//! The loading screen: the full-screen splash and progress bar over world entry and cross-map
//! teleports. The art resolves `Map.dbc` → `LoadingScreens.dbc` → BLP for every map kind; the bar
//! is two layers, `Loading-BarBorder` and `Loading-BarFill` (Background, Glow and Glass are never
//! drawn in 1.12).
//!
//! Event-raised and readiness-cleared, as in the reference: it rises at the character pick's
//! `Connected` edge and at `SMSG_TRANSFER_PENDING` (the reference's two entries into `0x406640`'s
//! tail) and clears on a per-frame readiness poll. The reference's one blocking stretch
//! (`SMSG_NEW_WORLD`'s `0x401b00` defers `0x401bc0` onto the deadline heap, drained at `0x420d0c`)
//! also suppresses input, which this client builds explicitly ([`input`]).
//!
//! A destination snap only ends a raise's wait ([`LoadingScreen::snap_landed`]). The screen clears
//! when the destination is scene-presentable ([`WorldLoadProgress`]), never on the body reaching
//! the ground.

use bevy::prelude::*;
use std::collections::HashMap;

use benilla_formats::{load_loading_screens, LoadingScreenCatalog};

use benilla_assets::LockRecover;
use benilla_assets::MapCatalogRes;
use benilla_assets::{AssetSet, WorldAssets};
use benilla_world::schedule::WorldStage;
use benilla_world::terrain_stream::WorldLoadProgress;
use benilla_world::world_map::CurrentMap;

/// The cover's input half: while it is up the client takes no input (a source cut in `PreUpdate`).
mod input;
pub(crate) use input::CoverInput;

// The bar, from the `LoadingScreen.cpp` descriptor table at `0x7ffd34` (read by `0x407150`):
// entry {cx, cy, halfW, halfH}, rect [cx ± halfW·0.5] × [cy ± halfH·0.5], fill right edge
// left + progress·halfW; Border {0.5, 0.075, 0.600, 0.050}, Fill {0.5, 0.075, 0.525, 0.025}.
// Viewport fractions, `cy` measured up from the bottom edge (Bevy UI `bottom:`).
const BORDER_LEFT: f32 = 0.200; // 0.5 − 0.600·0.5
const BORDER_WIDTH: f32 = 0.600;
const BORDER_BOTTOM: f32 = 0.050; // 0.075 − 0.050·0.5
const BORDER_HEIGHT: f32 = 0.050;
const FILL_LEFT: f32 = 0.2375; // 0.5 − 0.525·0.5
const FILL_BOTTOM: f32 = 0.0625; // 0.075 − 0.025·0.5
const FILL_HEIGHT: f32 = 0.025;
const FILL_MAX_WIDTH: f32 = 0.525; // halfW; fill width = progress · FILL_MAX_WIDTH

/// The glue and loading screens are authored 4:3; on a wider window the reference fits them to
/// height and pillarboxes. The square BLP is stretched to this aspect.
const BACKDROP_ASPECT: f32 = 4.0 / 3.0;
/// Consecutive fully resident frames before the clear: debounces the post-teleport frame where
/// `ready` reads 0 against a nonzero `total`.
const CLEAR_AFTER_READY_FRAMES: u32 = 3;
/// Once the screen has been up this long, log which term still blocks the clear, every
/// [`WAIT_LOG_EVERY`] seconds.
const WAIT_LOG_AFTER: f32 = 3.0;
const WAIT_LOG_EVERY: f32 = 2.0;
/// How far (yd) a same-map snap must move the body to count as a load. It clears every combat
/// relocation (charge and intercept 25 yd, blink 20, knockbacks under 30), which also ends in a
/// server teleport and must never black out the screen.
const SNAP_LOAD_MIN_YD: f32 = 100.0;

/// Consecutive covered, in-world frames before the cover is on the glass: renders are serial, so
/// at 3 the two frames before have presented.
const COVER_PRESENT_FRAMES: u32 = 3;

/// Whether the entry cover has reached the glass. The first covered frame is the first whose
/// render can draw the cover, so synchronous work on it freezes character select on screen.
/// Counted in `First` so `PreUpdate` and `Update` readers see the same frame's answer.
#[derive(Resource, Default)]
pub(crate) struct EntryCover {
    /// Consecutive covered+in-world frames; reset the moment either goes false.
    frames: u32,
}

impl EntryCover {
    /// Whether the cover has had enough frames to reach the glass; true when no cover is up, since
    /// a consumer would otherwise wait forever (a capture that boots straight in world).
    pub(crate) fn presented(&self) -> bool {
        self.frames == 0 || self.frames >= COVER_PRESENT_FRAMES
    }

    /// A cover is up and not yet presented: a renderer draws nothing but the cover this frame.
    pub(crate) fn owes_a_present(&self) -> bool {
        self.frames > 0 && self.frames < COVER_PRESENT_FRAMES
    }

    /// A cover is up and the client is in world.
    pub(crate) fn covering(&self) -> bool {
        self.frames > 0
    }

    /// Covered frames so far.
    #[cfg(test)]
    pub(crate) fn frames(&self) -> u32 {
        self.frames
    }
}

impl EntryCover {
    /// One frame's count; the system and the tests both go through this.
    pub(crate) fn tick(&mut self, covered: bool) {
        self.frames = if covered {
            self.frames.saturating_add(1)
        } else {
            0
        };
    }
}

/// `First`: advance or reset the covered-frame count.
fn count_entry_cover(
    screen: Res<LoadingScreen>,
    state: Res<State<crate::char_select::ClientState>>,
    mut cover: ResMut<EntryCover>,
) {
    let in_world = *state.get() == crate::char_select::ClientState::InWorld;
    cover.tick(screen.covering() && in_world);
}

/// The `LoadingScreenID` → BLP path table; [`MapCatalogRes`] maps a map to its `LoadingScreenID`.
#[derive(Resource)]
struct LoadingScreenCatalogRes(LoadingScreenCatalog);

/// What a raise means for the tip of the day.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub(crate) enum TipEdge {
    /// The glue→world entry: pick the next row and advance the cursor.
    Pick,
    /// Every other raise: this screen carries no tip.
    Clear,
}

/// Loading-screen state machine (event-raised, readiness-cleared).
#[derive(Resource, Default)]
pub(crate) struct LoadingScreen {
    active: bool,
    /// A raise from an entry edge holds until the destination snap lands, so the old location's
    /// residency cannot clear a screen raised for the new one (at world entry the login vista is
    /// resident well before `SMSG_LOGIN_VERIFY_WORLD`).
    awaiting_snap: bool,
    /// The map this screen's art resolves from, the reference's `[0x82f00c]`, set by every raise;
    /// `None` is its `-1`, no backdrop. Not `CurrentMap`: vmangos can relocate a character inside
    /// `Player::LoadFromDB` (`Player.cpp:15020`), under a live screen. Its writers: `0x4067e6` and
    /// `0x4072d3` store a map id, `0x406d0e`, `0x4073d4` and `0x407e59` store `-1`.
    map: Option<u32>,
    /// The reference's `[0x882e04]` texture handle, which latches the art: `0x406cf0` reads the map
    /// id only to reject `-1`, and `0x406cfc`/`0x406d01`/`0x406d03` skip the resolver `0x406e20`
    /// while it is set. Cleared by [`Self::dismiss`], never by a raise.
    art_resolved: bool,
    /// Plain black cover with no art or bar, for the world→glue cut; dropped once the state leaves
    /// `InWorld`.
    blackout: bool,
    /// Consecutive presentable frames while active ([`CLEAR_AFTER_READY_FRAMES`]).
    ready_frames: u32,
    /// Bar fill, 0..1, monotonic within a load: the raw residency ratio dips as the view moves.
    displayed: f32,
    /// Decoded backdrop art by BLP path.
    art_cache: HashMap<String, Handle<Image>>,
    /// Which tip the next raise carries, taken by [`crate::game_tip::drive_game_tip`].
    pub(crate) tip_edge: Option<TipEdge>,
    /// Capture only: the clear is skipped while set ([`Self::hold_for_capture`]).
    held: bool,

    /// `Time::elapsed_secs` at the last raise and at the last wait log line.
    active_since: f32,
    last_wait_log: f32,
    /// The avatar's position last frame, to measure a snap (applied in `Input`, a stage earlier).
    last_pos: Option<Vec3>,
}

impl LoadingScreen {
    /// Whether the opaque cover is up; the world camera renders under it, never behind the glue.
    pub(crate) fn covering(&self) -> bool {
        self.active
    }

    /// An active cover, for tests.
    #[cfg(test)]
    pub(crate) fn test_covering() -> Self {
        Self {
            active: true,
            ..Self::default()
        }
    }

    /// Take the pending raise's tip edge; read once, by [`crate::game_tip::drive_game_tip`].
    pub(crate) fn take_tip_edge(&mut self) -> Option<TipEdge> {
        self.tip_edge.take()
    }

    /// The capture instrument (`WOW_CAPTURE=loading-tip`): raise as the glue→world entry does,
    /// with art, bar and a `Pick` tip, and never clear. `map` latches the art as a raise's does.
    pub(crate) fn hold_for_capture(&mut self, map: Option<u32>) {
        self.active = true;
        self.blackout = false;
        self.awaiting_snap = false;
        self.map = map;
        self.held = true;
        self.tip_edge = Some(TipEdge::Pick);
    }

    /// Raise the screen for a fresh load, its art latched to `map` for its life (a caller with no
    /// announced destination passes the current map). Only an edge that reaches the reference's
    /// transition entries calls this, never a snap ([`Self::snap_landed`]).
    fn raise(&mut self, reason: &str, awaiting_snap: bool, map: Option<u32>, now: f32) {
        self.active = true;
        self.blackout = false;
        self.awaiting_snap = awaiting_snap;
        self.map = map;
        self.ready_frames = 0;
        self.displayed = 0.0; // restart the fill for the new load
        self.active_since = now;
        self.last_wait_log = now;
        info!("loading screen: up ({reason}, map {map:?})");
    }

    /// The destination snap (`SMSG_NEW_WORLD` or `SMSG_LOGIN_VERIFY_WORLD`) landed: it ends the
    /// raise's wait and nothing else, not the art, the tip or the bar. The reference's handlers
    /// (`0x401b00`, `0x401de0`) never touch the screen: the raise `0x406800` has three call sites,
    /// all inside `LoadingScreen.cpp`. `map` is `None` for a same-map teleport ack.
    fn snap_landed(&mut self, map: Option<u32>) {
        if let (Some(raised), Some(dest)) = (self.map, map) {
            if raised != dest {
                info!("loading screen: snap landed on map {dest} — raised for map {raised}, art holds");
            }
        }
        self.awaiting_snap = false;
    }

    /// A far snap: a screen already up is this snap's own, so the snap only ends its wait. Returns
    /// `true` when no screen is up and the caller should raise one, our backstop for a port with no
    /// announcing edge (the reference's blocking world load needs none).
    #[must_use]
    fn far_snap(&mut self, map: u32) -> bool {
        if !self.active {
            return true;
        }
        self.snap_landed(Some(map));
        false
    }

    /// The dismiss (the reference's `0x407e80`), the only place a tip clears: `[0x882e10]`'s
    /// writers are the `EnterWorld` setter `0x406630` and `0x407f2b` here.
    fn dismiss(&mut self) {
        self.active = false;
        self.blackout = false;
        self.tip_edge = Some(TipEdge::Clear);
        // `0x407ed7` clears `[0x882e04]`: the next screen resolves its own art.
        self.art_resolved = false;
    }
}

// UI entity markers.
#[derive(Component)]
struct LoadingRoot;
#[derive(Component)]
struct LoadingBackdrop;
#[derive(Component)]
struct LoadingBarFill;
#[derive(Component)]
struct LoadingBarBorder;
/// The tip-of-the-day `Text` root; its coloured runs are children, rebuilt when the tip changes.
#[derive(Component)]
pub(crate) struct LoadingTip;

pub(crate) struct LoadingScreenPlugin;

impl Plugin for LoadingScreenPlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<LoadingScreen>()
            .init_resource::<EntryCover>()
            // In `First`, ahead of every consumer in `PreUpdate` and `Update`.
            .add_systems(First, count_entry_cover)
            .add_systems(Startup, setup_loading_screen.after(AssetSet::Open))
            // In `WorldStage::Present`, after Input and Stream: a teleport snaps in Input and the
            // streamer refocuses in Stream, so the cover lands on the same frame, never a flash.
            .add_systems(Update, drive_loading_screen.in_set(WorldStage::Present));
        // The cover's input rule, registered here so the two cannot be registered apart.
        input::build(app);
    }
}

/// Startup: load the LoadingScreens catalog and the bar textures, and spawn the hidden UI tree.
fn setup_loading_screen(
    mut commands: Commands,
    world_assets: Option<ResMut<WorldAssets>>,
    mut images: ResMut<Assets<Image>>,
) {
    // The black pillarbox root spawns unconditionally: `covering()` consumers act as covered while
    // the screen is active, so missing art must still leave a black cover.
    let root = commands
        .spawn((
            LoadingRoot,
            Node {
                position_type: PositionType::Absolute,
                width: Val::Percent(100.0),
                height: Val::Percent(100.0),
                justify_content: JustifyContent::Center,
                align_items: AlignItems::Center,
                ..default()
            },
            BackgroundColor(Color::BLACK),
            // UI already paints after the 3D scene; this orders within UI.
            GlobalZIndex(1000),
            Visibility::Hidden,
        ))
        .id();

    let Some(mut assets) = world_assets else {
        return;
    };

    // Catalog (LoadingScreenID → BLP path).
    match load_loading_screens(&mut assets.chain.lock_recover()) {
        Ok(c) => {
            info!("LoadingScreens.dbc: {} screens catalogued", c.len());
            commands.insert_resource(LoadingScreenCatalogRes(c));
        }
        Err(e) => {
            error!("LoadingScreens.dbc unavailable — plain black cover, no art: {e:#}");
            return;
        }
    }

    // The two layers 1.12 draws, as sRGB clamp sprites.
    let mut tex = |path: &str| assets.sprite_texture(path, &mut images);
    let Some(border) = tex("Interface\\Glues\\LoadingBar\\Loading-BarBorder.blp") else {
        error!("loading bar textures missing — plain black cover, no art");
        return;
    };
    let fill = tex("Interface\\Glues\\LoadingBar\\Loading-BarFill.blp").unwrap_or_default();

    commands.entity(root).with_children(|root| {
        // One 4:3 area fit to the viewport height and centred; the bar's fractions are relative
        // to it. Paint order is spawn order: backdrop, tip, fill, border.
        root.spawn(Node {
            width: Val::Vh(100.0 * BACKDROP_ASPECT),
            height: Val::Vh(100.0),
            position_type: PositionType::Relative,
            ..default()
        })
        .with_children(|area| {
            // Tinted black until the art resolves.
            area.spawn((
                LoadingBackdrop,
                ImageNode {
                    color: Color::BLACK,
                    image_mode: NodeImageMode::Stretch,
                    ..default()
                },
                Node {
                    position_type: PositionType::Absolute,
                    width: Val::Percent(100.0),
                    height: Val::Percent(100.0),
                    ..default()
                },
            ));
            // The tip, between the backdrop and the bar as in the reference (`0x406e12`,
            // `0x406e18`), placed in percent of this area, the space of `crate::game_tip`.
            area.spawn((LoadingTip, crate::game_tip::tip_bundle()));
            // The fill art is a horizontally uniform gradient, so scaling its width is a reveal.
            area.spawn((
                LoadingBarFill,
                Node {
                    position_type: PositionType::Absolute,
                    left: Val::Percent(FILL_LEFT * 100.0),
                    bottom: Val::Percent(FILL_BOTTOM * 100.0),
                    width: Val::Percent(0.0), // set each frame
                    height: Val::Percent(FILL_HEIGHT * 100.0),
                    ..default()
                },
                ImageNode {
                    image: fill,
                    image_mode: NodeImageMode::Stretch,
                    ..default()
                },
            ));
            // Border frame, on top.
            area.spawn((
                LoadingBarBorder,
                Node {
                    position_type: PositionType::Absolute,
                    left: Val::Percent(BORDER_LEFT * 100.0),
                    bottom: Val::Percent(BORDER_BOTTOM * 100.0),
                    width: Val::Percent(BORDER_WIDTH * 100.0),
                    height: Val::Percent(BORDER_HEIGHT * 100.0),
                    ..default()
                },
                ImageNode {
                    image: border,
                    image_mode: NodeImageMode::Stretch,
                    ..default()
                },
            ));
        });
    });
}

/// Per frame: observe the lifecycle edges, run the raise and clear rules, resolve the backdrop and
/// set the bar.
#[allow(clippy::type_complexity)]
fn drive_loading_screen(
    mut screen: ResMut<LoadingScreen>,
    // Bundled to stay under Bevy's 16-parameter ceiling.
    stream: (
        Res<WorldLoadProgress>,
        Res<benilla_world::terrain_stream::ViewFocus>,
    ),
    current_map: Option<Res<CurrentMap>>,
    maps: Option<Res<MapCatalogRes>>,
    screens: Option<Res<LoadingScreenCatalogRes>>,
    mut assets: Option<ResMut<WorldAssets>>,
    mut images: ResMut<Assets<Image>>,
    mut root: Query<&mut Visibility, (With<LoadingRoot>, Without<LoadingBackdrop>)>,
    mut backdrop: Query<(&mut ImageNode, &mut Visibility), With<LoadingBackdrop>>,
    mut fill: Query<&mut Node, With<LoadingBarFill>>,
    mut bar_vis: Query<
        &mut Visibility,
        (
            Or<(With<LoadingBarFill>, With<LoadingBarBorder>)>,
            Without<LoadingRoot>,
            Without<LoadingBackdrop>,
        ),
    >,
    player: Option<Res<crate::player::Player>>,
    // Real time: `Time<Virtual>` clamps frames over 250 ms, and a load is made of those.
    time: Res<Time<Real>>,
    // The cover holds until the warm pass has compiled its pipelines.
    warm: Res<crate::pipe_warm::WarmPass>,
    // The world-entry UI load runs behind this cover; the reference's reveal always has the UI up.
    entry_ui_pending: Option<Res<crate::ui_script::PendingEntryUiLoad>>,
    edges: (
        Res<State<crate::char_select::ClientState>>,
        MessageReader<crate::net::EnteredWorldMessage>,
        MessageReader<crate::net::WorldportMessage>,
        MessageReader<crate::net::TeleportMessage>,
        MessageReader<crate::net::LoggedOutMessage>,
        MessageReader<crate::net::DisconnectedMessage>,
        MessageReader<crate::net::CharacterLoginFailedMessage>,
        Option<Res<crate::net::PendingTransfer>>,
        Option<Res<crate::char_select::Roster>>,
    ),
) {
    let (
        state,
        mut entered,
        mut worldports,
        mut teleports,
        mut logouts,
        mut lost,
        mut refusals,
        transfer,
        roster,
    ) = edges;
    let (progress, focus) = (&stream.0, &stream.1);
    let now = time.elapsed_secs();
    let map_id = current_map.as_ref().map(|m| m.0);
    // The physics hold releases on the same residency signal, so the body's world is live first.
    let player_settling = player.as_ref().is_some_and(|p| p.settling);

    // --- The edges. ---
    // A glue entry (not the seamless in-world reconnect), raised on the frame the glue tears down
    // and held across the server's character load; the art comes from the roster's map.
    if entered.read().next().is_some() && *state.get() != crate::char_select::ClientState::InWorld {
        let map = roster.as_ref().and_then(|r| r.pending_map());
        screen.raise("world entry", true, map, now);
        // The tip rides this edge alone: the reference's setter `0x406630` has one caller, in
        // `CGlueMgr::EnterWorld`, which neither `SMSG_TRANSFER_PENDING` arm reaches.
        screen.tip_edge = Some(TipEdge::Pick);
    }
    // A portal (`SMSG_TRANSFER_PENDING`, no transport): cover now, before the server unloads us, as
    // the reference does. A transport crossing rides visibly until its worldport lands.
    if let Some(t) = transfer.as_ref().filter(|t| t.is_changed()) {
        match &t.0 {
            Some(info) if info.transport_entry.is_none() => {
                screen.raise("transfer pending", true, Some(info.map_id), now);
            }
            // Cleared with no snap in flight is `SMSG_TRANSFER_ABORTED` (a worldport lands below
            // this frame): stop waiting, and the resident old world clears the screen.
            None => screen.awaiting_snap = false,
            Some(_) => {}
        }
    }
    // A snap never re-raises a live screen ([`LoadingScreen::far_snap`]).
    for w in worldports.read() {
        if screen.far_snap(w.map_id) {
            screen.raise("worldport", false, Some(w.map_id), now);
        }
    }
    // A same-map teleport ends any awaited snap; whether it needs a screen is decided below.
    let teleported = teleports.read().next().is_some();
    if teleported {
        screen.snap_landed(None);
    }
    // Logout, a lost session or a refused login: `CharSelect` applies next frame, so cover the torn
    // down world with black (the reference's world→glue cut), and disarm a snap that will not come.
    let session_over = lost.read().any(|m| m.session_over);
    let refused = refusals.read().next().is_some();
    if logouts.read().next().is_some() || session_over || refused {
        screen.active = true;
        screen.blackout = true;
        screen.awaiting_snap = false;
        screen.ready_frames = 0;
        info!(
            "loading screen: blackout ({})",
            if session_over {
                "session lost"
            } else if refused {
                "character login refused"
            } else {
                "logout"
            }
        );
    }
    if screen.blackout && *state.get() != crate::char_select::ClientState::InWorld {
        // The glue is up (it renders above this root); the cover's job is done.
        screen.dismiss();
    }

    // --- Backstop: the ground under the focus is not resident and nothing raised us. In world
    // only, since behind the glue nothing loads; and only while the focus is the body, since in a
    // cinematic or free-fly residency describes the camera's tile. ---
    if !screen.active
        && !progress.focus_resident
        && focus.follows_body()
        && *state.get() == crate::char_select::ClientState::InWorld
    {
        // Same map by construction: the ground under the body.
        screen.raise("focus not resident", false, map_id, now);
    }

    // --- At a snap, the same test against the clear's own predicate: a teleport inside the keep
    // band lands on resident terrain while the destination's buildings may still be arriving. ---
    let body = player.as_ref().map(|p| p.pos);
    let relocated = match (teleported, screen.last_pos, body) {
        (true, Some(was), Some(now_pos)) => was.distance(now_pos) >= SNAP_LOAD_MIN_YD,
        // No previous position (the entry frame): treat it as a relocation.
        (true, _, _) => true,
        _ => false,
    };
    screen.last_pos = body;
    if relocated
        && !screen.active
        && *state.get() == crate::char_select::ClientState::InWorld
        && !(progress.is_ready() && progress.presentable())
    {
        screen.raise("teleport, destination not presentable", false, map_id, now);
    }

    // --- Clear, sustained a few frames. ---
    if screen.active && !screen.held {
        if progress.is_ready()
            && progress.presentable()
            && !screen.awaiting_snap
            && !player_settling
            && warm.satisfied()
            && entry_ui_pending.is_none()
        {
            screen.ready_frames += 1;
            if screen.ready_frames >= CLEAR_AFTER_READY_FRAMES {
                screen.dismiss();
                info!(
                    "loading screen: cleared ({}/{} resident, {:.1}s)",
                    progress.ready,
                    progress.total,
                    now - screen.active_since
                );
            }
        } else {
            screen.ready_frames = 0;
            if now - screen.active_since > WAIT_LOG_AFTER
                && now - screen.last_wait_log >= WAIT_LOG_EVERY
            {
                screen.last_wait_log = now;
                info!(
                    "loading screen: waiting {:.1}s — {}/{} resident, {} placements pending, \
                     {} colliders pending, {} merges pending, awaiting_snap={}, settling={}, \
                     warm={}, ui_pending={}",
                    now - screen.active_since,
                    progress.ready,
                    progress.total,
                    progress.placements_pending,
                    progress.colliders_pending,
                    progress.merge_pending,
                    screen.awaiting_snap,
                    player_settling,
                    warm.satisfied(),
                    entry_ui_pending.is_some(),
                );
            }
        }
    }

    // --- Visibility: under blackout only the root's black shows. ---
    if let Ok(mut vis) = root.single_mut() {
        *vis = if screen.active {
            Visibility::Visible
        } else {
            Visibility::Hidden
        };
    }
    let content_vis = if screen.blackout {
        Visibility::Hidden
    } else {
        Visibility::Inherited
    };
    if let Ok((_, mut vis)) = backdrop.single_mut() {
        if *vis != content_vis {
            *vis = content_vis;
        }
    }
    for mut vis in &mut bar_vis {
        if *vis != content_vis {
            *vis = content_vis;
        }
    }
    if !screen.active || screen.blackout {
        return;
    }

    // --- Backdrop art, `0x406cf0`'s gate: the map id is read once per screen to resolve the
    // texture, so a raise onto a live screen repaints nothing. ---
    if !screen.art_resolved {
        // Black, never the last screen's texture (the reference holds a null handle, no quad).
        if let Ok((mut img, _)) = backdrop.single_mut() {
            if img.color != Color::BLACK {
                img.color = Color::BLACK;
            }
        }
        if let (Some(map_id), Some(maps), Some(screens), Some(assets)) =
            (screen.map, maps.as_ref(), screens.as_ref(), assets.as_mut())
        {
            let path = maps
                .0
                .loading_screen_id(map_id)
                .and_then(|id| screens.0.path(id))
                .map(str::to_string);
            let handle = path.and_then(|path| match screen.art_cache.get(&path) {
                Some(h) => Some(h.clone()),
                None => assets.sprite_texture(&path, &mut images).inspect(|h| {
                    screen.art_cache.insert(path.clone(), h.clone());
                }),
            });
            match (handle, backdrop.single_mut()) {
                (Some(handle), Ok((mut img, _))) => {
                    img.image = handle;
                    img.color = Color::WHITE; // untint to reveal the art
                    screen.art_resolved = true;
                    info!("loading screen: backdrop for map {map_id} resolved");
                }
                // No retry: `0x406d0e` writes `-1` into the map id and `0x406cf0` returns on it.
                _ => {
                    warn!("loading screen: no backdrop for map {map_id} — plain black this load");
                    screen.map = None;
                }
            }
        }
    }

    // --- Progress bar: zero until the snap lands (residency is still the old place's). ---
    if !screen.awaiting_snap {
        screen.displayed = screen.displayed.max(progress.fraction());
    }
    let frac = screen.displayed;
    if let Ok(mut node) = fill.single_mut() {
        node.width = Val::Percent(frac * FILL_MAX_WIDTH * 100.0);
    }
}

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

    #[test]
    fn the_cover_counts_frames_to_the_glass_and_resets_the_moment_it_drops() {
        let mut cover = EntryCover::default();
        assert!(
            cover.presented(),
            "no cover up: nothing is watching the previous present, so nothing waits"
        );
        assert!(!cover.owes_a_present(), "no cover owes no present");

        cover.tick(true);
        assert_eq!(cover.frames(), 1);
        assert!(
            !cover.presented(),
            "the cover's own render has not committed yet"
        );
        assert!(cover.owes_a_present());

        cover.tick(true);
        assert!(!cover.presented(), "one render committed, not two");

        cover.tick(true);
        assert!(
            cover.presented(),
            "at COVER_PRESENT_FRAMES the cover is provably on the glass"
        );
        assert!(!cover.owes_a_present());

        // A reveal drops the count to zero in one frame; the next raise earns its own.
        cover.tick(false);
        assert_eq!(cover.frames(), 0);
        assert!(cover.presented());
        cover.tick(true);
        assert!(!cover.presented(), "the next raise starts its own count");
    }
    /// vmangos can relocate a character out of an expired instance inside `Player::LoadFromDB`, so
    /// `SMSG_LOGIN_VERIFY_WORLD` names another map than the roster did.
    #[test]
    fn a_relocating_snap_cannot_move_the_art_the_screen_was_raised_with() {
        let mut screen = LoadingScreen::default();
        // The pick edge: art from the roster row, Shadowfang Keep, snap still to come.
        screen.raise("world entry", true, Some(33), 0.0);
        screen.tip_edge = Some(TipEdge::Pick);
        screen.displayed = 0.4;

        // `SMSG_LOGIN_VERIFY_WORLD`: the server seats us on map 0, at the instance's exit.
        assert!(
            !screen.far_snap(0),
            "a screen is already up — its own snap must not raise a second one"
        );
        assert_eq!(
            screen.map,
            Some(33),
            "the backdrop is the raise's and holds the whole way — the report"
        );
        assert!(
            !screen.awaiting_snap,
            "the snap the raise was waiting for has landed"
        );
        assert_eq!(
            screen.tip_edge,
            Some(TipEdge::Pick),
            "and the tip just picked survives it — a raise is the only thing that could \
             have cleared it, and no raise happened"
        );
        assert!(
            (screen.displayed - 0.4).abs() < f32::EPSILON,
            "nor does the bar restart mid-load"
        );
        assert!(screen.active, "the screen stays up across its own snap");
    }

    /// A cross-map port with no announcing edge still gets a cover: our backstop, which the
    /// reference's blocking world load does not need.
    #[test]
    fn a_snap_with_nothing_covering_it_asks_for_a_raise() {
        let mut screen = LoadingScreen::default();
        assert!(screen.far_snap(1), "nothing is covering this load");
        assert!(
            !screen.active,
            "far_snap answers the question; the caller does the raising, with its own reason"
        );
    }

    #[test]
    fn only_the_dismiss_clears_the_tip() {
        let mut screen = LoadingScreen::default();
        screen.raise("world entry", true, Some(0), 0.0);
        screen.tip_edge = Some(TipEdge::Pick);

        screen.raise("transfer pending", true, Some(389), 0.0);
        assert_eq!(
            screen.tip_edge,
            Some(TipEdge::Pick),
            "no raise clears a tip"
        );

        screen.dismiss();
        assert_eq!(screen.tip_edge, Some(TipEdge::Clear), "the dismiss does");
        assert!(!screen.active);
    }

    /// The reference's raises (`0x406640`/`0x4072c0`) store the map id with no guard.
    #[test]
    fn a_raise_onto_a_live_screen_repoints_the_map_but_never_the_picture() {
        let mut screen = LoadingScreen::default();
        screen.raise("world entry", true, Some(33), 0.0);
        screen.art_resolved = true; // the first plain-draw frame resolved Shadowfang Keep's art

        screen.raise("transfer pending", true, Some(389), 0.0);
        assert_eq!(screen.map, Some(389), "the map id is re-pointed, unguarded");
        assert!(
            screen.art_resolved,
            "…and the picture is not: the texture is still the one this screen resolved"
        );

        // The dismiss is the only thing that lets the next screen resolve its own.
        screen.dismiss();
        assert!(!screen.art_resolved);
    }
}