//! Criterion benchmark suite for `clawhdf5-onion`.
//!
//! Targets from the Phase 5 PRD:
//!
//! | Benchmark                              | Target        |
//! |----------------------------------------|---------------|
//! | Onion write overhead (vs unversioned)  | ≤ 10%         |
//! | open(rev=100) — no snapshot            | ≤ 1 ms        |
//! | open(rev=1000) — with snapshot         | ≤ 5 ms        |
//! | Manifest generation 100 revisions      | ≤ 50 ms       |
//! | BLAKE3 verify throughput               | ≥ 5 GB/s      |
//! | Branch fork                            | ≤ 100 µs      |
//! | GC keep_last_1000 on 10K revisions     | ≤ 2 s         |

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

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

const PAGE_SIZE: u32 = 4096;

fn tmp_onion_with_n(n: usize) -> (NamedTempFile, std::path::PathBuf, OnionFile, Vec<u8>) {
    let f = NamedTempFile::new().unwrap();
    let h5 = f.path().with_extension("h5");
    let base = b"\x89HDF\r\n\x1a\n".to_vec();
    std::fs::write(&h5, &base).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();
    }
    (f, h5, onion, base)
}

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

/// Benchmark: single revision write (commit_session overhead).
fn bench_write_one_revision(c: &mut Criterion) {
    let mut group = c.benchmark_group("write");
    group.throughput(Throughput::Elements(1));

    group.bench_function("commit_session/1_page", |b| {
        let f = NamedTempFile::new().unwrap();
        let h5 = f.path().with_extension("h5");
        std::fs::write(&h5, b"\x89HDF\r\n\x1a\n").unwrap();
        let mut onion = OnionFile::create(&h5, PAGE_SIZE).unwrap();
        b.iter(|| {
            let mut s = onion.begin_session(None).unwrap();
            s.record_page(0, black_box(&vec![0xABu8; PAGE_SIZE as usize]));
            black_box(onion.commit_session(s, None).unwrap());
        });
    });

    group.bench_function("commit_session/4_pages", |b| {
        let f = NamedTempFile::new().unwrap();
        let h5 = f.path().with_extension("h5");
        std::fs::write(&h5, b"\x89HDF\r\n\x1a\n").unwrap();
        let mut onion = OnionFile::create(&h5, PAGE_SIZE).unwrap();
        b.iter(|| {
            let mut s = onion.begin_session(None).unwrap();
            for i in 0u64..4 {
                s.record_page(
                    i * PAGE_SIZE as u64,
                    black_box(&vec![0xCDu8; PAGE_SIZE as usize]),
                );
            }
            black_box(onion.commit_session(s, None).unwrap());
        });
    });

    group.finish();
}

/// Benchmark: reconstruct_revision at various depths.
fn bench_reconstruct_revision(c: &mut Criterion) {
    let mut group = c.benchmark_group("reconstruct");

    for &depth in &[10usize, 50, 100] {
        let (_f, _h5, onion, base) = tmp_onion_with_n(depth);
        let target_rev = (depth - 1) as u64;

        group.bench_with_input(BenchmarkId::new("no_snapshot", depth), &depth, |b, _| {
            b.iter(|| {
                black_box(
                    onion
                        .reconstruct_revision(target_rev, black_box(&base))
                        .unwrap(),
                );
            });
        });
    }

    // With snapshot: create a real snapshot at midpoint via create_snapshot()
    for &depth in &[100usize, 200] {
        let (_f, _h5, mut onion, base) = tmp_onion_with_n(depth);
        // Insert a snapshot halfway through
        onion.create_snapshot(&base, Some("mid-snap")).unwrap();
        // Add a few more revisions after the snapshot
        for i in 0u8..5 {
            let mut s = onion.begin_session(None).unwrap();
            s.record_page(0, &vec![i; PAGE_SIZE as usize]);
            onion.commit_session(s, None).unwrap();
        }
        let target_rev = onion.revision_count() - 1;

        group.bench_with_input(BenchmarkId::new("with_snapshot", depth), &depth, |b, _| {
            b.iter(|| {
                black_box(
                    onion
                        .reconstruct_revision(target_rev, black_box(&base))
                        .unwrap(),
                );
            });
        });
    }

    group.finish();
}

/// Benchmark: list_revisions (manifest generation).
fn bench_manifest_generation(c: &mut Criterion) {
    let mut group = c.benchmark_group("manifest");

    for &n in &[10usize, 100, 500] {
        let (_f, _h5, onion, _base) = tmp_onion_with_n(n);

        group.bench_with_input(BenchmarkId::new("list_revisions", n), &n, |b, _| {
            b.iter(|| {
                black_box(onion.list_revisions());
            });
        });
    }

    group.finish();
}

/// Benchmark: BLAKE3 hashing throughput — single-threaded vs Rayon.
fn bench_blake3_throughput(c: &mut Criterion) {
    let mut group = c.benchmark_group("blake3");

    // Single-threaded path (best for small pages — dispatch overhead dominates above).
    for &size_kb in &[4usize, 64, 1024, 4096] {
        let data = vec![0xAAu8; size_kb * 1024];
        group.throughput(Throughput::Bytes(data.len() as u64));

        group.bench_with_input(
            BenchmarkId::new("single", format!("{size_kb}KB")),
            &data,
            |b, d| {
                b.iter(|| {
                    black_box(clawsync_core::checksum::blake3_hash(black_box(d)));
                });
            },
        );
    }

    // Rayon tree-parallel path (best for large inputs >= 128 KB).
    for &size_kb in &[128usize, 512, 1024, 4096] {
        let data = vec![0xAAu8; size_kb * 1024];
        group.throughput(Throughput::Bytes(data.len() as u64));

        group.bench_with_input(
            BenchmarkId::new("rayon", format!("{size_kb}KB")),
            &data,
            |b, d| {
                b.iter(|| {
                    black_box(clawsync_core::checksum::blake3_hash_large(black_box(d)));
                });
            },
        );
    }

    // Batch parallel: hash N independent 4 KB pages simultaneously.
    for &n_pages in &[16usize, 64, 256] {
        let pages: Vec<Vec<u8>> = (0..n_pages).map(|i| vec![(i % 256) as u8; 4096]).collect();
        let page_refs: Vec<&[u8]> = pages.iter().map(|p| p.as_slice()).collect();
        group.throughput(Throughput::Bytes((n_pages * 4096) as u64));

        group.bench_with_input(
            BenchmarkId::new("batch_pages", format!("{n_pages}x4KB")),
            &page_refs,
            |b, refs| {
                b.iter(|| {
                    black_box(clawsync_core::checksum::blake3_hash_batch(black_box(refs)));
                });
            },
        );
    }

    group.finish();
}

/// Benchmark: branch fork.
fn bench_branch_fork(c: &mut Criterion) {
    c.bench_function("branch/fork", |b| {
        let f = NamedTempFile::new().unwrap();
        let h5 = f.path().with_extension("h5");
        std::fs::write(&h5, b"\x89HDF\r\n\x1a\n").unwrap();
        let mut onion = OnionFile::create(&h5, PAGE_SIZE).unwrap();

        let mut s = onion.begin_session(None).unwrap();
        s.record_page(0, &vec![0u8; PAGE_SIZE as usize]);
        onion.commit_session(s, None).unwrap();

        let mut fork_count = 0usize;
        b.iter(|| {
            let name = format!("bench-{fork_count}");
            fork_count += 1;
            black_box(onion.create_branch(&name, "main").unwrap());
        });
    });
}

/// Benchmark: GC keep_last_N.
fn bench_gc(c: &mut Criterion) {
    let mut group = c.benchmark_group("gc");
    group.warm_up_time(std::time::Duration::from_millis(200));
    group.measurement_time(std::time::Duration::from_secs(3));

    for &(total, keep) in &[(200usize, 50usize), (500, 100)] {
        group.bench_with_input(
            BenchmarkId::new(format!("keep_last_{keep}"), total),
            &(total, keep),
            |b, &(total, keep)| {
                b.iter_with_setup(
                    || tmp_onion_with_n(total).2,
                    |mut onion| {
                        black_box(onion.gc(GcPolicy::KeepLastN(keep as u64)).unwrap());
                    },
                );
            },
        );
    }

    group.finish();
}

/// Benchmark: snapshot creation overhead.
fn bench_snapshot(c: &mut Criterion) {
    let mut group = c.benchmark_group("snapshot");

    for &n_revs in &[5usize, 20, 50] {
        group.bench_with_input(
            BenchmarkId::new("create_snapshot", n_revs),
            &n_revs,
            |b, &n_revs| {
                let (_f, _h5, mut onion, base) = tmp_onion_with_n(n_revs);
                b.iter(|| {
                    black_box(onion.create_snapshot(&base, Some("bench-snap")).unwrap());
                });
            },
        );
    }

    group.finish();
}

// ─────────────────────────────────────────────────────────────────────────────
// Registration
// ─────────────────────────────────────────────────────────────────────────────

criterion_group!(
    benches,
    bench_write_one_revision,
    bench_reconstruct_revision,
    bench_manifest_generation,
    bench_blake3_throughput,
    bench_branch_fork,
    bench_gc,
    bench_snapshot,
);
criterion_main!(benches);