defmodule Funx.Validate.Dsl.Executor do
  @moduledoc false
  # Converts Step nodes into executable validator functions.
  #
  # ## Output
  #
  # Generates a function: `(value, opts) -> Either.t()` that:
  #   - Runs all validators applicatively
  #   - Accumulates all errors
  #   - Returns Right(original_value) on success
  #   - Returns Left(ValidationError) on failure

  import Funx.Monad, only: [map: 2]

  alias Funx.Monad.Effect
  alias Funx.Monad.Either
  alias Funx.Monad.Either.{Left, Right}
  alias Funx.Monad.Maybe.{Just, Nothing}
  alias Funx.Optics.{Lens, Prism, Traversal}
  alias Funx.Validate.Dsl.Step

  @doc """
  Execute a list of Step nodes and generate a validator function.
  """
  def execute_steps(steps, mode \\ :sequential)

  def execute_steps(steps, :sequential) do
    quote do
      validator_fns = unquote(compile_steps_to_validators(steps, :sequential))

      # Return the validator function that always returns Either.t()
      fn value, opts ->
        Either.traverse_a(validator_fns, fn validator_fn ->
          validator_fn.(value, opts)
        end)
        |> map(fn _ -> value end)
      end
    end
  end

  def execute_steps(steps, :parallel) do
    quote do
      validator_fns = unquote(compile_steps_to_validators(steps, :parallel))

      # Return the validator function that always returns Either.t()
      fn value, opts ->
        Effect.traverse_a(validator_fns, fn effect_fn ->
          effect_fn.(value, opts)
        end)
        |> Effect.run()
        |> map(fn _ -> value end)
      end
    end
  end

  # Compile steps into validator functions
  defp compile_steps_to_validators(steps, mode) do
    Enum.map(steps, &compile_step(&1, mode))
  end

  # Compile a single step
  defp compile_step(%Step{optic: nil, validators: validators}, mode) do
    # Root validator - no projection
    compile_root_validators(validators, mode)
  end

  defp compile_step(%Step{optic: optic, validators: validators}, mode) do
    # Projected validator - apply optic then validate
    compile_projected_validators(optic, validators, mode)
  end

  # Compile root validators (no projection)
  defp compile_root_validators(validators, :sequential) do
    validator_calls = Enum.map(validators, &compile_validator_call/1)

    quote do
      fn value, opts ->
        validators = unquote(validator_calls)
        unquote(__MODULE__).apply_validators_return(value, value, validators, opts)
      end
    end
  end

  defp compile_root_validators(validators, :parallel) do
    validator_calls = Enum.map(validators, &compile_validator_call/1)

    quote do
      fn value, opts ->
        validators = unquote(validator_calls)

        Effect.lift_either(fn ->
          unquote(__MODULE__).apply_validators_return(value, value, validators, opts)
        end)
      end
    end
  end

  # Compile projected validators (with optic)
  defp compile_projected_validators(optic, validators, :sequential) do
    validator_calls = Enum.map(validators, &compile_validator_call/1)

    quote do
      fn value, opts ->
        optic = unquote(optic)
        projected = unquote(__MODULE__).project_optic(value, optic)
        unwrapped = unquote(__MODULE__).unwrap_maybe(projected)
        validators = unquote(validator_calls)

        unquote(__MODULE__).apply_validators_return(unwrapped, value, validators, opts)
      end
    end
  end

  defp compile_projected_validators(optic, validators, :parallel) do
    validator_calls = Enum.map(validators, &compile_validator_call/1)

    quote do
      fn value, opts ->
        optic = unquote(optic)
        projected = unquote(__MODULE__).project_optic(value, optic)
        unwrapped = unquote(__MODULE__).unwrap_maybe(projected)
        validators = unquote(validator_calls)

        Effect.lift_either(fn ->
          unquote(__MODULE__).apply_validators_return(unwrapped, value, validators, opts)
        end)
      end
    end
  end

  # Project to the value using the optic (public for use in quoted code)
  @doc false
  def project_optic(value, %Lens{} = optic) do
    # Lens = structural requirement, use view! to get raw value and raise on missing
    Lens.view!(value, optic)
  end

  def project_optic(value, %Prism{} = optic) do
    # Prism = optional field, returns Maybe (atoms are converted to Prism by parser)
    Prism.preview(value, optic)
  end

  def project_optic(value, %Traversal{} = optic) do
    Traversal.to_list(value, optic)
  end

  def project_optic(value, optic) when is_function(optic, 1) do
    # Plain projection function
    optic.(value)
  end

  # Unwrap Maybe values from Prism (public for use in quoted code)
  @doc false
  def unwrap_maybe(%Nothing{} = nothing), do: nothing
  def unwrap_maybe(%Just{value: v}), do: v
  def unwrap_maybe(value), do: value

  # Apply validators applicatively (public for use in quoted code)
  @doc false
  def apply_validators(value, validators, opts) do
    Either.traverse_a(validators, fn validator_fn ->
      validator_fn.(value, opts)
    end)
  end

  # Apply validators and return a specific value on success (public for use in quoted code)
  @doc false
  def apply_validators_return(validate_value, return_value, validators, opts) do
    apply_validators(validate_value, validators, opts)
    |> map(fn _ -> return_value end)
  end

  # Compile a single validator call
  # Handles: Module, {Module, opts}, or function validators
  defp compile_validator_call({validator_spec, validator_opts}) when is_list(validator_opts) do
    if module_spec?(validator_spec) do
      compile_module_validator_with_opts(validator_spec, validator_opts)
    else
      compile_function_validator_with_opts(validator_spec, validator_opts)
    end
  end

  defp compile_validator_call(validator_spec) do
    if module_spec?(validator_spec) do
      compile_module_validator(validator_spec)
    else
      compile_function_validator(validator_spec)
    end
  end

  # Check if validator_spec is a module (AST or atom)
  defp module_spec?({:__aliases__, _, _}), do: true
  defp module_spec?(spec) when is_atom(spec), do: true
  defp module_spec?(_), do: false

  # Compile module validator with options
  defp compile_module_validator_with_opts(module_spec, validator_opts) do
    quote do
      fn value, runtime_opts ->
        merged_opts = Keyword.merge(unquote(validator_opts), runtime_opts)
        env = Keyword.get(merged_opts, :env, %{})
        result = unquote(module_spec).validate(value, merged_opts, env)
        unquote(__MODULE__).normalize_validator_result(result, value)
      end
    end
  end

  # Compile module validator without options
  defp compile_module_validator(module_spec) do
    quote do
      fn value, opts ->
        env = Keyword.get(opts, :env, %{})
        result = unquote(module_spec).validate(value, opts, env)
        unquote(__MODULE__).normalize_validator_result(result, value)
      end
    end
  end

  # Compile function validator with options
  defp compile_function_validator_with_opts(validator_spec, validator_opts) do
    quote do
      fn value, runtime_opts ->
        merged_opts = Keyword.merge(unquote(validator_opts), runtime_opts)

        result =
          unquote(__MODULE__).call_validator_function(unquote(validator_spec), value, merged_opts)

        unquote(__MODULE__).normalize_validator_result(result, value)
      end
    end
  end

  # Compile function validator without options
  defp compile_function_validator(validator_spec) do
    quote do
      fn value, opts ->
        result = unquote(__MODULE__).call_validator_function(unquote(validator_spec), value, opts)
        unquote(__MODULE__).normalize_validator_result(result, value)
      end
    end
  end

  # Normalize validator return values to Either (public for use in quoted code)
  @doc false
  def normalize_validator_result(%Right{} = result, _value), do: result
  def normalize_validator_result(%Left{} = result, _value), do: result
  def normalize_validator_result(:ok, value), do: Either.right(value)
  def normalize_validator_result({:error, error}, _value), do: Either.left(error)

  # Call a function validator with appropriate arity (public for use in quoted code)
  @doc false
  def call_validator_function(validator, value, opts) do
    env = Keyword.get(opts, :env, %{})

    cond do
      is_function(validator, 3) ->
        validator.(value, opts, env)

      is_function(validator, 2) ->
        validator.(value, opts)

      is_function(validator, 1) ->
        validator.(value)

      true ->
        raise ArgumentError, "Validator must be a function with arity 1, 2, or 3, or a module"
    end
  end
end