import struct
from parse import records

POLY = 0xA001
def crc16(data, init=0, poly=POLY):
    c = init
    for b in data:
        c ^= b
        for _ in range(8):
            c = (c >> 1) ^ poly if c & 1 else c >> 1
    return c & 0xffff

rs = records()
for r in rs:
    r['chk'] = struct.unpack_from('<H', r['blk'], 1)[0]

# candidate ranges (start, end) end=None means to end of block
cands = []
for s in [0,1,3,5,7,0xb,0xf,0x10,0x11,0x14,0x16,0x20,0x116,0x117]:
    cands.append((s, None))
cands += [(0,3),(3,7),(0,0x116),(3,0x116),(7,0x116),(0x116,None)]

blks = [r['blk'] for r in rs]
chks = [r['chk'] for r in rs]

best = []
for (s,e) in cands:
    ok = 0
    for b,c in zip(blks,chks):
        seg = b[s:] if e is None else b[s:e]
        for init in (0, 0xffff):
            for xo in (0, 0xffff):
                pass
        if crc16(seg) == c: ok += 1
    if ok: print('range', hex(s), e, 'matches', ok, '/', len(rs))
    best.append((ok,s,e))
best.sort(reverse=True)
print('top:', best[:5])

# also try with the crc bytes zeroed
print('--- zeroed crc field ---')
for (s,e) in cands:
    ok=0
    for b,c in zip(blks,chks):
        bb = bytearray(b); bb[1]=0; bb[2]=0
        seg = bytes(bb[s:] if e is None else bb[s:e])
        if crc16(seg) == c: ok+=1
    if ok: print('range', hex(s), e, 'matches', ok)