defmodule Magik.Contract do
  @moduledoc """

  `Contract` helps to define a contract for function call, and do validate contract data with:

  - Validate type
  - Validate required
  - Validate `in`|`not_in` enum
  - Valiate length for `string`, `enumerable`
  - Validate number
  - Validate string against regex pattern
  - Custom validation function
  - With support nested type
  - Clean not allowed fields

  ```elixir

  @update_user_contract %{
    user: [type: User, required: true],
    attributes: [type: %{
      email: [type: :string],
      status: [type: :string, in: ~w(active in_active)]
      age: [type: :integer, number: [min: 10, max: 80]],
    }, required: true]
  }

  def update_user(contract) do
    with {:ok, validated_data} do
       validated_data.user
       |> Ecto.Changeset.change(validated_data.attributes)
       |> Repo.update
    else
      {:error, errors} -> IO.inspect(errors)
    end
  end

  ```

  **NOTES: Contract only validate data, not cast data**

  ## Support validation

  **Type**

  Support built-in types;
  - `boolean`
  - `integer`,
  - `float`
  - `number` - string or integer
  - `string`
  - `tuple`
  - `map`
  - `array`
  - `list`
  - `atom`
  - `function`
  - `keyword`
  - `struct`
  - `array` of type

  Example:

  ```elixir
  Magik.Contract.validate(%{name: "Bluz"}, %{name: [type: :string]})
  Magik.Contract.validate(%{id: 123}, %{name: [type: :integer]})
  Magik.Contract.validate(%{id: 123}, %{name: [type: {:array, :integer}]})
  Magik.Contract.validate(%{user: %User{}}, %{user: [type: User]})
  Magik.Contract.validate(%{user: %User{}}, %{user: [type: {:array: User}]})
  ```

  **Required**

  ```elixir
  Magik.Contract.validate(%{name: "Bluz"}, %{name: [type: :string, required: true]})
  ```

  **Allow nil**

  ```elixir
  Magik.Contract.validate(
                        %{name: "Bluz", email: nil},
                        %{
                          name: [type: :string],
                          email: [type: string, allow_nil: false]
                         })
  ```


  **Inclusion/Exclusion**

  ```elixir
  Magik.Contract.validate(
                  %{status: "active"},
                  %{status: [type: :string, in: ~w(active in_active)]}
                 )

  Magik.Contract.validate(
                  %{status: "active"},
                  %{status: [type: :string, not_in: ~w(banned locked)]}
                 )
  ```

  **Format**

  Validate string against regex pattern

  ```elixir
  Magik.Contract.validate(
                %{email: "Bluzblu@gm.com"},
                %{name: [type: :string, format: ~r/.+?@.+\.com/]
                })
  ```

  **Number**

  Validate number value

  ```elixir
  Magik.Contract.validate(
                %{age: 200},
                %{age: [type: :integer, number[greater_than: 0, less_than: 100]]
                })
  ```

  Support conditions
  - `equal_to`
  - `greater_than_or_equal_to` | `min`
  - `greater_than`
  - `less_than`
  - `less_than_or_equal_to` | `max`



  **Length**

  Check length of `list`, `map`, `string`, `keyword`, `tuple`
  Supported condtions are the same with **Number** check

  ```elixir
  Magik.Contract.validate(
                %{title: "Hello world"},
                %{age: [type: :string, length: [min: 10, max: 100]]
                })
  ```


  **Custom validation function**

  Invoke given function to validate value.
  The function signature must be

  ```
  func(field_name ::(String.t() | atom()), value :: any(), all_params :: map()) :: :ok | {:error, message}
  ```

  ```elixir
  Magik.Contract.validate(
                %{email: "blue@hmail.com"},
                %{email: [type: :string, func: &validate_email/3]})

  def validate_email(_name, email, _params) do
    if Regex.match?(~r/[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4}$/, email) do
      :ok
    else
      {:error, "not a valid email"}
    end
  end
  ```

  **Nested map**

  Nested map declaration is the same.

  ```elixir
  data =   %{name: "Doe John", address: %{city: "HCM", street: "NVL"} }
  schema = %{
      name: [type: :string],
      address: [type: %{
              city: [type: :string],
              street: [type: :string]
            }]
    }
  Magik.Contract.validate(data, schema)
  ```

  **Nested list**

  ```elixir
  data =   %{name: "Doe John", address: [%{city: "HCM", street: "NVL"}] }
  address = %{ city: [type: :string],  street: [type: :string] }
  schema = %{
      name: [type: :string],
      address: [type: {:array, address}]
     }
  Magik.Contract.validate(data, schema)
  ```
  """

  alias Magik.Validator

  @doc """
  Validate data against given schema
  """

  @spec validate(data :: map(), schema :: map()) :: {:ok, map()} | {:error, errors :: map()}
  def validate(data, schema) do
    {status, results} =
      schema
      |> Enum.map(fn {field_name, validations} ->
        value = Map.get(data, field_name, :__missing)

        validations =
          if Keyword.has_key?(validations, :allow_nil) do
            validations
          else
            [{:allow_nil, false} | validations]
          end

        {status, results} =
          Enum.reduce(validations, {:ok, value}, fn
            _, {:error, _} = error ->
              error

            validation, acc ->
              case do_validate(value, validation, data) do
                :ok -> acc
                {:ok, data} -> {:ok, data}
                {:error, msg} when is_list(msg) -> {:error, msg}
                {:error, msg} -> {:error, [msg]}
              end
          end)

        {status, {field_name, results}}
      end)
      |> collect_schema_result()

    {status, Map.new(results)}
  end

  defp do_validate(:__missing, {:required, true}, _opts) do
    {:error, "is required"}
  end

  defp do_validate(_, {:required, _}, _), do: :ok

  defp do_validate(:__missing, _, _), do: :ok

  defp do_validate(value, {:allow_nil, allow_nil}, _) when is_boolean(allow_nil) do
    if not is_nil(value) or allow_nil do
      :ok
    else
      {:error, "cannot be nil"}
    end
  end

  defp do_validate(nil, _, _), do: :ok

  # validate nested type
  defp do_validate(value, {:type, type}, _) when is_map(type) do
    Validator.validate_embed(value, {:embed, __MODULE__, type})
  end

  defp do_validate(value, {:type, {:array, type}}, _) when is_map(type) do
    Validator.validate_embed(value, {:array, {:embed, __MODULE__, type}})
  end

  defp do_validate(value, {:func, func}, opts) when is_function(func, 3) do
    func.(opts[:field_name], value, opts[:data])
  end

  defp do_validate(value, validation, _), do: Validator.validate(value, [validation])

  defp collect_schema_result(results) do
    Enum.reduce(results, {:ok, []}, fn
      {:ok, data}, {:ok, acc} -> {:ok, [data | acc]}
      {:error, error}, {:ok, _} -> {:error, [error]}
      {:error, error}, {:error, acc} -> {:error, [error | acc]}
      _, acc -> acc
    end)
  end
end