/**
 * Rate limit reason classification and backoff calculation utilities.
 * Ported from opencode-antigravity-auth plugin for consistency.
 */

export type RateLimitReason =
	| "QUOTA_EXHAUSTED"
	| "RATE_LIMIT_EXCEEDED"
	| "MODEL_CAPACITY_EXHAUSTED"
	| "SERVER_ERROR"
	| "UNKNOWN";

const QUOTA_EXHAUSTED_BACKOFF_MS = 30 * 60 * 1000; // 30 min
const RATE_LIMIT_EXCEEDED_BACKOFF_MS = 30 * 1000; // 30s
const MODEL_CAPACITY_BASE_MS = 45 * 1000; // 45s base
const MODEL_CAPACITY_JITTER_MS = 30 * 1000; // uniform +0–30s above base → 45–75s total
const SERVER_ERROR_BACKOFF_MS = 20 * 1000; // 20s

/**
 * Classify a rate-limit error message into a reason category.
 * Priority order: MODEL_CAPACITY > RATE_LIMIT > QUOTA > SERVER_ERROR > UNKNOWN.
 *
 * "resource exhausted" maps to MODEL_CAPACITY (transient, short wait)
 * "quota exceeded" maps to QUOTA_EXHAUSTED (long wait, switch account)
 */
export function parseRateLimitReason(errorMessage: string): RateLimitReason {
	const lower = errorMessage.toLowerCase();

	if (
		lower.includes("capacity") ||
		lower.includes("overloaded") ||
		lower.includes("529") ||
		lower.includes("503") ||
		lower.includes("resource exhausted")
	) {
		return "MODEL_CAPACITY_EXHAUSTED";
	}

	if (
		lower.includes("out_of_credits") ||
		lower.includes("request would exceed your account's rate limit") ||
		lower.includes("request would exceed your accounts rate limit")
	) {
		return "QUOTA_EXHAUSTED";
	}

	if (
		lower.includes("per minute") ||
		lower.includes("rate limit") ||
		lower.includes("too many requests") ||
		lower.includes("presque")
	) {
		return "RATE_LIMIT_EXCEEDED";
	}

	if (
		lower.includes("exhausted") ||
		lower.includes("quota") ||
		lower.includes("usage limit") ||
		lower.includes("model limit") ||
		lower.includes("model_limit") ||
		lower.includes("message limit") ||
		lower.includes("message_limit") ||
		lower.includes("limit for this model")
	) {
		return "QUOTA_EXHAUSTED";
	}

	if (lower.includes("500") || lower.includes("internal error") || lower.includes("internal server error")) {
		return "SERVER_ERROR";
	}

	return "UNKNOWN";
}

/**
 * Calculate backoff delay in ms for a given rate limit reason.
 * MODEL_CAPACITY gets jitter to prevent thundering herd.
 */
export function calculateRateLimitBackoffMs(reason: RateLimitReason): number {
	switch (reason) {
		case "QUOTA_EXHAUSTED":
			return QUOTA_EXHAUSTED_BACKOFF_MS;
		case "RATE_LIMIT_EXCEEDED":
			return RATE_LIMIT_EXCEEDED_BACKOFF_MS;
		case "MODEL_CAPACITY_EXHAUSTED":
			return MODEL_CAPACITY_BASE_MS + Math.random() * MODEL_CAPACITY_JITTER_MS;
		case "SERVER_ERROR":
			return SERVER_ERROR_BACKOFF_MS;
		default:
			return QUOTA_EXHAUSTED_BACKOFF_MS; // conservative default
	}
}

/** Detect usage/quota limit errors in error messages (persistent, requires credential switch). */
// ZAI reports durable token exhaustion as "[1310][Weekly/Monthly Limit Exhausted...]".
// Keep this explicit so generic "rate limit exhausted, retry..." throttles remain retryable.
const USAGE_LIMIT_PATTERN =
	/usage.?limit|usage_limit_reached|usage_not_included|limit_reached|model.?limit|model_limit_reached|message.?limit|message_limit_reached|limit for this model|weekly\/monthly\s+limit\s+exhausted|quota.?exceeded|out_of_credits|request would exceed your account.?s rate limit|resource has been exhausted[^\n]*(?:quota|limit)/i;
export function isUsageLimitError(errorMessage: string): boolean {
	return USAGE_LIMIT_PATTERN.test(errorMessage);
}