require 'open-uri'
require 'json/ld/expand'
require 'json/ld/compact'
require 'json/ld/flatten'
require 'json/ld/frame'
require 'json/ld/to_rdf'
require 'json/ld/from_rdf'

module JSON::LD
  ##
  # A JSON-LD processor implementing the JsonLdProcessor interface.
  #
  # This API provides a clean mechanism that enables developers to convert JSON-LD data into a a variety of output formats that
  # are easier to work with in various programming languages. If a JSON-LD API is provided in a programming environment, the
  # entirety of the following API must be implemented.
  #
  # @see http://json-ld.org/spec/latest/json-ld-api/#the-application-programming-interface
  # @author [Gregg Kellogg](http://greggkellogg.net/)
  class API
    include Expand
    include Compact
    include ToRDF
    include Flatten
    include FromRDF
    include Frame

    # Options used for open_file
    OPEN_OPTS = {
      :headers => %w(Accept: application/ld+json, application/json)
    }
    attr_accessor :value
    attr_accessor :context

    ##
    # Initialize the API, reading in any document and setting global options
    #
    # @param [String, #read, Hash, Array] input
    # @param [String, #read,, Hash, Array, JSON::LD::EvaluationContext] context
    #   An external context to use additionally to the context embedded in input when expanding the input.
    # @param  [Hash{Symbol => Object}] options
    # @option options [Boolean] :base
    #   The Base IRI to use when expanding the document. This overrides the value of `input` if it is a _IRI_. If not specified and `input` is not an _IRI_, the base IRI defaults to the current document IRI if in a browser context, or the empty string if there is no document context.
    # @option options [Boolean] :compactArrays (true)
    #   If set to `true`, the JSON-LD processor replaces arrays with just one element with that element during compaction. If set to `false`, all arrays will remain arrays even if they have just one element.
    # @option options [Proc] :conformanceCallback
    #   The purpose of this option is to instruct the processor about whether or not it should continue processing. If the value is null, the processor should ignore any key-value pair associated with any recoverable conformance issue and continue processing. More details about this feature can be found in the ConformanceCallback section.
    # @option options [Boolean, String, RDF::URI] :flatten
    #   If set to a value that is not `false`, the JSON-LD processor must modify the output of the Compaction Algorithm or the Expansion Algorithm by coalescing all properties associated with each subject via the Flattening Algorithm. The value of `flatten must` be either an _IRI_ value representing the name of the graph to flatten, or `true`. If the value is `true`, then the first graph encountered in the input document is selected and flattened.
    # @option options [Boolean] :optimize (false)
    #   If set to `true`, the JSON-LD processor is allowed to optimize the output of the Compaction Algorithm to produce even compacter representations. The algorithm for compaction optimization is beyond the scope of this specification and thus not defined. Consequently, different implementations *MAY* implement different optimization algorithms.
    #   (Presently, this is a noop).
    # @option options [Boolean] :useNativeDatatypes (true)
    # If set to `true`, the JSON-LD processor will use the expanded `rdf:type` IRI as the property instead of `@type` when converting from RDF.
    # @option options [Boolean] :useRdfType (false) If set to `true`, the JSON-LD processor will try to convert datatyped literals to JSON native types instead of using the expanded object form when converting from RDF. `xsd:boolean` values will be converted to `true` or `false`. `xsd:integer` and `xsd:double` values will be converted to JSON numbers.
    # @yield [api]
    # @yieldparam [API]
    def initialize(input, context, options = {}, &block)
      @options = {:compactArrays => true}.merge(options)
      @value = case input
      when Array, Hash then input.dup
      when IO, StringIO then JSON.parse(input.read)
      when String
        content = nil
        @options = {:base => input}.merge(@options)
        RDF::Util::File.open_file(input, OPEN_OPTS) {|f| content = JSON.parse(f.read)}
        content
      end
      @context = EvaluationContext.new(@options)
      @context = @context.parse(context) if context
      
      if block_given?
        case block.arity
          when 0, -1 then instance_eval(&block)
          else block.call(self)
        end
      end
    end
    
    ##
    # Expands the given input according to the steps in the Expansion Algorithm. The input must be copied, expanded and returned
    # if there are no errors. If the expansion fails, an appropriate exception must be thrown.
    #
    # The resulting `Array` is returned via the provided callback.
    #
    # Note that for Ruby, if the callback is not provided and a block is given, it will be yielded
    #
    # @param [String, #read, Hash, Array] input
    #   The JSON-LD object to copy and perform the expansion upon.
    # @param [String, #read, Hash, Array, JSON::LD::EvaluationContext] context
    #   An external context to use additionally to the context embedded in input when expanding the input.
    # @param [Proc] callback (&block)
    #   Alternative to using block, with same parameters.
    # @param  [Hash{Symbol => Object}] options
    #   See options in {JSON::LD::API#initialize}
    # @raise [InvalidContext]
    # @yield jsonld
    # @yieldparam [Array<Hash>] jsonld
    #   The expanded JSON-LD document
    # @return [Array<Hash>]
    #   The expanded JSON-LD document
    # @see http://json-ld.org/spec/latest/json-ld-api/#expansion-algorithm
    def self.expand(input, context = nil, callback = nil, options = {})
      result = nil
      API.new(input, context, options) do |api|
        result = api.expand(api.value, nil, api.context)
      end

      # If, after the algorithm outlined above is run, the resulting element is an
      # JSON object with just a @graph property, element is set to the value of @graph's value.
      result = result['@graph'] if result.is_a?(Hash) && result.keys == %w(@graph)

      # Finally, if element is a JSON object, it is wrapped into an array.
      result = [result] unless result.is_a?(Array)
      callback.call(result) if callback
      yield result if block_given?
      result
    end

    ##
    # Compacts the given input according to the steps in the Compaction Algorithm. The input must be copied, compacted and
    # returned if there are no errors. If the compaction fails, an appropirate exception must be thrown.
    #
    # If no context is provided, the input document is compacted using the top-level context of the document
    #
    # The resulting `Hash` is returned via the provided callback.
    #
    # Note that for Ruby, if the callback is not provided and a block is given, it will be yielded
    #
    # @param [String, #read, Hash, Array] input
    #   The JSON-LD object to copy and perform the compaction upon.
    # @param [String, #read, Hash, Array, JSON::LD::EvaluationContext] context
    #   The base context to use when compacting the input.
    # @param [Proc] callback (&block)
    #   Alternative to using block, with same parameters.
    # @param  [Hash{Symbol => Object}] options
    #   See options in {JSON::LD::API#initialize}
    #   Other options passed to {JSON::LD::API.expand}
    # @yield jsonld
    # @yieldparam [Hash] jsonld
    #   The compacted JSON-LD document
    # @return [Hash]
    #   The compacted JSON-LD document
    # @raise [InvalidContext, ProcessingError]
    # @see http://json-ld.org/spec/latest/json-ld-api/#compaction-algorithm
    def self.compact(input, context, callback = nil, options = {})
      expanded = result = nil

      # 1) Perform the Expansion Algorithm on the JSON-LD input.
      #    This removes any existing context to allow the given context to be cleanly applied.
      expanded = API.expand(input, nil, nil, options.merge(:debug => nil))

      API.new(expanded, context, options) do
        debug(".compact") {"expanded input: #{expanded.to_json(JSON_STATE)}"}
        result = compact(value, nil)

        # xxx) Add the given context to the output
        result = case result
        when Hash then self.context.serialize.merge(result)
        when Array
          kwgraph = self.context.compact_iri('@graph', :quiet => true)
          self.context.serialize.merge(kwgraph => result)
        when String
          kwid = self.context.compact_iri('@id', :quiet => true)
          self.context.serialize.merge(kwid => result)
        end
      end
      callback.call(result) if callback
      yield result if block_given?
      result
    end

    ##
    # Flattens the given input according to the steps in the Flattening Algorithm. The input must be flattened and returned if there are no errors. If the flattening fails, an appropriate exception must be thrown.
    #
    # The resulting `Array` is returned via the provided callback.
    #
    # Note that for Ruby, if the callback is not provided and a block is given, it will be yielded. If there is no block, the value will be returned.
    #
    # @param [String, #read, Hash, Array] input
    #   The JSON-LD object or array of JSON-LD objects to flatten or an IRI referencing the JSON-LD document to flatten.
    # @param [String, RDF::URI] graph
    #   The graph in the document that should be flattened. To return the default graph @default has to be passed, for the merged graph @merged and for any other graph the IRI identifying the graph has to be passed. The default value is @merged.
    # @param [String, #read, Hash, Array, JSON::LD::EvaluationContext] context
    #   An optional external context to use additionally to the context embedded in input when expanding the input.
    # @param [Proc] callback (&block)
    #   Alternative to using block, with same parameters.
    # @param  [Hash{Symbol => Object}] options
    #   See options in {JSON::LD::API#initialize}
    #   Other options passed to {JSON::LD::API.expand}
    # @yield jsonld
    # @yieldparam [Hash] jsonld
    #   The framed JSON-LD document
    # @return [Array<Hash>]
    #   The framed JSON-LD document
    # @raise [InvalidFrame]
    # @see http://json-ld.org/spec/latest/json-ld-api/#framing-algorithm
    def self.flatten(input, graph, context, callback = nil, options = {})
      result = nil
      graph ||= '@merged'

      # Expand input to simplify processing
      expanded_input = API.expand(input)

      # Initialize input using frame as context
      API.new(expanded_input, nil, options) do
        debug(".flatten") {"expanded input: #{value.to_json(JSON_STATE)}"}

        # Generate _nodeMap_
        node_map = Hash.ordered
        self.generate_node_map(value,
          node_map,
          (graph.to_s == '@merged' ? '@merged' : '@default'),
          nil,
          BlankNodeNamer.new("t"))
        
        result = []

        # If nodeMap has no property graph, return result, otherwise set definitions to its value.
        definitions = node_map.fetch(graph.to_s, {})
        
        # Foreach property and valud of definitions
        definitions.keys.sort.each do |prop|
          value = definitions[prop]
          result << value
        end
        
        result
      end

      callback.call(result) if callback
      yield result if block_given?
      result
    end

    ##
    # Frames the given input using the frame according to the steps in the Framing Algorithm. The input is used to build the
    # framed output and is returned if there are no errors. If there are no matches for the frame, null must be returned.
    # Exceptions must be thrown if there are errors.
    #
    # The resulting `Array` is returned via the provided callback.
    #
    # Note that for Ruby, if the callback is not provided and a block is given, it will be yielded
    #
    # @param [String, #read, Hash, Array] input
    #   The JSON-LD object to copy and perform the framing on.
    # @param [String, #read, Hash, Array] frame
    #   The frame to use when re-arranging the data.
    # @param [Proc] callback (&block)
    #   Alternative to using block, with same parameters.
    # @param  [Hash{Symbol => Object}] options
    #   See options in {JSON::LD::API#initialize}
    #   Other options passed to {JSON::LD::API.expand}
    # @option options [Boolean] :embed (true)
    #   a flag specifying that objects should be directly embedded in the output,
    #   instead of being referred to by their IRI.
    # @option options [Boolean] :explicit (false)
    #   a flag specifying that for properties to be included in the output,
    #   they must be explicitly declared in the framing context.
    # @option options [Boolean] :omitDefault (false)
    #   a flag specifying that properties that are missing from the JSON-LD
    #   input should be omitted from the output.
    # @yield jsonld
    # @yieldparam [Hash] jsonld
    #   The framed JSON-LD document
    # @return [Array<Hash>]
    #   The framed JSON-LD document
    # @raise [InvalidFrame]
    # @see http://json-ld.org/spec/latest/json-ld-api/#framing-algorithm
    def self.frame(input, frame, callback = nil, options = {})
      result = nil
      match_limit = 0
      framing_state = {
        :embed       => true,
        :explicit    => false,
        :omitDefault => false,
        :embeds      => nil,
      }
      framing_state[:embed] = options[:embed] if options.has_key?(:embed)
      framing_state[:explicit] = options[:explicit] if options.has_key?(:explicit)
      framing_state[:omitDefault] = options[:omitDefault] if options.has_key?(:omitDefault)

      # de-reference frame to create the framing object
      frame = case frame
      when Hash then frame.dup
      when IO, StringIO then JSON.parse(frame.read)
      when String
        content = nil
        RDF::Util::File.open_file(frame, OPEN_OPTS) {|f| content = JSON.parse(f.read)}
        content
      end

      # Expand frame to simplify processing
      expanded_frame = API.expand(frame)
      
      # Expand input to simplify processing
      expanded_input = API.expand(input)

      # Initialize input using frame as context
      API.new(expanded_input, nil, options) do
        #debug(".frame") {"context from frame: #{context.inspect}"}
        #debug(".frame") {"expanded frame: #{expanded_frame.to_json(JSON_STATE)}"}
        #debug(".frame") {"expanded input: #{value.to_json(JSON_STATE)}"}

        # Get framing nodes from expanded input, replacing Blank Node identifiers as necessary
        all_nodes = Hash.ordered
        depth do
          generate_node_map(value,
            all_nodes,
            '@merged',
            nil,
            BlankNodeNamer.new("t"))
        end
        @node_map = all_nodes['@merged']
        debug(".frame") {"node_map: #{@node_map.to_json(JSON_STATE)}"}

        result = []
        frame(framing_state, @node_map, expanded_frame[0], result, nil)
        debug(".frame") {"after frame: #{result.to_json(JSON_STATE)}"}
        
        # Initalize context from frame
        @context = depth {@context.parse(frame['@context'])}
        # Compact result
        compacted = depth {compact(result, nil)}
        compacted = [compacted] unless compacted.is_a?(Array)

        # Add the given context to the output
        kwgraph = context.compact_iri('@graph', :quiet => true)
        result = context.serialize.merge({kwgraph => compacted})
        debug(".frame") {"after compact: #{result.to_json(JSON_STATE)}"}
        result = cleanup_preserve(result)
      end

      callback.call(result) if callback
      yield result if block_given?
      result
    end

    ##
    # Processes the input according to the RDF Conversion Algorithm, calling the provided callback for each triple generated.
    #
    # Note that for Ruby, if the callback is not provided and a block is given, it will be yielded
    #
    # @param [String, #read, Hash, Array] input
    #   The JSON-LD object to process when outputting statements.
    # @param [String, #read, Hash, Array, JSON::LD::EvaluationContext] context
    #   An external context to use additionally to the context embedded in input when expanding the input.
    # @param [Proc] callback (&block)
    #   Alternative to using block, with same parameteres.
    # @param [{Symbol,String => Object}] options
    #   See options in {JSON::LD::API#initialize}
    #   Options passed to {JSON::LD::API.expand}
    # @raise [InvalidContext]
    # @yield statement
    # @yieldparam [RDF::Statement] statement
    def self.toRDF(input, context = nil, callback = nil, options = {})
      # 1) Perform the Expansion Algorithm on the JSON-LD input.
      #    This removes any existing context to allow the given context to be cleanly applied.
      expanded = expand(input, context, nil, options)

      API.new(expanded, nil, options) do
        debug(".expand") {"expanded input: #{value.to_json(JSON_STATE)}"}
        # Start generating statements
        statements("", value, nil, nil, nil) do |statement|
          callback.call(statement) if callback
          yield statement if block_given?
        end
      end
    end
    
    ##
    # Take an ordered list of RDF::Statements and turn them into a JSON-LD document.
    #
    # The resulting `Array` is returned via the provided callback.
    #
    # Note that for Ruby, if the callback is not provided and a block is given, it will be yielded
    #
    # @param [Array<RDF::Statement>] input
    # @param [Proc] callback (&block)
    #   Alternative to using block, with same parameteres.
    # @param  [Hash{Symbol => Object}] options
    #   See options in {JSON::LD::API#initialize}
    # @yield jsonld
    # @yieldparam [Hash] jsonld
    #   The JSON-LD document in expanded form
    # @return [Array<Hash>]
    #   The JSON-LD document in expanded form
    def self.fromRDF(input, callback = nil, options = {})
      options = {:useNativeTypes => true}.merge(options)
      result = nil

      API.new(nil, nil, options) do |api|
        result = api.from_statements(input)
      end

      callback.call(result) if callback
      yield result if block_given?
      result
    end
  end
end