"""Decode compact binary controller envelopes — v2 native binary, v1 legacy JSON blobs."""

import json
import struct

BINARY_ENVELOPE_VERSION_1 = 1
BINARY_ENVELOPE_VERSION_2 = 2
HEADER_LEN = 5


def _brightness_0_255_from_wire(wire):
    w = max(0, min(127, int(wire)))
    return min(255, (w * 255) // 127)


def _decode_preset_record(buf, off):
    nl = buf[off]
    off += 1
    name = buf[off : off + nl].decode("utf-8")
    off += nl
    pl = buf[off]
    off += 1
    pattern = buf[off : off + pl].decode("utf-8")
    off += pl
    nc = buf[off]
    off += 1
    colors = []
    for _ in range(nc):
        r, g, b = buf[off], buf[off + 1], buf[off + 2]
        off += 3
        colors.append("#%02x%02x%02x" % (r, g, b))
    if off + 16 > len(buf):
        raise ValueError("truncated")
    delay, br, auto, n1, n2, n3, n4, n5, n6 = struct.unpack_from(
        "<HBBhhhhhh", buf, off
    )
    off += 16
    preset = {
        "p": pattern,
        "c": colors,
        "d": delay,
        "b": br,
        "a": bool(auto),
        "n1": n1,
        "n2": n2,
        "n3": n3,
        "n4": n4,
        "n5": n5,
        "n6": n6,
    }
    return name, preset, off


def _decode_presets_blob(chunk):
    if not chunk:
        return {}
    off = 0
    count = chunk[off]
    off += 1
    out = {}
    for _ in range(count):
        name, preset, off = _decode_preset_record(chunk, off)
        out[name] = preset
    if off != len(chunk):
        raise ValueError("presets blob mismatch")
    return out


def _decode_select_blob(chunk):
    if not chunk:
        return {}
    off = 0
    count = chunk[off]
    off += 1
    out = {}
    for _ in range(count):
        dl = chunk[off]
        off += 1
        device = chunk[off : off + dl].decode("utf-8")
        off += dl
        pl = chunk[off]
        off += 1
        pname = chunk[off : off + pl].decode("utf-8")
        off += pl
        has_step = chunk[off]
        off += 1
        if has_step:
            step = struct.unpack_from("<H", chunk, off)[0]
            off += 2
            out[device] = [pname, step]
        else:
            out[device] = [pname]
    if off != len(chunk):
        raise ValueError("select blob mismatch")
    return out


def _decode_default_blob(chunk):
    if not chunk:
        return "", []
    off = 0
    nl = chunk[off]
    off += 1
    default_name = chunk[off : off + nl].decode("utf-8") if nl else ""
    off += nl
    nt = chunk[off]
    off += 1
    targets = []
    for _ in range(nt):
        tl = chunk[off]
        off += 1
        targets.append(chunk[off : off + tl].decode("utf-8"))
        off += tl
    if off != len(chunk):
        raise ValueError("default blob mismatch")
    return default_name, targets


def parse_binary_envelope_v2(buf):
    if not isinstance(buf, (bytes, bytearray)) or len(buf) < HEADER_LEN:
        return None
    if buf[0] != BINARY_ENVELOPE_VERSION_2:
        return None
    lp = buf[2]
    ls = buf[3]
    ld = buf[4]
    need = HEADER_LEN + lp + ls + ld
    if len(buf) != need:
        return None

    off = HEADER_LEN
    presets_chunk = buf[off : off + lp]
    off += lp
    select_chunk = buf[off : off + ls]
    off += ls
    default_chunk = buf[off : off + ld]

    data = {"v": "1"}
    br = buf[1]
    if br < 128:
        data["b"] = _brightness_0_255_from_wire(br)

    try:
        if lp:
            data["presets"] = _decode_presets_blob(presets_chunk)
        if ls:
            data["select"] = _decode_select_blob(select_chunk)
        if ld:
            dname, targets = _decode_default_blob(default_chunk)
            data["default"] = dname
            data["targets"] = targets
    except (ValueError, UnicodeError, TypeError, struct.error):
        return None

    return data


def parse_binary_envelope_v1(buf):
    if not isinstance(buf, (bytes, bytearray)) or len(buf) < HEADER_LEN:
        return None
    if buf[0] != BINARY_ENVELOPE_VERSION_1:
        return None
    lp = buf[2]
    ls = buf[3]
    ld = buf[4]
    need = HEADER_LEN + lp + ls + ld
    if len(buf) != need:
        return None

    off = HEADER_LEN
    presets_chunk = buf[off : off + lp]
    off += lp
    select_chunk = buf[off : off + ls]
    off += ls
    default_chunk = buf[off : off + ld]

    data = {"v": "1"}

    br = buf[1]
    if br < 128:
        data["b"] = _brightness_0_255_from_wire(br)

    if lp:
        try:
            data["presets"] = json.loads(presets_chunk.decode("utf-8"))
        except (ValueError, UnicodeError):
            return None
    if ls:
        try:
            data["select"] = json.loads(select_chunk.decode("utf-8"))
        except (ValueError, UnicodeError):
            return None
    if ld:
        try:
            extra = json.loads(default_chunk.decode("utf-8"))
        except (ValueError, UnicodeError):
            return None
        if isinstance(extra, dict):
            for k, v in extra.items():
                data[k] = v

    return data


def parse_binary_envelope(buf):
    d = parse_binary_envelope_v2(buf)
    if d is not None:
        return d
    return parse_binary_envelope_v1(buf)