//! The half of a 24 MP export that needs no GPU.
//!
//! # This cannot certify NFR-P7, and is not tagged as though it could
//!
//! NFR-P7 is "full-resolution export (24 MP, **full chain**) < 2 s". The full
//! chain is decode, demosaic, a GPU render at full resolution, a read-back,
//! and then everything `dr-export` does — resize, output sharpening, encode.
//! Only the last three of those run without an adapter, and the CI runner has
//! none. So what is measured here is the encode half, and no requirement tag
//! anywhere in this crate names NFR-P7.
//!
//! (Written without the tag's own spelling on purpose. `tools/traceability`
//! matches the marker anywhere on a line and parses the identifier after it, so
//! a sentence saying "there is no tag for NFR-P7" would *be* a tag for NFR-P7 —
//! a disclaimer that made itself false.)
//!
//! That is a deliberate refusal rather than an oversight. `CONTRIBUTING.md`
//! asks that a requirement be closed by a test that would fail if the
//! behaviour were removed, and `docs/dev/code-health.md` CH-4 records what the
//! coverage figure looks like when tags are hung on plumbing instead. A tag
//! here would say the export budget is checked; the GPU half of it would still
//! be unchecked.
//!
//! # What the number is still good for
//!
//! It is a **one-sided** gate, and that is worth having. The encode half is a
//! lower bound on the whole: if resizing, sharpening and encoding 24 MP alone
//! take longer than two seconds, NFR-P7 is violated no matter how fast the
//! render is. So the budget in `docs/dev/bench-baseline.json` is the requirement's
//! own 2000 ms, and exceeding it fails the build honestly. Coming in under it
//! proves nothing about the requirement, and the report says so rather than
//! printing a tick.
//!
//! # Two rows
//!
//! `Original` is the one the budget is judged on: it is the archival export,
//! the largest encode, and the case FR-EXP-9 is about. `LongEdge(2048)` is the
//! ordinary web export, where the resample does real work and the encode does
//! very little — it is reported because a regression in `size::resample` would
//! be invisible in the first row, where source and target dimensions are equal.

use std::time::Instant;

use anyhow::Result;
use dr_export::{export, Frame};
use dr_types::{ExportFormat, ExportSettings, OutputSharpening, SizingMode};

use crate::fixture::plausible_frame;
use crate::stats::{ms, Percentiles};

/// The frame every row exports.
///
/// 6000 × 4000 is 24.0 MP — a full-frame body, and the exact figure NFR-P7
/// names. As RGBA8 it is 96 MB, and the export path holds a resized copy and a
/// sharpened copy alongside it, so a run needs roughly 300 MB of headroom.
/// Worth knowing before a small runner reports this as a mysterious kill.
pub const SOURCE: (u32, u32) = (6000, 4000);

/// Measured exports per row. Not a hundred: one 24 MP encode is most of a
/// second, and a hundred of them would be a two-minute CI step to establish
/// what five establish. Nearest-rank p99 of five is the worst of the five,
/// which for a row this expensive is the honest reading anyway.
const RUNS: usize = 5;

/// A row of the export table.
pub struct EncodeRun {
    /// The name this row carries in `docs/dev/bench-baseline.json`.
    pub key: &'static str,
    pub label: &'static str,
    pub width: u32,
    pub height: u32,
    /// Encoded file size, so a row that silently stopped compressing is
    /// visible as well as a row that got slow.
    pub bytes: usize,
    pub times: Percentiles,
}

/// Export the same 24 MP frame at each sizing, timing `dr_export::export`.
pub fn measure() -> Result<Vec<EncodeRun>> {
    let (w, h) = SOURCE;
    // Detail at every scale, for the same reason the thumbnail fixture has it:
    // a flat frame compresses to almost nothing and would make the encoder
    // look several times faster than any photograph makes it.
    let frame = Frame::new(w, h, plausible_frame(w, h, 0))
        .map_err(|e| anyhow::anyhow!("building the 24 MP bench frame: {e}"))?;

    let sizings: [(&'static str, &'static str, SizingMode); 2] = [
        ("export_24mp_original_ms", "original", SizingMode::Original),
        (
            "export_24mp_long_edge_2048_ms",
            "long edge 2048",
            SizingMode::LongEdge(2048),
        ),
    ];

    let mut rows = Vec::with_capacity(sizings.len());
    for (key, label, sizing) in sizings {
        let settings = ExportSettings {
            format: ExportFormat::Jpeg,
            // 90 is the default and what a photographer would not need to
            // change; quality moves encode time, so it belongs in the record.
            quality: 90,
            sizing,
            sharpening: OutputSharpening::Screen,
            ..Default::default()
        };

        // Discarded. The first export of a process grows the allocator to hold
        // three 24 MP buffers, which is a cost paid once and not per file in
        // the batch export FR-EXP-7 describes.
        let warm = run_once(&frame, &settings)?;

        let mut samples = Vec::with_capacity(RUNS);
        let mut last = warm;
        for _ in 0..RUNS {
            let started = Instant::now();
            last = run_once(&frame, &settings)?;
            samples.push(ms(started.elapsed()));
        }

        rows.push(EncodeRun {
            key,
            label,
            width: last.0,
            height: last.1,
            bytes: last.2,
            times: Percentiles::of(samples),
        });
    }

    Ok(rows)
}

/// One export, returning what it produced rather than the pixels.
fn run_once(frame: &Frame, settings: &ExportSettings) -> Result<(u32, u32, usize)> {
    let encoded = export(frame, settings, "bench.jpg".to_string(), None)
        .map_err(|e| anyhow::anyhow!("exporting the bench frame: {e}"))?;
    Ok((encoded.width, encoded.height, encoded.bytes.len()))
}