defmodule Mix.Tasks.EventStore.Migrate do
  @moduledoc """
  Migrate an existing EventStore database.

  ## Examples

      mix event_store.migrate

  ## Command line options

    * `--quiet` - do not log output

  """

  use Mix.Task

  alias EventStore.Config
  alias EventStore.Storage.Database

  @shortdoc "Migrate an existing EventStore database"

  @doc false
  def run(args) do
    {:ok, _} = Application.ensure_all_started(:postgrex)

    config = Config.parsed()
    {opts, _, _} = OptionParser.parse(args, switches: [quiet: :boolean])

    migrate_database(config, opts)

    Mix.Task.reenable("event_store.migrate")
  end

  @available_migrations [
    "0.13.0",
    "0.14.0"
  ]

  defp migrate_database(config, opts) do
    migrations =
      case event_store_schema_version(config) do
        [] ->
          # run all migrations
          @available_migrations

        [event_store_version | _] ->
          # only run newer migrations
          @available_migrations
          |> Enum.filter(fn migration_version ->
            migration_version |> Version.parse!() |> Version.compare(event_store_version) == :gt
          end)
      end

    migrate(config, opts, migrations)
  end

  defp migrate(_config, opts, []) do
    unless opts[:quiet], do: Mix.shell().info("The EventStore database is already migrated.")
  end

  defp migrate(config, opts, migrations) do
    for migration <- migrations do
      unless opts[:quiet], do: Mix.shell().info("Running migration v#{migration}...")

      path = Application.app_dir(:eventstore, "priv/event_store/migrations/v#{migration}.sql")
      script = File.read!(path)

      case Database.migrate(config, script) do
        :ok ->
          :ok

        {:error, term} ->
          Mix.raise(
            "The EventStore database couldn't be migrated, reason given: #{inspect(term)}."
          )
      end
    end

    unless opts[:quiet], do: Mix.shell().info("The EventStore database has been migrated.")
  end

  defp event_store_schema_version(config) do
    config
    |> query_schema_migrations()
    |> Enum.sort(fn left, right ->
      case Version.compare(left, right) do
        :gt -> true
        _ -> false
      end
    end)
  end

  defp query_schema_migrations(config) do
    with {:ok, conn} <- Postgrex.start_link(config) do
      conn
      |> Postgrex.query!(
        "SELECT major_version, minor_version, patch_version FROM schema_migrations",
        [],
        pool: DBConnection.Poolboy
      )
      |> handle_response()
    end
  end

  defp handle_response(%Postgrex.Result{num_rows: 0}), do: []

  defp handle_response(%Postgrex.Result{rows: rows}) do
    Enum.map(rows, fn [major_version, minor_version, patch_version] ->
      Version.parse!("#{major_version}.#{minor_version}.#{patch_version}")
    end)
  end
end