"""Parse timestamps and pairing keys from calibration image filenames."""

from __future__ import annotations

import re
from pathlib import Path
from typing import Optional, Tuple

_TS_TOKEN = re.compile(r"ts(\d+)", re.IGNORECASE)
_SCAN_TOKEN = re.compile(r"scan(\d{6})", re.IGNORECASE)
_IR_SCAN = re.compile(r"^ir_scan_(\d+)", re.IGNORECASE)


def _digits_after_prefix(name: str, prefixes: Tuple[str, ...]) -> Optional[str]:
    lower = name.lower()
    for prefix in sorted(prefixes, key=len, reverse=True):
        if lower.startswith(prefix):
            remainder = lower[len(prefix) :].lstrip("_-.")
            m = re.match(r"(\d+)", remainder)
            if m:
                return m.group(1)
    return None


def parse_timestamp_sec(filename: str) -> Optional[float]:
    """
    Normalize filename timestamps to seconds for time-window pairing.

    Supports:
      - lc_ts1634840093_ck.... -> ms since epoch
      - lc_1778599872850705.bmp -> µs since epoch (16+ digits)
      - lc_1778599872850.bmp -> ms (13 digits)
    """
    name = Path(filename).name
    m = _TS_TOKEN.search(name)
    if m:
        digits = m.group(1)
        if len(digits) >= 16:
            return int(digits) / 1_000_000.0
        if len(digits) >= 13:
            return int(digits) / 1_000.0
        return int(digits) / 1_000.0

    prefixes = ("lc-ir", "lcir", "lc_ir", "lc", "rc", "rg", "rgb", "ir")
    digits = _digits_after_prefix(name, prefixes)
    if digits is None:
        return None

    if len(digits) >= 16:
        return int(digits) / 1_000_000.0
    if len(digits) >= 13:
        return int(digits) / 1_000.0
    return float(digits)


def parse_pair_key(filename: str) -> Optional[str]:
    """
    Filename key for legacy exact matching (IR scan ids, shared numeric tails).
    """
    name = Path(filename).name
    lower = name.lower()

    m = _IR_SCAN.match(lower)
    if m:
        return f"scan{int(m.group(1)):06d}"

    m = _SCAN_TOKEN.search(lower)
    if m:
        return m.group(0).lower()

    m = _TS_TOKEN.search(lower)
    if m:
        return f"ts{m.group(1)}"

    prefixes = ("lc-ir", "lcir", "lc_ir", "lc", "rc", "rg", "rgb", "ir")
    digits = _digits_after_prefix(lower, prefixes)
    if digits:
        return digits

    return Path(lower).stem