//! Zoom-ladder derivation benchmarks (T-1149, design doc §2/§7/§8 step 1).
//!
//! Measures `derive_at_metres` per-cell cost at district spacing (2,048 m) and
//! quarter spacing (512 m), with and without a `min_wavelength_m` octave
//! cutoff — the exact numbers the design doc flags as UNBUILT/UNMEASURED
//! (§7: "Octave-cutoff derive (min_wavelength_m-bearing) ... not measured").
//!
//! Manual `Instant`-based timing, matching every other bench in this repo
//! (`shadowcast_bench.rs`, `perf_bench.rs`) and the same technique
//! `aliveness_probe --render` used to produce the ~1.2–1.4 µs/district
//! release figure the design doc cites — no criterion dependency exists here.
//!
//! Run: `cargo test --release --test zoom_ladder_bench -- --ignored --nocapture`
//! (debug numbers are ~5x slower and not representative of the design doc's
//! release-build figures; run `--release` for numbers worth recording).

use std::time::Instant;

use settled_reach_server::atlas::district_profile::{
    derive_at_metres, BodyParams, ClimateConstants,
};
use settled_reach_server::atlas::drainage;
use settled_reach_server::atlas::features::TerrainAnalysis;
use settled_reach_server::atlas::heightmap::BodyHeightmap;
use settled_reach_server::atlas::scale;
use settled_reach_server::seed::{SeedChain, SeedDomain};

fn bench_hm() -> BodyHeightmap {
    // Same shape as district_profile.rs's own test_hm/window_test_hm fixtures
    // — a smooth gradient, deterministic, no PNG I/O.
    let (w, h) = (128u32, 64u32);
    let n = (w * h) as usize;
    let data = (0..n)
        .map(|i| {
            let r = (i / w as usize) as f32 / h as f32;
            let c = (i % w as usize) as f32 / w as f32;
            (r * 0.6 + c * 0.4).min(1.0)
        })
        .collect();
    BodyHeightmap {
        body_id: "bench".into(),
        width: w,
        height: h,
        data,
        sea_level: 0.3,
    }
}

fn bench_ta(hm: &BodyHeightmap) -> TerrainAnalysis {
    let dr = drainage::analyze(&hm.data, hm.width, hm.height, hm.sea_level);
    TerrainAnalysis::analyze(hm, &dr)
}

fn bench_params() -> BodyParams {
    BodyParams {
        hydrosphere: Some("ocean".into()),
        atmosphere: Some("breathable".into()),
        planet_class: Some("temperate".into()),
        body_radius_km: Some(6371.0),
        ..Default::default()
    }
}

/// Time `n_cells` sequential `derive_at_metres` calls on a spacing-`step_m`
/// grid starting at world origin, with the given octave cutoff. Returns
/// (total_elapsed, per_cell_ns).
fn time_derive_sweep(
    seed: SeedChain,
    body_id: &str,
    params: &BodyParams,
    ta: &TerrainAnalysis,
    climate: &ClimateConstants,
    grid_side: u32,
    step_m: f64,
    min_wavelength_m: f64,
) -> (std::time::Duration, f64) {
    let n_cells = (grid_side * grid_side) as u64;
    let t0 = Instant::now();
    for row in 0..grid_side {
        for col in 0..grid_side {
            let wx = col as f64 * step_m;
            let wy = row as f64 * step_m;
            let prof = derive_at_metres(
                seed,
                body_id,
                params,
                ta,
                wx,
                wy,
                climate,
                min_wavelength_m,
            );
            // Prevent the optimizer from hoisting the call out of the loop.
            std::hint::black_box(prof.elev_q);
        }
    }
    let elapsed = t0.elapsed();
    let per_cell_ns = elapsed.as_secs_f64() * 1e9 / n_cells as f64;
    (elapsed, per_cell_ns)
}

#[test]
#[ignore]
fn bench_derive_at_metres_district_and_quarter_spacing() {
    let hm = bench_hm();
    let ta = bench_ta(&hm);
    let params = bench_params();
    let climate = ClimateConstants::default();
    let seed = SeedChain::root(99).derive(SeedDomain::Body, 1);
    let grid_side = 64u32; // 4,096 cells per sweep — matches the D-226 window cap

    println!("\n=== T-1149 zoom-ladder derive_at_metres benchmark ===");
    println!(
        "grid: {grid_side}x{grid_side} = {} cells/sweep\n",
        grid_side * grid_side
    );

    let district_m = scale::DISTRICT_M as f64;
    let quarter_m = scale::QUARTER_M as f64;

    // District spacing (2,048 m), cutoff 0 — today's uncut behavior.
    let (elapsed, per_cell_ns) = time_derive_sweep(
        seed, "bench", &params, &ta, &climate, grid_side, district_m, 0.0,
    );
    println!(
        "district spacing, cutoff=0:      {:>8.2} ms total, {:>7.1} ns/cell ({:.3} µs/cell)",
        elapsed.as_secs_f64() * 1000.0,
        per_cell_ns,
        per_cell_ns / 1000.0
    );

    // District spacing, cutoff 2,048 m — truncates every OCTAVE_WAVELENGTHS_M
    // entry below the district's own spacing (finest is 4,096 m, so this
    // cutoff is BELOW that — confirms the cutoff plumbing at district scale
    // without changing which octaves survive, since 2,048 < 4,096 admits all
    // of them; recorded for the design doc's requested (district, cutoff
    // 2048) combination regardless).
    let (elapsed, per_cell_ns) = time_derive_sweep(
        seed,
        "bench",
        &params,
        &ta,
        &climate,
        grid_side,
        district_m,
        2_048.0,
    );
    println!(
        "district spacing, cutoff=2048m:  {:>8.2} ms total, {:>7.1} ns/cell ({:.3} µs/cell)",
        elapsed.as_secs_f64() * 1000.0,
        per_cell_ns,
        per_cell_ns / 1000.0
    );

    // Quarter spacing (512 m), cutoff 512 m — the T-1150 Option B rung: full
    // reclassification at quarter spacing with the matching octave cutoff.
    let (elapsed, per_cell_ns) = time_derive_sweep(
        seed,
        "bench",
        &params,
        &ta,
        &climate,
        grid_side,
        quarter_m,
        512.0,
    );
    println!(
        "quarter spacing, cutoff=512m:    {:>8.2} ms total, {:>7.1} ns/cell ({:.3} µs/cell)",
        elapsed.as_secs_f64() * 1000.0,
        per_cell_ns,
        per_cell_ns / 1000.0
    );

    println!();
}