#![allow(clippy::upper_case_acronyms)]

use std::{
    convert::{TryFrom, TryInto},
    fmt,
    iter::{Iterator, Peekable},
    rc::Rc,
};

use itertools::Itertools;

/// A location in a particular source file. Note that the
/// sizes of the internal unsigned integer types limit
/// the size of a source file to 2^32 lines of
/// at most 2^16 characters, which should be plenty big.
#[derive(Debug, Clone, Copy, PartialEq, Default)]
pub struct Location {
    pub(crate) line_num: u32,
    pub(crate) char_num: u16,
}

impl fmt::Display for Location {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}:{}", self.line_num, self.char_num)
    }
}

#[derive(Debug, PartialEq, Clone)]
pub enum TokenKind {
    Newline,
    Semicolon,

    LParen,
    RParen,
    LSquareBracket,
    RSquareBracket,
    LAngleBracket,
    RAngleBracket,
    LCurlyBrace,
    RCurlyBrace,
    Pipe,
    Backslash,
    AtSign,

    Comma,
    Period,
    Colon,
    Underscore,
    Slash,
    Equals,

    Operator(Rc<String>),
    DigitGroup(Rc<String>),
    HexLiteral(Rc<String>),
    BinNumberSigil,
    StrLiteral { s: Rc<String>, prefix: Option<Rc<String>> },
    Identifier(Rc<String>),
    Keyword(Kw),

    EOF,

    Error(String),
}
use self::TokenKind::*;

impl fmt::Display for TokenKind {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            &Operator(ref s) => write!(f, "Operator({})", **s),
            &DigitGroup(ref s) => write!(f, "DigitGroup({})", s),
            &HexLiteral(ref s) => write!(f, "HexLiteral({})", s),
            &StrLiteral { ref s, .. } => write!(f, "StrLiteral({})", s),
            &Identifier(ref s) => write!(f, "Identifier({})", s),
            &Error(ref s) => write!(f, "Error({})", s),
            other => write!(f, "{:?}", other),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq)]
pub enum Kw {
    If,
    Then,
    Else,
    Is,
    Func,
    For,
    While,
    Let,
    In,
    Mut,
    Return,
    Continue,
    Break,
    Alias,
    Type,
    SelfType,
    SelfIdent,
    Interface,
    Impl,
    True,
    False,
    Module,
    Import,
}

impl TryFrom<&str> for Kw {
    type Error = ();

    fn try_from(value: &str) -> Result<Self, Self::Error> {
        Ok(match value {
            "if" => Kw::If,
            "then" => Kw::Then,
            "else" => Kw::Else,
            "is" => Kw::Is,
            "fn" => Kw::Func,
            "for" => Kw::For,
            "while" => Kw::While,
            "let" => Kw::Let,
            "in" => Kw::In,
            "mut" => Kw::Mut,
            "return" => Kw::Return,
            "break" => Kw::Break,
            "continue" => Kw::Continue,
            "alias" => Kw::Alias,
            "type" => Kw::Type,
            "Self" => Kw::SelfType,
            "self" => Kw::SelfIdent,
            "interface" => Kw::Interface,
            "impl" => Kw::Impl,
            "true" => Kw::True,
            "false" => Kw::False,
            "module" => Kw::Module,
            "import" => Kw::Import,
            _ => return Err(()),
        })
    }
}

#[derive(Debug, Clone, PartialEq)]
pub struct Token {
    pub kind: TokenKind,
    pub(crate) location: Location,
}

impl Token {
    pub fn to_string_with_metadata(&self) -> String {
        format!("{}({})", self.kind, self.location)
    }

    pub fn get_kind(&self) -> TokenKind {
        self.kind.clone()
    }
}

const OPERATOR_CHARS: [char; 17] =
    ['!', '$', '%', '&', '*', '+', '-', '.', ':', '<', '>', '=', '?', '^', '|', '~', '`'];
fn is_operator(c: &char) -> bool {
    OPERATOR_CHARS.iter().any(|x| x == c)
}

type CharData = (usize, usize, char);

pub fn tokenize(input: &str) -> Vec<Token> {
    let mut tokens: Vec<Token> = Vec::new();

    let mut input = Iterator::intersperse(input.lines().enumerate(), (0, "\n"))
        .flat_map(|(line_idx, line)| line.chars().enumerate().map(move |(ch_idx, ch)| (line_idx, ch_idx, ch)))
        .peekable();

    while let Some((line_num, char_num, c)) = input.next() {
        let cur_tok_kind = match c {
            '/' => match input.peek().map(|t| t.2) {
                Some('/') => {
                    for (_, _, c) in input.by_ref() {
                        if c == '\n' {
                            break;
                        }
                    }
                    continue;
                }
                Some('*') => {
                    input.next();
                    let mut comment_level = 1;
                    while let Some((_, _, c)) = input.next() {
                        if c == '*' && input.peek().map(|t| t.2) == Some('/') {
                            input.next();
                            comment_level -= 1;
                        } else if c == '/' && input.peek().map(|t| t.2) == Some('*') {
                            input.next();
                            comment_level += 1;
                        }
                        if comment_level == 0 {
                            break;
                        }
                    }
                    if comment_level != 0 {
                        Error("Unclosed comment".to_string())
                    } else {
                        continue;
                    }
                }
                _ => Slash,
            },
            c if c.is_whitespace() && c != '\n' => continue,
            '\n' => Newline,
            ';' => Semicolon,
            ':' => Colon,
            ',' => Comma,
            '(' => LParen,
            ')' => RParen,
            '{' => LCurlyBrace,
            '}' => RCurlyBrace,
            '[' => LSquareBracket,
            ']' => RSquareBracket,
            '"' => handle_quote(&mut input, None),
            '\\' => Backslash,
            '@' => AtSign,
            c if c.is_digit(10) => handle_digit(c, &mut input),
            c if c.is_alphabetic() || c == '_' => handle_alphabetic(c, &mut input),
            c if is_operator(&c) => handle_operator(c, &mut input),
            unknown => Error(format!("Unexpected character: {}", unknown)),
        };
        let location =
            Location { line_num: line_num.try_into().unwrap(), char_num: char_num.try_into().unwrap() };
        tokens.push(Token { kind: cur_tok_kind, location });
    }
    tokens
}

fn handle_digit(c: char, input: &mut Peekable<impl Iterator<Item = CharData>>) -> TokenKind {
    let next_ch = input.peek().map(|&(_, _, c)| c);

    if c == '0' && next_ch == Some('x') {
        input.next();
        let rest: String = input
            .peeking_take_while(|&(_, _, ref c)| c.is_digit(16) || *c == '_')
            .map(|(_, _, c)| c)
            .collect();
        HexLiteral(Rc::new(rest))
    } else if c == '0' && next_ch == Some('b') {
        input.next();
        BinNumberSigil
    } else {
        let mut buf = c.to_string();
        buf.extend(input.peeking_take_while(|&(_, _, ref c)| c.is_digit(10)).map(|(_, _, c)| c));
        DigitGroup(Rc::new(buf))
    }
}

fn handle_quote(
    input: &mut Peekable<impl Iterator<Item = CharData>>,
    quote_prefix: Option<&str>,
) -> TokenKind {
    let mut buf = String::new();
    loop {
        match input.next().map(|(_, _, c)| c) {
            Some('"') => break,
            Some('\\') => {
                let next = input.peek().map(|&(_, _, c)| c);
                if next == Some('n') {
                    input.next();
                    buf.push('\n')
                } else if next == Some('"') {
                    input.next();
                    buf.push('"');
                } else if next == Some('t') {
                    input.next();
                    buf.push('\t');
                }
            }
            Some(c) => buf.push(c),
            None => return TokenKind::Error("Unclosed string".to_string()),
        }
    }
    TokenKind::StrLiteral { s: Rc::new(buf), prefix: quote_prefix.map(|s| Rc::new(s.to_string())) }
}

fn handle_alphabetic(c: char, input: &mut Peekable<impl Iterator<Item = CharData>>) -> TokenKind {
    let mut buf = String::new();
    buf.push(c);
    let next_is_alphabetic = input.peek().map(|&(_, _, c)| !c.is_alphabetic()).unwrap_or(true);
    if c == '_' && next_is_alphabetic {
        return TokenKind::Underscore;
    }

    loop {
        match input.peek().map(|&(_, _, c)| c) {
            Some(c) if c == '"' => {
                input.next();
                return handle_quote(input, Some(&buf));
            }
            Some(c) if c.is_alphanumeric() || c == '_' => {
                input.next();
                buf.push(c);
            }
            _ => break,
        }
    }

    match Kw::try_from(buf.as_str()) {
        Ok(kw) => TokenKind::Keyword(kw),
        Err(()) => TokenKind::Identifier(Rc::new(buf)),
    }
}

fn handle_operator(c: char, input: &mut Peekable<impl Iterator<Item = CharData>>) -> TokenKind {
    match c {
        '<' | '>' | '|' | '.' | '=' => {
            let next = &input.peek().map(|&(_, _, c)| c);
            let next_is_op = next.map(|n| is_operator(&n)).unwrap_or(false);
            if !next_is_op {
                return match c {
                    '<' => LAngleBracket,
                    '>' => RAngleBracket,
                    '|' => Pipe,
                    '.' => Period,
                    '=' => Equals,
                    _ => unreachable!(),
                };
            }
        }
        _ => (),
    };

    let mut buf = String::new();

    if c == '`' {
        loop {
            match input.peek().map(|&(_, _, c)| c) {
                Some(c) if c.is_alphabetic() || c == '_' => {
                    input.next();
                    buf.push(c);
                }
                Some('`') => {
                    input.next();
                    break;
                }
                _ => break,
            }
        }
    } else {
        buf.push(c);
        loop {
            match input.peek().map(|&(_, _, c)| c) {
                Some(c) if is_operator(&c) => {
                    input.next();
                    buf.push(c);
                }
                _ => break,
            }
        }
    }
    TokenKind::Operator(Rc::new(buf))
}

#[cfg(test)]
mod schala_tokenizer_tests {
    use super::{Kw::*, *};

    macro_rules! digit {
        ($ident:expr) => {
            DigitGroup(Rc::new($ident.to_string()))
        };
    }
    macro_rules! ident {
        ($ident:expr) => {
            Identifier(Rc::new($ident.to_string()))
        };
    }
    macro_rules! op {
        ($ident:expr) => {
            Operator(Rc::new($ident.to_string()))
        };
    }

    fn token_kinds(input: &str) -> Vec<TokenKind> {
        tokenize(input).into_iter().map(move |tok| tok.kind).collect()
    }

    #[test]
    fn tokens() {
        let output = token_kinds("let a: A<B> = c ++ d");
        assert_eq!(
            output,
            vec![
                Keyword(Let),
                ident!("a"),
                Colon,
                ident!("A"),
                LAngleBracket,
                ident!("B"),
                RAngleBracket,
                Equals,
                ident!("c"),
                op!("++"),
                ident!("d")
            ]
        );
    }

    #[test]
    fn underscores() {
        let output = token_kinds("4_8");
        assert_eq!(output, vec![digit!("4"), Underscore, digit!("8")]);

        let output = token_kinds("aba_yo");
        assert_eq!(output, vec![ident!("aba_yo")]);
    }

    #[test]
    fn comments() {
        let output = token_kinds("1  + /* hella /* bro */ */ 2");
        assert_eq!(output, vec![digit!("1"), op!("+"), digit!("2")]);

        let output = token_kinds("1  + /* hella /* bro */ 2");
        assert_eq!(output, vec![digit!("1"), op!("+"), Error("Unclosed comment".to_string())]);

        //TODO not sure if I want this behavior
        let output = token_kinds("1  + /* hella */ bro */ 2");
        assert_eq!(
            output,
            vec![
                digit!("1"),
                op!("+"),
                Identifier(Rc::new("bro".to_string())),
                Operator(Rc::new("*".to_string())),
                Slash,
                DigitGroup(Rc::new("2".to_string()))
            ]
        );
    }

    #[test]
    fn backtick_operators() {
        let output = token_kinds("1 `plus` 2");
        assert_eq!(output, vec![digit!("1"), op!("plus"), digit!("2")]);
    }

    #[test]
    fn string_literals() {
        let output = token_kinds(r#""some string""#);
        assert_eq!(output, vec![StrLiteral { s: Rc::new("some string".to_string()), prefix: None }]);

        let output = token_kinds(r#"b"some bytestring""#);
        assert_eq!(
            output,
            vec![StrLiteral {
                s: Rc::new("some bytestring".to_string()),
                prefix: Some(Rc::new("b".to_string()))
            }]
        );

        let output = token_kinds(r#""Do \n \" escapes work\t""#);
        assert_eq!(
            output,
            vec![StrLiteral { s: Rc::new("Do \n \" escapes work\t".to_string()), prefix: None }]
        );
    }
}