use crate::collections::StringRef;
use crate::protocol::ast::*;
use crate::protocol::input_source2::{
    InputSource2 as InputSource,
    InputPosition2 as InputPosition,
    InputSpan,
    ParseError,
};
use super::tokens::*;
use super::symbol_table2::*;
use super::{Module, ModuleCompilationPhase, PassCtx};

// Keywords
pub(crate) const KW_LET:       &'static [u8] = b"let";
pub(crate) const KW_AS:        &'static [u8] = b"as";
pub(crate) const KW_STRUCT:    &'static [u8] = b"struct";
pub(crate) const KW_ENUM:      &'static [u8] = b"enum";
pub(crate) const KW_UNION:     &'static [u8] = b"union";
pub(crate) const KW_FUNCTION:  &'static [u8] = b"function";
pub(crate) const KW_PRIMITIVE: &'static [u8] = b"primitive";
pub(crate) const KW_COMPOSITE: &'static [u8] = b"composite";
pub(crate) const KW_IMPORT:    &'static [u8] = b"import";

// Keywords - literals
pub(crate) const KW_LIT_TRUE:  &'static [u8] = b"true";
pub(crate) const KW_LIT_FALSE: &'static [u8] = b"false";
pub(crate) const KW_LIT_NULL:  &'static [u8] = b"null";

// Keywords - functions
pub(crate) const KW_FUNC_GET:    &'static [u8] = b"get";
pub(crate) const KW_FUNC_PUT:    &'static [u8] = b"put";
pub(crate) const KW_FUNC_FIRES:  &'static [u8] = b"fires";
pub(crate) const KW_FUNC_CREATE: &'static [u8] = b"create";
pub(crate) const KW_FUNC_LENGTH: &'static [u8] = b"length";

// Keywords - statements
pub(crate) const KW_STMT_CHANNEL:  &'static [u8] = b"channel";
pub(crate) const KW_STMT_IF:       &'static [u8] = b"if";
pub(crate) const KW_STMT_WHILE:    &'static [u8] = b"while";
pub(crate) const KW_STMT_BREAK:    &'static [u8] = b"break";
pub(crate) const KW_STMT_CONTINUE: &'static [u8] = b"continue";
pub(crate) const KW_STMT_GOTO:     &'static [u8] = b"goto";
pub(crate) const KW_STMT_RETURN:   &'static [u8] = b"return";
pub(crate) const KW_STMT_SYNC:     &'static [u8] = b"synchronous";
pub(crate) const KW_STMT_ASSERT:   &'static [u8] = b"assert";
pub(crate) const KW_STMT_NEW:      &'static [u8] = b"new";

// Keywords - types
pub(crate) const KW_TYPE_IN_PORT:  &'static [u8] = b"in";
pub(crate) const KW_TYPE_OUT_PORT: &'static [u8] = b"out";
pub(crate) const KW_TYPE_MESSAGE:  &'static [u8] = b"msg";
pub(crate) const KW_TYPE_BOOL:     &'static [u8] = b"bool";
pub(crate) const KW_TYPE_UINT8:    &'static [u8] = b"u8";
pub(crate) const KW_TYPE_UINT16:   &'static [u8] = b"u16";
pub(crate) const KW_TYPE_UINT32:   &'static [u8] = b"u32";
pub(crate) const KW_TYPE_UINT64:   &'static [u8] = b"u64";
pub(crate) const KW_TYPE_SINT8:    &'static [u8] = b"s8";
pub(crate) const KW_TYPE_SINT16:   &'static [u8] = b"s16";
pub(crate) const KW_TYPE_SINT32:   &'static [u8] = b"s32";
pub(crate) const KW_TYPE_SINT64:   &'static [u8] = b"s64";
pub(crate) const KW_TYPE_CHAR:     &'static [u8] = b"char";
pub(crate) const KW_TYPE_STRING:   &'static [u8] = b"string";
pub(crate) const KW_TYPE_INFERRED: &'static [u8] = b"auto";

/// Consumes a domain-name identifier: identifiers separated by a dot. For
/// simplification of later parsing and span identification the domain-name may
/// contain whitespace, but must reside on the same line.
pub(crate) fn consume_domain_ident<'a>(
    source: &'a InputSource, iter: &mut TokenIter
) -> Result<(&'a [u8], InputSpan), ParseError> {
    let (_, mut span) = consume_ident(source, iter)?;
    while let Some(TokenKind::Dot) = iter.next() {
        iter.consume();
        let (_, new_span) = consume_ident(source, iter)?;
        span.end = new_span.end;
    }

    // Not strictly necessary, but probably a reasonable restriction: this
    // simplifies parsing of module naming and imports.
    if span.begin.line != span.end.line {
        return Err(ParseError::new_error_str_at_span(source, span, "module names may not span multiple lines"));
    }

    // If module name consists of a single identifier, then it may not match any
    // of the reserved keywords
    let section = source.section_at_pos(span.begin, span.end);
    if is_reserved_keyword(section) {
        return Err(ParseError::new_error_str_at_span(source, span, "encountered reserved keyword"));
    }

    Ok((source.section_at_pos(span.begin, span.end), span))
}

/// Consumes a specific expected token. Be careful to only call this with tokens
/// that do not have a variable length.
pub(crate) fn consume_token(source: &InputSource, iter: &mut TokenIter, expected: TokenKind) -> Result<InputSpan, ParseError> {
    if Some(expected) != iter.next() {
        return Err(ParseError::new_error_at_pos(
            source, iter.last_valid_pos(),
            format!("expected '{}'", expected.token_chars())
        ));
    }
    let span = iter.next_span();
    iter.consume();
    Ok(span)
}

/// Consumes a comma-separated list of items if the opening delimiting token is
/// encountered. If not, then the iterator will remain at its current position.
/// Note that the potential cases may be:
/// - No opening delimiter encountered, then we return `false`.
/// - Both opening and closing delimiter encountered, but no items.
/// - Opening and closing delimiter encountered, and items were processed.
/// - Found an opening delimiter, but processing an item failed.
pub(crate) fn maybe_consume_comma_separated<T, F>(
    open_delim: TokenKind, close_delim: TokenKind, source: &InputSource, iter: &mut TokenIter,
    consumer_fn: F, target: &mut Vec<T>, item_name_and_article: &'static str,
    close_pos: Option<&mut InputPosition>
) -> Result<bool, ParseError>
    where F: Fn(&InputSource, &mut TokenIter) -> Result<T, ParseError>
{
    let mut next = iter.next();
    if Some(open_delim) != next {
        return Ok(false);
    }

    // Opening delimiter encountered, so must parse the comma-separated list.
    iter.consume();
    target.clear();
    let mut had_comma = true;
    loop {
        next = iter.next();
        if Some(close_delim) == next {
            if let Some(close_pos) = close_pos {
                // If requested return the position of the closing delimiter
                let (_, new_close_pos) = iter.next_positions();
                *close_pos = new_close_pos;
            }
            iter.consume();
            break;
        } else if !had_comma || next.is_none() {
            return Err(ParseError::new_error_at_pos(
                source, iter.last_valid_pos(),
                format!("expected a '{}', or {}", close_delim.token_chars(), item_name_and_article)
            ));
        }

        let new_item = consumer_fn(source, iter)?;
        target.push(new_item);

        next = iter.next();
        had_comma = next == Some(TokenKind::Comma);
        if had_comma {
            iter.consume();
        }
    }

    Ok(true)
}

pub(crate) fn maybe_consume_comma_separated_spilled<F: Fn(&InputSource, &mut TokenIter) -> Result<(), ParseError>>(
    open_delim: TokenKind, close_delim: TokenKind, source: &InputSource, iter: &mut TokenIter,
    consumer_fn: F, item_name_and_article: &'static str
) -> Result<bool, ParseError> {
    let mut next = iter.next();
    if Some(open_delim) != next {
        return Ok(false);
    }

    iter.consume();
    let mut had_comma = true;
    loop {
        next = iter.next();
        if Some(close_delim) == next {
            iter.consume();
            break;
        } else if !had_comma {
            return Err(ParseError::new_error_at_pos(
                source, iter.last_valid_pos(),
                format!("expected a '{}', or {}", close_delim.token_chars(), item_name_and_article)
            ));
        }

        consumer_fn(source, iter)?;
        next = iter.next();
        had_comma = next == Some(TokenKind::Comma);
        if had_comma {
            iter.consume();
        }
    }

    Ok(true)
}

/// Consumes a comma-separated list and expected the opening and closing
/// characters to be present. The returned array may still be empty
pub(crate) fn consume_comma_separated<T, F>(
    open_delim: TokenKind, close_delim: TokenKind, source: &InputSource, iter: &mut TokenIter,
    consumer_fn: F, target: &mut Vec<T>, item_name_and_article: &'static str,
    list_name_and_article: &'static str, close_pos: Option<&mut InputPosition>
) -> Result<(), ParseError>
    where F: Fn(&InputSource, &mut TokenIter) -> Result<T, ParseError>
{
    let first_pos = iter.last_valid_pos();
    match maybe_consume_comma_separated(
        open_delim, close_delim, source, iter, consumer_fn, target,
        item_name_and_article, close_pos
    ) {
        Ok(true) => Ok(()),
        Ok(false) => {
            return Err(ParseError::new_error_at_pos(
                source, first_pos,
                format!("expected {}", list_name_and_article)
            ));
        },
        Err(err) => Err(err)
    }
}

/// Consumes an integer literal, may be binary, octal, hexadecimal or decimal,
/// and may have separating '_'-characters.
pub(crate) fn consume_integer_literal(source: &InputSource, iter: &mut TokenIter, buffer: &mut String) -> Result<(u64, InputSpan), ParseError> {
    if Some(TokenKind::Integer) != iter.next() {
        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected an integer literal"));
    }
    let integer_span = iter.next_span();
    iter.consume();

    let integer_text = source.section_at_span(integer_span);

    // Determine radix and offset from prefix
    let (radix, input_offset, radix_name) =
        if integer_text.starts_with(b"0b") || integer_text.starts_with(b"0B") {
            // Binary number
            (2, 2, "binary")
        } else if integer_text.starts_with(b"0o") || integer_text.starts_with(b"0O") {
            // Octal number
            (8, 2, "octal")
        } else if integer_text.starts_with(b"0x") || integer_text.starts_with(b"0X") {
            // Hexadecimal number
            (16, 2, "hexadecimal")
        } else {
            (10, 0, "decimal")
        };

    // Take out any of the separating '_' characters
    buffer.clear();
    for char_idx in input_offset..integer_text.len() {
        let char = integer_text[char_idx];
        if char == b'_' {
            continue;
        }
        if !char.is_ascii_digit() {
            return Err(ParseError::new_error_at_span(
                source, integer_span,
                format!("incorrectly formatted {} number", radix_name)
            ));
        }
        buffer.push(char::from(char));
    }

    // Use the cleaned up string to convert to integer
    match u64::from_str_radix(&buffer, radix) {
        Ok(number) => Ok((number, integer_span)),
        Err(_) => Err(ParseError::new_error_at_span(
            source, integer_span,
            format!("incorrectly formatted {} number", radix_name)
        )),
    }
}

/// Consumes a character literal. We currently support a limited number of
/// backslash-escaped characters
pub(crate) fn consume_character_literal(source: &InputSource, iter: &mut TokenIter, buffer: &mut String) -> Result<char, ParseError> {
    if Some(TokenKind::Character) != iter.next() {
        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected a character literal"));
    }
    let char_span = iter.next_span();
    iter.consume();

    let char_text = source.section_at_span(char_span);

    //
}

/// Consumes a string literal. We currently support a limited number of
/// backslash-escaped characters.
pub(crate) fn consume_string_literal(source: &InputSource, iter: &mut TokenIter, buffer: &mut String) -> Result<(>

pub(crate) fn consume_pragma<'a>(source: &'a InputSource, iter: &mut TokenIter) -> Result<(&'a [u8], InputPosition, InputPosition), ParseError> {
    if Some(TokenKind::Pragma) != iter.next() {
        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected a pragma"));
    }
    let (pragma_start, pragma_end) = iter.next_positions();
    iter.consume();
    Ok((source.section_at_pos(pragma_start, pragma_end), pragma_start, pragma_end))
}

pub(crate) fn has_ident(source: &InputSource, iter: &mut TokenIter, expected: &[u8]) -> bool {
    peek_ident(source, iter).map_or(false, |section| section == expected)
}

pub(crate) fn peek_ident<'a>(source: &'a InputSource, iter: &mut TokenIter) -> Option<&'a [u8]> {
    if Some(TokenKind::Ident) == iter.next() {
        let (start, end) = iter.next_positions();
        return Some(source.section_at_pos(start, end))
    }

    None
}

/// Consumes any identifier and returns it together with its span. Does not
/// check if the identifier is a reserved keyword.
pub(crate) fn consume_any_ident<'a>(
    source: &'a InputSource, iter: &mut TokenIter
) -> Result<(&'a [u8], InputSpan), ParseError> {
    if Some(TokenKind::Ident) != iter.next() {
        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected an identifier"));
    }
    let (ident_start, ident_end) = iter.next_positions();
    iter.consume();
    Ok((source.section_at_pos(ident_start, ident_end), InputSpan::from_positions(ident_start, ident_end)))
}

/// Consumes a specific identifier. May or may not be a reserved keyword.
pub(crate) fn consume_exact_ident(source: &InputSource, iter: &mut TokenIter, expected: &[u8]) -> Result<InputSpan, ParseError> {
    let (ident, pos) = consume_any_ident(source, iter)?;
    if ident != expected {
        debug_assert!(expected.is_ascii());
        return Err(ParseError::new_error_at_pos(
            source, iter.last_valid_pos(),
            format!("expected the text '{}'", &String::from_utf8_lossy(expected))
        ));
    }
    Ok(pos)
}

/// Consumes an identifier that is not a reserved keyword and returns it
/// together with its span.
pub(crate) fn consume_ident<'a>(
    source: &'a InputSource, iter: &mut TokenIter
) -> Result<(&'a [u8], InputSpan), ParseError> {
    let (ident, span) = consume_any_ident(source, iter)?;
    if is_reserved_keyword(ident) {
        return Err(ParseError::new_error_str_at_span(source, span, "encountered reserved keyword"));
    }

    Ok((ident, span))
}

/// Consumes an identifier and immediately intern it into the `StringPool`
pub(crate) fn consume_ident_interned(
    source: &InputSource, iter: &mut TokenIter, ctx: &mut PassCtx
) -> Result<Identifier, ParseError> {
    let (value, span) = consume_ident(source, iter)?;
    let value = ctx.pool.intern(value);
    Ok(Identifier{ span, value })
}

fn is_reserved_definition_keyword(text: &[u8]) -> bool {
    match text {
        KW_STRUCT | KW_ENUM | KW_UNION | KW_FUNCTION | KW_PRIMITIVE | KW_COMPOSITE => true,
        _ => false,
    }
}

fn is_reserved_statement_keyword(text: &[u8]) -> bool {
    match text {
        KW_IMPORT | KW_AS |
        KW_STMT_CHANNEL | KW_STMT_IF | KW_STMT_WHILE |
        KW_STMT_BREAK | KW_STMT_CONTINUE | KW_STMT_GOTO | KW_STMT_RETURN |
        KW_STMT_SYNC | KW_STMT_ASSERT | KW_STMT_NEW => true,
        _ => false,
    }
}

fn is_reserved_expression_keyword(text: &[u8]) -> bool {
    match text {
        KW_LET |
        KW_LIT_TRUE | KW_LIT_FALSE | KW_LIT_NULL |
        KW_FUNC_GET | KW_FUNC_PUT | KW_FUNC_FIRES | KW_FUNC_CREATE | KW_FUNC_LENGTH => true,
        _ => false,
    }
}

fn is_reserved_type_keyword(text: &[u8]) -> bool {
    match text {
        KW_TYPE_IN_PORT | KW_TYPE_OUT_PORT | KW_TYPE_MESSAGE | KW_TYPE_BOOL |
        KW_TYPE_UINT8 | KW_TYPE_UINT16 | KW_TYPE_UINT32 | KW_TYPE_UINT64 |
        KW_TYPE_SINT8 | KW_TYPE_SINT16 | KW_TYPE_SINT32 | KW_TYPE_SINT64 |
        KW_TYPE_CHAR | KW_TYPE_STRING |
        KW_TYPE_INFERRED => true,
        _ => false,
    }
}

fn is_reserved_keyword(text: &[u8]) -> bool {
    return
        is_reserved_definition_keyword(text) ||
        is_reserved_statement_keyword(text) ||
        is_reserved_expression_keyword(text) ||
        is_reserved_type_keyword(text);
}

pub(crate) fn seek_module(modules: &[Module], root_id: RootId) -> Option<&Module> {
    for module in modules {
        if module.root_id == root_id {
            return Some(module)
        }
    }

    return None
}

/// Constructs a human-readable message indicating why there is a conflict of
/// symbols.
// Note: passing the `module_idx` is not strictly necessary, but will prevent
// programmer mistakes during development: we get a conflict because we're
// currently parsing a particular module.
pub(crate) fn construct_symbol_conflict_error(
    modules: &[Module], module_idx: usize, ctx: &PassCtx, new_symbol: &Symbol, old_symbol: &Symbol
) -> ParseError {
    let module = &modules[module_idx];
    let get_symbol_span_and_msg = |symbol: &Symbol| -> (String, InputSpan) {
        match symbol.introduced_at {
            Some(import_id) => {
                // Symbol is being imported
                let import = &ctx.heap[import_id];
                match import {
                    Import::Module(import) => (
                        format!("the module aliased as '{}' imported here", symbol.name.as_str()),
                        import.span
                    ),
                    Import::Symbols(symbols) => (
                        format!("the type '{}' imported here", symbol.name.as_str()),
                        symbols.span
                    ),
                }
            },
            None => {
                // Symbol is being defined
                debug_assert_eq!(symbol.defined_in_module, module.root_id);
                debug_assert_ne!(symbol.definition.symbol_class(), SymbolClass::Module);
                (
                    format!("the type '{}' defined here", symbol.name.as_str()),
                    symbol.identifier_span
                )
            }
        }
    };

    let (new_symbol_msg, new_symbol_span) = get_symbol_span_and_msg(new_symbol);
    let (old_symbol_msg, old_symbol_span) = get_symbol_span_and_msg(old_symbol);
    return ParseError::new_error_at_span(
        &module.source, new_symbol_span, format!("symbol is defined twice: {}", new_symbol_msg)
    ).with_info_at_span(
        &module.source, old_symbol_span, format!("it conflicts with {}", old_symbol_msg)
    )
}