import { createContext } from 'svelte';
import type { Stream, StreamSummary } from './types.ts';

export class StreamContext {
	streams: StreamSummary[];
	current = $state<Stream | null>(null);
	songIndex = $state<number | null>(null);
	#timestamps: number[] = [];

	constructor(streams: StreamSummary[]) {
		this.streams = streams;
	}

	setCurrent(stream: Stream) {
		this.current = stream;
		this.#timestamps = [-Infinity, ...stream.tracks.map((t) => t[0]), Infinity];
		this.songIndex = 0;
	}

	clearCurrent() {
		this.current = null;
		this.songIndex = null;
	}

	getSongAtTime(time: number): number {
		return this.#locationOf(time, this.#timestamps) - 1;
	}

	updateCurrentSong(currentTime: number, songIndex: number) {
		const ts = this.#timestamps;
		const recurse = (idx: number): number => {
			if (currentTime >= ts[idx + 2]) return recurse(idx + 1);
			if (currentTime < ts[idx + 1]) return recurse(idx - 1);
			return idx;
		};
		this.songIndex = recurse(songIndex);
	}

	#locationOf(element: number, array: number[], start = 0, end = array.length): number {
		const pivot = Math.floor(start + (end - start) / 2);
		if (end - start <= 1 || array[pivot] === element) return pivot;
		if (array[pivot] < element) return this.#locationOf(element, array, pivot, end);
		return this.#locationOf(element, array, start, pivot);
	}
}

export const [getStreamContext, setStreamContext] = createContext<StreamContext>();