"""Strategy cookbook: DCA (dollar-cost averaging). A drop-in strategy.py 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.py and keep dry_run = true in config.toml until the log shows
what you expect. decide(market, book, state) gets what the starter bot's strategy.py gets (prices, the wallet's
balances, and state kept in bot-state.json) and returns a list of Order. bot.py cuts every order to your limits.

An example to learn from, not advice: it makes no attempt to predict the price.
"""
import time
from dataclasses import dataclass


@dataclass
class Order:
    sell: str            # the token to sell, e.g. "ETH"
    buy: str             # the token to buy, e.g. "USDG"
    amount_usd: float    # how many dollars of `sell` to trade
    reason: str = ""     # why: shown in the console and bot-log.jsonl


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


def decide(market, book, state):
    s = state.setdefault("dca", {})                     # this strategy's own corner of state
    price = market.get("ETH")
    if price is None:
        return []                                       # no ETH price this tick: wait for the next one
    now = time.time()
    last = s.get("last_buy")
    if last is not None and now - last < EVERY_HOURS * 3600:
        return []                                       # not time yet
    if usd_of(book, "USDG") < BUY_USD:
        return []                                       # not enough USDG: nothing is recorded, so it tries next tick
    s["last_buy"] = now
    s["buys"] = s.get("buys", 0) + 1
    return [Order(sell="USDG", buy="ETH", amount_usd=BUY_USD,
                  reason=f"buy #{s['buys']}: ${BUY_USD:g} of ETH at ${price:,.2f}, every {EVERY_HOURS:g} h")]


def usd_of(book, token):
    """The wallet's holding of `token` in dollars (0 when it holds none, or the token has no price)."""
    return (book["balances"].get(token) or {}).get("usd") or 0