import { createHash } from 'node:crypto';
import type { CrawledFile, Snapshot } from '../core/crawl.ts';
import { mirrorPath } from '../core/paths.ts';
import { connect, migrate, type Db } from './db.ts';

/**
 * The crawl store: generations, diffing, and full-text search.
 *
 * Cursors are crawl ids, and diffs are computed by comparing generations on
 * entity identity and a content digest — never on upstream timestamps. That is
 * a deliberate response to a measured quirk: `GET /course-rooms/{id}/board`
 * returns the *request time* as `updatedAt` for most elements, so a
 * timestamp-based cursor would report every board as changed on every crawl.
 * Identity diffing also gives deletions for free, which no timestamp scheme can.
 */

export type NodeKind = 'course' | 'board' | 'lesson' | 'task' | 'file';

export interface StoredNode {
	kind: NodeKind;
	nodeId: string;
	courseId: string | null;
	title: string;
	body: string;
	path: string;
	meta: Record<string, unknown>;
	digest: string;
}

export interface SearchResult {
	kind: NodeKind;
	nodeId: string;
	courseId: string | null;
	courseTitle: string;
	title: string;
	path: string;
	snippet: string;
	rank: number;
}

export interface DiffResult {
	added: StoredNode[];
	changed: StoredNode[];
	removed: { kind: NodeKind; nodeId: string; title: string; path: string }[];
}

export interface ManifestEntry {
	fileId: string;
	name: string;
	path: string;
	size: number;
	mimeType: string;
	courseId: string | null;
	courseTitle: string;
	status: 'added' | 'unchanged' | 'removed';
}

export class Store {
	private readonly db: Db;

	private constructor(db: Db) {
		this.db = db;
	}

	/**
	 * Connects and migrates. Returns undefined rather than throwing when the
	 * database is unreachable: the index is an accelerator, and a Pi that loses
	 * its database should get slower, not broken.
	 */
	static async open(connectionString: string | undefined): Promise<Store | undefined> {
		if (!connectionString) return undefined;
		try {
			const db = await connect({ connectionString });
			const ran = await migrate(db);
			if (ran.length > 0) console.log(`[schulcloud-mcp] applied migrations: ${ran.join(', ')}`);
			return new Store(db);
		} catch (error) {
			console.error(
				`[schulcloud-mcp] postgres unavailable (${error instanceof Error ? error.message : String(error)}); ` +
					'running without the index — search falls back to live crawls.',
			);
			return undefined;
		}
	}

	async close(): Promise<void> {
		await this.db.end().catch(() => {});
	}

	// --- generations -----------------------------------------------------

	async latestCrawlId(): Promise<number | undefined> {
		const { rows } = await this.db.query<{ id: string }>(
			`SELECT id FROM crawls WHERE status = 'ok' ORDER BY id DESC LIMIT 1`,
		);
		return rows[0] ? Number(rows[0].id) : undefined;
	}

	async oldestCrawlId(): Promise<number | undefined> {
		const { rows } = await this.db.query<{ id: string }>(
			`SELECT id FROM crawls WHERE status = 'ok' ORDER BY id ASC LIMIT 1`,
		);
		return rows[0] ? Number(rows[0].id) : undefined;
	}

	/**
	 * Turns a `since` value into a crawl id.
	 *
	 * Accepts a crawl id (the real cursor) or an ISO timestamp, resolved to the
	 * newest crawl at or before it. The timestamp form is a convenience for
	 * humans typing `--since yesterday`; correctness never depends on it.
	 */
	async resolveCursor(since: string): Promise<number | undefined> {
		if (/^\d+$/.test(since)) return Number(since);
		const date = new Date(since);
		if (Number.isNaN(date.getTime())) return undefined;
		const { rows } = await this.db.query<{ id: string }>(
			`SELECT id FROM crawls WHERE status = 'ok' AND finished_at <= $1 ORDER BY id DESC LIMIT 1`,
			[date.toISOString()],
		);
		return rows[0] ? Number(rows[0].id) : undefined;
	}

	/**
	 * Persists a snapshot as a new generation.
	 *
	 * A per-course crawl carries the other courses' rows forward from the
	 * previous generation, so every completed crawl is a *complete* picture and
	 * any two can be diffed directly. Without that, a partial crawl would look
	 * like a mass deletion.
	 */
	async saveSnapshot(snapshot: Snapshot, scope: string): Promise<number> {
		const client = await this.db.connect();
		try {
			await client.query('BEGIN');
			const { rows } = await client.query<{ id: string }>(
				`INSERT INTO crawls (scope, course_count, file_count) VALUES ($1, $2, $3) RETURNING id`,
				[scope, snapshot.courses.length, snapshot.files.length],
			);
			const crawlId = Number(rows[0]!.id);
			const previous = await this.latestCrawlIdIn(client);

			if (previous !== undefined && scope !== 'full') {
				// Carry forward everything the partial crawl did not look at.
				await client.query(
					`INSERT INTO nodes (crawl_id, kind, node_id, course_id, title, body, path, meta, digest)
					 SELECT $1, kind, node_id, course_id, title, body, path, meta, digest
					 FROM nodes WHERE crawl_id = $2 AND course_id IS DISTINCT FROM $3`,
					[crawlId, previous, scope],
				);
				await client.query(
					`INSERT INTO search_docs (crawl_id, kind, node_id, course_id, course_title, title, body, path)
					 SELECT $1, kind, node_id, course_id, course_title, title, body, path
					 FROM search_docs WHERE crawl_id = $2 AND course_id IS DISTINCT FROM $3`,
					[crawlId, previous, scope],
				);
			}

			const nodes = snapshotToNodes(snapshot);
			await insertNodes(client, crawlId, nodes);
			await insertSearchDocs(client, crawlId, nodes, snapshot);

			await client.query(`UPDATE crawls SET status = 'ok', finished_at = now() WHERE id = $1`, [crawlId]);
			await client.query('COMMIT');
			return crawlId;
		} catch (error) {
			await client.query('ROLLBACK').catch(() => {});
			throw error;
		} finally {
			client.release();
		}
	}

	private async latestCrawlIdIn(client: { query: Db['query'] }): Promise<number | undefined> {
		const { rows } = await client.query<{ id: string }>(
			`SELECT id FROM crawls WHERE status = 'ok' ORDER BY id DESC LIMIT 1`,
		);
		return rows[0] ? Number(rows[0].id) : undefined;
	}

	/** Entities added, changed or removed between two generations. */
	async diff(from: number, to: number): Promise<DiffResult> {
		const added = await this.db.query<NodeRow>(
			`SELECT n.* FROM nodes n
			 WHERE n.crawl_id = $2
			   AND NOT EXISTS (SELECT 1 FROM nodes o WHERE o.crawl_id = $1 AND o.kind = n.kind AND o.node_id = n.node_id)`,
			[from, to],
		);
		const changed = await this.db.query<NodeRow>(
			`SELECT n.* FROM nodes n
			 JOIN nodes o ON o.crawl_id = $1 AND o.kind = n.kind AND o.node_id = n.node_id
			 WHERE n.crawl_id = $2 AND o.digest IS DISTINCT FROM n.digest`,
			[from, to],
		);
		const removed = await this.db.query<NodeRow>(
			`SELECT o.* FROM nodes o
			 WHERE o.crawl_id = $1
			   AND NOT EXISTS (SELECT 1 FROM nodes n WHERE n.crawl_id = $2 AND n.kind = o.kind AND n.node_id = o.node_id)`,
			[from, to],
		);
		return {
			added: added.rows.map(toNode),
			changed: changed.rows.map(toNode),
			removed: removed.rows.map((row) => ({
				kind: row.kind as NodeKind,
				nodeId: row.node_id,
				title: row.title,
				path: row.path,
			})),
		};
	}

	// --- search ----------------------------------------------------------

	/**
	 * Full-text search over the newest generation.
	 *
	 * Two arms, merged: the `german` dictionary for stemmed matching, and
	 * trigram similarity for what stemming misses — German compounds mean
	 * "Datenschutz" does not stem-match inside "Datenschutzgrundverordnung",
	 * and that is the common case, not an edge case.
	 */
	async search(query: string, options: { limit?: number; kinds?: NodeKind[] } = {}): Promise<SearchResult[]> {
		const crawlId = await this.latestCrawlId();
		if (crawlId === undefined) return [];
		const limit = options.limit ?? 30;
		const kinds = options.kinds ?? null;

		const fts = await this.db.query<SearchRow>(
			`SELECT kind, node_id, course_id, course_title, title, path,
			        ts_rank(fts, q) AS rank,
			        ts_headline('german', coalesce(nullif(body, ''), title), q,
			                    'MaxWords=32, MinWords=8, MaxFragments=1, StartSel=**, StopSel=**') AS snippet
			   FROM search_docs, websearch_to_tsquery('german', $2) q
			  WHERE crawl_id = $1 AND fts @@ q AND ($3::text[] IS NULL OR kind = ANY($3))
			  ORDER BY rank DESC LIMIT $4`,
			[crawlId, query, kinds, limit],
		);

		const trgm = await this.db.query<SearchRow>(
			`SELECT kind, node_id, course_id, course_title, title, path,
			        similarity(title, $2) AS rank,
			        title AS snippet
			   FROM search_docs
			  WHERE crawl_id = $1 AND title %> $2 AND ($3::text[] IS NULL OR kind = ANY($3))
			  ORDER BY rank DESC LIMIT $4`,
			[crawlId, query, kinds, limit],
		);

		const seen = new Set<string>();
		const merged: SearchResult[] = [];
		for (const row of [...fts.rows, ...trgm.rows]) {
			const key = `${row.kind}:${row.node_id}`;
			if (seen.has(key)) continue;
			seen.add(key);
			merged.push({
				kind: row.kind as NodeKind,
				nodeId: row.node_id,
				courseId: row.course_id,
				courseTitle: row.course_title,
				title: row.title,
				path: row.path,
				snippet: (row.snippet ?? '').replace(/\s+/g, ' ').trim(),
				rank: Number(row.rank),
			});
		}
		return merged.sort((a, b) => b.rank - a.rank).slice(0, limit);
	}

	// --- files -----------------------------------------------------------

	/** File records in the newest generation, optionally diffed against a cursor. */
	async manifest(since?: number): Promise<{ crawlId: number; entries: ManifestEntry[] }> {
		const crawlId = await this.latestCrawlId();
		if (crawlId === undefined) return { crawlId: 0, entries: [] };

		const current = await this.db.query<NodeRow & { course_title: string }>(
			`SELECT n.*, coalesce(s.course_title, '') AS course_title
			   FROM nodes n LEFT JOIN search_docs s
			     ON s.crawl_id = n.crawl_id AND s.kind = n.kind AND s.node_id = n.node_id
			  WHERE n.crawl_id = $1 AND n.kind = 'file'`,
			[crawlId],
		);

		let previousIds = new Set<string>();
		if (since !== undefined) {
			const previous = await this.db.query<{ node_id: string }>(
				`SELECT node_id FROM nodes WHERE crawl_id = $1 AND kind = 'file'`,
				[since],
			);
			previousIds = new Set(previous.rows.map((row) => row.node_id));
		}

		const entries: ManifestEntry[] = current.rows.map((row) => {
			const meta = row.meta as { size?: number; mimeType?: string };
			return {
				fileId: row.node_id,
				name: row.title,
				path: row.path,
				size: Number(meta.size ?? 0),
				mimeType: String(meta.mimeType ?? 'application/octet-stream'),
				courseId: row.course_id,
				courseTitle: row.course_title,
				status: since === undefined ? 'added' : previousIds.has(row.node_id) ? 'unchanged' : 'added',
			};
		});

		if (since !== undefined) {
			const currentIds = new Set(current.rows.map((row) => row.node_id));
			const gone = await this.db.query<NodeRow>(
				`SELECT * FROM nodes WHERE crawl_id = $1 AND kind = 'file'`,
				[since],
			);
			for (const row of gone.rows) {
				if (currentIds.has(row.node_id)) continue;
				const meta = row.meta as { size?: number; mimeType?: string };
				entries.push({
					fileId: row.node_id,
					name: row.title,
					path: row.path,
					size: Number(meta.size ?? 0),
					mimeType: String(meta.mimeType ?? 'application/octet-stream'),
					courseId: row.course_id,
					courseTitle: '',
					status: 'removed',
				});
			}
		}

		return { crawlId, entries };
	}

	/** File ids in the newest generation that have no extracted text yet. */
	async filesNeedingText(): Promise<{ fileId: string; name: string; mimeType: string; size: number }[]> {
		const crawlId = await this.latestCrawlId();
		if (crawlId === undefined) return [];
		const { rows } = await this.db.query<{ node_id: string; title: string; meta: Record<string, unknown> }>(
			`SELECT n.node_id, n.title, n.meta FROM nodes n
			  WHERE n.crawl_id = $1 AND n.kind = 'file'
			    AND NOT EXISTS (SELECT 1 FROM file_texts f WHERE f.file_id = n.node_id AND f.extracted_at IS NOT NULL)`,
			[crawlId],
		);
		return rows.map((row) => ({
			fileId: row.node_id,
			name: row.title,
			mimeType: String((row.meta as { mimeType?: string }).mimeType ?? ''),
			size: Number((row.meta as { size?: number }).size ?? 0),
		}));
	}

	async recordFileText(entry: {
		fileId: string;
		name: string;
		mimeType: string;
		size: number;
		content: string | null;
		note: string;
		mirrorPath: string | null;
		mirrorSize: number | null;
	}): Promise<void> {
		await this.db.query(
			`INSERT INTO file_texts (file_id, name, mime_type, size, content, extract_note, extracted_at, mirror_path, mirror_size, mirrored_at)
			 VALUES ($1,$2,$3,$4,$5,$6, now(), $7,$8, CASE WHEN $7::text IS NULL THEN NULL ELSE now() END)
			 ON CONFLICT (file_id) DO UPDATE SET
			   content = EXCLUDED.content, extract_note = EXCLUDED.extract_note, extracted_at = now(),
			   mirror_path = COALESCE(EXCLUDED.mirror_path, file_texts.mirror_path),
			   mirror_size = COALESCE(EXCLUDED.mirror_size, file_texts.mirror_size),
			   mirrored_at = CASE WHEN EXCLUDED.mirror_path IS NULL THEN file_texts.mirrored_at ELSE now() END`,
			[
				entry.fileId,
				entry.name,
				entry.mimeType,
				entry.size,
				entry.content,
				entry.note,
				entry.mirrorPath,
				entry.mirrorSize,
			],
		);
		// Make the newly extracted text searchable in the current generation.
		await this.db.query(
			`UPDATE search_docs SET body = $2
			  WHERE kind = 'file' AND node_id = $1
			    AND crawl_id = (SELECT id FROM crawls WHERE status = 'ok' ORDER BY id DESC LIMIT 1)`,
			[entry.fileId, entry.content ?? ''],
		);
	}

	async mirrorEntry(fileId: string): Promise<{ path: string; size: number; name: string; mimeType: string } | undefined> {
		const { rows } = await this.db.query<{ mirror_path: string | null; mirror_size: string | null; name: string; mime_type: string | null }>(
			`SELECT mirror_path, mirror_size, name, mime_type FROM file_texts WHERE file_id = $1`,
			[fileId],
		);
		const row = rows[0];
		if (!row?.mirror_path) return undefined;
		return {
			path: row.mirror_path,
			size: Number(row.mirror_size ?? 0),
			name: row.name,
			mimeType: row.mime_type ?? 'application/octet-stream',
		};
	}

	async stats(): Promise<{ crawlId?: number; crawledAt?: string; nodes: number; files: number; extracted: number; mirrored: number }> {
		const crawlId = await this.latestCrawlId();
		if (crawlId === undefined) return { nodes: 0, files: 0, extracted: 0, mirrored: 0 };
		const { rows } = await this.db.query<{ crawled_at: string; nodes: string; files: string; extracted: string; mirrored: string }>(
			`SELECT (SELECT finished_at FROM crawls WHERE id = $1) AS crawled_at,
			        (SELECT count(*) FROM nodes WHERE crawl_id = $1) AS nodes,
			        (SELECT count(*) FROM nodes WHERE crawl_id = $1 AND kind = 'file') AS files,
			        (SELECT count(*) FROM file_texts WHERE extracted_at IS NOT NULL) AS extracted,
			        (SELECT count(*) FROM file_texts WHERE mirror_path IS NOT NULL) AS mirrored`,
			[crawlId],
		);
		const row = rows[0]!;
		return {
			crawlId,
			crawledAt: row.crawled_at,
			nodes: Number(row.nodes),
			files: Number(row.files),
			extracted: Number(row.extracted),
			mirrored: Number(row.mirrored),
		};
	}
}

// --- mapping -------------------------------------------------------------

interface NodeRow {
	kind: string;
	node_id: string;
	course_id: string | null;
	title: string;
	body: string;
	path: string;
	meta: Record<string, unknown>;
	digest: string;
}

interface SearchRow {
	kind: string;
	node_id: string;
	course_id: string | null;
	course_title: string;
	title: string;
	path: string;
	snippet: string | null;
	rank: string;
}

function toNode(row: NodeRow): StoredNode {
	return {
		kind: row.kind as NodeKind,
		nodeId: row.node_id,
		courseId: row.course_id,
		title: row.title,
		body: row.body,
		path: row.path,
		meta: row.meta,
		digest: row.digest,
	};
}

/** Content fingerprint — what "changed" means, independent of any timestamp. */
function digestOf(parts: unknown[]): string {
	return createHash('sha256').update(JSON.stringify(parts)).digest('hex').slice(0, 32);
}

export function snapshotToNodes(snapshot: Snapshot): StoredNode[] {
	const nodes: StoredNode[] = [];

	for (const course of snapshot.courses) {
		nodes.push({
			kind: 'course',
			nodeId: course.course.id,
			courseId: course.course.id,
			title: course.title,
			body: '',
			path: course.title,
			meta: { shortTitle: course.course.shortTitle, isLocked: course.course.isLocked ?? false },
			digest: digestOf([course.title, course.course.isLocked ?? false]),
		});

		for (const board of course.boards) {
			nodes.push({
				kind: 'board',
				nodeId: board.id,
				courseId: course.course.id,
				title: board.title,
				body: board.text,
				path: `${course.title}/${board.title}`,
				meta: { columns: board.board.columns.length, fileCount: board.board.fileCount },
				digest: digestOf([board.title, board.text]),
			});
		}

		for (const lesson of course.lessons) {
			nodes.push({
				kind: 'lesson',
				nodeId: lesson.id,
				courseId: course.course.id,
				title: lesson.name,
				body: lesson.text,
				path: `${course.title}/${lesson.name}`,
				meta: { hidden: lesson.hidden, materials: lesson.materials },
				digest: digestOf([lesson.name, lesson.text, lesson.hidden]),
			});
		}

		for (const task of course.tasks) {
			nodes.push({
				kind: 'task',
				nodeId: task.id,
				courseId: course.course.id,
				title: task.task.name,
				body: task.text,
				path: `${course.title}/${task.task.name}`,
				meta: { dueDate: task.task.dueDate ?? null, status: task.task.status },
				digest: digestOf([task.task.name, task.text, task.task.dueDate ?? null]),
			});
		}
	}

	for (const file of snapshot.files) {
		nodes.push(fileNode(file));
	}
	return nodes;
}

function fileNode(file: CrawledFile): StoredNode {
	const path = mirrorPath(file.at, file.record.name, file.record.id);
	return {
		kind: 'file',
		nodeId: file.record.id,
		courseId: file.at.courseId,
		title: file.record.name,
		body: '',
		path,
		meta: {
			size: file.record.size,
			mimeType: file.record.mimeType,
			parentType: file.parentType,
			parentId: file.parentId,
			securityCheckStatus: file.record.securityCheckStatus,
			at: file.at,
		},
		// File records are less immutable than they look: `PATCH /file/rename/{id}`
		// changes the name in place, keeping the id and the size, and teachers do
		// rename files. Leaving the name out made that invisible to what_changed —
		// the file simply reappeared under its new name with nothing reported.
		// Size still catches a record rewritten in place under the same name.
		digest: digestOf([file.record.id, file.record.name, file.record.size]),
	};
}

async function insertNodes(client: { query: Db['query'] }, crawlId: number, nodes: StoredNode[]): Promise<void> {
	const CHUNK = 200;
	for (let i = 0; i < nodes.length; i += CHUNK) {
		const batch = nodes.slice(i, i + CHUNK);
		const values: unknown[] = [];
		const tuples = batch.map((node, index) => {
			const base = index * 9;
			values.push(crawlId, node.kind, node.nodeId, node.courseId, node.title, node.body, node.path, node.meta, node.digest);
			return `($${base + 1},$${base + 2},$${base + 3},$${base + 4},$${base + 5},$${base + 6},$${base + 7},$${base + 8},$${base + 9})`;
		});
		await client.query(
			`INSERT INTO nodes (crawl_id, kind, node_id, course_id, title, body, path, meta, digest)
			 VALUES ${tuples.join(',')}
			 ON CONFLICT (crawl_id, kind, node_id) DO UPDATE SET
			   title = EXCLUDED.title, body = EXCLUDED.body, path = EXCLUDED.path,
			   meta = EXCLUDED.meta, digest = EXCLUDED.digest, course_id = EXCLUDED.course_id`,
			values,
		);
	}
}

async function insertSearchDocs(
	client: { query: Db['query'] },
	crawlId: number,
	nodes: StoredNode[],
	snapshot: Snapshot,
): Promise<void> {
	const courseTitles = new Map(snapshot.courses.map((course) => [course.course.id, course.title]));
	const CHUNK = 200;
	for (let i = 0; i < nodes.length; i += CHUNK) {
		const batch = nodes.slice(i, i + CHUNK);
		const values: unknown[] = [];
		const tuples = batch.map((node, index) => {
			const base = index * 8;
			values.push(
				crawlId,
				node.kind,
				node.nodeId,
				node.courseId,
				courseTitles.get(node.courseId ?? '') ?? '',
				node.title,
				node.body,
				node.path,
			);
			return `($${base + 1},$${base + 2},$${base + 3},$${base + 4},$${base + 5},$${base + 6},$${base + 7},$${base + 8})`;
		});
		await client.query(
			`INSERT INTO search_docs (crawl_id, kind, node_id, course_id, course_title, title, body, path)
			 VALUES ${tuples.join(',')}
			 ON CONFLICT (crawl_id, kind, node_id) DO UPDATE SET
			   course_title = EXCLUDED.course_title, title = EXCLUDED.title,
			   body = EXCLUDED.body, path = EXCLUDED.path`,
			values,
		);
	}
	// File bodies live in file_texts and survive re-crawls; pull them in so
	// already-extracted PDFs are searchable in this generation immediately.
	await client.query(
		`UPDATE search_docs s SET body = coalesce(f.content, '')
		   FROM file_texts f
		  WHERE s.crawl_id = $1 AND s.kind = 'file' AND s.node_id = f.file_id AND f.content IS NOT NULL`,
		[crawlId],
	);
}