import { json, error } from '@sveltejs/kit';
import type { RequestHandler } from './$types.js';
import { cardDependencySchema } from '$lib/server/validation.js';
import { withTenant } from '$lib/server/rls.js';
import { requireBoardEditor } from '$lib/server/guards.js';
import { broadcast } from '$lib/server/realtime.js';
import { logActivity } from '$lib/server/activity.js';

// Get all dependencies for cards on this board
export const GET: RequestHandler = async ({ params, locals }) => {
	const tenant = locals.tenant;
	if (!tenant) throw error(400, 'Unknown tenant');

	const dependencies = await withTenant(tenant.id, async (tx) => {
		return tx.cardDependency.findMany({
			where: {
				blockingCard: {
					column: { board: { id: params.boardId, tenantId: tenant.id } }
				}
			},
			include: {
				blockingCard: { select: { id: true, title: true } },
				blockedCard: { select: { id: true, title: true } }
			}
		});
	});

	return json({ dependencies });
};

// Create a dependency
export const POST: RequestHandler = async ({ params, request, locals }) => {
	const tenant = locals.tenant;
	if (!tenant) throw error(400, 'Unknown tenant');

	const body = await request.json();
	const result = cardDependencySchema.safeParse(body);
	if (!result.success) {
		throw error(400, result.error.issues[0].message);
	}

	const { blockingCardId, blockedCardId } = result.data;

	if (blockingCardId === blockedCardId) {
		throw error(400, 'A card cannot depend on itself');
	}

	const dependency = await withTenant(tenant.id, async (tx) => {
		await requireBoardEditor(tx, locals.user, params.boardId, tenant.id);

		// Verify both cards belong to this board
		const blockingCard = await tx.card.findFirst({
			where: { id: blockingCardId, column: { board: { id: params.boardId } } },
			select: { id: true, title: true }
		});
		const blockedCard = await tx.card.findFirst({
			where: { id: blockedCardId, column: { board: { id: params.boardId } } },
			select: { id: true, title: true }
		});

		if (!blockingCard || !blockedCard) {
			throw error(400, 'Both cards must belong to this board');
		}

		// Check for existing dependency
		const existing = await tx.cardDependency.findUnique({
			where: { blockingCardId_blockedCardId: { blockingCardId, blockedCardId } }
		});
		if (existing) {
			throw error(400, 'This dependency already exists');
		}

		// Cycle detection via DFS
		const hasCycle = await detectCycle(tx, blockingCardId, blockedCardId);
		if (hasCycle) {
			throw error(400, 'Adding this dependency would create a circular dependency');
		}

		const dep = await tx.cardDependency.create({
			data: { blockingCardId, blockedCardId },
			include: {
				blockingCard: { select: { id: true, title: true } },
				blockedCard: { select: { id: true, title: true } }
			}
		});

		await logActivity(tx, {
			boardId: params.boardId,
			userId: locals.user!.id,
			action: 'dependency.created',
			cardId: blockedCardId,
			metadata: { blockingCardTitle: blockingCard.title, blockedCardTitle: blockedCard.title }
		});

		return dep;
	});

	const socketId = request.headers.get('X-Socket-ID');
	broadcast(params.boardId, 'card:updated', { cardId: blockingCardId, socketId });
	broadcast(params.boardId, 'card:updated', { cardId: blockedCardId, socketId });

	return json({ dependency }, { status: 201 });
};

// Delete a dependency
export const DELETE: RequestHandler = async ({ params, request, locals }) => {
	const tenant = locals.tenant;
	if (!tenant) throw error(400, 'Unknown tenant');

	const body = await request.json();
	const { id } = body;
	if (!id) throw error(400, 'Dependency id is required');

	const deleted = await withTenant(tenant.id, async (tx) => {
		await requireBoardEditor(tx, locals.user, params.boardId, tenant.id);

		const dep = await tx.cardDependency.findUnique({
			where: { id },
			include: {
				blockingCard: { select: { id: true, title: true, column: { select: { board: { select: { id: true, tenantId: true } } } } } },
				blockedCard: { select: { id: true, title: true } }
			}
		});
		if (!dep) throw error(404, 'Dependency not found');
		if (dep.blockingCard.column.board.id !== params.boardId) {
			throw error(404, 'Dependency not found');
		}

		await tx.cardDependency.delete({ where: { id } });

		await logActivity(tx, {
			boardId: params.boardId,
			userId: locals.user!.id,
			action: 'dependency.removed',
			cardId: dep.blockedCardId,
			metadata: { blockingCardTitle: dep.blockingCard.title, blockedCardTitle: dep.blockedCard.title }
		});

		return dep;
	});

	const socketId = request.headers.get('X-Socket-ID');
	broadcast(params.boardId, 'card:updated', { cardId: deleted.blockingCardId, socketId });
	broadcast(params.boardId, 'card:updated', { cardId: deleted.blockedCardId, socketId });

	return json({ ok: true });
};

// DFS cycle detection: would adding blockingCardId -> blockedCardId create a cycle?
// A cycle exists if we can reach blockingCardId by following dependencies from blockedCardId
async function detectCycle(tx: any, blockingCardId: string, blockedCardId: string): Promise<boolean> {
	const visited = new Set<string>();
	const stack = [blockedCardId];

	while (stack.length > 0) {
		const current = stack.pop()!;
		if (current === blockingCardId) return true;
		if (visited.has(current)) continue;
		visited.add(current);

		// Find all cards that `current` blocks
		const deps = await tx.cardDependency.findMany({
			where: { blockingCardId: current },
			select: { blockedCardId: true }
		});
		for (const dep of deps) {
			stack.push(dep.blockedCardId);
		}
	}

	return false;
}