/**
 * SearchService — FTS5-backed full-text search over snippets and repositories.
 *
 * Implements keyword search using SQLite's built-in BM25 ranking via the
 * `bm25()` function exposed by FTS5 virtual tables. Library search uses
 * LIKE-based matching on the `repositories` table with a composite relevance
 * score.
 */

import type Database from 'better-sqlite3';
import type { Repository, RepositoryVersion, Snippet } from '$lib/types';
import { preprocessQuery } from './query-preprocessor';

// ---------------------------------------------------------------------------
// Public interface types
// ---------------------------------------------------------------------------

export interface SnippetSearchOptions {
	repositoryId: string;
	versionId?: string;
	type?: 'code' | 'info';
	/** Number of results to return. Default: 20. */
	limit?: number;
	/** Number of results to skip. Default: 0. */
	offset?: number;
}

export interface SnippetSearchResult {
	snippet: Snippet;
	/** BM25 rank — negative value; lower (more negative) = more relevant. */
	score: number;
	repository: Pick<Repository, 'id' | 'title'>;
}

export interface LibrarySearchOptions {
	libraryName: string;
	/** Semantic relevance hint (reserved for future hybrid use). */
	query?: string;
	/** Number of results to return. Default: 10. */
	limit?: number;
}

export interface LibrarySearchResult {
	repository: Repository;
	versions: RepositoryVersion[];
	/** Composite relevance score. Higher = more relevant. */
	score: number;
}

// ---------------------------------------------------------------------------
// Raw DB row types
// ---------------------------------------------------------------------------

/** Raw row returned by the snippet FTS query (snake_case column names). */
interface RawSnippetRow {
	id: string;
	document_id: string;
	repository_id: string;
	version_id: string | null;
	type: 'code' | 'info';
	title: string | null;
	content: string;
	language: string | null;
	breadcrumb: string | null;
	token_count: number | null;
	created_at: number;
	repo_id: string;
	repo_title: string;
	score: number;
}

/** Raw row returned by the library search query. */
interface RawRepoRow {
	id: string;
	title: string;
	description: string | null;
	source: 'github' | 'local';
	source_url: string;
	branch: string | null;
	state: 'pending' | 'indexing' | 'indexed' | 'error';
	total_snippets: number | null;
	total_tokens: number | null;
	trust_score: number | null;
	benchmark_score: number | null;
	stars: number | null;
	github_token: string | null;
	last_indexed_at: number | null;
	created_at: number;
	updated_at: number;
	exact_match: number;
	prefix_match: number;
	desc_match: number;
	snippet_score: number;
	trust_component: number;
}

/** Raw row returned by the version query. */
interface RawVersionRow {
	id: string;
	repository_id: string;
	tag: string;
	title: string | null;
	state: 'pending' | 'indexing' | 'indexed' | 'error';
	total_snippets: number | null;
	indexed_at: number | null;
	created_at: number;
}

// ---------------------------------------------------------------------------
// Mappers: raw DB rows → domain types
// ---------------------------------------------------------------------------

function mapSnippet(row: RawSnippetRow): Snippet {
	return {
		id: row.id,
		documentId: row.document_id,
		repositoryId: row.repository_id,
		versionId: row.version_id,
		type: row.type,
		title: row.title,
		content: row.content,
		language: row.language,
		breadcrumb: row.breadcrumb,
		tokenCount: row.token_count,
		createdAt: new Date(row.created_at * 1000)
	};
}

function mapRepository(row: RawRepoRow): Repository {
	return {
		id: row.id,
		title: row.title,
		description: row.description,
		source: row.source,
		sourceUrl: row.source_url,
		branch: row.branch,
		state: row.state,
		totalSnippets: row.total_snippets,
		totalTokens: row.total_tokens,
		trustScore: row.trust_score,
		benchmarkScore: row.benchmark_score,
		stars: row.stars,
		githubToken: row.github_token,
		lastIndexedAt: row.last_indexed_at ? new Date(row.last_indexed_at * 1000) : null,
		createdAt: new Date(row.created_at * 1000),
		updatedAt: new Date(row.updated_at * 1000)
	};
}

function mapVersion(row: RawVersionRow): RepositoryVersion {
	return {
		id: row.id,
		repositoryId: row.repository_id,
		tag: row.tag,
		title: row.title,
		state: row.state,
		totalSnippets: row.total_snippets,
		indexedAt: row.indexed_at ? new Date(row.indexed_at * 1000) : null,
		createdAt: new Date(row.created_at * 1000)
	};
}

// ---------------------------------------------------------------------------
// SearchService
// ---------------------------------------------------------------------------

export class SearchService {
	constructor(private readonly db: Database.Database) {}

	// -------------------------------------------------------------------------
	// searchSnippets
	// -------------------------------------------------------------------------

	/**
	 * Search snippets within a repository using FTS5 BM25 ranking.
	 *
	 * The query is preprocessed (whitespace normalization + prefix wildcard)
	 * before being passed to the MATCH expression. Results are ordered by BM25
	 * score ascending (lower = more relevant).
	 */
	searchSnippets(query: string, options: SnippetSearchOptions): SnippetSearchResult[] {
		const { repositoryId, versionId, type, limit = 20, offset = 0 } = options;

		const processedQuery = preprocessQuery(query);
		if (!processedQuery) return [];

		// Build the WHERE clause dynamically based on optional filters.
		const conditions: string[] = [
			'snippets_fts MATCH ?',
			's.repository_id = ?'
		];
		const params: unknown[] = [processedQuery, repositoryId];

		if (versionId !== undefined) {
			conditions.push('s.version_id = ?');
			params.push(versionId);
		}

		if (type !== undefined) {
			conditions.push('s.type = ?');
			params.push(type);
		}

		params.push(limit, offset);

		const sql = `
      SELECT
        s.id,
        s.document_id,
        s.repository_id,
        s.version_id,
        s.type,
        s.title,
        s.content,
        s.language,
        s.breadcrumb,
        s.token_count,
        s.created_at,
        r.id   AS repo_id,
        r.title AS repo_title,
        bm25(snippets_fts) AS score
      FROM snippets_fts
      JOIN snippets s ON s.rowid = snippets_fts.rowid
      JOIN repositories r ON r.id = s.repository_id
      WHERE ${conditions.join(' AND ')}
      ORDER BY score ASC
      LIMIT ? OFFSET ?
    `;

		const rows = this.db.prepare(sql).all(...params) as RawSnippetRow[];

		return rows.map((row) => ({
			snippet: mapSnippet(row),
			score: row.score,
			repository: { id: row.repo_id, title: row.repo_title }
		}));
	}

	// -------------------------------------------------------------------------
	// searchRepositories
	// -------------------------------------------------------------------------

	/**
	 * Search repositories by library name using LIKE-based matching.
	 *
	 * Applies a composite scoring model:
	 * - Exact title match  : 100 pts
	 * - Prefix title match : 50 pts
	 * - Description match  : 20 pts
	 * - Snippet density    : total_snippets / 100
	 * - Trust score        : trust_score * 10
	 */
	searchRepositories(options: LibrarySearchOptions): LibrarySearchResult[] {
		const { libraryName, limit = 10 } = options;

		const rows = this.db
			.prepare(
				`
      SELECT r.*,
        CASE WHEN LOWER(r.title) = LOWER(?)       THEN 100 ELSE 0 END AS exact_match,
        CASE WHEN LOWER(r.title) LIKE LOWER(?)    THEN 50  ELSE 0 END AS prefix_match,
        CASE WHEN LOWER(r.description) LIKE LOWER(?) THEN 20 ELSE 0 END AS desc_match,
        (COALESCE(r.total_snippets, 0) / 100.0)  AS snippet_score,
        COALESCE(r.trust_score, 0) * 10           AS trust_component
      FROM repositories r
      WHERE r.state = 'indexed'
        AND (
          LOWER(r.title)       LIKE LOWER(?)
          OR LOWER(r.id)       LIKE LOWER(?)
          OR LOWER(r.description) LIKE LOWER(?)
        )
      ORDER BY (exact_match + prefix_match + desc_match + snippet_score + trust_component) DESC
      LIMIT ?
    `
			)
			.all(
				libraryName, // exact_match
				`${libraryName}%`, // prefix_match
				`%${libraryName}%`, // desc_match
				`%${libraryName}%`, // WHERE title LIKE
				`%${libraryName}%`, // WHERE id LIKE
				`%${libraryName}%`, // WHERE description LIKE
				limit
			) as RawRepoRow[];

		return rows.map((row) => {
			const repository = mapRepository(row);
			const compositeScore =
				row.exact_match + row.prefix_match + row.desc_match + row.snippet_score + row.trust_component;
			return {
				repository,
				versions: this.getVersions(row.id),
				score: compositeScore
			};
		});
	}

	// -------------------------------------------------------------------------
	// Private helpers
	// -------------------------------------------------------------------------

	private getVersions(repositoryId: string): RepositoryVersion[] {
		const rows = this.db
			.prepare(
				`SELECT * FROM repository_versions WHERE repository_id = ? ORDER BY created_at DESC`
			)
			.all(repositoryId) as RawVersionRow[];
		return rows.map(mapVersion);
	}
}