//! Lexing `&str` into a sequence of Rust tokens.
//!
//! Note that strictly speaking the parser in this crate is not required to work
//! on tokens which originated from text. Macros, eg, can synthesize tokes out
//! of thin air. So, ideally, lexer should be an orthogonal crate. It is however
//! convenient to include a text-based lexer here!

use crate::{
    SyntaxKind::{self, *},
    T,
};

#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct LexerToken {
    pub kind: SyntaxKind,
    pub len: usize,
    pub error: Option<String>,
}

impl LexerToken {
    pub fn new(kind: SyntaxKind, len: usize) -> Self {
        Self { kind, len, error: None }
    }

    /// Lexes text as a sequence of tokens.
    pub fn tokenize(text: &str) -> Vec<LexerToken> {
        let mut res = Vec::new();
        let mut offset = 0;

        if let Some(shebang_len) = rustc_lexer::strip_shebang(text) {
            res.push(LexerToken::new(SHEBANG, shebang_len));
            offset = shebang_len
        };

        for token in rustc_lexer::tokenize(&text[offset..]) {
            let token_text = &text[offset..][..token.len];
            offset += token.len;

            let (kind, err) = from_rustc(&token.kind, token_text);
            let mut token = LexerToken::new(kind, token.len);
            token.error = err.map(|it| it.to_string());
            res.push(token);
        }

        res
    }
    /// Lexes text as a single token. Returns `None` if there's leftover text.
    pub fn from_str(text: &str) -> Option<LexerToken> {
        if text.is_empty() {
            return None;
        }

        let token = rustc_lexer::first_token(text);
        if token.len != text.len() {
            return None;
        }

        let (kind, err) = from_rustc(&token.kind, text);

        let mut token = LexerToken::new(kind, token.len);
        token.error = err.map(|it| it.to_string());
        Some(token)
    }
}

/// Returns `SyntaxKind` and an optional tokenize error message.
fn from_rustc(
    kind: &rustc_lexer::TokenKind,
    token_text: &str,
) -> (SyntaxKind, Option<&'static str>) {
    // A note on an intended tradeoff:
    // We drop some useful information here (see patterns with double dots `..`)
    // Storing that info in `SyntaxKind` is not possible due to its layout requirements of
    // being `u16` that come from `rowan::SyntaxKind`.
    let mut err = "";

    let syntax_kind = {
        match kind {
            rustc_lexer::TokenKind::LineComment { doc_style: _ } => COMMENT,
            rustc_lexer::TokenKind::BlockComment { doc_style: _, terminated } => {
                if !terminated {
                    err = "Missing trailing `*/` symbols to terminate the block comment";
                }
                COMMENT
            }

            rustc_lexer::TokenKind::Whitespace => WHITESPACE,

            rustc_lexer::TokenKind::Ident if token_text == "_" => UNDERSCORE,
            rustc_lexer::TokenKind::Ident => SyntaxKind::from_keyword(token_text).unwrap_or(IDENT),

            rustc_lexer::TokenKind::RawIdent => IDENT,
            rustc_lexer::TokenKind::Literal { kind, .. } => return from_rustc_literal(kind),

            rustc_lexer::TokenKind::Lifetime { starts_with_number } => {
                if *starts_with_number {
                    err = "Lifetime name cannot start with a number";
                }
                LIFETIME_IDENT
            }

            rustc_lexer::TokenKind::Semi => T![;],
            rustc_lexer::TokenKind::Comma => T![,],
            rustc_lexer::TokenKind::Dot => T![.],
            rustc_lexer::TokenKind::OpenParen => T!['('],
            rustc_lexer::TokenKind::CloseParen => T![')'],
            rustc_lexer::TokenKind::OpenBrace => T!['{'],
            rustc_lexer::TokenKind::CloseBrace => T!['}'],
            rustc_lexer::TokenKind::OpenBracket => T!['['],
            rustc_lexer::TokenKind::CloseBracket => T![']'],
            rustc_lexer::TokenKind::At => T![@],
            rustc_lexer::TokenKind::Pound => T![#],
            rustc_lexer::TokenKind::Tilde => T![~],
            rustc_lexer::TokenKind::Question => T![?],
            rustc_lexer::TokenKind::Colon => T![:],
            rustc_lexer::TokenKind::Dollar => T![$],
            rustc_lexer::TokenKind::Eq => T![=],
            rustc_lexer::TokenKind::Bang => T![!],
            rustc_lexer::TokenKind::Lt => T![<],
            rustc_lexer::TokenKind::Gt => T![>],
            rustc_lexer::TokenKind::Minus => T![-],
            rustc_lexer::TokenKind::And => T![&],
            rustc_lexer::TokenKind::Or => T![|],
            rustc_lexer::TokenKind::Plus => T![+],
            rustc_lexer::TokenKind::Star => T![*],
            rustc_lexer::TokenKind::Slash => T![/],
            rustc_lexer::TokenKind::Caret => T![^],
            rustc_lexer::TokenKind::Percent => T![%],
            rustc_lexer::TokenKind::Unknown => ERROR,
        }
    };

    let err = if err.is_empty() { None } else { Some(err) };
    (syntax_kind, err)
}

fn from_rustc_literal(kind: &rustc_lexer::LiteralKind) -> (SyntaxKind, Option<&'static str>) {
    let mut err = "";

    let syntax_kind = match *kind {
        rustc_lexer::LiteralKind::Int { empty_int, base: _ } => {
            if empty_int {
                err = "Missing digits after the integer base prefix";
            }
            INT_NUMBER
        }
        rustc_lexer::LiteralKind::Float { empty_exponent, base: _ } => {
            if empty_exponent {
                err = "Missing digits after the exponent symbol";
            }
            FLOAT_NUMBER
        }
        rustc_lexer::LiteralKind::Char { terminated } => {
            if !terminated {
                err = "Missing trailing `'` symbol to terminate the character literal";
            }
            CHAR
        }
        rustc_lexer::LiteralKind::Byte { terminated } => {
            if !terminated {
                err = "Missing trailing `'` symbol to terminate the byte literal";
            }
            BYTE
        }
        rustc_lexer::LiteralKind::Str { terminated } => {
            if !terminated {
                err = "Missing trailing `\"` symbol to terminate the string literal";
            }
            STRING
        }
        rustc_lexer::LiteralKind::ByteStr { terminated } => {
            if !terminated {
                err = "Missing trailing `\"` symbol to terminate the byte string literal";
            }
            BYTE_STRING
        }
        rustc_lexer::LiteralKind::RawStr { err: raw_str_err, .. } => {
            if let Some(raw_str_err) = raw_str_err {
                err = match raw_str_err {
                    rustc_lexer::RawStrError::InvalidStarter { .. } => "Missing `\"` symbol after `#` symbols to begin the raw string literal",
                    rustc_lexer::RawStrError::NoTerminator { expected, found, .. } => if expected == found {
                        "Missing trailing `\"` to terminate the raw string literal"
                    } else {
                        "Missing trailing `\"` with `#` symbols to terminate the raw string literal"
                    },
                    rustc_lexer::RawStrError::TooManyDelimiters { .. } => "Too many `#` symbols: raw strings may be delimited by up to 65535 `#` symbols",
                };
            };
            STRING
        }
        rustc_lexer::LiteralKind::RawByteStr { err: raw_str_err, .. } => {
            if let Some(raw_str_err) = raw_str_err {
                err = match raw_str_err {
                    rustc_lexer::RawStrError::InvalidStarter { .. } => "Missing `\"` symbol after `#` symbols to begin the raw byte string literal",
                    rustc_lexer::RawStrError::NoTerminator { expected, found, .. } => if expected == found {
                        "Missing trailing `\"` to terminate the raw byte string literal"
                    } else {
                        "Missing trailing `\"` with `#` symbols to terminate the raw byte string literal"
                    },
                    rustc_lexer::RawStrError::TooManyDelimiters { .. } => "Too many `#` symbols: raw byte strings may be delimited by up to 65535 `#` symbols",
                };
            };

            BYTE_STRING
        }
    };

    let err = if err.is_empty() { None } else { Some(err) };
    (syntax_kind, err)
}