defmodule Mix.Tasks.ExDav.Gen.Migration do
  @shortdoc "Generate an ExDav migration"
  @moduledoc """
  Generates Ecto migration files for ExDav schema changes.

  ## Usage

      mix ex_dav.gen.migration upgrade_to_0_4_0

  ## Available migrations

    * `upgrade_to_0_4_0` — rename tables from `caldav_*` to `dav_*`,
      add `kind` and `properties` to collections, rename `ical` → `body`
      on resources, add `content_type` to resources.

  The migration is written to `priv/repo/migrations/` in the current Mix
  project (i.e. the consumer's app, not ex_dav itself).
  """

  use Mix.Task

  @migrations %{
    "upgrade_to_0_4_0" => :migration_0_4_0
  }

  @impl Mix.Task
  def run([name | _]) do
    case Map.fetch(@migrations, name) do
      {:ok, fun} ->
        content = apply(__MODULE__, fun, [])
        write_migration(name, content)

      :error ->
        raise "Unknown migration: #{name}. Available: #{Enum.join(Map.keys(@migrations), ", ")}"
    end
  end

  def run([]) do
    raise "Usage: mix ex_dav.gen.migration <name>"
  end

  defp write_migration(name, content) do
    migrations_dir = "priv/repo/migrations"
    File.mkdir_p!(migrations_dir)

    timestamp = timestamp()
    filename = "#{timestamp}_ex_dav_#{name}.exs"
    path = Path.join(migrations_dir, filename)

    File.write!(path, content)
    IO.puts("* creating #{path}")
  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.iodata_to_binary()
  end

  @doc false
  def migration_0_4_0 do
    """
    defmodule ExDav.Repo.Migrations.ExDavUpgradeTo040 do
      use Ecto.Migration

      def up do
        # ---- rename calendars table -> collections -------------------------
        rename table(:caldav_calendars), to: table(:dav_collections)

        # add kind column; backfill all legacy rows as :calendar
        alter table(:dav_collections) do
          add :kind, :string, null: false, default: "calendar"
          add :properties, :map, default: %{}
        end

        # move components array into properties['components'], drop old column
        execute \"\"\"
          UPDATE dav_collections
          SET properties = jsonb_build_object('components', to_jsonb(components))
          WHERE components IS NOT NULL AND array_length(components, 1) > 0
        \"\"\", ""

        alter table(:dav_collections) do
          remove :components
        end

        drop_if_exists unique_index(:caldav_calendars, [:user_id, :name])
        create unique_index(:dav_collections, [:user_id, :name, :kind])

        # ---- rename objects table -> resources --------------------------------
        rename table(:caldav_calendar_objects), to: table(:dav_resources)

        alter table(:dav_resources) do
          add :content_type, :string
        end

        execute \"\"\"
          ALTER TABLE dav_resources
            RENAME COLUMN ical TO body
        \"\"\", \"\"\"
          ALTER TABLE dav_resources
            RENAME COLUMN body TO ical
        \"\"\"

        execute \"\"\"
          UPDATE dav_resources r
          SET content_type = 'text/calendar; charset=utf-8'
        \"\"\", ""

        # ---- tombstones table rename ----------------------------------------
        rename table(:caldav_calendar_object_tombstones), to: table(:dav_tombstones)

        execute \"\"\"
          ALTER TABLE dav_tombstones
            RENAME COLUMN calendar_id TO collection_id
        \"\"\", \"\"\"
          ALTER TABLE dav_tombstones
            RENAME COLUMN collection_id TO calendar_id
        \"\"\"

        execute \"\"\"
          ALTER TABLE dav_resources
            RENAME COLUMN calendar_id TO collection_id
        \"\"\", \"\"\"
          ALTER TABLE dav_resources
            RENAME COLUMN collection_id TO calendar_id
        \"\"\"

        # Update FK constraint names (Postgres auto-names them)
        execute \"\"\"
          ALTER TABLE dav_resources
            DROP CONSTRAINT IF EXISTS caldav_calendar_objects_calendar_id_fkey
        \"\"\", ""

        execute \"\"\"
          ALTER TABLE dav_resources
            ADD CONSTRAINT dav_resources_collection_id_fkey
            FOREIGN KEY (collection_id) REFERENCES dav_collections(id) ON DELETE CASCADE
        \"\"\", ""

        execute \"\"\"
          ALTER TABLE dav_tombstones
            DROP CONSTRAINT IF EXISTS caldav_calendar_object_tombstones_calendar_id_fkey
        \"\"\", ""

        execute \"\"\"
          ALTER TABLE dav_tombstones
            ADD CONSTRAINT dav_tombstones_collection_id_fkey
            FOREIGN KEY (collection_id) REFERENCES dav_collections(id) ON DELETE CASCADE
        \"\"\", ""

        execute \"\"\"
          ALTER TABLE dav_collections
            DROP CONSTRAINT IF EXISTS caldav_calendars_user_id_fkey
        \"\"\", ""

        execute \"\"\"
          ALTER TABLE dav_collections
            ADD CONSTRAINT dav_collections_user_id_fkey
            FOREIGN KEY (user_id) REFERENCES caldav_users(id) ON DELETE CASCADE
        \"\"\", ""
      end

      def down do
        rename table(:dav_collections), to: table(:caldav_calendars)

        alter table(:caldav_calendars) do
          add :components, {:array, :string}, default: ["VEVENT", "VTODO"]
        end

        execute \"\"\"
          UPDATE caldav_calendars
          SET components = ARRAY(SELECT jsonb_array_elements_text(properties->'components'))
          WHERE properties ? 'components'
        \"\"\", ""

        alter table(:caldav_calendars) do
          remove :kind
          remove :properties
        end

        rename table(:dav_resources), to: table(:caldav_calendar_objects)

        execute \"\"\"
          ALTER TABLE caldav_calendar_objects
            RENAME COLUMN body TO ical
        \"\"\", ""

        execute \"\"\"
          ALTER TABLE caldav_calendar_objects
            RENAME COLUMN collection_id TO calendar_id
        \"\"\", ""

        alter table(:caldav_calendar_objects) do
          remove :content_type
        end

        rename table(:dav_tombstones), to: table(:caldav_calendar_object_tombstones)

        execute \"\"\"
          ALTER TABLE caldav_calendar_object_tombstones
            RENAME COLUMN collection_id TO calendar_id
        \"\"\", ""
      end
    end
    """
  end
end