"""In-memory PCM validation and conversion."""

from __future__ import annotations

from array import array
import struct

MAX_PCM_BYTES = 5 * 60 * 16_000 * 2


class AudioError(ValueError):
    pass


def pcm_s16le_to_floats(pcm: bytes, *, max_bytes: int = MAX_PCM_BYTES) -> array[float]:
    """Convert mono little-endian signed-16 PCM to a bounded float32 array."""

    if len(pcm) > max_bytes:
        raise AudioError("PCM exceeds the five-minute duration limit")
    if len(pcm) % 2:
        raise AudioError("PCM byte length must be even")
    return array("f", (sample[0] / 32768.0 for sample in struct.iter_unpack("<h", pcm)))