Move price calculation from products plugin to RevBank::Products

- Adds price tag calculation. Addons tagged #OPAQUE are excluded from the
price tag.
- BREAKING CHANGE: instead of abusing $product->{price} for a percent,
$product->{percent} is no longer a boolean but the actual percent, so
$product->{price} is the calculated amount.

The total price of a product is now calculated in two places, once when
reading the product list, and once as the result of adding the entry and
its contras when adding the product. Although this involves some
duplication and the sums are calculated in different ways, it hinges on
the existing assertion to make sure that the entry is balanced to ensure
that both sums are the same. Because of that, this code duplication
actually strengthens the integrity.

lib/RevBank/Products.pm

@@ -87,9 +87,10 @@ sub read_products($filename = "revbank.products", $default_contra = "+sales/prod
                 warn "Percentage invalid for non-addon at $filename line $linenr.\n";
                 next;
             }
-            $price = 0 + $price;
+            $percent = $sign * (0 + $price);
+            $price = undef;  # calculated later
         } else {
-            $price = eval { parse_amount($price) };
+            $price = $sign * eval { parse_amount($price) };
             if (not defined $price) {
                 warn "Invalid price for '$ids[0]' at $filename line $linenr.\n";
                 next;
@@ -100,18 +101,25 @@ sub read_products($filename = "revbank.products", $default_contra = "+sales/prod
 
             $products{$id} = {
                 id          => $ids[0],
-                price       => $sign * $price,
-                percent     => $percent,
                 description => $desc,
                 contra      => $contra || $default_contra,
                 _addon_ids  => \@addon_ids,
                 line        => $linenr,
                 tags        => \%tags,
                 config      => $canonical,
+
+                percent     => $percent,
+                price       => $price,  # base price
+
+                # The following are calculated below, for top-level products only:
+                # tag_price   => base price + sum of transparent addons
+                # hidden_fees => sum of opaque addons
+                # total_price => tag_price + hidden_fees
             };
         }
     }
 
+    # Resolve addons
     PRODUCT: for my $product (values %products) {
         my %ids_seen = ($product->{id} => 1);
         my @addon_ids = @{ $product->{_addon_ids} };
@@ -124,7 +132,7 @@ sub read_products($filename = "revbank.products", $default_contra = "+sales/prod
                 next PRODUCT;
             }
 
-            my $addon = $products{$addon_id};
+            my $addon = { %{ $products{$addon_id} } };  # shallow copy to overwrite ->{price} later
             if (not $addon) {
                 warn "Addon '$addon_id' does not exist for '$product->{id}' at $filename line $product->{line}.\n";
                 next PRODUCT;
@@ -135,6 +143,39 @@ sub read_products($filename = "revbank.products", $default_contra = "+sales/prod
         }
     }
 
+    # Calculate tag and total price
+    PRODUCT: for my $product (values %products) {
+        next if $product->{id} =~ /^\+/;
+
+        my $tag_price = $product->{price} || 0;
+        my $hidden = 0;
+
+        my @seen = ($product);
+        for my $addon (@{ $product->{addons} }) {
+            if ($addon->{percent}) {
+                my $sum = List::Util::sum map {
+                    $_->{price}
+                } grep {
+                    $_->{contra} eq $addon->{contra}
+                } @seen;
+
+                $addon->{price} = $addon->{percent} / 100 * $sum;
+            }
+
+            if ($addon->{tags}{OPAQUE}) {
+                $hidden += $addon->{price};
+            } else {
+                $tag_price += $addon->{price};
+            }
+
+            push @seen, $addon;
+        }
+
+        $product->{tag_price} = $tag_price;
+        $product->{hidden_fees} = $hidden;
+        $product->{total_price} = $tag_price + $hidden;
+    }
+
     return $cache{$filename} = \%products;
 }
 

plugins/products

@@ -8,19 +8,12 @@ sub command :Tab(&tab) ($self, $cart, $command, @) {
     $command =~ /^\+/ and return NEXT;
 
     my $products = read_products;
+
     my $product = $products->{ $command } or return NEXT;
     my $price = $product->{price};
 
-    my $contra_desc = "\$you bought $product->{description}";
-
-    my @addons = @{ $product->{addons} // [] };
-
-    my $display = undef;
-    $display = "Product"       if @addons and $price->cents > 0;
-    $display = "Reimbursement" if @addons and $price->cents < 0;
-
     my $entry = $cart->add(
-        -$price,
+        -$product->{total_price},
         $product->{description},
         {
             product_id => $product->{id},
@@ -29,6 +22,13 @@ sub command :Tab(&tab) ($self, $cart, $command, @) {
             deduplicate => join("/", $self->id, $product->{id}),
         }
     );
+
+    my $contra_desc = "\$you bought $product->{description}";
+    my @addons = @{ $product->{addons} // [] };
+    my $display = undef;
+    $display = "Product"       if @addons and $price->cents > 0;
+    $display = "Reimbursement" if @addons and $price->cents < 0;
+
     $entry->add_contra(
         $product->{contra},
         +$price,
@@ -37,22 +37,9 @@ sub command :Tab(&tab) ($self, $cart, $command, @) {
     );
 
     for my $addon (@addons) {
-        my $addon_price = $addon->{price};
-        if ($addon->{percent}) {
-            my $sum = List::Util::sum map {
-                $_->{amount}
-            } grep {
-                $_->{user} eq $addon->{contra}
-            } $entry->contras;
-
-            $addon_price = $addon_price / 100 * $sum;
-        }
-
-        $entry->amount( $entry->amount - $addon_price );
-
         $entry->add_contra(
             $addon->{contra},
-            $addon_price,
+            $addon->{price},
             "$addon->{description} ($contra_desc)",
             $addon->{description}
         );