phoenix_kit_posts

defmodule PhoenixKitPosts.PostView do
  @moduledoc """
  Schema for post view tracking (analytics).

  Tracks when posts are viewed for analytics purposes. Supports session-based
  deduplication to avoid counting multiple views from the same visitor.

  ## Fields

  - `post_uuid` - Reference to the viewed post
  - `user_uuid` - Reference to the viewer (nullable for guests)
  - `ip_address` - Hashed IP for privacy
  - `user_agent_hash` - Hashed browser fingerprint
  - `session_id` - Session identifier for deduplication
  - `viewed_at` - Timestamp of view

  ## Examples

      # Logged-in user view
      %PostView{
        post_uuid: "018e3c4a-9f6b-7890-abcd-ef1234567890",
        user_uuid: "018e3c4a-1234-5678-abcd-ef1234567890",
        ip_address: "hashed_ip",
        user_agent_hash: "hashed_ua",
        session_id: "session_abc123",
        viewed_at: ~U[2025-01-01 12:00:00Z]
      }

      # Guest view
      %PostView{
        post_uuid: "018e3c4a-9f6b-7890-abcd-ef1234567890",
        user_uuid: nil,
        ip_address: "hashed_ip",
        user_agent_hash: "hashed_ua",
        session_id: "session_xyz789",
        viewed_at: ~U[2025-01-01 13:30:00Z]
      }
  """
  use Ecto.Schema
  import Ecto.Changeset
  alias PhoenixKit.Utils.Date, as: UtilsDate

  @primary_key {:uuid, UUIDv7, autogenerate: true}

  @type t :: %__MODULE__{
          uuid: UUIDv7.t() | nil,
          post_uuid: UUIDv7.t(),
          user_uuid: UUIDv7.t() | nil,
          ip_address: String.t() | nil,
          user_agent_hash: String.t() | nil,
          session_id: String.t() | nil,
          viewed_at: DateTime.t(),
          post: PhoenixKitPosts.Post.t() | Ecto.Association.NotLoaded.t(),
          user: PhoenixKit.Users.Auth.User.t() | Ecto.Association.NotLoaded.t() | nil,
          inserted_at: DateTime.t() | nil,
          updated_at: DateTime.t() | nil
        }

  schema "phoenix_kit_post_views" do
    field(:ip_address, :string)
    field(:user_agent_hash, :string)
    field(:session_id, :string)
    field(:viewed_at, :utc_datetime)

    belongs_to(:post, PhoenixKitPosts.Post,
      foreign_key: :post_uuid,
      references: :uuid,
      type: UUIDv7
    )

    belongs_to(:user, PhoenixKit.Users.Auth.User,
      foreign_key: :user_uuid,
      references: :uuid,
      type: UUIDv7
    )

    timestamps(type: :utc_datetime)
  end

  @doc """
  Changeset for creating a post view record.

  ## Required Fields

  - `post_uuid` - Reference to post
  - `viewed_at` - Timestamp of view

  ## Validation Rules

  - viewed_at must not be in the future
  """
  def changeset(view, attrs) do
    view
    |> cast(attrs, [
      :post_uuid,
      :user_uuid,
      :ip_address,
      :user_agent_hash,
      :session_id,
      :viewed_at
    ])
    |> validate_required([:post_uuid, :viewed_at])
    |> validate_viewed_at_not_future()
    |> foreign_key_constraint(:post_uuid)
    |> foreign_key_constraint(:user_uuid)
  end

  @doc """
  Hash an IP address for privacy.
  """
  def hash_ip(ip_address) when is_binary(ip_address) do
    salt = Application.get_env(:phoenix_kit_posts, :hash_salt, "phoenix_kit_posts_default_salt")
    :crypto.hash(:sha256, salt <> ip_address) |> Base.encode16(case: :lower)
  end

  @doc """
  Hash a user agent for privacy.
  """
  def hash_user_agent(user_agent) when is_binary(user_agent) do
    salt = Application.get_env(:phoenix_kit_posts, :hash_salt, "phoenix_kit_posts_default_salt")
    :crypto.hash(:sha256, salt <> user_agent) |> Base.encode16(case: :lower)
  end

  # Private Functions

  defp validate_viewed_at_not_future(changeset) do
    viewed_at = get_field(changeset, :viewed_at)

    if viewed_at && DateTime.compare(viewed_at, UtilsDate.utc_now()) == :gt do
      add_error(changeset, :viewed_at, "cannot be in the future")
    else
      changeset
    end
  end
end