from __future__ import annotations

ARM_MACHINES = frozenset({"aarch64", "arm64", "armv7l", "armv8l"})


def resolve_live_video_encoder(
    requested_encoder: str,
    ffmpeg_encoders_text: str,
    machine: str,
    *,
    has_mpp_service: bool = False,
    has_render_node: bool = False,
    has_v4l2_device: bool = False,
    usable_encoders: set[str] | None = None,
) -> tuple[str, str]:
    requested = (requested_encoder or "").strip()
    blob = ffmpeg_encoders_text or ""
    machine_norm = (machine or "").strip().lower()
    is_arm = machine_norm in ARM_MACHINES

    def has_encoder(name: str) -> bool:
        return bool(name) and name in blob

    def is_usable(name: str) -> bool:
        return usable_encoders is None or name in usable_encoders

    arm_candidates: list[str] = []
    if has_encoder("h264_rkmpp") and has_mpp_service and is_usable("h264_rkmpp"):
        arm_candidates.append("h264_rkmpp")
    if has_encoder("h264_v4l2m2m") and has_v4l2_device and is_usable("h264_v4l2m2m"):
        arm_candidates.append("h264_v4l2m2m")

    if is_arm:
        if requested == "h264_vaapi":
            if arm_candidates:
                return arm_candidates[0], f"LIVE_VIDEO_ENCODER=h264_vaapi is not stable on ARM, fallback to {arm_candidates[0]}"
            return "", "LIVE_VIDEO_ENCODER=h264_vaapi is not supported on ARM, fallback to libx264"
        if requested == "h264_v4l2m2m" and not has_v4l2_device:
            return "", "LIVE_VIDEO_ENCODER=h264_v4l2m2m requires /dev/video* on this ARM host, fallback to libx264"
        if requested and has_encoder(requested) and usable_encoders is not None and requested not in usable_encoders:
            if arm_candidates:
                return arm_candidates[0], f"LIVE_VIDEO_ENCODER={requested} failed encoder smoke test, fallback to {arm_candidates[0]}"
            return "", f"LIVE_VIDEO_ENCODER={requested} failed encoder smoke test, fallback to libx264"
        if requested:
            if requested in arm_candidates:
                return requested, ""
            if requested.startswith("h264_") and has_encoder(requested) and is_usable(requested):
                return requested, ""
            if arm_candidates:
                return arm_candidates[0], f"LIVE_VIDEO_ENCODER={requested} is unavailable on this ARM host, fallback to {arm_candidates[0]}"
            return "", f"LIVE_VIDEO_ENCODER={requested} is unavailable on this ARM host, fallback to libx264"
        if arm_candidates:
            return arm_candidates[0], ""
        return "", ""

    if requested == "h264_qsv":
        if has_encoder("h264_vaapi") and has_render_node and is_usable("h264_vaapi"):
            return "h264_vaapi", "LIVE_VIDEO_ENCODER=h264_qsv is not enabled in this Linux stack yet, fallback to h264_vaapi"
        return "", "LIVE_VIDEO_ENCODER=h264_qsv is not enabled in this Linux stack yet, fallback to libx264"
    if requested == "h264_vaapi" and not has_render_node:
        return "", "LIVE_VIDEO_ENCODER=h264_vaapi requires /dev/dri/renderD*; fallback to libx264"
    if requested and has_encoder(requested) and usable_encoders is not None and requested not in usable_encoders:
        return "", f"LIVE_VIDEO_ENCODER={requested} failed encoder smoke test, fallback to libx264"
    if requested and requested.startswith("h264_") and has_encoder(requested) and is_usable(requested):
        return requested, ""
    if requested:
        return "", f"LIVE_VIDEO_ENCODER={requested} is unavailable on this host, fallback to libx264"
    return "", ""