use super::tokens::Token;
use super::errors::*;
use super::common::{ImmutableString, Range};

/// Converts text into a stream of tokens.
pub struct Scanner {
    char_index: usize,
    byte_index: usize,
    line_number: usize,
    token_start: usize,
    token_start_line: usize,
    chars: Vec<char>, // todo: use an iterator instead?
    current_token: Option<Token>,
    text_length: usize,
}

impl Scanner {
    /// Creates a new scanner based on the provided text.
    pub fn new(text: &str) -> Scanner {
        Scanner {
            char_index: 0,
            byte_index: 0,
            line_number: 0,
            token_start: 0,
            token_start_line: 0,
            chars: text.chars().collect(),
            current_token: None,
            text_length: text.len(),
        }
    }

    /// Moves to and returns the next token.
    pub fn scan(&mut self) -> Result<Option<Token>, ParseError> {
        self.skip_whitespace();
        self.token_start = self.byte_index;
        self.token_start_line = self.line_number;
        if let Some(current_char) = self.current_char() {
            let token_result = match current_char {
                '{' => {
                    self.move_next_char();
                    Ok(Token::OpenBrace)
                },
                '}' => {
                    self.move_next_char();
                    Ok(Token::CloseBrace)
                },
                '[' => {
                    self.move_next_char();
                    Ok(Token::OpenBracket)
                },
                ']' => {
                    self.move_next_char();
                    Ok(Token::CloseBracket)
                },
                ',' => {
                    self.move_next_char();
                    Ok(Token::Comma)
                },
                ':' => {
                    self.move_next_char();
                    Ok(Token::Colon)
                },
                '\'' | '"' => self.parse_string(),
                '/' => {
                    match self.peek_char() {
                        Some('/') => Ok(self.parse_comment_line()),
                        Some('*') => self.parse_comment_block(),
                        _ => Err(self.create_error_for_current_token("Unexpected token")),
                    }
                },
                _ => {
                    if current_char == '-' || self.is_digit() {
                        self.parse_number()
                    } else if self.try_move_word("true") {
                        Ok(Token::Boolean(true))
                    } else if self.try_move_word("false") {
                        Ok(Token::Boolean(false))
                    } else if self.try_move_word("null") {
                        Ok(Token::Null)
                    } else {
                        self.parse_word()
                    }
                }
            };
            match token_result {
                Ok(token) => {
                    self.current_token = Some(token.clone());
                    Ok(Some(token))
                },
                Err(err) => Err(err),
            }
        } else {
            self.current_token = None;
            Ok(None)
        }
    }

    /// Gets the start position of the token.
    pub fn token_start(&self) -> usize {
        self.token_start
    }

    /// Gets the end position of the token.
    pub fn token_end(&self) -> usize {
        self.byte_index
    }

    /// Gets the line the token starts on.
    pub fn token_start_line(&self) -> usize {
        self.token_start_line
    }

    /// Gets the line the token ends on.
    pub fn token_end_line(&self) -> usize {
        self.line_number
    }

    /// Gets the current token.
    pub fn token(&self) -> Option<Token> {
        self.current_token.as_ref().map(|x| x.to_owned())
    }

    pub(super) fn create_error_for_current_token(&self, message: &str) -> ParseError {
        self.create_error_for_start_and_line(self.token_start, self.token_start_line, message)
    }

    pub(super) fn create_error_for_current_char(&self, message: &str) -> ParseError {
        self.create_error_for_start_and_line(self.byte_index, self.line_number, message)
    }

    pub(super) fn create_error_for_start_and_line(&self, start: usize, start_line: usize, message: &str) -> ParseError {
        let range = Range {
            start,
            start_line,
            end: std::cmp::min(self.byte_index + 1, self.text_length),
            end_line: self.line_number,
        };
        ParseError::new(range, message)
    }

    fn parse_string(&mut self) -> Result<Token, ParseError> {
        debug_assert!(self.current_char() == Some('\'') || self.current_char() == Some('"'), "Expected \", was {:?}", self.current_char());
        let is_double_quote = self.current_char() == Some('"');
        let mut text = String::new();
        let mut last_was_backslash = false;
        let mut found_end_string = false;

        while let Some(current_char) = self.move_next_char() {
            if last_was_backslash {
                let escape_start = self.byte_index - 1; // -1 for backslash
                let escape_start_line = self.line_number;
                match current_char {
                    '"' => {
                        if !is_double_quote {
                            return Err(self.create_error_for_start_and_line(escape_start, escape_start_line, "Invalid escape in single quote string"));
                        } else {
                            text.push(current_char);
                        }
                    }
                    '\'' => {
                        if is_double_quote {
                            return Err(self.create_error_for_start_and_line(escape_start, escape_start_line, "Invalid escape in double quote string"));
                        } else {
                            text.push(current_char);
                        }
                    }
                    '\\' => { text.push('\\'); }
                    '/' => { text.push('/'); }
                    'b' => { text.push('\u{08}'); }
                    'f' => { text.push('\u{0C}'); }
                    'n' => { text.push('\n'); }
                    'r' => { text.push('\r'); }
                    't' => { text.push('\t'); }
                    'u' => {
                        let mut hex_text = String::new();
                        // expect four hex values
                        for _ in 0..4 {
                            let current_char = self.move_next_char();
                            if !self.is_hex() {
                                return Err(self.create_error_for_start_and_line(escape_start, escape_start_line, "Expected four hex digits"));
                            }
                            if let Some(current_char) = current_char {
                                hex_text.push(current_char);
                            }
                        }
                        let decimal = match u8::from_str_radix(&hex_text, 16) {
                            Ok(decimal) => decimal,
                            Err(err) => return Err(self.create_error_for_start_and_line(
                                escape_start,
                                escape_start_line,
                                &format!("Error converting hex of {} to u8. {:?}", hex_text, err),
                            )),
                        };
                        text.push(decimal as char);
                    },
                    _ => return Err(self.create_error_for_start_and_line(escape_start, escape_start_line, "Invalid escape")),
                }
                last_was_backslash = false;
            } else if is_double_quote && current_char == '"' || !is_double_quote && current_char == '\'' {
                found_end_string = true;
                break;
            } else {
                last_was_backslash = current_char == '\\';
                if !last_was_backslash {
                    text.push(current_char);
                }
            }
        }

        if found_end_string {
            self.move_next_char();
            Ok(Token::String(ImmutableString::new(text)))
        } else {
            Err(self.create_error_for_current_token("Unterminated string literal"))
        }
    }

    fn parse_number(&mut self) -> Result<Token, ParseError> {
        let mut text = String::new();

        if self.is_negative_sign() {
            text.push('-');
            self.move_next_char();
        }

        if self.is_zero() {
            text.push('0');
            self.move_next_char();
        } else if self.is_one_nine() {
            text.push(self.current_char().unwrap());
            self.move_next_char();
            while self.is_digit() {
                text.push(self.current_char().unwrap());
                self.move_next_char();
            }
        } else {
            return Err(self.create_error_for_current_char("Expected a digit to follow a negative sign"));
        }

        if self.is_decimal_point() {
            text.push('.');
            self.move_next_char();

            if !self.is_digit() {
                return Err(self.create_error_for_current_char("Expected a digit"));
            }

            while self.is_digit() {
                text.push(self.current_char().unwrap());
                self.move_next_char();
            }
        }

        match self.current_char() {
            Some('e') | Some('E') => {
                text.push(self.current_char().unwrap());
                match self.move_next_char() {
                    Some('-') | Some('+') => {
                        text.push(self.current_char().unwrap());
                        self.move_next_char();
                        if !self.is_digit() {
                            return Err(self.create_error_for_current_char("Expected a digit"));
                        }
                        while self.is_digit() {
                            text.push(self.current_char().unwrap());
                            self.move_next_char();
                        }
                    }
                    _ => {
                        return Err(self.create_error_for_current_char("Expected plus or minus symbol in number literal"));
                    }
                }
            }
            _ => {},
        }


        Ok(Token::Number(ImmutableString::new(text)))
    }

    fn parse_comment_line(&mut self) -> Token {
        let mut text = String::new();
        self.assert_then_move_char('/');
        #[cfg(debug_assertions)]
        self.assert_char('/');

        while let Some(current_char) = self.move_next_char() {
            if self.is_new_line() {
                break;
            }
            text.push(current_char);
        }

        Token::CommentLine(ImmutableString::new(text))
    }

    fn parse_comment_block(&mut self) -> Result<Token, ParseError> {
        let mut text = String::new();
        self.assert_then_move_char('/');
        #[cfg(debug_assertions)]
        self.assert_char('*');
        let mut found_end = false;

        while let Some(current_char) = self.move_next_char() {
            if current_char == '*' && self.peek_char() == Some('/') {
                found_end = true;
                break;
            }
            text.push(current_char);
        }

        if found_end {
            self.assert_then_move_char('*');
            self.assert_then_move_char('/');
            Ok(Token::CommentBlock(ImmutableString::new(text)))
        } else {
            Err(self.create_error_for_current_token("Unterminated comment block"))
        }
    }

    fn skip_whitespace(&mut self) {
        while let Some(current_char) = self.current_char() {
            if current_char.is_whitespace() {
                self.move_next_char();
            } else {
                break;
            }
        }
    }

    fn try_move_word(&mut self, text: &str) -> bool {
        // todo: debug assert no newlines
        let mut char_index = self.char_index;
        let mut byte_index = self.byte_index;
        for c in text.chars() {
            if let Some(current_char) = self.chars.get(char_index) {
                if *current_char != c {
                    return false;
                }

                char_index += 1;
                byte_index += current_char.len_utf8();
            } else {
                return false;
            }
        }

        if let Some(next_char) = self.chars.get(char_index) {
            if next_char.is_alphanumeric() {
                return false;
            }
        }

        self.char_index = char_index;
        self.byte_index = byte_index;
        true
    }

    fn parse_word(&mut self) -> Result<Token, ParseError> {
        let mut text = String::new();

        while let Some(current_char) = self.current_char() {
            if current_char.is_whitespace() || current_char == '\r' || current_char == '\n' || current_char == ':' {
                break;
            }
            if !current_char.is_alphanumeric() && current_char != '-' {
                return Err(self.create_error_for_current_token("Unexpected token"));
            }

            text.push(current_char);

            self.move_next_char();
        }

        if text.len() == 0 {
            return Err(self.create_error_for_current_token("Unexpected token"));
        }

        Ok(Token::Word(ImmutableString::new(text)))
    }

    fn assert_then_move_char(&mut self, _character: char) {
        #[cfg(debug_assertions)]
        self.assert_char(_character);

        self.move_next_char();
    }

    #[cfg(debug_assertions)]
    fn assert_char(&mut self, character: char) {
        let current_char = self.current_char();
        debug_assert!(current_char == Some(character), "Expected {:?}, was {:?}", character, current_char);
    }

    fn move_next_char(&mut self) -> Option<char> {
        if let Some(current_char) = self.current_char() {
            if current_char == '\n' {
                self.line_number += 1;
            }
            self.char_index += 1;
            self.byte_index += current_char.len_utf8();
        }
        self.current_char()
    }

    fn peek_char(&self) -> Option<char> {
        self.chars.get(self.char_index + 1).map(|x| x.to_owned())
    }

    fn current_char(&self) -> Option<char> {
        self.chars.get(self.char_index).map(|x| x.to_owned())
    }

    fn is_new_line(&self) -> bool {
        match self.current_char() {
            Some('\n') => true,
            Some('\r') => self.peek_char() == Some('\n'),
            _ => false,
        }
    }

    fn is_hex(&self) -> bool {
        self.is_digit() || match self.current_char() {
            Some(current_char) => current_char >= 'a' && current_char <= 'f'
                || current_char >= 'A' && current_char <= 'F',
            _ => false,
        }
    }

    fn is_digit(&self) -> bool {
        self.is_one_nine() || self.is_zero()
    }

    fn is_zero(&self) -> bool {
        self.current_char() == Some('0')
    }

    fn is_one_nine(&self) -> bool {
        match self.current_char() {
            Some(current_char) => current_char >= '1' && current_char <= '9',
            _ => false,
        }
    }

    fn is_negative_sign(&self) -> bool {
        self.current_char() == Some('-')
    }

    fn is_decimal_point(&self) -> bool {
        self.current_char() == Some('.')
    }
}

#[cfg(test)]
mod tests {
    use super::Scanner;
    use super::super::common::{ImmutableString};
    use super::super::tokens::{Token};

    #[test]
    fn it_tokenizes_string() {
        assert_has_tokens(
            r#""t\"est", "\t\r\n\n\u0020","#,
            vec![
                Token::String(ImmutableString::from(r#"t"est"#)),
                Token::Comma,
                Token::String(ImmutableString::from("\t\r\n\n ")),
                Token::Comma,
            ]
        );
    }

    #[test]
    fn it_errors_escaping_single_quote_in_double_quote() {
        assert_has_error(r#""t\'est""#, "Invalid escape in double quote string on line 1 column 3.");
    }

    #[test]
    fn it_tokenizes_single_quote_string() {
        assert_has_tokens(
            r#"'t\'est','a',"#,
            vec![
                Token::String(ImmutableString::from(r#"t'est"#)),
                Token::Comma,
                Token::String(ImmutableString::from("a")),
                Token::Comma,
            ]
        );
    }

    #[test]
    fn it_errors_escaping_double_quote_in_single_quote() {
        assert_has_error(r#"'t\"est'"#, "Invalid escape in single quote string on line 1 column 3.");
    }

    #[test]
    fn it_errors_for_word_starting_with_invalid_token() {
        assert_has_error(r#"{ &test }"#, "Unexpected token on line 1 column 3.");
    }

    #[test]
    fn it_tokenizes_numbers() {
        assert_has_tokens(
            "0, 0.123, -198, 0e-345, 0.3e+025,",
            vec![
                Token::Number(ImmutableString::from("0")),
                Token::Comma,
                Token::Number(ImmutableString::from("0.123")),
                Token::Comma,
                Token::Number(ImmutableString::from("-198")),
                Token::Comma,
                Token::Number(ImmutableString::from("0e-345")),
                Token::Comma,
                Token::Number(ImmutableString::from("0.3e+025")),
                Token::Comma,
            ]
        );
    }

    #[test]
    fn it_tokenizes_simple_tokens() {
        assert_has_tokens(
            "{}[],:true,false,null,",
            vec![
                Token::OpenBrace,
                Token::CloseBrace,
                Token::OpenBracket,
                Token::CloseBracket,
                Token::Comma,
                Token::Colon,
                Token::Boolean(true),
                Token::Comma,
                Token::Boolean(false),
                Token::Comma,
                Token::Null,
                Token::Comma,
            ]);
    }

    #[test]
    fn it_tokenizes_comment_line() {
        assert_has_tokens(
            "//test\n//t\r\n// test\n,",
            vec![
                Token::CommentLine(ImmutableString::from("test")),
                Token::CommentLine(ImmutableString::from("t")),
                Token::CommentLine(ImmutableString::from(" test")),
                Token::Comma,
            ]);
    }

    #[test]
    fn it_tokenizes_comment_blocks() {
        assert_has_tokens(
            "/*test\n *//* test*/,",
            vec![
                Token::CommentBlock(ImmutableString::from("test\n ")),
                Token::CommentBlock(ImmutableString::from(" test")),
                Token::Comma,
            ]);
    }

    fn assert_has_tokens(text: &str, tokens: Vec<Token>) {
        let mut scanner = Scanner::new(text);
        let mut scanned_tokens = Vec::new();

        loop {
            match scanner.scan() {
                Ok(Some(token)) => scanned_tokens.push(token),
                Ok(None) => break,
                Err(err) => panic!("Error parsing: {:?}", err),
            }
        }

        assert_eq!(scanned_tokens, tokens);
    }

    fn assert_has_error(text: &str, message: &str) {
        let mut scanner = Scanner::new(text);
        let mut error_message = String::new();

        loop {
            match scanner.scan() {
                Ok(Some(_)) => {},
                Ok(None) => break,
                Err(err) => {
                    error_message = err.get_message_with_range(text);
                    break;
                },
            }
        }

        assert_eq!(error_message, message);
    }
}