use crate::{
    commands,
    compositor::{Component, Compositor, Context, EventResult},
    key,
    keymap::{self, Keymaps},
    ui::text_color,
};

use helix_core::{
    syntax::{self, HighlightEvent},
    Position, Range,
};
use helix_view::{document::Mode, Document, Editor, Theme, View};
use std::borrow::Cow;

use crossterm::{
    cursor,
    event::{read, Event, EventStream, KeyCode, KeyEvent, KeyModifiers},
};
use tui::{
    backend::CrosstermBackend,
    buffer::Buffer as Surface,
    layout::Rect,
    style::{Color, Modifier, Style},
};

pub struct EditorView {
    keymap: Keymaps,
    on_next_key: Option<Box<dyn FnOnce(&mut commands::Context, KeyEvent)>>,
    status_msg: Option<String>,
    last_insert: (commands::Command, Vec<KeyEvent>),
}

const OFFSET: u16 = 7; // 1 diagnostic + 5 linenr + 1 gutter

impl EditorView {
    pub fn new() -> Self {
        Self {
            keymap: keymap::default(),
            on_next_key: None,
            status_msg: None,
            last_insert: (commands::normal_mode, Vec::new()),
        }
    }

    pub fn render_view(
        &self,
        doc: &Document,
        view: &View,
        viewport: Rect,
        surface: &mut Surface,
        theme: &Theme,
        is_focused: bool,
    ) {
        let area = Rect::new(
            viewport.x + OFFSET,
            viewport.y,
            viewport.width - OFFSET,
            viewport.height.saturating_sub(1),
        ); // - 1 for statusline
        self.render_buffer(doc, view, area, surface, theme, is_focused);

        // clear with background color
        // TODO: this seems to prevent setting style later
        // surface.set_style(viewport, theme.get("ui.background"));

        self.render_diagnostics(doc, view, area, surface, theme, is_focused);

        let area = Rect::new(
            viewport.x,
            viewport.y + viewport.height.saturating_sub(1),
            viewport.width,
            1,
        );
        self.render_statusline(doc, area, surface, theme, is_focused);

        // render status
        if let Some(status_msg) = &self.status_msg {
            let style = Style::default().fg(Color::Rgb(164, 160, 232)); // lavender
            surface.set_string(viewport.x, viewport.y + viewport.height, status_msg, style);
        }
    }

    pub fn render_buffer(
        &self,
        doc: &Document,
        view: &View,
        viewport: Rect,
        surface: &mut Surface,
        theme: &Theme,
        is_focused: bool,
    ) {
        let text = doc.text().slice(..);

        let last_line = view.last_line(doc);

        let range = {
            // calculate viewport byte ranges
            let start = text.line_to_byte(view.first_line);
            let end = text.line_to_byte(last_line + 1);

            start..end
        };

        // TODO: range doesn't actually restrict source, just highlight range
        // TODO: cache highlight results
        // TODO: only recalculate when state.doc is actually modified
        let highlights: Vec<_> = match doc.syntax() {
            Some(syntax) => {
                syntax
                    .highlight_iter(text.slice(..), Some(range), None, |_| None)
                    .collect() // TODO: we collect here to avoid holding the lock, fix later
            }
            None => vec![Ok(HighlightEvent::Source {
                start: range.start,
                end: range.end,
            })],
        };
        let mut spans = Vec::new();
        let mut visual_x = 0;
        let mut line = 0u16;
        let tab_width = doc.tab_width();

        'outer: for event in highlights {
            match event.unwrap() {
                HighlightEvent::HighlightStart(span) => {
                    spans.push(span);
                }
                HighlightEvent::HighlightEnd => {
                    spans.pop();
                }
                HighlightEvent::Source { start, end } => {
                    // TODO: filter out spans out of viewport for now..

                    // TODO: do these before iterating
                    let start = text.byte_to_char(start);
                    let end = text.byte_to_char(end);

                    let text = text.slice(start..end);

                    use helix_core::graphemes::{grapheme_width, RopeGraphemes};

                    // TODO: scope matching: biggest union match? [string] & [html, string], [string, html] & [ string, html]
                    // can do this by sorting our theme matches based on array len (longest first) then stopping at the
                    // first rule that matches (rule.all(|scope| scopes.contains(scope)))
                    let style = match spans.first() {
                        Some(span) => theme.get(theme.scopes()[span.0].as_str()),
                        None => Style::default().fg(Color::Rgb(164, 160, 232)), // lavender
                    };

                    // TODO: we could render the text to a surface, then cache that, that
                    // way if only the selection/cursor changes we can copy from cache
                    // and paint the new cursor.
                    // We could keep a single resizable surface on the View for that.

                    let mut char_index = start;

                    // iterate over range char by char
                    for grapheme in RopeGraphemes::new(text) {
                        if grapheme == "\n" {
                            visual_x = 0;
                            line += 1;

                            // TODO: with proper iter this shouldn't be necessary
                            if line >= viewport.height {
                                break 'outer;
                            }
                        } else if grapheme == "\t" {
                            visual_x += (tab_width as u16);
                        } else {
                            if visual_x >= viewport.width {
                                // if we're offscreen just keep going until we hit a new line
                                // TODO: will need tweaking when we also take into account
                                // horizontal scrolling
                                continue;
                            }

                            // Cow will prevent allocations if span contained in a single slice
                            // which should really be the majority case
                            let grapheme = Cow::from(grapheme);
                            let width = grapheme_width(&grapheme) as u16;

                            // ugh,interleave highlight spans with diagnostic spans
                            let is_diagnostic = doc.diagnostics.iter().any(|diagnostic| {
                                diagnostic.range.start <= char_index
                                    && diagnostic.range.end > char_index
                            });

                            let style = if is_diagnostic {
                                style.clone().add_modifier(Modifier::UNDERLINED)
                            } else {
                                style
                            };

                            surface.set_string(
                                viewport.x + visual_x,
                                viewport.y + line,
                                grapheme,
                                style,
                            );

                            visual_x += width;
                        }

                        char_index += 1;
                    }
                }
            }
        }

        // render selections

        if is_focused {
            let screen = {
                let start = text.line_to_char(view.first_line);
                let end = text.line_to_char(last_line + 1);
                Range::new(start, end)
            };
            let cursor_style = Style::default()
                // .bg(Color::Rgb(255, 255, 255))
                .add_modifier(Modifier::REVERSED);

            // let selection_style = Style::default().bg(Color::Rgb(94, 0, 128));
            let selection_style = Style::default().bg(Color::Rgb(84, 0, 153));

            for selection in doc
                .selection(view.id)
                .iter()
                .filter(|range| range.overlaps(&screen))
            {
                // TODO: render also if only one of the ranges is in viewport
                let mut start = view.screen_coords_at_pos(doc, text, selection.anchor);
                let mut end = view.screen_coords_at_pos(doc, text, selection.head);

                // cursor
                if let Some(end) = end {
                    surface.set_style(
                        Rect::new(
                            viewport.x + end.col as u16,
                            viewport.y + end.row as u16,
                            1,
                            1,
                        ),
                        cursor_style,
                    );
                }

                if selection.head < selection.anchor {
                    std::mem::swap(&mut start, &mut end);
                }
                let start = start.unwrap_or_else(|| Position::new(0, 0));
                let end = end.unwrap_or_else(|| {
                    Position::new(viewport.height as usize, viewport.width as usize)
                });

                if start.row == end.row {
                    surface.set_style(
                        Rect::new(
                            viewport.x + start.col as u16,
                            viewport.y + start.row as u16,
                            (end.col - start.col) as u16,
                            1,
                        ),
                        selection_style,
                    );
                } else {
                    surface.set_style(
                        Rect::new(
                            viewport.x + start.col as u16,
                            viewport.y + start.row as u16,
                            // text.line(view.first_line).len_chars() as u16 - start.col as u16,
                            viewport.width - start.col as u16,
                            1,
                        ),
                        selection_style,
                    );
                    for i in start.row + 1..end.row {
                        surface.set_style(
                            Rect::new(
                                viewport.x,
                                viewport.y + i as u16,
                                // text.line(view.first_line + i).len_chars() as u16,
                                viewport.width,
                                1,
                            ),
                            selection_style,
                        );
                    }
                    surface.set_style(
                        Rect::new(viewport.x, viewport.y + end.row as u16, end.col as u16, 1),
                        selection_style,
                    );
                }
            }
        }

        // render gutters

        let style: Style = theme.get("ui.linenr");
        let warning: Style = theme.get("warning");
        let error: Style = theme.get("error");
        let info: Style = theme.get("info");
        let hint: Style = theme.get("hint");

        for (i, line) in (view.first_line..last_line).enumerate() {
            use helix_core::diagnostic::Severity;
            if let Some(diagnostic) = doc.diagnostics.iter().find(|d| d.line == line) {
                surface.set_stringn(
                    viewport.x - OFFSET,
                    viewport.y + i as u16,
                    "●",
                    1,
                    match diagnostic.severity {
                        Some(Severity::Error) => error,
                        Some(Severity::Warning) | None => warning,
                        Some(Severity::Info) => info,
                        Some(Severity::Hint) => hint,
                    },
                );
            }

            surface.set_stringn(
                viewport.x + 1 - OFFSET,
                viewport.y + i as u16,
                format!("{:>5}", line + 1),
                5,
                style,
            );
        }
    }

    pub fn render_diagnostics(
        &self,
        doc: &Document,
        view: &View,
        viewport: Rect,
        surface: &mut Surface,
        theme: &Theme,
        is_focused: bool,
    ) {
        use helix_core::diagnostic::Severity;
        use tui::{
            layout::Alignment,
            text::Text,
            widgets::{Paragraph, Widget},
        };

        let cursor = doc.selection(view.id).cursor();
        let line = doc.text().char_to_line(cursor);

        let diagnostics = doc.diagnostics.iter().filter(|diagnostic| {
            diagnostic.range.start <= cursor && diagnostic.range.end >= cursor
        });

        let warning: Style = theme.get("warning");
        let error: Style = theme.get("error");
        let info: Style = theme.get("info");
        let hint: Style = theme.get("hint");

        // Vec::with_capacity(diagnostics.len()); // rough estimate
        let mut lines = Vec::new();
        for diagnostic in diagnostics {
            let text = Text::styled(
                &diagnostic.message,
                match diagnostic.severity {
                    Some(Severity::Error) => error,
                    Some(Severity::Warning) | None => warning,
                    Some(Severity::Info) => info,
                    Some(Severity::Hint) => hint,
                },
            );
            lines.extend(text.lines);
        }

        let paragraph = Paragraph::new(lines).alignment(Alignment::Right);
        let width = 80.min(viewport.width);
        let height = 15.min(viewport.height);
        paragraph.render(
            Rect::new(
                viewport.right() - width,
                viewport.y as u16 + 1,
                width,
                height,
            ),
            surface,
        );
    }

    pub fn render_statusline(
        &self,
        doc: &Document,
        viewport: Rect,
        surface: &mut Surface,
        theme: &Theme,
        is_focused: bool,
    ) {
        let mode = match doc.mode() {
            Mode::Insert => "INS",
            Mode::Select => "SEL",
            Mode::Normal => "NOR",
        };
        // TODO: share text_color styles inside theme
        let text_color = if is_focused {
            Style::default().fg(Color::Rgb(219, 191, 239)) // lilac
        } else {
            Style::default().fg(Color::Rgb(164, 160, 232)) // lavender
        };
        // statusline
        surface.set_style(
            Rect::new(viewport.x, viewport.y, viewport.width, 1),
            theme.get("ui.statusline"),
        );
        if is_focused {
            surface.set_string(viewport.x + 1, viewport.y, mode, text_color);
        }

        if let Some(path) = doc.relative_path() {
            let path = path.to_string_lossy();

            let title = format!("{}{}", path, if doc.modified() { "[+]" } else { "" });
            surface.set_stringn(
                viewport.x + 6,
                viewport.y,
                title,
                viewport.width.saturating_sub(6) as usize,
                text_color,
            );
        }

        surface.set_string(
            viewport.x + viewport.width.saturating_sub(10),
            viewport.y,
            format!("{}", doc.diagnostics.len()),
            text_color,
        );
    }

    fn insert_mode(&self, cxt: &mut commands::Context, event: KeyEvent) {
        if let Some(command) = self.keymap[&Mode::Insert].get(&event) {
            command(cxt);
        } else if let KeyEvent {
            code: KeyCode::Char(ch),
            ..
        } = event
        {
            commands::insert::insert_char(cxt, ch);
        }
    }

    fn command_mode(&self, mode: Mode, cxt: &mut commands::Context, event: KeyEvent) {
        match event {
            // count handling
            key!(i @ '0'..='9') => {
                let i = i.to_digit(10).unwrap() as usize;
                cxt.editor.count = Some(cxt.editor.count.map_or(i, |c| c * 10 + i));
            }
            // special handling for repeat operator
            key!('.') => {
                // first execute whatever put us into insert mode
                (self.last_insert.0)(cxt);
                // then replay the inputs
                for key in &self.last_insert.1 {
                    self.insert_mode(cxt, *key)
                }
            }
            _ => {
                // set the count
                cxt.count = cxt.editor.count.take().unwrap_or(1);
                // TODO: edge case: 0j -> reset to 1
                // if this fails, count was Some(0)
                // debug_assert!(cxt.count != 0);

                if let Some(command) = self.keymap[&mode].get(&event) {
                    command(cxt);
                }
            }
        }
    }
}

impl Component for EditorView {
    fn handle_event(&mut self, event: Event, cx: &mut Context) -> EventResult {
        match event {
            Event::Resize(width, height) => {
                // HAXX: offset the render area height by 1 to account for prompt/commandline
                cx.editor.resize(Rect::new(0, 0, width, height - 1));
                EventResult::Consumed(None)
            }
            Event::Key(event) => {
                let view = cx.editor.view();
                let view_id = view.id;
                let id = view.doc;
                let mode = cx.editor.document(id).unwrap().mode();

                let mut cxt = commands::Context {
                    editor: &mut cx.editor,
                    view_id,
                    count: 1,
                    callback: None,
                    callbacks: cx.callbacks,
                    on_next_key_callback: None,
                    status_msg: None,
                };

                // clear status
                self.status_msg = None;

                if let Some(on_next_key) = self.on_next_key.take() {
                    // if there's a command waiting input, do that first
                    on_next_key(&mut cxt, event);
                } else {
                    match mode {
                        Mode::Insert => {
                            // record last_insert key
                            self.last_insert.1.push(event);

                            self.insert_mode(&mut cxt, event)
                        }
                        mode => self.command_mode(mode, &mut cxt, event),
                    }
                }
                self.on_next_key = cxt.on_next_key_callback.take();
                self.status_msg = cxt.status_msg.take();
                // appease borrowck
                let callback = cxt.callback.take();

                cx.editor.ensure_cursor_in_view(cx.editor.tree.focus);

                if mode == Mode::Normal && cx.editor.document(id).unwrap().mode() == Mode::Insert {
                    // HAXX: if we just entered insert mode from normal, clear key buf
                    // and record the command that got us into this mode.

                    // how we entered insert mode is important, and we should track that so
                    // we can repeat the side effect.

                    self.last_insert.0 = self.keymap[&mode][&event];
                    self.last_insert.1.clear();
                };

                EventResult::Consumed(callback)
            }
            Event::Mouse(_) => EventResult::Ignored,
        }
    }

    fn render(&self, mut area: Rect, surface: &mut Surface, cx: &mut Context) {
        for (view, is_focused) in cx.editor.tree.views() {
            let doc = cx.editor.document(view.doc).unwrap();
            self.render_view(doc, view, view.area, surface, &cx.editor.theme, is_focused);
        }
    }

    fn cursor_position(&self, area: Rect, editor: &Editor) -> Option<Position> {
        // match view.doc.mode() {
        //     Mode::Insert => write!(stdout, "\x1B[6 q"),
        //     mode => write!(stdout, "\x1B[2 q"),
        // };
        // return editor.cursor_position()

        // It's easier to just not render the cursor and use selection rendering instead.
        None
    }
}