use minimad::{Composite, CompositeStyle, Compound, Line};
use ratatui::layout::{Constraint, Layout, Rect};
use ratatui::style::{Color, Modifier, Style};
use ratatui::text::{Line as RLine, Span};
use ratatui::widgets::{Block, Borders, List, ListItem, Padding, Paragraph, Wrap};
use ratatui::Frame;

use crate::app::App;
use crate::views::highlight;

// To add a new help topic: drop a .md file in docs/ and add one line here.
const DOCS: &[(&str, &str)] = &[
    ("Welcome", include_str!("../../docs/welcome.md")),
    ("Keybindings", include_str!("../../docs/keybindings.md")),
    ("Sequencer", include_str!("../../docs/sequencer.md")),
];

pub fn topic_count() -> usize {
    DOCS.len()
}

pub fn render(frame: &mut Frame, app: &App, area: Rect) {
    let [topics_area, content_area] =
        Layout::horizontal([Constraint::Length(18), Constraint::Fill(1)]).areas(area);

    render_topics(frame, app, topics_area);
    render_content(frame, app, content_area);
}

fn render_topics(frame: &mut Frame, app: &App, area: Rect) {
    let items: Vec<ListItem> = DOCS
        .iter()
        .enumerate()
        .map(|(i, (name, _))| {
            let selected = i == app.ui.help_topic;
            let style = if selected {
                Style::new().fg(Color::Cyan).add_modifier(Modifier::BOLD)
            } else {
                Style::new().fg(Color::White)
            };
            let prefix = if selected { "> " } else { "  " };
            ListItem::new(format!("{prefix}{name}")).style(style)
        })
        .collect();

    let list = List::new(items).block(Block::default().borders(Borders::ALL).title("Topics"));
    frame.render_widget(list, area);
}

fn render_content(frame: &mut Frame, app: &App, area: Rect) {
    let (name, md) = DOCS[app.ui.help_topic];
    let query = &app.ui.help_search_query;
    let has_query = !query.is_empty();
    let query_lower = query.to_lowercase();

    let lines = parse_markdown(md);

    let has_search_bar = app.ui.help_search_active || has_query;
    let search_bar_height: u16 = u16::from(has_search_bar);
    let visible_height = area.height.saturating_sub(6 + search_bar_height) as usize;
    let max_scroll = lines.len().saturating_sub(visible_height);
    let scroll = app.ui.help_scroll().min(max_scroll);

    let visible: Vec<RLine> = lines
        .into_iter()
        .skip(scroll)
        .take(visible_height)
        .map(|line| {
            if has_query {
                highlight_line(line, &query_lower)
            } else {
                line
            }
        })
        .collect();

    let content_area = if has_search_bar {
        let [content, search] =
            Layout::vertical([Constraint::Fill(1), Constraint::Length(1)]).areas(area);
        render_search_bar(frame, app, search);
        content
    } else {
        area
    };

    let para = Paragraph::new(visible)
        .block(
            Block::default()
                .borders(Borders::ALL)
                .title(name)
                .padding(Padding::new(2, 2, 2, 2)),
        )
        .wrap(Wrap { trim: false });
    frame.render_widget(para, content_area);
}

fn render_search_bar(frame: &mut Frame, app: &App, area: Rect) {
    let style = if app.ui.help_search_active {
        Style::new().fg(Color::Yellow)
    } else {
        Style::new().fg(Color::DarkGray)
    };
    let cursor = if app.ui.help_search_active { "█" } else { "" };
    let text = format!(" /{}{cursor}", app.ui.help_search_query);
    frame.render_widget(Paragraph::new(text).style(style), area);
}

fn highlight_line<'a>(line: RLine<'a>, query: &str) -> RLine<'a> {
    let mut result: Vec<Span<'a>> = Vec::new();
    for span in line.spans {
        let lower = span.content.to_lowercase();
        if !lower.contains(query) {
            result.push(span);
            continue;
        }
        let content = span.content.to_string();
        let base_style = span.style;
        let hl_style = base_style.bg(Color::Yellow).fg(Color::Black);
        let mut start = 0;
        let lower_bytes = lower.as_bytes();
        let query_bytes = query.as_bytes();
        while let Some(pos) = find_bytes(&lower_bytes[start..], query_bytes) {
            let abs = start + pos;
            if abs > start {
                result.push(Span::styled(content[start..abs].to_string(), base_style));
            }
            result.push(Span::styled(
                content[abs..abs + query.len()].to_string(),
                hl_style,
            ));
            start = abs + query.len();
        }
        if start < content.len() {
            result.push(Span::styled(content[start..].to_string(), base_style));
        }
    }
    RLine::from(result)
}

fn find_bytes(haystack: &[u8], needle: &[u8]) -> Option<usize> {
    haystack.windows(needle.len()).position(|w| w == needle)
}

/// Find first line matching query across all topics. Returns (topic_index, line_index).
pub fn find_match(query: &str) -> Option<(usize, usize)> {
    let query = query.to_lowercase();
    for (topic_idx, (_, content)) in DOCS.iter().enumerate() {
        for (line_idx, line) in content.lines().enumerate() {
            if line.to_lowercase().contains(&query) {
                return Some((topic_idx, line_idx));
            }
        }
    }
    None
}

fn code_border_style() -> Style {
    Style::new().fg(Color::Rgb(60, 60, 70))
}

fn parse_markdown(md: &str) -> Vec<RLine<'static>> {
    let text = minimad::Text::from(md);
    let mut lines = Vec::new();

    let mut code_line_nr: usize = 0;

    for line in text.lines {
        match line {
            Line::Normal(composite) if composite.style == CompositeStyle::Code => {
                code_line_nr += 1;
                let raw: String = composite.compounds.iter().map(|c| &*c.src).collect();
                let mut spans = vec![
                    Span::styled(format!(" {code_line_nr:>2} "), code_border_style()),
                    Span::styled("│ ", code_border_style()),
                ];
                spans.extend(
                    highlight::highlight_line(&raw)
                        .into_iter()
                        .map(|(style, text)| Span::styled(text, style)),
                );
                lines.push(RLine::from(spans));
            }
            Line::Normal(composite) => {
                code_line_nr = 0;
                lines.push(composite_to_line(composite));
            }
            _ => {
                lines.push(RLine::from(""));
            }
        }
    }

    lines
}

fn composite_to_line(composite: Composite) -> RLine<'static> {
    let base_style = match composite.style {
        CompositeStyle::Header(1) => Style::new()
            .fg(Color::Cyan)
            .add_modifier(Modifier::BOLD | Modifier::UNDERLINED),
        CompositeStyle::Header(2) => Style::new().fg(Color::Yellow).add_modifier(Modifier::BOLD),
        CompositeStyle::Header(_) => Style::new().fg(Color::Magenta).add_modifier(Modifier::BOLD),
        CompositeStyle::ListItem(_) => Style::new().fg(Color::White),
        CompositeStyle::Quote => Style::new().fg(Color::Rgb(150, 150, 150)),
        CompositeStyle::Code => Style::new().fg(Color::Green),
        CompositeStyle::Paragraph => Style::new().fg(Color::White),
    };

    let prefix = match composite.style {
        CompositeStyle::ListItem(_) => "  • ",
        CompositeStyle::Quote => "  │ ",
        _ => "",
    };

    let mut spans: Vec<Span<'static>> = Vec::new();
    if !prefix.is_empty() {
        spans.push(Span::styled(prefix.to_string(), base_style));
    }

    for compound in composite.compounds {
        spans.push(compound_to_span(compound, base_style));
    }

    RLine::from(spans)
}

fn compound_to_span(compound: Compound, base: Style) -> Span<'static> {
    let mut style = base;

    if compound.bold {
        style = style.add_modifier(Modifier::BOLD);
    }
    if compound.italic {
        style = style.add_modifier(Modifier::ITALIC);
    }
    if compound.code {
        style = Style::new().fg(Color::Green);
    }
    if compound.strikeout {
        style = style.add_modifier(Modifier::CROSSED_OUT);
    }

    Span::styled(compound.src.to_string(), style)
}