defmodule Numscriptex do
  @moduledoc """
  NumscriptEx is a library that allows its users to run [Numscripts](https://docs.formance.com/numscript/)
  via Elixir.
  """

  alias Numscriptex.AssetsManager
  alias Numscriptex.Balance
  alias Numscriptex.Posting
  alias Numscriptex.Run
  alias Numscriptex.Utilities

  require AssetsManager

  AssetsManager.ensure_wasm_binary_is_valid()

  @type run_result() :: %{
          required(:balances) => list(Balance.t()),
          required(:postings) => list(Posting.t()),
          required(:accountsMeta) => map(),
          required(:txMeta) => map()
        }

  @type errors() :: %{
          required(:reason) => any(),
          optional(:details) => any()
        }

  @doc """
  `version/0` simply shows a map with both [Numscript-WASM](https://github.com/PagoPlus/numscript-wasm) and NumscriptEx versions. Ex:

  ```elixir
  iex> Numscriptex.version()
  %{numscriptex: "v0.2.6", numscript_wasm: "v0.1.0"}
  ```
  """
  @spec version() :: %{numscriptex: binary(), numscript_wasm: binary()}
  def version do
    numscriptex_version =
      :numscriptex
      |> Application.spec(:vsn)
      |> to_string()
      |> then(fn vsn -> "v#{vsn}" end)

    case execute_command(:version) do
      {:ok, numscript_wasm_version} ->
        Map.put(numscript_wasm_version, :numscriptex, numscriptex_version)

      {:error, _reason} ->
        %{numscript_wasm: "unknown", numscriptex: numscriptex_version}
    end
  end

  @doc """
  To use `run/2` your first argument must be your script, and the second must
  be a `%Numscriptex.Run{}` (go to `Numscriptex.Run` module to see more) struct.
  Ex:

  ```elixir
  iex> script = "send [USD/2 100] (source = @foo destination = @bar)"
  ...> balances = %{"foo" => %{"USD/2" => 500, "EUR/2" => 300}}
  ...>
  ...> struct =
  ...> Numscriptex.Run.new()
  ...> |> Numscriptex.Run.put!(:balances, balances)
  ...> |> Numscriptex.Run.put!(:metadata, %{})
  ...> |> Numscriptex.Run.put!(:variables, %{})
  ...>
  ...> Numscriptex.run(script, struct)
  ```
  """
  @spec run(binary(), Numscriptex.Run.t()) :: {:ok, run_result()} | {:error, errors()}
  def run(numscript, %Numscriptex.Run{} = run_struct) do
    initial_balance = Map.get(run_struct, :balances)

    run_struct
    |> Run.normalize_to_map()
    |> Map.merge(%{script: numscript})
    |> JSON.encode!()
    |> execute_command(:run)
    |> maybe_put_final_balance(initial_balance)
    |> standardize_run_result()
  end

  def run(_numscript, _run_struct), do: {:error, %{reason: :badarg}}

  defp standardize_run_result({:ok, result}) do
    standardized_result =
      result
      |> Map.put_new(:accountsMeta, %{})
      |> Map.put_new(:txMeta, %{})
      |> Map.update!(:postings, &Posting.from_list/1)

    {:ok, standardized_result}
  end

  defp standardize_run_result({:error, _reason} = errors), do: errors

  defp maybe_put_final_balance({:ok, %{"postings" => postings} = result}, initial_balance) do
    balances = Balance.put(initial_balance, postings)

    normalized_result =
      result
      |> Utilities.normalize_keys(:atom)
      |> Map.put(:balances, balances)

    {:ok, normalized_result}
  end

  defp maybe_put_final_balance({:error, _reason} = error, _initial_balance),
    do: error

  defp execute_command(input \\ "", operation)

  defp execute_command(input, operation) do
    {:ok, stdout_pipe} = Wasmex.Pipe.new()
    {:ok, stdin_pipe} = Wasmex.Pipe.new()
    {:ok, stderr_pipe} = Wasmex.Pipe.new()

    Wasmex.Pipe.write(stdin_pipe, input)
    Wasmex.Pipe.seek(stdin_pipe, 0)

    wasi = %Wasmex.Wasi.WasiOptions{
      args: ["numscript.wasm", to_string(operation)],
      stdout: stdout_pipe,
      stdin: stdin_pipe,
      stderr: stderr_pipe
    }

    binary_path = AssetsManager.binary_path()

    with {:ok, binary} <- File.read(binary_path),
         {:ok, pid} <- Wasmex.start_link(%{bytes: binary, wasi: wasi}),
         {{:ok, _}, _pid} <- {Wasmex.call_function(pid, :_start, []), pid} do
      GenServer.stop(pid, :normal)
      process(pid, stdout_pipe, stderr_pipe, operation)
    else
      {{:error, _reason}, pid} ->
        GenServer.stop(pid)
        process(pid, stdout_pipe, stderr_pipe, operation)

      {:error, reason} when is_atom(reason) ->
        {:error, %{reason: handle_posix_errors(reason)}}

      {:error, reason} ->
        {:error, %{reason: reason}}
    end
  end

  defp process(pid, stdout_pipe, stderr_pipe, operation) when is_pid(pid) do
    Wasmex.Pipe.seek(stdout_pipe, 0)
    stdout = Wasmex.Pipe.read(stdout_pipe)

    Wasmex.Pipe.seek(stderr_pipe, 0)
    error = Wasmex.Pipe.read(stderr_pipe)

    stdout
    |> maybe_decode_json(operation)
    |> handle_operation_result(operation)
    |> maybe_put_stderr(error)
    |> handle_errors()
  end

  defp handle_posix_errors(reason) do
    file_read_error =
      reason
      |> :file.format_error()
      |> to_string()

    if file_read_error =~ "unknown POSIX error" do
      reason
    else
      "Can't read the WASM binary due to: #{file_read_error}"
    end
  end

  defp maybe_put_stderr({:error, reason}, stderr) when is_map(reason) do
    is_stderr_empty? =
      stderr
      |> String.replace(" ", "")
      |> Kernel.==("")

    if is_stderr_empty?, do: {:error, reason}, else: {:error, Map.put(reason, :details, stderr)}
  end

  defp maybe_put_stderr(data, _stderr), do: data

  defp maybe_decode_json(result, :version), do: result
  defp maybe_decode_json(result, _operation), do: JSON.decode(result)

  defp handle_operation_result(result, operation)

  defp handle_operation_result(result, :version) when is_binary(result) do
    {:ok, %{numscript_wasm: String.trim(result)}}
  end

  defp handle_operation_result({:ok, %{"postings" => postings} = result}, :run) do
    if Enum.empty?(postings),
      do: {:error, %{reason: :invalid_input}},
      else: {:ok, result}
  end

  defp handle_operation_result({:error, reason}, _operation), do: {:error, %{reason: reason}}
  defp handle_operation_result({:ok, _data} = result, _operation), do: result
  defp handle_operation_result(result, _operation), do: result

  defp handle_errors({:ok, _} = result), do: result

  defp handle_errors({:error, %{reason: reason, details: details}}) do
    {:error, %{reason: normalize_error(reason), details: normalize_error(details)}}
  end

  defp handle_errors({:error, %{reason: reason}}) do
    {:error, %{reason: normalize_error(reason)}}
  end

  defp normalize_error(error) when is_binary(error) do
    error
    |> String.replace("panic:", "")
    |> String.trim()
  end

  defp normalize_error(error), do: error
end