import random
from datetime import datetime

MONTH_CODES = "ABCDEFGHIJKL"
SAFE_CHARS = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789"  # No 0, O, 1, I — avoids label confusion

# Family segment (chars 3-6 of segment 1, after "BS")
BOARD_FAMILY_CODES = {
    "vesper":      "VSPR",
    "vesper_plus": "VSPR",
    "vesper_pro":  "VSPR",
    "agnus":       "AGNS",
    "agnus_mini":  "AGNS",
    "chronos":     "CRNS",
    "chronos_pro": "CRNS",
}

# Variant segment (first 3 chars of segment 3)
BOARD_VARIANT_CODES = {
    "vesper":      "STD",
    "vesper_plus": "PLS",
    "vesper_pro":  "PRO",
    "agnus":       "STD",
    "agnus_mini":  "MIN",
    "chronos":     "STD",
    "chronos_pro": "PRO",
}


def _version_suffix(board_version: str) -> str:
    """Convert version string to 3-char suffix.

    Rules:
    - Strip the dot: "2.3" → "23", "10.2" → "102"
    - If result is 2 digits, append "R": "23" → "23R"
    - If result is already 3 digits, use as-is: "102" → "102"
    """
    digits = board_version.replace(".", "")
    if len(digits) >= 3:
        return digits[:3]
    return digits.ljust(2, "0") + "R"


def generate_serial(board_type: str, board_version: str) -> str:
    """Generate a serial number in the format BSFFFF-YYMDDFX-VVVHHH-XXXXXX.

    Format: BSFFFF-YYMDDf-VVVvvv-XXXXXX
      BS     = Bell Systems (static)
      FFFF   = 4-char family code (VSPR, AGNS, CRNS)
      YY     = 2-digit year
      M      = month code A-L
      DD     = 2-digit day
      f      = random filler char
      VVV    = 3-char variant (STD, PLS, PRO, MIN)
      vvv    = 3-char version suffix (e.g. 23R, 102)
      XXXXXX = 6-char random suffix

    board_type: enum value e.g. 'vesper', 'vesper_plus', 'vesper_pro'
    board_version: version string e.g. '2.3', '10.2'
    """
    key = board_type.lower()
    family  = BOARD_FAMILY_CODES.get(key, "UNKN")
    variant = BOARD_VARIANT_CODES.get(key, "UNK")
    ver     = _version_suffix(board_version)

    now = datetime.utcnow()
    year  = now.strftime("%y")
    month = MONTH_CODES[now.month - 1]
    day   = now.strftime("%d")
    filler = random.choice(SAFE_CHARS)
    suffix = "".join(random.choices(SAFE_CHARS, k=6))

    seg1 = f"BS{family}"           # e.g. BSVSPR
    seg2 = f"{year}{month}{day}{filler}"  # e.g. 26C13X
    seg3 = f"{variant}{ver}"       # e.g. PRO23R
    seg4 = suffix                  # e.g. X9K4M2

    return f"{seg1}-{seg2}-{seg3}-{seg4}"