use std::ops::{Deref, DerefMut};

use crate::prelude::*;
use cosmic_text::{Affinity, Attrs, Cursor, FontSystem, LayoutRun, Motion};
use unicode_segmentation::UnicodeSegmentation;
use winit::{
    event::KeyEvent,
    keyboard::{Key, NamedKey},
};

pub struct TextEdit {
    view: TextView,
    selection: TextSelection,
    history: Vec<(String, TextSelection)>,
    double_hit: Option<Cursor>,
    pub single_line: bool,
}

impl TextEdit {
    pub fn new(view: TextView, single_line: bool) -> Self {
        Self {
            view,
            selection: Default::default(),
            history: Default::default(),
            double_hit: None,
            single_line,
        }
    }
    pub fn select_content(&self, start: Cursor, end: Cursor) -> String {
        let (start, end) = sort_cursors(start, end);
        let mut iter = self.buf.lines.iter().skip(start.line);
        let first = iter.next().unwrap();
        if start.line == end.line {
            first.text()[start.index..end.index].to_string()
        } else {
            let mut str = first.text()[start.index..].to_string();
            for _ in (start.line + 1)..end.line {
                str = str + "\n" + iter.next().unwrap().text();
            }
            let last = iter.next().unwrap();
            str = str + "\n" + &last.text()[..end.index];
            str
        }
    }
}

impl Widget for TextEdit {
    fn draw(&mut self, painter: &mut Painter) {
        let base = painter.layer;
        painter.child_layer();
        self.view.draw(painter);
        painter.layer = base;
        let region = self.region();

        let size = vec2(1, self.attrs.line_height);
        match self.selection {
            TextSelection::None => (),
            TextSelection::Pos(cursor) => {
                if let Some(offset) = cursor_pos(cursor, &self.buf) {
                    painter.primitive_within(
                        RectPrimitive::color(Color::WHITE),
                        size.align(Align::TOP_LEFT).offset(offset).within(&region),
                    );
                }
            }
            TextSelection::Span { start, end } => {
                let (start, end) = sort_cursors(start, end);
                for (l, x, width) in iter_layout_lines(start, end, &self.buf) {
                    let top_left = vec2(x, self.attrs.line_height * l as f32);
                    painter.primitive_within(
                        RectPrimitive::color(Color::SKY),
                        size.with_x(width)
                            .align(Align::TOP_LEFT)
                            .offset(top_left)
                            .within(&region),
                    );
                }
                if let Some(end_offset) = cursor_pos(end, &self.buf) {
                    painter.primitive_within(
                        RectPrimitive::color(Color::WHITE),
                        size.align(Align::TOP_LEFT)
                            .offset(end_offset)
                            .within(&region),
                    );
                }
            }
        }
    }

    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
        self.view.desired_width(ctx)
    }

    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
        self.view.desired_height(ctx)
    }
}

/// provides top left + width
fn iter_layout_lines(
    start: Cursor,
    end: Cursor,
    buf: &TextBuffer,
) -> impl Iterator<Item = (usize, f32, f32)> {
    gen move {
        let mut iter = buf.layout_runs().enumerate();
        for (i, line) in iter.by_ref() {
            if line.line_i == start.line
                && let Some(start_x) = index_x(&line, start.index)
            {
                if start.line == end.line
                    && let Some(end_x) = index_x(&line, end.index)
                {
                    yield (i, start_x, end_x - start_x);
                    return;
                }
                yield (i, start_x, line.line_w - start_x);
                break;
            }
        }
        for (i, line) in iter {
            if line.line_i > end.line {
                return;
            }
            if line.line_i == end.line
                && let Some(end_x) = index_x(&line, end.index)
            {
                yield (i, 0.0, end_x);
                return;
            }
            yield (i, 0.0, line.line_w);
        }
    }
}

/// copied & modified from fn found in Editor in cosmic_text
/// returns x pos of a (non layout) index within an layout run
fn index_x(run: &LayoutRun, index: usize) -> Option<f32> {
    for glyph in run.glyphs.iter() {
        if index == glyph.start {
            return Some(glyph.x);
        } else if index > glyph.start && index < glyph.end {
            // Guess x offset based on characters
            let mut before = 0;
            let mut total = 0;

            let cluster = &run.text[glyph.start..glyph.end];
            for (i, _) in cluster.grapheme_indices(true) {
                if glyph.start + i < index {
                    before += 1;
                }
                total += 1;
            }

            let offset = glyph.w * (before as f32) / (total as f32);
            return Some(glyph.x + offset);
        }
    }
    None
}

/// returns top of line segment where cursor should visually select
fn cursor_pos(cursor: Cursor, buf: &TextBuffer) -> Option<Vec2> {
    let mut prev = None;
    for run in buf
        .layout_runs()
        .skip_while(|r| r.line_i < cursor.line)
        .take_while(|r| r.line_i == cursor.line)
    {
        prev = Some(vec2(run.line_w, run.line_top));
        if let Some(pos) = index_x(&run, cursor.index) {
            return Some(vec2(pos, run.line_top));
        }
    }
    prev
}

pub struct TextEditCtx<'a> {
    pub text: &'a mut TextEdit,
    pub font_system: &'a mut FontSystem,
}

impl<'a> TextEditCtx<'a> {
    pub fn take(&mut self) -> String {
        let text = self
            .text
            .buf
            .lines
            .drain(..)
            .map(|l| l.into_text())
            .collect::<Vec<_>>()
            .join("\n");
        self.text
            .buf
            .set_text(self.font_system, "", &Attrs::new(), SHAPING, None);
        self.text.selection.clear();
        text
    }

    pub fn set(&mut self, text: &str) {
        let text = self.string(text);
        self.text
            .buf
            .set_text(self.font_system, &text, &Attrs::new(), SHAPING, None);
        self.text.selection.clear();
    }

    pub fn motion(&mut self, motion: Motion, select: bool) {
        if let TextSelection::Pos(cursor) = self.text.selection
            && let Some(new) = self.buf_motion(cursor, motion)
        {
            if select {
                self.text.selection = TextSelection::Span {
                    start: cursor,
                    end: new,
                };
            } else {
                self.text.selection = TextSelection::Pos(new);
            }
        } else if let TextSelection::Span { start, end } = self.text.selection {
            if select {
                if let Some(cursor) = self.buf_motion(end, motion) {
                    self.text.selection = TextSelection::Span { start, end: cursor };
                }
            } else {
                let (start, end) = sort_cursors(start, end);
                let sel = &mut self.text.selection;
                match motion {
                    Motion::Left | Motion::LeftWord => *sel = TextSelection::Pos(start),
                    Motion::Right | Motion::RightWord => *sel = TextSelection::Pos(end),
                    _ => {
                        if let Some(cursor) = self.buf_motion(end, motion) {
                            self.text.selection = TextSelection::Pos(cursor);
                        }
                    }
                }
            }
        }
    }

    pub fn replace(&mut self, len: usize, text: &str) {
        let text = self.string(text);
        for _ in 0..len {
            self.delete(false);
        }
        self.insert_inner(&text, false);
    }

    fn string(&self, text: &str) -> String {
        if self.text.single_line {
            text.replace('\n', "")
        } else {
            text.to_string()
        }
    }

    pub fn insert(&mut self, text: &str) {
        let text = self.string(text);
        let mut lines = text.split('\n');
        let Some(first) = lines.next() else {
            return;
        };
        self.insert_inner(first, true);
        for line in lines {
            self.newline();
            self.insert_inner(line, true);
        }
    }

    pub fn clear_span(&mut self) -> bool {
        if let TextSelection::Span { start, end } = self.text.selection {
            self.delete_between(start, end);
            let (start, _) = sort_cursors(start, end);
            self.text.selection = TextSelection::Pos(start);
            true
        } else {
            false
        }
    }

    pub fn delete_between(&mut self, start: Cursor, end: Cursor) {
        let lines = &mut self.text.view.buf.lines;
        let (start, end) = sort_cursors(start, end);
        if start.line == end.line {
            let line = &mut lines[start.line];
            let text = line.text();
            let text = text[..start.index].to_string() + &text[end.index..];
            edit_line(line, text);
        } else {
            // start
            let start_text = lines[start.line].text()[..start.index].to_string();
            let end_text = &lines[end.line].text()[end.index..];
            let text = start_text + end_text;
            edit_line(&mut lines[start.line], text);
        }
        // between
        let range = (start.line + 1)..=end.line;
        if !range.is_empty() {
            lines.splice(range, None);
        }
    }

    fn insert_inner(&mut self, text: &str, mov: bool) {
        self.clear_span();
        if let TextSelection::Pos(cursor) = &mut self.text.selection {
            let line = &mut self.text.view.buf.lines[cursor.line];
            let mut line_text = line.text().to_string();
            line_text.insert_str(cursor.index, text);
            edit_line(line, line_text);
            if mov {
                for _ in 0..text.chars().count() {
                    self.motion(Motion::Right, false);
                }
            }
        }
    }

    pub fn newline(&mut self) {
        if self.text.single_line {
            return;
        }
        self.clear_span();
        if let TextSelection::Pos(cursor) = &mut self.text.selection {
            let lines = &mut self.text.view.buf.lines;
            let line = &mut lines[cursor.line];
            let new = line.split_off(cursor.index);
            cursor.line += 1;
            lines.insert(cursor.line, new);
            cursor.index = 0;
        }
    }

    pub fn backspace(&mut self, word: bool) {
        if !self.clear_span()
            && let TextSelection::Pos(cursor) = &mut self.text.selection
            && (cursor.index != 0 || cursor.line != 0)
        {
            self.motion(if word { Motion::LeftWord } else { Motion::Left }, false);
            self.delete(word);
        }
    }

    pub fn delete(&mut self, word: bool) {
        if !self.clear_span()
            && let TextSelection::Pos(cursor) = &mut self.text.selection
        {
            if word {
                let start = *cursor;
                if let Some(end) = self.buf_motion(start, Motion::RightWord) {
                    self.delete_between(start, end);
                }
            } else {
                let lines = &mut self.text.view.buf.lines;
                let line = &mut lines[cursor.line];
                if cursor.index == line.text().len() {
                    if cursor.line == lines.len() - 1 {
                        return;
                    }
                    let add = lines.remove(cursor.line + 1).into_text();
                    let line = &mut lines[cursor.line];
                    let mut cur = line.text().to_string();
                    cur.push_str(&add);
                    edit_line(line, cur);
                } else {
                    let mut text = line.text().to_string();
                    text.remove(cursor.index);
                    edit_line(line, text);
                }
            }
        }
    }

    fn buf_motion(&mut self, cursor: Cursor, motion: Motion) -> Option<Cursor> {
        self.text
            .buf
            .cursor_motion(self.font_system, cursor, None, motion)
            .map(|r| r.0)
    }

    pub fn select_word_at(&mut self, cursor: Cursor) {
        if let (Some(start), Some(end)) = (
            self.buf_motion(cursor, Motion::LeftWord),
            self.buf_motion(cursor, Motion::RightWord),
        ) {
            self.text.selection = TextSelection::Span { start, end };
        }
    }

    pub fn select_line_at(&mut self, cursor: Cursor) {
        let end = self.text.buf.lines[cursor.line].text().len();
        self.text.selection = TextSelection::Span {
            start: Cursor::new(cursor.line, 0),
            end: Cursor::new(cursor.line, end),
        }
    }

    pub fn select(&mut self, pos: Vec2, size: Vec2, drag: bool, recent: bool) {
        let pos = pos - self.text.region().top_left().to_abs(size);
        let hit = self.text.buf.hit(pos.x, pos.y);
        let sel = &mut self.text.selection;
        match sel {
            TextSelection::None => {
                if !drag && let Some(hit) = hit {
                    *sel = TextSelection::Pos(hit)
                }
            }
            TextSelection::Pos(pos) => match (hit, drag) {
                (None, false) => *sel = TextSelection::None,
                (None, true) => (),
                (Some(hit), false) => {
                    if recent && hit == *pos {
                        self.text.double_hit = Some(hit);
                        return self.select_word_at(hit);
                    } else {
                        *pos = hit
                    }
                }
                (Some(end), true) => *sel = TextSelection::Span { start: *pos, end },
            },
            TextSelection::Span { start, end } => match (hit, drag) {
                (None, false) => *sel = TextSelection::None,
                (None, true) => *sel = TextSelection::Pos(*start),
                (Some(hit), false) => {
                    if recent
                        && let Some(double) = self.text.double_hit
                        && double == hit
                    {
                        return self.select_line_at(hit);
                    } else {
                        *sel = TextSelection::Pos(hit)
                    }
                }
                (Some(hit), true) => *end = hit,
            },
        }
        if let TextSelection::Span { start, end } = sel
            && start == end
        {
            *sel = TextSelection::Pos(*start);
        }
    }

    pub fn deselect(&mut self) {
        self.text.selection = TextSelection::None;
    }

    pub fn apply_event(&mut self, event: &KeyEvent, modifiers: &Modifiers) -> TextInputResult {
        let old = (self.text.content(), self.text.selection);
        let mut undo = false;
        let res = self.apply_event_inner(event, modifiers, &mut undo);
        if undo && let Some((old, selection)) = self.text.history.pop() {
            self.set(&old);
            self.text.selection = selection;
        } else if self.text.content() != old.0 {
            self.text.history.push(old);
        }
        res
    }

    fn apply_event_inner(
        &mut self,
        event: &KeyEvent,
        modifiers: &Modifiers,
        undo: &mut bool,
    ) -> TextInputResult {
        match &event.logical_key {
            Key::Named(named) => match named {
                NamedKey::Backspace => self.backspace(modifiers.control),
                NamedKey::Delete => self.delete(modifiers.control),
                NamedKey::Space => self.insert(" "),
                NamedKey::Enter => {
                    if modifiers.shift {
                        self.newline();
                    } else {
                        return TextInputResult::Submit;
                    }
                }
                NamedKey::ArrowRight => {
                    if modifiers.control {
                        self.motion(Motion::RightWord, modifiers.shift)
                    } else {
                        self.motion(Motion::Right, modifiers.shift)
                    }
                }
                NamedKey::ArrowLeft => {
                    if modifiers.control {
                        self.motion(Motion::LeftWord, modifiers.shift)
                    } else {
                        self.motion(Motion::Left, modifiers.shift)
                    }
                }
                NamedKey::ArrowUp => self.motion(Motion::Up, modifiers.shift),
                NamedKey::ArrowDown => self.motion(Motion::Down, modifiers.shift),
                NamedKey::Escape => {
                    self.deselect();
                    return TextInputResult::Unfocus;
                }
                _ => return TextInputResult::Unused,
            },
            Key::Character(text) => {
                if modifiers.control {
                    match text.as_str() {
                        "v" => return TextInputResult::Paste,
                        "c" => {
                            if let TextSelection::Span { start, end } = self.text.selection {
                                let content = self.text.select_content(start, end);
                                return TextInputResult::Copy(content);
                            }
                        }
                        "x" => {
                            if let TextSelection::Span { start, end } = self.text.selection {
                                let content = self.text.select_content(start, end);
                                self.clear_span();
                                return TextInputResult::Copy(content);
                            }
                        }
                        "a" => {
                            if !self.text.buf.lines[0].text().is_empty()
                                || self.text.buf.lines.len() > 1
                            {
                                let lines = &self.text.buf.lines;
                                let last_line = lines.len() - 1;
                                let last_idx = lines[last_line].text().len();
                                self.text.selection = TextSelection::Span {
                                    start: Cursor::new(0, 0),
                                    end: Cursor::new(last_line, last_idx),
                                };
                            }
                        }
                        "z" => {
                            *undo = true;
                        }
                        _ => self.insert(text),
                    }
                } else {
                    self.insert(text);
                }
            }
            _ => return TextInputResult::Unused,
        }
        TextInputResult::Used
    }
}

#[derive(Default)]
pub struct Modifiers {
    pub shift: bool,
    pub control: bool,
}

impl Modifiers {
    pub fn clear(&mut self) {
        self.shift = false;
        self.control = false;
    }
}

pub enum TextInputResult {
    Used,
    Unused,
    Unfocus,
    Submit,
    Copy(String),
    Paste,
}

#[derive(Debug, Default, Clone, Copy)]
pub enum TextSelection {
    #[default]
    None,
    Pos(Cursor),
    Span {
        start: Cursor,
        end: Cursor,
    },
}

impl TextSelection {
    pub fn clear(&mut self) {
        match self {
            TextSelection::None => (),
            TextSelection::Pos(cursor) => {
                cursor.line = 0;
                cursor.index = 0;
                cursor.affinity = Affinity::default();
            }
            TextSelection::Span { start: _, end: _ } => {
                *self = TextSelection::None;
            }
        }
    }
}

impl TextInputResult {
    pub fn unfocus(&self) -> bool {
        matches!(self, TextInputResult::Unfocus)
    }
}

impl Deref for TextEdit {
    type Target = TextView;

    fn deref(&self) -> &Self::Target {
        &self.view
    }
}

impl DerefMut for TextEdit {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.view
    }
}