import {
	chmodSync,
	copyFileSync,
	existsSync,
	lstatSync,
	mkdirSync,
	rmSync,
	statSync,
	symlinkSync,
	unlinkSync,
} from "node:fs";
import { delimiter, join } from "node:path";

type ManagedTool = "fd" | "rg";

interface ToolSpec {
	targetName: string;
	candidates: string[];
}

const TOOL_SPECS: Record<ManagedTool, ToolSpec> = {
	fd: {
		targetName: process.platform === "win32" ? "fd.exe" : "fd",
		candidates:
			process.platform === "win32"
				? ["fd.exe", "fd", "fdfind.exe", "fdfind"]
				: ["fd", "fdfind"],
	},
	rg: {
		targetName: process.platform === "win32" ? "rg.exe" : "rg",
		candidates: process.platform === "win32" ? ["rg.exe", "rg"] : ["rg"],
	},
};

function splitPath(pathValue: string | undefined): string[] {
	if (!pathValue) return [];
	return pathValue
		.split(delimiter)
		.map((segment) => segment.trim())
		.filter(Boolean);
}

function getCandidateNames(name: string): string[] {
	if (process.platform !== "win32") return [name];
	const lower = name.toLowerCase();
	if (
		lower.endsWith(".exe") ||
		lower.endsWith(".cmd") ||
		lower.endsWith(".bat")
	)
		return [name];
	return [name, `${name}.exe`, `${name}.cmd`, `${name}.bat`];
}

function isRegularFile(path: string): boolean {
	try {
		const stat = lstatSync(path);
		return stat.isFile() || stat.isSymbolicLink();
	} catch {
		return false;
	}
}

function pathExistsIncludingBrokenSymlink(path: string): boolean {
	try {
		lstatSync(path);
		return true;
	} catch {
		return false;
	}
}

function isBrokenSymlink(path: string): boolean {
	try {
		const stat = lstatSync(path);
		if (!stat.isSymbolicLink()) return false;
		try {
			statSync(path);
			return false;
		} catch {
			return true;
		}
	} catch {
		return false;
	}
}

function removeTargetPath(path: string): void {
	try {
		const stat = lstatSync(path);
		if (stat.isSymbolicLink()) {
			unlinkSync(path);
			return;
		}
		rmSync(path, { force: true });
	} catch {
		// Path already absent.
	}
}

export function resolveToolFromPath(
	tool: ManagedTool,
	pathValue: string | undefined = process.env.PATH,
): string | null {
	const spec = TOOL_SPECS[tool];
	for (const dir of splitPath(pathValue)) {
		for (const candidate of spec.candidates) {
			for (const name of getCandidateNames(candidate)) {
				const fullPath = join(dir, name);
				if (existsSync(fullPath) && isRegularFile(fullPath)) {
					return fullPath;
				}
			}
		}
	}
	return null;
}

function provisionTool(
	targetDir: string,
	tool: ManagedTool,
	sourcePath: string,
): string {
	const targetPath = join(targetDir, TOOL_SPECS[tool].targetName);
	const brokenTarget = isBrokenSymlink(targetPath);
	if (pathExistsIncludingBrokenSymlink(targetPath)) {
		if (!brokenTarget) return targetPath;
		removeTargetPath(targetPath);
	}

	mkdirSync(targetDir, { recursive: true });

	if (!brokenTarget) {
		try {
			symlinkSync(sourcePath, targetPath);
			return targetPath;
		} catch {
			// Fall back to copying below.
		}
	}

	removeTargetPath(targetPath);
	copyFileSync(sourcePath, targetPath);
	chmodSync(targetPath, 0o755);

	return targetPath;
}

export function ensureManagedTools(
	targetDir: string,
	pathValue: string | undefined = process.env.PATH,
): string[] {
	const provisioned: string[] = [];

	for (const tool of Object.keys(TOOL_SPECS) as ManagedTool[]) {
		const targetPath = join(targetDir, TOOL_SPECS[tool].targetName);
		if (
			pathExistsIncludingBrokenSymlink(targetPath) &&
			!isBrokenSymlink(targetPath)
		)
			continue;
		const sourcePath = resolveToolFromPath(tool, pathValue);
		if (!sourcePath) continue;
		provisioned.push(provisionTool(targetDir, tool, sourcePath));
	}

	return provisioned;
}