/**
 * The director: which match a channel shows. Pure, so it is easy to test.
 *
 * It never cuts away from a map in progress, lingers on a result long enough
 * for it to be seen, and otherwise goes where it is most exciting: tournament
 * matches first, then close series near match point, tiebreakers, and crowds.
 */
import { DECIDED, type LiveMatch } from '$lib/live';
import type { ChannelMode } from './channel';

export const RESULT_LINGER_MS = 30_000;

export interface DirectorInput {
	mode: ChannelMode;
	matchId: string | null;
	tournamentId: string | null;
	current: string | null;
	/** When the current match was first seen decided. */
	decidedSince: number | null;
	live: LiveMatch[];
	now: number;
}

export function pickMatch(input: DirectorInput): string | null {
	if (input.mode === 'match') return input.matchId;
	const candidates = input.live.filter(
		(match) =>
			input.mode === 'auto' ||
			(input.tournamentId != null && match.tournament?.id === input.tournamentId)
	);
	const current = candidates.find((match) => match.id === input.current);
	if (current) {
		const decided = DECIDED.includes(current.phase);
		if (!decided) {
			// Stay through a map; between maps, only leave for a much better match.
			const best = best_(candidates);
			if (current.phase === 'playing' || !best || best.id === current.id) return current.id;
			return interest(best) > interest(current) + 60 ? best.id : current.id;
		}
		if (input.decidedSince != null && input.now - input.decidedSince < RESULT_LINGER_MS)
			return current.id;
	}
	return best_(candidates)?.id ?? null;
}

function best_(candidates: LiveMatch[]): LiveMatch | null {
	return (
		candidates
			.filter((match) => !DECIDED.includes(match.phase))
			.sort((a, b) => interest(b) - interest(a) || a.id.localeCompare(b.id))[0] ?? null
	);
}

/** How much a match is worth watching right now. */
export function interest(match: LiveMatch): number {
	const [a, b] = match.sides;
	const needed = Math.max(1, match.winsNeeded);
	const closeness = 1 - Math.abs(a.points - b.points) / needed;
	const progress = (a.points + b.points) / (2 * needed - 1);
	return (
		(match.tournament ? 100 : 0) +
		(match.simulated ? 0 : 40) +
		Math.min(80, match.viewers * 4) +
		closeness * progress * 60 +
		(match.phase === 'tb' || match.map?.category === 'TB' ? 50 : 0) +
		(match.phase === 'playing' ? 15 : 0)
	);
}