require 'json'
require 'bigdecimal'

module Chartjs
  module ChartHelpers

    CHART_TYPES = %w[ bar bubble doughnut horizontal_bar line pie polar_area radar scatter ]

    module Explicit
      CHART_TYPES.each do |type|
        define_method "chartjs_#{type}_chart" do |data, options = {}, plugins = {}|    # def chartjs_polar_area_chart(data, options = {}, plugins = {})
          chart type, data, options, plugins                                           #   chart 'polar_area', data, options, plugins
        end                                                                            # end
      end
      include Chartjs::ChartHelpers
    end

    module Implicit
      CHART_TYPES.each do |type|
        define_method "#{type}_chart" do |data, options = {}, plugins = {}|            # def polar_area_chart(data, options = {}, plugins = {})
          chart type, data, options, plugins                                           #   chart 'polar_area', data, options, plugins
        end                                                                            # end
      end
      include Chartjs::ChartHelpers
    end

    private

    def chart(type, data, options, plugins)
      opts = options.dup

      @chart_id ||= -1
      element_id = opts.delete(:id)     || "chart-#{@chart_id += 1}"
      css_class  = opts.delete(:class)  || 'chart'
      width      = opts.delete(:width)  || '400'
      height     = opts.delete(:height) || '400'

      canvas = content_tag :canvas, '', id: element_id, class: css_class, width: width, height: height

      script = javascript_tag(nonce: true) do
        <<-END.squish.html_safe
        (function() {
          var initChart = function() {
            var ctx = document.getElementById(#{element_id.to_json});
            var chart = new Chart(ctx, {
              type:    "#{camel_case type}",
              data:    #{to_javascript_string data},
              options: #{to_javascript_string opts},
              plugins: #{to_javascript_string plugins},
            });
          };

          if (typeof Chart !== "undefined" && Chart !== null) {
            initChart();
          }
          else {
            /* W3C standard */
            if (window.addEventListener) {
              window.addEventListener("load", initChart, false);
            }
            /* IE */
            else if (window.attachEvent) {
              window.attachEvent("onload", initChart);
            }
          }
        })();
        END
      end

      canvas + script
    end

    # polar_area -> polarArea
    def camel_case(string)
      string.gsub(/_([a-z])/) { $1.upcase }
    end

    def to_javascript_string(element)
      case element
      when Hash
        hash_elements = []
        element.each do |key, value|
          hash_elements << camel_case(key.to_s).to_json + ':' + to_javascript_string(value)
        end
        '{' + hash_elements.join(',') + '}'
      when Array
        array_elements = []
        element.each do |value|
          array_elements << to_javascript_string(value)
        end
        '[' + array_elements.join(',') + ']'
      when String
        if element.match(/^\s*function.*}\s*$/m)
          # Raw-copy function definitions to the output without surrounding quotes.
          element
        else
          element.to_json
        end
      when BigDecimal
        element.to_s
      else
        element.to_json
      end
    end

  end
end