//! The `.slb` leading segment — recovered, and scoped.
//!
//! `VOICE_D_453` used to decode to 0.14 s because its line lives in a headerless
//! packet stream *before* the first `RIFF`, and the decoder started at the
//! `RIFF`. The banks that looked fine were the ones whose leading segment is
//! silence. One rule, two outcomes.

use std::path::Path;
use std::sync::OnceLock;

use sylpheed_formats::{slb, PakArchive};

mod common;
use common::skip_without_disc;

/// One archive for the whole binary.
///
/// `PakArchive` holds the entire concatenated payload in memory, and
/// `sound.pak` is **1.01 GB** (`sound.p00`-`.p04`). Opening it per call — which
/// the helpers below did, inside loops — put one copy per test thread in flight,
/// so at the default thread count the suite needed ~6 GB and was SIGKILLed by
/// the CI container's 7 GB cap (`--memory-swap` equals `--memory`, so there is
/// no swap to absorb it). A killed suite prints no `test result:` line at all,
/// so it vanishes from the tally rather than failing visibly.
///
/// The archive is immutable once open and every accessor takes `&self`, so one
/// shared instance is equivalent to N private ones — at 1/N the memory.
fn sound(root: &Path) -> &'static PakArchive {
    static SOUND: OnceLock<PakArchive> = OnceLock::new();
    // Every caller passes the same `disc_root()`, so first-writer-wins is the
    // same archive whichever test initialises it.
    SOUND.get_or_init(|| PakArchive::open(root.join("dat/sound.pak")).expect("sound.pak"))
}

fn bank(root: &Path, n: u32) -> Vec<u8> {
    let snd = sound(root);
    let path = format!("eng\\etc\\VOICE_D_{n}.slb");
    let entry = snd.find_by_name(&path).expect("bank present");
    snd.read(entry).expect("read")
}

/// The boundary is arithmetic and has no tunable: the first `RIFF` sits at
/// exactly `HEADERLESS_DATA_OFFSET + n*XMA1_PACKET` in every resupply bank.
#[test]
fn leading_segment_is_a_whole_number_of_packets() {
    skip_without_disc!(root);
    for (n, packets) in [(450u32, 8usize), (451, 1), (452, 7), (453, 22), (454, 29)] {
        let b = bank(&root, n);
        let ri = b.windows(4).position(|w| w == b"RIFF").expect("has a RIFF");
        assert!(ri > slb::HEADERLESS_DATA_OFFSET, "VOICE_D_{n}");
        let lead = ri - slb::HEADERLESS_DATA_OFFSET;
        assert_eq!(
            lead % slb::XMA1_PACKET,
            0,
            "VOICE_D_{n} not a whole packet count"
        );
        assert_eq!(lead / slb::XMA1_PACKET, packets, "VOICE_D_{n} packet count");
    }
}

/// The two banks whose line lives in the leading segment now yield it.
#[test]
fn broken_banks_recover_their_line() {
    skip_without_disc!(root);
    // (bank, sub-waves expected, payload of the leading one)
    for (n, waves, lead_len) in [(453u32, 2usize, 45116usize), (454, 2, 59452)] {
        let riffs = slb::to_xma_riffs(&bank(&root, n));
        assert_eq!(riffs.len(), waves, "VOICE_D_{n} sub-wave count");
        assert_eq!(riffs[0].len(), lead_len, "VOICE_D_{n} leading segment");
        // It must be the LARGER part: that is the whole point.
        assert!(
            riffs[0].len() > riffs[1].len() * 5,
            "VOICE_D_{n}: leading segment should dominate"
        );
    }
}

/// `VOICE_D_451`'s leading region is all zeros — the guard must skip it, so the
/// rule cannot prepend silence to a bank that does not need it.
#[test]
fn all_zero_leading_region_is_skipped() {
    skip_without_disc!(root);
    let b = bank(&root, 451);
    let ri = b.windows(4).position(|w| w == b"RIFF").unwrap();
    assert!(
        b[slb::HEADERLESS_DATA_OFFSET..ri].iter().all(|x| *x == 0),
        "expected an all-zero leading region"
    );
    // Two sub-waves, both from the RIFF section — no synthesised third.
    assert_eq!(slb::to_xma_riffs(&b).len(), 2);
}

fn bank_named(root: &Path, path: &str) -> Vec<u8> {
    let snd = sound(root);
    let entry = snd
        .find_by_name(path)
        .unwrap_or_else(|| panic!("{path} present"));
    snd.read(entry).expect("read")
}

/// `HEADERLESS_DATA_OFFSET` is the `<lang>\etc\` case, not the format.
///
/// The leading stream is a whole number of packets ending at the first `RIFF`,
/// so its start is `first_riff % XMA1_PACKET`. Disc-wide that takes four values
/// and only 1392 matches the old constant — assuming it elsewhere starts the
/// decode mid-packet. See docs/re/structures/slb-data-offset.md.
#[test]
fn leading_data_offset_is_derived_not_assumed() {
    skip_without_disc!(root);
    // (bank, expected derived offset). The `etc` banks must still land on the
    // old constant — that is the no-regression half of the test.
    for (path, want) in [
        ("eng\\etc\\VOICE_D_452.slb", 1392usize),
        ("eng\\etc\\VOICE_D_453.slb", 1392),
        ("eng\\Voice\\VOICE_TCAF_592.slb", 1468),
        ("jpn\\Voice\\VOICE_TCAF_592.slb", 1728),
        ("jpn\\etc\\VOICE_D_452.slb", 1600),
    ] {
        let b = bank_named(&root, path);
        let ri = b.windows(4).position(|w| w == b"RIFF").expect("has a RIFF");
        let got = slb::leading_data_offset(ri);
        assert_eq!(got, want, "{path}: derived offset");
        assert_eq!(
            (ri - got) % slb::XMA1_PACKET,
            0,
            "{path}: leading stream is not a whole packet count"
        );
        assert!(
            got >= slb::HEADERLESS_DATA_OFFSET,
            "{path}: offsets below the old constant are unexplained"
        );
    }
}

/// The banks the old constant mis-decoded now carry a leading sub-wave, and the
/// ones it decoded correctly are untouched.
#[test]
fn derived_offset_recovers_voice_banks_without_regressing_etc() {
    skip_without_disc!(root);
    for path in [
        "eng\\Voice\\VOICE_TCAF_592.slb",
        "jpn\\Voice\\VOICE_TCAF_592.slb",
    ] {
        let b = bank_named(&root, path);
        let ri = b.windows(4).position(|w| w == b"RIFF").expect("has a RIFF");
        // Under the old constant this leading region was not a whole packet
        // count, so `to_xma_riffs` emitted no leading sub-wave at all.
        assert_ne!(
            (ri - slb::HEADERLESS_DATA_OFFSET) % slb::XMA1_PACKET,
            0,
            "{path}: expected the OLD constant to mis-align here"
        );
        let riffs = slb::to_xma_riffs(&b);
        assert!(
            riffs.len() >= 2,
            "{path}: expected a leading sub-wave plus at least one RIFF, got {}",
            riffs.len()
        );
    }
    // Control: an `etc` bank still produces what it did before.
    let b = bank_named(&root, "eng\\etc\\VOICE_D_452.slb");
    assert_eq!(
        slb::leading_data_offset(b.windows(4).position(|w| w == b"RIFF").unwrap()),
        slb::HEADERLESS_DATA_OFFSET
    );
}

/// The scan agrees with the truth wherever the truth is knowable.
///
/// A bank carrying a `RIFF` has its offset *forced* to `first_riff % 2048`, so
/// those banks are a labelled set for a rule meant to serve the ones without a
/// `RIFF`. Over the whole labelled set the scan is right 99.6 % of the time and
/// its only failures are ties. This test walks a slice of it.
#[test]
fn scan_data_offset_agrees_with_the_riff_derived_answer() {
    skip_without_disc!(root);
    let snd = sound(&root);
    let mut checked = 0usize;
    let mut agreed = 0usize;
    for lang in ["eng", "jpn"] {
        for (dir, lo, hi) in [("Voice", 1u32, 120u32), ("etc", 1, 120)] {
            for n in lo..hi {
                let path = format!("{lang}\\{dir}\\VOICE_TCAF_{n:03}.slb");
                let Some(entry) = snd.find_by_name(&path) else {
                    continue;
                };
                let Ok(b) = snd.read(entry) else { continue };
                let Some(ri) = b.windows(4).position(|w| w == b"RIFF") else {
                    continue;
                };
                if ri <= slb::HEADERLESS_DATA_OFFSET {
                    continue;
                }
                if !b[slb::HEADERLESS_DATA_OFFSET..ri].iter().any(|v| *v != 0) {
                    continue;
                }
                checked += 1;
                if slb::scan_data_offset(&b) == slb::leading_data_offset(ri) {
                    agreed += 1;
                }
            }
        }
    }
    assert!(
        checked >= 20,
        "expected a usable labelled set, got {checked}"
    );
    // The whole-disc rate is 99.62%; allow a little slack for a small slice.
    let rate = agreed as f64 / checked as f64;
    assert!(
        rate >= 0.95,
        "scan agreed on {agreed}/{checked} ({:.1}%), expected >=95%",
        rate * 100.0
    );
}

/// Every offset the scan can return is one of the four seen on disc.
#[test]
fn scan_only_returns_known_offsets() {
    skip_without_disc!(root);
    let snd = sound(&root);
    let mut seen = 0usize;
    for n in 1u32..200 {
        for path in [
            format!("eng\\Voice\\VOICE_ADAN_{n:03}.slb"),
            format!("jpn\\Voice\\VOICE_ADAN_{n:03}.slb"),
        ] {
            let Some(entry) = snd.find_by_name(&path) else {
                continue;
            };
            let Ok(b) = snd.read(entry) else { continue };
            let got = slb::scan_data_offset(&b);
            assert!(
                slb::DATA_OFFSET_CANDIDATES.contains(&got),
                "{path}: scan returned {got}, not a known offset"
            );
            seen += 1;
        }
    }
    assert!(seen >= 20, "expected banks to test, saw {seen}");
}

/// A wave's boundary is exact: `seek` magic sits at `data_at + declared_size`.
///
/// Established 2026-08-26 (docs/re/structures/slb-data-offset.md). Every
/// `RIFF`-bearing entry on the disc satisfies it — **7 620/7 620** in the full
/// sweep — and the `seek` chunk's little-endian packet count at `+12` times
/// 2048 equals the declared size. This is the decoder-independent boundary, and
/// it is what proves the declared sizes honest rather than over-stated.
///
/// The test walks a bounded slice so it stays fast; the identity is disc-wide.
#[test]
fn a_waves_declared_size_is_confirmed_by_the_next_seek() {
    skip_without_disc!(root);
    let snd = sound(&root);
    let mut checked = 0usize;
    for n in 1u32..400 {
        for path in [
            format!("eng\\etc\\VOICE_D_{n}.slb"),
            format!("eng\\Voice\\VOICE_TCAF_{n:03}.slb"),
            format!("jpn\\Voice\\VOICE_ADAN_{n:03}.slb"),
        ] {
            let Some(entry) = snd.find_by_name(&path) else {
                continue;
            };
            let Ok(b) = snd.read(entry) else { continue };
            let Some(ri) = b.windows(4).position(|w| w == b"RIFF") else {
                continue;
            };
            let Some(rel) = b[ri..].windows(4).position(|w| w == b"data") else {
                continue;
            };
            let di = ri + rel;
            let Some(sz) = b.get(di + 4..di + 8) else {
                continue;
            };
            let declared = u32::from_le_bytes(sz.try_into().unwrap()) as usize;
            // The boundary lies outside this entry's own TOC window whenever the
            // declared size overruns it, which is the common case — so read from
            // the archive's flat data rather than from the entry slice.
            let probe = entry.offset as usize + di + 8 + declared;
            let Some(tag) = snd.data_at(probe, 16) else {
                continue;
            };
            assert_eq!(
                &tag[0..4],
                b"seek",
                "{path}: expected `seek` at data_at+declared ({probe})"
            );
            let packets = u32::from_le_bytes(tag[12..16].try_into().unwrap()) as usize;
            assert_eq!(
                packets * slb::XMA1_PACKET,
                declared,
                "{path}: seek packet count x 2048 != declared data size"
            );
            checked += 1;
        }
    }
    assert!(checked >= 30, "expected banks to check, got {checked}");
    eprintln!("wave-boundary identity held for {checked} banks");
}

/// A **music** bank has no leading segment — the bytes before its first `RIFF`
/// are the bank header, and emitting them made `BGM_103` look like three stems.
///
/// The header sizes itself (`+0x24`, in 2048-byte blocks), and on every bank on
/// this disc that size lands exactly on the first `RIFF`. So the guard is not a
/// heuristic and has no threshold: if a bank states a header, believe it.
#[test]
fn a_bank_that_states_its_own_header_has_no_leading_segment() {
    skip_without_disc!(root);
    let snd = sound(&root);
    let mut with_header = 0usize;
    let mut mid_bank = 0usize;
    // Peek at the 56-byte header through the archive's flat data rather than
    // decompressing 9 519 entries: `sound.pak` stores them uncompressed, and a
    // full read of all of them is several GB (it OOM-killed the test runner).
    for entry in snd.entries() {
        let Some(head) = snd.data_at(entry.offset as usize, 0x38) else {
            continue;
        };
        match slb::bank_header_len(head) {
            Some(h) => {
                let b = snd.read(entry).expect("read a bank that states a header");
                let ri = b.windows(4).position(|w| w == b"RIFF").expect("has a RIFF");
                // Declared header ends exactly at the first RIFF: no gap, so
                // nothing before it can be a packet stream.
                assert_eq!(h, ri, "a bank header that does not end at its first RIFF");
                with_header += 1;
            }
            None => mid_bank += 1,
        }
    }
    // 28 music banks (ids 1001-1023, 1101-1105); the rest are mid-bank windows,
    // where the leading region IS real and must keep being emitted.
    assert_eq!(
        with_header, 28,
        "banks stating their own header at offset 0"
    );
    assert!(mid_bank > 9000, "mid-bank windows, got {mid_bank}");
    eprintln!("{with_header} banks state a header; {mid_bank} mid-bank windows");
}

/// The regression itself: the menu's music bank is **two** sub-waves, and they
/// are the two the corpus names — matching the executable's `BGM_103` and the
/// two streams the runtime XMA probe saw at the main menu.
#[test]
fn the_menu_music_bank_is_exactly_two_sub_waves() {
    skip_without_disc!(root);
    let snd = sound(&root);
    for (name, sizes) in [
        ("BGM_103.slb", [3_876_864usize, 3_930_112]),
        ("BGM_001.slb", [4_466_688, 4_673_536]),
    ] {
        let entry = snd.find_by_name(name).expect("bank present");
        let b = snd.read(entry).expect("read");
        let riffs = slb::to_xma_riffs(&b);
        assert_eq!(riffs.len(), 2, "{name}: sub-wave count");
        for (r, want) in riffs.iter().zip(sizes) {
            let di = r.windows(4).position(|w| w == b"data").expect("data chunk");
            let got = u32::from_le_bytes(r[di + 4..di + 8].try_into().unwrap()) as usize;
            assert_eq!(got, want, "{name}: sub-wave payload size");
        }
    }
}