//! `cargo run --release --example benchmark` — compares tile-rasterization and section-meshing
//! throughput across the `cpu`/`gpu`/`hybrid` `RenderBackend`s on a synthetic workload sized to
//! match `main.rs`'s real batching (one `RENDER_PROFILE=server` xread batch's worth of chunks —
//! see `config::batch_size_for`), run through the same rayon-parallel-batch shape `main.rs` uses.
//! This is the Phase 8 plan's "measure throughput difference" verification step; `render::gpu`'s
//! own tests already cover byte-for-byte output equivalence, so this only measures timing.
use std::time::{Duration, Instant};

use mcmapper_worker::config::{batch_size_for, Profile};
use mcmapper_worker::mesh;
use mcmapper_worker::render::{
    ColumnPixel, CpuRenderBackend, GpuRenderBackend, HybridRenderBackend, RenderBackend,
};
use rayon::prelude::*;

fn synthetic_columns() -> Vec<ColumnPixel> {
    let mut columns = Vec::with_capacity(256);
    for x in 0..16u8 {
        for z in 0..16u8 {
            let block_id = ((x as u16 + z as u16) % 20) + 1;
            columns.push(ColumnPixel { local_x: x, local_z: z, block_id, block_meta: 0 });
        }
    }
    columns
}

/// A wavy, partially-solid section — not fully solid (which greedy-merges to almost nothing) or
/// fully empty (no work at all), so meshing does a realistic amount of face-mask/merge work.
fn synthetic_section(seed: i32) -> [u16; 4096] {
    let mut blocks = [0u16; 4096];
    for y in 0..16i32 {
        for z in 0..16i32 {
            for x in 0..16i32 {
                let height = 6 + (x + z + seed) % 6;
                if y <= height {
                    let block_id = 1 + ((x * 3 + z * 7 + y * 11 + seed) % 12) as u16;
                    blocks[((y as usize) * 16 + z as usize) * 16 + x as usize] = block_id << 4;
                }
            }
        }
    }
    blocks
}

fn bench_tiles(backend: &dyn RenderBackend, columns: &[ColumnPixel], batch: usize) -> Duration {
    let start = Instant::now();
    (0..batch).into_par_iter().for_each(|_| {
        backend.rasterize_tile(columns).expect("rasterize_tile must not fail on synthetic input");
    });
    start.elapsed()
}

fn bench_meshing(backend: &dyn RenderBackend, sections: &[[u16; 4096]]) -> Duration {
    let start = Instant::now();
    sections.par_iter().for_each(|blocks| {
        let _ = mesh::mesh_section(blocks, backend);
    });
    start.elapsed()
}

fn run_backend(name: &str, backend: &dyn RenderBackend, columns: &[ColumnPixel], sections: &[[u16; 4096]], batch: usize) {
    // One warmup pass per stage so pipeline/shader compilation and first-dispatch driver
    // overhead (real on GPU, one-time) doesn't get counted as steady-state throughput.
    backend.rasterize_tile(columns).unwrap();
    let _ = mesh::mesh_section(&sections[0], backend);

    let tiles = bench_tiles(backend, columns, batch);
    let meshes = bench_meshing(backend, sections);
    println!(
        "{name:<8} tiles: {batch} in {tiles:>9.2?} ({:>8.1}/s)   sections: {} in {meshes:>9.2?} ({:>8.1}/s)",
        batch as f64 / tiles.as_secs_f64(),
        sections.len(),
        sections.len() as f64 / meshes.as_secs_f64(),
    );
}

#[tokio::main]
async fn main() {
    let batch = batch_size_for(Profile::Server);
    let columns = synthetic_columns();
    let sections: Vec<[u16; 4096]> = (0..batch as i32).map(synthetic_section).collect();

    println!("Synthetic workload: {batch} tiles + {} sections per backend (RENDER_PROFILE=server batch size)\n", sections.len());

    let cpu = CpuRenderBackend::new();
    run_backend("cpu", &cpu, &columns, &sections, batch);

    match GpuRenderBackend::try_new().await {
        Some(gpu) => {
            println!("GPU adapter: {}", gpu.adapter_name());
            run_backend("gpu", &gpu, &columns, &sections, batch);
        }
        None => println!("gpu      (skipped — no compatible GPU adapter found)"),
    }

    match GpuRenderBackend::try_new().await {
        Some(gpu) => {
            let hybrid = HybridRenderBackend::new(gpu);
            run_backend("hybrid", &hybrid, &columns, &sections, batch);
        }
        None => println!("hybrid   (skipped — no compatible GPU adapter found)"),
    }
}