub parser_type: ParserType,
    pub identifier: Identifier,
}

#[derive(Debug, Clone)]
pub struct Local {
    pub this: LocalId,
    // Phase 1: parser
    pub identifier: Identifier,
    pub parser_type: ParserType,
    // Phase 2: linker
    pub relative_pos_in_block: u32,
}

#[derive(Debug, Clone)]
pub enum Definition {
    Struct(StructDefinition),
    Enum(EnumDefinition),
    Union(UnionDefinition),
    Component(ComponentDefinition),
    Function(FunctionDefinition),
}

impl Definition {
    pub fn is_struct(&self) -> bool {
        match self {
            Definition::Struct(_) => true,
            _ => false
        }
    }
    pub(crate) fn as_struct(&self) -> &StructDefinition {
        match self {
            Definition::Struct(result) => result,
            _ => panic!("Unable to cast 'Definition' to 'StructDefinition'"),
        }
    }
    pub(crate) fn as_struct_mut(&mut self) -> &mut StructDefinition {
        match self {
            Definition::Struct(result) => result,
            _ => panic!("Unable to cast 'Definition' to 'StructDefinition'"),
        }
    }
    pub fn is_enum(&self) -> bool {
        match self {
            Definition::Enum(_) => true,
            _ => false,
        }
    }
    pub(crate) fn as_enum(&self) -> &EnumDefinition {
        match self {
            Definition::Enum(result) => result,
            _ => panic!("Unable to cast 'Definition' to 'EnumDefinition'"),
        }
    }
    pub(crate) fn as_enum_mut(&mut self) -> &mut EnumDefinition {
        match self {
            Definition::Enum(result) => result,
            _ => panic!("Unable to cast 'Definition' to 'EnumDefinition'"),
        }
    }
    pub fn is_union(&self) -> bool {
        match self {
            Definition::Union(_) => true,
            _ => false,
        }
    }
    pub(crate) fn as_union(&self) -> &UnionDefinition {
        match self {
            Definition::Union(result) => result, 
            _ => panic!("Unable to cast 'Definition' to 'UnionDefinition'"),
        }
    }
    pub(crate) fn as_union_mut(&mut self) -> &mut UnionDefinition {
        match self {
            Definition::Union(result) => result,
            _ => panic!("Unable to cast 'Definition' to 'UnionDefinition'"),
        }
    }
    pub fn is_component(&self) -> bool {
        match self {
            Definition::Component(_) => true,
            _ => false,
        }
    }
    pub(crate) fn as_component(&self) -> &ComponentDefinition {
        match self {
            Definition::Component(result) => result,
            _ => panic!("Unable to cast `Definition` to `Component`"),
        }
    }
    pub(crate) fn as_component_mut(&mut self) -> &mut ComponentDefinition {
        match self {
            Definition::Component(result) => result,
            _ => panic!("Unable to cast `Definition` to `Component`"),
        }
    }
    pub fn is_function(&self) -> bool {
        match self {
            Definition::Function(_) => true,
            _ => false,
        }
    }
    pub(crate) fn as_function(&self) -> &FunctionDefinition {
        match self {
            Definition::Function(result) => result,
            _ => panic!("Unable to cast `Definition` to `Function`"),
        }
    }
    pub(crate) fn as_function_mut(&mut self) -> &mut FunctionDefinition {
        match self {
            Definition::Function(result) => result,
            _ => panic!("Unable to cast `Definition` to `Function`"),
        }
    }
    pub fn defined_in(&self) -> RootId {
        match self {
            Definition::Struct(def) => def.defined_in,
            Definition::Enum(def) => def.defined_in,
            Definition::Union(def) => def.defined_in,
            Definition::Component(def) => def.defined_in,
            Definition::Function(def) => def.defined_in,
        }
    }
    pub fn identifier(&self) -> &Identifier {
        match self {
            Definition::Struct(def) => &def.identifier,
            Definition::Enum(def) => &def.identifier,
            Definition::Union(def) => &def.identifier,
            Definition::Component(def) => &def.identifier,
            Definition::Function(def) => &def.identifier,
        }
    }
    pub fn parameters(&self) -> &Vec<ParameterId> {
        // TODO: Fix this
        static EMPTY_VEC: Vec<ParameterId> = Vec::new();
        match self {
            Definition::Component(com) => &com.parameters,
            Definition::Function(fun) => &fun.parameters,
            _ => &EMPTY_VEC,
        }
    }
    pub fn body(&self) -> BlockStatementId {
        match self {
            Definition::Component(com) => com.body,
            Definition::Function(fun) => fun.body,
            _ => panic!("cannot retrieve body (for EnumDefinition/UnionDefinition or StructDefinition)")
        }
    }
    pub fn poly_vars(&self) -> &Vec<Identifier> {
        match self {
            Definition::Struct(def) => &def.poly_vars,
            Definition::Enum(def) => &def.poly_vars,
            Definition::Union(def) => &def.poly_vars,
            Definition::Component(def) => &def.poly_vars,
            Definition::Function(def) => &def.poly_vars,
        }
    }
}

#[derive(Debug, Clone)]
pub struct StructFieldDefinition {
    pub span: InputSpan,
    pub field: Identifier,
    pub parser_type: ParserType,
}

#[derive(Debug, Clone)]
pub struct StructDefinition {
    pub this: StructDefinitionId,
    pub defined_in: RootId,
    // Phase 1: symbol scanning
    pub span: InputSpan,
    pub identifier: Identifier,
    pub poly_vars: Vec<Identifier>,
    // Phase 2: parsing
    pub fields: Vec<StructFieldDefinition>
}

impl StructDefinition {
    pub(crate) fn new_empty(
        this: StructDefinitionId, defined_in: RootId, span: InputSpan,
        identifier: Identifier, poly_vars: Vec<Identifier>
    ) -> Self {
        Self{ this, defined_in, span, identifier, poly_vars, fields: Vec::new() }
    }
}

#[derive(Debug, Clone)]
pub enum EnumVariantValue {
    None,
    Integer(i64),
}

#[derive(Debug, Clone)]
pub struct EnumVariantDefinition {
    pub identifier: Identifier,
    pub value: EnumVariantValue,
}

#[derive(Debug, Clone)]
pub struct EnumDefinition {
    pub this: EnumDefinitionId,
    pub defined_in: RootId,
    // Phase 1: symbol scanning
    pub span: InputSpan,
    pub identifier: Identifier,
    pub poly_vars: Vec<Identifier>,
    // Phase 2: parsing
    pub variants: Vec<EnumVariantDefinition>,
}

impl EnumDefinition {
    pub(crate) fn new_empty(
        this: EnumDefinitionId, defined_in: RootId, span: InputSpan,
        identifier: Identifier, poly_vars: Vec<Identifier>
    ) -> Self {
        Self{ this, defined_in, span, identifier, poly_vars, variants: Vec::new() }
    }
}

#[derive(Debug, Clone)]
pub enum UnionVariantValue {
    None,
    Embedded(Vec<ParserType>),
}

#[derive(Debug, Clone)]
pub struct UnionVariantDefinition {
    pub span: InputSpan,
    pub identifier: Identifier,
    pub value: UnionVariantValue,
}

#[derive(Debug, Clone)]
pub struct UnionDefinition {
    pub this: UnionDefinitionId,
    pub defined_in: RootId,
    // Phase 1: symbol scanning
    pub span: InputSpan,
    pub identifier: Identifier,
    pub poly_vars: Vec<Identifier>,
    // Phase 2: parsing
    pub variants: Vec<UnionVariantDefinition>,
}

impl UnionDefinition {
    pub(crate) fn new_empty(
        this: UnionDefinitionId, defined_in: RootId, span: InputSpan,
        identifier: Identifier, poly_vars: Vec<Identifier>
    ) -> Self {
        Self{ this, defined_in, span, identifier, poly_vars, variants: Vec::new() }
    }
}

#[derive(Debug, Clone, Copy)]
pub enum ComponentVariant {
    Primitive,
    Composite,
}

#[derive(Debug, Clone)]
pub struct ComponentDefinition {
    pub this: ComponentDefinitionId,
    pub defined_in: RootId,
    // Phase 1: symbol scanning
    pub span: InputSpan,
    pub variant: ComponentVariant,
    pub identifier: Identifier,
    pub poly_vars: Vec<Identifier>,
    // Phase 2: parsing
    pub parameters: Vec<ParameterId>,
    pub body: BlockStatementId,
}

impl ComponentDefinition {
    pub(crate) fn new_empty(
        this: ComponentDefinitionId, defined_in: RootId, span: InputSpan,
        variant: ComponentVariant, identifier: Identifier, poly_vars: Vec<Identifier>
    ) -> Self {
        Self{ 
            this, defined_in, span, variant, identifier, poly_vars,
            parameters: Vec::new(), 
            body: BlockStatementId::new_invalid()
        }
    }
}

// Note that we will have function definitions for builtin functions as well. In
// that case the span, the identifier span and the body are all invalid.
#[derive(Debug, Clone)]
pub struct FunctionDefinition {
    pub this: FunctionDefinitionId,
    pub defined_in: RootId,
    // Phase 1: symbol scanning
    pub builtin: bool,
    pub span: InputSpan,
    pub identifier: Identifier,
    pub poly_vars: Vec<Identifier>,
    // Phase 2: parsing
    pub return_types: Vec<ParserType>,
    pub parameters: Vec<ParameterId>,
    pub body: BlockStatementId,
}

impl FunctionDefinition {
    pub(crate) fn new_empty(
        this: FunctionDefinitionId, defined_in: RootId, span: InputSpan,
        identifier: Identifier, poly_vars: Vec<Identifier>
    ) -> Self {
        Self {
            this, defined_in,
            builtin: false,
            span, identifier, poly_vars,
            return_types: Vec::new(),
            parameters: Vec::new(),
            body: BlockStatementId::new_invalid(),
        }
    }
}

#[derive(Debug, Clone)]
pub enum Statement {
    Block(BlockStatement),
    Local(LocalStatement),
    Labeled(LabeledStatement),
    If(IfStatement),
    EndIf(EndIfStatement),
    While(WhileStatement),
    EndWhile(EndWhileStatement),
    Break(BreakStatement),
    Continue(ContinueStatement),
    Synchronous(SynchronousStatement),
    EndSynchronous(EndSynchronousStatement),
    Return(ReturnStatement),
    Goto(GotoStatement),
    New(NewStatement),
    Expression(ExpressionStatement),
}

impl Statement {
    pub fn is_block(&self) -> bool {
        match self {
            Statement::Block(_) => true,
            _ => false,
        }
    }
    pub fn as_block(&self) -> &BlockStatement {
        match self {
            Statement::Block(result) => result,
            _ => panic!("Unable to cast `Statement` to `BlockStatement`"),
        }
    }
    pub fn as_block_mut(&mut self) -> &mut BlockStatement {
        match self {
            Statement::Block(result) => result,
            _ => panic!("Unable to cast `Statement` to `BlockStatement`"),
        }
    }
    pub fn as_local(&self) -> &LocalStatement {
        match self {
            Statement::Local(result) => result,
            _ => panic!("Unable to cast `Statement` to `LocalStatement`"),
        }
    }
    pub fn as_memory(&self) -> &MemoryStatement {
        self.as_local().as_memory()
    }
    pub fn as_channel(&self) -> &ChannelStatement {
        self.as_local().as_channel()
    }
    pub fn as_skip(&self) -> &SkipStatement {
        match self {
            Statement::Skip(result) => result,
            _ => panic!("Unable to cast `Statement` to `SkipStatement`"),
        }
    }
    pub fn as_labeled(&self) -> &LabeledStatement {
        match self {
            Statement::Labeled(result) => result,
            _ => panic!("Unable to cast `Statement` to `LabeledStatement`"),
        }
    }
    pub fn as_labeled_mut(&mut self) -> &mut LabeledStatement {
        match self {
            Statement::Labeled(result) => result,
            _ => panic!("Unable to cast `Statement` to `LabeledStatement`"),
        }
    }
    pub fn as_if(&self) -> &IfStatement {
        match self {
            Statement::If(result) => result,
            _ => panic!("Unable to cast `Statement` to `IfStatement`"),
        }
    }
    pub fn as_if_mut(&mut self) -> &mut IfStatement {
        match self {
            Statement::If(result) => result,
            _ => panic!("Unable to cast 'Statement' to 'IfStatement'"),
        }
    }
    pub fn as_end_if(&self) -> &EndIfStatement {
        match self {
            Statement::EndIf(result) => result,
            _ => panic!("Unable to cast `Statement` to `EndIfStatement`"),
        }
    }
    pub fn is_while(&self) -> bool {
        match self {
            Statement::While(_) => true,
            _ => false,
        }
    }
    pub fn as_while(&self) -> &WhileStatement {
        match self {
            Statement::While(result) => result,
            _ => panic!("Unable to cast `Statement` to `WhileStatement`"),
        }
    }
    pub fn as_while_mut(&mut self) -> &mut WhileStatement {
        match self {
            Statement::While(result) => result,
            _ => panic!("Unable to cast `Statement` to `WhileStatement`"),
        }
    }
    pub fn as_end_while(&self) -> &EndWhileStatement {
        match self {
            Statement::EndWhile(result) => result,
            _ => panic!("Unable to cast `Statement` to `EndWhileStatement`"),
        }
    }
    pub fn as_break(&self) -> &BreakStatement {
        match self {
            Statement::Break(result) => result,
            _ => panic!("Unable to cast `Statement` to `BreakStatement`"),
        }
    }
    pub fn as_break_mut(&mut self) -> &mut BreakStatement {
        match self {
            Statement::Break(result) => result,
            _ => panic!("Unable to cast `Statement` to `BreakStatement`"),
        }
    }
    pub fn as_continue(&self) -> &ContinueStatement {
        match self {
            Statement::Continue(result) => result,
            _ => panic!("Unable to cast `Statement` to `ContinueStatement`"),
        }
    }
    pub fn as_continue_mut(&mut self) -> &mut ContinueStatement {
        match self {
            Statement::Continue(result) => result,
            _ => panic!("Unable to cast `Statement` to `ContinueStatement`"),
        }
    }
    pub fn as_synchronous(&self) -> &SynchronousStatement {
        match self {
            Statement::Synchronous(result) => result,
            _ => panic!("Unable to cast `Statement` to `SynchronousStatement`"),
        }
    }
    pub fn as_synchronous_mut(&mut self) -> &mut SynchronousStatement {
        match self {
            Statement::Synchronous(result) => result,
            _ => panic!("Unable to cast `Statement` to `SynchronousStatement`"),
        }
    }
    pub fn as_end_synchronous(&self) -> &EndSynchronousStatement {
        match self {
            Statement::EndSynchronous(result) => result,
            _ => panic!("Unable to cast `Statement` to `EndSynchronousStatement`"),
        }
    }
    pub fn as_return(&self) -> &ReturnStatement {
        match self {
            Statement::Return(result) => result,
            _ => panic!("Unable to cast `Statement` to `ReturnStatement`"),
        }
    }
    pub fn as_goto(&self) -> &GotoStatement {
        match self {
            Statement::Goto(result) => result,
            _ => panic!("Unable to cast `Statement` to `GotoStatement`"),
        }
    }
    pub fn as_goto_mut(&mut self) -> &mut GotoStatement {
        match self {
            Statement::Goto(result) => result,
            _ => panic!("Unable to cast `Statement` to `GotoStatement`"),
        }
    }
    pub fn as_new(&self) -> &NewStatement {
        match self {
            Statement::New(result) => result,
            _ => panic!("Unable to cast `Statement` to `NewStatement`"),
        }
    }
    pub fn as_expression(&self) -> &ExpressionStatement {
        match self {
            Statement::Expression(result) => result,
            _ => panic!("Unable to cast `Statement` to `ExpressionStatement`"),
        }
    }
    pub fn span(&self) -> InputSpan {
        match self {
            Statement::Block(v) => v.span,
            Statement::Local(v) => v.span(),
            Statement::Labeled(v) => v.label.span,
            Statement::If(v) => v.span,
            Statement::While(v) => v.span,
            Statement::Break(v) => v.span,
            Statement::Continue(v) => v.span,
            Statement::Synchronous(v) => v.span,
            Statement::Return(v) => v.span,
            Statement::Goto(v) => v.span,
            Statement::New(v) => v.span,
            Statement::Expression(v) => v.span,
            Statement::EndIf(_) | Statement::EndWhile(_) | Statement::EndSynchronous(_) => unreachable!(),
        }
    }
    pub fn link_next(&mut self, next: StatementId) {
        match self {
            Statement::Block(_) => todo!(),
            Statement::Local(stmt) => match stmt {
                LocalStatement::Channel(stmt) => stmt.next = Some(next),
                LocalStatement::Memory(stmt) => stmt.next = Some(next),
            },
            Statement::EndIf(stmt) => stmt.next = Some(next),
            Statement::EndWhile(stmt) => stmt.next = Some(next),
            Statement::EndSynchronous(stmt) => stmt.next = Some(next),
            Statement::New(stmt) => stmt.next = Some(next),
            Statement::Expression(stmt) => stmt.next = Some(next),
            Statement::Return(_)
            | Statement::Break(_)
            | Statement::Continue(_)
            | Statement::Synchronous(_)
            | Statement::Goto(_)
            | Statement::While(_)
            | Statement::Labeled(_)
            | Statement::If(_) => unreachable!(),
        }
    }
}

#[derive(Debug, Clone)]
pub struct BlockStatement {
    pub this: BlockStatementId,
    // Phase 1: parser
    pub is_implicit: bool,
    pub span: InputSpan, // of the complete block
    pub statements: Vec<StatementId>,
    // Phase 2: linker
    pub parent_scope: Option<Scope>,
    pub relative_pos_in_parent: u32,
    pub locals: Vec<LocalId>,
    pub labels: Vec<LabeledStatementId>,
}

impl BlockStatement {
    pub fn parent_block(&self, h: &Heap) -> Option<BlockStatementId> {
        let parent = self.parent_scope.unwrap();
        match parent {
            Scope::Definition(_) => {
                // If the parent scope is a definition, then there is no
                // parent block.
                None
            }
            Scope::Synchronous((parent, _)) => {
                // It is always the case that when this function is called,
                // the parent of a synchronous statement is a block statement:
                // nested synchronous statements are flagged illegal,
                // and that happens before resolving variables that
                // creates the parent_scope references in the first place.
                Some(h[parent].parent_scope(h).unwrap().to_block())
            }
            Scope::Regular(parent) => {
                // A variable scope is either a definition, sync, or block.
                Some(parent)
            }
        }
    }
    pub fn first(&self) -> StatementId {
        // It is an invariant (guaranteed by the lexer) that block statements have at least one stmt
        *self.statements.first().unwrap()
    }
}

#[derive(Debug, Clone)]
pub enum LocalStatement {
    Memory(MemoryStatement),
    Channel(ChannelStatement),
}

impl LocalStatement {
    pub fn this(&self) -> LocalStatementId {
        match self {
            LocalStatement::Memory(stmt) => stmt.this.upcast(),
            LocalStatement::Channel(stmt) => stmt.this.upcast(),
        }
    }
    pub fn as_memory(&self) -> &MemoryStatement {
        match self {
            LocalStatement::Memory(result) => result,
            _ => panic!("Unable to cast `LocalStatement` to `MemoryStatement`"),
        }
    }
    pub fn as_channel(&self) -> &ChannelStatement {
        match self {
            LocalStatement::Channel(result) => result,
            _ => panic!("Unable to cast `LocalStatement` to `ChannelStatement`"),
        }
    }
    pub fn span(&self) -> InputSpan {
        match self {
            LocalStatement::Channel(v) => v.span,
            LocalStatement::Memory(v) => v.span,
        }
    }
    pub fn next(&self) -> Option<StatementId> {
        match self {
            LocalStatement::Memory(stmt) => stmt.next,
            LocalStatement::Channel(stmt) => stmt.next,
        }
    }
}

#[derive(Debug, Clone)]
pub struct MemoryStatement {
    pub this: MemoryStatementId,
    // Phase 1: parser
    pub span: InputSpan,
    pub variable: LocalId,
    // Phase 2: linker
    pub next: Option<StatementId>,
}

/// ChannelStatement is the declaration of an input and output port associated
/// with the same channel. Note that the polarity of the ports are from the
/// point of view of the component. So an output port is something that a
/// component uses to send data over (i.e. it is the "input end" of the
/// channel), and vice versa.
#[derive(Debug, Clone)]
pub struct ChannelStatement {
    pub this: ChannelStatementId,
    // Phase 1: parser
    pub span: InputSpan, // of the "channel" keyword
    pub from: LocalId, // output
    pub to: LocalId,   // input
    // Phase 2: linker
    pub relative_pos_in_block: u32,
    pub next: Option<StatementId>,
}

#[derive(Debug, Clone)]
pub struct LabeledStatement {
    pub this: LabeledStatementId,
    // Phase 1: parser
    pub label: Identifier,
    pub body: StatementId,
    // Phase 2: linker
    pub relative_pos_in_block: u32,
    pub in_sync: Option<SynchronousStatementId>,
}

#[derive(Debug, Clone)]
pub struct IfStatement {
    pub this: IfStatementId,
    // Phase 1: parser
    pub span: InputSpan, // of the "if" keyword
    pub test: ExpressionId,
    pub true_body: BlockStatementId,
    pub false_body: Option<BlockStatementId>,
    // Phase 2: linker
    pub end_if: Option<EndIfStatementId>,
}

#[derive(Debug, Clone)]
pub struct EndIfStatement {
    pub this: EndIfStatementId,
    pub start_if: IfStatementId,
    // Phase 2: linker
    pub next: Option<StatementId>,
}

#[derive(Debug, Clone)]
pub struct WhileStatement {
    pub this: WhileStatementId,
    // Phase 1: parser
    pub span: InputSpan, // of the "while" keyword
    pub test: ExpressionId,
    pub body: BlockStatementId,
    // Phase 2: linker
    pub end_while: Option<EndWhileStatementId>,
    pub in_sync: Option<SynchronousStatementId>,
}

#[derive(Debug, Clone)]
pub struct EndWhileStatement {
    pub this: EndWhileStatementId,
    pub start_while: WhileStatementId,
    // Phase 2: linker
    pub next: Option<StatementId>,
}

#[derive(Debug, Clone)]
pub struct BreakStatement {
    pub this: BreakStatementId,
    // Phase 1: parser
    pub span: InputSpan, // of the "break" keyword
    pub label: Option<Identifier>,
    // Phase 2: linker
    pub target: Option<EndWhileStatementId>,
}

#[derive(Debug, Clone)]
pub struct ContinueStatement {
    pub this: ContinueStatementId,
    // Phase 1: parser
    pub span: InputSpan, // of the "continue" keyword
    pub label: Option<Identifier>,
    // Phase 2: linker
    pub target: Option<WhileStatementId>,
}

#[derive(Debug, Clone)]
pub struct SynchronousStatement {
    pub this: SynchronousStatementId,
    // Phase 1: parser
    pub span: InputSpan, // of the "sync" keyword
    pub body: BlockStatementId,
    // Phase 2: linker
    pub end_sync: Option<EndSynchronousStatementId>,
    pub parent_scope: Option<Scope>,
}

#[derive(Debug, Clone)]
pub struct EndSynchronousStatement {
    pub this: EndSynchronousStatementId,
    pub start_sync: SynchronousStatementId,
    // Phase 2: linker
    pub next: Option<StatementId>,
}

#[derive(Debug, Clone)]
pub struct ReturnStatement {
    pub this: ReturnStatementId,
    // Phase 1: parser
    pub span: InputSpan, // of the "return" keyword
    pub expressions: Vec<ExpressionId>,
}

#[derive(Debug, Clone)]
pub struct GotoStatement {
    pub this: GotoStatementId,
    // Phase 1: parser
    pub span: InputSpan, // of the "goto" keyword
    pub label: Identifier,
    // Phase 2: linker
    pub target: Option<LabeledStatementId>,
}

#[derive(Debug, Clone)]
pub struct NewStatement {
    pub this: NewStatementId,
    // Phase 1: parser
    pub span: InputSpan, // of the "new" keyword
    pub expression: CallExpressionId,
    // Phase 2: linker
    pub next: Option<StatementId>,
}

#[derive(Debug, Clone)]
pub struct ExpressionStatement {
    pub this: ExpressionStatementId,
    // Phase 1: parser
    pub span: InputSpan,
    pub expression: ExpressionId,
    // Phase 2: linker
    pub next: Option<StatementId>,
}

#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum ExpressionParent {
    None, // only set during initial parsing
    If(IfStatementId),
    While(WhileStatementId),
    Return(ReturnStatementId),
    New(NewStatementId),
    ExpressionStmt(ExpressionStatementId),
    Expression(ExpressionId, u32) // index within expression (e.g LHS or RHS of expression)
}

#[derive(Debug, Clone)]
pub enum Expression {
    Assignment(AssignmentExpression),
    Binding(BindingExpression),
    Conditional(ConditionalExpression),
    Binary(BinaryExpression),
    Unary(UnaryExpression),
    Indexing(IndexingExpression),
    Slicing(SlicingExpression),
    Select(SelectExpression),
    Literal(LiteralExpression),
    Call(CallExpression),
    Variable(VariableExpression),
}

impl Expression {
    pub fn as_assignment(&self) -> &AssignmentExpression {
        match self {
            Expression::Assignment(result) => result,
            _ => panic!("Unable to cast `Expression` to `AssignmentExpression`"),
        }
    }
    pub fn as_conditional(&self) -> &ConditionalExpression {
        match self {
            Expression::Conditional(result) => result,
            _ => panic!("Unable to cast `Expression` to `ConditionalExpression`"),
        }
    }
    pub fn as_binary(&self) -> &BinaryExpression {
        match self {
            Expression::Binary(result) => result,
            _ => panic!("Unable to cast `Expression` to `BinaryExpression`"),
        }
    }
    pub fn as_unary(&self) -> &UnaryExpression {
        match self {
            Expression::Unary(result) => result,
            _ => panic!("Unable to cast `Expression` to `UnaryExpression`"),
        }
    }
    pub fn as_indexing(&self) -> &IndexingExpression {
        match self {
            Expression::Indexing(result) => result,
            _ => panic!("Unable to cast `Expression` to `IndexingExpression`"),
        }
    }
    pub fn as_slicing(&self) -> &SlicingExpression {
        match self {
            Expression::Slicing(result) => result,
            _ => panic!("Unable to cast `Expression` to `SlicingExpression`"),
        }
    }
    pub fn as_select(&self) -> &SelectExpression {
        match self {
            Expression::Select(result) => result,
            _ => panic!("Unable to cast `Expression` to `SelectExpression`"),
        }
    }
    pub fn as_array(&self) -> &ArrayExpression {
        match self {
            Expression::Array(result) => result,
            _ => panic!("Unable to cast `Expression` to `ArrayExpression`"),
        }
    }
    pub fn as_constant(&self) -> &LiteralExpression {
        match self {
            Expression::Literal(result) => result,
            _ => panic!("Unable to cast `Expression` to `ConstantExpression`"),
        }
    }
    pub fn as_call(&self) -> &CallExpression {
        match self {
            Expression::Call(result) => result,
            _ => panic!("Unable to cast `Expression` to `CallExpression`"),
        }
    }
    pub fn as_call_mut(&mut self) -> &mut CallExpression {
        match self {
            Expression::Call(result) => result,
            _ => panic!("Unable to cast `Expression` to `CallExpression`"),
        }
    }
    pub fn as_variable(&self) -> &VariableExpression {
        match self {
            Expression::Variable(result) => result,
            _ => panic!("Unable to cast `Expression` to `VariableExpression`"),
        }
    }
    pub fn as_variable_mut(&mut self) -> &mut VariableExpression {
        match self {
            Expression::Variable(result) => result,
            _ => panic!("Unable to cast `Expression` to `VariableExpression`"),
        }
    }
    pub fn span(&self) -> InputSpan {
        match self {
            Expression::Assignment(expr) => expr.span,
            Expression::Binding(expr) => expr.span,
            Expression::Conditional(expr) => expr.span,
            Expression::Binary(expr) => expr.span,
            Expression::Unary(expr) => expr.span,
            Expression::Indexing(expr) => expr.span,
            Expression::Slicing(expr) => expr.span,
            Expression::Select(expr) => expr.span,
            Expression::Literal(expr) => expr.span,
            Expression::Call(expr) => expr.span,
            Expression::Variable(expr) => expr.identifier.span,
        }
    }
    // TODO: @cleanup
    pub fn parent(&self) -> &ExpressionParent {
        match self {
            Expression::Assignment(expr) => &expr.parent,
            Expression::Binding(expr) => &expr.parent,
            Expression::Conditional(expr) => &expr.parent,
            Expression::Binary(expr) => &expr.parent,
            Expression::Unary(expr) => &expr.parent,
            Expression::Indexing(expr) => &expr.parent,
            Expression::Slicing(expr) => &expr.parent,
            Expression::Select(expr) => &expr.parent,
            Expression::Literal(expr) => &expr.parent,
            Expression::Call(expr) => &expr.parent,
            Expression::Variable(expr) => &expr.parent,
        }
    }
    // TODO: @cleanup
    pub fn parent_expr_id(&self) -> Option<ExpressionId> {
        if let ExpressionParent::Expression(id, _) = self.parent() {
            Some(*id)
        } else {
            None
        }
    }
    // TODO: @cleanup
    pub fn set_parent(&mut self, parent: ExpressionParent) {
        match self {
            Expression::Assignment(expr) => expr.parent = parent,
            Expression::Binding(expr) => expr.parent = parent,
            Expression::Conditional(expr) => expr.parent = parent,
            Expression::Binary(expr) => expr.parent = parent,
            Expression::Unary(expr) => expr.parent = parent,
            Expression::Indexing(expr) => expr.parent = parent,
            Expression::Slicing(expr) => expr.parent = parent,
            Expression::Select(expr) => expr.parent = parent,
            Expression::Literal(expr) => expr.parent = parent,
            Expression::Call(expr) => expr.parent = parent,
            Expression::Variable(expr) => expr.parent = parent,
        }
    }
    pub fn get_type(&self) -> &ConcreteType {
        match self {
            Expression::Assignment(expr) => &expr.concrete_type,
            Expression::Binding(expr) => &expr.concrete_type,
            Expression::Conditional(expr) => &expr.concrete_type,
            Expression::Binary(expr) => &expr.concrete_type,
            Expression::Unary(expr) => &expr.concrete_type,
            Expression::Indexing(expr) => &expr.concrete_type,
            Expression::Slicing(expr) => &expr.concrete_type,
            Expression::Select(expr) => &expr.concrete_type,
            Expression::Literal(expr) => &expr.concrete_type,
            Expression::Call(expr) => &expr.concrete_type,
            Expression::Variable(expr) => &expr.concrete_type,
        }
    }

    // TODO: @cleanup
    pub fn get_type_mut(&mut self) -> &mut ConcreteType {
        match self {
            Expression::Assignment(expr) => &mut expr.concrete_type,
            Expression::Binding(expr) => &mut expr.concrete_type,
            Expression::Conditional(expr) => &mut expr.concrete_type,
            Expression::Binary(expr) => &mut expr.concrete_type,
            Expression::Unary(expr) => &mut expr.concrete_type,
            Expression::Indexing(expr) => &mut expr.concrete_type,
            Expression::Slicing(expr) => &mut expr.concrete_type,
            Expression::Select(expr) => &mut expr.concrete_type,
            Expression::Literal(expr) => &mut expr.concrete_type,
            Expression::Call(expr) => &mut expr.concrete_type,
            Expression::Variable(expr) => &mut expr.concrete_type,
        }
    }
}

#[derive(Debug, Clone)]
pub enum AssignmentOperator {
    Set,
    Multiplied,
    Divided,
    Remained,
    Added,
    Subtracted,
    ShiftedLeft,
    ShiftedRight,
    BitwiseAnded,
    BitwiseXored,
    BitwiseOred,
}

#[derive(Debug, Clone)]
pub struct AssignmentExpression {
    pub this: AssignmentExpressionId,
    // Phase 2: parser
    pub span: InputSpan, // of the operator
    pub left: ExpressionId,
    pub operation: AssignmentOperator,
    pub right: ExpressionId,
    // Phase 3: linker
    pub parent: ExpressionParent,
    // Phase 4: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone)]
pub struct BindingExpression {
    pub this: BindingExpressionId,
    // Phase 1: parser
    pub span: InputSpan,
    pub left: LiteralExpressionId,
    pub right: ExpressionId,
    // Phase 2: linker
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone)]
pub struct ConditionalExpression {
    pub this: ConditionalExpressionId,
    // Phase 1: parser
    pub span: InputSpan, // of question mark operator
    pub test: ExpressionId,
    pub true_expression: ExpressionId,
    pub false_expression: ExpressionId,
    // Phase 2: linker
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum BinaryOperator {
    Concatenate,
    LogicalOr,
    LogicalAnd,
    BitwiseOr,
    BitwiseXor,
    BitwiseAnd,
    Equality,
    Inequality,
    LessThan,
    GreaterThan,
    LessThanEqual,
    GreaterThanEqual,
    ShiftLeft,
    ShiftRight,
    Add,
    Subtract,
    Multiply,
    Divide,
    Remainder,
}

#[derive(Debug, Clone)]
pub struct BinaryExpression {
    pub this: BinaryExpressionId,
    // Phase 1: parser
    pub span: InputSpan, // of the operator
    pub left: ExpressionId,
    pub operation: BinaryOperator,
    pub right: ExpressionId,
    // Phase 2: linker
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum UnaryOperation {
    Positive,
    Negative,
    BitwiseNot,
    LogicalNot,
    PreIncrement,
    PreDecrement,
    PostIncrement,
    PostDecrement,
}

#[derive(Debug, Clone)]
pub struct UnaryExpression {
    pub this: UnaryExpressionId,
    // Phase 1: parser
    pub span: InputSpan, // of the operator
    pub operation: UnaryOperation,
    pub expression: ExpressionId,
    // Phase 2: linker
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone)]
pub struct IndexingExpression {
    pub this: IndexingExpressionId,
    // Phase 1: parser
    pub span: InputSpan,
    pub subject: ExpressionId,
    pub index: ExpressionId,
    // Phase 2: linker
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone)]
pub struct SlicingExpression {
    pub this: SlicingExpressionId,
    // Phase 1: parser
    pub span: InputSpan, // from '[' to ']';
    pub subject: ExpressionId,
    pub from_index: ExpressionId,
    pub to_index: ExpressionId,
    // Phase 2: linker
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone)]
pub struct SelectExpression {
    pub this: SelectExpressionId,
    // Phase 1: parser
    pub span: InputSpan, // of the '.'
    pub subject: ExpressionId,
    pub field: Field,
    // Phase 2: linker
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone)]
pub struct CallExpression {
    pub this: CallExpressionId,
    // Phase 1: parser
    pub span: InputSpan,
    pub parser_type: ParserType, // of the function call
    pub method: Method,
    pub arguments: Vec<ExpressionId>,
    pub definition: DefinitionId,
    // Phase 2: linker
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone)]
pub enum Method {
    // Builtin
    Get,
    Put,
    Fires,
    Create,
    Length,
    Assert,
    UserFunction,
    UserComponent,
}

#[derive(Debug, Clone)]
pub struct MethodSymbolic {
    pub(crate) parser_type: ParserType,
    pub(crate) definition: DefinitionId
}

#[derive(Debug, Clone)]
pub struct LiteralExpression {
    pub this: LiteralExpressionId,
    // Phase 1: parser
    pub span: InputSpan,
    pub value: Literal,
    // Phase 2: linker
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}

#[derive(Debug, Clone)]
pub enum Literal {
    Null, // message
    True,
    False,
    Character(char),
    String(StringRef<'static>),
    Integer(LiteralInteger),
    Struct(LiteralStruct),
    Enum(LiteralEnum),
    Union(LiteralUnion),
    Array(Vec<ExpressionId>),
}

impl Literal {
    pub(crate) fn as_struct(&self) -> &LiteralStruct {
        if let Literal::Struct(literal) = self{
            literal
        } else {
            unreachable!("Attempted to obtain {:?} as Literal::Struct", self)
        }
    }

    pub(crate) fn as_struct_mut(&mut self) -> &mut LiteralStruct {
        if let Literal::Struct(literal) = self{
            literal
        } else {
            unreachable!("Attempted to obtain {:?} as Literal::Struct", self)
        }
    }

    pub(crate) fn as_enum(&self) -> &LiteralEnum {
        if let Literal::Enum(literal) = self {
            literal
        } else {
            unreachable!("Attempted to obtain {:?} as Literal::Enum", self)
        }
    }

    pub(crate) fn as_union(&self) -> &LiteralUnion {
        if let Literal::Union(literal) = self {
            literal
        } else {
            unreachable!("Attempted to obtain {:?} as Literal::Union", self)
        }
    }
}

#[derive(Debug, Clone)]
pub struct LiteralInteger {
    pub(crate) unsigned_value: u64,
    pub(crate) negated: bool, // for constant expression evaluation, TODO
}

#[derive(Debug, Clone)]
pub struct LiteralStructField {
    // Phase 1: parser
    pub(crate) identifier: Identifier,
    pub(crate) value: ExpressionId,
    // Phase 2: linker
    pub(crate) field_idx: usize, // in struct definition
}

#[derive(Debug, Clone)]
pub struct LiteralStruct {
    // Phase 1: parser
    pub(crate) parser_type: ParserType,
    pub(crate) fields: Vec<LiteralStructField>,
    pub(crate) definition: DefinitionId,
}

#[derive(Debug, Clone)]
pub struct LiteralEnum {
    // Phase 1: parser
    pub(crate) parser_type: ParserType,
    pub(crate) variant: Identifier,
    pub(crate) definition: DefinitionId,
    // Phase 2: linker
    pub(crate) variant_idx: usize, // as present in the type table
}

#[derive(Debug, Clone)]
pub struct LiteralUnion {
    // Phase 1: parser
    pub(crate) parser_type: ParserType,
    pub(crate) variant: Identifier,
    pub(crate) values: Vec<ExpressionId>,
    pub(crate) definition: DefinitionId,
    // Phase 2: linker
    pub(crate) variant_idx: usize, // as present in type table
}

#[derive(Debug, Clone)]
pub struct VariableExpression {
    pub this: VariableExpressionId,
    // Phase 1: parser
    pub identifier: Identifier,
    // Phase 2: linker
    pub declaration: Option<VariableId>,
    pub parent: ExpressionParent,
    // Phase 3: type checking
    pub concrete_type: ConcreteType,
}