/**
 * Strategy cookbook: DCA (dollar-cost averaging). A drop-in strategy.ts for the Orblivion starter bot.
 *
 * It buys BUY_USD of ETH with USDG every EVERY_HOURS hours, whatever the price. The first buy comes on the first tick
 * with a price; the time of the last buy is kept in state, so a restart doesn't buy again early.
 *
 * To use it, copy this file over the starter bot's strategy.ts and keep "dry_run": true in config.json until the log
 * shows what you expect. decide(market, book, state) gets what the starter bot's strategy.ts gets (prices, the wallet's
 * balances, and state kept in bot-state.json) and returns a list of orders. bot.ts cuts every order to your limits.
 *
 * An example to learn from, not advice: it makes no attempt to predict the price.
 */

export type Market = Record<string, number>
export type Holding = { units: number | null; usd: number | null }
export type Book = { balances: Record<string, Holding>; totalUsd: number }
export type State = Record<string, any>
export type Order = {
  sell: string // the token to sell, e.g. 'ETH'
  buy: string // the token to buy, e.g. 'USDG'
  amountUsd: number // how many dollars of `sell` to trade
  reason?: string // why: shown in the console and bot-log.jsonl
}

const BUY_USD = 5 // dollars of USDG to spend on each buy
const EVERY_HOURS = 24 // hours between buys: more hours, fewer buys

export function decide(market: Market, book: Book, state: State): Order[] {
  const s = (state.dca ??= {}) // this strategy's own corner of state
  const price = market.ETH
  if (price === undefined) return [] // no ETH price this tick: wait for the next one
  const now = Date.now() / 1000
  const last: number | undefined = s.lastBuy
  if (last !== undefined && now - last < EVERY_HOURS * 3600) return [] // not time yet
  if (usdOf(book, 'USDG') < BUY_USD) return [] // not enough USDG: nothing is recorded, so it tries next tick
  s.lastBuy = now
  s.buys = (s.buys ?? 0) + 1
  return [{ sell: 'USDG', buy: 'ETH', amountUsd: BUY_USD, reason: `buy #${s.buys}: $${BUY_USD} of ETH at $${price.toFixed(2)}, every ${EVERY_HOURS} h` }]
}

/** The wallet's holding of `token` in dollars (0 when it holds none, or the token has no price). */
const usdOf = (book: Book, token: string) => book.balances[token]?.usd ?? 0