#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Pos {
    pub source: usize,
    pub line: usize,
    pub col: usize,
    pub byte: usize,
    pub len: usize,
}

impl Default for Pos {
    fn default() -> Self {
        Pos {
            source: 0,
            line: 0,
            col: 0,
            byte: 0,
            len: 1,
        }
    }
}

impl Pos {
    pub fn from_char(c: char, source: usize, line: usize, col: usize, byte: usize) -> Self {
        Pos {
            source, line, col, byte, len: c.len_utf8(),
        }
    }

    pub fn next_char(&self, c: char) -> Self {
        Pos {
            source: self.source + 1,
            line: self.line,
            col: self.col + 1,
            byte: self.byte + self.len,
            len: c.len_utf8(),
        }
    }

    pub fn adv_char(&mut self, c: char) {
        *self = self.next_char(c);
    }

    pub fn adv_str(&mut self, s: &str) {
        for c in s.chars() {
            self.adv_char(c);
        }
    }

    pub fn min(self, other: Self) -> Self {
        if self.byte < other.byte {
            self
        } else {
            other
        }
    }

    pub fn max(self, other: Self) -> Self {
        if self.byte > other.byte {
            self
        } else {
            other
        }
    }
}

#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub struct Span {
    pub start: Pos,
    pub end: Pos,
}

impl Span {
    pub fn union(self, other: Self) -> Self {
        let start = self.start.min(other.start);
        let end = self.end.max(other.end);
        Span { start, end }
    }
}

pub trait Spanned {
    fn span(&self) -> Span;

    fn text_at<'t>(&self, text: &'t str) -> &'t str {
        let Span { start, end } = self.span();
        &text[start.byte .. end.byte]
    }
}

impl Spanned for Span {
    fn span(&self) -> Span {
        *self
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_pos_min() {
        let small = Pos::default();
        let large = Pos { 
            source: 1,
            byte: 1,
            ..Default::default()
        };

        assert_eq!(small.min(large), small);
        assert_eq!(large.min(small), small);
    }

    #[test]
    fn test_pos_max() {
        let small = Pos::default();
        let large = Pos { 
            source: 1,
            byte: 1,
            ..Default::default()
        };

        assert_eq!(small.max(large), large);
        assert_eq!(large.max(small), large);
    }

    #[test]
    fn test_span_union() {
        let first = Span {
            start: Pos::default(),
            end: Pos {
                source: 15,
                col: 15,
                byte: 15,
                ..Default::default()
            }
        };

        let second = Span {
            start: Pos {
                source: 25,
                col: 25,
                byte: 25,
                ..Default::default()
            },
            end: Pos {
                source: 27,
                col: 27,
                byte: 27,
                ..Default::default()
            }
        };

        let expected = Span {
            start: first.start,
            end: second.end,
        };

        assert_eq!(first.union(second), expected);
        assert_eq!(second.union(first), expected);
    }
}