/**
 * EmbeddingService — batches embedding requests and persists results to
 * the snippet_embeddings table.
 */

import type Database from 'better-sqlite3';
import type { EmbeddingProvider } from './provider.js';
import { SqliteVecStore } from '$lib/server/search/sqlite-vec.store.js';
import {
	upsertEmbeddings,
	type PersistedEmbedding
} from '$lib/server/pipeline/write-operations.js';

interface SnippetRow {
	id: string;
	title: string | null;
	breadcrumb: string | null;
	content: string;
}

const BATCH_SIZE = 50;
const TEXT_MAX_CHARS = 2048;

export class EmbeddingService {
	private readonly sqliteVecStore: SqliteVecStore;

	constructor(
		private readonly db: Database.Database,
		private readonly provider: EmbeddingProvider,
		private readonly profileId: string = 'local-default',
		private readonly persistenceDelegate?: {
			persistEmbeddings?: (embeddings: PersistedEmbedding[]) => Promise<void>;
		}
	) {
		this.sqliteVecStore = new SqliteVecStore(db);
	}

	findSnippetIdsMissingEmbeddings(repositoryId: string, versionId: string | null): string[] {
		if (versionId) {
			const rows = this.db
				.prepare<[string, string, string], { id: string }>(
					`SELECT snippets.id
					 FROM snippets
					 LEFT JOIN snippet_embeddings
					   ON snippet_embeddings.snippet_id = snippets.id
					  AND snippet_embeddings.profile_id = ?
					 WHERE snippets.repository_id = ?
					   AND snippets.version_id = ?
					   AND snippet_embeddings.snippet_id IS NULL
					 ORDER BY snippets.id`
				)
				.all(this.profileId, repositoryId, versionId);

			return rows.map((row) => row.id);
		}

		const rows = this.db
			.prepare<[string, string], { id: string }>(
				`SELECT snippets.id
				 FROM snippets
				 LEFT JOIN snippet_embeddings
				   ON snippet_embeddings.snippet_id = snippets.id
				  AND snippet_embeddings.profile_id = ?
				 WHERE snippets.repository_id = ?
				   AND snippets.version_id IS NULL
				   AND snippet_embeddings.snippet_id IS NULL
				 ORDER BY snippets.id`
			)
			.all(this.profileId, repositoryId);

		return rows.map((row) => row.id);
	}

	/**
	 * Embed the given snippet IDs and store the results in snippet_embeddings.
	 *
	 * Only snippets that actually exist in the database are processed.
	 * Results are upserted (INSERT OR REPLACE) so re-embedding is idempotent.
	 *
	 * @param snippetIds - Array of snippet UUIDs to embed.
	 * @param onProgress - Optional callback invoked after each batch with
	 *                     (completedCount, totalCount).
	 */
	async embedSnippets(
		snippetIds: string[],
		onProgress?: (done: number, total: number) => void
	): Promise<void> {
		if (snippetIds.length === 0) return;

		const placeholders = snippetIds.map(() => '?').join(',');
		const snippets = this.db
			.prepare<
				string[],
				SnippetRow
			>(`SELECT id, title, breadcrumb, content FROM snippets WHERE id IN (${placeholders})`)
			.all(...snippetIds);

		if (snippets.length === 0) return;

		const texts = snippets.map((s) =>
			[s.title, s.breadcrumb, s.content].filter(Boolean).join('\n').slice(0, TEXT_MAX_CHARS)
		);

		for (let i = 0; i < snippets.length; i += BATCH_SIZE) {
			const batchSnippets = snippets.slice(i, i + BATCH_SIZE);
			const batchTexts = texts.slice(i, i + BATCH_SIZE);

			const embeddings = await this.provider.embed(batchTexts);
			const persistedEmbeddings: PersistedEmbedding[] = batchSnippets.map((snippet, index) => {
				const embedding = embeddings[index];
				return {
					snippetId: snippet.id,
					profileId: this.profileId,
					model: embedding.model,
					dimensions: embedding.dimensions,
					embedding: Buffer.from(
						embedding.values.buffer,
						embedding.values.byteOffset,
						embedding.values.byteLength
					)
				};
			});

			if (this.persistenceDelegate?.persistEmbeddings) {
				await this.persistenceDelegate.persistEmbeddings(persistedEmbeddings);
			} else {
				upsertEmbeddings(this.db, persistedEmbeddings);
			}

			onProgress?.(Math.min(i + BATCH_SIZE, snippets.length), snippets.length);
		}
	}

	/**
	 * Retrieve a stored embedding for a snippet as a Float32Array.
	 * Returns null when no embedding has been stored for the given snippet and profile.
	 *
	 * @param snippetId - Snippet UUID
	 * @param profileId - Embedding profile ID (default: 'local-default')
	 */
	getEmbedding(snippetId: string, profileId: string = 'local-default'): Float32Array | null {
		const row = this.db
			.prepare<
				[string, string],
				{ embedding: Buffer; dimensions: number }
			>(`SELECT embedding, dimensions FROM snippet_embeddings WHERE snippet_id = ? AND profile_id = ?`)
			.get(snippetId, profileId);

		if (!row) return null;

		return new Float32Array(row.embedding.buffer, row.embedding.byteOffset, row.dimensions);
	}
}