//! What does `forced_backdrop` cost IN PIXELS on the screens it decides?
//!
//! `forced_backdrop_necessity.rs` answers "does the derived ORDER move", which is
//! a property of the sort. The port agent then pointed out — correctly — that its
//! re-run of that probe was **my code executed twice**, not a second witness, so
//! the disc-wide 62 has one measurement behind it and only `GP_TITLE` has two.
//!
//! This does not fix that (it is still this crate), but it moves the question to a
//! **different layer**: render each deciding build twice, once in the order
//! `compose` derives and once with the `forced_backdrop` fallback removed, and
//! count the pixels that differ. "The order moved" and "the picture moved" are not
//! the same claim, and the second is the one anybody cares about — the tie-break
//! work already found overlapping reorders that cost exactly zero pixels.
//!
//! Each entry carries its own CONTROL: the pixel count of the composite itself.
//! If a build renders empty, its zero means the instrument saw nothing, not that
//! the rule is free.
//!
//!     cargo run -p sylpheed-formats --example forced_backdrop_pixel_cost -- [pak...]
//!
//! With no argument it walks **every `dat/*.pak`** — the necessity probe defaulted
//! to `GP_TITLE`, which made a bare run report a thirteenth of the census and read
//! like the whole thing.

use std::path::PathBuf;

use sylpheed_formats::{pak::PakArchive, ui_layout};
use ui_layout::ComposeOptions;

fn order_without_rule(build: &ui_layout::UiBuild, bundle: &[u8]) -> Vec<usize> {
    let mut idx: Vec<usize> = (0..build.elements.len()).collect();
    idx.sort_by_key(|&i| {
        let el = &build.elements[i];
        (
            ui_layout::sprite_layer_key(build, bundle, el)
                .or_else(|| ui_layout::implied_layer_key(&el.name))
                .unwrap_or(u32::MAX),
            i,
        )
    });
    idx
}

fn main() {
    let root = PathBuf::from(std::env::var("SYLPHEED_DISC").expect("SYLPHEED_DISC"));
    let mut paks: Vec<PathBuf> = std::env::args().skip(1).map(PathBuf::from).collect();
    if paks.is_empty() {
        let mut all: Vec<PathBuf> = std::fs::read_dir(root.join("dat"))
            .expect("dat/")
            .filter_map(|e| e.ok().map(|e| e.path()))
            .filter(|p| p.extension().is_some_and(|x| x == "pak"))
            .collect();
        all.sort();
        paks = all;
    }
    eprintln!("# scanning {} archive(s)", paks.len());

    let opts = ComposeOptions {
        include_primitives: true,
        backdrop: [0, 0, 0, 255],
        ..Default::default()
    };

    println!("# archive  entry  element  changed_px  total_px  ink_px(control)  pct");
    let (mut decided, mut zero_cost, mut blind) = (0usize, 0usize, 0usize);
    for pak in &paks {
        let Ok(ar) = PakArchive::open(pak) else {
            continue;
        };
        let name = pak.file_name().unwrap().to_string_lossy().to_string();
        for (i, e) in ar.entries().iter().enumerate() {
            let Ok(by) = ar.read(e) else { continue };
            let Some(b) = ui_layout::parse_build(&by) else {
                continue;
            };
            let with = ui_layout::derived_paint_order(&b, &by);
            let without = order_without_rule(&b, &by);
            if with == without {
                continue;
            }
            let forced: Vec<&str> = b
                .elements
                .iter()
                .filter(|el| ui_layout::forced_backdrop(&b, el))
                .map(|el| el.name.as_str())
                .collect();

            let a = ui_layout::compose_with_order(&b, &by, opts, None, Some(&with));
            let c = ui_layout::compose_with_order(&b, &by, opts, None, Some(&without));
            let n = a
                .rgba
                .as_chunks::<4>()
                .0
                .iter()
                .zip(c.rgba.as_chunks::<4>().0.iter())
                .filter(|(x, y)| x != y)
                .count();
            // Control: does this build put any ink down at all, against the bare
            // backdrop? A build that renders to nothing cannot show a reorder.
            let ink = a
                .rgba
                .as_chunks::<4>()
                .0
                .iter()
                .filter(|p| p[..3] != [0, 0, 0])
                .count();
            let total = a.rgba.len() / 4;

            decided += 1;
            if ink == 0 {
                blind += 1;
            } else if n == 0 {
                zero_cost += 1;
            }
            println!(
                "  {name}  {i}  {}  {n}  {total}  {ink}  {:.2}%",
                forced.join(","),
                100.0 * n as f64 / total as f64
            );
        }
    }
    println!("\n# builds whose ORDER the rule decides: {decided}");
    println!("# of those, costing ZERO pixels:        {zero_cost}");
    println!("# of those, BLIND (build renders no ink, control fails): {blind}");
}