# src/connection.js

    // @flow

    import assert from 'assert';
    import {parse as urlParse, format as urlFormat} from 'url';
    import fetch from 'node-fetch';
    import jayson from 'jayson/lib/client/browser';
    import {struct} from 'superstruct';
    import {Client as RpcWebSocketClient} from 'rpc-websockets';

    import {Transaction} from './transaction';
    import {PublicKey} from './publickey';
    import {sleep} from './util/sleep';
    import type {Account} from './account';
    import type {TransactionSignature, TransactionId} from './transaction';

    type RpcRequest = (methodName: string, args: Array<any>) => any;

    function createRpcRequest(url): RpcRequest {
      const server = jayson(async (request, callback) => {
        const options = {
          method: 'POST',
          body: request,
          headers: {
            'Content-Type': 'application/json',
          },
        };

        try {
          const res = await fetch(url, options);
          const text = await res.text();
          callback(null, text);
        } catch (err) {
          callback(err);
        }
      });

      return (method, args) => {
        return new Promise((resolve, reject) => {
          server.request(method, args, (err, response) => {
            if (err) {
              reject(err);
              return;
            }
            resolve(response);
          });
        });
      };
    }

    /**
     * Expected JSON RPC response for the "getBalance" message
     */
    const GetBalanceRpcResult = struct({
      jsonrpc: struct.literal('2.0'),
      id: 'string',
      error: 'any?',
      result: 'number?',
    });

    /**
     * @private
     */
    function jsonRpcResult(resultDescription: any) {
      const jsonRpcVersion = struct.literal('2.0');
      return struct.union([
        struct({
          jsonrpc: jsonRpcVersion,
          id: 'string',
          error: 'any',
        }),
        struct({
          jsonrpc: jsonRpcVersion,
          id: 'string',
          error: 'null?',
          result: resultDescription,
        }),
      ]);
    }

    /**
     * @private
     */
    const AccountInfoResult = struct({
      executable: 'boolean',
      loader: 'array',
      owner: 'array',
      tokens: 'number',
      userdata: 'array',
    });

    /**
     * Expected JSON RPC response for the "getAccountInfo" message
     */
    const GetAccountInfoRpcResult = jsonRpcResult(AccountInfoResult);

    /***
     * Expected JSON RPC response for the "accountNotification" message
     */
    const AccountNotificationResult = struct({
      subscription: 'number',
      result: AccountInfoResult,
    });

    /**
     * Expected JSON RPC response for the "confirmTransaction" message
     */
    const ConfirmTransactionRpcResult = jsonRpcResult('boolean');

    /**
     * Expected JSON RPC response for the "getSignatureStatus" message
     */
    const GetSignatureStatusRpcResult = jsonRpcResult(
      struct.enum([
        'AccountInUse',
        'Confirmed',
        'GenericFailure',
        'ProgramRuntimeError',
        'SignatureNotFound',
      ]),
    );

    /**
     * Expected JSON RPC response for the "getTransactionCount" message
     */
    const GetTransactionCountRpcResult = jsonRpcResult('number');

    /**
     * Expected JSON RPC response for the "getLastId" message
     */
    const GetLastId = jsonRpcResult('string');

    /**
     * Expected JSON RPC response for the "getFinality" message
     */
    const GetFinalityRpcResult = jsonRpcResult('number');

    /**
     * Expected JSON RPC response for the "requestAirdrop" message
     */
    const RequestAirdropRpcResult = jsonRpcResult('string');

    /**
     * Expected JSON RPC response for the "sendTransaction" message
     */
    const SendTokensRpcResult = jsonRpcResult('string');

    /**
     * Information describing an account
     *
     * @typedef {Object} AccountInfo
     * @property {number} tokens Number of tokens assigned to the account
     * @property {PublicKey} owner Identifier of the program that owns the account
     * @property {?Buffer} userdata Optional userdata assigned to the account
     * @property {PublicKey} loader Identifier of the loader for this account
     * @property {boolean} executable `true` if this account's userdata contains a loaded program
     */
    type AccountInfo = {
      executable: boolean,
      loader: PublicKey,
      owner: PublicKey,
      tokens: number,
      userdata: Buffer,
    };

    /**
     * Callback function for account change notifications
     */
    export type AccountChangeCallback = (accountInfo: AccountInfo) => void;

    /**
     * @private
     */
    type AccountSubscriptionInfo = {
      publicKey: string, // PublicKey of the account as a base 58 string
      callback: AccountChangeCallback,
      subscriptionId: null | number, // null when there's no current server subscription id
    };

    /**
     * Possible signature status values
     *
     * @typedef {string} SignatureStatus
     */
    export type SignatureStatus =
      | 'Confirmed'
      | 'AccountInUse'
      | 'SignatureNotFound'
      | 'ProgramRuntimeError'
      | 'GenericFailure';

    /**
     * A connection to a fullnode JSON RPC endpoint
     */
    export class Connection {
      _rpcRequest: RpcRequest;
      _rpcWebSocket: RpcWebSocketClient;
      _rpcWebSocketConnected: boolean = false;

      _lastIdInfo: {
        lastId: TransactionId | null,
        seconds: number,
        transactionSignatures: Array<string>,
      };
      _disableLastIdCaching: boolean = false;
      _accountChangeSubscriptions: {[number]: AccountSubscriptionInfo} = {};
      _accountChangeSubscriptionCounter: number = 0;

      /**
       * Establish a JSON RPC connection
       *
       * @param endpoint URL to the fullnode JSON RPC endpoint
       */
      constructor(endpoint: string) {
        let url = urlParse(endpoint);

        this._rpcRequest = createRpcRequest(url.href);
        this._lastIdInfo = {
          lastId: null,
          seconds: -1,
          transactionSignatures: [],
        };

        url.protocol = url.protocol === 'https:' ? 'wss:' : 'ws:';
        url.host = '';
        url.port = String(Number(url.port) + 1);
        if (url.port === '1') {
          url.port = url.protocol === 'wss:' ? '8901' : '8900';
        }
        this._rpcWebSocket = new RpcWebSocketClient(urlFormat(url), {
          autoconnect: false,
          max_reconnects: Infinity,
        });
        this._rpcWebSocket.on('open', this._wsOnOpen.bind(this));
        this._rpcWebSocket.on('error', this._wsOnError.bind(this));
        this._rpcWebSocket.on('close', this._wsOnClose.bind(this));
        this._rpcWebSocket.on(
          'accountNotification',
          this._wsOnAccountNotification.bind(this),
        );
      }

      /**
       * Fetch the balance for the specified public key
       */
      async getBalance(publicKey: PublicKey): Promise<number> {
        const unsafeRes = await this._rpcRequest('getBalance', [
          publicKey.toBase58(),
        ]);
        const res = GetBalanceRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch all the account info for the specified public key
       */
      async getAccountInfo(publicKey: PublicKey): Promise<AccountInfo> {
        const unsafeRes = await this._rpcRequest('getAccountInfo', [
          publicKey.toBase58(),
        ]);
        const res = GetAccountInfoRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(res.error.message);
        }

        const {result} = res;
        assert(typeof result !== 'undefined');

        return {
          executable: result.executable,
          loader: new PublicKey(result.loader),
          owner: new PublicKey(result.owner),
          tokens: result.tokens,
          userdata: Buffer.from(result.userdata),
        };
      }

      /**
       * Confirm the transaction identified by the specified signature
       */
      async confirmTransaction(signature: TransactionSignature): Promise<boolean> {
        const unsafeRes = await this._rpcRequest('confirmTransaction', [signature]);
        const res = ConfirmTransactionRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the current transaction count of the network
       */
      async getSignatureStatus(
        signature: TransactionSignature,
      ): Promise<SignatureStatus> {
        const unsafeRes = await this._rpcRequest('getSignatureStatus', [signature]);
        const res = GetSignatureStatusRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the current transaction count of the network
       */
      async getTransactionCount(): Promise<number> {
        const unsafeRes = await this._rpcRequest('getTransactionCount', []);
        const res = GetTransactionCountRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return Number(res.result);
      }

      /**
       * Fetch the identifier to the latest transaction on the network
       */
      async getLastId(): Promise<TransactionId> {
        const unsafeRes = await this._rpcRequest('getLastId', []);
        const res = GetLastId(unsafeRes);
        if (res.error) {
          throw new Error(res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Return the current network finality time in millliseconds
       */
      async getFinality(): Promise<number> {
        const unsafeRes = await this._rpcRequest('getFinality', []);
        const res = GetFinalityRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return Number(res.result);
      }

      /**
       * Request an allocation of tokens to the specified account
       */
      async requestAirdrop(
        to: PublicKey,
        amount: number,
      ): Promise<TransactionSignature> {
        const unsafeRes = await this._rpcRequest('requestAirdrop', [
          to.toBase58(),
          amount,
        ]);
        const res = RequestAirdropRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Sign and send a transaction
       */
      async sendTransaction(
        transaction: Transaction,
        ...signers: Array<Account>
      ): Promise<TransactionSignature> {
        for (;;) {
          // Attempt to use the previous last id for up to 1 second
          const seconds = new Date().getSeconds();
          if (
            this._lastIdInfo.lastId != null &&
            this._lastIdInfo.seconds === seconds
          ) {
            transaction.lastId = this._lastIdInfo.lastId;
            transaction.sign(...signers);
            if (!transaction.signature) {
              throw new Error('!signature'); // should never happen
            }

            // If the signature of this transaction has not been seen before with the
            // current lastId, all done.
            const signature = transaction.signature.toString();
            if (!this._lastIdInfo.transactionSignatures.includes(signature)) {
              this._lastIdInfo.transactionSignatures.push(signature);
              if (this._disableLastIdCaching) {
                this._lastIdInfo.seconds = -1;
              }
              break;
            }
          }

          // Fetch a new last id
          let attempts = 0;
          const startTime = Date.now();
          for (;;) {
            const lastId = await this.getLastId();

            if (this._lastIdInfo.lastId != lastId) {
              this._lastIdInfo = {
                lastId,
                seconds: new Date().getSeconds(),
                transactionSignatures: [],
              };
              break;
            }
            if (attempts === 8) {
              throw new Error(
                `Unable to obtain a new last id after ${Date.now() - startTime}ms`,
              );
            }
            await sleep(250);
            ++attempts;
          }
        }

        const wireTransaction = transaction.serialize();
        return await this.sendRawTransaction(wireTransaction);
      }

      /**
       * Send a transaction that has already been signed and serialized into the
       * wire format
       */
      async sendRawTransaction(
        wireTransaction: Buffer,
      ): Promise<TransactionSignature> {
        const unsafeRes = await this._rpcRequest('sendTransaction', [
          [...wireTransaction],
        ]);
        const res = SendTokensRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        assert(res.result);
        return res.result;
      }

      /**
       * @private
       */
      _wsOnOpen() {
        this._rpcWebSocketConnected = true;
        this._updateSubscriptions();
      }

      /**
       * @private
       */
      _wsOnError(err: Error) {
        console.log('ws error:', err.message);
      }

      /**
       * @private
       */
      _wsOnClose(code: number, message: string) {
        // 1000 means _rpcWebSocket.close() was called explicitly
        if (code !== 1000) {
          console.log('ws close:', code, message);
        }
        this._rpcWebSocketConnected = false;
      }

      /**
       * @private
       */
      _wsOnAccountNotification(notification: Object) {
        const res = AccountNotificationResult(notification);
        if (res.error) {
          throw new Error(res.error.message);
        }

        const keys = Object.keys(this._accountChangeSubscriptions).map(Number);
        for (let id of keys) {
          const sub = this._accountChangeSubscriptions[id];
          if (sub.subscriptionId === res.subscription) {
            const {result} = res;
            assert(typeof result !== 'undefined');

            sub.callback({
              executable: result.executable,
              loader: new PublicKey(result.loader),
              owner: new PublicKey(result.owner),
              tokens: result.tokens,
              userdata: Buffer.from(result.userdata),
            });
            return true;
          }
        }
      }

      /**
       * @private
       */
      async _updateSubscriptions() {
        const keys = Object.keys(this._accountChangeSubscriptions).map(Number);
        if (keys.length === 0) {
          this._rpcWebSocket.close();
          return;
        }

        if (!this._rpcWebSocketConnected) {
          for (let id of keys) {
            this._accountChangeSubscriptions[id].subscriptionId = null;
          }
          this._rpcWebSocket.connect();
          return;
        }

        for (let id of keys) {
          const {subscriptionId, publicKey} = this._accountChangeSubscriptions[id];
          if (subscriptionId === null) {
            try {
              this._accountChangeSubscriptions[
                id
              ].subscriptionId = await this._rpcWebSocket.call('accountSubscribe', [
                publicKey,
              ]);
            } catch (err) {
              console.log(
                `accountSubscribe error for ${publicKey}: ${err.message}`,
              );
            }
          }
        }
      }

      /**
       * Register a callback to be invoked whenever the specified account changes
       *
       * @param publickey Public key of the account to monitor
       * @param callback Function to invoke whenever the account is changed
       * @return subscription id
       */
      onAccountChange(
        publicKey: PublicKey,
        callback: AccountChangeCallback,
      ): number {
        const id = ++this._accountChangeSubscriptionCounter;
        this._accountChangeSubscriptions[id] = {
          publicKey: publicKey.toBase58(),
          callback,
          subscriptionId: null,
        };
        this._updateSubscriptions();
        return id;
      }

      /**
       * Deregister an account notification callback
       *
       * @param id subscription id to deregister
       */
      async removeAccountChangeListener(id: number): Promise<void> {
        if (this._accountChangeSubscriptions[id]) {
          const {subscriptionId} = this._accountChangeSubscriptions[id];
          delete this._accountChangeSubscriptions[id];
          if (subscriptionId !== null) {
            try {
              await this._rpcWebSocket.call('accountUnsubscribe', [subscriptionId]);
            } catch (err) {
              console.log('accountUnsubscribe error:', err.message);
            }
          }
          this._updateSubscriptions();
        } else {
          throw new Error(`Unknown account change id: ${id}`);
        }
      }
    }