#!/usr/bin/env python3
"""Read the QR code back off a captured crash screen.

This is the acceptance test for the crash channel, and it is deliberately
end-to-end: it does not ask the encoder what it produced, it reads the pixels
that were actually painted on the framebuffer. Everything in between -- payload
construction in panic context, the encoder, the scaling into modules, the card
and quiet zone -- is covered by whether this comes back as text.

    pwsh -File tools/crashshot.ps1          # crash on purpose, screendump it
    PYTHONPATH=<dir> python tools/crashqr.py

Needs opencv-python-headless and numpy; see tools/qrcheck.py for the install.
"""

import sys

try:
    import cv2
    import numpy as np
except ImportError:
    sys.exit("crashqr: needs opencv-python-headless and numpy")

PPM = sys.argv[1] if len(sys.argv) > 1 else "build/crashscreen.ppm"

try:
    data = open(PPM, "rb").read()
except OSError as e:
    sys.exit(f"crashqr: {e} -- run tools/crashshot.ps1 first")

# PPM P6 header: three whitespace-separated fields after the magic. Parsed by
# scanning rather than assuming a fixed length, because QEMU's is compact but
# nothing guarantees that.
pos, fields = 2, []
while len(fields) < 3:
    while data[pos:pos + 1].isspace():
        pos += 1
    start = pos
    while not data[pos:pos + 1].isspace():
        pos += 1
    fields.append(int(data[start:pos]))
pos += 1

w, h = fields[0], fields[1]
img = np.frombuffer(data[pos:pos + w * h * 3], np.uint8).reshape(h, w, 3)
grey = cv2.cvtColor(img, cv2.COLOR_RGB2GRAY)

# The symbol sits on the only light panel on an otherwise purple screen, so a
# brightness threshold finds it without needing to know the layout. The white
# report text passes the same threshold, which does not matter -- the detector
# locates the symbol by its finder patterns, and handing it extra screen
# costs nothing.
mask = (grey > 240).astype(np.uint8)
ys, xs = np.nonzero(mask)
if len(xs) == 0:
    sys.exit("crashqr: no light region found -- was a crash screen captured?")
crop = grey[ys.min():ys.max() + 1, xs.min():xs.max() + 1]

# OpenCV's detector is sensitive to scale in ways unrelated to the encoding,
# so try a few before concluding anything. See the note in tools/qrcheck.py.
text = ""
for scale in (1, 2, 3, 4):
    up = cv2.resize(crop, None, fx=scale, fy=scale, interpolation=cv2.INTER_NEAREST)
    up = cv2.copyMakeBorder(up, 40, 40, 40, 40, cv2.BORDER_CONSTANT, value=255)
    text, _, _ = cv2.QRCodeDetector().detectAndDecode(up)
    if text:
        break

if not text:
    print("crashqr: FAILED -- the symbol on the crash screen did not decode")
    sys.exit(1)

print("crashqr: decoded the crash screen's QR\n")
for line in text.split("\n"):
    print("   ", line)

# The payload is a contract with whatever reads these later, so check its shape
# rather than only that something came back.
lines = text.split("\n")
ok = lines[0] == "SXPSOGM1"
print()
if not ok:
    print(f"crashqr: FAILED -- expected magic 'SXPSOGM1', got {lines[0]!r}")
    sys.exit(1)
print(f"crashqr: passed ({len(text)} bytes, {len(lines)} fields)")