# frozen_string_literal: true

# = Active Storage \Blob
#
# A blob is a record that contains the metadata about a file and a key for where that file resides on the service.
# Blobs can be created in two ways:
#
# 1. Ahead of the file being uploaded server-side to the service, via <tt>create_and_upload!</tt>. A rewindable
#    <tt>io</tt> with the file contents must be available at the server for this operation.
# 2. Ahead of the file being directly uploaded client-side to the service, via <tt>create_before_direct_upload!</tt>.
#
# The first option doesn't require any client-side JavaScript integration, and can be used by any other back-end
# service that deals with files. The second option is faster, since you're not using your own server as a staging
# point for uploads, and can work with deployments like Heroku that do not provide large amounts of disk space.
#
# Blobs are intended to be immutable in as-so-far as their reference to a specific file goes. You're allowed to
# update a blob's metadata on a subsequent pass, but you should not update the key or change the uploaded file.
# If you need to create a derivative or otherwise change the blob, simply create a new blob and purge the old one.
class ActiveStorage::Blob < ActiveStorage::Record
  include Analyzable
  include Identifiable
  include Representable
  include Servable

  MINIMUM_TOKEN_LENGTH = 28

  has_secure_token :key, length: MINIMUM_TOKEN_LENGTH
  store :metadata, accessors: [ :analyzed, :identified, :composed ], coder: ActiveRecord::Coders::JSON

  class_attribute :services, default: {}
  class_attribute :service, instance_accessor: false

  ##
  # :method:
  #
  # Returns the associated ActiveStorage::Attachment instances.
  has_many :attachments

  ##
  # :singleton-method:
  #
  # Returns the blobs that aren't attached to any record.
  scope :unattached, -> { where.missing(:attachments) }

  after_initialize do
    self.service_name ||= self.class.service&.name
  end

  after_update :touch_attachment_records

  after_update_commit :update_service_metadata, if: -> { content_type_previously_changed? || metadata_previously_changed? }

  before_destroy(prepend: true) do
    raise ActiveRecord::InvalidForeignKey if attachments.exists?
  end

  validates :service_name, presence: true
  validates :checksum, presence: true, unless: :composed

  validate do
    if service_name_changed? && service_name.present?
      services.fetch(service_name) do
        errors.add(:service_name, :invalid)
      end
    end
  end

  class << self
    # You can use the signed ID of a blob to refer to it on the client side without fear of tampering.
    # This is particularly helpful for direct uploads where the client-side needs to refer to the blob
    # that was created ahead of the upload itself on form submission.
    #
    # The signed ID is also used to create stable URLs for the blob through the BlobsController.
    def find_signed(id, record: nil, purpose: :blob_id)
      super(id, purpose: purpose)
    end

    # Works like +find_signed+, but will raise an +ActiveSupport::MessageVerifier::InvalidSignature+
    # exception if the +signed_id+ has either expired, has a purpose mismatch, is for another record,
    # or has been tampered with. It will also raise an +ActiveRecord::RecordNotFound+ exception if
    # the valid signed id can't find a record.
    def find_signed!(id, record: nil, purpose: :blob_id)
      super(id, purpose: purpose)
    end

    def build_after_unfurling(key: nil, io:, filename:, content_type: nil, metadata: nil, service_name: nil, identify: true, record: nil) # :nodoc:
      new(key: key, filename: filename, content_type: content_type, metadata: metadata, service_name: service_name).tap do |blob|
        blob.unfurl(io, identify: identify)
      end
    end

    def create_after_unfurling!(key: nil, io:, filename:, content_type: nil, metadata: nil, service_name: nil, identify: true, record: nil) # :nodoc:
      build_after_unfurling(key: key, io: io, filename: filename, content_type: content_type, metadata: metadata, service_name: service_name, identify: identify).tap(&:save!)
    end

    # Creates a new blob instance and then uploads the contents of
    # the given <tt>io</tt> to the service. The blob instance is going to
    # be saved before the upload begins to prevent the upload clobbering another due to key collisions.
    # When providing a content type, pass <tt>identify: false</tt> to bypass
    # automatic content type inference.
    def create_and_upload!(key: nil, io:, filename:, content_type: nil, metadata: nil, service_name: nil, identify: true, record: nil)
      create_after_unfurling!(key: key, io: io, filename: filename, content_type: content_type, metadata: metadata, service_name: service_name, identify: identify).tap do |blob|
        blob.upload_without_unfurling(io)
      end
    end

    # Returns a saved blob _without_ uploading a file to the service. This blob will point to a key where there is
    # no file yet. It's intended to be used together with a client-side upload, which will first create the blob
    # in order to produce the signed URL for uploading. This signed URL points to the key generated by the blob.
    # Once the form using the direct upload is submitted, the blob can be associated with the right record using
    # the signed ID.
    def create_before_direct_upload!(key: nil, filename:, byte_size:, checksum:, content_type: nil, metadata: nil, service_name: nil, record: nil)
      create! key: key, filename: filename, byte_size: byte_size, checksum: checksum, content_type: content_type, metadata: metadata, service_name: service_name
    end

    # To prevent problems with case-insensitive filesystems, especially in combination
    # with databases which treat indices as case-sensitive, all blob keys generated are going
    # to only contain the base-36 character alphabet and will therefore be lowercase. To maintain
    # the same or higher amount of entropy as in the base-58 encoding used by +has_secure_token+
    # the number of bytes used is increased to 28 from the standard 24
    def generate_unique_secure_token(length: MINIMUM_TOKEN_LENGTH)
      SecureRandom.base36(length)
    end

    # Customize signed ID purposes for backwards compatibility.
    def combine_signed_id_purposes(purpose) # :nodoc:
      purpose.to_s
    end

    # Customize the default signed ID verifier for backwards compatibility.
    #
    # We override the reader (.signed_id_verifier) instead of just calling the writer (.signed_id_verifier=)
    # to guard against the case where ActiveStorage.verifier isn't yet initialized at load time.
    def signed_id_verifier # :nodoc:
      @signed_id_verifier ||= ActiveStorage.verifier
    end

    def scope_for_strict_loading # :nodoc:
      if strict_loading_by_default? && ActiveStorage.track_variants
        includes(
          variant_records: { image_attachment: :blob },
          preview_image_attachment: { blob: { variant_records: { image_attachment: :blob } } }
        )
      else
        all
      end
    end

    # Concatenate multiple blobs into a single "composed" blob.
    def compose(blobs, filename:, content_type: nil, metadata: nil)
      raise ActiveRecord::RecordNotSaved, "All blobs must be persisted." if blobs.any?(&:new_record?)

      content_type ||= blobs.pluck(:content_type).compact.first

      new(filename: filename, content_type: content_type, metadata: metadata, byte_size: blobs.sum(&:byte_size)).tap do |combined_blob|
        combined_blob.compose(blobs.pluck(:key))
        combined_blob.save!
      end
    end
  end

  # Returns a signed ID for this blob that's suitable for reference on the client-side without fear of tampering.
  def signed_id(purpose: :blob_id, expires_in: nil, expires_at: nil)
    super
  end

  # Returns the key pointing to the file on the service that's associated with this blob. The key is the
  # secure-token format from \Rails in lower case. So it'll look like: xtapjjcjiudrlk3tmwyjgpuobabd.
  # This key is not intended to be revealed directly to the user.
  # Always refer to blobs using the signed_id or a verified form of the key.
  def key
    # We can't wait until the record is first saved to have a key for it
    self[:key] ||= self.class.generate_unique_secure_token(length: MINIMUM_TOKEN_LENGTH)
  end

  # Returns an ActiveStorage::Filename instance of the filename that can be
  # queried for basename, extension, and a sanitized version of the filename
  # that's safe to use in URLs.
  def filename
    ActiveStorage::Filename.new(self[:filename])
  end

  def custom_metadata
    self[:metadata][:custom] || {}
  end

  def custom_metadata=(metadata)
    self[:metadata] = self[:metadata].merge(custom: metadata)
  end

  # Returns true if the content_type of this blob is in the image range, like image/png.
  def image?
    content_type.start_with?("image")
  end

  # Returns true if the content_type of this blob is in the audio range, like audio/mpeg.
  def audio?
    content_type.start_with?("audio")
  end

  # Returns true if the content_type of this blob is in the video range, like video/mp4.
  def video?
    content_type.start_with?("video")
  end

  # Returns true if the content_type of this blob is in the text range, like text/plain.
  def text?
    content_type.start_with?("text")
  end

  # Returns the URL of the blob on the service. This returns a permanent URL for public files, and returns a
  # short-lived URL for private files. Private files are signed, and not for public use. Instead,
  # the URL should only be exposed as a redirect from a stable, possibly authenticated URL. Hiding the
  # URL behind a redirect also allows you to change services without updating all URLs.
  def url(expires_in: ActiveStorage.service_urls_expire_in, disposition: :inline, filename: nil, **options)
    service.url key, expires_in: expires_in, filename: ActiveStorage::Filename.wrap(filename || self.filename),
      content_type: content_type_for_serving, disposition: forced_disposition_for_serving || disposition, **options
  end

  # Returns a URL that can be used to directly upload a file for this blob on the service. This URL is intended to be
  # short-lived for security and only generated on-demand by the client-side JavaScript responsible for doing the uploading.
  def service_url_for_direct_upload(expires_in: ActiveStorage.service_urls_expire_in)
    service.url_for_direct_upload key, expires_in: expires_in, content_type: content_type, content_length: byte_size, checksum: checksum, custom_metadata: custom_metadata
  end

  # Returns a Hash of headers for +service_url_for_direct_upload+ requests.
  def service_headers_for_direct_upload
    service.headers_for_direct_upload key, filename: filename, content_type: content_type, content_length: byte_size, checksum: checksum, custom_metadata: custom_metadata
  end


  # Uploads the +io+ to the service on the +key+ for this blob. Blobs are intended to be immutable, so you shouldn't be
  # using this method after a file has already been uploaded to fit with a blob. If you want to create a derivative blob,
  # you should instead simply create a new blob based on the old one.
  #
  # Prior to uploading, we compute the checksum, which is sent to the service for transit integrity validation. If the
  # checksum does not match what the service receives, an exception will be raised. We also measure the size of the +io+
  # and store that in +byte_size+ on the blob record. The content type is automatically extracted from the +io+ unless
  # you specify a +content_type+ and pass +identify+ as false.
  #
  # Normally, you do not have to call this method directly at all. Use the +create_and_upload!+ class method instead.
  # If you do use this method directly, make sure you are using it on a persisted Blob as otherwise another blob's
  # data might get overwritten on the service.
  def upload(io, identify: true)
    unfurl io, identify: identify
    upload_without_unfurling io
  end

  def unfurl(io, identify: true) # :nodoc:
    self.checksum     = compute_checksum_in_chunks(io)
    self.content_type = extract_content_type(io) if content_type.nil? || identify
    self.byte_size    = io.size
    self.identified   = true
  end

  def upload_without_unfurling(io) # :nodoc:
    service.upload key, io, checksum: checksum, **service_metadata
  end

  def compose(keys) # :nodoc:
    self.composed = true
    service.compose(keys, key, **service_metadata)
  end

  # Downloads the file associated with this blob. If no block is given, the entire file is read into memory and returned.
  # That'll use a lot of RAM for very large files. If a block is given, then the download is streamed and yielded in chunks.
  def download(&block)
    service.download key, &block
  end

  # Downloads a part of the file associated with this blob.
  def download_chunk(range)
    service.download_chunk key, range
  end

  # Downloads the blob to a tempfile on disk. Yields the tempfile.
  #
  # The tempfile's name is prefixed with +ActiveStorage-+ and the blob's ID. Its extension matches that of the blob.
  #
  # By default, the tempfile is created in <tt>Dir.tmpdir</tt>. Pass +tmpdir:+ to create it in a different directory:
  #
  #   blob.open(tmpdir: "/path/to/tmp") do |file|
  #     # ...
  #   end
  #
  # The tempfile is automatically closed and unlinked after the given block is executed.
  #
  # Raises ActiveStorage::IntegrityError if the downloaded data does not match the blob's checksum.
  def open(tmpdir: nil, &block)
    service.open(
      key,
      checksum: checksum,
      verify: !composed,
      name: [ "ActiveStorage-#{id}-", filename.extension_with_delimiter ],
      tmpdir: tmpdir,
      &block
    )
  end

  def mirror_later # :nodoc:
    service.mirror_later key, checksum: checksum if service.respond_to?(:mirror_later)
  end

  # Deletes the files on the service associated with the blob. This should only be done if the blob is going to be
  # deleted as well or you will essentially have a dead reference. It's recommended to use #purge and #purge_later
  # methods in most circumstances.
  def delete
    service.delete(key)
    service.delete_prefixed("variants/#{key}/") if image?
  end

  # Destroys the blob record and then deletes the file on the service. This is the recommended way to dispose of unwanted
  # blobs. Note, though, that deleting the file off the service will initiate an HTTP connection to the service, which may
  # be slow or prevented, so you should not use this method inside a transaction or in callbacks. Use #purge_later instead.
  def purge
    destroy
    delete if previously_persisted?
  rescue ActiveRecord::InvalidForeignKey
  end

  # Enqueues an ActiveStorage::PurgeJob to call #purge. This is the recommended way to purge blobs from a transaction,
  # an Active Record callback, or in any other real-time scenario.
  def purge_later
    ActiveStorage::PurgeJob.perform_later(self)
  end

  # Returns an instance of service, which can be configured globally or per attachment
  def service
    services.fetch(service_name)
  end

  private
    def compute_checksum_in_chunks(io)
      raise ArgumentError, "io must be rewindable" unless io.respond_to?(:rewind)

      OpenSSL::Digest::MD5.new.tap do |checksum|
        while chunk = io.read(5.megabytes)
          checksum << chunk
        end

        io.rewind
      end.base64digest
    end

    def extract_content_type(io)
      Marcel::MimeType.for io, name: filename.to_s, declared_type: content_type
    end

    def web_image?
      ActiveStorage.web_image_content_types.include?(content_type)
    end

    def service_metadata
      if forcibly_serve_as_binary?
        { content_type: ActiveStorage.binary_content_type, disposition: :attachment, filename: filename, custom_metadata: custom_metadata }
      elsif !allowed_inline?
        { content_type: content_type, disposition: :attachment, filename: filename, custom_metadata: custom_metadata }
      else
        { content_type: content_type, custom_metadata: custom_metadata }
      end
    end

    def touch_attachment_records
      attachments.includes(:record).each do |attachment|
        attachment.touch
      end
    end

    def update_service_metadata
      service.update_metadata key, **service_metadata if service_metadata.any?
    end
end

ActiveSupport.run_load_hooks :active_storage_blob, ActiveStorage::Blob