// compare.rs — F7 compare screen: side-by-side test-model regen of
// every assistant response in the current context.

use ratatui::{
    layout::{Constraint, Layout, Rect},
    style::{Color, Modifier, Style},
    text::{Line, Span},
    widgets::{Block, Borders, List, ListItem, ListState, Paragraph, Wrap},
    Frame,
};
use ratatui::crossterm::event::{Event, KeyCode, KeyEvent};

use super::{App, ScreenView, screen_legend, truncate};

pub use crate::subconscious::compare::CompareCandidate;

pub(crate) struct CompareScreen {
    list_state: ListState,
    mind_tx: tokio::sync::mpsc::UnboundedSender<crate::mind::MindCommand>,
}

impl CompareScreen {
    pub fn new(
        mind_tx: tokio::sync::mpsc::UnboundedSender<crate::mind::MindCommand>,
    ) -> Self {
        Self { list_state: ListState::default(), mind_tx }
    }
}

impl ScreenView for CompareScreen {
    fn label(&self) -> &'static str { "compare" }

    fn tick(&mut self, frame: &mut Frame, area: Rect,
            events: &[Event], app: &mut App) {
        let n = app.compare_candidates.len();
        for event in events {
            if let Event::Key(KeyEvent { code, .. }) = event {
                match code {
                    KeyCode::Up | KeyCode::Char('k') => {
                        let i = self.list_state.selected().unwrap_or(0);
                        self.list_state.select(Some(i.saturating_sub(1)));
                    }
                    KeyCode::Down | KeyCode::Char('j') => {
                        let i = self.list_state.selected().unwrap_or(0);
                        self.list_state.select(Some((i + 1).min(n.saturating_sub(1))));
                    }
                    KeyCode::Char('c') | KeyCode::Enter => {
                        let _ = self.mind_tx.send(crate::mind::MindCommand::Compare);
                    }
                    _ => {}
                }
            }
        }
        if n > 0 {
            let sel = self.list_state.selected().unwrap_or(0).min(n - 1);
            self.list_state.select(Some(sel));
        }

        let test_backend = crate::config::app().compare.test_backend.clone();
        let block = Block::default()
            .title_top(Line::from(screen_legend()).left_aligned())
            .title_top(Line::from(" compare ").right_aligned())
            .borders(Borders::ALL)
            .border_style(Style::default().fg(Color::Magenta));
        let inner = block.inner(area);
        frame.render_widget(block, area);

        let [settings_area, content_area] = Layout::vertical([
            Constraint::Length(1), Constraint::Min(0),
        ]).areas(inner);

        let backend_label = if test_backend.is_empty() {
            ("(unset — set compare.test_backend)", Color::Red)
        } else {
            (test_backend.as_str(), Color::Yellow)
        };
        frame.render_widget(Paragraph::new(Line::from(vec![
            Span::raw(" test model: "),
            Span::styled(backend_label.0.to_string(), Style::default().fg(backend_label.1)),
        ])), settings_area);

        let candidates = &app.compare_candidates;
        if candidates.is_empty() {
            let err = app.mind_state.as_ref().and_then(|ms| ms.compare_error.as_deref());
            let mut lines = vec![Line::from(""),
                Line::styled("  Press c/Enter to compare against the configured test model.",
                    Style::default().fg(Color::DarkGray))];
            if let Some(e) = err {
                lines.push(Line::from(""));
                lines.push(Line::from(vec![
                    Span::raw("  "),
                    Span::styled(format!("error: {}", e), Style::default().fg(Color::Red)),
                ]));
            }
            frame.render_widget(Paragraph::new(lines), content_area);
        } else {
            let [list_area, detail_area] = Layout::horizontal([
                Constraint::Percentage(40), Constraint::Percentage(60),
            ]).areas(content_area);

            let items: Vec<ListItem> = candidates.iter().map(|c| ListItem::new(Line::from(vec![
                Span::styled(format!("#{:<3} ", c.entry_idx), Style::default().fg(Color::DarkGray)),
                Span::raw(truncate(&c.original_text, 30)),
            ]))).collect();
            frame.render_stateful_widget(
                List::new(items)
                    .block(Block::default().borders(Borders::RIGHT).title(" candidates "))
                    .highlight_style(Style::default().add_modifier(Modifier::REVERSED)),
                list_area, &mut self.list_state,
            );

            if let Some(c) = self.list_state.selected().and_then(|i| candidates.get(i)) {
                let mut text = String::new();
                if !c.prior_context.is_empty() {
                    text.push_str(&c.prior_context);
                    text.push_str("\n\n─── original ───\n\n");
                }
                text.push_str(&c.original_text);
                text.push_str("\n\n─── test model ───\n\n");
                text.push_str(&c.alternate_text);
                frame.render_widget(
                    Paragraph::new(text)
                        .block(Block::default().borders(Borders::TOP)
                            .title(format!(" entry {} ", c.entry_idx)))
                        .wrap(Wrap { trim: false }),
                    detail_area,
                );
            }
        }

        let help = Line::from(vec![
            Span::styled(" j/k/\u{2191}\u{2193}", Style::default().fg(Color::Cyan)),
            Span::raw("=nav  "),
            Span::styled("c/Enter", Style::default().fg(Color::Green)),
            Span::raw("=run "),
        ]);
        frame.render_widget(
            Paragraph::new(help),
            Rect { y: area.y + area.height - 1, height: 1, ..area },
        );
    }
}