/**
 * 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, randomUUID } from 'node:crypto';
import type Database from 'better-sqlite3';
import type { Document, NewDocument, NewSnippet, TrueRefConfig, IndexingStage } 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 '$lib/server/models/repository.js';
import { SqliteVecStore } from '$lib/server/search/sqlite-vec.store.js';
import { resolveConfig, type ParsedConfig } from '$lib/server/config/config-parser.js';
import { parseFile } from '$lib/server/parser/index.js';
import { computeTrustScore } from '$lib/server/search/trust-score.js';
import { computeDiff } from './diff.js';
import { buildDifferentialPlan, type DifferentialPlan } from './differential-strategy.js';
import {
	cloneFromAncestor as cloneFromAncestorInDatabase,
	replaceSnippets as replaceSnippetsInDatabase,
	updateRepo as updateRepoInDatabase,
	updateVersion as updateVersionInDatabase,
	type CloneFromAncestorRequest
} from './write-operations.js';
import type { SerializedFields } from './worker-types.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 {
	private readonly sqliteVecStore: SqliteVecStore;

	constructor(
		private readonly db: Database.Database,
		private readonly githubCrawl: typeof GithubCrawlFn,
		private readonly localCrawler: LocalCrawler,
		private readonly embeddingService: EmbeddingService | null,
		private readonly writeDelegate?: {
			persistJobUpdates?: boolean;
			replaceSnippets?: (
				changedDocIds: string[],
				newDocuments: NewDocument[],
				newSnippets: NewSnippet[]
			) => Promise<void>;
			cloneFromAncestor?: (request: CloneFromAncestorRequest) => Promise<void>;
			updateRepo?: (repositoryId: string, fields: SerializedFields) => Promise<void>;
			updateVersion?: (versionId: string, fields: SerializedFields) => Promise<void>;
			upsertRepoConfig?: (
				repositoryId: string,
				versionId: string | null,
				rules: string[]
			) => Promise<void>;
		}
	) {
		this.sqliteVecStore = new SqliteVecStore(db);
	}

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

	async run(
		job: IndexingJob,
		onStageChange?: (
			stage: IndexingStage,
			detail?: string,
			progress?: number,
			processedFiles?: number,
			totalFiles?: number
		) => void
	): 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 };

		// Helper to report stage transitions and invoke optional callback.
		const reportStage = (
			stage: IndexingStage,
			detail?: string,
			progress?: number,
			processed?: number,
			total?: number
		) => {
			this.updateJob(job.id, { stage, stageDetail: detail ?? null });
			onStageChange?.(stage, detail, progress, processed, total);
		};

		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.
			await this.updateRepo(repo.id, { state: 'indexing' });
			if (normJob.versionId) {
				await this.updateVersion(normJob.versionId, { state: 'indexing' });
			}

			const versionTag = normJob.versionId ? this.getVersionTag(normJob.versionId) : undefined;

			// ---- Stage 0: Differential strategy (TRUEREF-0021) ----------------------
			// When indexing a tagged version, check if we can inherit unchanged files
			// from an already-indexed ancestor version instead of crawling everything.
			let differentialPlan: DifferentialPlan | null = null;
			if (normJob.versionId && versionTag) {
				reportStage('differential');
				differentialPlan = await buildDifferentialPlan({
					repo,
					targetTag: versionTag,
					db: this.db
				}).catch((err) => {
					console.warn(
						`[IndexingPipeline] Differential plan failed, falling back to full crawl: ${err instanceof Error ? err.message : String(err)}`
					);
					return null;
				});
			}

			// If a differential plan exists, clone unchanged files from ancestor.
			if (differentialPlan && differentialPlan.unchangedPaths.size > 0) {
				reportStage('cloning');
				await this.cloneFromAncestor({
					ancestorVersionId: differentialPlan.ancestorVersionId,
					targetVersionId: normJob.versionId!,
					repositoryId: repo.id,
					unchangedPaths: [...differentialPlan.unchangedPaths]
				});
				console.info(
					`[IndexingPipeline] Differential indexing: cloned ${differentialPlan.unchangedPaths.size} unchanged files from ${differentialPlan.ancestorTag}`
				);
			}

			// ---- Stage 1: Crawl -------------------------------------------------
			// Pass changedPaths as allowlist so crawl only fetches/returns changed files.
			reportStage('crawling');
			const crawlAllowedPaths = differentialPlan ? differentialPlan.changedPaths : undefined;
			const crawlResult = await this.crawl(repo, versionTag, crawlAllowedPaths);

			// Resolve trueref.json / context7.json configuration.
			// Prefer the pre-parsed config carried in the CrawlResult (set by
			// LocalCrawler so it is available even when a `folders` allowlist
			// excludes the repo root and trueref.json never appears in files[]).
			// Fall back to locating the file in crawlResult.files for GitHub crawls
			// which do not yet populate CrawlResult.config.
			let parsedConfig: ReturnType<typeof resolveConfig> | null = null;
			if (crawlResult.config) {
				// Config was pre-parsed by the crawler — wrap it in a ParsedConfig
				// shell so the rest of the pipeline can use it uniformly.
				parsedConfig = {
					config: crawlResult.config,
					source: 'trueref.json',
					warnings: []
				} satisfies ParsedConfig;
			} else {
				const configFile = crawlResult.files.find(
					(f) => f.path === 'trueref.json' || f.path === 'context7.json'
				);
				parsedConfig = configFile
					? resolveConfig([{ filename: configFile.path, content: configFile.content }])
					: null;
			}
			const excludeFiles: string[] = parsedConfig?.config.excludeFiles ?? [];

			// Filter out excluded files before diff computation.
			const filteredFiles =
				excludeFiles.length > 0
					? crawlResult.files.filter(
							(f) =>
								!excludeFiles.some((pattern) =>
									IndexingPipeline.matchesExcludePattern(f.path, pattern)
								)
						)
					: crawlResult.files;

			const totalFiles = filteredFiles.length;
			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);

			// Exclude files that were cloned from the ancestor — they are not candidates
			// for deletion or re-processing (computeDiff must not see them in existingDocs).
			const clonedPaths = differentialPlan?.unchangedPaths ?? new Set<string>();
			const existingDocsForDiff =
				clonedPaths.size > 0
					? existingDocs.filter((d) => !clonedPaths.has(d.filePath))
					: existingDocs;

			const diff = computeDiff(filteredFiles, existingDocsForDiff);

			// 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 = existingDocsForDiff.find((d) => d.filePath === file.path);
				if (existing) changedDocIds.push(existing.id);
			}
			for (const filePath of diff.deleted) {
				const existing = existingDocsForDiff.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 });
			}

			// Yield the event loop and flush progress every N files.
			// Lower = more responsive UI; higher = less overhead.
			const YIELD_EVERY = 20;

			reportStage('parsing', `0 / ${totalFiles} files`);

			for (const [i, file] of filesToProcess.entries()) {
				// Yield the Node.js event loop periodically so the HTTP server can
				// handle incoming requests (navigation, polling) between file parses.
				// Without this, the synchronous parse + SQLite work blocks the thread
				// entirely and the UI becomes unresponsive during indexing.
				if (i > 0 && i % YIELD_EVERY === 0) {
					await new Promise<void>((resolve) => setImmediate(resolve));
				}

				const checksum = file.sha || sha256(file.content);

				// Create new document record.
				const documentId = 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);

				// Write progress to the DB only on yield boundaries or the final file.
				// Avoids a synchronous SQLite UPDATE on every single iteration.
				const totalProcessed = diff.unchanged.length + i + 1;
				const isLast = i === filesToProcess.length - 1;
				if (isLast || i % YIELD_EVERY === YIELD_EVERY - 1) {
					const progress = calculateProgress(
						totalProcessed,
						totalFiles,
						0,
						0,
						this.embeddingService !== null
					);
					this.updateJob(job.id, { processedFiles: totalProcessed, progress });
					reportStage(
						'parsing',
						`${totalProcessed} / ${totalFiles} files`,
						progress,
						totalProcessed,
						totalFiles
					);
				}
			}

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

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

			// ---- Stage 4: Embeddings (if provider is configured) ----------------
			if (this.embeddingService) {
				reportStage('embedding');
				const snippetIds = this.embeddingService.findSnippetIdsMissingEmbeddings(
					repo.id,
					normJob.versionId
				);

				if (snippetIds.length === 0) {
					// No missing embeddings for the active profile; parsing progress is final.
				} else {
					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'
			});

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

			if (normJob.versionId) {
				const versionStats = this.computeVersionStats(normJob.versionId);
				await this.updateVersion(normJob.versionId, {
					state: 'indexed',
					totalSnippets: versionStats.totalSnippets,
					indexedAt: Math.floor(Date.now() / 1000)
				});
			}

			// ---- Stage 6: Persist rules from config ----------------------------
			if (parsedConfig?.config.rules?.length) {
				if (!normJob.versionId) {
					// Main-branch job: write the repo-wide entry only.
					await this.upsertRepoConfig(repo.id, null, parsedConfig.config.rules);
				} else {
					// Version job: write only the version-specific entry.
					// Writing to the NULL row here would overwrite repo-wide rules
					// with whatever the last-indexed version happened to carry.
					await this.upsertRepoConfig(repo.id, normJob.versionId, parsedConfig.config.rules);
				}
			}

			reportStage('done');
			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}`);

			reportStage('failed');
			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.
			await this.updateRepo(repositoryId, { state: 'error' });
			if (normJob.versionId) {
				await this.updateVersion(normJob.versionId, { state: 'error' });
			}

			throw error;
		}
	}

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

	private async crawl(
		repo: Repository,
		ref?: string,
		allowedPaths?: Set<string>
	): Promise<{
		files: Array<{ path: string; content: string; sha: string; size: number; language: string }>;
		totalFiles: number;
		/** Pre-parsed trueref.json / context7.json, or undefined when absent. */
		config?: TrueRefConfig;
	}> {
		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: ref ?? repo.branch ?? undefined,
				token: repo.githubToken ?? undefined
			});

			// Apply allowedPaths filter for differential indexing.
			const githubFinalFiles =
				allowedPaths && allowedPaths.size > 0
					? result.files.filter((f) => allowedPaths.has(f.path))
					: result.files;
			return { files: githubFinalFiles, totalFiles: result.totalFiles };
		} else {
			// Local filesystem crawl.
			const result = await this.localCrawler.crawl({
				rootPath: repo.sourceUrl,
				ref: ref ?? (repo.branch !== 'main' ? (repo.branch ?? undefined) : undefined)
			});

			// Apply allowedPaths filter for differential indexing.
			const localFinalFiles =
				allowedPaths && allowedPaths.size > 0
					? result.files.filter((f) => allowedPaths.has(f.path))
					: result.files;
			return { files: localFinalFiles, totalFiles: result.totalFiles, config: result.config };
		}
	}

	private getVersionTag(versionId: string): string | undefined {
		const row = this.db
			.prepare<[string], { tag: string }>(`SELECT tag FROM repository_versions WHERE id = ?`)
			.get(versionId);
		return row?.tag;
	}

	// -------------------------------------------------------------------------
	// Private — differential clone (TRUEREF-0021)
	// -------------------------------------------------------------------------

	/**
	 * Clone documents, snippets, and embeddings from an ancestor version into
	 * the target version for all unchanged file paths.
	 *
	 * Runs in a single SQLite transaction for atomicity.
	 */
	private async cloneFromAncestor(
		requestOrAncestorVersionId: CloneFromAncestorRequest | string,
		targetVersionId?: string,
		repositoryId?: string,
		unchangedPaths?: Set<string>
	): Promise<void> {
		const request: CloneFromAncestorRequest =
			typeof requestOrAncestorVersionId === 'string'
				? {
						ancestorVersionId: requestOrAncestorVersionId,
						targetVersionId: targetVersionId!,
						repositoryId: repositoryId!,
						unchangedPaths: [...(unchangedPaths ?? new Set<string>())]
					}
				: requestOrAncestorVersionId;

		if (request.unchangedPaths.length === 0) {
			return;
		}

		if (this.writeDelegate?.cloneFromAncestor) {
			await this.writeDelegate.cloneFromAncestor(request);
			return;
		}

		cloneFromAncestorInDatabase(this.db, request);
	}

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

	private async replaceSnippets(
		_repositoryId: string,
		changedDocIds: string[],
		newDocuments: NewDocument[],
		newSnippets: NewSnippet[]
	): Promise<void> {
		if (this.writeDelegate?.replaceSnippets) {
			await this.writeDelegate.replaceSnippets(changedDocIds, newDocuments, newSnippets);
			return;
		}

		replaceSnippetsInDatabase(this.db, changedDocIds, newDocuments, newSnippets);
	}

	// -------------------------------------------------------------------------
	// 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 computeVersionStats(versionId: string): { totalSnippets: number } {
		const row = this.db
			.prepare<
				[string],
				{ total_snippets: number }
			>(`SELECT COUNT(*) as total_snippets FROM snippets WHERE version_id = ?`)
			.get(versionId);

		return { totalSnippets: row?.total_snippets ?? 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 {
		if (this.writeDelegate?.persistJobUpdates === false) {
			return;
		}

		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 async updateRepo(id: string, fields: SerializedFields): Promise<void> {
		if (this.writeDelegate?.updateRepo) {
			await this.writeDelegate.updateRepo(id, fields);
			return;
		}

		updateRepoInDatabase(this.db, id, fields);
	}

	private async updateVersion(id: string, fields: SerializedFields): Promise<void> {
		if (this.writeDelegate?.updateVersion) {
			await this.writeDelegate.updateVersion(id, fields);
			return;
		}

		updateVersionInDatabase(this.db, id, fields);
	}

	private async upsertRepoConfig(
		repositoryId: string,
		versionId: string | null,
		rules: string[]
	): Promise<void> {
		if (this.writeDelegate?.upsertRepoConfig) {
			await this.writeDelegate.upsertRepoConfig(repositoryId, versionId, rules);
			return;
		}

		const now = Math.floor(Date.now() / 1000);
		// Use DELETE + INSERT because ON CONFLICT … DO UPDATE doesn't work reliably
		// with partial unique indexes in all SQLite versions.
		if (versionId === null) {
			this.db
				.prepare(`DELETE FROM repository_configs WHERE repository_id = ? AND version_id IS NULL`)
				.run(repositoryId);
		} else {
			this.db
				.prepare(`DELETE FROM repository_configs WHERE repository_id = ? AND version_id = ?`)
				.run(repositoryId, versionId);
		}
		this.db
			.prepare(
				`INSERT INTO repository_configs (repository_id, version_id, rules, updated_at)
         VALUES (?, ?, ?, ?)`
			)
			.run(repositoryId, versionId, JSON.stringify(rules), now);
	}

	// -------------------------------------------------------------------------
	// Private — static helpers
	// -------------------------------------------------------------------------

	/**
	 * Returns true when `filePath` matches the given exclude `pattern`.
	 *
	 * Supported patterns:
	 * - Plain filename: `migration-guide.md` matches any path ending in `/migration-guide.md`
	 *   or equal to `migration-guide.md`.
	 * - Glob prefix with wildcard: `docs/migration*` matches paths that start with `docs/migration`.
	 * - Exact path: `src/legacy/old-api.ts` matches exactly that path.
	 */
	private static matchesExcludePattern(filePath: string, pattern: string): boolean {
		if (pattern.includes('*')) {
			// Glob-style: treat everything before the '*' as a required prefix.
			const prefix = pattern.slice(0, pattern.indexOf('*'));
			return filePath.startsWith(prefix);
		}

		// No wildcard — treat as plain name or exact path.
		if (!pattern.includes('/')) {
			// Plain filename: match basename (path ends with /<pattern> or equals pattern).
			return filePath === pattern || filePath.endsWith('/' + pattern);
		}

		// Contains a slash — exact path match.
		return filePath === pattern;
	}
}

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

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