"""
COMP-3 Packed Decimal Verification for COBOL Migration Platform.
Validates that binary COMP-3 fields in RATE.dat are correctly encoded.

Usage: python verify_comp3.py

COMP-3 format: each byte holds 2 nibbles (4-bit digits),
last nibble = sign (0xC/0xF = positive, 0xD = negative).
PIC 9(1)V9(4) = 5 digits + sign = 3 bytes.
"""

import struct
import sys


def unpack_comp3(data: bytes) -> tuple[int, int, str]:
    """Unpack COMP-3 bytes -> (integer_value, decimal_places, sign)."""
    nibbles = []
    for byte in data:
        nibbles.append((byte >> 4) & 0x0F)
        nibbles.append(byte & 0x0F)

    sign_nibble = nibbles[-1]
    digit_nibbles = nibbles[:-1]

    value = 0
    for n in digit_nibbles:
        value = value * 10 + n

    if sign_nibble in (0xC, 0xF):
        sign = "positive"
    elif sign_nibble == 0xD:
        sign = "negative"
    else:
        sign = f"unknown(0x{sign_nibble:X})"

    return value, sign, data.hex()


def main():
    rate_path = "D:/jcl-cobol/data/input/rate.dat"

    with open(rate_path, "rb") as f:
        data = f.read()

    rec_size = 12  # PIC X(1) + PIC 9(1)V9(4) COMP-3(3) + PIC 9(8)
    num_records = len(data) // rec_size

    print(f"File: {rate_path}")
    print(f"Size: {len(data)} bytes")
    print(f"Records: {num_records}")
    print()

    expected = {
        "C": ("Cash rate", 0.0005),
        "O": ("Overdue rate", 0.0500),
    }

    all_ok = True

    for i in range(num_records):
        offset = i * rec_size
        rec = data[offset : offset + rec_size]

        rate_type = chr(rec[0])
        pct_bytes = rec[1:4]
        eff_date = rec[4:12].decode("ascii")

        value, sign, pct_hex = unpack_comp3(pct_bytes)
        int_part = value // 10000
        dec_part = value % 10000
        pct_float = int_part + dec_part / 10000

        name, expected_val = expected.get(rate_type, ("Unknown", None))

        match = abs(pct_float - expected_val) < 0.0001 if expected_val else False
        status = "PASS" if match else "FAIL"
        if not match:
            all_ok = False

        print(f"[{status}] Record {i+1}: type={rate_type} ({name})")
        print(f"       COMP-3 hex: {pct_hex}")
        print(f"       packed int: {value}")
        print(f"       float val:  {pct_float:.4f}")
        print(f"       expected:   {expected_val}")
        print(f"       eff date:   {eff_date}")
        print()

    if all_ok:
        print("=== ALL COMP-3 VALUES VERIFIED ===")
    else:
        print("=== COMP-3 MISMATCH DETECTED ===")
        sys.exit(1)


if __name__ == "__main__":
    main()