/**
 * IndexingPipeline — orchestrates the full crawl → parse → store → embed
 * flow for a single repository indexing job (TRUEREF-0009).
 *
 * Atomicity guarantee:
 *   Old documents/snippets for changed files are deleted and replaced inside
 *   a single SQLite transaction. If anything fails after that transaction the
 *   already-committed data stays intact and the job is marked failed so
 *   callers can retry.
 *
 * Progress model:
 *   - Without embeddings: crawl+parse = 100 %
 *   - With embeddings   : crawl+parse = 80 %, embeddings = 20 %
 */

import { createHash } from 'node:crypto';
import type Database from 'better-sqlite3';
import type { Document, NewDocument, NewSnippet } from '$lib/types';
import type { crawl as GithubCrawlFn } from '$lib/server/crawler/github.crawler.js';
import type { LocalCrawler } from '$lib/server/crawler/local.crawler.js';
import type { EmbeddingService } from '$lib/server/embeddings/embedding.service.js';
import { RepositoryMapper } from '$lib/server/mappers/repository.mapper.js';
import { IndexingJob } from '$lib/server/models/indexing-job.js';
import { Repository, RepositoryEntity } from '$lib/server/models/repository.js';
import { parseFile } from '$lib/server/parser/index.js';
import { computeTrustScore } from '$lib/server/search/trust-score.js';
import { computeDiff } from './diff.js';

// ---------------------------------------------------------------------------
// Progress calculation
// ---------------------------------------------------------------------------

function calculateProgress(
	processedFiles: number,
	totalFiles: number,
	embeddingsDone: number,
	embeddingsTotal: number,
	hasEmbeddings: boolean
): number {
	if (totalFiles === 0) return 0;

	if (!hasEmbeddings) {
		return Math.round((processedFiles / totalFiles) * 100);
	}

	const parseProgress = (processedFiles / totalFiles) * 80;
	const embedProgress = embeddingsTotal > 0 ? (embeddingsDone / embeddingsTotal) * 20 : 0;
	return Math.round(parseProgress + embedProgress);
}

// ---------------------------------------------------------------------------
// SHA-256 helper
// ---------------------------------------------------------------------------

function sha256(content: string): string {
	return createHash('sha256').update(content, 'utf-8').digest('hex');
}

// ---------------------------------------------------------------------------
// IndexingPipeline
// ---------------------------------------------------------------------------

export class IndexingPipeline {
	constructor(
		private readonly db: Database.Database,
		private readonly githubCrawl: typeof GithubCrawlFn,
		private readonly localCrawler: LocalCrawler,
		private readonly embeddingService: EmbeddingService | null
	) {}

	// -------------------------------------------------------------------------
	// Public — run a job end to end
	// -------------------------------------------------------------------------

	async run(job: IndexingJob): Promise<void> {
		// better-sqlite3 raw queries return snake_case keys; Drizzle types use camelCase.
		// Accept both so the pipeline works when called from raw SQL contexts.
		const raw = job as unknown as Record<string, unknown>;
		const repositoryId = (job.repositoryId ?? raw['repository_id']) as string;
		const versionId = (job.versionId ?? raw['version_id'] ?? null) as string | null;

		// Rebuild a normalised job view for the rest of this method.
		const normJob = { ...job, repositoryId, versionId };

		this.updateJob(job.id, { status: 'running', startedAt: Math.floor(Date.now() / 1000) });

		try {
			const repo = this.getRepository(repositoryId);
			if (!repo) throw new Error(`Repository ${repositoryId} not found`);

			// Mark repo as actively indexing.
			this.updateRepo(repo.id, { state: 'indexing' });

			// ---- Stage 1: Crawl -------------------------------------------------
			const crawlResult = await this.crawl(repo, normJob);
			const totalFiles = crawlResult.totalFiles;

			this.updateJob(job.id, { totalFiles });

			// ---- Stage 2: Parse & diff ------------------------------------------
			// Load all existing documents for this repo so computeDiff can
			// classify every crawled file and detect deletions.
			const existingDocs = this.getExistingDocuments(repo.id, normJob.versionId);
			const diff = computeDiff(crawlResult.files, existingDocs);

			// Accumulate new documents/snippets; skip unchanged files.
			const newDocuments: NewDocument[] = [];
			const newSnippets: NewSnippet[] = [];
			const changedDocIds: string[] = [];

			// Schedule stale documents (modified + deleted) for deletion.
			for (const file of diff.modified) {
				const existing = existingDocs.find((d) => d.filePath === file.path);
				if (existing) changedDocIds.push(existing.id);
			}
			for (const filePath of diff.deleted) {
				const existing = existingDocs.find((d) => d.filePath === filePath);
				if (existing) changedDocIds.push(existing.id);
			}

			// Only parse and embed files that are new or have changed.
			const filesToProcess = [...diff.added, ...diff.modified];
			let processedFiles = diff.unchanged.length; // unchanged files count as processed

			// Report unchanged files as already processed so the progress bar
			// immediately reflects real work done (especially on incremental re-index
			// where most or all files are unchanged).
			if (processedFiles > 0) {
				const initialProgress = calculateProgress(
					processedFiles,
					totalFiles,
					0,
					0,
					this.embeddingService !== null
				);
				this.updateJob(job.id, { processedFiles, progress: initialProgress });
			}

			for (const [i, file] of filesToProcess.entries()) {
				const checksum = file.sha || sha256(file.content);

				// Create new document record.
				const documentId = crypto.randomUUID();
				const now = new Date();
				const newDoc: NewDocument = {
					id: documentId,
					repositoryId: repo.id,
					versionId: normJob.versionId ?? null,
					filePath: file.path,
					title: null,
					language: file.language,
					tokenCount: 0,
					checksum,
					indexedAt: now
				};

				// Parse into snippets.
				const snippets = parseFile(file, {
					repositoryId: repo.id,
					documentId,
					versionId: normJob.versionId ?? undefined
				});

				// Update document token count from snippet totals.
				const tokenCount = snippets.reduce((sum, s) => sum + (s.tokenCount ?? 0), 0);
				newDoc.tokenCount = tokenCount;

				newDocuments.push(newDoc);
				newSnippets.push(...snippets);

				// Count ALL files (including skipped unchanged ones) in progress.
				const totalProcessed = diff.unchanged.length + i + 1;
				const progress = calculateProgress(
					totalProcessed,
					totalFiles,
					0,
					0,
					this.embeddingService !== null
				);
				this.updateJob(job.id, { processedFiles: totalProcessed, progress });
			}

			// After the loop processedFiles should reflect the full count.
			processedFiles = diff.unchanged.length + filesToProcess.length;

			// ---- Stage 3: Atomic replacement ------------------------------------
			this.replaceSnippets(repo.id, changedDocIds, newDocuments, newSnippets);

			// ---- Stage 4: Embeddings (if provider is configured) ----------------
			if (this.embeddingService && newSnippets.length > 0) {
				const snippetIds = newSnippets.map((s) => s.id!);
				const embeddingsTotal = snippetIds.length;

				await this.embeddingService.embedSnippets(snippetIds, (done) => {
					const progress = calculateProgress(
						processedFiles,
						totalFiles,
						done,
						embeddingsTotal,
						true
					);
					this.updateJob(job.id, { progress });
				});
			}

			// ---- Stage 5: Update repository stats --------------------------------
			const stats = this.computeStats(repo.id);
			const freshRepo = this.getRepository(repo.id)!;
			const trustScore = computeTrustScore({
				...freshRepo,
				totalSnippets: stats.totalSnippets,
				totalTokens: stats.totalTokens,
				state: 'indexed'
			});

			this.updateRepo(repo.id, {
				state: 'indexed',
				totalSnippets: stats.totalSnippets,
				totalTokens: stats.totalTokens,
				trustScore,
				lastIndexedAt: Math.floor(Date.now() / 1000)
			});

			this.updateJob(job.id, {
				status: 'done',
				progress: 100,
				completedAt: Math.floor(Date.now() / 1000)
			});
		} catch (error) {
			const message = error instanceof Error ? error.message : String(error);
			console.error(`[IndexingPipeline] Job ${job.id} failed: ${message}`);

			this.updateJob(job.id, {
				status: 'failed',
				error: message,
				completedAt: Math.floor(Date.now() / 1000)
			});

			// Restore repo to error state but preserve any existing indexed data.
			this.updateRepo(repositoryId, { state: 'error' });

			throw error;
		}
	}

	// -------------------------------------------------------------------------
	// Private — crawl
	// -------------------------------------------------------------------------

	private async crawl(
		repo: Repository,
		job: IndexingJob
	): Promise<{ files: Array<{ path: string; content: string; sha: string; size: number; language: string }>; totalFiles: number }> {
		if (repo.source === 'github') {
			// Parse owner/repo from the canonical ID: "/owner/repo"
			const parts = repo.id.replace(/^\//, '').split('/');
			const owner = parts[0];
			const repoName = parts[1];

			if (!owner || !repoName) {
				throw new Error(`Cannot parse GitHub owner/repo from id: ${repo.id}`);
			}

			const result = await this.githubCrawl({
				owner,
				repo: repoName,
				ref: repo.branch ?? undefined,
				token: repo.githubToken ?? undefined
			});

			return { files: result.files, totalFiles: result.totalFiles };
		} else {
			// Local filesystem crawl.
			const result = await this.localCrawler.crawl({
				rootPath: repo.sourceUrl,
				ref: repo.branch !== 'main' ? (repo.branch ?? undefined) : undefined
			});

			return { files: result.files, totalFiles: result.totalFiles };
		}
	}

	// -------------------------------------------------------------------------
	// Private — atomic snippet replacement
	// -------------------------------------------------------------------------

	private replaceSnippets(
		_repositoryId: string,
		changedDocIds: string[],
		newDocuments: NewDocument[],
		newSnippets: NewSnippet[]
	): void {
		const insertDoc = this.db.prepare(
			`INSERT INTO documents
         (id, repository_id, version_id, file_path, title, language,
          token_count, checksum, indexed_at)
       VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`
		);

		const insertSnippet = this.db.prepare(
			`INSERT INTO snippets
         (id, document_id, repository_id, version_id, type, title,
          content, language, breadcrumb, token_count, created_at)
       VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
		);

		this.db.transaction(() => {
			// Delete stale documents (cascade deletes their snippets via FK).
			if (changedDocIds.length > 0) {
				const placeholders = changedDocIds.map(() => '?').join(',');
				this.db
					.prepare(`DELETE FROM documents WHERE id IN (${placeholders})`)
					.run(...changedDocIds);
			}

			// Insert new documents.
			for (const doc of newDocuments) {
				const indexedAtSeconds =
					doc.indexedAt instanceof Date
						? Math.floor(doc.indexedAt.getTime() / 1000)
						: Math.floor(Date.now() / 1000);

				insertDoc.run(
					doc.id,
					doc.repositoryId,
					doc.versionId ?? null,
					doc.filePath,
					doc.title ?? null,
					doc.language ?? null,
					doc.tokenCount ?? 0,
					doc.checksum,
					indexedAtSeconds
				);
			}

			// Insert new snippets.
			for (const snippet of newSnippets) {
				const createdAtSeconds =
					snippet.createdAt instanceof Date
						? Math.floor(snippet.createdAt.getTime() / 1000)
						: Math.floor(Date.now() / 1000);

				insertSnippet.run(
					snippet.id,
					snippet.documentId,
					snippet.repositoryId,
					snippet.versionId ?? null,
					snippet.type,
					snippet.title ?? null,
					snippet.content,
					snippet.language ?? null,
					snippet.breadcrumb ?? null,
					snippet.tokenCount ?? 0,
					createdAtSeconds
				);
			}
		})();
	}

	// -------------------------------------------------------------------------
	// Private — stats
	// -------------------------------------------------------------------------

	private computeStats(repositoryId: string): { totalSnippets: number; totalTokens: number } {
		const row = this.db
			.prepare<[string], { total_snippets: number; total_tokens: number }>(
				`SELECT COUNT(*) as total_snippets,
                COALESCE(SUM(token_count), 0) as total_tokens
         FROM snippets WHERE repository_id = ?`
			)
			.get(repositoryId);

		return {
			totalSnippets: row?.total_snippets ?? 0,
			totalTokens: row?.total_tokens ?? 0
		};
	}

	// -------------------------------------------------------------------------
	// Private — DB helpers
	// -------------------------------------------------------------------------

	private getExistingDocuments(repositoryId: string, versionId: string | null): Document[] {
		if (versionId) {
			return this.db
				.prepare<[string, string], Document>(
					`SELECT id, repository_id as repositoryId, version_id as versionId,
                  file_path as filePath, title, language, token_count as tokenCount,
                  checksum, indexed_at as indexedAt
           FROM documents WHERE repository_id = ? AND version_id = ?`
				)
				.all(repositoryId, versionId) as Document[];
		}
		return this.db
			.prepare<[string], Document>(
				`SELECT id, repository_id as repositoryId, version_id as versionId,
                file_path as filePath, title, language, token_count as tokenCount,
                checksum, indexed_at as indexedAt
         FROM documents WHERE repository_id = ? AND version_id IS NULL`
			)
			.all(repositoryId) as Document[];
	}

	private getRepository(id: string): Repository | null {
		const raw = this.db
			.prepare<[string], RepositoryEntity>(`SELECT * FROM repositories WHERE id = ?`)
			.get(id);
		return raw ? RepositoryMapper.fromEntity(new RepositoryEntity(raw)) : null;
	}

	private updateJob(id: string, fields: Record<string, unknown>): void {
		const sets = Object.keys(fields)
			.map((k) => `${toSnake(k)} = ?`)
			.join(', ');
		const values = [...Object.values(fields), id];
		this.db.prepare(`UPDATE indexing_jobs SET ${sets} WHERE id = ?`).run(...values);
	}

	private updateRepo(id: string, fields: Record<string, unknown>): void {
		const now = Math.floor(Date.now() / 1000);
		const allFields = { ...fields, updatedAt: now };
		const sets = Object.keys(allFields)
			.map((k) => `${toSnake(k)} = ?`)
			.join(', ');
		const values = [...Object.values(allFields), id];
		this.db.prepare(`UPDATE repositories SET ${sets} WHERE id = ?`).run(...values);
	}
}

// ---------------------------------------------------------------------------
// Utility
// ---------------------------------------------------------------------------

/** Convert camelCase to snake_case for DB column mapping. */
function toSnake(key: string): string {
	return key.replace(/[A-Z]/g, (c) => `_${c.toLowerCase()}`);
}