//! What orders a UI screen's elements, and where each one lands.
//!
//! The composite is checked against a **framebuffer capture of the running
//! game** (`docs/re/captures/title-screen-oracle.png`), not against itself.
//! Two things were settled that way on 2026-08-18, and this pins both:
//!
//! * a keyframe's scale grows the element **about its declared pivot**, so a
//!   200 % background at (320,180) with pivot (320,180) is the full screen, not
//!   a quarter-screen slab at 320..1600;
//! * the placement region is **not** a second ordering of the elements — it
//!   stores its keyframe groups in declaration order on every build on the
//!   disc, so it cannot be the paint order the title screen needs.
//!
//! Skipped (as no-ops) when the extracted disc is absent.

use std::path::{Path, PathBuf};

use sylpheed_formats::{
    pak::PakArchive,
    t8ad,
    ui_layout::{self, ComposeOptions},
};

fn disc_root() -> Option<PathBuf> {
    if let Ok(p) = std::env::var("SYLPHEED_DISC") {
        let p = PathBuf::from(p);
        if p.join("dat").is_dir() {
            return Some(p);
        }
    }
    let default = Path::new(
        "/home/fabi/RE - Project Sylpheed/Project Sylpheed - Arc of Deception (USA, Europe) (En,Ja)",
    );
    if default.join("dat").is_dir() {
        return Some(default.to_path_buf());
    }
    None
}

macro_rules! skip_without_disc {
    ($root:ident) => {
        let Some($root) = disc_root() else {
            eprintln!("SKIP: extracted disc not found (set SYLPHEED_DISC to enable)");
            return;
        };
    };
}

/// Every parseable screen build on the disc, as (pak name, bundle bytes).
fn builds(root: &Path) -> Vec<(String, Vec<u8>)> {
    let mut paks: Vec<PathBuf> = std::fs::read_dir(root.join("dat"))
        .expect("dat/")
        .flatten()
        .map(|e| e.path())
        .filter(|p| p.extension().and_then(|s| s.to_str()) == Some("pak"))
        .collect();
    paks.sort();
    let mut out = Vec::new();
    for p in &paks {
        let name = p.file_name().unwrap().to_string_lossy().to_string();
        let Ok(arc) = PakArchive::open(p) else {
            continue;
        };
        for e in arc.entries() {
            let Ok(bytes) = arc.read(e) else { continue };
            if ui_layout::is_build(&bytes) {
                out.push((name.clone(), bytes));
            }
        }
    }
    out
}

/// The builds of one pak, in the order `sylpheed-cli screen list` numbers them.
fn pak_builds(root: &Path, pak: &str) -> Vec<Vec<u8>> {
    let arc = PakArchive::open(root.join("dat").join(pak)).expect("open pak");
    arc.entries()
        .iter()
        .filter_map(|e| arc.read(e).ok())
        .filter(|b| ui_layout::is_build(b))
        .collect()
}

#[test]
fn placement_region_order_is_never_a_second_ordering() {
    skip_without_disc!(root);
    let all = builds(&root);
    assert!(
        all.len() > 500,
        "expected the disc's screen builds, got {}",
        all.len()
    );
    let mut checked = 0usize;
    for (pak, bytes) in &all {
        let Some(b) = ui_layout::parse_build(bytes) else {
            continue;
        };
        if b.from_fallback {
            continue; // the fallback path invents the order, so it proves nothing
        }
        checked += 1;
        let identity: Vec<usize> = (0..b.placement_order.len()).collect();
        assert_eq!(
            b.placement_order, identity,
            "{pak}: the placement region stores groups in a DIFFERENT order from \
             the declaration table — that would be a candidate paint order and \
             the note in docs/re/BACKLOG.md needs revisiting"
        );
    }
    assert!(
        checked > 500,
        "only {checked} builds carried a declaration table"
    );
}

#[test]
fn title_background_is_full_screen() {
    skip_without_disc!(root);
    let bs = pak_builds(&root, "GP_TITLE.pak");
    let bytes = &bs[7]; // the full title sequence: 30 elements, 24 sprites
    let b = ui_layout::parse_build(bytes).expect("build 7 parses");
    let base = b
        .elements
        .iter()
        .find(|e| e.name == "ptbase2.t32")
        .expect("the title background element");
    assert_eq!((base.pivot_x, base.pivot_y), (320, 180));
    let k = base.rest().expect("a resting keyframe");
    assert_eq!((k.x, k.y, k.scale_x, k.scale_y), (320, 180, 200, 200));

    // Draw that element and nothing else, on black. Anchored at the pivot it is
    // exactly the 1280x720 screen; anchored at the keyframe corner it would
    // leave the whole top-left quadrant untouched.
    let mut visible = vec![false; b.elements.len()];
    visible[base.index] = true;
    let screen = ui_layout::compose(
        &b,
        bytes,
        ComposeOptions {
            backdrop: [0, 0, 0, 0],
            ..Default::default()
        },
        Some(&visible),
    );
    assert_eq!(screen.drawn, vec![base.index]);
    let uncovered = screen.rgba.chunks_exact(4).filter(|p| p[3] == 0).count();
    assert_eq!(
        uncovered,
        0,
        "{uncovered} of {} pixels are not covered by the background",
        screen.width * screen.height
    );
}

/// How much of the disc the pivot-anchored rule actually touches, and how much
/// of it could tell "about the pivot" apart from "about the sprite centre".
///
/// Stated as numbers rather than left implicit: at 100 % the pivot cancels, so
/// only a scaled element moves at all, and only a scaled element whose pivot is
/// not half its decoded size distinguishes the two rules. The oracle settled
/// `ptbase2`, whose pivot *is* half its size — so the centre reading is not
/// excluded by measurement, only by the pivot field existing at all.
#[test]
fn scaled_elements_are_a_small_and_mostly_undiscriminating_minority() {
    skip_without_disc!(root);
    let (mut total, mut scaled, mut discriminating) = (0usize, 0usize, 0usize);
    let (mut pivot_is_half, mut pivot_off_by_lots) = (0usize, 0usize);
    for (_, bytes) in builds(&root) {
        let Some(b) = ui_layout::parse_build(&bytes) else {
            continue;
        };
        for el in &b.elements {
            let Some(k) = el.rest() else { continue };
            let Some(sprite) = el.sprite.as_ref() else {
                continue;
            };
            let Some(&(off, size)) = b.sprites.get(sprite) else {
                continue;
            };
            let Some(img) = t8ad::parse(&bytes[off..off + size]) else {
                continue;
            };
            total += 1;
            let dpx = (el.pivot_x as i64 * 2 - img.width as i64).abs();
            let dpy = (el.pivot_y as i64 * 2 - img.height as i64).abs();
            if dpx <= 1 && dpy <= 1 {
                pivot_is_half += 1;
            } else if dpx > 16 || dpy > 16 {
                pivot_off_by_lots += 1;
            }
            let sx = if k.scale_x == 0 { 100 } else { k.scale_x };
            let sy = if k.scale_y == 0 { 100 } else { k.scale_y };
            if sx == 100 && sy == 100 {
                continue;
            }
            scaled += 1;
            // "About the pivot" and "about the centre" differ by
            // (pivot - size/2) * (scale - 1); a pixel of disagreement needs
            // both a real scale change and a pivot away from the centre.
            let dx =
                (el.pivot_x as i64 - img.width as i64 / 2).abs() * (sx as i64 - 100).abs() / 100;
            let dy =
                (el.pivot_y as i64 - img.height as i64 / 2).abs() * (sy as i64 - 100).abs() / 100;
            if dx.max(dy) >= 2 {
                discriminating += 1;
            }
        }
    }
    eprintln!("resting placements with a decoded sprite: {total}");
    eprintln!("  pivot*2 == decoded size (+-1 px):        {pivot_is_half}");
    eprintln!("  pivot*2 off by more than 16 px:          {pivot_off_by_lots}");
    eprintln!("  of those, scaled != 100%: {scaled}");
    eprintln!("  of those, pivot-vs-centre differ by >= 2 px: {discriminating}");
    assert!(
        total > 4000,
        "expected thousands of placements, got {total}"
    );
}