multicrypt/src/SharedValue.ts

import {EncodedValue, KeyValue} from './types'
import {KeyPackage} from './KeyPackage'
import {Payload} from './Payload'

/** Interface for a JSON-serializable shared value. */
export interface SerializedSharedValue<T> {
    value: EncodedValue,
    envelopes: EncodedValue[],
}

/**
 * A value that is shared and accessible by multiple encryption keys.
 */
export class SharedValue<T> {
    /** The package of keys allowed to access the encoded value. */
    public readonly package: KeyPackage

    /**
     * Create a new shared value.
     * @param initialSharerKey - an initial key, used to give access to the encoded value
     * @param value - the value to be encoded and shared
     */
    public static async create<T>(initialSharerKey: KeyValue, value: T): Promise<SharedValue<T>> {
        const keyPackage = await KeyPackage.fromInitialSharer(initialSharerKey)
        const cryptor = await keyPackage.getCryptor(initialSharerKey)
        const payload = new Payload<T>(value)

        const serialized = {
            value: await cryptor.encode(payload.encode()),
            ...(keyPackage.toJSON()),
        }

        return new SharedValue<T>(serialized)
    }

    constructor(
        /** The serialized data for this shared value. */
        private serialized: SerializedSharedValue<T>,
        public readonly validator: (w: unknown) => w is T = (w: unknown): w is T => true,
    ) {
        this.package = KeyPackage.fromJSON(serialized)
    }

    /**
     * Get a Payload instance of the decoded value.
     * @param key - valid key to decode the payload
     */
    async payload(key: KeyValue): Promise<Payload<T>> {
        const cryptor = await this.package.getCryptor(key)
        const decodedValue = await cryptor.decode(this.serialized.value)
        return Payload.from<T>(decodedValue)
    }

    /**
     * Get the value of this secret.
     * @param key - valid key to decode the value
     */
    async get(key: KeyValue): Promise<T> {
        const payload = await this.payload(key)
        const value = payload.value
        if ( !this.validator(value) ) {
            throw new TypeError('Invalid encoded value!')
        }

        return value
    }

    /**
     * Set a new value for this secret.
     * @param key - valid key to encode the value
     * @param value - new value to encode
     */
    async set(key: KeyValue, value: T): Promise<void> {
        const cryptor = await this.package.getCryptor(key)
        const payload = new Payload<T>(value)
        this.serialized.value = await cryptor.encode(payload.encode())
    }

    /**
     * Add a new key to the key package for this shared value. This allows
     * the `shareeKey` to access this shared value.
     * @param sharerKey - a currently valid key
     * @param shareeKey - the new key to add
     */
    async addKey(sharerKey: KeyValue, shareeKey?: KeyValue): Promise<KeyValue> {
        return this.package.addCryptor(sharerKey, shareeKey)
    }

    /** Serialize the shared value securely. */
    toJSON(): SerializedSharedValue<T> {
        return {
            value: this.serialized.value,
            ...(this.package.toJSON()),
        }
    }
}