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

  import Macro, only: [camelize: 1, underscore: 1]
  import Mix.Generator
  import Mix.Ecto
  import Mix.EctoSQL

  @shortdoc "Generates a new migration for the repo"

  @aliases [
    r: :repo
  ]

  @switches [
    change: :string,
    repo: [:string, :keep],
    no_compile: :boolean,
    no_deps_check: :boolean,
    migrations_path: :string
  ]

  @moduledoc """
  Generates a migration.

  The repository must be set under `:ecto_repos` in the
  current app configuration or given via the `-r` option.

  ## Examples

      $ mix ecto.gen.migration add_posts_table
      $ mix ecto.gen.migration add_posts_table -r Custom.Repo

  The generated migration filename will be prefixed with the current
  timestamp in UTC which is used for versioning and ordering.

  By default, the migration will be generated to the
  "priv/YOUR_REPO/migrations" directory of the current application
  but it can be configured to be any subdirectory of `priv` by
  specifying the `:priv` key under the repository configuration.

  This generator will automatically open the generated file if
  you have `ECTO_EDITOR` set in your environment variable.

  ## Command line options

    * `-r`, `--repo` - the repo to generate migration for
    * `--no-compile` - does not compile applications before running
    * `--no-deps-check` - does not check dependencies before running
    * `--migrations-path` - the path to run the migrations from, defaults to `priv/repo/migrations`

  ## Configuration

  If the current app configuration specifies a custom migration module
  the generated migration code will use that rather than the default
  `Ecto.Migration`:

      config :ecto_sql, migration_module: MyApplication.CustomMigrationModule

  """

  @impl true
  def run(args) do
    repos = parse_repo(args)

    Enum.map repos, fn repo ->
      case OptionParser.parse!(args, strict: @switches, aliases: @aliases) do
        {opts, [name]} ->
          ensure_repo(repo, args)
          path = opts[:migrations_path] || Path.join(source_repo_priv(repo), "migrations")
          base_name = "#{underscore(name)}.exs"
          file = Path.join(path, "#{timestamp()}_#{base_name}")
          unless File.dir?(path), do: create_directory path

          fuzzy_path = Path.join(path, "*_#{base_name}")
          if Path.wildcard(fuzzy_path) != [] do
            Mix.raise "migration can't be created, there is already a migration file with name #{name}."
          end

          # The :change option may be used by other tasks but not the CLI
          assigns = [mod: Module.concat([repo, Migrations, camelize(name)]), change: opts[:change]]
          create_file file, migration_template(assigns)

          if open?(file) and Mix.shell().yes?("Do you want to run this migration?") do
            Mix.Task.run "ecto.migrate", ["-r", inspect(repo), "--migrations-path", path]
          end

          file

        {_, _} ->
          Mix.raise "expected ecto.gen.migration to receive the migration file name, " <>
                    "got: #{inspect Enum.join(args, " ")}"
      end
    end
  end

  defp timestamp do
    {{y, m, d}, {hh, mm, ss}} = :calendar.universal_time()
    "#{y}#{pad(m)}#{pad(d)}#{pad(hh)}#{pad(mm)}#{pad(ss)}"
  end

  defp pad(i) when i < 10, do: <<?0, ?0 + i>>
  defp pad(i), do: to_string(i)

  defp migration_module do
    case Application.get_env(:ecto_sql, :migration_module, Ecto.Migration) do
      migration_module when is_atom(migration_module) -> migration_module
      other -> Mix.raise "Expected :migration_module to be a module, got: #{inspect(other)}"
    end
  end

  embed_template :migration, """
  defmodule <%= inspect @mod %> do
    use <%= inspect migration_module() %>

    def change do
  <%= @change %>
    end
  end
  """
end