#!/usr/bin/env python3
"""Debug wind extraction by examining actual packet bytes."""

import struct

PCAP_MAGIC = 0xa1b2c3d4

def decode_float(data, offset):
    if offset + 4 > len(data):
        return None
    try:
        return struct.unpack('<f', data[offset:offset+4])[0]
    except:
        return None

def read_pcap(filename):
    packets = []
    with open(filename, 'rb') as f:
        header = f.read(24)
        magic = struct.unpack('<I', header[0:4])[0]
        swapped = magic == 0xd4c3b2a1
        endian = '>' if swapped else '<'

        while True:
            pkt_header = f.read(16)
            if len(pkt_header) < 16:
                break
            ts_sec, ts_usec, incl_len, orig_len = struct.unpack(f'{endian}IIII', pkt_header)
            pkt_data = f.read(incl_len)
            if len(pkt_data) < incl_len:
                break

            if len(pkt_data) > 42 and pkt_data[12:14] == b'\x08\x00':
                ip_header_len = (pkt_data[14] & 0x0F) * 4
                payload_start = 14 + ip_header_len + 8
                if payload_start < len(pkt_data):
                    packets.append(pkt_data[payload_start:])
    return packets

packets = read_pcap("raymarine_sample.pcap")

# Find packets of different sizes
sizes_seen = {}
for pkt in packets:
    plen = len(pkt)
    if plen not in sizes_seen:
        sizes_seen[plen] = pkt

print("Examining wind data at known offsets:\n")

for target_size in [344, 446, 788, 888, 1472]:
    # Find a packet close to this size
    for plen, pkt in sizes_seen.items():
        if abs(plen - target_size) <= 10:
            print(f"=== Packet size {plen} ===")

            # Show bytes around expected wind offsets
            if 340 <= plen <= 350:
                offsets = [0x00a0, 0x00a5, 0x00c3, 0x00c8]
            elif 440 <= plen <= 500:
                offsets = [0x00a7, 0x00ac, 0x00ca, 0x00b1]
            elif 780 <= plen <= 900:
                offsets = [0x0090, 0x00c5, 0x00ca, 0x00cf]
            elif 1400 <= plen <= 1500:
                offsets = [0x00fc, 0x0101, 0x0106]
            else:
                offsets = []

            for off in offsets:
                if off + 8 <= plen:
                    hex_bytes = ' '.join(f'{b:02x}' for b in pkt[off:off+8])
                    float_val = decode_float(pkt, off)
                    # Also try treating as m/s and rad
                    speed_kts = float_val * 1.94384 if float_val else 0
                    dir_deg = float_val * 57.2958 if float_val else 0
                    print(f"  0x{off:04x}: {hex_bytes}  ->  float={float_val:.4f}  ({speed_kts:.1f} kts or {dir_deg:.1f}°)")
            print()
            break