/**
 * Centralized generated/artifact detection.
 *
 * This module is intentionally lightweight and synchronous because it is used by
 * hot-path source collection and dispatch role detection. It combines cheap
 * path/name heuristics with optional header inspection for common generated-code
 * banners.
 */

import * as fs from "node:fs";
import * as path from "node:path";

const DEFAULT_HEADER_BYTES = 4096;

const GENERATED_DIR_NAMES = new Set([
	"generated",
	"__generated__",
	"codegen",
	"__codegen__",
	"generated-sources",
	"generated_sources",
	"openapi-generated",
	".openapi-generator",
]);

const GENERATED_HEADER_PATTERNS = [
	/@generated\b/i,
	/@ts-nocheck\b/i,
	/\bcode generated\b/i,
	/\bdo not edit\b/i,
	/\bautomatically generated\b/i,
	/\bthis file was generated\b/i,
	/\bgenerated by protoc\b/i,
	/\bgenerated by graphql-code-generator\b/i,
	/\bgenerated by openapi-generator\b/i,
	/\bgenerated by swagger codegen\b/i,
];

const GENERATED_FILE_PATTERNS = [
	/(^|[._-])generated([._-]|$)/i,
	/(^|[._-])gen([._-])/i,
	/_generated\.(go|rs|py|rb|java|kt|ts|tsx|js|jsx|mjs|cjs)$/i,
	/_gen\.(go|rs|py|rb|java|kt|ts|tsx|js|jsx|mjs|cjs)$/i,
	/\.pb\.(go|ts|tsx|js|jsx|mjs|cjs)$/i,
	/_pb2(_grpc)?\.py$/i,
	/\.sql\.(go|ts|js)$/i,
	/_sqlc\.go$/i,
	/\.g\.([jt]sx?|mjs|cjs|rs|go)$/i,
	/\.min\.(js|mjs|cjs|css)$/i,
	/\.(bundle|chunk)\.(js|mjs|cjs|css)$/i,
];

const DECLARATION_FILE_PATTERNS = [/\.d\.ts$/i, /\.d\.mts$/i, /\.d\.cts$/i];

export interface GeneratedArtifactOptions {
	/** Optional file content or prefix. When omitted, content markers are skipped. */
	content?: string;
	/** Read a small file prefix to detect generated-code banners. */
	readContentHeader?: boolean;
	/** Number of bytes to read when readContentHeader is true. */
	maxHeaderBytes?: number;
	/** Treat declaration stubs (.d.ts/.d.mts/.d.cts) as artifacts. */
	includeDeclarations?: boolean;
}

function pathSegments(filePath: string): string[] {
	return path
		.normalize(filePath)
		.split(/[\\/]+/)
		.filter(Boolean);
}

export function isGeneratedArtifactDirectoryName(dirName: string): boolean {
	return GENERATED_DIR_NAMES.has(dirName.trim().toLowerCase());
}

export function isDeclarationFile(filePath: string): boolean {
	const base = path.basename(filePath).toLowerCase();
	return DECLARATION_FILE_PATTERNS.some((pattern) => pattern.test(base));
}

function hasGeneratedArtifactPath(filePath: string): boolean {
	const segments = pathSegments(filePath);
	const dirSegments = segments.slice(0, -1);
	if (
		dirSegments.some((segment) => isGeneratedArtifactDirectoryName(segment))
	) {
		return true;
	}

	const base = path.basename(filePath);
	return GENERATED_FILE_PATTERNS.some((pattern) => pattern.test(base));
}

function hasGeneratedArtifactContent(content: string): boolean {
	const header = content.slice(0, DEFAULT_HEADER_BYTES);
	return GENERATED_HEADER_PATTERNS.some((pattern) => pattern.test(header));
}

function readFileHeader(
	filePath: string,
	maxBytes = DEFAULT_HEADER_BYTES,
): string | undefined {
	let fd: number | undefined;
	try {
		fd = fs.openSync(filePath, "r");
		const buffer = Buffer.alloc(Math.max(0, maxBytes));
		const bytesRead = fs.readSync(fd, buffer, 0, buffer.length, 0);
		return buffer.toString("utf8", 0, bytesRead);
	} catch {
		return undefined;
	} finally {
		if (fd !== undefined) {
			try {
				fs.closeSync(fd);
			} catch {
				/* ignore close errors */
			}
		}
	}
}

export function isGeneratedOrArtifact(
	filePath: string,
	options: GeneratedArtifactOptions = {},
): boolean {
	if (hasGeneratedArtifactPath(filePath)) return true;
	if (options.includeDeclarations && isDeclarationFile(filePath)) return true;

	if (options.content !== undefined) {
		return hasGeneratedArtifactContent(options.content);
	}

	if (options.readContentHeader) {
		const header = readFileHeader(filePath, options.maxHeaderBytes);
		return header !== undefined && hasGeneratedArtifactContent(header);
	}

	return false;
}