defmodule Mix.Tasks.AshMeilisearch.Reindex do
  @shortdoc "Reindex all records of an AshMeilisearch-enabled resource"
  @moduledoc """
  Reindex all records of a given AshMeilisearch-enabled resource.

  ## Usage

      mix ash_meilisearch.reindex MyApp.Blog.Post
      mix ash_meilisearch.reindex MyApp.Blog.Post --batch-size 200

  ## Options

    * `--batch-size` - Number of records per batch (default: 100)
    * `--help` - Show help message

  The task uses keyset pagination for memory-efficient processing of large datasets.
  """

  use Mix.Task

  require Ash.Query

  @impl Mix.Task
  def run(args) do
    Mix.Task.run("app.start")
    Logger.configure(level: :warning)

    {options, args, _} =
      OptionParser.parse(args,
        switches: [batch_size: :integer, help: :boolean],
        aliases: [b: :batch_size, h: :help]
      )

    if options[:help] || length(args) == 0 do
      print_help()
      System.halt(0)
    end

    resource_module_name = List.first(args)
    resource_module = Module.concat([resource_module_name])
    batch_size = options[:batch_size] || 100

    validate_resource!(resource_module, resource_module_name)

    Mix.shell().info("Reindexing #{resource_module_name}...")

    total_count = Ash.count!(Ash.Query.new(resource_module))
    Mix.shell().info("Found #{total_count} records")

    if total_count == 0 do
      Mix.shell().info("No records to reindex.")
      System.halt(0)
    end

    Mix.shell().info("Processing #{total_count} records in batches of #{batch_size}")

    start_time = System.monotonic_time(:millisecond)
    final_stats = process_batches(resource_module, batch_size)
    elapsed_seconds = div(System.monotonic_time(:millisecond) - start_time, 1000)

    records_per_second =
      if elapsed_seconds > 0,
        do: Float.round(final_stats.successful / elapsed_seconds, 1),
        else: "N/A"

    Mix.shell().info(
      "Reindex complete. Processed #{final_stats.successful}/#{total_count} records in #{elapsed_seconds}s (#{records_per_second} records/sec)"
    )

    if final_stats.failed > 0 do
      Mix.shell().error("#{final_stats.failed} records failed to reindex")

      final_stats.failed_ids
      |> Enum.take(10)
      |> Enum.each(&Mix.shell().error("  Failed ID: #{&1}"))

      if length(final_stats.failed_ids) > 10 do
        Mix.shell().error("  ... and #{length(final_stats.failed_ids) - 10} more")
      end
    end
  end

  defp validate_resource!(resource_module, resource_module_name) do
    unless Code.ensure_loaded?(resource_module) and
             function_exported?(resource_module, :spark_dsl_config, 0) do
      Mix.shell().error("Error: '#{resource_module_name}' is not an Ash resource")
      System.halt(1)
    end

    unless AshMeilisearch.Info.meilisearch_configured?(resource_module) do
      Mix.shell().error(
        "Error: '#{resource_module_name}' does not have AshMeilisearch configured"
      )

      System.halt(1)
    end

    unless Ash.Resource.Info.action(resource_module, :reindex) do
      Mix.shell().error("Error: '#{resource_module_name}' does not have a :reindex action")
      System.halt(1)
    end
  end

  defp print_help do
    Mix.shell().info("""
    AshMeilisearch Resource Reindex Task

    Usage: mix ash_meilisearch.reindex [ResourceModule] [options]

    Arguments:
      ResourceModule    The Ash resource module to reindex (e.g., MyApp.Blog.Post)

    Options:
      -b, --batch-size  Number of records per batch (default: 100)
      -h, --help        Show this help message
    """)
  end

  defp process_batches(
         resource_module,
         batch_size,
         page \\ nil,
         acc \\ %{successful: 0, failed: 0, failed_ids: []}
       ) do
    page =
      if page do
        Ash.page!(page, :next)
      else
        query =
          resource_module
          |> Ash.Query.new()
          |> Ash.Query.load(:search_document)
          |> Ash.Query.sort(id: :asc)
          |> Ash.Query.page(limit: batch_size)

        Ash.read!(query)
      end

    valid_documents =
      Enum.filter(page.results, fn record ->
        record.search_document not in [nil, %{}]
      end)

    new_acc =
      if length(valid_documents) > 0 do
        batch_documents = Enum.map(valid_documents, & &1.search_document)

        case AshMeilisearch.add_documents(resource_module, batch_documents) do
          {:ok, _task} ->
            %{acc | successful: acc.successful + length(valid_documents)}

          {:error, error} ->
            Mix.shell().error("Batch failed: #{inspect(error)}")
            failed_ids = Enum.map(page.results, & &1.id)

            %{
              acc
              | failed: acc.failed + length(page.results),
                failed_ids: acc.failed_ids ++ failed_ids
            }
        end
      else
        acc
      end

    if page.more? do
      process_batches(resource_module, batch_size, page, new_acc)
    else
      new_acc
    end
  end
end