/**
 * Deduplication Rule
 *
 * Removes duplicate tool outputs based on content hash.
 * Messages with identical content are considered duplicates,
 * and only the first occurrence is kept.
 */

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

export const deduplicationRule: PruneRule = {
	name: "deduplication",
	description: "Remove duplicate tool outputs based on content hash",

	/**
	 * Prepare phase: Hash each message for comparison
	 */
	prepare(msg, ctx) {
		// Hash the message content
		msg.metadata.hash = hashMessage(msg.message);
	},

	/**
	 * Process phase: Mark duplicates for pruning
	 */
	process(msg, ctx) {
		// Skip if already marked for pruning by another rule
		if (msg.metadata.shouldPrune) return;

		// Never prune user messages
		if (msg.message.role === "user") return;

		// Check if we've seen this exact content before
		const currentHash = msg.metadata.hash;
		if (!currentHash) return;

		// Look for earlier message with same hash
		const seenBefore = ctx.messages.slice(0, ctx.index).some((m) => m.metadata.hash === currentHash);

		if (seenBefore) {
			msg.metadata.shouldPrune = true;
			msg.metadata.pruneReason = "duplicate content";

			if (ctx.config.debug) {
				console.log(`[pi-dcp] Dedup: marking duplicate message at index ${ctx.index} (hash: ${currentHash})`);
			}
		}
	},
};