/**
 * Challenge responder: produce a response given a challenge + BlockStore.
 *
 * For MST challenges: generates MST proofs via generateMstProof.
 * For block-sample challenges: checks block availability and returns prefixes.
 */

import type { BlockStore } from "../../ipfs.js";
import type {
	StorageChallenge,
	StorageChallengeResponse,
	BlockResult,
} from "./types.js";
import { DEFAULT_CHALLENGE_CONFIG } from "./types.js";
import { generateMstProof, type MstProof } from "../mst-proof.js";

/**
 * Produce a challenge response.
 *
 * Calls generateMstProof for MST challenges, checks block availability
 * and provides prefixes for block-sample challenges.
 */
export async function respondToChallenge(
	challenge: StorageChallenge,
	blockStore: BlockStore,
	responderDid: string,
	config?: { blockPrefixLength?: number },
): Promise<StorageChallengeResponse> {
	const prefixLength =
		config?.blockPrefixLength ?? DEFAULT_CHALLENGE_CONFIG.blockPrefixLength;

	let mstProofs: MstProof[] | undefined;
	let blockResults: BlockResult[] | undefined;

	// Handle MST proof challenges
	if (
		challenge.challengeType === "mst-proof" ||
		challenge.challengeType === "combined"
	) {
		mstProofs = [];
		for (const recordPath of challenge.recordPaths) {
			try {
				const proof = await generateMstProof(
					blockStore,
					challenge.commitCid,
					recordPath,
				);
				mstProofs.push(proof);
			} catch {
				// If we can't generate a proof (missing blocks), add an empty proof
				mstProofs.push({
					commitBlock: {
						cid: challenge.commitCid,
						bytes: new Uint8Array(0),
					},
					nodes: [],
					recordCid: null,
					found: false,
				});
			}
		}
	}

	// Handle block-sample challenges
	if (
		challenge.challengeType === "block-sample" ||
		challenge.challengeType === "combined"
	) {
		if (challenge.blockCids) {
			blockResults = [];
			for (const cid of challenge.blockCids) {
				const bytes = await blockStore.getBlock(cid);
				if (bytes) {
					blockResults.push({
						cid,
						available: true,
						prefix: bytes.slice(0, prefixLength),
					});
				} else {
					blockResults.push({
						cid,
						available: false,
					});
				}
			}
		}
	}

	return {
		challengeId: challenge.id,
		responderDid,
		mstProofs,
		blockResults,
		respondedAt: new Date().toISOString(),
	};
}