audit_trail

defmodule Mix.Tasks.AuditTrail.Gen.Migration do
  use Mix.Task

  @shortdoc "Generate the AuditTrail audit_logs table migration"

  @moduledoc """
  Generates an Ecto migration for the `audit_logs` table.

  The generated migration is tailored to whichever storage adapter
  is configured in your application:

  - `AuditTrail.Adapters.Postgres`    → standard Postgres table + indexes
  - `AuditTrail.Adapters.TimescaleDB` → same table + `create_hypertable` call

  ## Usage

      mix audit_trail.gen.migration

  Options:

      --repo MyApp.Repo          Ecto repo to target (default: auto-detected from config)
      --migrations-path PATH     Where to write the file (default: priv/repo/migrations)

  After generating, run:

      mix ecto.migrate
  """

  @switches [repo: :string, migrations_path: :string]

  @impl Mix.Task
  def run(args) do
    {opts, _, _} = OptionParser.parse(args, switches: @switches)

    repo_mod = resolve_repo(opts)
    adapter = detect_adapter()
    mig_path = migrations_path(opts, repo_mod)
    timestamp = timestamp()
    filename = "#{timestamp}_create_audit_logs.exs"
    dest = Path.join(mig_path, filename)

    content = migration_content(adapter, repo_mod)

    File.mkdir_p!(mig_path)
    File.write!(dest, content)

    Mix.shell().info([:green, "* creating ", :reset, dest])
    Mix.shell().info("")
    Mix.shell().info("Run the migration with:")
    Mix.shell().info("  mix ecto.migrate")

    if adapter == :timescaledb do
      Mix.shell().info("")

      Mix.shell().info([
        :yellow,
        "TimescaleDB note: ",
        :reset,
        "run compression setup manually after migrating — see AuditTrail.Adapters.TimescaleDB docs."
      ])
    end
  end

  # ── Helpers ─────────────────────────────────────────────────────────────────

  defp detect_adapter do
    case AuditTrail.Config.storage_adapter() do
      {AuditTrail.Adapters.TimescaleDB, _} -> :timescaledb
      {AuditTrail.Adapters.Postgres, _} -> :postgres
      AuditTrail.Adapters.TimescaleDB -> :timescaledb
      AuditTrail.Adapters.Postgres -> :postgres
      _ -> :postgres
    end
  end

  defp resolve_repo(opts) do
    cond do
      repo = opts[:repo] ->
        Module.concat([repo])

      repo = repo_from_config() ->
        repo

      true ->
        Mix.raise("""
        Could not determine the Ecto Repo to use.

        Pass it explicitly:
          mix audit_trail.gen.migration --repo MyApp.Repo

        Or configure it:
          config :audit_trail,
            storage_adapter: {AuditTrail.Adapters.Postgres, repo: MyApp.Repo}
        """)
    end
  end

  defp repo_from_config do
    case AuditTrail.Config.storage_adapter() do
      {_, opts} when is_list(opts) -> Keyword.get(opts, :repo)
      _ -> nil
    end
  end

  defp migrations_path(opts, repo_mod) do
    cond do
      path = opts[:migrations_path] ->
        path

      function_exported?(repo_mod, :config, 0) ->
        priv = repo_mod.config() |> Keyword.get(:priv, "priv/repo")
        Path.join(priv, "migrations")

      true ->
        "priv/repo/migrations"
    end
  end

  defp timestamp do
    {{y, mo, d}, {h, mi, s}} = :calendar.universal_time()

    :io_lib.format("~4..0B~2..0B~2..0B~2..0B~2..0B~2..0B", [y, mo, d, h, mi, s])
    |> IO.chardata_to_string()
  end

  # ── Migration templates ──────────────────────────────────────────────────────

  defp migration_content(:timescaledb, repo_mod) do
    module_name = migration_module_name(repo_mod)

    """
    defmodule #{module_name}.CreateAuditLogs do
      use Ecto.Migration

      def up do
        create table(:audit_logs, primary_key: false) do
          add :id,          :bigserial, primary_key: true
          add :event_id,    :text
          add :event_type,  :text, null: false
          add :actor_id,    :text
          add :actor_name,  :text
          add :actor_email, :text
          add :payload,     :map, null: false, default: %{}
          add :inserted_at, :utc_datetime, null: false, default: fragment("NOW()")
        end

        create index(:audit_logs, [:event_type])
        create index(:audit_logs, [:actor_id])
        create index(:audit_logs, [:inserted_at])
        execute "CREATE INDEX audit_logs_payload_gin ON audit_logs USING GIN (payload jsonb_path_ops)"

        # Convert to TimescaleDB hypertable, partitioned by inserted_at.
        # Chunk interval of 1 day is a good default for audit logs.
        execute "SELECT create_hypertable('audit_logs', 'inserted_at', chunk_time_interval => INTERVAL '1 day')"
      end

      def down do
        drop table(:audit_logs)
      end
    end
    """
  end

  defp migration_content(:postgres, repo_mod) do
    module_name = migration_module_name(repo_mod)

    """
    defmodule #{module_name}.CreateAuditLogs do
      use Ecto.Migration

      def up do
        create table(:audit_logs) do
          add :event_id,    :text
          add :event_type,  :text, null: false
          add :actor_id,    :text
          add :actor_name,  :text
          add :actor_email, :text
          add :payload,     :map, null: false, default: %{}
          timestamps(updated_at: false, type: :utc_datetime)
        end

        create index(:audit_logs, [:event_type])
        create index(:audit_logs, [:actor_id])
        create index(:audit_logs, [:inserted_at])
        execute "CREATE INDEX audit_logs_payload_gin ON audit_logs USING GIN (payload jsonb_path_ops)"
      end

      def down do
        drop table(:audit_logs)
      end
    end
    """
  end

  defp migration_module_name(repo_mod) do
    repo_mod
    |> Module.split()
    |> Enum.drop(-1)
    |> Module.concat()
    |> then(fn prefix ->
      if prefix == :"", do: "Migrations", else: "#{prefix}.Migrations"
    end)
  end
end