defmodule AshDispatch.RecipientResolver.Resolver do
  @moduledoc """
  Resolution logic for audience-based recipient lookup.

  This module implements the various resolution strategies:
  - `from_context` - Extract from event context
  - `from_resource` - Extract email/name fields from resource (for non-user recipients)
  - `query` - Query user resource with Ash filter
  - `path` - Follow relationship path on resource
  - `combine` - Union of other audiences
  - `resolve` - Custom resolver function
  """

  require Logger

  @doc """
  Resolve recipients for an audience using the DSL configuration.
  """
  @spec resolve(module(), atom(), struct() | nil, map()) :: [map()]
  def resolve(resolver_module, audience, resource, context) do
    audiences = resolver_module.__audiences__()

    case find_audience(audiences, audience) do
      nil ->
        available = Enum.map(audiences, & &1.name)

        Logger.warning("""
        [AshDispatch.RecipientResolver] Unknown audience: #{inspect(audience)}
        Available audiences: #{inspect(available)}
        Resolver module: #{inspect(resolver_module)}
        """)

        []

      config ->
        users =
          config
          |> resolve_by_strategy(resource, context, resolver_module)
          |> apply_filter(config.filter)

        # Skip to_recipient conversion if:
        # - raw: true (explicitly marked as returning pre-formatted maps)
        # - combine: audiences (sub-audiences already applied to_recipient)
        # - from_resource: audiences (returns pre-built recipient maps)
        if config.raw || config.combine || config.from_resource do
          users
        else
          Enum.map(users, &resolver_module.to_recipient/1)
        end
    end
  end

  # Apply filter conditions to recipients
  defp apply_filter(recipients, nil), do: recipients
  defp apply_filter(recipients, []), do: recipients

  defp apply_filter(recipients, filter) when is_list(filter) do
    Enum.filter(recipients, fn recipient ->
      Enum.all?(filter, fn {key, expected_value} ->
        actual_value = Map.get(recipient, key)
        matches_filter?(actual_value, expected_value)
      end)
    end)
  end

  # Match filter values - supports atoms, strings, and lists
  defp matches_filter?(actual, expected) when is_atom(expected) do
    actual == expected or to_string(actual) == to_string(expected)
  end

  defp matches_filter?(actual, expected) when is_binary(expected) do
    to_string(actual) == expected
  end

  defp matches_filter?(actual, expected) when is_list(expected) do
    actual in expected or to_string(actual) in Enum.map(expected, &to_string/1)
  end

  defp matches_filter?(actual, expected) do
    actual == expected
  end

  defp find_audience(audiences, name) do
    Enum.find(audiences, &(&1.name == name))
  end

  defp resolve_by_strategy(config, resource, context, resolver_module) do
    cond do
      config.from_context ->
        resolve_from_context(config.from_context, config.extract, context)

      config.from_resource ->
        resolve_from_resource(config.from_resource, resource)

      config.query ->
        resolve_by_query(config.query, resolver_module.__user_resource__())

      config.path ->
        resolve_by_path(config.path, resource)

      config.combine ->
        resolve_combined(config.combine, resource, context, resolver_module)

      config.resolve ->
        resolve_custom(config.resolve, resource, context, resolver_module)

      true ->
        Logger.warning(
          "[AshDispatch.RecipientResolver] No resolution strategy for audience: #{inspect(config.name)}"
        )

        []
    end
  end

  # ===========================================================================
  # Resolution Strategies
  # ===========================================================================

  @doc """
  Extract recipients from context.data.

  ## Examples

      # Single key
      resolve_from_context(:user, nil, context)
      # => extracts context.data.user

      # Multiple keys (fallback chain)
      resolve_from_context([:user, :assignee], nil, context)
      # => tries :user first, falls back to :assignee

      # With extract option
      resolve_from_context([:meeting, :participants], :user, context)
      # => extracts context.data.meeting.participants, then .user from each
  """
  def resolve_from_context(key, extract, context) when is_atom(key) do
    case get_in_data(context, [key]) do
      nil ->
        []

      value when is_list(value) ->
        extract_from_collection(value, extract)

      value when is_struct(value) ->
        [value]

      # Support bare maps with :id — manual pipeline events pass %{id: user_id}
      # instead of full User structs (avoids DB lookup on every broadcast)
      %{id: _} = value ->
        [value]

      _ ->
        []
    end
  end

  def resolve_from_context(keys, extract, context) when is_list(keys) do
    # Could be a path or a fallback chain
    # If all atoms, first try as a path, then as fallback chain
    result = get_in_data(context, keys)

    case result do
      nil ->
        # Try as fallback chain - find first non-nil single key
        Enum.find_value(keys, [], fn key ->
          case get_in_data(context, [key]) do
            nil -> nil
            value when is_struct(value) -> [value]
            %{id: _} = value -> [value]
            value when is_list(value) -> extract_from_collection(value, extract)
            _ -> nil
          end
        end)

      value when is_list(value) ->
        extract_from_collection(value, extract)

      value when is_struct(value) ->
        [value]

      %{id: _} = value ->
        [value]

      _ ->
        []
    end
  end

  defp get_in_data(context, keys) do
    data = Map.get(context, :data, %{})

    Enum.reduce_while(keys, data, fn key, acc ->
      case acc do
        %Ash.NotLoaded{} ->
          {:halt, nil}

        map when is_map(map) ->
          {:cont, Map.get(map, key)}

        _ ->
          {:halt, nil}
      end
    end)
  end

  defp extract_from_collection(items, nil), do: items

  defp extract_from_collection(items, extract_field) when is_list(items) do
    items
    |> Enum.map(&Map.get(&1, extract_field))
    |> Enum.reject(&is_nil/1)
  end

  @doc """
  Extract email/name from resource fields to create a raw recipient map.

  This is a declarative alternative to writing a custom resolver function
  for non-user recipients (e.g., lead contact emails).

  The output map uses field names from your `recipient_fields` config so that
  `RecipientExtractor` can find them. This ensures compatibility with your
  transport configuration.

  ## Options (keyword list)

  * `:email` (required) - Field name on the resource containing the email address
  * `:name` (optional) - Field name on the resource containing the display name
  * `:id` (optional) - Field name for unique identifier (defaults to `:id`)

  ## How it works

  1. Reads your `recipient_fields` config to determine output field names
  2. Extracts values from the specified resource fields
  3. Creates a recipient map with keys that match your config

  For example, with config:
      recipient_fields: [email: [identifier: :email, name: :first_name]]

  And DSL:
      from_resource: [email: :contact_email, name: :contact_name]

  Creates:
      %{id: resource.id, email: resource.contact_email, first_name: resource.contact_name}

  ## Examples

      # Basic usage - just email
      resolve_from_resource([email: :contact_email], lead)

      # With name
      resolve_from_resource([email: :contact_email, name: :contact_name], lead)

      # With custom id field
      resolve_from_resource([email: :email, name: :name, id: :external_id], record)
  """
  def resolve_from_resource(_field_map, nil), do: []

  def resolve_from_resource(field_map, resource) when is_list(field_map) do
    email_input_field = Keyword.fetch!(field_map, :email)
    name_input_field = Keyword.get(field_map, :name)
    id_input_field = Keyword.get(field_map, :id, :id)

    email_value = extract_field_value(resource, email_input_field)

    # Only return a recipient if email is present
    if email_value && email_value != "" do
      id_value = extract_field_value(resource, id_input_field)
      name_value = if name_input_field, do: extract_field_value(resource, name_input_field)

      # Get output field names from recipient_fields config
      # This ensures compatibility with RecipientExtractor
      {email_output_key, name_output_keys} = get_output_field_names()

      recipient = %{
        :id => id_value,
        email_output_key => to_string(email_value)
      }

      # Add name fields if name is available
      # We populate all configured name fields for maximum compatibility
      recipient =
        if name_value && name_value != "" do
          name_str = to_string(name_value)

          Enum.reduce(name_output_keys, recipient, fn key, acc ->
            Map.put(acc, key, name_str)
          end)
        else
          recipient
        end

      [recipient]
    else
      log_missing_field_warning(resource, email_input_field, :email)
      []
    end
  end

  # Get output field names from recipient_fields config
  # Returns {identifier_key, [name_keys]} for email transport
  defp get_output_field_names do
    config = AshDispatch.Config.recipient_fields()

    # Get email transport config (primary use case for from_resource)
    email_config = Keyword.get(config, :email, [])

    # Get identifier field (defaults to :email for backwards compatibility)
    identifier_key = Keyword.get(email_config, :identifier, :email)

    # Get name field(s) - can be atom or list of atoms
    name_config = Keyword.get(email_config, :name, [:display_name, :first_name])

    name_keys =
      case name_config do
        keys when is_list(keys) -> keys
        key when is_atom(key) -> [key]
        _ -> [:display_name, :first_name]
      end

    {identifier_key, name_keys}
  end

  # Extract a field value from a struct/map, handling CiString
  defp extract_field_value(resource, field) when is_atom(field) do
    value = Map.get(resource, field)

    case value do
      nil ->
        nil

      %{string: str} ->
        str

      %Ash.NotLoaded{} ->
        resource_type =
          if is_struct(resource), do: inspect(resource.__struct__), else: "map"

        Logger.warning("""
        [AshDispatch.from_resource] Field #{inspect(field)} is not loaded on resource.

        Resource type: #{resource_type}

        Make sure to load this field before dispatching the event.
        You can add it to the action's `load` option or use Ash.load/3.
        """)

        nil

      other ->
        other
    end
  end

  defp log_missing_field_warning(resource, field, purpose) do
    resource_type =
      if is_struct(resource), do: inspect(resource.__struct__), else: "map"

    available_keys =
      resource
      |> Map.keys()
      |> Enum.reject(&(&1 == :__struct__))
      |> Enum.take(10)
      |> inspect()

    Logger.warning("""
    [AshDispatch.from_resource] No #{purpose} found - field #{inspect(field)} is nil or empty.

    Resource type: #{resource_type}
    Available keys (first 10): #{available_keys}

    The audience will return no recipients for this resource.
    If this is unexpected, check that:
    1. The field name in from_resource matches your resource attribute
    2. The field has a value on this particular resource
    """)
  end

  @doc """
  Query user resource with Ash filter.

  ## Example

      resolve_by_query([role: :admin, is_active: true], MyApp.Accounts.User)
  """
  def resolve_by_query(filter, user_resource) when is_list(filter) do
    # Dispatch is a side-channel — recipient resolution must NEVER raise
    # into the caller. `Ash.read` returns `{:ok, _} | {:error, _}` for
    # normal Ash error paths, but two failure modes raise through the
    # call:
    #
    #   1. Query construction — `Ash.Query.filter_input/2` raises when
    #      `user_resource` isn't a valid Ash resource module (e.g. a
    #      misconfigured `recipient_user_resource`).
    #   2. Auto-loaded calculations during read — e.g. AshCloak
    #      `decrypt_by_default` raises through the calculation pipeline
    #      when the Cloak vault hasn't started. (Mosis 2026-05-20
    #      receipt: minimal-boot mix task fired binding_declared
    #      dispatch → resolver → User read → vault-not-started crash;
    #      aborted the parent binding creation.)
    #
    # A raise here would bubble up to the parent operation that
    # triggered the dispatch and abort it. The whole point of dispatch
    # is to be observational; degrade to "no recipients delivered" +
    # structured warning instead.
    try do
      query =
        user_resource
        |> Ash.Query.filter_input(filter)
        |> scope_to_recipient_fields(user_resource)

      case Ash.read(query, authorize?: false) do
        {:ok, users} ->
          users

        {:error, error} ->
          Logger.warning("[AshDispatch.RecipientResolver] Query failed: #{inspect(error)}")

          []
      end
    rescue
      error ->
        Logger.warning("""
        [AshDispatch.RecipientResolver] resolve_by_query/2 raised — dispatch \
        side-channel degraded to [] recipients to protect parent operation.
          resource: #{inspect(user_resource)}
          filter:   #{inspect(filter)}
          error:    #{Exception.format(:error, error, __STACKTRACE__)}\
        """)

        []
    end
  end

  # Narrow the user-resource read to attributes the dispatch pipeline
  # actually reads. Without this scoping, `Ash.read` defaults to selecting
  # every attribute, which triggers any auto-loaded calculations on the
  # resource (e.g. AshCloak `decrypt_by_default` decrypt calcs). For a
  # recipient-lookup query that only needs identifier + display fields,
  # decrypting unrelated PII columns is gratuitous work and a needless
  # failure surface (vault not started, key rotation in progress, etc.).
  #
  # Falls back to the unscoped query if `recipient_fields` config is
  # empty or none of the configured fields exist on the resource (mis-
  # configuration — preserve previous behavior rather than read zero
  # columns).
  defp scope_to_recipient_fields(query, user_resource) do
    case recipient_field_select(user_resource) do
      [] -> query
      fields -> Ash.Query.select(query, fields)
    end
  end

  defp recipient_field_select(user_resource) do
    configured =
      AshDispatch.Config.recipient_fields()
      |> Enum.flat_map(fn {_transport, transport_config} ->
        identifier = transport_config |> Keyword.get(:identifier) |> List.wrap()
        name = transport_config |> Keyword.get(:name, []) |> List.wrap()
        identifier ++ name
      end)
      |> Enum.reject(&is_nil/1)
      |> then(&[:id | &1])
      |> Enum.uniq()

    resource_attrs =
      user_resource
      |> Ash.Resource.Info.attributes()
      |> MapSet.new(& &1.name)

    Enum.filter(configured, &MapSet.member?(resource_attrs, &1))
  end

  @doc """
  Follow relationship path on resource.

  ## Example

      resolve_by_path([:customer, :customer_users, :user], lead)
  """
  def resolve_by_path(_path, nil), do: []

  def resolve_by_path(path, resource) when is_list(path) do
    result =
      Enum.reduce_while(path, resource, fn rel, acc ->
        case acc do
          %Ash.NotLoaded{} ->
            {:halt, nil}

          list when is_list(list) ->
            # Flatten if we encounter a list
            nested =
              Enum.flat_map(list, fn item ->
                case Map.get(item, rel) do
                  nil -> []
                  %Ash.NotLoaded{} -> []
                  value when is_list(value) -> value
                  value -> [value]
                end
              end)

            {:cont, nested}

          map when is_map(map) ->
            case Map.get(map, rel) do
              %Ash.NotLoaded{} -> {:halt, nil}
              nil -> {:halt, nil}
              value -> {:cont, value}
            end

          _ ->
            {:halt, nil}
        end
      end)

    case result do
      nil -> []
      list when is_list(list) -> list
      value -> [value]
    end
  end

  @doc """
  Combine multiple audiences (union, deduped by id).

  ## Example

      resolve_combined([:owner, :team], resource, context, MyApp.RecipientResolver)
  """
  def resolve_combined(audience_names, resource, context, resolver_module) do
    audience_names
    |> Enum.flat_map(fn name ->
      resolve(resolver_module, name, resource, context)
    end)
    |> Enum.uniq_by(& &1.id)
  end

  @doc """
  Call custom resolver function.

  ## Examples

      # Atom - calls resolver_module.resolve_owner(resource, context)
      resolve_custom(:resolve_owner, resource, context, resolver_module)

      # Tuple - calls Module.function(resource, context)
      resolve_custom({Module, :function}, resource, context, resolver_module)
  """
  def resolve_custom(func_name, resource, context, resolver_module) when is_atom(func_name) do
    if function_exported?(resolver_module, func_name, 2) do
      case apply(resolver_module, func_name, [resource, context]) do
        result when is_list(result) -> result
        nil -> []
        value -> [value]
      end
    else
      Logger.warning("""
      [AshDispatch.RecipientResolver] Custom resolver function not found: #{func_name}/2
      Module: #{inspect(resolver_module)}
      """)

      []
    end
  end

  def resolve_custom({module, func}, resource, context, _resolver_module) do
    case apply(module, func, [resource, context]) do
      result when is_list(result) -> result
      nil -> []
      value -> [value]
    end
  end

  def resolve_custom({module, func, extra_args}, resource, context, _resolver_module) do
    case apply(module, func, [resource, context | extra_args]) do
      result when is_list(result) -> result
      nil -> []
      value -> [value]
    end
  end
end