defmodule AshPhoenixGenApi do
  @moduledoc """
  Ash extension for generating PhoenixGenApi function configurations from Ash resources.

  `AshPhoenixGenApi` bridges the Ash Framework and PhoenixGenApi by allowing you to
  define PhoenixGenApi endpoints directly in your Ash resource and domain DSLs. It
  automatically generates `PhoenixGenApi.Structs.FunConfig` structs from your Ash
  actions, including type mappings, argument ordering, and configuration defaults.

  ## Architecture

  The extension consists of two main parts:

  ### Resource Extension (`AshPhoenixGenApi.Resource`)

  Added to Ash resources to define which actions should be exposed as PhoenixGenApi
  endpoints. Each action is configured with routing, timeout, permission, and other
  settings.

  ### Domain Extension (`AshPhoenixGenApi.Domain`)

  Added to Ash domains to provide domain-level defaults and auto-generate a
  "supporter" module that aggregates FunConfigs from all resources in the domain.
  The supporter module implements the PhoenixGenApi client config interface
  (`get_config/1`, `get_config_version/1`), allowing gateway nodes to pull API
  configurations from service nodes.

  ## Quick Start

  ### 1. Add the extensions to your resource and domain

      # In your resource:
      defmodule MyApp.Chat.DirectMessage do
        use Ash.Resource,
          extensions: [AshPhoenixGenApi.Resource]

        gen_api do
          service "chat"
          nodes {ClusterHelper, :get_nodes, [:chat]}
          choose_node_mode :random
          timeout 5_000
          response_type :async
          request_info true

          action :send_direct_message do
            request_type "send_direct_message"
            timeout 10_000
            check_permission {:arg, "from_user_id"}
          end

          action :get_conversation do
            timeout 5_000
          end

          action :create do
            # Minimal config — request_type and args are auto-derived
          end
        end

        attributes do
          uuid_primary_key :id
          attribute :from_user_id, :uuid
          attribute :to_user_id, :uuid
          attribute :content, :string
          attribute :reply_to_id, :uuid
          attribute :file_id, :uuid
        end

        actions do
          create :create do
            accept [:from_user_id, :to_user_id, :content, :reply_to_id, :file_id]
          end

          read :read do
            primary? true
          end
        end
      end

      # In your domain:
      defmodule MyApp.Chat do
        use Ash.Domain,
          extensions: [AshPhoenixGenApi.Domain]

        gen_api do
          service "chat"
          nodes {ClusterHelper, :get_nodes, [:chat]}
          choose_node_mode :random
          version "0.0.1"
          supporter_module MyApp.Chat.GenApiSupporter
        end

        resources do
          resource MyApp.Chat.DirectMessage
          resource MyApp.Chat.GroupMessage
        end
      end

  ### 2. The supporter module is auto-generated

  After compilation, `MyApp.Chat.GenApiSupporter` will be available with:

      # Get all FunConfigs (for PhoenixGenApi pull)
      MyApp.Chat.GenApiSupporter.fun_configs()
      #=> [%PhoenixGenApi.Structs.FunConfig{request_type: "send_direct_message", ...}, ...]

      # Get config for remote pull
      MyApp.Chat.GenApiSupporter.get_config(:gateway_1)
      #=> {:ok, [%PhoenixGenApi.Structs.FunConfig{...}, ...]}

      # Get config version
      MyApp.Chat.GenApiSupporter.get_config_version(:gateway_1)
      #=> {:ok, "0.0.1"}

      # Find a specific FunConfig by request_type
      MyApp.Chat.GenApiSupporter.get_fun_config("send_direct_message")
      #=> %PhoenixGenApi.Structs.FunConfig{request_type: "send_direct_message", ...}

      # List all request types
      MyApp.Chat.GenApiSupporter.list_request_types()
      #=> ["send_direct_message", "get_conversation", ...]

      # Push config to a gateway node (active push)
      MyApp.Chat.GenApiSupporter.push_to_gateway(:"gateway1@host")
      #=> {:ok, :accepted}

      # Push config on application startup
      MyApp.Chat.GenApiSupporter.push_on_startup(:"gateway1@host")
      #=> {:ok, :accepted}

      # Push to all configured push_nodes
      MyApp.Chat.GenApiSupporter.push_to_configured_nodes()
      #=> {:ok, [{:"gateway1@host", {:ok, :accepted}}, ...]}

  ### 3. Configure the gateway node

  On the Phoenix gateway node, configure `phoenix_gen_api` in `config.exs`:

      config :phoenix_gen_api, :gen_api,
        service_configs: [
          %{
            service: "chat",
            nodes: {ClusterHelper, :get_nodes, [:chat]},
            module: MyApp.Chat.GenApiSupporter,
            function: :get_config,
            args: [:gateway_1]
          }
        ]

  ## Code Interface

  When `code_interface?` is `true` (the default), the extension auto-generates
  Elixir functions on the resource module for each gen_api action. This allows
  you to call actions directly without building queries or changesets manually.

      # Create action — auto-generates create/2 and create!/2
      {:ok, message} = MyApp.Chat.DirectMessage.create(%{content: "Hello"})
      message = MyApp.Chat.DirectMessage.create!(%{content: "Hello"})

      # Read action — auto-generates read/2 and read!/2
      {:ok, messages} = MyApp.Chat.DirectMessage.read()
      messages = MyApp.Chat.DirectMessage.read!()

      # Update action — auto-generates update/3 and update!/3 (requires record)
      {:ok, updated} = MyApp.Chat.DirectMessage.update(message, %{content: "Updated"})
      updated = MyApp.Chat.DirectMessage.update!(message, %{content: "Updated"})

      # Destroy action — auto-generates destroy/3 and destroy!/3 (requires record)
      :ok = MyApp.Chat.DirectMessage.destroy(message)
      :ok = MyApp.Chat.DirectMessage.destroy!(message)

      # Generic action — auto-generates action_name/2 and action_name!/2
      {:ok, result} = MyApp.Chat.DirectMessage.greet(%{name: "World"})

  You can disable code interface generation at the section level or per-action:

      gen_api do
        service "chat"
        code_interface? false  # Disable for all actions

        action :create do
          code_interface? true  # Re-enable for this action only
        end

        action :read  # Inherits section-level false
      end

  ## Permission Callback

  In addition to the built-in permission modes (`false`, `:any_authenticated`,
  `{:arg, "arg_name"}`, `{:role, ["admin"]}`), you can specify a custom
  callback function for permission checking using `permission_callback`.

  The callback receives `request_type` (string) and `args` (map) as arguments
  and returns `true` (continue) or `false` (permission denied).

      defmodule MyApp.Permissions do
        def check_permission(request_type, args) do
          case request_type do
            "delete_user" -> args["role"] == "admin"
            "update_profile" -> args["user_id"] == args["target_user_id"]
            _ -> true
          end
        end
      end

      gen_api do
        service "chat"
        permission_callback {MyApp.Permissions, :check_permission, []}

        action :delete_user do
          # Uses the section-level permission_callback
        end

        action :admin_action do
          # Override with a different callback
          permission_callback {MyApp.Permissions, :check_admin, []}
        end
      end

  When `permission_callback` is set, it takes precedence over `check_permission`
  and is stored as `{:callback, {Module, :function, []}}` in the FunConfig's
  `check_permission` field.

  ## Active Push Configuration

  In addition to the pull-based model (where the gateway pulls config from
  service nodes), you can configure the supporter module to **actively push**
  its configuration to gateway nodes.

      gen_api do
        service "chat"
        supporter_module MyApp.Chat.GenApiSupporter
        version "0.0.1"
        push_nodes [:"gateway1@host", :"gateway2@host"]
        # Or use an MFA tuple for runtime resolution:
        # push_nodes {ClusterHelper, :get_gateway_nodes, []}
      end

  Then push config during application startup:

      def start(_type, _args) do
        # ... start supervision tree, then:
        MyApp.Chat.GenApiSupporter.push_to_configured_nodes()
        # Or push to a specific node:
        MyApp.Chat.GenApiSupporter.push_on_startup(:"gateway1@host")
      end

  The generated supporter module includes these push functions:
  - `build_push_config/0` - Builds a `PushConfig` struct from the domain config
  - `push_to_gateway/2` - Pushes config to a specific gateway node
  - `push_on_startup/2` - Pushes config on application startup
  - `verify_on_gateway/2` - Verifies config version on a gateway node
  - `resolve_push_nodes/0` - Resolves `push_nodes` at runtime
  - `push_to_configured_nodes/1` - Pushes to all configured push_nodes

  ## Result Encoder

  By default, the auto-generated code interface functions return Ash resource
  structs as-is. You can configure `result_encoder` to transform the result
  before returning it to the caller.

  ### Encoder Modes

  - `:struct` — Return the Ash resource struct as-is (default)
  - `:map` — Convert the Ash resource struct to a map containing only public fields
    (using `Ash.Resource.Info.public_fields/1` to filter; falls back to
    `Map.from_struct/1` for non-Ash-resource structs)
  - `{Module, :function, args}` — Custom encoder MFA. The function receives
    the result as its first argument, followed by `args`, and must return
    the encoded result.

  ### Configuration

  `result_encoder` can be set at the domain, resource section, or action level:

      # Domain-level default
      gen_api do
        service "chat"
        result_encoder :map
        supporter_module MyApp.Chat.GenApiSupporter
      end

      # Resource-level default
      gen_api do
        service "chat"
        result_encoder :map

        action :create
        action :read
      end

      # Action-level override
      gen_api do
        service "chat"
        result_encoder :struct

        action :create do
          result_encoder :map  # Override section-level default
        end

        action :read  # Inherits section-level :struct
      end

      # Custom encoder MFA
      gen_api do
        service "chat"
        result_encoder {MyApp.Encoder, :to_api_format, []}

        action :create
      end

  ### Encoding Behavior

  For `:map` encoding:
  - Ash resource structs are converted to maps containing only their public fields
    (attributes, calculations, aggregates, relationships) using
    `Ash.Resource.Info.public_fields/1` to filter
  - Non-Ash-resource structs fall back to `Map.from_struct/1`
  - Lists of structs are mapped accordingly
  - The atom `:ok` (from destroy actions) is returned as-is
  - Non-struct values (e.g., generic action results) are returned as-is

  For custom MFA encoders:
  - The function receives the raw result value as its first argument
  - For read actions, the value is a list of structs
  - For create/update actions, the value is a single struct
  - For destroy actions, the value is `:ok`
  - The function must return the encoded value

  ### Important Note

  When using `:map` or custom encoding, the bang (!) functions return encoded
  values. Since update and destroy actions require a struct as their first
  argument, you cannot chain encoded results directly. Use the non-bang
  versions or create records directly via Ash if you need to chain operations:

      # This works — create returns struct, update accepts struct
      {:ok, record} = MyResource.create(%{name: "test"})
      {:ok, updated} = MyResource.update(record, %{name: "updated"})

      # This does NOT work — create! returns map, update requires struct
      record = MyResource.create!(%{name: "test"})  # Returns map with :map encoder
      MyResource.update(record, %{name: "updated"}) # Error: record must be a struct

  ## Type Mapping

  Ash types are automatically mapped to PhoenixGenApi argument types:

  | Ash Type | PhoenixGenApi Type |
  |----------|-------------------|
  | `:string`, `:uuid`, `:boolean`, `:date`, etc. | `:string` |
  | `:integer`, `:float`, `:decimal` | `:num` |
  | `{:array, :string}`, `{:array, :uuid}` | `{:list_string, max_items, max_item_length}` |
  | `{:array, :integer}`, `{:array, :float}` | `{:list_num, max_items}` |

  See `AshPhoenixGenApi.TypeMapper` for the complete mapping table.

  ## Resolution Order

  Configuration values are resolved in this order (highest priority first):

  1. **Action-level explicit config** — e.g., `action :foo do timeout 10_000 end`
  2. **Resource section-level defaults** — e.g., `gen_api do timeout 5_000 end`
  3. **Domain section-level defaults** — e.g., `gen_api do timeout 5_000 end`
  4. **Built-in defaults** — e.g., timeout defaults to `5000`

  ## Modules

  - `AshPhoenixGenApi.Resource` — Resource-level DSL extension
  - `AshPhoenixGenApi.Resource.Info` — Resource introspection helpers
  - `AshPhoenixGenApi.Resource.ActionConfig` — Action configuration struct
  - `AshPhoenixGenApi.Domain` — Domain-level DSL extension
  - `AshPhoenixGenApi.Domain.Info` — Domain introspection helpers
  - `AshPhoenixGenApi.TypeMapper` — Ash type to PhoenixGenApi type mapping
  - `AshPhoenixGenApi.JsonConfig` — JSON function config list generation utilities
  - `AshPhoenixGenApi.Codec` — Result encoding for Ash resource structs
  - `AshPhoenixGenApi.Transformers.DefineFunConfigs` — Resource transformer
  - `AshPhoenixGenApi.Transformers.DefineDomainSupporter` — Domain transformer
  - `AshPhoenixGenApi.Verifiers.VerifyActionConfigs` — Resource verifier
  - `AshPhoenixGenApi.Verifiers.VerifyDomainConfig` — Domain verifier
  """

  @doc """
  Lists all modules that are part of the AshPhoenixGenApi extension.

  Returns a list of module atoms for the resource extension, domain extension,
  and their supporting modules.

  ## Examples

      iex> AshPhoenixGenApi.modules()
      [
        AshPhoenixGenApi.Resource,
        AshPhoenixGenApi.Resource.Info,
        AshPhoenixGenApi.Resource.ActionConfig,
        AshPhoenixGenApi.Domain,
        AshPhoenixGenApi.Domain.Info,
        AshPhoenixGenApi.TypeMapper,
        ...
      ]
  """
  @spec modules() :: [module()]
  def modules do
    [
      AshPhoenixGenApi.Resource,
      AshPhoenixGenApi.Resource.Info,
      AshPhoenixGenApi.Resource.ActionConfig,
      AshPhoenixGenApi.Domain,
      AshPhoenixGenApi.Domain.Info,
      AshPhoenixGenApi.TypeMapper,
      AshPhoenixGenApi.JsonConfig,
      AshPhoenixGenApi.Codec,
      AshPhoenixGenApi.Transformers.DefineFunConfigs,
      AshPhoenixGenApi.Transformers.DefineDomainSupporter,
      AshPhoenixGenApi.Verifiers.VerifyActionConfigs,
      AshPhoenixGenApi.Verifiers.VerifyDomainConfig
    ]
  end

  @doc """
  Returns the list of Spark DSL extensions provided by AshPhoenixGenApi.

  These are the extensions you add to your Ash resources and domains:

  - `AshPhoenixGenApi.Resource` — Add to Ash resources
  - `AshPhoenixGenApi.Domain` — Add to Ash domains

  ## Examples

      iex> AshPhoenixGenApi.extensions()
      [AshPhoenixGenApi.Resource, AshPhoenixGenApi.Domain]
  """
  @spec extensions() :: [module()]
  def extensions do
    [
      AshPhoenixGenApi.Resource,
      AshPhoenixGenApi.Domain
    ]
  end

  @doc """
  Returns the built-in defaults for the gen_api DSL section.

  These defaults are used when no explicit value is provided at any level:

  - `timeout` — `5000` (5 seconds)
  - `response_type` — `:async`
  - `request_info` — `true`
  - `check_permission` — `false`
  - `permission_callback` — `nil` (no custom callback)
  - `choose_node_mode` — `:random`
  - `nodes` — `:local`
  - `version` — `"0.0.1"`
  - `retry` — `nil` (no retry)
  - `code_interface?` — `true` (auto-generate code interface functions)
  - `push_nodes` — `nil` (no push nodes)
  - `push_on_startup` — `false`
  - `result_encoder` — `:struct` (return Ash resource struct as-is)
  """
  @spec defaults() :: map()
  def defaults do
    %{
      timeout: 5_000,
      response_type: :async,
      request_info: true,
      check_permission: false,
      permission_callback: nil,
      choose_node_mode: :random,
      nodes: :local,
      version: "0.0.1",
      retry: nil,
      code_interface?: true,
      push_nodes: nil,
      push_on_startup: false,
      result_encoder: :struct
    }
  end

  @doc """
  Returns the version of the AshPhoenixGenApi library.
  """
  @spec version() :: String.t()
  def version do
    unquote(Mix.Project.config()[:version] || "0.1.0")
  end
end