require 'zendesk_api/resource'
require 'zendesk_api/resources'

module ZendeskAPI
  # Represents a collection of resources. Lazily loaded, resources aren't
  # actually fetched until explicitly needed (e.g. #each, {#fetch}).
  class Collection
    include ZendeskAPI::Sideloading

    # Options passed in that are automatically converted from an array to a comma-separated list.
    SPECIALLY_JOINED_PARAMS = [:ids, :only]

    include Rescue

    # @return [ZendeskAPI::Association] The class association
    attr_reader :association

    # @return [Faraday::Response] The last response
    attr_reader :response

    # @return [Hash] query options
    attr_reader :options

    # Creates a new Collection instance. Does not fetch resources.
    # Additional options are: verb (default: GET), path (default: resource param), page, per_page.
    # @param [Client] client The {Client} to use.
    # @param [String] resource The resource being collected.
    # @param [Hash] options Any additional options to be passed in.
    def initialize(client, resource, options = {})
      @client, @resource_class, @resource = client, resource, resource.resource_name
      @options = Hashie::Mash.new(options)

      set_association_from_options
      join_special_params

      @verb = @options.delete(:verb)
      @includes = Array(@options.delete(:include))

      # Used for Attachments, TicketComment
      if @resource_class.is_a?(Class) && @resource_class.superclass == ZendeskAPI::Data
        @resources = []
        @fetchable = false
      else
        @fetchable = true
      end
    end

    # Passes arguments and the proper path to the resource class method.
    # @param [Hash] attributes Attributes to pass to Create#create
    def create(attributes = {})
      attributes.merge!(:association => @association)
      @resource_class.create(@client, @options.merge(attributes))
    end

    # (see #create)
    def find(opts = {})
      opts.merge!(:association => @association)
      @resource_class.find(@client, @options.merge(opts))
    end

    # (see #create)
    def update(opts = {})
      opts.merge!(:association => @association)
      @resource_class.update(@client, @options.merge(opts))
    end

    # (see #create)
    def destroy(opts = {})
      opts.merge!(:association => association)
      @resource_class.destroy(@client, @options.merge(opts))
    end

    # @return [Number] The total number of resources server-side (disregarding pagination).
    def count
      fetch
      @count || -1
    end

    # Changes the per_page option. Returns self, so it can be chained. No execution.
    # @return [Collection] self
    def per_page(count)
      clear_cache if count
      @options["per_page"] = count
      self
    end

    # Changes the page option. Returns self, so it can be chained. No execution.
    # @return [Collection] self
    def page(number)
      clear_cache if number
      @options["page"] = number
      self
    end

    def first_page?
      !@options["page"] || @options["page"].to_i <= 1
    end

    def last_page?
      !@options["page"] || @options["page"].to_i * @options["per_page"].to_i >= count
    end

    # Saves all newly created resources stored in this collection.
    # @return [Collection] self
    def save
      if @resources
        @resources.map! do |item|
          unless !item.respond_to?(:save) || item.changes.empty?
            item.save
          end

          item
        end
      end

      self
    end

    # Adds an item (or items) to the list of side-loaded resources to request
    # @option sideloads [Symbol or String] The item(s) to sideload
    def include(*sideloads)
      self.tap { @includes.concat(sideloads.map(&:to_s)) }
    end

    # Adds an item to this collection
    # @option item [ZendeskAPI::Data] the resource to add
    # @raise [ArgumentError] if the resource doesn't belong in this collection
    def <<(item)
      fetch
      if item.is_a?(Resource)
        if item.is_a?(@resource_class)
          @resources << item
        else
          raise "this collection is for #{@resource_class}"
        end
      else
        item.merge!(:association => @association) if item.is_a?(Hash)
        @resources << @resource_class.new(@client, item)
      end
    end

    # The API path to this collection
    def path
      @association.generate_path(:with_parent => true)
    end

    # Executes actual GET from API and loads resources into proper class.
    # @param [Boolean] reload Whether to disregard cache
    def fetch(reload = false)
      if @resources && (!@fetchable || !reload)
        return @resources
      elsif association && association.options.parent && association.options.parent.new_record?
        return @resources = []
      end

      @response = get_response(@query || self.path)
      handle_response(@response.body.dup)

      @query = nil
      @resources
    end

    rescue_client_error :fetch, :with => lambda { Array.new }

    # Alias for fetch(false)
    def to_a
      fetch
    end

    # Calls #each on every page with the passed in block
    # @param [Block] block Passed to #each
    def each_page(start_page = @options["page"], &block)
      page(start_page)
      clear_cache

      while !empty?
        each do |resource|
          arguments = [resource, @options["page"] || 1]

          if block.arity >= 0
            arguments = arguments.take(block.arity)
          end

          block.call(*arguments)
        end

        self.next
      end
    end

    # Replaces the current (loaded or not) resources with the passed in collection
    # @option collection [Array] The collection to replace this one with
    # @raise [ArgumentError] if any resources passed in don't belong in this collection
    def replace(collection)
      raise "this collection is for #{@resource_class}" if collection.any?{|r| !r.is_a?(@resource_class) }
      @resources = collection
    end

    # Find the next page. Does one of three things:
    # * If there is already a page number in the options hash, it increases it and invalidates the cache, returning the new page number.
    # * If there is a next_page url cached, it executes a fetch on that url and returns the results.
    # * Otherwise, returns an empty array.
    def next
      if @options["page"]
        clear_cache
        @options["page"] += 1
      elsif @query = @next_page
        fetch(true)
      else
        clear_cache
        @resources = []
      end
    end

    # Find the previous page. Does one of three things:
    # * If there is already a page number in the options hash, it increases it and invalidates the cache, returning the new page number.
    # * If there is a prev_page url cached, it executes a fetch on that url and returns the results.
    # * Otherwise, returns an empty array.
    def prev
      if @options["page"] && @options["page"] > 1
        clear_cache
        @options["page"] -= 1
      elsif @query = @prev_page
        fetch(true)
      else
        clear_cache
        @resources = []
      end
    end

    # Clears all cached resources and associated values.
    def clear_cache
      @resources = nil
      @count = nil
      @next_page = nil
      @prev_page = nil
      @query = nil
    end

    # @private
    def to_ary; nil; end

    # Sends methods to underlying array of resources.
    def method_missing(name, *args, &block)
      if resource_methods.include?(name)
        collection_method(name, *args, &block)
      elsif Array.new.respond_to?(name)
        array_method(name, *args, &block)
      else
        next_collection(name, *args, &block)
      end
    end

    # @private
    def to_s
      if @resources
        @resources.inspect
      else
        inspect = []
        inspect << "options=#{@options.inspect}" if @options.any?
        inspect << "path=#{path}"
        "#{Inflection.singular(@resource)} collection [#{inspect.join(",")}]"
      end
    end

    alias :to_str :to_s

    private

    def set_page_and_count(body)
      @count = (body["count"] || @resources.size).to_i
      @next_page, @prev_page = body["next_page"], body["previous_page"]

      if @next_page =~ /page=(\d+)/
        @options["page"] = $1.to_i - 1
      elsif @prev_page =~ /page=(\d+)/
        @options["page"] = $1.to_i + 1
      end
    end

    ## Initialize

    def join_special_params
      # some params use comma-joined strings instead of query-based arrays for multiple values
      @options.each do |k, v|
        if SPECIALLY_JOINED_PARAMS.include?(k.to_sym) && v.is_a?(Array)
          @options[k] = v.join(',')
        end
      end
    end

    def set_association_from_options
      @collection_path = @options.delete(:collection_path)

      association_options = { :path => @options.delete(:path) }
      association_options[:path] ||= @collection_path.join("/") if @collection_path
      @association = @options.delete(:association) || Association.new(association_options.merge(:class => @resource_class))

      @collection_path ||= [@resource]
    end

    ## Fetch

    def get_response(path)
      @response = @client.connection.send(@verb || "get", path) do |req|
        opts = @options.delete_if {|_, v| v.nil?}

        req.params.merge!(:include => @includes.join(",")) if @includes.any?

        if %w{put post}.include?(@verb.to_s)
          req.body = opts
        else
          req.params.merge!(opts)
        end
      end
    end

    def handle_response(body)
      results = body.delete(@resource_class.model_key) || body.delete("results")
      @resources = results.map {|res| @resource_class.new(@client, res)}

      set_page_and_count(body)
      set_includes(@resources, @includes, body)
    end

    ## Method missing

    def array_method(name, *args, &block)
      to_a.send(name, *args, &block)
    end

    def next_collection(name, *args, &block)
      opts = args.last.is_a?(Hash) ? args.last : {}
      opts.merge!(:collection_path => @collection_path.dup.push(name))
      self.class.new(@client, @resource_class, @options.merge(opts))
    end

    def collection_method(name, *args, &block)
      @resource_class.send(name, @client, *args, &block)
    end

    def resource_methods
      @resource_methods ||= @resource_class.singleton_methods(false).map(&:to_sym)
    end
  end
end