// lib/storage.js
// -----------------------------------------------------------------------------
// Central abstraction layer for reading files and directories from the NAS
// share mounted at `NAS_ROOT_PATH` (e.g. `/mnt/niederlassungen`).
//
// All access to the branch/year/month/day/PDF structure should go through
// these functions instead of using `fs` directly in route handlers.
//
// - Read-only: no write/delete operations here.
// - Async only: uses `fs/promises` + async/await to avoid blocking the event loop.
// -----------------------------------------------------------------------------

import fs from "node:fs/promises"; // Promise-based filesystem API
import path from "node:path"; // Safe path utilities (handles separators)

// Root directory of the NAS share, injected via environment variable.
// On the Linux app server, this is typically `/mnt/niederlassungen`.
// Do NOT cache process.env.NAS_ROOT_PATH at module load time.
// Instead, resolve it on demand so tests (and runtime) can change it.
function getRoot() {
	const root = process.env.NAS_ROOT_PATH;

	if (!root) {
		throw new Error("NAS_ROOT_PATH environment variable is not set");
	}

	return root;
}

// Build an absolute path below the NAS root from a list of segments.
function fullPath(...segments) {
	const root = getRoot();
	return path.join(root, ...segments.map(String));
}

// Compare strings that represent numbers in a numeric way.
// This ensures "2" comes before "10" (2 < 10), not after.
function sortNumericStrings(a, b) {
	const na = parseInt(a, 10);
	const nb = parseInt(b, 10);

	if (!Number.isNaN(na) && !Number.isNaN(nb)) {
		return na - nb;
	}

	// Fallback to localeCompare if parsing fails
	return a.localeCompare(b, "en");
}

// -----------------------------------------------------------------------------
// 1. Branches (NL01, NL02, ...)
// Path pattern: `${ROOT}/NLxx`
// -----------------------------------------------------------------------------

export async function listBranches() {
	// Read the root directory of the NAS share.
	// `withFileTypes: true` returns `Dirent` objects so we can call `isDirectory()`
	// without extra stat() calls, which is more efficient.
	const entries = await fs.readdir(fullPath(), { withFileTypes: true });

	return (
		entries
			.filter(
				(entry) =>
					entry.isDirectory() && // only directories
					entry.name !== "@Recently-Snapshot" && // ignore QNAP snapshot folder
					/^NL\d+$/i.test(entry.name) // keep only names like "NL01", "NL02", ...
			)
			.map((entry) => entry.name)
			// Sort by numeric branch number: NL1, NL2, ..., NL10
			.sort((a, b) =>
				sortNumericStrings(a.replace("NL", ""), b.replace("NL", ""))
			)
	);
}

// -----------------------------------------------------------------------------
// 2. Years (2023, 2024, ...)
// Path pattern: `${ROOT}/${branch}/${year}`
// -----------------------------------------------------------------------------

export async function listYears(branch) {
	const dir = fullPath(branch);
	const entries = await fs.readdir(dir, { withFileTypes: true });

	return entries
		.filter(
			(entry) => entry.isDirectory() && /^\d{4}$/.test(entry.name) // exactly 4 digits → year folders like "2024"
		)
		.map((entry) => entry.name)
		.sort(sortNumericStrings);
}

// -----------------------------------------------------------------------------
// 3. Months (01–12)
// Path pattern: `${ROOT}/${branch}/${year}/${month}`
// -----------------------------------------------------------------------------

export async function listMonths(branch, year) {
	const dir = fullPath(branch, year);
	const entries = await fs.readdir(dir, { withFileTypes: true });

	return (
		entries
			.filter(
				(entry) => entry.isDirectory() && /^\d{1,2}$/.test(entry.name) // supports "1" or "10", we normalize below
			)
			// Normalize to two digits so the UI shows "01", "02", ..., "12"
			.map((entry) => entry.name.trim().padStart(2, "0"))
			.sort(sortNumericStrings)
	);
}

// -----------------------------------------------------------------------------
// 4. Days (01–31)
// Path pattern: `${ROOT}/${branch}/${year}/${month}/${day}`
// -----------------------------------------------------------------------------

export async function listDays(branch, year, month) {
	const dir = fullPath(branch, year, month);
	const entries = await fs.readdir(dir, { withFileTypes: true });

	return entries
		.filter(
			(entry) => entry.isDirectory() && /^\d{1,2}$/.test(entry.name) // supports "1" or "23"
		)
		.map((entry) => entry.name.trim().padStart(2, "0"))
		.sort(sortNumericStrings);
}

// -----------------------------------------------------------------------------
// 5. Files (PDFs) for a given day
// Path pattern: `${ROOT}/${branch}/${year}/${month}/${day}/<file>.pdf`
// -----------------------------------------------------------------------------

export async function listFiles(branch, year, month, day) {
	const dir = fullPath(branch, year, month, day);
	const entries = await fs.readdir(dir);

	return (
		entries
			// We only care about PDF files at the moment
			.filter((name) => name.toLowerCase().endsWith(".pdf"))
			.sort((a, b) => a.localeCompare(b, "en"))
			.map((name) => ({
				// Just the file name, e.g. "Stapel-1_Seiten-1_Zeit-1048.pdf"
				name,
				// Relative path from the NAS root, used for download URLs etc.
				// Example: "NL01/2024/10/23/Stapel-1_Seiten-1_Zeit-1048.pdf"
				relativePath: `${branch}/${year}/${month}/${day}/${name}`,
			}))
	);
}