Convert from Flow to Typescript (#816)

* convert to typescript
* add docs for custom node typing
* update webpack, gulpfile

src/ledger/orderbook.ts

@@ -0,0 +1,109 @@
+import * as _ from 'lodash'
+import * as utils from './utils'
+import parseOrderbookOrder from './parse/orderbook-order'
+import {validate} from '../common'
+import {Connection} from '../common'
+import {OrdersOptions, OrderSpecification} from './types'
+import {Amount, Issue} from '../common/types'
+
+type Orderbook = {
+  base: Issue,
+  counter: Issue
+}
+
+type OrderbookItem = {
+   specification: OrderSpecification,
+   properties: {
+    maker: string,
+    sequence: number,
+    makerExchangeRate: string
+  },
+  state?: {
+    fundedAmount: Amount,
+    priceOfFundedAmount: Amount
+  }
+}
+
+type OrderbookOrders = Array<OrderbookItem>
+
+type GetOrderbook = {
+  bids: OrderbookOrders,
+  asks: OrderbookOrders
+}
+
+// account is to specify a "perspective", which affects which unfunded offers
+// are returned
+function getBookOffers(connection: Connection, account: string,
+  ledgerVersion: number|undefined, limit: number|undefined, takerGets: Issue,
+  takerPays: Issue
+): Promise<Object[]> {
+  const orderData = utils.renameCounterpartyToIssuerInOrder({
+    taker_gets: takerGets,
+    taker_pays: takerPays
+  })
+  return connection.request({
+    command: 'book_offers',
+    taker_gets: orderData.taker_gets,
+    taker_pays: orderData.taker_pays,
+    ledger_index: ledgerVersion || 'validated',
+    limit: limit,
+    taker: account
+  }).then(data => data.offers)
+}
+
+function isSameIssue(a: Amount, b: Amount) {
+  return a.currency === b.currency && a.issuer === b.issuer
+}
+
+function directionFilter(direction: string, order: OrderbookItem) {
+  return order.specification.direction === direction
+}
+
+function flipOrder(order: OrderbookItem) {
+  const specification = order.specification
+  const flippedSpecification = {
+    quantity: specification.totalPrice,
+    totalPrice: specification.quantity,
+    direction: specification.direction === 'buy' ? 'sell' : 'buy'
+  }
+  const newSpecification = _.merge({}, specification, flippedSpecification)
+  return _.merge({}, order, {specification: newSpecification})
+}
+
+function alignOrder(base: Amount, order: OrderbookItem) {
+  const quantity = order.specification.quantity
+  return isSameIssue(quantity, base) ? order : flipOrder(order)
+}
+
+function formatBidsAndAsks(orderbook: Orderbook, offers) {
+  // the "base" currency is the currency that you are buying or selling
+  // the "counter" is the currency that the "base" is priced in
+  // a "bid"/"ask" is an order to buy/sell the base, respectively
+  // for bids: takerGets = totalPrice = counter, takerPays = quantity = base
+  // for asks: takerGets = quantity = base, takerPays = totalPrice = counter
+  // quality = takerPays / takerGets; price = totalPrice / quantity
+  // for bids: lowest quality => lowest quantity/totalPrice => highest price
+  // for asks: lowest quality => lowest totalPrice/quantity => lowest price
+  // for both bids and asks, lowest quality is closest to mid-market
+  // we sort the orders so that earlier orders are closer to mid-market
+  const orders = _.sortBy(offers, 'quality').map(parseOrderbookOrder)
+  const alignedOrders = orders.map(_.partial(alignOrder, orderbook.base))
+  const bids = alignedOrders.filter(_.partial(directionFilter, 'buy'))
+  const asks = alignedOrders.filter(_.partial(directionFilter, 'sell'))
+  return {bids, asks}
+}
+
+function getOrderbook(address: string, orderbook: Orderbook,
+  options: OrdersOptions = {}
+): Promise<GetOrderbook> {
+  validate.getOrderbook({address, orderbook, options})
+
+  const getter = _.partial(getBookOffers, this.connection, address,
+    options.ledgerVersion, options.limit)
+  const getOffers = _.partial(getter, orderbook.base, orderbook.counter)
+  const getReverseOffers = _.partial(getter, orderbook.counter, orderbook.base)
+  return Promise.all([getOffers(), getReverseOffers()]).then(data =>
+    formatBidsAndAsks(orderbook, _.flatten(data)))
+}
+
+export default getOrderbook