#![allow(clippy::unwrap_used, clippy::cast_precision_loss)]

//! Criterion benchmarks for cold-start recovery time.
//!
//! Measures the open-to-ready latency when `TidalDb::builder().open()` replays
//! a WAL + checkpoint from a previously populated database. This is the metric
//! operators care about most during restarts and crash recovery.
//!
//! ## Benchmarks
//!
//! - **`cold_start_10k_items`**: Measures checkpoint restore + in-memory index
//!   rebuild from a clean checkpoint (no WAL backlog). This is the realistic
//!   production recovery path for graceful shutdowns.
//!
//! - **`cold_start_with_wal_backlog_10k`**: Measures recovery from a checkpoint
//!   plus 2K WAL backlog signals that were never checkpointed (simulating a crash
//!   before checkpoint). The WAL backlog is re-injected after each iteration's
//!   `close()` to ensure every iteration measures the same replay workload.
//!
//! ## Scale
//!
//! The Criterion benchmark uses 10K entities (scaled down from the 1M specified
//! in task-05 for local iteration speed). Hard SLA bounds are enforced by the
//! integration tests in `tests/m7_recovery_sla.rs` (run as part of `cargo test`).
//! The full 1M-item SLA test (`recovery_under_30_seconds`) is marked
//! `#[ignore = "expensive"]` and must be run explicitly:
//!
//! ```bash
//! cargo test --manifest-path tidal/Cargo.toml --test m7_recovery_sla -- --ignored
//! ```

use std::time::Duration;

use criterion::{Criterion, criterion_group, criterion_main};
use tidaldb::TidalDb;
use tidaldb::replication::ShardId;
use tidaldb::schema::{DecaySpec, EntityId, EntityKind, SchemaBuilder, Timestamp, Window};
use tidaldb::wal::checkpoint::CheckpointManager;
use tidaldb::wal::format::{EventRecord, MAX_EVENTS_PER_BATCH, encode_batch};
use tidaldb::wal::segment::segment_filename;

fn bench_schema() -> tidaldb::schema::Schema {
    let mut builder = SchemaBuilder::new();
    let _ = builder
        .signal(
            "view",
            EntityKind::Item,
            DecaySpec::Exponential {
                half_life: Duration::from_secs(7 * 24 * 3600),
            },
        )
        .windows(&[Window::AllTime])
        .velocity(false)
        .add();
    builder.build().expect("valid schema")
}

fn generate_test_data(dir: &std::path::Path) {
    let schema = bench_schema();

    // Write 10K entities with signals (scaled down from 1M for CI).
    // The benchmark is designed for local profiling; the smoke test (below)
    // is the gatekeeping test for CI.
    let db = TidalDb::builder()
        .with_data_dir(dir)
        .with_schema(schema)
        .open()
        .expect("open should succeed");

    let base_ns = 1_000_000_000_000u64;

    // Write signals for entities.
    let entity_count = 10_000u64;
    for entity_id in 1..=entity_count {
        let ts = Timestamp::from_nanos(base_ns + entity_id * 1_000_000);
        db.signal("view", EntityId::new(entity_id), 1.0, ts)
            .expect("signal should succeed");
    }

    // Force clean shutdown (triggers checkpoint + WAL compaction).
    db.close().expect("close should succeed");
}

/// Inject `backlog_count` raw WAL signal events into the WAL directory,
/// starting at sequence `checkpoint_seq + 1`. Uses entity IDs
/// `base_entity + 1 ..= base_entity + backlog_count` with `signal_type = 0`
/// ("view", the only signal in `bench_schema`, assigned ID 0 alphabetically).
fn inject_wal_backlog(data_dir: &std::path::Path, base_entity: u64, backlog_count: u64) {
    let wal_dir = data_dir.join("wal");
    std::fs::create_dir_all(&wal_dir).expect("create wal dir");

    // Read the current checkpoint to determine where to start injected seqs.
    let checkpoint = CheckpointManager::read(&wal_dir).expect("read checkpoint");
    let checkpoint_seq = checkpoint.map_or(0, |(seq, _)| seq);

    let base_ns = 1_000_000_000_000u64;

    // Build event records for the backlog.
    let events: Vec<EventRecord> = (1..=backlog_count)
        .map(|i| EventRecord {
            entity_id: base_entity + i,
            signal_type: 0, // "view" is the only signal, assigned ID 0
            weight: 1.0,
            timestamp_nanos: base_ns + (base_entity + i) * 1_000_000,
        })
        .collect();

    // Encode into batches (max 256 events per batch), write as a single
    // WAL segment file starting at checkpoint_seq + 1.
    let mut seq = checkpoint_seq + 1;
    let seg_path = wal_dir.join(segment_filename(ShardId::SINGLE, seq));
    let mut segment_bytes: Vec<u8> = Vec::new();

    for chunk in events.chunks(usize::from(MAX_EVENTS_PER_BATCH)) {
        let batch_ts = chunk[0].timestamp_nanos;
        let batch_bytes = encode_batch(chunk, seq, batch_ts).expect("encode batch");
        segment_bytes.extend_from_slice(&batch_bytes);
        seq += chunk.len() as u64;
    }

    std::fs::write(&seg_path, &segment_bytes).expect("write WAL segment");
}

fn recovery_benchmark(c: &mut Criterion) {
    let mut group = c.benchmark_group("recovery");
    // Recovery benchmarks can be slower -- allow more time.
    group.sample_size(10);
    group.measurement_time(Duration::from_secs(30));

    // Generate the test data directory (done once, reused across iterations).
    let dir = tempfile::tempdir().expect("tempdir");
    generate_test_data(dir.path());

    let schema = bench_schema();
    group.bench_function("cold_start_10k_items", |b| {
        b.iter(|| {
            let db = TidalDb::builder()
                .with_data_dir(dir.path())
                .with_schema(schema.clone())
                .open()
                .expect("open should succeed");

            // Verify the database is actually functional.
            let count = db
                .read_windowed_count(EntityId::new(1), "view", Window::AllTime)
                .expect("read should succeed");
            assert!(count > 0, "entity 1 should have signals after recovery");

            db.close().expect("close should succeed");
        });
    });

    group.finish();
}

/// Generates a data directory with a clean checkpoint (10K base items)
/// plus 2K WAL backlog signals on entity IDs `10_001..=12_000` that are
/// NOT covered by the checkpoint.
///
/// The approach:
///   1. Write 10K base signals, call `close()` -> checkpoint + WAL compaction.
///   2. Inject raw WAL segment files with 2K events at sequence numbers above
///      the checkpoint boundary, simulating events written to the WAL but never
///      checkpointed (i.e., a crash before checkpoint).
///
/// NOTE: We inject WAL segments post-close rather than using `std::mem::forget`
/// because `TidalDb::Drop` calls `shutdown_inner()` which checkpoints + compacts,
/// and `forget` would leak the file lock preventing reopen in the same process.
fn generate_wal_backlog_data(dir: &std::path::Path) {
    // Phase 1: Write base signals and checkpoint via clean close.
    generate_test_data(dir);

    // Phase 2: Inject raw WAL events that simulate a crash before checkpoint.
    inject_wal_backlog(dir, 10_000, 2_000);
}

fn recovery_with_wal_backlog_benchmark(c: &mut Criterion) {
    let mut group = c.benchmark_group("recovery_wal_backlog");
    group.sample_size(10);
    group.measurement_time(Duration::from_secs(30));

    // Generate the test data directory once (checkpoint + WAL backlog).
    let dir = tempfile::tempdir().expect("tempdir");
    generate_wal_backlog_data(dir.path());

    let schema = bench_schema();
    group.bench_function("cold_start_with_wal_backlog_10k", |b| {
        b.iter(|| {
            let db = TidalDb::builder()
                .with_data_dir(dir.path())
                .with_schema(schema.clone())
                .open()
                .expect("open should succeed");

            // Verify that a backlog entity was replayed from WAL.
            let count = db
                .read_windowed_count(EntityId::new(10_001), "view", Window::AllTime)
                .expect("read should succeed");
            assert!(
                count > 0,
                "backlog entity 10001 should have signals after WAL replay"
            );

            db.close().expect("close should succeed");

            // Re-inject WAL backlog for next iteration (close() checkpoints it away)
            inject_wal_backlog(dir.path(), 10_000, 2_000);
        });
    });

    group.finish();
}

criterion_group!(
    benches,
    recovery_benchmark,
    recovery_with_wal_backlog_benchmark
);
criterion_main!(benches);