import binascii

RAW_FILE = r"u:\PycharmProjects\NewsGroups\downloads\raw\part_001.raw"

# --------------------------------------------------
# yEnc decoder (offline, minimal, correct)
# --------------------------------------------------
def yenc_decode(lines: list[bytes]) -> bytes:
    out = bytearray()

    for line in lines:
        # undo NNTP dot-stuffing
        if line.startswith(b".."):
            line = line[1:]
        elif line.startswith(b"."):
            line = line[1:]

        i = 0
        while i < len(line):
            c = line[i]
            if c == ord("="):
                i += 1
                c = (line[i] - 64) & 0xFF
            out.append((c - 42) & 0xFF)
            i += 1

    return bytes(out)

# --------------------------------------------------
# 1. read RAW file
# --------------------------------------------------
with open(RAW_FILE, "rb") as f:
    raw_lines = f.read().splitlines()

print(f"📄 RAW lines: {len(raw_lines)}")

# --------------------------------------------------
# 2. split parts
# --------------------------------------------------
ybegin = None
ypart = None
yend = None
data_lines = []

for line in raw_lines:
    if line.startswith(b"=ybegin"):
        ybegin = line.decode(errors="replace")
        continue

    if line.startswith(b"=ypart"):
        ypart = line.decode(errors="replace")
        continue

    if line.startswith(b"=yend"):
        yend = line.decode(errors="replace")
        continue

    data_lines.append(line)

print("🧾 ybegin:", ybegin)
print("🧾 ypart :", ypart)
print("🧾 yend  :", yend)
print(f"📦 DATA lines: {len(data_lines)}")

# --------------------------------------------------
# 3. decode yEnc DATA
# --------------------------------------------------
decoded = yenc_decode(data_lines)

print(f"📦 Decoded bytes: {len(decoded)}")

# --------------------------------------------------
# 4. extract pcrc32
# --------------------------------------------------
pcrc = None
if "pcrc32=" in yend:
    pcrc = yend.split("pcrc32=")[1].strip()

if not pcrc:
    raise RuntimeError("No pcrc32 found")

# --------------------------------------------------
# 5. compute CRC32
# --------------------------------------------------
crc_calc = f"{binascii.crc32(decoded) & 0xffffffff:08x}"

print(f"🔎 CRC expected: {pcrc}")
print(f"🔎 CRC computed: {crc_calc}")

if crc_calc == pcrc:
    print("✅ CRC MATCH — PART IS PERFECT")
else:
    print("❌ CRC MISMATCH — DATA IS BROKEN")