/**
 * DCP Context Event Handler
 * 
 * Handles the 'context' event which fires before each LLM call.
 * Applies pruning workflow to reduce token usage while preserving coherence.
 */

import type { ContextEvent, ExtensionContext } from "@mariozechner/pi-coding-agent";
import type { DcpConfigWithPruneRuleObjects } from "../types";
import type { StatsTracker } from "../cmds/stats.ts";
import { applyPruningWorkflow } from "../workflow";

export interface ContextEventHandlerOptions {
	config: DcpConfigWithPruneRuleObjects;
	statsTracker: StatsTracker;
}

/**
 * Creates a context event handler that applies pruning to messages.
 * 
 * @param options - Configuration and stats tracker
 * @returns Event handler function
 */
export function createContextEventHandler(options: ContextEventHandlerOptions) {
	const { config, statsTracker } = options;

	return async (event: ContextEvent, ctx: ExtensionContext) => {
		try {
			const originalCount = event.messages.length;

			// Apply pruning workflow
			const prunedMessages = applyPruningWorkflow(event.messages, config);

			const prunedCount = originalCount - prunedMessages.length;
			statsTracker.totalPruned += prunedCount;
			statsTracker.totalProcessed += originalCount;

			if (prunedCount > 0) {
				// Show toast notification when pruning occurs
				// ctx. //(`DCP: Pruned ${prunedCount}/${originalCount} messages`, "info");
			}

			if (config.debug) {
				ctx.ui.notify(`[pi-dcp] Pruned ${prunedCount} / ${originalCount} messages`);
			}

			return { messages: prunedMessages };
		} catch (error) {
			const errorMessage = error instanceof Error ? error.message : String(error);
			ctx.ui.notify(`[pi-dcp] Error in pruning workflow: ${errorMessage}`, "error");
			// Fail-safe: return original messages on error
			return { messages: event.messages };
		}
	};
}