add artifact image download service and job

app/jobs/download_artifact_images_job.rb

@@ -0,0 +1,87 @@
+# frozen_string_literal: true
+
+# Background job for downloading artifact images from Granblue servers to S3.
+# Stores progress in Redis for status polling.
+#
+# @example Enqueue a download job
+#   job = DownloadArtifactImagesJob.perform_later(artifact.id)
+#   # Poll status with: DownloadArtifactImagesJob.status(artifact.id)
+class DownloadArtifactImagesJob < ApplicationJob
+  queue_as :downloads
+
+  retry_on StandardError, wait: :exponentially_longer, attempts: 3
+
+  discard_on ActiveRecord::RecordNotFound do |job, _error|
+    artifact_id = job.arguments.first
+    Rails.logger.error "[DownloadArtifactImages] Artifact #{artifact_id} not found"
+    update_status(artifact_id, 'failed', error: 'Artifact not found')
+  end
+
+  # Status keys for Redis storage
+  REDIS_KEY_PREFIX = 'artifact_image_download'
+  STATUS_TTL = 1.hour.to_i
+
+  class << self
+    # Get the current status of a download job for an artifact
+    #
+    # @param artifact_id [String] UUID of the artifact
+    # @return [Hash] Status hash with :status, :progress, :images_downloaded, :images_total, :error
+    def status(artifact_id)
+      data = redis.get(redis_key(artifact_id))
+      return { status: 'not_found' } unless data
+
+      JSON.parse(data, symbolize_names: true)
+    end
+
+    def redis_key(artifact_id)
+      "#{REDIS_KEY_PREFIX}:#{artifact_id}"
+    end
+
+    def redis
+      @redis ||= Redis.new(url: ENV.fetch('REDIS_URL', 'redis://localhost:6379/0'))
+    end
+
+    def update_status(artifact_id, status, **attrs)
+      data = { status: status, updated_at: Time.current.iso8601 }.merge(attrs)
+      redis.setex(redis_key(artifact_id), STATUS_TTL, data.to_json)
+    end
+  end
+
+  def perform(artifact_id, force: false, size: 'all')
+    Rails.logger.info "[DownloadArtifactImages] Starting download for artifact #{artifact_id}"
+
+    artifact = Artifact.find(artifact_id)
+    update_status(artifact_id, 'processing', progress: 0, images_downloaded: 0)
+
+    service = ArtifactImageDownloadService.new(
+      artifact,
+      force: force,
+      size: size,
+      storage: :s3
+    )
+
+    result = service.download
+
+    if result.success?
+      Rails.logger.info "[DownloadArtifactImages] Completed for artifact #{artifact_id}"
+      update_status(
+        artifact_id,
+        'completed',
+        progress: 100,
+        images_downloaded: result.total,
+        images_total: result.total,
+        images: result.images
+      )
+    else
+      Rails.logger.error "[DownloadArtifactImages] Failed for artifact #{artifact_id}: #{result.error}"
+      update_status(artifact_id, 'failed', error: result.error)
+      raise StandardError, result.error # Trigger retry
+    end
+  end
+
+  private
+
+  def update_status(artifact_id, status, **attrs)
+    self.class.update_status(artifact_id, status, **attrs)
+  end
+end

app/services/artifact_image_download_service.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+# Service wrapper for downloading artifact images from Granblue servers to S3.
+# Uses the existing ArtifactDownloader but provides a cleaner interface for controllers.
+#
+# @example Download images for an artifact
+#   service = ArtifactImageDownloadService.new(artifact)
+#   result = service.download
+#   if result.success?
+#     puts result.images
+#   else
+#     puts result.error
+#   end
+class ArtifactImageDownloadService
+  Result = Struct.new(:success?, :images, :error, :total, keyword_init: true)
+
+  def initialize(artifact, options = {})
+    @artifact = artifact
+    @force = options[:force] || false
+    @size = options[:size] || 'all'
+    @storage = options[:storage] || :s3
+  end
+
+  # Downloads images for the artifact
+  #
+  # @return [Result] Struct with success status, images manifest, and any errors
+  def download
+    downloader = Granblue::Downloaders::ArtifactDownloader.new(
+      @artifact.granblue_id,
+      storage: @storage,
+      force: @force,
+      verbose: Rails.env.development?
+    )
+
+    selected_size = @size == 'all' ? nil : @size
+    downloader.download(selected_size)
+
+    manifest = build_image_manifest
+
+    Result.new(
+      success?: true,
+      images: manifest,
+      total: count_total_images(manifest)
+    )
+  rescue StandardError => e
+    Rails.logger.error "[ArtifactImageDownload] Failed for #{@artifact.granblue_id}: #{e.message}"
+    Result.new(
+      success?: false,
+      error: e.message
+    )
+  end
+
+  private
+
+  def build_image_manifest
+    sizes = Granblue::Downloaders::ArtifactDownloader::SIZES
+
+    sizes.each_with_object({}) do |size, manifest|
+      manifest[size] = ["#{@artifact.granblue_id}.jpg"]
+    end
+  end
+
+  def count_total_images(manifest)
+    manifest.values.sum(&:size)
+  end
+end