//! Criterion benchmarks for epoch-based (lazy) GC vs immediate GC.
//!
//! Measures:
//! - `gc_keepn_immediate/N` — existing O(N·P) immediate compact path
//! - `gc_epoch_flip/N`      — new O(N) mark-only path
//! - `flush_after_epoch_gc/N` — deferred compaction cost inside flush()
//!
//! Run:
//!   cargo bench -p clawhdf5-onion -- epoch_gc

use clawhdf5_onion::gc::GcPolicy;
use clawhdf5_onion::writer::OnionFile;
use criterion::{BenchmarkId, Criterion, black_box, criterion_group, criterion_main};
use tempfile::NamedTempFile;

const PAGE_SIZE: u32 = 4096;

// ─────────────────────────────────────────────────────────────────────────────
// Helpers
// ─────────────────────────────────────────────────────────────────────────────

fn make_onion(n: usize) -> (NamedTempFile, std::path::PathBuf, OnionFile) {
    let tmp = NamedTempFile::new().unwrap();
    let h5 = tmp.path().with_extension("h5");
    std::fs::write(&h5, b"\x89HDF\r\n\x1a\n").unwrap();
    let mut onion = OnionFile::create(&h5, PAGE_SIZE).unwrap();
    for i in 0..n {
        let mut s = onion.begin_session(None).unwrap();
        s.record_page(0, &vec![(i % 256) as u8; PAGE_SIZE as usize]);
        onion.commit_session(s, None).unwrap();
    }
    (tmp, h5, onion)
}

// ─────────────────────────────────────────────────────────────────────────────
// Benchmarks
// ─────────────────────────────────────────────────────────────────────────────

fn bench_epoch_gc(c: &mut Criterion) {
    let sizes = [100usize, 500, 1000];

    // ── Immediate GC (baseline) ───────────────────────────────────────────────
    let mut group = c.benchmark_group("epoch_gc/immediate");
    for &n in &sizes {
        group.bench_with_input(BenchmarkId::new("keep_last_half", n), &n, |b, &n| {
            b.iter_with_setup(
                || make_onion(n),
                |(_tmp, _h5, mut onion)| {
                    let _ = onion
                        .gc(black_box(GcPolicy::KeepLastN((n / 2) as u64)))
                        .unwrap();
                },
            );
        });
    }
    group.finish();

    // ── Epoch flip (mark only, no compaction) ─────────────────────────────────
    let mut group = c.benchmark_group("epoch_gc/epoch_flip_mark");
    for &n in &sizes {
        group.bench_with_input(BenchmarkId::new("keep_last_half", n), &n, |b, &n| {
            b.iter_with_setup(
                || make_onion(n),
                |(_tmp, _h5, mut onion)| {
                    let _ = onion
                        .gc(black_box(GcPolicy::EpochFlip(Box::new(
                            GcPolicy::KeepLastN((n / 2) as u64),
                        ))))
                        .unwrap();
                },
            );
        });
    }
    group.finish();

    // ── Flush after epoch flip (deferred compaction cost) ────────────────────
    let mut group = c.benchmark_group("epoch_gc/flush_after_epoch_flip");
    for &n in &sizes {
        group.bench_with_input(BenchmarkId::new("keep_last_half", n), &n, |b, &n| {
            b.iter_with_setup(
                || {
                    let (tmp, h5, mut onion) = make_onion(n);
                    onion
                        .gc(GcPolicy::EpochFlip(Box::new(GcPolicy::KeepLastN(
                            (n / 2) as u64,
                        ))))
                        .unwrap();
                    (tmp, h5, onion)
                },
                |(_tmp, _h5, mut onion)| {
                    onion.flush().unwrap();
                },
            );
        });
    }
    group.finish();

    // ── Comparison: flush without any GC (baseline for flush cost) ───────────
    let mut group = c.benchmark_group("epoch_gc/flush_no_gc");
    for &n in &sizes {
        group.bench_with_input(BenchmarkId::new("n_revisions", n), &n, |b, &n| {
            b.iter_with_setup(
                || make_onion(n),
                |(_tmp, _h5, mut onion)| {
                    onion.flush().unwrap();
                },
            );
        });
    }
    group.finish();
}

criterion_group!(benches, bench_epoch_gc);
criterion_main!(benches);