use crate::frontend::source_registry::{SourceId, SourcePosition, SourceSlice};
use crate::frontend::tokens::{LiteralValue, Token, TokenType};
use crate::result::{LoxError, LoxResult};

pub struct Lexer {
    input: String,
    start_char: usize,
    current_char: usize,
    start_pos: SourcePosition,
    end_pos: SourcePosition,
    source_id: SourceId,
}

fn get_keyword_token(word: &str) -> Option<TokenType> {
    match word {
        "and" => Some(TokenType::And),
        "class" => Some(TokenType::Class),
        "do" => Some(TokenType::StartBlock),
        "end" => Some(TokenType::EndBlock),
        "false" => Some(TokenType::False),
        "for" => Some(TokenType::For),
        "fun" => Some(TokenType::Fun),
        "if" => Some(TokenType::If),
        "elif" => Some(TokenType::Elif),
        "else" => Some(TokenType::Else),
        "or" => Some(TokenType::Or),
        "print" => Some(TokenType::Print),
        "return" => Some(TokenType::Return),
        "super" => Some(TokenType::Super),
        "this" => Some(TokenType::This),
        "true" => Some(TokenType::True),
        "var" => Some(TokenType::Var),
        "val" => Some(TokenType::Val),
        "while" => Some(TokenType::While),
        "True" => Some(TokenType::True),
        "False" => Some(TokenType::False),
        "Nil" => Some(TokenType::Nil),
        _ => None,
    }
}

impl Lexer {
    pub fn new(input: String, source_id: SourceId) -> Lexer {
        Lexer {
            input,
            start_char: 0,
            current_char: 0,
            start_pos: SourcePosition::default(),
            end_pos: SourcePosition::default(),
            source_id,
        }
    }

    fn advance_column(&mut self) {
        self.current_char += 1;
        self.end_pos.column += 1;
    }

    fn advance_line(&mut self) {
        self.end_pos.line += 1;
        self.end_pos.column = 0;
    }

    pub fn scans_tokens(&mut self) -> LoxResult<Vec<Token>> {
        let mut tokens = Vec::new();
        while !self.is_at_end() {
            self.start_char = self.current_char;
            self.start_pos = self.end_pos.clone();
            match self.scan_token() {
                Ok(Some(token)) => tokens.push(token),
                Ok(None) => {}
                Err(err) => return Err(err),
            }
        }
        tokens.push(self.make_token(TokenType::Eof));
        println!("Tokens:");
        tokens.iter().for_each(|val| println!("{}", val));
        Ok(tokens)
    }

    fn is_at_end(&self) -> bool {
        self.current_char >= self.input.len()
    }

    fn advance(&mut self) -> char {
        self.advance_column();
        self.input.chars().nth(self.current_char - 1).unwrap()
    }

    fn peek(&self) -> char {
        if self.is_at_end() {
            '\0'
        } else {
            self.input.chars().nth(self.current_char).unwrap()
        }
    }

    fn peek_next(&self) -> char {
        if self.current_char + 1 >= self.input.len() {
            '\0'
        } else {
            self.input.chars().nth(self.current_char + 1).unwrap()
        }
    }

    fn make_token(&self, token_type: TokenType) -> Token {
        let text = self.input[self.start_char..self.current_char].to_string();
        Token::new(
            token_type,
            text,
            SourceSlice::from_positions(
                self.source_id.clone(),
                self.start_pos.clone(),
                self.end_pos.clone(),
            ),
        )
    }
    fn make_token_with_literal(&self, token_type: TokenType, literal: LiteralValue) -> Token {
        let text = self.input[self.start_char..self.current_char].to_string();
        Token::new_complete(
            token_type,
            text,
            Some(literal),
            SourceSlice::from_positions(
                self.source_id.clone(),
                self.start_pos.clone(),
                self.end_pos.clone(),
            ),
        )
    }

    fn scan_token(&mut self) -> LoxResult<Option<Token>> {
        let c = self.advance();
        match (c, self.peek()) {
            ('(', _) => Ok(Some(self.make_token(TokenType::LeftParen))),
            (')', _) => Ok(Some(self.make_token(TokenType::RightParen))),
            ('{', _) => Ok(Some(self.make_token(TokenType::LeftBrace))),
            ('}', _) => Ok(Some(self.make_token(TokenType::RightBrace))),
            ('[', _) => Ok(Some(self.make_token(TokenType::LeftBracket))),
            (']', _) => Ok(Some(self.make_token(TokenType::RightBracket))),
            (',', _) => Ok(Some(self.make_token(TokenType::Comma))),
            ('.', _) => Ok(Some(self.make_token(TokenType::Dot))),
            ('-', _) => Ok(Some(self.make_token(TokenType::Minus))),
            ('+', _) => Ok(Some(self.make_token(TokenType::Plus))),
            (';', _) => Ok(Some(self.make_token(TokenType::Semicolon))),
            ('*', _) => Ok(Some(self.make_token(TokenType::Star))),
            ('!', '=') => {
                self.advance(); // consuma il '='
                Ok(Some(self.make_token(TokenType::BangEqual)))
            }
            ('!', _) => Ok(Some(self.make_token(TokenType::Bang))),
            ('=', '=') => {
                self.advance(); // consuma il '='
                Ok(Some(self.make_token(TokenType::EqualEqual)))
            }
            ('=', _) => Ok(Some(self.make_token(TokenType::Equal))),
            ('<', '=') => {
                self.advance(); // consuma il '='
                Ok(Some(self.make_token(TokenType::LessEqual)))
            }
            ('<', _) => Ok(Some(self.make_token(TokenType::Less))),
            ('>', '=') => {
                self.advance(); // consuma il '='
                Ok(Some(self.make_token(TokenType::GreaterEqual)))
            }
            ('>', _) => Ok(Some(self.make_token(TokenType::Greater))),
            ('/', '/') => {
                // Commento single-line
                while self.peek() != '\n' && !self.is_at_end() {
                    self.advance();
                }
                Ok(None)
            }
            ('/', '*') => {
                // Commento multi-line
                while (self.peek() != '*' || self.peek_next() != '/') && !self.is_at_end() {
                    if self.peek() == '\n' {
                        self.advance_line();
                    }
                    self.advance();
                }
                if self.is_at_end() {
                    return Err(LoxError::LexicalError {
                        source_slice: SourceSlice::from_positions(
                            self.source_id.clone(),
                            self.start_pos.clone(),
                            self.end_pos.clone(),
                        ),
                        message: "Unterminated comment".to_string(),
                    });
                } else {
                    self.advance(); // consuma '*'
                    self.advance(); // consuma '/'
                }
                Ok(None)
            }
            ('/', _) => Ok(Some(self.make_token(TokenType::Slash))),
            (' ', _) | ('\r', _) | ('\t', _) => Ok(None),
            ('\n', _) => {
                self.advance_line();
                Ok(None)
            }
            ('"', _) => self.string(),
            (c, _) if c.is_digit(10) => self.number(),
            (c, _) if c.is_alphanumeric() || c == '_' => self.identifier(),
            _ => Err(LoxError::LexicalError {
                source_slice: SourceSlice::from_positions(
                    self.source_id.clone(),
                    self.start_pos.clone(),
                    self.end_pos.clone(),
                ),
                message: format!("Unexpected character: {}", c),
            }),
        }
    }

    fn string(&mut self) -> LoxResult<Option<Token>> {
        while self.peek() != '"' && !self.is_at_end() {
            self.advance();
        }
        if self.is_at_end() {
            return Err(LoxError::LexicalError {
                source_slice: SourceSlice::from_positions(
                    self.source_id.clone(),
                    self.start_pos.clone(),
                    self.end_pos.clone(),
                ),
                message: "Unterminated string".to_string(),
            });
        }
        self.advance();
        Ok(Some(self.make_token_with_literal(
            TokenType::String,
            LiteralValue::String(self.input[self.start_char..self.current_char].to_string()),
        )))
    }

    fn number(&mut self) -> LoxResult<Option<Token>> {
        while self.peek().is_digit(10) {
            self.advance();
        }
        if self.peek() == '.' && self.peek_next().is_digit(10) {
            self.advance();
            while self.peek().is_digit(10) {
                self.advance();
            }
        }
        Ok(Some(
            self.make_token_with_literal(
                TokenType::Number,
                LiteralValue::Number(
                    self.input[self.start_char..self.current_char]
                        .parse()
                        .unwrap(),
                ),
            ),
        ))
    }

    fn identifier(&mut self) -> LoxResult<Option<Token>> {
        while self.peek().is_alphanumeric() {
            self.advance();
        }
        let text = self.input[self.start_char..self.current_char].to_string();
        match get_keyword_token(&text) {
            Some(TokenType::True) => Ok(Some(
                self.make_token_with_literal(TokenType::True, LiteralValue::Boolean(true)),
            )),
            Some(TokenType::False) => Ok(Some(
                self.make_token_with_literal(TokenType::False, LiteralValue::Boolean(false)),
            )),
            Some(TokenType::Nil) => Ok(Some(
                self.make_token_with_literal(TokenType::Nil, LiteralValue::Nil),
            )),
            Some(token_type) => Ok(Some(self.make_token(token_type))),
            None => Ok(Some(self.make_token_with_literal(
                TokenType::Identifier,
                LiteralValue::String(text.clone()),
            ))),
        }
    }
}