Class: Coupon::ItemizableDiscountCalculator

Inherits:
Object
  • Object
show all
Defined in:
app/services/coupon/itemizable_discount_calculator.rb

Overview

This class is responsible for calculating and applying coupons
to an itemizable

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(itemizable, options = {}) ⇒ ItemizableDiscountCalculator

Returns a new instance of ItemizableDiscountCalculator.



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# File 'app/services/coupon/itemizable_discount_calculator.rb', line 7

def initialize(itemizable, options = {})
  @logger = options[:logger] || Rails.logger
  @options = options
  @itemizable = itemizable
  @customer = @itemizable.customer
  @qualifier = Coupon::Qualifier.new
  # When the itemizable or its line items are unsaved (new_record?), we cannot
  # persist discounts/line_discounts independently — the parent's autosave chain
  # will handle it. This happens during order splits and synchronize_lines.
  @deferred_persistence = @itemizable.new_record? || @itemizable.line_items.any?(&:new_record?)
  # Force reload of line_items to ensure we have the latest shipping lines
  # after retrieve_shipping_costs has destroyed/recreated them
  # Eager load critical associations to prevent N+1 queries
  # BUT don't reset if there are unsaved line items (they would be lost!)
  if @itemizable.line_items.loaded? && @itemizable.line_items.none?(&:new_record?)
    @itemizable.line_items.reset
  end
  # @active_lines is now set in calculate() with preloads
end

Instance Attribute Details

#active_lines ⇒ Object (readonly)

Returns the value of attribute active_lines.



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# File 'app/services/coupon/itemizable_discount_calculator.rb', line 5

def active_lines
  @active_lines
end

#customer ⇒ Object (readonly)

Returns the value of attribute customer.



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# File 'app/services/coupon/itemizable_discount_calculator.rb', line 5

def customer
  @customer
end

#itemizable ⇒ Object (readonly)

Returns the value of attribute itemizable.



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# File 'app/services/coupon/itemizable_discount_calculator.rb', line 5

def itemizable
  @itemizable
end

#logger ⇒ Object (readonly)

Returns the value of attribute logger.



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# File 'app/services/coupon/itemizable_discount_calculator.rb', line 5

def logger
  @logger
end

#options ⇒ Object (readonly)

Returns the value of attribute options.



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# File 'app/services/coupon/itemizable_discount_calculator.rb', line 5

def options
  @options
end

#qualifier ⇒ Object (readonly)

Returns the value of attribute qualifier.



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# File 'app/services/coupon/itemizable_discount_calculator.rb', line 5

def qualifier
  @qualifier
end

Instance Method Details

#calculate ⇒ Object

Main Method, responsible for running the calculations
on an itemizable, apply auto coupons, and calculate them



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# File 'app/services/coupon/itemizable_discount_calculator.rb', line 29

def calculate
  # Cleanup — skip for unsaved itemizables (no persisted data to clean up)
  cleanup_invalid_line_discounts unless @deferred_persistence

  # Set @active_lines BEFORE checking if empty, to ensure we have fresh line items
  # Preload associations to prevent N+1 queries during discount calculations
  # BUT if there are unsaved line items, use the in-memory collection directly
  # (querying the database would miss them and incorrectly show empty cart)
  @active_lines = load_active_lines

  # same if no line items.
  if active_lines.empty?
    logger.warn 'No line items to process, deleting discounts and returning'
    @itemizable.discounts.destroy_all unless @deferred_persistence
    return true
  end

  # Apply tier2 pricing
  logger.debug 'Applying tier 2 pricing'
  tpp = apply_tier2_pricing
  logger.debug "Tier 2 pricing applied: #{tpp.inspect}"

  logger.debug 'Removing invalid coupons'
  removed_discount_ids = remove_invalid_coupons

  # Reload discounts to exclude any that were destroyed in remove_invalid_coupons
  # MUST happen BEFORE apply_auto_coupons so new discounts aren't wiped out
  # @itemizable.discounts.reload
  logger.debug 'Applying auto coupons'
  # Check for any auto apply discounts, pass in the previously invalid coupon ids so we don't bother checking them again
  apply_auto_coupons(exclude_coupon_ids: removed_discount_ids)

  # Re-set @active_lines to ensure we have fresh line items after any auto-coupon changes or shipping recalculation
  # This is critical for F3-A and other shipping discounts after reset_discount
  @active_lines = load_active_lines

  # Reset all discounts amount in line items
  active_lines.each do |li|
    li.discounted_price = li.price # Start at MSRP
  end

  # iterate through each discounts in order of priority and calculate
  dc_list = if @deferred_persistence
              @itemizable.discounts.select(&:coupon).sort_by { |disc| [disc.coupon.type, disc.coupon.position] }
            else
              persisted_discounts = @itemizable.discounts.includes(coupon: :product_filters, line_discounts: :line_item).to_a
              new_discounts = @itemizable.discounts.select(&:new_record?)
              (persisted_discounts + new_discounts).uniq.select(&:coupon).sort_by { |disc| [disc.coupon.type, disc.coupon.position] }
            end
  dc_list.each do |discount|
    discount.amount = 0.0
    logger.info "Processing discount id:#{discount.id} for coupon code #{discount.coupon.code}"
    process_discount(discount)
  end

  # Persist discounted_price changes and recalculate tax for all line items.
  # This is necessary because Order's line_items association doesn't have autosave: true,
  # so saving the order alone won't persist line item changes made during discount calculation.
  #
  # CRITICAL: We must reload line_discounts and recalculate tax for ALL line items,
  # not just those where li.changed? is true. Here's why:
  #
  # 1. line_discounts were preloaded at the start of calculate() but new line_discounts
  #    were created/saved during process_discount(). The preloaded association is stale.
  #
  # 2. If discounted_price goes from $0 → $16.99 → $0 (reset then discount applied),
  #    Rails' changed? returns false (no net change), but tax still needs recalculation
  #    because the line_discounts changed.
  #
  # 3. The before_update callback calculates tax using taxable_total which relies on
  #    line_discounts.map(&:amount).sum - this uses stale data without reload.
  #
  # This was causing issues like $1.72 tax on $0 shipping (free shipping with discount)
  # because tax was calculated on pre-discount amount.
  active_lines.each do |li|
    if @deferred_persistence
      # Unsaved line items — update in-memory discounted_price only;
      # the parent's autosave chain will persist everything.
      next
    end

    # Always reload line_discounts to get fresh data from database
    li.line_discounts.reload

    # Recalculate tax using fresh line_discounts data
    # This ensures tax is based on post-discount amount (taxable_total uses discounted_total
    # which now correctly includes the reloaded line_discounts)
    if li.tax_rate.present?
      new_tax_total = (li.taxable_total.to_f * li.tax_rate).round(2)
      li.tax_total = new_tax_total if li.tax_total != new_tax_total
    end

    li.save! if li.changed?
  end
end