use crate::*;

use std::path::PathBuf;


/// Break a character stream down into individual tokens.
pub struct Tokeniser {
    /// Characters waiting to be parsed, in reverse order.
    pub chars: Vec<char>,
    /// Path of the whole source file.
    pub source_path: Option<PathBuf>,
    /// Original path of the embedded source file.
    pub embedded_path: Option<PathBuf>,
    /// Line where the embedded source file begins.
    pub embedded_first_line: usize,
    /// Position of the next character to be consumed.
    pub position: SourcePosition,
    /// Position of the most recently consumed character.
    pub prev_position: SourcePosition,
    /// Position of the first character of the current token.
    pub start_position: SourcePosition,
    /// The source characters consumed for the current token.
    pub consumed: String,
    /// List of characters that start a new token.
    pub delimiters: Vec<char>,
    /// List of characters that terminate a token.
    pub terminators: Vec<char>,
}


impl Tokeniser {
    pub fn new<P: Into<PathBuf>>(source_code: &str, path: Option<P>) -> Self {
        Self {
            chars: source_code.chars().rev().collect(),
            source_path: path.map(|p| p.into()),
            embedded_path: None,
            embedded_first_line: 0,
            position: SourcePosition::ZERO,
            prev_position: SourcePosition::ZERO,
            start_position: SourcePosition::ZERO,
            consumed: String::new(),
            delimiters: Vec::new(),
            terminators: Vec::new(),
        }
    }

    pub fn add_delimiters(&mut self, delimiters: &[char]) {
        self.delimiters.extend_from_slice(delimiters);
    }

    pub fn add_terminators(&mut self, terminators: &[char]) {
        self.terminators.extend_from_slice(terminators);
    }

    /// Return the next character without consuming it.
    pub fn peek_char(&self) -> Option<char> {
        self.chars.last().copied()
    }

    /// Consume and return the next character.
    pub fn eat_char(&mut self) -> Option<char> {
        let option = self.chars.pop();
        if let Some(c) = option {
            self.prev_position = self.position;
            self.position.advance(c);
            self.consumed.push(c);
        }
        return option;
    }

    /// Remove the next character.
    pub fn drop_char(&mut self) {
        if let Some(c) = self.chars.pop() {
            self.prev_position = self.position;
            self.position.advance(c);
        }
    }

    /// Remove whitespace.
    pub fn drop_whitespace(&mut self) {
        while let Some(c) = self.peek_char() {
            match c.is_whitespace() {
                true => self.drop_char(),
                false => break,
            }
        }
    }

    /// Remove a full token from the queue.
    pub fn eat_token(&mut self) -> String {
        let mut token = String::new();
        while let Some(peek) = self.peek_char() {
            if peek.is_whitespace() || self.delimiters.contains(&peek) {
                break;
            }
            let c = self.eat_char().unwrap();
            token.push(c);
            if self.terminators.contains(&c) {
                break;
            }
        }
        return token;
    }

    /// Consume and return all characters up to and including the delimiter.
    /// Returns None if end of source is reached before delimiter is found.
    pub fn eat_to_delimiter(&mut self, delim: char) -> Option<String> {
        let mut token = String::new();
        while let Some(c) = self.eat_char() {
            self.consumed.push(c);
            match c == delim {
                true => return Some(token),
                false => token.push(c),
            }
        }
        return None;
    }

    /// Returns true if the remainder of the line is whitespace.
    pub fn end_of_line(&self) -> bool {
        for c in self.chars.iter().rev() {
            if *c == '\n' {
                return true;
            }
            if !c.is_whitespace() {
                return false
            }
        }
        return true;
    }

    /// Mark the next character to be consumed as the start character.
    pub fn mark_start_position(&mut self) {
        self.start_position = self.position;
        self.consumed.clear();
    }

    /// Mark the previously-consumed character as the start character.
    pub fn mark_prev_start_position(&mut self) {
        self.start_position = self.prev_position;
        let c = self.consumed.chars().last();
        self.consumed.clear();
        // Keep the previously pushed character.
        if let Some(c) = c {
            self.consumed.push(c);
        }
    }

    /// Only call this once per span, it consumes the token string.
    pub fn get_source_span(&mut self) -> SourceSpan {
        let in_merged = SourceLocation {
            path: self.source_path.to_owned(),
            start: self.start_position,
            end: self.prev_position,
        };
        let in_source = if self.start_position.line >= self.embedded_first_line {
            if let Some(embedded_path) = &self.embedded_path {
                let offset = self.embedded_first_line;
                Some(
                    SourceLocation {
                        path: Some(embedded_path.to_owned()),
                        start: SourcePosition {
                            line: in_merged.start.line.saturating_sub(offset),
                            column: in_merged.start.column,
                        },
                        end: SourcePosition {
                            line: in_merged.end.line.saturating_sub(offset),
                            column: in_merged.end.column,
                        }
                    }
                )
            } else {
                None
            }
        } else {
            None
        };

        let string = std::mem::take(&mut self.consumed);
        SourceSpan { string, in_merged, in_source }
    }
}