//! P5-47 — TDS Custom Window Chrome (opt-in, runtime-reversible).
//!
//! When the user opts into custom window chrome, the web client renders its own
//! `<TitleBar/>` (folds/TDS styled) and we strip the OS-native window frame so
//! the two don't stack. This is entirely opt-in; the default is the untouched
//! native frame. On Windows and macOS the window is built with the native frame
//! and `set_custom_chrome` toggles it at runtime. On Linux the saved choice
//! decides the frame when the window is built, because on native Wayland a
//! runtime change doesn't reach the compositor (it then applies next launch).
//! `set_custom_chrome` reports whether the frame is stripped *now*, and the web
//! client shows its titlebar only then.
//!
//! Everything here goes through the cross-platform Tauri v2 window API (plus a
//! Windows-only `window_vibrancy` dance in `set_custom_chrome`, since Mica and a
//! frameless window can't coexist). Each command resolves the "main" window and
//! silently no-ops if it isn't present (e.g. during teardown); the `Result`s are
//! intentionally ignored since a failed chrome tweak should never surface as an
//! error to the user.

use std::sync::atomic::{AtomicBool, Ordering};

use tauri::{AppHandle, Manager};

/// Whether the native frame is **actually** stripped right now, which is not
/// always what the user last asked for: on Linux / native Wayland GTK only
/// negotiates decorations with the compositor when the window is created, so a
/// runtime `set_decorated` leaves the compositor's frame in place (KDE drew its
/// buttons around the Lotus titlebar). There the choice is applied when the
/// window is built (from the persisted file) and takes effect next launch.
pub struct ChromeState {
    active: AtomicBool,
}

impl ChromeState {
    /// `built_undecorated`: the main window was created without a frame.
    pub fn new(built_undecorated: bool) -> Self {
        Self {
            active: AtomicBool::new(built_undecorated),
        }
    }
}

/// Where the custom-chrome choice is kept natively, so the main window can be
/// built with the right frame before the web client has loaded.
fn custom_chrome_file(app: &AppHandle) -> Option<std::path::PathBuf> {
    app.path()
        .app_config_dir()
        .ok()
        .map(|dir| dir.join("custom-chrome"))
}

/// The saved choice; defaults to off (native frame).
pub fn read_custom_chrome(app: &AppHandle) -> bool {
    custom_chrome_file(app)
        .and_then(|path| std::fs::read_to_string(path).ok())
        .is_some_and(|value| value.trim() == "1")
}

fn write_custom_chrome(app: &AppHandle, enabled: bool) {
    let Some(path) = custom_chrome_file(app) else {
        return;
    };
    if let Some(dir) = path.parent() {
        let _ = std::fs::create_dir_all(dir);
    }
    let _ = std::fs::write(path, if enabled { "1" } else { "0" });
}

/// Whether `set_decorations` takes effect on a live window here. False only on
/// Linux with GTK on native Wayland. Pure, for tests.
pub(crate) fn runtime_toggle_works(linux: bool, native_wayland: bool) -> bool {
    !(linux && native_wayland)
}

/// Whether the main window should be built without a frame: only on Linux,
/// where a runtime toggle may not apply. Windows keeps building with the native
/// frame and toggling at runtime (Mica needs it there, see below).
pub fn build_undecorated(app: &AppHandle) -> bool {
    cfg!(target_os = "linux") && read_custom_chrome(app)
}

/// Apply the custom-chrome choice. `enabled` = custom chrome on, which means
/// the OS decorations must come **off** (`set_decorations(!enabled)`). The
/// choice is saved for the next launch; where the frame can change at runtime
/// (Windows, macOS, Linux on X11) it changes now.
///
/// Returns whether the native frame is stripped **now**, so the web client
/// shows its own titlebar only then (never two titlebars, never none).
#[tauri::command]
pub fn set_custom_chrome(app: AppHandle, enabled: bool) -> bool {
    write_custom_chrome(&app, enabled);
    let native_wayland =
        crate::gpu_workarounds::gtk_native_wayland(&|k: &str| std::env::var(k).ok());
    let can_toggle = runtime_toggle_works(cfg!(target_os = "linux"), native_wayland);
    let state = app.try_state::<ChromeState>();
    if !can_toggle {
        return state
            .map(|s| s.active.load(Ordering::Relaxed))
            .unwrap_or(false);
    }
    if let Some(window) = app.get_webview_window("main") {
        // Windows: the Mica backdrop (applied at startup in lib.rs) and a
        // frameless window are a known-bad combo — stripping WS_CAPTION under a
        // system backdrop glitches the whole surface (black/blank window). Drop
        // the backdrop before undecorating, and restore it together with the
        // native frame when custom chrome turns off.
        #[cfg(target_os = "windows")]
        if enabled {
            let _ = window_vibrancy::clear_mica(&window);
        }
        let _ = window.set_decorations(!enabled);
        // Re-assert the DWM shadow so a frameless window keeps its drop shadow
        // and resize borders on Windows (no-op / harmless elsewhere).
        let _ = window.set_shadow(true);
        #[cfg(target_os = "windows")]
        if !enabled {
            let _ = window_vibrancy::apply_mica(&window, Some(true));
        }
        if let Some(state) = &state {
            state.active.store(enabled, Ordering::Relaxed);
        }
    }
    state
        .map(|s| s.active.load(Ordering::Relaxed))
        .unwrap_or(false)
}

/// Minimize the main window (custom titlebar min button).
#[tauri::command]
pub fn window_minimize(app: AppHandle) {
    if let Some(window) = app.get_webview_window("main") {
        let _ = window.minimize();
    }
}

/// Toggle maximize/restore the main window (custom titlebar max button and
/// drag-region double-click).
#[tauri::command]
pub fn window_toggle_maximize(app: AppHandle) {
    if let Some(window) = app.get_webview_window("main") {
        if window.is_maximized().unwrap_or(false) {
            let _ = window.unmaximize();
        } else {
            let _ = window.maximize();
        }
    }
}

/// Begin an OS-level window drag from the custom titlebar drag region. The web
/// side also marks the drag area with `data-tauri-drag-region`; this command is
/// the explicit fallback so behaviour is identical across platforms.
#[tauri::command]
pub fn window_start_drag(app: AppHandle) {
    if let Some(window) = app.get_webview_window("main") {
        let _ = window.start_dragging();
    }
}

/// Close from the custom titlebar. Mirrors the app's close-to-tray behaviour
/// (see the `CloseRequested` handler in `lib.rs`): we `hide()` the window rather
/// than exiting, so the tray keeps the app running and the tray menu remains the
/// single explicit quit path.
#[tauri::command]
pub fn window_close(app: AppHandle) {
    // Same rules as the OS close button (tray / quit / first-close dialog,
    // cinny-desktop #5).
    crate::handle_close_request(&app);
}

#[cfg(test)]
mod tests {
    use super::runtime_toggle_works;

    #[test]
    fn only_linux_on_native_wayland_needs_a_restart() {
        assert!(!runtime_toggle_works(true, true));
        assert!(runtime_toggle_works(true, false)); // Linux on X11 / XWayland
        assert!(runtime_toggle_works(false, false)); // Windows / macOS
        assert!(runtime_toggle_works(false, true));
    }
}