module ROCrate
  ##
  # A class to handle reading of RO-Crates from Zip files or directories.
  class Reader
    ##
    # Reads an RO-Crate from a directory or zip file.
    #
    # @param source [String, ::File, Pathname, #read] The location of the zip or directory, or an IO-like object containing a zip.
    # @param target_dir [String, ::File, Pathname] The target directory where the crate should be unzipped (if its a Zip file).
    # @return [Crate] The RO-Crate.
    def self.read(source, target_dir: Dir.mktmpdir)
      begin
        is_dir = ::File.directory?(source)
      rescue TypeError
        is_dir = false
      end

      if is_dir
        read_directory(source)
      else
        read_zip(source, target_dir: target_dir)
      end
    end

    ##
    # Extract the contents of the given Zip file/data to the given directory.
    #
    # @param source [String, ::File, Pathname, #read] The location of the zip file, or an IO-like object.
    # @param target [String, ::File, Pathname] The target directory where the file should be unzipped.
    def self.unzip_to(source, target)
      source = Pathname.new(::File.expand_path(source)) if source.is_a?(String)

      if source.is_a?(Pathname) || source.respond_to?(:path)
        unzip_file_to(source, target)
      else
        unzip_io_to(source, target)
      end
    end

    ##
    # Extract the given Zip file data to the given directory.
    #
    # @param source [#read] An IO-like object containing a Zip file.
    # @param target [String, ::File, Pathname] The target directory where the file should be unzipped.
    def self.unzip_io_to(io, target)
      Dir.chdir(target) do
        Zip::InputStream.open(io) do |input|
          while (entry = input.get_next_entry)
            unless ::File.exist?(entry.name) || entry.name_is_directory?
              FileUtils::mkdir_p(::File.dirname(entry.name))
              ::File.binwrite(entry.name, input.read)
            end
          end
        end
      end
    end

    ##
    # Extract the contents of the given Zip file to the given directory.
    #
    # @param source [String, ::File, Pathname] The location of the zip file.
    # @param target [String, ::File, Pathname] The target directory where the file should be unzipped.
    def self.unzip_file_to(file_or_path, target)
      Dir.chdir(target) do
        Zip::File.open(file_or_path) do |zipfile|
          zipfile.each do |entry|
            unless ::File.exist?(entry.name)
              FileUtils::mkdir_p(::File.dirname(entry.name))
              zipfile.extract(entry, entry.name)
            end
          end
        end
      end
    end

    ##
    # Reads an RO-Crate from a zip file. It first extracts the Zip file to a temporary directory, and then calls
    # #read_directory.
    #
    # @param source [String, ::File, Pathname, #read] The location of the zip file, or an IO-like object.
    # @param target_dir [String, ::File, Pathname] The target directory where the crate should be unzipped.
    # @return [Crate] The RO-Crate.
    def self.read_zip(source, target_dir: Dir.mktmpdir)
      raise ROCrate::ReadException, "Target is not a directory!" unless ::File.directory?(target_dir)

      unzip_to(source, target_dir)

      # Traverse the unzipped directory to try and find the crate's root
      root_dir = detect_root_directory(target_dir)

      read_directory(root_dir)
    end

    ##
    # Reads an RO-Crate from a directory.
    #
    # @param source [String, ::File, Pathname] The location of the directory.
    # @return [Crate] The RO-Crate.
    def self.read_directory(source)
      raise ROCrate::ReadException, "Source is not a directory!" unless ::File.directory?(source)

      source = ::File.expand_path(source)
      metadata_file = Dir.entries(source).detect { |entry| entry == ROCrate::Metadata::IDENTIFIER ||
          entry == ROCrate::Metadata::IDENTIFIER_1_0 }

      if metadata_file
        metadata_json = ::File.read(::File.join(source, metadata_file))
        begin
          metadata = JSON.parse(metadata_json)
        rescue JSON::ParserError => e
          raise ROCrate::ReadException.new("Error parsing metadata", e)
        end

        entities = entities_from_metadata(metadata)
        context = metadata['@context']

        build_crate(entities, source, context: context)
      else
        raise ROCrate::ReadException, "No metadata found!"
      end
    end

    ##
    # Extracts all the entities from the @graph of the RO-Crate Metadata.
    #
    # @param metadata [Hash] A Hash containing the parsed metadata JSON.
    # @return [Hash{String => Hash}] A Hash of all the entities, mapped by their @id.
    def self.entities_from_metadata(metadata)
      graph = metadata['@graph']

      if graph
        # Collect all the things in the graph, mapped by their @id
        entities = {}
        graph.each do |entity|
          entities[entity['@id']] = entity
        end

        # Do some normalization...
        entities[ROCrate::Metadata::IDENTIFIER] = extract_metadata_entity(entities)
        raise ROCrate::ReadException, "No metadata entity found in @graph!" unless entities[ROCrate::Metadata::IDENTIFIER]
        entities[ROCrate::Preview::IDENTIFIER] = extract_preview_entity(entities)
        entities[ROCrate::Crate::IDENTIFIER] = extract_root_entity(entities)
        raise ROCrate::ReadException, "No root entity (with @id: #{entities[ROCrate::Metadata::IDENTIFIER].dig('about', '@id')}) found in @graph!" unless entities[ROCrate::Crate::IDENTIFIER]

        entities
      else
        raise ROCrate::ReadException, "No @graph found in metadata!"
      end
    end

    ##
    # Create and populate crate from the given set of entities.
    #
    # @param entity_hash [Hash{String => Hash}] A Hash containing all the entities in the @graph, mapped by their @id.
    # @param source [String, ::File, Pathname] The location of the RO-Crate being read.
    # @param crate_class [Class] The class to use to instantiate the crate,
    #   useful if you have created a subclass of ROCrate::Crate that you want to use. (defaults to ROCrate::Crate).
    # @param context [nil, String, Array, Hash] A custom JSON-LD @context (parsed), or nil to use default.
    # @return [Crate] The RO-Crate.
    def self.build_crate(entity_hash, source, crate_class: ROCrate::Crate, context:)
      crate = initialize_crate(entity_hash, source, crate_class: crate_class, context: context)

      extract_data_entities(crate, source, entity_hash).each do |entity|
        crate.add_data_entity(entity)
      end

      # The remaining entities in the hash must be contextual.
      extract_contextual_entities(crate, entity_hash).each do |entity|
        crate.add_contextual_entity(entity)
      end

      crate
    end

    ##
    # Initialize a crate from the given set of entities.
    #
    # @param entity_hash [Hash{String => Hash}] A Hash containing all the entities in the @graph, mapped by their @id.
    # @param source [String, ::File, Pathname] The location of the RO-Crate being read.
    # @param crate_class [Class] The class to use to instantiate the crate,
    #   useful if you have created a subclass of ROCrate::Crate that you want to use. (defaults to ROCrate::Crate).
    # @param context [nil, String, Array, Hash] A custom JSON-LD @context (parsed), or nil to use default.
    # @return [Crate] The RO-Crate.
    def self.initialize_crate(entity_hash, source, crate_class: ROCrate::Crate, context:)
      crate_class.new.tap do |crate|
        crate.properties = entity_hash.delete(ROCrate::Crate::IDENTIFIER)
        crate.metadata.properties = entity_hash.delete(ROCrate::Metadata::IDENTIFIER)
        crate.metadata.context = context
        preview_properties = entity_hash.delete(ROCrate::Preview::IDENTIFIER)
        preview_path = ::File.join(source, ROCrate::Preview::IDENTIFIER)
        preview_path = ::File.exist?(preview_path) ? Pathname.new(preview_path) : nil
        if preview_properties || preview_path
          crate.preview = ROCrate::Preview.new(crate, preview_path, preview_properties || {})
        end
        crate.add_all(source, false)
      end
    end

    ##
    # Discover data entities from the `hasPart` property of a crate, and create DataEntity objects for them.
    # Entities are looked up in the given `entity_hash` (and then removed from it).
    # @param crate [Crate] The RO-Crate being read.
    # @param source [String, ::File, Pathname] The location of the RO-Crate being read.
    # @param entity_hash [Hash] A Hash containing all the entities in the @graph, mapped by their @id.
    # @return [Array<ROCrate::File, ROCrate::Directory>] The extracted DataEntity objects.
    def self.extract_data_entities(crate, source, entity_hash)
      (crate.raw_properties['hasPart'] || []).map do |ref|
        entity_props = entity_hash.delete(ref['@id'])
        next unless entity_props
        entity_class = ROCrate::DataEntity.specialize(entity_props)
        entity = create_data_entity(crate, entity_class, source, entity_props)
        next if entity.nil?
        entity
      end.compact
    end

    ##
    # Create appropriately specialized ContextualEntity objects from the given hash of entities and their properties.
    # @param crate [Crate] The RO-Crate being read.
    # @param entity_hash [Hash] A Hash containing all the entities in the @graph, mapped by their @id.
    # @return [Array<ContextualEntity>] The extracted ContextualEntity objects.
    def self.extract_contextual_entities(crate, entity_hash)
      entities = []

      entity_hash.each do |id, entity_props|
        entity_class = ROCrate::ContextualEntity.specialize(entity_props)
        entity = entity_class.new(crate, id, entity_props)
        entities << entity
      end

      entities
    end

    ##
    # Create a DataEntity of the given class.
    # @param crate [Crate] The RO-Crate being read.
    # @param source [String, ::File, Pathname] The location of the RO-Crate being read.
    # @param entity_props [Hash] A Hash containing the entity's properties, including its @id.
    # @return [ROCrate::File, ROCrate::Directory, nil] The DataEntity object,
    #          or nil if it referenced a local file that wasn't found.
    def self.create_data_entity(crate, entity_class, source, entity_props)
      id = entity_props.delete('@id')
      raise ROCrate::ReadException, "Data Entity missing '@id': #{entity_props.inspect}" unless id
      decoded_id = URI.decode_www_form_component(id)
      path = nil
      uri = URI(id) rescue nil
      if uri&.absolute?
        path = uri
        decoded_id = nil
      elsif !id.start_with?('#')
        [id, decoded_id].each do |i|
          fullpath = ::File.join(source, i)
          path = Pathname.new(fullpath) if ::File.exist?(fullpath)
        end
        if path.nil?
          raise ROCrate::ReadException, "Local Data Entity not found in crate: #{id}"
        end
      end

      entity_class.new(crate, path, decoded_id, entity_props)
    end


    ##
    # Extract the metadata entity from the entity hash, according to the rules defined here:
    # https://www.researchobject.org/ro-crate/1.1/root-data-entity.html#finding-the-root-data-entity
    # @return [nil, Hash{String => Hash}] A Hash containing (hopefully) one value, the metadata entity's properties
    # mapped by its @id, or nil if nothing is found.
    def self.extract_metadata_entity(entities)
      key = entities.detect do |_, props|
        conforms = props['conformsTo']
        conforms = [conforms] unless conforms.is_a?(Array)
        conforms.compact.any? { |c| c['@id']&.start_with?(ROCrate::Metadata::RO_CRATE_BASE) }
      end&.first

      return entities.delete(key) if key

      # Legacy support
      (entities.delete("./#{ROCrate::Metadata::IDENTIFIER}") ||
          entities.delete(ROCrate::Metadata::IDENTIFIER) ||
          entities.delete("./#{ROCrate::Metadata::IDENTIFIER_1_0}") ||
          entities.delete(ROCrate::Metadata::IDENTIFIER_1_0))
    end

    ##
    # Extract the ro-crate-preview entity from the entity hash.
    # @return [Hash{String => Hash}] A Hash containing the preview entity's properties mapped by its @id, or nil if nothing is found.
    def self.extract_preview_entity(entities)
      entities.delete("./#{ROCrate::Preview::IDENTIFIER}") || entities.delete(ROCrate::Preview::IDENTIFIER)
    end

    ##
    # Extract the root entity from the entity hash, according to the rules defined here:
    # https://www.researchobject.org/ro-crate/1.1/root-data-entity.html#finding-the-root-data-entity
    # @return [Hash{String => Hash}] A Hash containing (hopefully) one value, the root entity's properties,
    # mapped by its @id.
    def self.extract_root_entity(entities)
      root_id = entities[ROCrate::Metadata::IDENTIFIER].dig('about', '@id')
      raise ROCrate::ReadException, "Metadata entity does not reference any root entity" unless root_id
      entities.delete(root_id)
    end

    ##
    # Finds an RO-Crate's root directory (where `ro-crate-metdata.json` is located) within a given directory.
    #
    # @param source [String, ::File, Pathname] The location of the directory.
    # @return [Pathname, nil] The path to the root, or nil if not found.
    def self.detect_root_directory(source)
      Pathname(source).find do |entry|
        if entry.file?
          name = entry.basename.to_s
          if name == ROCrate::Metadata::IDENTIFIER || name == ROCrate::Metadata::IDENTIFIER_1_0
            return entry.parent
          end
        end
      end

      nil
    end
  end
end