import { AudioCodec, MediaContainer, VideoCodec } from "music-server-shared/types";
import {
	audioCodecToken,
	containerMimeType,
	containerNamesCodecs,
	createRFC6381String,
	ladderMaxWidth,
	type VideoStreamInfo,
	videoCodecToken,
} from "music-server-shared/utils";
import { StreamingMode, VIDEO_BITRATES } from "./types";

export interface Support {
	supported: boolean;
	reason?: string;
}

//what a transcoding profile would produce, which is all it takes to decide whether a browser can play it.
//deliberately the shape of AppOptions' two settings objects, so either can be passed straight in and a
//single field varied with a spread - no argument threading and no positional mix-ups at the call sites
export interface Combination {
	container: MediaContainer;
	streamingMode: StreamingMode;
	audioCodec: AudioCodec;
	videoCodec?: VideoCodec;
	videoBitrate?: number;
}

export const hasMediaSource = "MediaSource" in window;
export const DEFAULT_STREAMING_MODE = hasMediaSource ? StreamingMode.mse : StreamingMode.progressive;

//the W3C MSE Byte Stream Format Registry is a closed list: ISO BMFF, WebM, MPEG-2 TS and MPEG Audio. a
//container missing from it cannot be fed to a SourceBuffer by any conforming browser, no matter how well
//that same browser plays it progressively - so this is a fact about the spec, not something to probe for
const MSE_BYTE_STREAM_FORMATS: MediaContainer[] = [MediaContainer.mp4, MediaContainer.webm, MediaContainer.mp3];

//audio codecs that are at least plausible in each container - ffmpeg refuses the rest outright, so there
//is no browser verdict to ask for
const CONTAINER_AUDIO_CODECS: Record<MediaContainer, AudioCodec[]> = {
	[MediaContainer.mp4]: [AudioCodec.mp3, AudioCodec.opus, AudioCodec.aac, AudioCodec.flac],
	[MediaContainer.webm]: [AudioCodec.opus, AudioCodec.vorbis],
	[MediaContainer.ogg]: [AudioCodec.opus, AudioCodec.vorbis, AudioCodec.flac],
	[MediaContainer.mp3]: [AudioCodec.mp3],
};

const CONTAINER_VIDEO_CODECS: Record<MediaContainer, VideoCodec[]> = {
	[MediaContainer.mp4]: [VideoCodec.av1, VideoCodec.h264, VideoCodec.h265, VideoCodec.vp9],
	[MediaContainer.webm]: [VideoCodec.av1, VideoCodec.vp9],
	[MediaContainer.ogg]: [],
	[MediaContainer.mp3]: [],
};

export function containerAudioCodecs(container: MediaContainer): AudioCodec[] {
	return CONTAINER_AUDIO_CODECS[container] ?? [];
}

export function containerVideoCodecs(container: MediaContainer): VideoCodec[] {
	return [...(CONTAINER_VIDEO_CODECS[container] ?? []), VideoCodec.none];
}

//actual values don't seem to matter, besides for a possible "smoothnes" verdict
//though any valid codec string should result in the same playability result for the same codec
const NOMINAL_FRAMERATE = 30;
const NOMINAL_UNSCALED_WIDTH = 3840;

function nominalVideoStream(videoBitrate: number): VideoStreamInfo {
	const width = ladderMaxWidth(videoBitrate) ?? NOMINAL_UNSCALED_WIDTH;
	return {
		sourceWidth: width,
		sourceHeight: Math.round(width / (16 / 9) / 2) * 2,
		frameRate: NOMINAL_FRAMERATE,
		interlaced: false,
		bitrate: videoBitrate,
	};
}

let probeElement: HTMLVideoElement | undefined;

function progressivelyPlayable(mimeType: string): boolean {
	probeElement ??= document.createElement("video");
	return probeElement.canPlayType(mimeType) !== "";
}

//MediaSource.isTypeSupported is the cheap gate but a lenient one: it parses the type and checks the
//codecs in isolation, so it says yes to combinations the decoder then refuses. decodingInfo asks the
//actual decoder pipeline, per track, with the resolution and framerate attached
const decodingCache = new Map<string, { supported: boolean; smooth: boolean }>();
const pending = new Map<string, Promise<void>>();

function startDecodingProbe(key: string, configuration: MediaDecodingConfiguration) {
	const existing = pending.get(key);
	if (existing) return existing;
	const probe = navigator.mediaCapabilities
		.decodingInfo(configuration)
		.then((info) => {
			decodingCache.set(key, { supported: info.supported, smooth: info.smooth });
		})
		.catch(() => {
			//a configuration this browser cannot even parse tells us nothing beyond what the sync checks
			//already established, so record the permissive answer rather than disabling a working option
			decodingCache.set(key, { supported: true, smooth: true });
		})
		.finally(() => {
			pending.delete(key);
		});
	pending.set(key, probe);
	return probe;
}

export function checkSupport(combination: Combination): Support {
	const { container, streamingMode, audioCodec } = combination;
	const videoCodec = combination.videoCodec ?? VideoCodec.none;
	const hasVideo = videoCodec !== VideoCodec.none;
	if (streamingMode === StreamingMode.mse) {
		if (!hasMediaSource) return { supported: false, reason: "this browser has no MediaSource support" };
		if (!MSE_BYTE_STREAM_FORMATS.includes(container))
			return {
				supported: false,
				reason: `${container} has no registered MSE byte stream format, so no browser can stream it - pick progressive or buffered`,
			};
		//measured against -live 1, -dash 1, -default_mode infer, explicit dispositions, forced cluster
		//limits and both track orders: the append succeeds, updateend fires, and buffered stays empty
		if (container === MediaContainer.webm && hasVideo)
			return {
				supported: false,
				reason: "effectively unsupported by browsers in mse",
			};
	}

	const video = hasVideo ? nominalVideoStream(combination.videoBitrate ?? 0) : undefined;
	const mimeType = createRFC6381String(container, videoCodec, audioCodec, video);

	if (streamingMode === StreamingMode.mse) {
		if (!MediaSource.isTypeSupported(mimeType))
			return { supported: false, reason: `the browser rejects ${mimeType} in a SourceBuffer` };
	} else if (!progressivelyPlayable(mimeType)) {
		return { supported: false, reason: `the browser cannot play ${mimeType}` };
	}

	//decodingInfo needs one content type per track, which is why the tokens are built here rather than
	//reusing the combined string above. a container that names no codec has nothing to ask about
	if (!containerNamesCodecs(container)) return { supported: true };
	const configuration: MediaDecodingConfiguration = {
		type: streamingMode === StreamingMode.mse ? "media-source" : "file",
		audio: { contentType: `${containerMimeType(container, false)}; codecs="${audioCodecToken(audioCodec)}"` },
		...(video
			? {
					video: {
						contentType: `${containerMimeType(container, true)}; codecs="${videoCodecToken(videoCodec, video)}"`,
						width: video.sourceWidth,
						height: video.sourceHeight,
						bitrate: video.bitrate,
						framerate: video.frameRate,
					},
				}
			: {}),
	};

	//keyed on the bitrate only when there is a video track, so an audio-only probe is not re-run once per
	//resolution ladder rung for an answer that cannot depend on it
	const key = `${configuration.type}|${configuration.audio?.contentType}|${configuration.video?.contentType}|${video?.bitrate}`;
	const cached = decodingCache.get(key);
	if (!cached) {
		void startDecodingProbe(key, configuration);
		return { supported: true };
	}
	if (!cached.supported) return { supported: false, reason: `the browser's decoders reject ${mimeType}` };
	if (!cached.smooth)
		return { supported: true, reason: "supported, but the browser does not expect to decode this smoothly" };
	return { supported: true };
}

//a container is offerable when at least one codec combination inside it works in the current mode
function checkContainer(combination: Combination, videoCodecs: VideoCodec[]): Support {
	let firstFailure: Support | undefined;
	for (const videoCodec of videoCodecs) {
		for (const audioCodec of containerAudioCodecs(combination.container)) {
			const support = checkSupport({ ...combination, videoCodec, audioCodec });
			if (support.supported) return { supported: true };
			firstFailure ??= support;
		}
	}
	return firstFailure ?? { supported: false, reason: `${combination.container} offers no usable codecs` };
}

export function checkVideoContainerSupport(combination: Combination): Support {
	return checkContainer(combination, containerVideoCodecs(combination.container));
}

//an audio-only profile must not be told mp4 works because mp4 video works, only because mp4 audio does
export function checkAudioContainerSupport(combination: Combination): Support {
	return checkContainer(combination, [VideoCodec.none]);
}

function usableAudioCodecs(combination: Combination): AudioCodec[] {
	return containerAudioCodecs(combination.container).filter(
		(audioCodec) => checkSupport({ ...combination, audioCodec }).supported,
	);
}

function usableVideoCodecs(combination: Combination): VideoCodec[] {
	return containerVideoCodecs(combination.container).filter(
		(videoCodec) => checkContainer(combination, [videoCodec]).supported,
	);
}

function usableContainers(combination: Combination): MediaContainer[] {
	const check = combination.videoCodec === undefined ? checkAudioContainerSupport : checkVideoContainerSupport;
	return Object.values(MediaContainer).filter((container) => check({ ...combination, container }).supported);
}

//used to decide whether the video section is worth showing at all - it is not when nothing but "none" would
//be selectable
export function selectableVideoCodecs(combination: Combination): VideoCodec[] {
	return usableVideoCodecs(combination).filter((videoCodec) => videoCodec !== VideoCodec.none);
}

function firstUsable<T>(current: T, usable: T[]): T | undefined {
	return usable.includes(current) ? current : usable[0];
}

function knownMember<T extends string>(values: T[], value: T, fallback: T): T {
	return values.includes(value) ? value : fallback;
}

//make sure settings are playable (e.g. might come from an older browser version with different codec support)
export function playableSettings<T extends Combination>(settings: T): T {
	const known = {
		...settings,
		streamingMode: knownMember(Object.values(StreamingMode), settings.streamingMode, DEFAULT_STREAMING_MODE),
		container: knownMember(Object.values(MediaContainer), settings.container, MediaContainer.mp4),
		audioCodec: knownMember(Object.values(AudioCodec), settings.audioCodec, AudioCodec.opus),
		...(settings.videoCodec === undefined
			? {}
			: { videoCodec: knownMember(Object.values(VideoCodec), settings.videoCodec, VideoCodec.none) }),
	};
	if (checkSupport(known).supported) return known;

	//outermost field first: the container decides which codecs are on offer, and the video codec decides
	//which audio codecs are left over
	const container = firstUsable(known.container, usableContainers(known));
	if (container === undefined) {
		if (known.streamingMode === DEFAULT_STREAMING_MODE) return known;
		return playableSettings({ ...known, streamingMode: DEFAULT_STREAMING_MODE });
	}
	const withContainer = { ...known, container };

	const videoCodec =
		known.videoCodec === undefined ? undefined : firstUsable(known.videoCodec, usableVideoCodecs(withContainer));
	const withVideoCodec = videoCodec === undefined ? withContainer : { ...withContainer, videoCodec };

	const audioCodec = firstUsable(withVideoCodec.audioCodec, usableAudioCodecs(withVideoCodec));
	//the container was only offered because some codec pair inside it works, so this cannot come up empty
	if (audioCodec === undefined) return known;
	return { ...withVideoCodec, audioCodec };
}

export async function initCapabilities(): Promise<void> {
	for (const streamingMode of Object.values(StreamingMode)) {
		for (const container of Object.values(MediaContainer)) {
			for (const audioCodec of containerAudioCodecs(container)) {
				for (const videoCodec of containerVideoCodecs(container)) {
					//the bitrate picks the resolution ladder rung and with it the codec level, so each one the
					//menu offers is its own probe. an audio-only combination has none to vary - and "none" is
					//exactly what an absent videoCodec resolves to in checkSupport
					const videoBitrates = videoCodec === VideoCodec.none ? [undefined] : VIDEO_BITRATES;
					for (const videoBitrate of videoBitrates) {
						checkSupport({ container, streamingMode, audioCodec, videoCodec, videoBitrate });
					}
				}
			}
		}
	}
	//every probe started above resolves into the same map, and settling one cannot start another
	await Promise.all(pending.values());
}