defmodule CCXT.Signing.HmacSha512Gate do
  @moduledoc """
  HMAC-SHA512 Gate.io-style signing pattern.

  Used by: Gate.io

  ## How it works

  1. Hash the body with SHA512 (empty string if no body)
  2. Generate timestamp (seconds)
  3. Build newline-separated payload: `METHOD\\npath\\nquery\\nbody_hash\\ntimestamp`
  4. Sign with HMAC-SHA512, encode as hex
  5. Secret used raw (NOT base64 decoded)

  ## Configuration

      signing: %{
        pattern: :hmac_sha512_gate,
        api_key_header: "KEY",
        signature_header: "SIGN",
        timestamp_header: "Timestamp",
        signing_path_prefix: "/api/v4"
      }
  """

  @behaviour CCXT.Signing.Behaviour

  alias CCXT.Credentials
  alias CCXT.Signing

  @impl true
  @spec sign(Signing.request(), Credentials.t(), Signing.config()) :: Signing.signed_request()
  def sign(request, credentials, config) do
    timestamp_string = to_string(Signing.timestamp_seconds_from_config(config))
    query_string = Signing.urlencode(request.params)

    # Gate.io requires hashing even empty body
    body = request.body || ""
    body_hash = body |> Signing.sha512() |> Signing.encode_hex()

    signing_path = Map.get(config, :signing_path_prefix, "/api/v4") <> request.path
    method = request.method |> to_string() |> String.upcase()
    payload = Enum.join([method, signing_path, query_string, body_hash, timestamp_string], "\n")

    signature =
      payload
      |> Signing.hmac_sha512(credentials.secret)
      |> Signing.encode_hex()

    url = if query_string == "", do: request.path, else: request.path <> "?" <> query_string
    headers = build_headers(credentials, signature, timestamp_string, config)

    %{
      url: url,
      method: request.method,
      headers: headers,
      body: if(body == "", do: nil, else: body)
    }
  end

  defp build_headers(credentials, signature, timestamp, config) do
    api_key_header = Map.get(config, :api_key_header, "KEY")
    signature_header = Map.get(config, :signature_header, "SIGN")
    timestamp_header = Map.get(config, :timestamp_header, "Timestamp")

    [
      {api_key_header, credentials.api_key},
      {signature_header, signature},
      {timestamp_header, timestamp},
      {"Content-Type", "application/json"}
    ]
  end
end