#![allow(clippy::upper_case_acronyms)]

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

/// 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,

  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,
  Const, Let, In,
  Mut,
  Return,
  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,
      "const" => Kw::Const,
      "let" => Kw::Let,
      "in" => Kw::In,
      "mut" => Kw::Mut,
      "return" => Kw::Return,
      "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; 18] = ['!', '$', '%', '&', '*', '+', '-', '.', ':', '<', '>', '=', '?', '@', '^', '|', '~', '`'];
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,
      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::*;
  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 }]);
  }
}