// Isomorphic, dependency-free schedule helpers. Used by the server service
// layer, the v2 serializers and the client-side Block modal (for live
// pre-validation), so it must not import Prisma or any server-only code.

export const MAX_BLOCKS = 4;
export const MINUTES_PER_DAY = 24 * 60;
export const SNAP_MINUTES = 15;
export const MINUTE_STEP = 5;

export type BlockSibling = {
	id?: string;
	startMinutes: number;
	endMinutes: number;
};

export type BlockInput = {
	startMinutes: number;
	endMinutes: number;
	proclamationIds: string[];
	/** When true the kiosk enables dynamic audio for the block's duration. */
	dynamicAudio?: boolean;
};

export type ValidationResult = { ok: true } | { ok: false; error: string };

function normalizeMinutes(minutes: number): number {
	return (((Math.trunc(minutes) % MINUTES_PER_DAY) + MINUTES_PER_DAY) % MINUTES_PER_DAY) | 0;
}

/** Format minutes-from-midnight as a 12-hour clock label, e.g. `6:00 AM`. */
export function formatTime(minutes: number): string {
	const normalized = normalizeMinutes(minutes);
	const hours24 = Math.floor(normalized / 60);
	const mins = normalized % 60;
	const period = hours24 < 12 ? 'AM' : 'PM';
	const hours12 = hours24 % 12 === 0 ? 12 : hours24 % 12;
	return `${hours12}:${String(mins).padStart(2, '0')} ${period}`;
}

/** Format minutes-from-midnight as a 24-hour `HH:MM` string. */
export function toHm(minutes: number): string {
	const normalized = normalizeMinutes(minutes);
	const hours = Math.floor(normalized / 60);
	const mins = normalized % 60;
	return `${String(hours).padStart(2, '0')}:${String(mins).padStart(2, '0')}`;
}

/**
 * Parse a 24-hour `HH:MM` string into minutes from midnight. Returns null when
 * the input is not a valid 24-hour time.
 */
export function hmToMinutes(hm: string): number | null {
	const match = /^(\d{2}):(\d{2})$/.exec(hm.trim());
	if (!match) return null;
	const hours = Number(match[1]);
	const minutes = Number(match[2]);
	if (hours > 23 || minutes > 59) return null;
	return hours * 60 + minutes;
}

export type TimeInputResult = { ok: true; minutes: number } | { ok: false; error: string };

/**
 * Parse a user-typed 12-hour clock time into minutes from midnight. Tolerant of
 * "7:05 pm", "7:05PM", "7pm", "7:7", "12:00 am". A period is optional; when
 * present the hour must be 1-12, so "13:00 PM" is rejected. Minutes may be any
 * value 00-59, not just the 5-minute steps.
 */
export function parseTimeInput(raw: string): TimeInputResult {
	const text = raw.trim().toLowerCase();
	if (!text) return { ok: false, error: 'Enter a time.' };

	const match = /^(\d{1,2})(?::(\d{1,2}))?\s*(am|pm|a|p)?$/.exec(text);
	if (!match) return { ok: false, error: 'Enter a time like 7:05 PM.' };

	const hour = Number(match[1]);
	const minute = match[2] === undefined ? 0 : Number(match[2]);
	const period = match[3];

	if (minute > 59) return { ok: false, error: 'Minutes must be 00-59.' };

	if (period) {
		if (hour < 1 || hour > 12) {
			return { ok: false, error: 'Hour must be 1-12 when AM/PM is given.' };
		}
		const isPm = period === 'pm' || period === 'p';
		const hours24 = (hour % 12) + (isPm ? 12 : 0);
		return { ok: true, minutes: hours24 * 60 + minute };
	}

	if (hour > 23) return { ok: false, error: 'Hour must be 0-23.' };
	return { ok: true, minutes: hour * 60 + minute };
}

/** The 5-minute clock options (00:00, 00:05, ..., 23:55) in play order. */
export function fiveMinuteOptions(): number[] {
	const options: number[] = [];
	for (let minutes = 0; minutes < MINUTES_PER_DAY; minutes += 5) {
		options.push(minutes);
	}
	return options;
}

/** Snap a minute value to the nearest `SNAP_MINUTES` interval, clamped to 24h. */
export function snapMinutes(minutes: number): number {
	const snapped = Math.round(minutes / SNAP_MINUTES) * SNAP_MINUTES;
	return Math.max(0, Math.min(MINUTES_PER_DAY, snapped));
}

/** A Block whose end clock time is at or before its start wraps past midnight. */
export function isOvernight(block: { startMinutes: number; endMinutes: number }): boolean {
	return block.endMinutes <= block.startMinutes;
}

/** Block length in minutes, counting a wrap past midnight as the next day. */
export function blockDuration(block: { startMinutes: number; endMinutes: number }): number {
	if (block.endMinutes > block.startMinutes) {
		return block.endMinutes - block.startMinutes;
	}
	return block.endMinutes - block.startMinutes + MINUTES_PER_DAY;
}

/**
 * Split a Block into the linear half-open `[start, end)` segments it occupies
 * within the 24h day. An overnight block produces two segments (start→midnight
 * and midnight→end); a zero-length block produces none.
 */
export function blockSegments(block: {
	startMinutes: number;
	endMinutes: number;
}): [number, number][] {
	if (block.startMinutes < block.endMinutes) {
		return [[block.startMinutes, block.endMinutes]];
	}
	if (block.startMinutes > block.endMinutes) {
		return [
			[block.startMinutes, MINUTES_PER_DAY],
			[0, block.endMinutes]
		];
	}
	return [];
}

function segmentsIntersect(a: [number, number], b: [number, number]): boolean {
	return a[0] < b[1] && b[0] < a[1];
}

/**
 * First sibling whose occupied time intersects the input. Works for overnight
 * (midnight-crossing) blocks by comparing their linear segments; ranges that
 * only touch at an endpoint (e.g. 9PM–9AM vs 9AM–9PM) do not overlap.
 */
export function findOverlap(
	input: { startMinutes: number; endMinutes: number },
	siblings: BlockSibling[]
): BlockSibling | null {
	const inputSegments = blockSegments(input);
	for (const sibling of siblings) {
		const siblingSegments = blockSegments(sibling);
		for (const segment of inputSegments) {
			for (const other of siblingSegments) {
				if (segmentsIntersect(segment, other)) return sibling;
			}
		}
	}
	return null;
}

/**
 * Validate a Block against the schedule's other Blocks. `siblings` must exclude
 * the Block being edited. `isCreate` enables the 4-block maximum (an update
 * never increases the count).
 */
export function validateBlock(
	input: BlockInput,
	siblings: BlockSibling[],
	opts: { isCreate?: boolean } = {}
): ValidationResult {
	const { startMinutes, endMinutes, proclamationIds } = input;

	if (
		!Number.isInteger(startMinutes) ||
		!Number.isInteger(endMinutes) ||
		startMinutes < 0 ||
		startMinutes > MINUTES_PER_DAY ||
		endMinutes < 0 ||
		endMinutes > MINUTES_PER_DAY
	) {
		return { ok: false, error: 'Enter a valid start and end time.' };
	}

	// Equal clock times would be a zero- or full-length block; both are
	// ambiguous, so reject them. Overnight ranges (end before start) are valid.
	if (startMinutes === endMinutes) {
		return { ok: false, error: "Start and end time can't be the same." };
	}

	if (!Array.isArray(proclamationIds) || proclamationIds.length === 0) {
		return { ok: false, error: 'Select at least one proclamation.' };
	}

	if (opts.isCreate && siblings.length >= MAX_BLOCKS) {
		return { ok: false, error: `You can have at most ${MAX_BLOCKS} blocks.` };
	}

	const overlap = findOverlap(input, siblings);
	if (overlap) {
		return {
			ok: false,
			error: `This overlaps with your ${formatTime(overlap.startMinutes)}–${formatTime(
				overlap.endMinutes
			)} block.`
		};
	}

	return { ok: true };
}