/**
 * Recency Rule
 *
 * Always preserves recent messages from pruning.
 * The last N messages (configurable via keepRecentCount) are protected
 * regardless of what other rules decide.
 *
 * This rule should typically run LAST in the process phase to override
 * other pruning decisions for recent messages.
 */

import type { PruneRule } from "../types";

export const recencyRule: PruneRule = {
	name: "recency",
	description: "Always preserve recent messages from pruning",

	/**
	 * No prepare phase needed - recency is determined during processing
	 */

	/**
	 * Process phase: Protect recent messages from pruning
	 */
	process(msg, ctx) {
		// Calculate distance from the end of the message list
		const distanceFromEnd = ctx.messages.length - ctx.index - 1;

		// If within the keepRecentCount threshold, protect it
		if (distanceFromEnd < ctx.config.keepRecentCount) {
			// Unmark for pruning if it was marked
			const wasPruned = msg.metadata.shouldPrune;
			msg.metadata.shouldPrune = false;
			msg.metadata.pruneReason = undefined;
			msg.metadata.protectedByRecency = true;

			if (ctx.config.debug && wasPruned) {
				console.log(
					`[pi-dcp] Recency: protecting message at index ${ctx.index} ` +
						`(distance from end: ${distanceFromEnd}, threshold: ${ctx.config.keepRecentCount})`,
				);
			}
		}
	},
};