defmodule Polymarket.RPC do
  @moduledoc """
  Stateless JSON-RPC 2.0 client for Polygon (and any other EVM chain
  that speaks standard `eth_*` JSON-RPC).

  The building blocks a transaction-submission layer needs:

    * `call/3` — raw JSON-RPC call returning the parsed `result`.
    * `chain_id/1`, `block_number/1`, `gas_price/1` — uint helpers.
    * `nonce/2`/`nonce/3` — `eth_getTransactionCount`, default block
      tag `"pending"`.
    * `estimate_gas/2` — `eth_estimateGas` with Elixir-friendly param
      shape (atom keys, integer amounts).
    * `send_raw_transaction/2` — accepts a hex string, raw binary, or
      a signed `Polymarket.Tx` struct.

  This module is intentionally stateless. The `Polymarket.RPC` struct
  carries `:url`, `:headers`, `:timeout`, `:retry`, `:max_retries`,
  and `:plug` (test-only). No GenServer, no connection pool of our
  own — Req's Finch pool handles transport. Caller threads the struct
  through calls.

  ## Response contract

    * `{:ok, result}` — successful RPC response. `result` is the
      decoded `result` field (a hex string for most `eth_*` calls, a
      map or list for others). Typed helpers parse `result` into a
      typed value before returning.
    * `{:error, {:rpc_error, code, message, data}}` — JSON-RPC
      protocol error returned by the node. `data` is `nil` when the
      node didn't include it.
    * `{:error, {:http_error, status, body}}` — non-2xx HTTP response
      from the node.
    * `{:error, {:transport_error, reason}}` — Req-level transport
      failure.
    * `{:error, {:invalid_response, body_or_message}}` — well-formed
      HTTP 200 but the body is missing the expected `result` /
      `error` shape, or a typed helper got back something it couldn't
      parse (e.g. `chain_id/1` got non-hex).

  ## Scope

  This module ships **only** the JSON-RPC client and nonce/gas
  primitives. Higher-level submit wrappers
  (`Polymarket.CTF.redeem_positions/2` etc.) compose calldata
  (`Polymarket.ABI`) + tx serialization (`Polymarket.Tx`) + this RPC
  layer.

  ## Options

    * `:url` *(required)* — RPC endpoint URL (e.g. `"https://polygon-rpc.com"`).
    * `:headers` — extra request headers (default `[]`).
    * `:timeout` — `receive_timeout` in milliseconds (default `15_000`).
    * `:retry` — Req retry policy. Default `false`. JSON-RPC POSTs are
      not idempotent at the application layer (sending a tx twice
      double-spends nonce); leave retry off unless the caller knows
      the specific RPC method is safe to retry.
    * `:max_retries` — Req max retries (default `0`).
    * `:plug` — test-only; injects a Req.Test plug into the request.
  """

  alias Polymarket.Tx

  @type t :: %__MODULE__{
          url: String.t(),
          headers: list(),
          timeout: pos_integer(),
          retry: term(),
          max_retries: non_neg_integer(),
          plug: term()
        }

  defstruct url: nil,
            headers: [],
            timeout: 15_000,
            retry: false,
            max_retries: 0,
            plug: nil

  @default_timeout 15_000

  @doc """
  Builds a `Polymarket.RPC` config struct.

  Required: `:url`. Optional: `:headers`, `:timeout`, `:retry`,
  `:max_retries`, `:plug`.
  """
  @spec new(keyword()) :: t()
  def new(opts) do
    url = Keyword.fetch!(opts, :url)

    unless is_binary(url) and url != "" do
      raise ArgumentError, ":url must be a non-empty string"
    end

    %__MODULE__{
      url: url,
      headers: Keyword.get(opts, :headers, []),
      timeout: Keyword.get(opts, :timeout, @default_timeout),
      retry: Keyword.get(opts, :retry, false),
      max_retries: Keyword.get(opts, :max_retries, 0),
      plug: Keyword.get(opts, :plug)
    }
  end

  @doc """
  Performs a raw JSON-RPC call. Returns the decoded `result` field on
  success; see the moduledoc for the full error shape.
  """
  @spec call(t(), String.t(), list()) :: {:ok, term()} | {:error, term()}
  def call(%__MODULE__{} = client, method, params)
      when is_binary(method) and is_list(params) do
    body = %{
      "jsonrpc" => "2.0",
      "id" => 1,
      "method" => method,
      "params" => params
    }

    req_opts =
      [
        method: :post,
        url: client.url,
        json: body,
        headers: client.headers,
        receive_timeout: client.timeout,
        retry: client.retry,
        max_retries: client.max_retries
      ]
      |> maybe_put(:plug, client.plug)

    req_opts
    |> Req.request()
    |> normalize_rpc()
  end

  # ── Typed helpers ──

  @doc "Calls `eth_chainId`. Returns the chain id as a non-negative integer."
  @spec chain_id(t()) :: {:ok, non_neg_integer()} | {:error, term()}
  def chain_id(%__MODULE__{} = client) do
    client |> call("eth_chainId", []) |> parse_uint_hex()
  end

  @doc "Calls `eth_blockNumber`. Returns the latest block number as an integer."
  @spec block_number(t()) :: {:ok, non_neg_integer()} | {:error, term()}
  def block_number(%__MODULE__{} = client) do
    client |> call("eth_blockNumber", []) |> parse_uint_hex()
  end

  @doc "Calls `eth_gasPrice`. Returns wei as an integer."
  @spec gas_price(t()) :: {:ok, non_neg_integer()} | {:error, term()}
  def gas_price(%__MODULE__{} = client) do
    client |> call("eth_gasPrice", []) |> parse_uint_hex()
  end

  @doc """
  Calls `eth_getTransactionCount(address, block_tag)`. Default block
  tag is `"pending"` so the returned nonce is suitable for the next
  transaction the caller will sign.
  """
  @spec nonce(t(), String.t(), String.t()) :: {:ok, non_neg_integer()} | {:error, term()}
  def nonce(%__MODULE__{} = client, address, block_tag \\ "pending")
      when is_binary(block_tag) do
    validated = validate_address!(:address, address)

    client
    |> call("eth_getTransactionCount", [validated, block_tag])
    |> parse_uint_hex()
  end

  @doc """
  Calls `eth_estimateGas`. `params` is a map with optional keys:

    * `:from` — sender address (`0x`-prefixed hex).
    * `:to` — destination address (`0x`-prefixed hex).
    * `:value` — non-negative integer (wei).
    * `:gas` — non-negative integer (gas units).
    * `:gas_price` — non-negative integer (wei).
    * `:data` — binary or `0x`-prefixed hex string.

  Integer amounts are encoded as `0x`-prefixed hex on the wire.
  """
  @spec estimate_gas(t(), map()) :: {:ok, non_neg_integer()} | {:error, term()}
  def estimate_gas(%__MODULE__{} = client, params) when is_map(params) do
    rpc_params = format_call_params(params)
    client |> call("eth_estimateGas", [rpc_params]) |> parse_uint_hex()
  end

  @doc """
  Calls `eth_sendRawTransaction(signed_bytes)`. Returns the
  `0x`-prefixed transaction hash from the node on success.

  Accepts:

    * a `Polymarket.Tx` struct that has been signed (`:v` populated);
    * a `0x`-prefixed hex string;
    * a raw binary (will be hex-encoded with `0x` prefix).
  """
  @spec send_raw_transaction(t(), Tx.t() | binary()) :: {:ok, String.t()} | {:error, term()}
  def send_raw_transaction(%__MODULE__{} = client, %Tx{v: v} = tx) when is_integer(v) do
    send_raw_transaction(client, Tx.serialize(tx))
  end

  def send_raw_transaction(%__MODULE__{} = client, "0x" <> _ = signed_hex) do
    case call(client, "eth_sendRawTransaction", [signed_hex]) do
      {:ok, "0x" <> _ = tx_hash} -> {:ok, tx_hash}
      {:ok, other} -> {:error, {:invalid_response, other}}
      {:error, _} = err -> err
    end
  end

  def send_raw_transaction(%__MODULE__{} = client, signed) when is_binary(signed) do
    send_raw_transaction(client, "0x" <> Base.encode16(signed, case: :lower))
  end

  # ── Private ──

  defp normalize_rpc({:ok, %{status: 200, body: %{"result" => result}}}) do
    {:ok, result}
  end

  defp normalize_rpc(
         {:ok, %{status: 200, body: %{"error" => %{"code" => code, "message" => msg} = err}}}
       )
       when is_integer(code) and is_binary(msg) do
    {:error, {:rpc_error, code, msg, Map.get(err, "data")}}
  end

  defp normalize_rpc({:ok, %{status: 200, body: body}}) do
    {:error, {:invalid_response, body}}
  end

  defp normalize_rpc({:ok, %{status: status, body: body}}) do
    {:error, {:http_error, status, body}}
  end

  defp normalize_rpc({:error, reason}) do
    {:error, {:transport_error, reason}}
  end

  defp parse_uint_hex({:ok, "0x" <> hex}) do
    case Integer.parse(hex, 16) do
      {n, ""} -> {:ok, n}
      _ -> {:error, {:invalid_response, "expected hex integer, got: 0x#{hex}"}}
    end
  end

  defp parse_uint_hex({:ok, other}) do
    {:error, {:invalid_response, other}}
  end

  defp parse_uint_hex({:error, _} = err), do: err

  defp format_call_params(params) do
    # Each helper threads (wire_key, user_key, value). The wire_key is
    # the JSON-RPC field name on the request body; the user_key is the
    # Elixir atom the caller passed and is what error messages
    # reference, so a `:gas_price` validation error says ":gas_price",
    # not "gasPrice".
    %{}
    |> maybe_put_address("from", :from, Map.get(params, :from))
    |> maybe_put_address("to", :to, Map.get(params, :to))
    |> maybe_put_uint_hex("value", :value, Map.get(params, :value))
    |> maybe_put_uint_hex("gas", :gas, Map.get(params, :gas))
    |> maybe_put_uint_hex("gasPrice", :gas_price, Map.get(params, :gas_price))
    |> maybe_put_data("data", :data, Map.get(params, :data))
  end

  defp maybe_put_address(map, _wire_key, _user_key, nil), do: map

  defp maybe_put_address(map, wire_key, user_key, value) do
    Map.put(map, wire_key, validate_address!(user_key, value))
  end

  # Same standard as `Polymarket.Tx.validate_to/1`: 0x-prefixed, exactly
  # 40 hex characters after the prefix (= 20 bytes), and the hex must
  # actually decode. The pre-Phase-11c.1 implementation accepted any
  # `"0x" <> binary`, which let placeholders like `"0xto"` flow onto
  # the wire as wire-format addresses.
  defp validate_address!(user_key, "0x" <> hex = full) when byte_size(hex) == 40 do
    case Base.decode16(hex, case: :mixed) do
      {:ok, _bytes} ->
        full

      :error ->
        raise ArgumentError,
              "#{inspect(user_key)} must be a 0x-prefixed 20-byte hex address, got: #{inspect(full)}"
    end
  end

  defp validate_address!(user_key, other) do
    raise ArgumentError,
          "#{inspect(user_key)} must be a 0x-prefixed 20-byte hex address, got: #{inspect(other)}"
  end

  defp maybe_put_uint_hex(map, _wire_key, _user_key, nil), do: map

  defp maybe_put_uint_hex(map, wire_key, _user_key, n) when is_integer(n) and n >= 0 do
    Map.put(map, wire_key, "0x" <> hex_lower(n))
  end

  defp maybe_put_uint_hex(_map, _wire_key, user_key, other) do
    raise ArgumentError,
          "#{inspect(user_key)} must be a non-negative integer, got: #{inspect(other)}"
  end

  defp maybe_put_data(map, _wire_key, _user_key, nil), do: map

  defp maybe_put_data(map, wire_key, _user_key, "0x" <> _ = hex) when is_binary(hex) do
    Map.put(map, wire_key, hex)
  end

  defp maybe_put_data(map, wire_key, _user_key, bin) when is_binary(bin) do
    Map.put(map, wire_key, "0x" <> Base.encode16(bin, case: :lower))
  end

  # Explicit fallback for non-binary `:data`. Without this clause,
  # `RPC.estimate_gas(client, %{data: 123})` would raise
  # `FunctionClauseError` while invalid addresses and integer fields
  # raise `ArgumentError`. Harmonizing the error shape here means
  # callers don't have to special-case data validation at the boundary.
  defp maybe_put_data(_map, _wire_key, user_key, other) do
    raise ArgumentError,
          "#{inspect(user_key)} must be a binary or 0x-prefixed hex string, got: #{inspect(other)}"
  end

  defp hex_lower(n) when is_integer(n) and n >= 0 do
    n |> Integer.to_string(16) |> String.downcase()
  end

  defp maybe_put(opts, _key, nil), do: opts
  defp maybe_put(opts, key, value), do: Keyword.put(opts, key, value)
end