// namespace keys are free text a person types. this is the only place that
// decides what a key may look like; the hash that names the space is taken
// over the sanitized form, so two spellings that sanitize alike are one space.
export const MAX_KEY_LENGTH = 200;

export type KeyProblem = "empty" | "too-long" | "control-characters" | "reserved";

/** names the extension keeps for itself */
export const RESERVED = new Set(["lore-registry"]);

export type Sanitized = { ok: true; key: string } | { ok: false; problem: KeyProblem };

const isControl = (code: number): boolean => code < 0x20 || code === 0x7f;

/** a slug: lowercased, every run of anything but letters, digits, and hyphens becomes one hyphen,
 * none at the ends; refuse empty, overlong, control characters, or reserved names. */
export function sanitizeKey(raw: string): Sanitized {
	for (const ch of raw.replace(/[\t\n\r]/g, " ")) if (isControl(ch.codePointAt(0) ?? 0)) return { ok: false, problem: "control-characters" };
	const collapsed = raw.toLowerCase().replace(/[^\p{L}\p{N}-]+/gu, "-").replace(/-{2,}/g, "-").replace(/^-+|-+$/g, "");
	if (!collapsed) return { ok: false, problem: "empty" };
	if (collapsed.length > MAX_KEY_LENGTH) return { ok: false, problem: "too-long" };
	if (RESERVED.has(collapsed)) return { ok: false, problem: "reserved" };
	return { ok: true, key: collapsed };
}

export function explain(problem: KeyProblem): string {
	switch (problem) {
		case "empty":
			return "a key needs at least one character";
		case "too-long":
			return `a key is at most ${MAX_KEY_LENGTH} characters`;
		case "control-characters":
			return "a key cannot contain control characters";
		case "reserved":
			return "that name is reserved";
	}
}