/**
 * Context Manager Core — pressure estimation, TTL, prioritization (RFC-0010)
 */

import type {
	PressureLevel,
	TriggerPolicy,
	ContextItem,
	SessionScope,
} from "./types.js";

export const DEFAULT_POLICY: TriggerPolicy = {
	warningThreshold: 0.6,
	compactThreshold: 0.7,
	hardStopThreshold: 0.85,
};

/** Estimate context pressure as a ratio (0-1). */
export function estimatePressure(
	currentTokens: number,
	maxTokens: number,
): number {
	if (maxTokens <= 0) return 1;
	return Math.min(currentTokens / maxTokens, 1);
}

/** Determine pressure level from a ratio. */
export function getPressureLevel(
	pressure: number,
	policy: TriggerPolicy = DEFAULT_POLICY,
): PressureLevel {
	if (pressure >= policy.hardStopThreshold) return "hard_stop";
	if (pressure >= policy.compactThreshold) return "compact";
	if (pressure >= policy.warningThreshold) return "warning";
	return "normal";
}

/** Create a new session-scoped context bucket. */
export function createSessionScope(id: string): SessionScope {
	return { id, items: [], ttlMs: 30 * 60 * 1000, createdAt: Date.now() };
}

/** Set TTL on a scope (in milliseconds). */
export function setTTL(scope: SessionScope, ttlMs: number): SessionScope {
	return { ...scope, ttlMs };
}

/** Add an item to a session scope. */
export function addToScope(
	scope: SessionScope,
	item: ContextItem,
): SessionScope {
	return { ...scope, items: [...scope.items, item] };
}

/** Remove expired items from a scope based on TTL. */
export function evictExpired(scope: SessionScope): SessionScope {
	const now = Date.now();
	return {
		...scope,
		items: scope.items.filter((item) => {
			if (!item.expiresAt) return true;
			return item.expiresAt > now;
		}),
	};
}

/** Prioritize items: lower priority number = higher importance. */
export function prioritize(
	items: ContextItem[],
	limit?: number,
): ContextItem[] {
	const sorted = [...items].sort((a, b) => a.priority - b.priority);
	return limit ? sorted.slice(0, limit) : sorted;
}

/** Count tokens using a simple word-based estimator (4 chars/token). */
export function estimateTokens(text: string): number {
	return Math.ceil(text.length / 4);
}

/** Calculate total tokens in a list of items. */
export function calculateTotalTokens(items: ContextItem[]): number {
	return items.reduce((sum, item) => sum + item.tokens, 0);
}