use std::{
    cmp,
    fmt,
    time::Instant,
};

use crate::{FontLayoutLine, FontMatches, FontShapeLine};

/// An action to perform on a [TextBuffer]
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum TextAction {
    Left,
    Right,
    Up,
    Down,
    Backspace,
    Delete,
    PageUp,
    PageDown,
    Insert(char),
    Click { x: i32, y: i32 },
    Scroll(i32),
}

/// Current cursor location
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub struct TextCursor {
    pub line: usize,
    pub glyph: usize,
}

impl TextCursor {
    pub const fn new(line: usize, glyph: usize) -> Self {
        Self { line, glyph }
    }
}

/// Index of a text line
#[derive(Clone, Copy, Eq, PartialEq, Ord, PartialOrd)]
pub struct TextLineIndex(usize);

impl TextLineIndex {
    pub fn new(index: usize) -> Self {
        Self(index)
    }

    pub fn get(&self) -> usize {
        self.0
    }
}

/// Metrics of text
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub struct TextMetrics {
    /// Font size in pixels
    pub font_size: i32,
    /// Line height in pixels
    pub line_height: i32,
}

impl TextMetrics {
    pub const fn new(font_size: i32, line_height: i32) -> Self {
        Self { font_size, line_height }
    }

    pub const fn scale(self, scale: i32) -> Self {
        Self {
            font_size: self.font_size * scale,
            line_height: self.line_height * scale,
        }
    }
}

impl fmt::Display for TextMetrics {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}px / {}px", self.font_size, self.line_height)
    }
}

/// A buffer of text that is shaped and laid out
pub struct TextBuffer<'a> {
    font_matches: &'a FontMatches<'a>,
    text_lines: Vec<String>,
    shape_lines: Vec<FontShapeLine<'a>>,
    layout_lines: Vec<FontLayoutLine<'a>>,
    metrics: TextMetrics,
    width: i32,
    height: i32,
    scroll: i32,
    pub cursor: TextCursor,
    pub redraw: bool,
}

impl<'a> TextBuffer<'a> {
    pub fn new(
        font_matches: &'a FontMatches<'a>,
        text: &str,
        metrics: TextMetrics,
    ) -> Self {
        let mut text_lines: Vec<String> = text.lines().map(String::from).collect();
        if text_lines.is_empty() {
            text_lines.push(String::new());
        }
        Self {
            font_matches,
            text_lines,
            shape_lines: Vec::new(),
            layout_lines: Vec::new(),
            metrics,
            width: 0,
            height: 0,
            scroll: 0,
            cursor: TextCursor::default(),
            redraw: false,
        }
    }

    /// Pre-shape lines in the buffer, up to `lines`
    pub fn shape_until(&mut self, lines: i32) {
        let instant = Instant::now();

        let mut reshaped = 0;
        while self.shape_lines.len() < self.text_lines.len()
            && (self.layout_lines.len() as i32) < lines
        {
            let line_i = TextLineIndex::new(self.shape_lines.len());
            self.reshape_line(line_i);
            reshaped += 1;
        }

        let duration = instant.elapsed();
        if reshaped > 0 {
            log::debug!("shape_until {}: {:?}", reshaped, duration);
        }
    }

    fn shape_until_scroll(&mut self) {
        let lines = self.lines();

        let scroll_end = self.scroll + lines;
        self.shape_until(scroll_end);

        self.scroll = cmp::max(
            0,
            cmp::min(
                self.layout_lines().len() as i32 - (lines - 1),
                self.scroll,
            ),
        );
    }

    fn reshape_line(&mut self, line_i: TextLineIndex) {
        let instant = Instant::now();

        let shape_line = self
            .font_matches
            .shape_line(line_i, &self.text_lines[line_i.get()]);
        if line_i.get() < self.shape_lines.len() {
            self.shape_lines[line_i.get()] = shape_line;
        } else {
            self.shape_lines.insert(line_i.get(), shape_line);
        }

        let duration = instant.elapsed();
        log::debug!("reshape line {}: {:?}", line_i.get(), duration);

        self.relayout_line(line_i);
    }

    fn relayout(&mut self) {
        let instant = Instant::now();

        self.layout_lines.clear();
        for line in self.shape_lines.iter() {
            let layout_i = self.layout_lines.len();
            line.layout(
                self.metrics.font_size,
                self.width,
                &mut self.layout_lines,
                layout_i,
            );
        }

        self.redraw = true;

        let duration = instant.elapsed();
        log::debug!("relayout: {:?}", duration);
    }

    fn relayout_line(&mut self, line_i: TextLineIndex) {
        let instant = Instant::now();

        let mut insert_opt = None;
        let mut layout_i = 0;
        while layout_i < self.layout_lines.len() {
            let layout_line = &self.layout_lines[layout_i];
            if layout_line.line_i == line_i {
                if insert_opt.is_none() {
                    insert_opt = Some(layout_i);
                }
                self.layout_lines.remove(layout_i);
            } else {
                layout_i += 1;
            }
        }

        let insert_i = insert_opt.unwrap_or(self.layout_lines.len());

        let shape_line = &self.shape_lines[line_i.get()];
        shape_line.layout(
            self.metrics.font_size,
            self.width,
            &mut self.layout_lines,
            insert_i,
        );

        self.redraw = true;

        let duration = instant.elapsed();
        log::debug!("relayout line {}: {:?}", line_i.get(), duration);
    }

    /// Get the current [TextMetrics]
    pub fn metrics(&self) -> TextMetrics {
        self.metrics
    }

    /// Set the current [TextMetrics]
    pub fn set_metrics(&mut self, metrics: TextMetrics) {
        if metrics != self.metrics {
            self.metrics = metrics;
            self.relayout();
            self.shape_until_scroll();
        }
    }

    /// Get the current buffer dimensions (width, height)
    pub fn size(&self) -> (i32, i32) {
        (self.width, self.height)
    }

    /// Set the current buffer dimensions
    pub fn set_size(&mut self, width: i32, height: i32) {
        if width != self.width {
            self.width = width;
            self.relayout();
            self.shape_until_scroll();
        }

        if height != self.height {
            self.height = height;
            self.shape_until_scroll();
        }
    }

    /// Get the current scroll location
    pub fn scroll(&self) -> i32 {
        self.scroll
    }

    /// Get the number of lines that can be viewed in the buffer
    pub fn lines(&self) -> i32 {
        self.height / self.metrics.line_height
    }

    /// Get the lines after layout for rendering
    pub fn layout_lines(&self) -> &[FontLayoutLine] {
        &self.layout_lines
    }

    /// Get the lines of the original text
    pub fn text_lines(&self) -> &[String] {
        &self.text_lines
    }

    /// Perform a [TextAction] on the buffer
    pub fn action(&mut self, action: TextAction) {
        match action {
            TextAction::Left => {
                let line = &self.layout_lines[self.cursor.line];
                if self.cursor.glyph > line.glyphs.len() {
                    self.cursor.glyph = line.glyphs.len();
                    self.redraw = true;
                }
                if self.cursor.glyph > 0 {
                    self.cursor.glyph -= 1;
                    self.redraw = true;
                }
            },
            TextAction::Right => {
                let line = &self.layout_lines[self.cursor.line];
                if self.cursor.glyph > line.glyphs.len() {
                    self.cursor.glyph = line.glyphs.len();
                    self.redraw = true;
                }
                if self.cursor.glyph < line.glyphs.len() {
                    self.cursor.glyph += 1;
                    self.redraw = true;
                }
            },
            TextAction::Up => {
                if self.cursor.line > 0 {
                    self.cursor.line -= 1;
                    self.redraw = true;

                    let lines = self.lines();
                    if (self.cursor.line as i32) < self.scroll
                    || (self.cursor.line as i32) >= self.scroll + lines
                    {
                        self.scroll = self.cursor.line as i32;
                    }
                }
            },
            TextAction::Down => {
                if self.cursor.line < self.layout_lines.len() {
                    self.cursor.line += 1;
                    self.redraw = true;

                    let lines = self.lines();
                    if (self.cursor.line as i32) < self.scroll
                    || (self.cursor.line as i32) >= self.scroll + lines
                    {
                        self.scroll = self.cursor.line as i32 - (lines - 1);
                        self.shape_until_scroll();
                    }
                }
            },
            TextAction::Backspace => {
                let line = &self.layout_lines[self.cursor.line];
                if self.cursor.glyph > line.glyphs.len() {
                    self.cursor.glyph = line.glyphs.len();
                    self.redraw = true;
                }
                if self.cursor.glyph > 0 {
                    self.cursor.glyph -= 1;
                    let glyph = &line.glyphs[self.cursor.glyph];
                    let text_line = &mut self.text_lines[line.line_i.get()];
                    text_line.remove(glyph.start);
                    self.reshape_line(line.line_i);
                }
            },
            TextAction::Delete => {
                let line = &self.layout_lines[self.cursor.line];
                if self.cursor.glyph < line.glyphs.len() {
                    let glyph = &line.glyphs[self.cursor.glyph];
                    let text_line = &mut self.text_lines[line.line_i.get()];
                    text_line.remove(glyph.start);
                    self.reshape_line(line.line_i);
                }
            },
            TextAction::PageUp => {
                self.scroll -= self.lines();
                self.redraw = true;
                self.shape_until_scroll();
            },
            TextAction::PageDown => {
                self.scroll += self.lines();
                self.redraw = true;
                self.shape_until_scroll();
            },
            TextAction::Insert(character) => {
                //TODO: handle Enter
                let line = &self.layout_lines[self.cursor.line];
                if self.cursor.glyph >= line.glyphs.len() {
                    match line.glyphs.last() {
                        Some(glyph) => {
                            let text_line = &mut self.text_lines[line.line_i.get()];
                            text_line.insert(glyph.end, character);
                            self.cursor.glyph += 1;
                            self.reshape_line(line.line_i);
                        }
                        None => {
                            let text_line = &mut self.text_lines[line.line_i.get()];
                            text_line.push(character);
                            self.cursor.glyph += 1;
                            self.reshape_line(line.line_i);
                        }
                    }
                } else {
                    let glyph = &line.glyphs[self.cursor.glyph];
                    let text_line = &mut self.text_lines[line.line_i.get()];
                    text_line.insert(glyph.start, character);
                    self.cursor.glyph += 1;
                    self.reshape_line(line.line_i);
                }
            },
            TextAction::Click { x, y } => {

            },
            TextAction::Scroll(lines) => {
                self.scroll += lines;
                self.redraw = true;
                self.shape_until_scroll();
            }
        }
    }
}