// Copyright (c) 2016-2021 Fabian Schuiki

use crate::lexer::bundler::Bundle;
use crate::lexer::token::*;
use moore_common::errors::*;
use moore_common::grind::{Grinder, Lookahead};
use moore_common::name::*;
use moore_common::source::*;

/// A grinder that combines character bundles into lexical tokens. This is the
/// last stage of lexical analysis.
pub struct Tokenizer<T: Grinder> {
    inner: Lookahead<T>,
}

impl<T: Grinder> Tokenizer<T>
where
    T: Grinder<Item = Option<Spanned<Bundle>>, Error = DiagBuilder2>,
{
    /// Create a new bundler.
    pub fn new<I>(inner: I) -> Tokenizer<T>
    where
        I: Into<Lookahead<T>>,
    {
        Tokenizer {
            inner: inner.into(),
        }
    }

    /// Returns the next bundle in the input for which `is_significant` is true.
    fn next_significant(&mut self) -> Option<Spanned<Bundle>> {
        while let Some(v) = self.inner.next() {
            if v.value.is_significant() {
                return Some(v);
            }
        }
        None
    }

    /// Parses a bit string literal with an optional size already parsed. These
    /// are of the form `<size>[B|O|X|D|UB|UO|UX|SB|SO|SX]"<bits>"`.
    fn parse_bit_string_literal(
        &mut self,
        int: Option<Spanned<Name>>,
        base: Spanned<String>,
        mut value: Spanned<String>,
    ) -> Spanned<Token> {
        let (int, mut span) = match int {
            Some(Spanned { value, span }) => (Some(value), span),
            None => (None, base.span),
        };
        span.end = value.span.end;

        // Parse the base.
        let base = match base.value.to_uppercase().as_str() {
            "B" => BitStringBase::B,
            "O" => BitStringBase::O,
            "X" => BitStringBase::X,
            "D" => BitStringBase::D,
            "UB" => BitStringBase::UB,
            "UO" => BitStringBase::UO,
            "UX" => BitStringBase::UX,
            "SB" => BitStringBase::SB,
            "SO" => BitStringBase::SO,
            "SX" => BitStringBase::SX,
            _ => {
                self.emit(
                    DiagBuilder2::error(format!(
                        "`{}` is not a valid base for a bit string literal",
                        base.value
                    ))
                    .span(base.span)
                    .add_note("Valid bases are B, O, X, UB, UO, UX, SB, SO, SX, D"),
                );
                BitStringBase::B
            }
        };

        // Parse the value.
        let mut parsed_value = String::new();
        for c in value.value.drain(..) {
            if !c.is_whitespace() {
                if c != '_' {
                    parsed_value.push(c);
                }
            } else {
                self.emit(
                    DiagBuilder2::error(format!(
                        "Character `{}` may not appear in a bit string literal",
                        c
                    ))
                    .span(value.span),
                );
            }
        }
        let value = get_name_table().intern(&parsed_value, true);

        Spanned::new(Lit(Literal::BitString(int, base, value)), span)
    }

    /// Parse an integer, i.e. a sequence of digits with optional intermittent
    /// underscores '_'.
    fn parse_integer(&mut self, mut s: String, mut sp: Span) -> Spanned<Name> {
        loop {
            match self.inner.next() {
                Some(Spanned {
                    value: Bundle::Digits(n),
                    span,
                }) => {
                    s.push_str(&n);
                    sp.end = span.end;
                }
                Some(Spanned {
                    value: Bundle::Special('_'),
                    ..
                }) => (),
                n => {
                    self.inner.undo(n);
                    break;
                }
            }
        }
        Spanned::new(get_name_table().intern(&s, true), sp)
    }

    /// Parse an based integer, i.e. a sequence of letters and digits with
    /// optional intermittent underscores '_'.
    fn parse_based_integer(&mut self) -> Spanned<Name> {
        let (mut s, mut sp) = match self.inner.next() {
            Some(Spanned {
                value: Bundle::Letters(n),
                span,
            })
            | Some(Spanned {
                value: Bundle::Digits(n),
                span,
            }) => (n, span),
            Some(n) => {
                let sp = n.span.begin().into();
                self.emit(DiagBuilder2::error("Expected digits or letters").span(sp));
                self.inner.undo(Some(n));
                return Spanned::new(get_name_table().intern("", true), sp);
            }
            None => {
                self.emit(DiagBuilder2::error("Expected digits or letters"));
                self.inner.undo(None);
                return Spanned::new(get_name_table().intern("", true), INVALID_SPAN);
            }
        };
        loop {
            match self.inner.next() {
                Some(Spanned {
                    value: Bundle::Letters(n),
                    span,
                })
                | Some(Spanned {
                    value: Bundle::Digits(n),
                    span,
                }) => {
                    s.push_str(&n);
                    sp.end = span.end;
                }
                Some(Spanned {
                    value: Bundle::Special('_'),
                    ..
                }) => (),
                n => {
                    self.inner.undo(n);
                    break;
                }
            }
        }
        Spanned::new(get_name_table().intern(&s, true), sp)
    }

    /// Try to parse an exponent, introduced by a `E` character.
    fn try_exponent(&mut self) -> Option<Spanned<Exponent>> {
        match self.inner.next() {
            Some(Spanned {
                value: Bundle::Letters(ref l),
                span: mut sp,
            }) if l == "e" || l == "E" => {
                let mut n = self.inner.next();
                let sign = match n {
                    Some(Spanned {
                        value: Bundle::Special('+'),
                        ..
                    }) => {
                        n = self.inner.next();
                        ExponentSign::Positive
                    }
                    Some(Spanned {
                        value: Bundle::Special('-'),
                        ..
                    }) => {
                        n = self.inner.next();
                        ExponentSign::Negative
                    }
                    _ => ExponentSign::Positive,
                };
                match n {
                    Some(Spanned {
                        value: Bundle::Digits(s),
                        span,
                    }) => {
                        let int = self.parse_integer(s, span);
                        sp.end = int.span.end;
                        Some(Spanned::new(Exponent(sign, int.value), sp))
                    }
                    n => {
                        self.emit(
                            DiagBuilder2::error(format!("Expected exponent after `{}`", l))
                                .span(sp),
                        );
                        self.inner.undo(n);
                        None
                    }
                }
            }
            n => {
                self.inner.undo(n);
                None
            }
        }
    }

    /// Parse any of the symbols in the language. `c0` comes from a
    /// `Bundle::Special` that has already been parsed.
    fn parse_symbol(&mut self, c0: char, mut span: Span) -> Option<Spanned<Token>> {
        let n1 = self.inner.next();
        let n2 = self.inner.next();

        // Try to parse a three-character symbol.
        if let (
            &Some(Spanned {
                value: Bundle::Special(c1),
                ..
            }),
            &Some(Spanned {
                value: Bundle::Special(c2),
                span: sp,
            }),
        ) = (&n1, &n2)
        {
            if let Some(tkn) = match (c0, c1, c2) {
                ('?', '/', '=') => Some(MatchNeq),
                ('?', '<', '=') => Some(MatchLeq),
                ('?', '>', '=') => Some(MatchGeq),
                _ => None,
            } {
                span.expand(sp);
                return Some(Spanned::new(tkn, span));
            }
        }
        self.inner.undo(n2);

        // Try to parse a two-character symbol.
        if let &Some(Spanned {
            value: Bundle::Special(c1),
            span: sp,
        }) = &n1
        {
            if let Some(tkn) = match (c0, c1) {
                ('=', '>') => Some(Arrow),
                ('?', '?') => Some(Condition),
                ('<', '>') => Some(LtGt),
                (':', '=') => Some(VarAssign),
                ('<', '<') => Some(Lshift),
                ('>', '>') => Some(Rshift),
                ('/', '=') => Some(Neq),
                ('<', '=') => Some(Leq),
                ('>', '=') => Some(Geq),
                ('?', '=') => Some(MatchEq),
                ('?', '<') => Some(MatchLt),
                ('?', '>') => Some(MatchGt),
                ('*', '*') => Some(Pow),
                _ => None,
            } {
                span.expand(sp);
                return Some(Spanned::new(tkn, span));
            }
        }
        self.inner.undo(n1);

        // Try to parse a one-character symbol.
        if let Some(tkn) = match c0 {
            '(' => Some(OpenDelim(Paren)),
            ')' => Some(CloseDelim(Paren)),
            '[' => Some(OpenDelim(Brack)),
            ']' => Some(CloseDelim(Brack)),
            '.' => Some(Period),
            ',' => Some(Comma),
            ':' => Some(Colon),
            ';' => Some(Semicolon),
            '\'' => Some(Apostrophe),
            '&' => Some(Ampersand),
            '=' => Some(Eq),
            '<' => Some(Lt),
            '>' => Some(Gt),
            '+' => Some(Add),
            '-' => Some(Sub),
            '*' => Some(Mul),
            '/' => Some(Div),
            '|' => Some(Pipe),
            '?' => Some(Qmark),
            _ => None,
        } {
            return Some(Spanned::new(tkn, span));
        }

        // If we get here, we parsed something which is allowed in VHDL source
        // text, but is not a valid symbol on its own.
        self.emit(DiagBuilder2::error(format!("`{}` is not a valid symbol", c0)).span(span));
        None
    }
}

impl<T> Grinder for Tokenizer<T>
where
    T: Grinder<Item = Option<Spanned<Bundle>>, Error = DiagBuilder2>,
{
    type Item = Option<Spanned<Token>>;
    type Error = DiagBuilder2;

    fn emit(&mut self, err: Self::Error) {
        self.inner.emit(err);
    }

    fn next(&mut self) -> Self::Item {
        let b = match self.next_significant() {
            Some(v) => v,
            None => return None,
        };

        match b.value {
            Bundle::Letters(mut s) => {
                let mut m = self.inner.next();
                if let Some(Spanned {
                    value: Bundle::StringLiteral(v),
                    span,
                }) = m
                {
                    // If the letters are immediately followed by a string literal,
                    // parse this as a bit string literal.
                    Some(self.parse_bit_string_literal(
                        None,
                        Spanned::new(s, b.span),
                        Spanned::new(v, span),
                    ))
                } else {
                    // Parse a basic identifier.
                    let mut sp = b.span;
                    loop {
                        match m {
                            Some(Spanned {
                                value: Bundle::Letters(n),
                                span,
                            })
                            | Some(Spanned {
                                value: Bundle::Digits(n),
                                span,
                            }) => {
                                s.push_str(&n);
                                sp.end = span.end;
                                m = self.inner.next();
                            }
                            Some(Spanned {
                                value: Bundle::Special('_'),
                                span,
                            }) => {
                                s.push('_');
                                sp.end = span.end;
                                m = self.inner.next();
                            }
                            n => {
                                self.inner.undo(n);
                                break;
                            }
                        }
                    }

                    // See if this identifier is a keyword.
                    Some(Spanned::new(
                        if let Some(kw) = find_keyword(&s) {
                            Keyword(kw)
                        } else {
                            Ident(get_name_table().intern(&s, false))
                        },
                        sp,
                    ))
                }
            }

            Bundle::ExtendedIdent(s) => Some(Spanned::new(
                Ident(get_name_table().intern(&s, true)),
                b.span,
            )),

            Bundle::Digits(s) => {
                // Parse the integer and decide how to continue.
                let int = self.parse_integer(s, b.span);
                match (self.inner.next(), self.inner.next()) {
                    // If the integer is followed by some letters and a string
                    // literal, interpret this as a bit string literal.
                    (
                        Some(Spanned {
                            value: Bundle::Letters(b),
                            span: sp1,
                        }),
                        Some(Spanned {
                            value: Bundle::StringLiteral(s),
                            span: sp2,
                        }),
                    ) => Some(self.parse_bit_string_literal(
                        Some(int),
                        Spanned::new(b, sp1),
                        Spanned::new(s, sp2),
                    )),

                    // If the integer is followed by a period '.', parse the
                    // following fractional part.
                    (
                        Some(Spanned {
                            value: Bundle::Special('.'),
                            ..
                        }),
                        Some(Spanned {
                            value: Bundle::Digits(s),
                            span,
                        }),
                    ) => {
                        let frac = self.parse_integer(s, span);
                        let exp = self.try_exponent();
                        let mut sp = int.span;
                        let exp = match exp {
                            Some(Spanned { value, span }) => {
                                sp.end = span.end;
                                Some(value)
                            }
                            _ => {
                                sp.end = frac.span.end;
                                None
                            }
                        };
                        Some(Spanned::new(
                            Lit(Literal::Abstract(None, int.value, Some(frac.value), exp)),
                            sp,
                        ))
                    }

                    // If the integer is followed by a hashtag '#', parse this
                    // as a based literal.
                    (
                        Some(Spanned {
                            value: Bundle::Special('#'),
                            ..
                        }),
                        n,
                    ) => {
                        self.inner.undo(n);
                        let base = int;
                        let int = self.parse_based_integer();
                        let mut sp = Span::union(base.span, int.span);

                        // Parse the optional fractional part.
                        let n = self.inner.next();
                        let frac = if let Some(Spanned {
                            value: Bundle::Special('.'),
                            ..
                        }) = n
                        {
                            let f = self.parse_based_integer();
                            sp.expand(f.span);
                            Some(f.value)
                        } else {
                            self.inner.undo(n);
                            None
                        };

                        // Match the second `#`.
                        match self.inner.next() {
                            Some(Spanned {
                                value: Bundle::Special('#'),
                                span,
                            }) => {
                                sp.expand(span);
                            }
                            n => {
                                self.emit(
                                    DiagBuilder2::error(
                                        "Expected `#` after digits of based literal",
                                    )
                                    .span(sp.end()),
                                );
                                self.inner.undo(n);
                            }
                        }

                        // Parse the optional exponent.
                        let exp = match self.try_exponent() {
                            Some(Spanned { value, span }) => {
                                sp.end = span.end;
                                Some(value)
                            }
                            _ => None,
                        };

                        Some(Spanned::new(
                            Lit(Literal::Abstract(Some(base.value), int.value, frac, exp)),
                            sp,
                        ))
                    }

                    // Otherwise, simply check for an exponent and we're done.
                    (n, m) => {
                        self.inner.undo(m);
                        self.inner.undo(n);
                        let exp = self.try_exponent();
                        let mut sp = int.span;
                        let exp = match exp {
                            Some(Spanned { value, span }) => {
                                sp.end = span.end;
                                Some(value)
                            }
                            _ => {
                                sp.end = int.span.end;
                                None
                            }
                        };
                        Some(Spanned::new(
                            Lit(Literal::Abstract(None, int.value, None, exp)),
                            sp,
                        ))
                    }
                }
            }

            Bundle::StringLiteral(s) => Some(Spanned::new(
                Lit(Literal::String(get_name_table().intern(&s, true))),
                b.span,
            )),

            Bundle::BitLiteral(c) => Some(Spanned::new(Lit(Literal::Char(c)), b.span)),

            Bundle::Special(c0) => self.parse_symbol(c0, b.span),
            Bundle::Space | Bundle::Comment => unreachable!(),
        }
    }
}