/**
 * Pure helpers for saving inbound Telegram files to disk (mode 1).
 *
 * When a user sends a non-image file to the bot, we download it and write it
 * into the configured directory (or Pi's working directory), then tell the
 * model the absolute path so it can open the file with its normal tools. This
 * module only computes names/sizes — the actual download and write live in the
 * composition root, so this stays unit-testable.
 */
import type { AttachmentRef } from "./media";

/** A file that was saved to disk, as reported to the model in the prompt. */
export interface SavedFileNote {
	/** Absolute path the file was written to. */
	path: string;
	/** Attachment kind (document/video/audio/voice/animation). */
	kind: string;
	/** Size in bytes actually written. */
	bytes: number;
	mimeType?: string;
}

/** A minimal extension guess for files that arrive without a filename. */
const MIME_EXTENSION: Record<string, string> = {
	"application/pdf": "pdf",
	"application/zip": "zip",
	"application/json": "json",
	"text/plain": "txt",
	"text/csv": "csv",
	"audio/mpeg": "mp3",
	"audio/ogg": "ogg",
	"video/mp4": "mp4",
	"image/jpeg": "jpg",
	"image/png": "png",
	"image/gif": "gif",
	"image/webp": "webp",
};

/** Strip directory separators and control chars so a filename can't escape the dir. */
function sanitizeFileName(name: string): string {
	const cleaned = name
		.replace(/[/\\]+/g, "_")
		// biome-ignore lint/suspicious/noControlCharactersInRegex: stripping control chars from a filename is intentional
		.replace(/[ -]+/g, "")
		.replace(/^\.+/, "")
		.trim();
	return cleaned || "file";
}

/** A default base name for an attachment that carries no filename of its own. */
function defaultBaseName(ref: AttachmentRef): string {
	const ext = ref.mimeType ? MIME_EXTENSION[ref.mimeType] : undefined;
	const stamp = ref.fileId.slice(-8).replace(/[^a-zA-Z0-9]/g, "");
	return ext
		? `telegram-${ref.kind}-${stamp}.${ext}`
		: `telegram-${ref.kind}-${stamp}`;
}

/**
 * Choose a safe, unique filename for a saved attachment. Uses the message's own
 * filename when present, else a stable default from the kind/mime. If the name
 * is already taken (in `used`), a numeric suffix is inserted before the
 * extension. The chosen name is added to `used`.
 */
export function resolveSaveName(ref: AttachmentRef, used: Set<string>): string {
	const base = sanitizeFileName(ref.fileName ?? defaultBaseName(ref));
	if (!used.has(base)) {
		used.add(base);
		return base;
	}
	const dot = base.lastIndexOf(".");
	const stem = dot > 0 ? base.slice(0, dot) : base;
	const ext = dot > 0 ? base.slice(dot) : "";
	for (let i = 1; ; i++) {
		const candidate = `${stem}-${i}${ext}`;
		if (!used.has(candidate)) {
			used.add(candidate);
			return candidate;
		}
	}
}

/** Human-readable byte size, e.g. `1.2 MB`. */
export function formatBytes(bytes: number): string {
	if (bytes < 1024) return `${bytes} B`;
	const units = ["KB", "MB", "GB"];
	let value = bytes / 1024;
	let unit = 0;
	while (value >= 1024 && unit < units.length - 1) {
		value /= 1024;
		unit++;
	}
	return `${value.toFixed(value < 10 ? 1 : 0)} ${units[unit]}`;
}