//! Criterion benchmark: conditional `effects_dirty` skip guard.
//!
//! ## Purpose
//! Verifies that `render_composite_region()` / `apply_effects_and_sync_tiles()`
//! skips the expensive effects pipeline for layers that have **no effects or
//! styles**. If a regression removes the `effects.is_empty() && styles.is_empty()`
//! early-exit or unconditionally sets `effects_dirty = true`, composite cost
//! on effect-free documents will increase dramatically.
//!
//! ## Logic & Workflow
//! 1. Creates a 3840×2160, 10-layer document (all filled, no effects).
//! 2. **no_effects**: Benchmarks `render_composite_region()` where every layer
//!    has empty `effects` and `styles` vectors → the effects pipeline is
//!    completely skipped.
//! 3. **with_one_effect**: Same document but one layer has a DropShadow style
//!    → the effects pipeline runs for that single layer.
//!
//! When the conditional skip works, `no_effects` should be measurably faster
//! than `with_one_effect` because no `apply_layer_effects` calls are made.
//!
//! ## Arguments & Returns
//! Standard criterion benchmark — run with:
//! ```bash
//! cargo bench -p hcie-engine-api --bench effects_skip
//! ```
//!
//! ## Side Effects / Dependencies
//! Allocates ~400 MB (10 layers × 4K RGBA + composite buffers).

use criterion::{criterion_group, criterion_main, Criterion};
use hcie_engine_api::{BrushStyle, BrushTip, Engine, LayerStyle};

/// Canvas dimensions — 4K UHD.
const W: u32 = 3840;
const H: u32 = 2160;
/// Number of raster layers.
const LAYERS: usize = 10;

/// Builds a 10-layer 4K document with NO effects on any layer.
///
/// **Purpose:** Creates the baseline scenario where the effects pipeline
/// should be completely skipped during compositing.
/// **Returns:** `(Engine, top_layer_id, all_layer_ids)`.
fn setup_no_effects_engine() -> (Engine, u64, Vec<u64>) {
    let mut engine = Engine::new(W, H);

    let bg_id = engine.active_layer_id();
    engine.set_active_layer(bg_id);
    engine.draw_filled_rect_rgba(0, 0, W, H, [240, 240, 240, 255]);

    let mut layer_ids = vec![bg_id];
    for i in 1..LAYERS {
        let id = engine.add_layer(&format!("Layer {}", i));
        engine.set_active_layer(id);
        let color = match i % 4 {
            0 => [180, 80, 80, 255],
            1 => [80, 180, 80, 255],
            2 => [80, 80, 180, 255],
            _ => [160, 140, 100, 255],
        };
        engine.draw_filled_rect_rgba(0, 0, W, H, color);
        layer_ids.push(id);
    }

    let top_id = *layer_ids.last().unwrap();
    engine.set_active_layer(top_id);

    let mut tip = BrushTip::default();
    tip.style = BrushStyle::Round;
    tip.size = 24.0;
    tip.opacity = 1.0;
    tip.hardness = 0.85;
    tip.spacing = 0.1;
    engine.set_brush_tip(tip);
    engine.set_color([220, 60, 60, 255]);
    engine.set_eraser(false);

    (engine, top_id, layer_ids)
}

/// Performs a stroke + composite cycle and returns.
///
/// **Purpose:** Creates a dirty region and composites it, exercising the
/// effects pipeline path.
/// **Arguments:** `engine` — mutable engine, `layer_id` — target layer,
/// `offset` — position variation.
/// **Side Effects:** Mutates layer pixels, triggers composite.
fn stroke_and_composite(engine: &mut Engine, layer_id: u64, offset: f32) {
    let cx = W as f32 / 2.0 + offset;
    let cy = H as f32 / 2.0 + offset;
    engine.begin_stroke(layer_id, cx, cy);
    for i in 1..=5 {
        let d = i as f32 * 8.0;
        engine.stroke_to(layer_id, cx + d, cy + d, 0.8);
    }
    let (_region, ptr, _size) = engine.render_composite_region();
    assert!(!ptr.is_null());
    engine.end_stroke(layer_id);
    std::thread::sleep(std::time::Duration::from_millis(10));
    engine.commit_pending_history();
}

/// Benchmark group: effects-free composite vs single-effect composite.
///
/// **Purpose:** Detects regressions where the effects pipeline runs
/// unnecessarily on layers with no effects, causing wasted CPU cycles
/// (apply_layer_effects + 33 MB buffer clone per affected layer).
///
/// **Logic & Workflow:**
/// - `no_effects_composite`: All 10 layers have empty effects/styles.
///   `apply_effects_and_sync_tiles()` should skip the effects pass entirely.
/// - `with_one_dropshadow`: Layer 5 has a DropShadow style enabled.
///   The effects pipeline runs for that single layer but skips the other 9.
///   This should be slightly slower than `no_effects_composite` but not 10×
///   slower (which would indicate the skip logic is broken).
fn bench_effects_skip(c: &mut Criterion) {
    let mut group = c.benchmark_group("effects_skip");

    // ── No effects on any layer ──
    group.bench_function("no_effects_composite", |b| {
        let (mut engine, layer_id, _ids) = setup_no_effects_engine();
        // Warm up composite scratch
        stroke_and_composite(&mut engine, layer_id, 0.0);

        let mut offset = 0.0_f32;
        b.iter(|| {
            offset += 3.0;
            stroke_and_composite(&mut engine, layer_id, offset);
        });
    });

    // ── One layer has a DropShadow effect ──
    group.bench_function("with_one_dropshadow", |b| {
        let (mut engine, layer_id, layer_ids) = setup_no_effects_engine();

        // Add a DropShadow style to layer 5 (middle of the stack)
        let target_layer_id = layer_ids[5];
        engine.update_layer_style(
            target_layer_id,
            LayerStyle::DropShadow {
                enabled: true,
                opacity: 0.6,
                angle: 135.0,
                distance: 5.0,
                spread: 0.0,
                size: 10.0,
                color: [0, 0, 0, 255],
                blend_mode: hcie_engine_api::BlendMode::Normal,
            },
        );

        // Warm up
        stroke_and_composite(&mut engine, layer_id, 0.0);

        let mut offset = 0.0_f32;
        b.iter(|| {
            offset += 3.0;
            stroke_and_composite(&mut engine, layer_id, offset);
        });
    });

    group.finish();
}

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