#!/usr/bin/env python3
"""Compare two QA captures pixel by pixel.

Usage: compare.py vanilla.png gpu.png OUT_PREFIX [--threshold PCT] [--delta N]

Counts pixels whose max channel delta exceeds --delta (default 16, the
value the development parity harness settled on: below that it is
antialiasing fringe, not structure). PASS if the percentage of such
pixels is below --threshold (default 0.5).

Writes OUT_PREFIX-triptych.png (vanilla | gpu | diff heatmap) and prints
one JSON line with the verdict.
"""
import json
import sys

from PIL import Image, ImageChops, ImageFilter


def main():
    args = [a for a in sys.argv[1:] if not a.startswith("--")]
    opts = {a.split("=")[0].lstrip("-"): float(a.split("=")[1])
            for a in sys.argv[1:] if a.startswith("--")}
    vanilla_path, gpu_path, prefix = args
    threshold = opts.get("threshold", 0.5)
    delta = int(opts.get("delta", 16))

    a = Image.open(vanilla_path).convert("RGB")
    b = Image.open(gpu_path).convert("RGB")
    if a.size != b.size:
        print(json.dumps({"pass": False, "error": "size mismatch",
                          "vanilla": a.size, "gpu": b.size}))
        return 1

    diff = ImageChops.difference(a, b)
    # max channel delta per pixel, then threshold
    gray = diff.convert("L")
    mask = gray.point(lambda p: 255 if p > delta else 0)
    hist = mask.histogram()
    bad = hist[255]
    total = a.size[0] * a.size[1]
    pct = 100.0 * bad / total

    # Anti-aliasing fringe is a 1px halo on glyph edges and varies between
    # rasterizers; real defects (wrong color, missing decoration, shifted
    # block) are contiguous blobs. A 3x3 erosion kills the halo and keeps
    # the blobs, so the PASS gate runs on the eroded mask.
    blob_mask = mask.filter(ImageFilter.MinFilter(3))
    blob_bad = blob_mask.histogram()[255]
    blob_pct = 100.0 * blob_bad / total

    # triptych: vanilla | gpu | heatmap (red = blobs that gate the verdict,
    # dark red = AA fringe that does not)
    heat = a.point(lambda p: p // 3)
    fringe = Image.new("RGB", a.size, (110, 24, 24))
    heat.paste(fringe, mask=mask)
    red = Image.new("RGB", a.size, (255, 32, 32))
    heat.paste(red, mask=blob_mask)
    strip = Image.new("RGB", (a.size[0] * 3 + 20, a.size[1]), (24, 24, 24))
    strip.paste(a, (0, 0))
    strip.paste(b, (a.size[0] + 10, 0))
    strip.paste(heat, (a.size[0] * 2 + 20, 0))
    strip.save(prefix + "-triptych.png")

    ok = blob_pct <= threshold
    print(json.dumps({"pass": ok, "blob_pct": round(blob_pct, 4),
                      "fringe_pct": round(pct, 4),
                      "blob_pixels": blob_bad, "total": total,
                      "threshold_pct": threshold, "delta": delta}))
    return 0 if ok else 1


if __name__ == "__main__":
    sys.exit(main())