use std::ops::{Add, AddAssign, Neg, Range, Sub, SubAssign};

use crossterm::style::ContentStyle;

use crate::styled::Styled;
use crate::widthdb::WidthDB;
use crate::wrap;

#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
pub struct Size {
    pub width: u16,
    pub height: u16,
}

impl Size {
    pub const ZERO: Self = Self::new(0, 0);

    pub const fn new(width: u16, height: u16) -> Self {
        Self { width, height }
    }
}

impl Add for Size {
    type Output = Self;

    fn add(self, rhs: Self) -> Self {
        Self::new(self.width + rhs.width, self.height + rhs.height)
    }
}

impl AddAssign for Size {
    fn add_assign(&mut self, rhs: Self) {
        self.width += rhs.width;
        self.height += rhs.height;
    }
}

impl Sub for Size {
    type Output = Self;

    fn sub(self, rhs: Self) -> Self {
        Self::new(self.width - rhs.width, self.height - rhs.height)
    }
}

impl SubAssign for Size {
    fn sub_assign(&mut self, rhs: Self) {
        self.width -= rhs.width;
        self.height -= rhs.height;
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Pos {
    pub x: i32,
    pub y: i32,
}

impl Pos {
    pub const ZERO: Self = Self::new(0, 0);

    pub const fn new(x: i32, y: i32) -> Self {
        Self { x, y }
    }
}

impl From<Size> for Pos {
    fn from(s: Size) -> Self {
        Self::new(s.width.into(), s.height.into())
    }
}

impl Add for Pos {
    type Output = Self;

    fn add(self, rhs: Self) -> Self {
        Self::new(self.x + rhs.x, self.y + rhs.y)
    }
}

impl Add<Size> for Pos {
    type Output = Self;

    fn add(self, rhs: Size) -> Self {
        Self::new(self.x + rhs.width as i32, self.y + rhs.height as i32)
    }
}

impl AddAssign for Pos {
    fn add_assign(&mut self, rhs: Self) {
        self.x += rhs.x;
        self.y += rhs.y;
    }
}

impl AddAssign<Size> for Pos {
    fn add_assign(&mut self, rhs: Size) {
        self.x += rhs.width as i32;
        self.y += rhs.height as i32;
    }
}

impl Sub for Pos {
    type Output = Self;

    fn sub(self, rhs: Self) -> Self {
        Self::new(self.x - rhs.x, self.y - rhs.y)
    }
}

impl Sub<Size> for Pos {
    type Output = Self;

    fn sub(self, rhs: Size) -> Self {
        Self::new(self.x - rhs.width as i32, self.y - rhs.height as i32)
    }
}

impl SubAssign for Pos {
    fn sub_assign(&mut self, rhs: Self) {
        self.x -= rhs.x;
        self.y -= rhs.y;
    }
}

impl SubAssign<Size> for Pos {
    fn sub_assign(&mut self, rhs: Size) {
        self.x -= rhs.width as i32;
        self.y -= rhs.height as i32;
    }
}

impl Neg for Pos {
    type Output = Self;

    fn neg(self) -> Self {
        Self::new(-self.x, -self.y)
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Cell {
    pub content: Box<str>,
    pub style: ContentStyle,
    pub width: u8,
    pub offset: u8,
}

impl Default for Cell {
    fn default() -> Self {
        Self {
            content: " ".to_string().into_boxed_str(),
            style: ContentStyle::default(),
            width: 1,
            offset: 0,
        }
    }
}

#[derive(Debug, Default)]
pub struct Buffer {
    size: Size,
    data: Vec<Cell>,
    /// A stack of rectangular drawing areas.
    ///
    /// When rendering to the buffer with a nonempty stack, it behaves as if it
    /// was the size of the topmost stack element, and characters are translated
    /// by the position of the topmost stack element. No characters can be
    /// placed outside the area described by the topmost stack element.
    stack: Vec<(Pos, Size)>,
}

impl Buffer {
    /// Ignores the stack.
    fn index(&self, x: u16, y: u16) -> usize {
        assert!(x < self.size.width);
        assert!(y < self.size.height);

        let x: usize = x.into();
        let y: usize = y.into();
        let width: usize = self.size.width.into();

        y * width + x
    }

    /// Ignores the stack.
    pub(crate) fn at(&self, x: u16, y: u16) -> &Cell {
        assert!(x < self.size.width);
        assert!(y < self.size.height);
        let i = self.index(x, y);
        &self.data[i]
    }

    /// Ignores the stack.
    fn at_mut(&mut self, x: u16, y: u16) -> &mut Cell {
        assert!(x < self.size.width);
        assert!(y < self.size.height);
        let i = self.index(x, y);
        &mut self.data[i]
    }

    pub fn push(&mut self, pos: Pos, size: Size) {
        let cur_pos = self.stack.last().map(|(p, _)| *p).unwrap_or(Pos::ZERO);
        self.stack.push((cur_pos + pos, size));
    }

    pub fn pop(&mut self) {
        self.stack.pop();
    }

    fn drawable_area(&self) -> (Pos, Size) {
        self.stack.last().copied().unwrap_or((Pos::ZERO, self.size))
    }

    /// Size of the currently drawable area.
    pub fn size(&self) -> Size {
        self.drawable_area().1
    }

    /// Min (inclusive) and max (not inclusive) coordinates of the currently
    /// drawable area.
    fn legal_ranges(&self) -> (Range<i32>, Range<i32>) {
        let (top_left, size) = self.drawable_area();
        let min_x = top_left.x.max(0);
        let min_y = top_left.y.max(0);
        let max_x = (top_left.x + size.width as i32).min(self.size.width as i32);
        let max_y = (top_left.y + size.height as i32).min(self.size.height as i32);
        (min_x..max_x, min_y..max_y)
    }

    /// Resize the buffer and reset its contents.
    ///
    /// The buffer's contents are reset even if the buffer is already the
    /// correct size. The stack is reset as well.
    pub fn resize(&mut self, size: Size) {
        if size == self.size {
            self.data.fill_with(Cell::default);
        } else {
            let width: usize = size.width.into();
            let height: usize = size.height.into();
            let len = width * height;

            self.size = size;
            self.data.clear();
            self.data.resize_with(len, Cell::default);
        }

        self.stack.clear();
    }

    /// Reset the contents and stack of the buffer.
    ///
    /// `buf.reset()` is equivalent to `buf.resize(buf.size())`.
    pub fn reset(&mut self) {
        self.data.fill_with(Cell::default);
        self.stack.clear();
    }

    /// Remove the grapheme at the specified coordinates from the buffer.
    ///
    /// Removes the entire grapheme, not just the cell at the coordinates.
    /// Preserves the style of the affected cells. Works even if the coordinates
    /// don't point to the beginning of the grapheme.
    ///
    /// Ignores the stack.
    fn erase(&mut self, x: u16, y: u16) {
        let cell = self.at(x, y);
        let width: u16 = cell.width.into();
        let offset: u16 = cell.offset.into();
        for x in (x - offset)..(x - offset + width) {
            let cell = self.at_mut(x, y);
            let style = cell.style;
            *cell = Cell::default();
            cell.style = style;
        }
    }

    pub fn write(&mut self, widthdb: &mut WidthDB, tab_width: u8, pos: Pos, styled: &Styled) {
        let pos = self.drawable_area().0 + pos;
        let (xrange, yrange) = self.legal_ranges();
        // If we're not even visible, there's nothing to do
        if !yrange.contains(&pos.y) {
            return;
        }
        let y = pos.y as u16;

        let mut col: usize = 0;
        for styled_grapheme in styled.styled_graphemes() {
            let x = pos.x + col as i32;
            let g = *styled_grapheme.content();
            let style = *styled_grapheme.style();
            if g == "\t" {
                let width = wrap::tab_width_at_column(tab_width, col);
                col += width as usize;
                for dx in 0..width {
                    self.write_grapheme(&xrange, x + dx as i32, y, width, " ", style);
                }
            } else {
                let width = widthdb.grapheme_width(g);
                col += width as usize;
                if width > 0 {
                    self.write_grapheme(&xrange, x, y, width, g, style);
                }
            }
        }
    }

    /// Assumes that `pos.y` is in range.
    fn write_grapheme(
        &mut self,
        xrange: &Range<i32>,
        x: i32,
        y: u16,
        width: u8,
        grapheme: &str,
        style: ContentStyle,
    ) {
        let min_x = xrange.start;
        let max_x = xrange.end - 1; // Last possible cell

        let start_x = x;
        let end_x = x + width as i32 - 1; // Coordinate of last cell

        if start_x > max_x || end_x < min_x {
            return; // Not visible
        }

        if start_x >= min_x && end_x <= max_x {
            // Fully visible, write actual grapheme
            for offset in 0..width {
                let x = start_x as u16 + offset as u16;
                self.erase(x, y);
                *self.at_mut(x, y) = Cell {
                    content: grapheme.to_string().into_boxed_str(),
                    style,
                    width,
                    offset,
                };
            }
        } else {
            // Partially visible, write empty cells with correct style
            let start_x = start_x.max(0) as u16;
            let end_x = end_x.min(max_x) as u16;
            for x in start_x..=end_x {
                self.erase(x, y);
                *self.at_mut(x, y) = Cell {
                    style,
                    ..Default::default()
                };
            }
        }
    }

    pub fn cells(&self) -> Cells<'_> {
        Cells {
            buffer: self,
            x: 0,
            y: 0,
        }
    }
}

pub struct Cells<'a> {
    buffer: &'a Buffer,
    x: u16,
    y: u16,
}

impl<'a> Iterator for Cells<'a> {
    type Item = (u16, u16, &'a Cell);

    fn next(&mut self) -> Option<Self::Item> {
        if self.y >= self.buffer.size.height {
            return None;
        }

        let (x, y) = (self.x, self.y);
        let cell = self.buffer.at(self.x, self.y);
        assert!(cell.offset == 0);

        self.x += cell.width as u16;
        if self.x >= self.buffer.size.width {
            self.x = 0;
            self.y += 1;
        }

        Some((x, y, cell))
    }
}