/**
 * @license
 * Copyright 2022-2026 Matter.js Authors
 * SPDX-License-Identifier: Apache-2.0
 */

import { ImplementationError } from "#MatterError.js";
import { Bytes } from "#util/Bytes.js";
import { Crypto, ec } from "./Crypto.js";
import { CurveType, Key, KeyType, PrivateKey } from "./Key.js";
import { StandardCrypto } from "./StandardCrypto.js";

/**
 * WARNING: ONLY FOR USE IN PROTECTED TESTING ENVIRONMENTS WHERE SECURITY IS NOT A CONCERN
 *
 * A {@link Crypto} with sources of entropy replaced to produce stable values based on an input index.
 *
 * This is useful in testing environments where Matter logic is difficult to test with true entropy.
 *
 * Depending on implementation some methods may need further mocking to remove entropy entirely.  Mocking is sufficient
 * for current testing purposes.
 */
export interface MockCrypto extends Crypto {
    /**
     * The index of the random space.  May be modified to adjust computations going forward.
     */
    index: number;

    /**
     * Control whether the implementation supplies normal randomness (false by default).
     */
    entropic: boolean;
}

export function MockCrypto(index: number = 0x80, implementation: new () => Crypto = StandardCrypto) {
    if (index < 0 || index > 255) {
        throw new ImplementationError(`Index for stable crypto must be 0-255`);
    }

    const crypto = new implementation();

    const { randomBytes, createKeyPair } = crypto;

    Object.defineProperties(crypto, {
        index: {
            get() {
                return index;
            },

            set(newIndex: number) {
                index = newIndex % 256;
            },
        },

        entropic: {
            get() {
                return crypto.randomBytes === randomBytes;
            },

            set(entropic: boolean) {
                if (entropic) {
                    crypto.randomBytes = randomBytes;
                    crypto.createKeyPair = createKeyPair;
                } else {
                    disableEntropy();
                }
            },
        },
    });

    disableEntropy();

    return crypto as MockCrypto;

    function disableEntropy() {
        // Create random data consisting of index repeated
        crypto.randomBytes = function getRandomDataNONENTROPIC(length) {
            const result = new Uint8Array(length);
            result.fill(index);
            return result;
        };

        // Ensure EC key generation uses our own "entropy" source rather than the platform's
        crypto.createKeyPair = function getRandomDataNONENTROPIC() {
            const privateBits = ec.mapHashToField(Bytes.of(crypto.randomBytes(48)), ec.p256.Point.CURVE().n);
            return Key({
                kty: KeyType.EC,
                crv: CurveType.p256,
                privateBits,
            }) as PrivateKey;
        };
    }
}