Proof of concept for variants with associated headings

variants.rb

require 'ostruct'
require 'set'
require 'rspec'

# rspec variants.rb
#
RSpec.describe "grouping variants by headings, and using variant headings to filter products" do
  before do
    # Create shop
    @shop = Shop.new

    # Create product
    @p1 = Product.new(
      'P1',
      attributes: {
        'Altura' => '100cm'
      },
      # customize variant headings for this product
      # the shop owner does this by editing the column names
      # in a product's variant list, or similar
      #
      # opt1 (Color)  | opt2 (Talla) | sku  | stock
      # --------------|--------------|------|--------
      # rojo          | 36           | abc  | 10
      # verde         | 36           | bca  | 11
      #
      variant_headings: {
        opt1: 'Color',
        opt2: 'Talla'
      }
    )

    # add product to shop
    @shop.products << @p1

    # create a couple of variants
    @v1 = OpenStruct.new(
      opt1: "rojo",
      opt2: 36,
      sku: 'abc',
      stock: 10
    )

    @v2 = OpenStruct.new(
      opt1: "verde",
      opt2: 40,
      sku: 'bca',
      stock: 11
    )

    # add variants to product
    @p1.variants << @v1
    @p1.variants << @v2


    # Create another product
    # This one has "Talla" as an attribute, not a variant
    @p2 = Product.new(
      'P2',
      attributes: {
        'Altura' => '110cm',
        'Talla' => 'XL',
      },
      # customize variant headings for this product
      variant_headings: {
        opt1: 'Material',
        opt2: 'Color',
      }
    )

    @shop.products << @p2

    # create a variant for second product
    @v3 = OpenStruct.new(
      opt1: 'cuero',
      opt2: "rojo",
      sku: 'abc',
      stock: 1
    )
    @p2.variants << @v3
  end

  # this data structure is only useful internally
  it "lists all unique variant/attribute headings in shop" do
    list = @shop.searchable_attribute_names

    expect(list).to eq %w(Color Talla Altura Material)
  end

  # for a Storefronts menu that lists all 'tallas' in the shop
  it "lists all values for 'Talla' in shop" do
    list = @shop.values_for('Talla')

    expect(list).to eq [36, 40, 'XL']
  end

  # for a Storefronts menu that lists all 'materiales' in the shop
  it "lists all values for 'Material' in shop" do
    list = @shop.values_for('Material')

    expect(list).to eq ["cuero"]
  end

  # for a Storefronts menu that lists all 'colors' in the shop
  it "lists all values for 'Color' in shop" do
    list = @shop.values_for('Color')

    expect(list).to eq ["rojo", "verde"]
  end

  # The user select a Color from menu and filters products by it
  it "filters products that have variants or attributes with heading 'Color' and value 'rojo'" do
    products = @shop.filter_products('Color:rojo')

    expect(products.map(&:name)).to eq %w(P1 P2)
  end

  it "filters products that have variants or attributes heading 'Color' and value 'verde'" do
    products = @shop.filter_products('Color:verde')

    expect(products.map(&:name)).to eq %w(P1)
  end

  it "filters products that have attribute heading 'Talla' and value 'XL'" do
    products = @shop.filter_products('Talla:XL')

    expect(products.map(&:name)).to eq %w(P2)
  end
end

## Quick and ugly implementation. Here be dragons!!

class Shop
  attr_reader :products
  def initialize
    @products = []
  end

  def filter_products(term)
    key, value = term.split(':')
    index.search key, value
  end

  def searchable_attribute_names
    index.keys
  end

  def values_for(key)
    index.keys_at key
  end

  private

  # Material:
  #  cuero: [p1, p2]
  # Color:
  #   rojo: [p1]
  #   verde: [p2]
  def index
    @index ||= build_index
  end

  def build_index
    idx = Index.new
    products.each do |pr|
      # index variants
      mappings = pr.variant_headings
      pr.variants.each do |vr|
        mappings.each do |k, v|
          value = vr.public_send(k)
          idx.add(v, value, pr) if value
        end
      end

      # index attributes
      pr.attributes.each do |k, v|
        idx.add(k, v, pr)
      end
    end

    idx
  end
end

# idx = Index.new
# idx.add 'Color', 'rojo', p1
# idx.add 'Color', 'verde', p2
# idx.add 'Talla', 'XL', p2
#
# idx.search('Color', 'rojo') # [p1]
# idx.keys # ['Color', 'Talla']
# idx.keys_at('Color') # ['rojo', 'verde']
#
class Index
  def initialize
    @data = Hash.new{|h, k|
      h[k] = Hash.new{|h2,k2| h2[k2] = Set.new}
    }
  end

  def add(level1, level2, product)
    @data[level1][level2].add product
  end

  def search(level1, level2)
    @data[level1][level2].to_a
  end

  def keys
    @data.keys
  end

  def keys_at(key)
    @data[key].keys
  end
end

class Product
  attr_reader :variants, :name, :attributes, :variant_headings
  
  def initialize(name, attributes: {}, variant_headings: {})
    @variants = []
    @name = name
    @attributes = attributes
    @variant_headings = variant_headings
  end
end