loc-chain-backend/src/app/units/Blockchain.ts

import { Singleton, Inject } from "@extollo/di"
import { Unit, Logging, Config, Application } from "@extollo/lib"
import { FirebaseUnit } from "./FirebaseUnit"
import { BlockEncounterTransaction, BlockResource, BlockResourceItem, BlockTransaction } from "../rtdb/BlockResource"
import { TransactionResourceItem } from "../rtdb/TransactionResource"
import * as openpgp from "openpgp"
import * as crypto from "crypto"
import { collect, uuid_v4 } from "@extollo/util"
import {ExposureResourceItem} from "../rtdb/ExposureResource";

/**
 * Utility wrapper class for a block in the chain.
 */
export class Block implements BlockResourceItem {
    firebaseID: string
    seqID: number
    uuid: string
    transactions: BlockTransaction[]
    timestamp: number
    lastBlockHash: string
    lastBlockUUID: string
    proof: string

    get config(): Config {
        return Application.getApplication().make(Config)
    }

    constructor(rec: BlockResourceItem) {
        this.firebaseID = rec.firebaseID
        this.seqID = rec.seqID
        this.uuid = rec.uuid
        this.transactions = rec.transactions
        this.lastBlockHash = rec.lastBlockHash
        this.lastBlockUUID = rec.lastBlockUUID
        this.proof = rec.proof
        this.timestamp = rec.timestamp
    }

    /** Returns true if this is the genesis block. */
    async isGenesis() {
        // first block will be guaranteed uuid 0000
        if (this.uuid !== '0000') {
            return false
        }
        const proof = this.proof
        const publicKey = this.config.get("app.gpg.key.public")

        const result = await openpgp.verify({
            publicKeys: await openpgp.readKey({
                armoredKey: publicKey,
            }),
            message: await openpgp.readMessage({
                armoredMessage: proof,
            }),
        })

        return !!(await result.signatures?.[0]?.verified)
    }

    /** Generate the hash for this block. */
    hash() {
        return crypto.createHash('sha256')
            .update(this.toString(), 'utf-8')
            .digest('hex')
    }

    /** Cast the Block's data to a plain object. */
    toItem(): BlockResourceItem {
        return {
            seqID: this.seqID,
            firebaseID: this.firebaseID,
            uuid: this.uuid,
            transactions: this.transactions,
            lastBlockHash: this.lastBlockHash,
            lastBlockUUID: this.lastBlockUUID,
            proof: this.proof,
            timestamp: this.timestamp,
        }
    }

    /** Generate the deterministic hash-able string. */
    toString() {
        return [
            this.uuid,
            JSON.stringify(this.transactions || [], undefined, 0),
            this.lastBlockHash,
            this.lastBlockUUID,
        ].join('%')
    }
}

/**
 * Interface representing a federated peer.
 */
export interface Peer {
    host: string,
    name?: string,
}

/**
 * Blockchain Unit
 * ---------------------------------------
 * Main service for interacting with the contact blockchain.
 */
@Singleton()
export class Blockchain extends Unit {
    @Inject()
    protected readonly logging!: Logging

    @Inject()
    protected readonly firebase!: FirebaseUnit

    @Inject()
    protected readonly config!: Config

    /**
     * Returns true if the given host is registered as a peer.
     * @param host
     */
    public async hasPeer(host: string): Promise<boolean> {
        const peers = await this.getPeers()
        return peers.some(peer => peer.host.toLowerCase() === host.toLowerCase())
    }

    /**
     * Get a list of all registered peers.
     */
    public async getPeers(): Promise<Peer[]> {
        const data = await this.firebase.ref('peers').once('value')
        return (data.val() as Peer[]) || []
    }

    /**
     * Register a new host as a peer of this instance.
     * @param peer
     */
    public async registerPeer(peer: Peer) {
        if (!(await this.hasPeer(peer.host))) {
            await this.firebase.ref('peers').push().set(peer)
        }
    }

    /**
     * Given an array of blocks in chain-order, validate the chain.
     * @param chain
     * @return boolean - true if the chain is valid
     */
    public async validate(chain: Block[]) {
        const blocks = collect<Block>(chain)
        return (
            await blocks.promiseMap(async (block, idx) => {
                if ( await block.isGenesis() ) {
                    return true
                }

                const previous: Block | undefined = blocks.at(idx - 1)
                if ( !previous ) {
                    this.logging.debug(`Chain is invalid: block ${idx} is missing previous ${idx - 1}.`)
                    return false;
                }

                if ( !(await this.validateProofOfWork(block, previous)) ) {
                    this.logging.debug(`Chain is invalid: block ${idx} failed proof of work validation`)
                    return false;
                }



                const pass = (
                    block.lastBlockUUID === previous.uuid
                    && block.lastBlockHash === previous.hash()
                )

                if ( !pass ) {
                    this.logging.debug(`Chain is invalid: block ${idx} does not match previous.`)
                    this.logging.debug({
                        lastBlockUUID: block.lastBlockUUID,
                        computedLastUUID: previous.uuid,
                        lastBlockHash: block.lastBlockHash,
                        computedLastHash: previous.hash(),
                    })
                }

                return pass
            })
        ).every(Boolean)
    }

    public async refresh() {

    }

    /**
     * Submit a group of encounter transactions to be added to the chain.
     * @param group
     */
    public async submitTransactions(group: [TransactionResourceItem, TransactionResourceItem]) {
        const lastBlock = await this.getLastBlock()

        this.logging.verbose('Last block:')
        this.logging.verbose(lastBlock)

        const block: BlockResourceItem = {
            timestamp: (new Date).getTime(),
            uuid: uuid_v4(),
            transactions: group.map(item => this.getEncounterTransaction(item)),
            lastBlockHash: lastBlock!.hash(),
            lastBlockUUID: lastBlock!.uuid,
            proof: await this.generateProofOfWork(lastBlock!),

            firebaseID: '',
            seqID: -1,
        }

        await (<BlockResource>this.app().make(BlockResource)).push(block)
        return new Block(block)
    }

    /**
     * Submit the given exposure notifications onto the blockchain.
     * @param exposures
     */
    public async submitExposures(...exposures: ExposureResourceItem[]) {
        const lastBlock = await this.getLastBlock()

        this.logging.verbose('Last block:')
        this.logging.verbose(lastBlock)

        const block: BlockResourceItem = {
            timestamp: (new Date).getTime(),
            uuid: uuid_v4(),
            transactions: exposures,
            lastBlockHash: lastBlock!.hash(),
            lastBlockUUID: lastBlock!.uuid,
            proof: await this.generateProofOfWork(lastBlock),

            firebaseID: '',
            seqID: -1,
        }

        await (<BlockResource>this.app().make(BlockResource)).push(block)
        return new Block(block)
    }

    /**
     * Instantiate the genesis block of the entire chain.
     */
    public async getGenesisBlock(): Promise<Block> {
        const message = openpgp.Message.fromText("0000")
        const privateKey = this.config.get("app.gpg.key.private")

        return new Block({
            timestamp: (new Date).getTime(),
            uuid: '0000',
            transactions: [],
            lastBlockHash: '',
            lastBlockUUID: '',
            proof: (await openpgp.sign({
                message,
                privateKeys: await openpgp.readKey({
                    armoredKey: privateKey
                }),
            })),
            firebaseID: '',
            seqID: -1,
        })
    }

    /**
     * Get the last block in the blockchain, or push the genesis if one doesn't already exist.
     */
    public async getLastBlock(): Promise<Block> {
        const rec: BlockResourceItem | undefined = await BlockResource.collect().last()
        if (rec) return new Block(rec)

        const genesis = (await this.getGenesisBlock()).toItem()
        await (<BlockResource>this.app().make(BlockResource)).push(genesis)
        return new Block(genesis)
    }

    /**
     * Get a list of all blocks in the chain, in order.
     */
    public async read(): Promise<BlockResourceItem[]> {
        return BlockResource.collect().all()
    }

    /**
     * Given a client-submitted transaction, generate a block encounter transaction record.
     * @param item
     * @protected
     */
    protected getEncounterTransaction(item: TransactionResourceItem): BlockEncounterTransaction {
        return {
            combinedHash: item.combinedHash,
            timestamp: item.timestamp,
            encodedGPSLocation: item.encodedGPSLocation,
        }
    }

    /**
     * Generate a proof of work string for the block that follows lastBlock.
     * @param lastBlock
     * @protected
     */
    protected async generateProofOfWork(lastBlock: Block): Promise<string> {
        const hashString = lastBlock.hash()
        const privateKey = this.config.get("app.gpg.key.private")
        const message = openpgp.Message.fromText(hashString)

        // Sign the hash using the server's private key
        return (await openpgp.sign({
            message,
            privateKeys: await openpgp.readKey({
                armoredKey: privateKey,
            })
        }))
    }

    /**
     * Validate that the proof of work of currentBlock is accurate relative to lastBlock.
     * @param currentBlock
     * @param lastBlock
     * @protected
     */
    protected async validateProofOfWork(currentBlock: Block, lastBlock: Block): Promise<boolean> {
        const proof = lastBlock.proof
        const publicKey = this.config.get("app.gpg.key.public")

        const result = await openpgp.verify({
            publicKeys: await openpgp.readKey({
                armoredKey: publicKey,
            }),
            message: await openpgp.readMessage({
                armoredMessage: proof,
            }),
        })

        return !!(await result.signatures?.[0]?.verified)
    }
}