import { existsSync } from "node:fs";
import { win32 } from "node:path";
import { spawnSync } from "node:child_process";
import type { PwshNativeConfig } from "./config.ts";

const KNOWN_PWSH_PATH = "C:\\Program Files\\PowerShell\\7\\pwsh.exe";
const VERSION_PROBE = "[Console]::Out.Write($PSVersionTable.PSVersion.ToString())";

export interface PowerShellRuntime {
	executable: string;
	version: string;
}

export interface RuntimeDependencies {
	exists: (path: string) => boolean;
	findOnPath: () => string[];
	probe: (path: string) => string | null;
}

export class RuntimeError extends Error {
	constructor(message: string) {
		super(message);
		this.name = "RuntimeError";
	}
}

function defaultFindOnPath(): string[] {
	const result = spawnSync("where.exe", ["pwsh.exe"], {
		encoding: "utf8",
		timeout: 5_000,
		windowsHide: true,
	});
	if (result.error || result.status !== 0 || !result.stdout) return [];
	return result.stdout
		.split(/\r?\n/)
		.map((path) => path.trim())
		.filter(Boolean);
}

function defaultProbe(path: string): string | null {
	const result = spawnSync(
		path,
		["-NoLogo", "-NoProfile", "-NonInteractive", "-Command", VERSION_PROBE],
		{
			encoding: "utf8",
			timeout: 5_000,
			windowsHide: true,
		},
	);
	if (result.error || result.status !== 0) return null;
	const version = result.stdout.trim();
	return /^\d+(?:\.\d+){1,3}(?:[-+][0-9A-Za-z.-]+)?$/.test(version) ? version : null;
}

const DEFAULT_DEPENDENCIES: RuntimeDependencies = {
	exists: existsSync,
	findOnPath: defaultFindOnPath,
	probe: defaultProbe,
};

function majorVersion(version: string): number | null {
	const match = /^(\d+)/.exec(version);
	return match ? Number(match[1]) : null;
}

function uniquePaths(paths: string[]): string[] {
	const seen = new Set<string>();
	const result: string[] = [];
	for (const path of paths) {
		const normalized = win32.normalize(path);
		const key = normalized.toLowerCase();
		if (seen.has(key)) continue;
		seen.add(key);
		result.push(normalized);
	}
	return result;
}

export function resolvePowerShellRuntime(
	config: PwshNativeConfig,
	dependencies: RuntimeDependencies = DEFAULT_DEPENDENCIES,
): PowerShellRuntime {
	const explicit = config.executable !== "auto";
	const candidates = explicit
		? [config.executable]
		: uniquePaths([...dependencies.findOnPath(), KNOWN_PWSH_PATH]);
	const failures: string[] = [];

	for (const candidate of candidates) {
		const path = win32.normalize(candidate);
		if (!win32.isAbsolute(path)) {
			failures.push(`${path}: not an absolute path`);
			continue;
		}
		if (!dependencies.exists(path)) {
			failures.push(`${path}: file not found`);
			continue;
		}
		const version = dependencies.probe(path);
		if (!version) {
			failures.push(`${path}: failed to start or returned an invalid version`);
			continue;
		}
		const major = majorVersion(version);
		if (major === null || major < 7) {
			failures.push(`${path}: PowerShell ${version} is unsupported; version 7 or newer is required`);
			continue;
		}
		return { executable: path, version };
	}

	const prefix = explicit
		? `Configured PowerShell executable ${JSON.stringify(config.executable)} is unavailable.`
		: "PowerShell 7 or newer was not found.";
	const details = failures.length > 0 ? ` Checked: ${failures.join("; ")}.` : "";
	throw new RuntimeError(`${prefix}${details} Install PowerShell 7 or configure an absolute pwsh.exe path.`);
}