//! Comparing the open file with its last committed version.

use super::*;

impl App {
    /// Load the diff for the current file, ready for the diff window.
    pub(super) fn open_diff(&mut self) {
        self.save_current();
        let Some(name) = self.selected.and_then(|i| self.files.get(i)).cloned() else {
            self.status = "Open a file first".to_string();
            return;
        };
        // Git is run from the work tree, and the workspace may be below it.
        let root = self.repo_root.clone();
        let Some(root) = root else {
            self.diff_text = "This workspace is not in a git repository.".to_string();
            self.show_diff = true;
            return;
        };
        if !gitsync::has_commits(&root) {
            self.diff_text = "The repository has no commits yet, so there is \
                              nothing to compare against."
                .to_string();
            self.show_diff = true;
            return;
        }
        let abs = self.path_for(&name);
        let rel = abs
            .strip_prefix(&root)
            .map(|p| p.to_string_lossy().replace('\\', "/"))
            .unwrap_or_else(|_| name.clone());
        self.diff_text = match gitsync::diff_file(&root, &rel) {
            Ok(text) if text.trim().is_empty() => {
                format!("{name} matches the last commit — no changes.")
            }
            Ok(text) => text,
            Err(e) => format!("Could not diff {name}:\n{e}"),
        };
        self.diff_title = name;
        self.show_diff = true;
    }

    /// The diff window: added and removed lines since the last commit.
    pub(super) fn diff_window(&mut self, ctx: &egui::Context) {
        let mut open = self.show_diff;
        let mut refresh = false;
        egui::Window::new(format!("Changes — {}", self.diff_title))
            .open(&mut open)
            .resizable(true)
            .collapsible(false)
            .default_width(680.0)
            .default_height(460.0)
            .show(ctx, |ui| {
                ui.horizontal(|ui| {
                    if ui.button("⟳ Refresh").clicked() {
                        refresh = true;
                    }
                    ui.label(
                        egui::RichText::new("compared with the last commit")
                            .small()
                            .weak(),
                    );
                });
                ui.separator();
                egui::ScrollArea::vertical()
                    .auto_shrink([false, false])
                    .show(ui, |ui| {
                        for line in self.diff_text.lines() {
                            // Colour the diff the way git does, so additions and
                            // removals are separable at a glance.
                            let (color, strong) = match line.as_bytes().first() {
                                Some(b'+') if !line.starts_with("+++") => {
                                    (Some(egui::Color32::from_rgb(0x3F, 0x9E, 0x4F)), false)
                                }
                                Some(b'-') if !line.starts_with("---") => {
                                    (Some(egui::Color32::from_rgb(0xC0, 0x50, 0x50)), false)
                                }
                                Some(b'@') => {
                                    (Some(egui::Color32::from_rgb(0x3B, 0x82, 0xF6)), true)
                                }
                                _ => (None, false),
                            };
                            let mut text = egui::RichText::new(line).monospace();
                            if let Some(color) = color {
                                text = text.color(color);
                            }
                            if strong {
                                text = text.strong();
                            }
                            ui.label(text);
                        }
                    });
            });
        if refresh {
            self.open_diff();
        }
        self.show_diff = open;
    }
}