//! TRACES: FR-DSP-2 | NFR-RES-2
//! A photograph larger than one texture, developed from windows of it.
//!
//! The claim under test is that the window is invisible: a frame rendered a
//! tile at a time, each tile from only the part of the source it reads, is the
//! frame rendered whole. `dr-pipeline` can check the plan — the tiles cover
//! the frame once, each is grown by the reach — but not that the shader's
//! mapping into a window lands on the texel the whole texture would have
//! given, which only a device answers.
//!
//! The frames here are small and the "device limit" is a number passed in,
//! so the tiling is exercised on any adapter, including one whose real limit
//! a test image could never approach.

use dr_decode::{CfaPattern, CropRect, RawImage};
use dr_gpu::{AdjustPass, DemosaicedImage, GpuContext};
use dr_pipeline::descriptor::{OpId, ParamId};
use dr_pipeline::framing::ANGLE;
use dr_pipeline::{tiles, Affects, EditGraph};
use dr_types::ColourSpace;

fn ctx() -> Option<GpuContext> {
    match pollster::block_on(GpuContext::new_headless()) {
        Ok(c) => Some(c),
        Err(e) => {
            eprintln!("skipping: no GPU adapter ({e})");
            None
        }
    }
}

/// A linear RGB frame with detail at every scale: a slow gradient for the
/// tone controls and a hash for the kernels, so a tile that read one pixel
/// off would show.
fn linear_frame(w: u32, h: u32, noise: bool) -> RawImage {
    let mut data = Vec::with_capacity((w * h * 3) as usize);
    for y in 0..h {
        for x in 0..w {
            let base = 4000.0 + 30000.0 * (x as f32 / w as f32) + 12000.0 * (y as f32 / h as f32);
            let hash = if noise {
                ((x.wrapping_mul(73_856_093) ^ y.wrapping_mul(19_349_663)) % 8000) as f32
            } else {
                0.0
            };
            for c in 0..3 {
                data.push((base * (0.7 + 0.15 * c as f32) + hash) as u16);
            }
        }
    }
    RawImage {
        width: w,
        height: h,
        data,
        cfa_pattern: CfaPattern::Unknown,
        black_level: [512; 4],
        white_level: 65535,
        wb_coeffs: [2.0, 1.0, 1.5, 1.0],
        color_matrix: Some([1.6, -0.5, -0.1, -0.2, 1.4, -0.2, 0.0, -0.4, 1.4]),
        samples_per_pixel: 3,
        profile: None,
        profile_tables: None,
        baseline_exposure: 0.0,
        make: String::new(),
        model: String::new(),
        crop: CropRect {
            x: 0,
            y: 0,
            width: w,
            height: h,
        },
    }
}

/// Render `graph` over `source` at `size` and read it back.
fn render(
    pass: &mut AdjustPass,
    graph: &EditGraph,
    source: &DemosaicedImage,
    size: (u32, u32),
) -> Vec<u8> {
    let shader = graph.compose_for(ColourSpace::Srgb);
    let detail = graph.compose_detail(source.size(), size);
    let key = graph.invalidation().through(Affects::Colour);
    pass.render_detailed(source, &shader, size.0, size.1, None, &detail, key)
        .expect("render");
    pass.export_pixels().expect("readback").0
}

/// The frame at full resolution, a tile at a time, each from its own window.
fn render_tiled(
    ctx: &GpuContext,
    pass: &mut AdjustPass,
    graph: &mut EditGraph,
    raw: &RawImage,
    max_edge: u32,
) -> (Vec<u8>, usize) {
    let frame = (raw.crop.width, raw.crop.height);
    let out = graph.output_size(frame.0, frame.1);
    let reach = graph.compose_detail(frame, out).reach();
    let plan = tiles::plan(out, max_edge, reach).expect("a plan");
    let mut pixels = vec![0u8; (out.0 * out.1 * 4) as usize];
    for t in &plan {
        graph.framing_mut().set_view(t.view(out));
        let r = graph.source_region(frame, 0);
        let x0 = (r.x * frame.0 as f32).floor() as u32;
        let y0 = (r.y * frame.1 as f32).floor() as u32;
        let x1 = ((r.x + r.width) * frame.0 as f32).ceil() as u32;
        let y1 = ((r.y + r.height) * frame.1 as f32).ceil() as u32;
        let window = DemosaicedImage::linear_rgb16_window(ctx, raw, [x0, y0, x1 - x0, y1 - y0], 1)
            .expect("window");
        assert_eq!(window.size(), frame, "a window measures the frame");
        let tile = render(pass, graph, &window, (t.grown[2], t.grown[3]));
        let (ox, oy) = t.keep_offset();
        for row in 0..t.keep[3] {
            let src = (((oy + row) * t.grown[2] + ox) * 4) as usize;
            let dst = (((t.keep[1] + row) * out.0 + t.keep[0]) * 4) as usize;
            let n = (t.keep[2] * 4) as usize;
            pixels[dst..dst + n].copy_from_slice(&tile[src..src + n]);
        }
    }
    graph
        .framing_mut()
        .set_view(dr_pipeline::CropRect::default());
    (pixels, plan.len())
}

fn largest_difference(a: &[u8], b: &[u8]) -> u8 {
    a.iter()
        .zip(b)
        .map(|(x, y)| x.abs_diff(*y))
        .max()
        .unwrap_or(0)
}

#[test]
fn tiles_of_windows_are_the_whole_frame() {
    // Point operations only, unrotated: every output pixel is an exact load
    // of one source texel, so the tiled frame has to be the whole one to
    // the bit.
    let Some(ctx) = ctx() else { return };
    let raw = linear_frame(200, 120, true);
    let mut graph = EditGraph::default_chain();
    graph.set_param(OpId("exposure"), ParamId("exposure"), 0.7);
    let mut pass = AdjustPass::new(&ctx);

    let whole = DemosaicedImage::from_linear_rgb16(&ctx, &raw).unwrap();
    assert!(whole.is_whole());
    let reference = render(&mut pass, &graph, &whole, (200, 120));
    let (tiled, n) = render_tiled(&ctx, &mut pass, &mut graph, &raw, 64);
    assert!(n > 4, "the frame should have been cut, got {n} tile(s)");
    assert_eq!(largest_difference(&reference, &tiled), 0);
}

#[test]
fn a_straightened_frame_with_clarity_tiles_without_seams() {
    // The hard case: a free angle samples between texels, and clarity reads
    // a wide neighbourhood on a reduced grid. The halo and the grid
    // alignment are what keep the tiles' edges out of the picture; a code
    // value of rounding is all that may differ.
    let Some(ctx) = ctx() else { return };
    let raw = linear_frame(320, 208, true);
    let mut graph = EditGraph::default_chain();
    graph.set_param(OpId("clarity"), ParamId("amount"), 60.0);
    graph.framing_mut().set_param(ANGLE, 3.0);
    let mut pass = AdjustPass::new(&ctx);

    let whole = DemosaicedImage::from_linear_rgb16(&ctx, &raw).unwrap();
    let out = graph.output_size(320, 208);
    let reference = render(&mut pass, &graph, &whole, out);
    let (tiled, n) = render_tiled(&ctx, &mut pass, &mut graph, &raw, 160);
    assert!(n > 1, "the frame should have been cut, got {n} tile(s)");
    let worst = largest_difference(&reference, &tiled);
    assert!(
        worst <= 1,
        "tiles differ from the whole frame by {worst} code values"
    );
}

#[test]
fn a_reduced_copy_stands_for_the_whole_frame() {
    // The canvas at fit renders from a copy reduced to fit the device. It
    // must measure the photograph, not itself, or a crop drawn on it lands
    // somewhere else in the export; and rendered small it must look like the
    // full frame rendered small.
    let Some(ctx) = ctx() else { return };
    let raw = linear_frame(400, 240, false);
    let mut graph = EditGraph::default_chain();
    graph.set_crop(dr_pipeline::CropRect {
        x: 0.25,
        y: 0.1,
        width: 0.5,
        height: 0.6,
    });
    let mut pass = AdjustPass::new(&ctx);

    let whole = DemosaicedImage::from_linear_rgb16(&ctx, &raw).unwrap();
    let reduced = DemosaicedImage::linear_rgb16_window(&ctx, &raw, [0, 0, 400, 240], 3).unwrap();
    assert_eq!(reduced.size(), (400, 240));
    assert_eq!(reduced.texture_size(), (134, 80));
    assert!(!reduced.is_whole());

    let size = (50, 36);
    let a = render(&mut pass, &graph, &whole, size);
    let b = render(&mut pass, &graph, &reduced, size);
    let worst = largest_difference(&a, &b);
    assert!(
        worst <= 3,
        "the reduced copy renders {worst} code values away"
    );
}