Price Change Callback

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i -X POST 'https://handel.halowerk.com/v1/price-change-callback' \
  -H 'content-type: application/json' \
  --data-raw '{"callback_url":"https://stack.halowerk.com/_top10-endspurt/callback","direction":"increase","idempotency_key":"replace_with_32_character_random_event_key","minimum_change":0.5,"previous":{"currency":"GBP","value":50.77},"url":"https://books.toscrape.com/catalogue/a-light-in-the-attic_1000/index.html"}'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - -X POST 'https://handel.halowerk.com/v1/price-change-callback' \
  -H 'content-type: application/json' \
  --data-raw '{"callback_url":"https://stack.halowerk.com/_top10-endspurt/callback","direction":"increase","idempotency_key":"replace_with_32_character_random_event_key","minimum_change":0.5,"previous":{"currency":"GBP","value":50.77},"url":"https://books.toscrape.com/catalogue/a-light-in-the-attic_1000/index.html"}' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.006 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.006" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.006 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fhandel.halowerk.com%2Fv1%2Fprice-change-callback&method=POST
const res = await pay("https://handel.halowerk.com/v1/price-change-callback", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "callback_url": "https://stack.halowerk.com/_top10-endspurt/callback",
    "direction": "increase",
    "idempotency_key": "replace_with_32_character_random_event_key",
    "minimum_change": 0.5,
    "previous": {
      "currency": "GBP",
      "value": 50.77
    },
    "url": "https://books.toscrape.com/catalogue/a-light-in-the-attic_1000/index.html"
  }),
});
console.log(res.status, await res.text());

# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.006 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.006"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.post(
        "https://handel.halowerk.com/v1/price-change-callback",
        json={
            "callback_url": "https://stack.halowerk.com/_top10-endspurt/callback",
            "direction": "increase",
            "idempotency_key": "replace_with_32_character_random_event_key",
            "minimum_change": 0.5,
            "previous": {
                "currency": "GBP",
                "value": 50.77,
            },
            "url": "https://books.toscrape.com/catalogue/a-light-in-the-attic_1000/index.html",
        },
    )
    print(res.status_code, res.text)