Show the invoice subtotal, taxes, and total when creating it

The design calls for rendering all amounts with their currency symbol,
but golang.org/x/text’s currency package always render the symbol in
front, which is wrong in Catalan and Spanish, and a lot of other
languages.

Consulting the Internet, the most popular package for that is
accounting[0], which is almost as useless because they confuse locale
with the currency’s country of origin’s “usual locale” (e.g., en-US for
USD), which is also wrong: in Catalan i need to write USD prices as
"1.234,56 $" regardless of what Americans do.

With accounting i have the recourse of initializing the struct that
holds all the “locale” information, which is also wrong because i have
to define the decimal and thousands separators, something that depends
only on the locale, next to the currency’s precision, that is
locale-independent.  But, since all CLDR data from golang.org/x/text
is inside an internal package, i can not access it and would need to
define all that information myself, which defeats the purpose of using
an external package.

Since for now i only need the format pattern for currency, i just saved
it into the database of available languages, that i do not expect to
grow too much.

[0]: https://github.com/leekchan/accounting

deploy/available_languages.sql

@@ -4,10 +4,10 @@
 
 begin;
 
-insert into public.language (lang_tag, name, endonym, selectable)
-values ('und', 'Undefined', 'Undefined', false)
-     , ('ca', 'Catalan', 'català', true)
-     , ('es', 'Spanish', 'español', true)
+insert into public.language (lang_tag, name, endonym, selectable, currency_pattern)
+values ('und', 'Undefined', 'Undefined', false, '%[3]s%.[1]*[2]f')
+     , ('ca', 'Catalan', 'català', true, '%.[1]*[2]f %[3]s')
+     , ('es', 'Spanish', 'español', true, '%.[1]*[2]f %[3]s')
 ;
 
 commit;

deploy/compute_new_invoice_amount.sql

@@ -0,0 +1,64 @@
+-- Deploy numerus:compute_new_invoice_amount to pg
+-- requires: schema_numerus
+-- requires: company
+-- requires: currency
+-- requires: tax
+-- requires: new_invoice_product
+-- requires: new_invoice_amount
+
+begin;
+
+set search_path to numerus, public;
+
+create or replace function compute_new_invoice_amount(company_id integer, products new_invoice_product[]) returns new_invoice_amount as
+$$
+declare
+	result new_invoice_amount;
+begin
+	if array_length(products, 1) is null then
+		select to_price(0, decimal_digits), array[]::text[][], to_price(0, decimal_digits)
+		from company
+		join currency using (currency_code)
+		where company.company_id = compute_new_invoice_amount.company_id
+		into result.subtotal, result.taxes, result.total;
+	else
+		with product as (
+			select round(parse_price(price, currency.decimal_digits) * quantity * (1 - discount_rate))::integer as subtotal
+			, tax
+			, decimal_digits
+			from unnest(products)
+			join company on company.company_id = compute_new_invoice_amount.company_id
+			join currency using (currency_code)
+		)
+		, tax_amount as (
+			select tax_id
+			, sum(round(subtotal * tax.rate)::integer)::integer as amount
+			, decimal_digits
+			from product, unnest(product.tax) as product_tax(tax_id)
+			join tax using (tax_id)
+			group by tax_id, decimal_digits
+		)
+		, tax_total as (
+			select sum(amount)::integer as amount, array_agg(array[name, to_price(amount, decimal_digits)]) as taxes
+			from tax_amount
+			join tax using (tax_id)
+		)
+		select to_price(sum(subtotal)::integer, decimal_digits)
+		, coalesce(taxes, array[]::text[][])
+		, to_price(sum(subtotal)::integer + coalesce(tax_total.amount, 0), decimal_digits) as total
+		from product, tax_total
+		group by tax_total.amount, taxes, decimal_digits
+		into result.subtotal, result.taxes, result.total;
+	end if;
+
+	return result;
+end
+$$
+language plpgsql
+stable;
+
+revoke execute on function compute_new_invoice_amount(integer, new_invoice_product[]) from public;
+grant execute on function compute_new_invoice_amount(integer, new_invoice_product[]) to invoicer;
+grant execute on function compute_new_invoice_amount(integer, new_invoice_product[]) to admin;
+
+commit;

deploy/language.sql

@@ -9,7 +9,8 @@ create table language (
 	lang_tag text primary key check (length(lang_tag) < 36), -- RFC5646 recommends 35 at least
 	name text not null,
 	endonym text not null,
-	selectable boolean not null
+	selectable boolean not null,
+	currency_pattern text not null
 );
 
 grant select on table language to guest;

deploy/new_invoice_amount.sql

@@ -0,0 +1,14 @@
+-- Deploy numerus:new_invoice_amount to pg
+-- requires: schema_numerus
+
+begin;
+
+set search_path to numerus, public;
+
+create type new_invoice_amount as (
+	subtotal text,
+	taxes text[][],
+	total text
+);
+
+commit;

deploy/parse_price.sql

@@ -11,7 +11,13 @@ declare
 	parts text[];
 	result int;
 	frac_part text;
+	sign int := 1;
 begin
+	if price like '-%' Then
+		sign := -1;
+		price := substring(price from 2);
+	end if;
+
 	parts := string_to_array(price, '.');
 	if array_length(parts, 1) > 2 then
 		raise invalid_parameter_value using message = price || ' is not a valid price representation.';	
@@ -31,7 +37,7 @@ begin
 		result := result + frac_part::integer;
 	end if;
 
-	return result;
+	return sign * result;
 end;
 $$
 language plpgsql

deploy/to_price.sql

@@ -10,9 +10,14 @@ $$
 declare
 	result text;
 	scale integer := 10^decimal_digits;
+	sign text := '';
 begin
+	if cents < 0 then
+		sign := '-';
+		cents = -cents;
+	end if;
 	result = cents::text;
-	return (cents / scale)::text || '.' || to_char(mod(cents, scale), rpad('FM', decimal_digits + 2, '0'));
+	return sign || (cents / scale)::text || '.' || to_char(mod(cents, scale), rpad('FM', decimal_digits + 2, '0'));
 end;
 $$
 language plpgsql

pkg/invoices.go

@@ -66,10 +66,31 @@ func GetInvoiceForm(w http.ResponseWriter, r *http.Request, params httprouter.Pa
 	}
 }
 
+type newInvoicePage struct {
+	Form     *invoiceForm
+	Subtotal string
+	Taxes    [][]string
+	Total    string
+}
+
+func newNewInvoicePage(form *invoiceForm, r *http.Request) *newInvoicePage {
+	page := &newInvoicePage{
+		Form: form,
+	}
+	conn := getConn(r)
+	company := mustGetCompany(r)
+	err := conn.QueryRow(r.Context(), "select subtotal, taxes, total from compute_new_invoice_amount($1, $2)", company.Id, NewInvoiceProductArray(form.Products)).Scan(&page.Subtotal, &page.Taxes, &page.Total)
+	if err != nil {
+		panic(err)
+	}
+	return page
+}
+
 func mustRenderNewInvoiceForm(w http.ResponseWriter, r *http.Request, form *invoiceForm) {
 	locale := getLocale(r)
 	form.Customer.EmptyLabel = gettext("Select a customer to bill.", locale)
-	mustRenderAppTemplate(w, r, "invoices/new.gohtml", form)
+	page := newNewInvoicePage(form, r)
+	mustRenderAppTemplate(w, r, "invoices/new.gohtml", page)
 }
 
 func mustRenderNewInvoiceProductsForm(w http.ResponseWriter, r *http.Request, form *invoiceForm) {
@@ -158,7 +179,7 @@ func HandleAddProductsToInvoice(w http.ResponseWriter, r *http.Request, _ httpro
 
 	index := len(form.Products)
 	productsId := r.Form["id"]
-	rows := conn.MustQuery(r.Context(), "select product_id, name, description, to_price(price, decimal_digits), 1 as quantity, 0 as discount, array_agg(tax_id) from product join company using (company_id) join currency using (currency_code) left join product_tax using (product_id) where product_id = any ($1) group by product_id, name, description, price, decimal_digits", productsId)
+	rows := conn.MustQuery(r.Context(), "select product_id, name, description, to_price(price, decimal_digits), 1 as quantity, 0 as discount, array_remove(array_agg(tax_id), null) from product join company using (company_id) join currency using (currency_code) left join product_tax using (product_id) where product_id = any ($1) group by product_id, name, description, price, decimal_digits", productsId)
 	defer rows.Close()
 	for rows.Next() {
 		product := newInvoiceProductForm(index, company, locale, form.Tax.Options)

pkg/locale.go

@@ -12,27 +12,31 @@ const contextLocaleKey = "numerus-locale"
 
 type Locale struct {
 	*gotext.Locale
+	CurrencyPattern string
 	Language        language.Tag
 }
 
-func NewLocale(lang language.Tag) *Locale {
+func NewLocale(lang availableLanguage) *Locale {
 	return &Locale{
-		gotext.NewLocale("locales", lang.String()),
-		lang,
+		gotext.NewLocale("locales", lang.tag.String()),
+		lang.currencyPattern,
+		lang.tag,
 	}
 }
 
 func LocaleSetter(db *Db, next http.Handler) http.Handler {
 	availableLanguages := mustGetAvailableLanguages(db)
-	var matcher = language.NewMatcher(availableLanguages)
 
 	locales := map[language.Tag]*Locale{}
+	var tags []language.Tag
 	for _, lang := range availableLanguages {
 		locale := NewLocale(lang)
 		locale.AddDomain("numerus")
-		locales[lang] = locale
+		locales[lang.tag] = locale
+		tags = append(tags, lang.tag)
 	}
 	defaultLocale := locales[language.Catalan]
+	var matcher = language.NewMatcher(tags)
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		var locale *Locale
@@ -70,21 +74,27 @@ func gettext(str string, locale *Locale) string {
 	return locale.Get(str)
 }
 
-func mustGetAvailableLanguages(db *Db) []language.Tag {
-	rows, err := db.Query(context.Background(), "select lang_tag from language where selectable")
+type availableLanguage struct {
+	tag             language.Tag
+	currencyPattern string
+}
+
+func mustGetAvailableLanguages(db *Db) []availableLanguage {
+	rows, err := db.Query(context.Background(), "select lang_tag, currency_pattern from language where selectable")
 	if err != nil {
 		panic(err)
 	}
 	defer rows.Close()
 
-	var langs []language.Tag
+	var langs []availableLanguage
 	for rows.Next() {
 		var langTag string
-		err = rows.Scan(&langTag)
+		var currencyPattern string
+		err = rows.Scan(&langTag, &currencyPattern)
 		if err != nil {
 			panic(err)
 		}
-		langs = append(langs, language.MustParse(langTag))
+		langs = append(langs, availableLanguage{language.MustParse(langTag), currencyPattern})
 	}
 	if rows.Err() != nil {
 		panic(rows.Err())

pkg/template.go

@@ -38,7 +38,7 @@ func mustRenderTemplate(wr io.Writer, r *http.Request, layout string, filename s
 			if err != nil {
 				f = math.NaN()
 			}
-			return p.Sprintf("%.*f", company.DecimalDigits, number.Decimal(f))
+			return p.Sprintf(locale.CurrencyPattern, company.DecimalDigits, number.Decimal(f), company.CurrencySymbol)
 		},
 		"formatDate": func(time time.Time) string {
 			return time.Format("02/01/2006")

revert/compute_new_invoice_amount.sql

@@ -0,0 +1,7 @@
+-- Revert numerus:compute_new_invoice_amount from pg
+
+begin;
+
+drop function if exists numerus.compute_new_invoice_amount(integer, numerus.new_invoice_product[]);
+
+commit;

revert/new_invoice_amount.sql

@@ -0,0 +1,7 @@
+-- Revert numerus:new_invoice_amount from pg
+
+begin;
+
+drop type if exists numerus.new_invoice_amount;
+
+commit;

sqitch.plan

@@ -58,3 +58,5 @@ next_invoice_number [schema_numerus invoice_number_counter] 2023-02-17T13:21:48Z
 add_invoice [schema_numerus invoice company currency parse_price new_invoice_product tax invoice_product invoice_product_tax next_invoice_number] 2023-02-16T21:12:46Z jordi fita mas <jordi@tandem.blog> # Add function to create new invoices
 invoice_tax_amount [schema_numerus invoice_product invoice_product_tax] 2023-02-22T12:08:35Z jordi fita mas <jordi@tandem.blog> # Add view for invoice tax amount
 invoice_amount [schema_numerus invoice_product invoice_tax_amount] 2023-02-22T12:58:46Z jordi fita mas <jordi@tandem.blog> # Add view to compute subtotal and total for invoices
+new_invoice_amount [schema_numerus] 2023-02-23T12:08:25Z jordi fita mas <jordi@tandem.blog> # Add type to return when computing new invoice amounts
+compute_new_invoice_amount [schema_numerus company currency tax new_invoice_product new_invoice_amount] 2023-02-23T12:20:13Z jordi fita mas <jordi@tandem.blog> # Add function to compute the subtotal, taxes, and total amounts for a new invoice

test/compute_new_invoice_amount.sql

@@ -0,0 +1,66 @@
+-- Test compute_new_invoice_amount
+set client_min_messages to warning;
+create extension if not exists pgtap;
+reset client_min_messages;
+
+begin;
+
+select plan(14);
+
+set search_path to numerus, auth, public;
+
+select has_function('numerus', 'compute_new_invoice_amount', array ['integer', 'new_invoice_product[]']);
+select function_lang_is('numerus', 'compute_new_invoice_amount', array ['integer', 'new_invoice_product[]'], 'plpgsql');
+select function_returns('numerus', 'compute_new_invoice_amount', array ['integer', 'new_invoice_product[]'], 'new_invoice_amount');
+select isnt_definer('numerus', 'compute_new_invoice_amount', array ['integer', 'new_invoice_product[]']);
+select volatility_is('numerus', 'compute_new_invoice_amount', array ['integer', 'new_invoice_product[]'], 'stable');
+select function_privs_are('numerus', 'compute_new_invoice_amount', array ['integer', 'new_invoice_product[]'], 'guest', array []::text[]);
+select function_privs_are('numerus', 'compute_new_invoice_amount', array ['integer', 'new_invoice_product[]'], 'invoicer', array ['EXECUTE']);
+select function_privs_are('numerus', 'compute_new_invoice_amount', array ['integer', 'new_invoice_product[]'], 'admin', array ['EXECUTE']);
+select function_privs_are('numerus', 'compute_new_invoice_amount', array ['integer', 'new_invoice_product[]'], 'authenticator', array []::text[]);
+
+set client_min_messages to warning;
+truncate tax cascade;
+truncate company cascade;
+reset client_min_messages;
+
+insert into company (company_id, business_name, vatin, trade_name, phone, email, web, address, city, province, postal_code, country_code, currency_code)
+values (1, 'Company 1', 'XX123', '', '555-555-555', 'a@a', '', '', '', '', '', 'ES', 'EUR')
+;
+
+insert into tax (tax_id, company_id, name, rate)
+values (2, 1, 'IRPF -15 %', -0.15)
+     , (3, 1, 'IVA 4 %', 0.04)
+     , (4, 1, 'IVA 10 %', 0.10)
+     , (5, 1, 'IVA 21 %', 0.21)
+;
+
+select is(
+	compute_new_invoice_amount(1, '{}'),
+	'(0.00,"{}",0.00)'::new_invoice_amount
+);
+
+select is(
+	compute_new_invoice_amount(1, '{"(6,P,D,1.00,1,0.0,\"{2,5}\")","(6,P,D,2.00,2,0.1,{3})"}'),
+	'(4.60,"{{IRPF -15 %,-0.15},{IVA 4 %,0.14},{IVA 21 %,0.21}}",4.80)'::new_invoice_amount
+);
+
+select is(
+	compute_new_invoice_amount(1, '{"(6,P,D,2.22,3,0.0,\"{2,4,5}\")","(6,P,D,3.33,4,0.2,{4})"}'),
+	'(17.32,"{{IRPF -15 %,-1.00},{IVA 10 %,1.74},{IVA 21 %,1.40}}",19.46)'::new_invoice_amount
+);
+
+select is(
+	compute_new_invoice_amount(1, '{"(6,P,D,4.44,5,0.0,\"{4,5}\")","(6,P,D,5.55,6,0.1,\"{5,3}\")"}'),
+	'(52.17,"{{IVA 4 %,1.20},{IVA 10 %,2.22},{IVA 21 %,10.95}}",66.54)'::new_invoice_amount
+);
+
+select is(
+	compute_new_invoice_amount(1, '{"(6,P,D,7.77,8,0.0,\"{}\")"}'),
+	'(62.16,"{}",62.16)'::new_invoice_amount
+);
+
+select *
+from finish();
+
+rollback;

test/language.sql

@@ -7,7 +7,7 @@ begin;
 
 set search_path to public;
 
-select plan(23);
+select plan(27);
 
 select has_table('language');
 select has_pk('language');
@@ -37,6 +37,11 @@ select col_type_is('language', 'selectable', 'boolean');
 select col_not_null('language', 'selectable');
 select col_hasnt_default('language', 'selectable');
 
+select has_column('language', 'currency_pattern');
+select col_type_is('language', 'currency_pattern', 'text');
+select col_not_null('language', 'currency_pattern');
+select col_hasnt_default('language', 'currency_pattern');
+
 select *
 from finish();
 

test/new_invoice_amount.sql

@@ -0,0 +1,22 @@
+-- Test new_invoice_amount
+set client_min_messages to warning;
+create extension if not exists pgtap;
+reset client_min_messages;
+
+begin;
+
+select plan(5);
+
+set search_path to numerus, public;
+
+select has_composite('numerus', 'new_invoice_amount', 'Composite type numerus.new_invoice_amount should exist');
+select columns_are('numerus', 'new_invoice_amount', array['subtotal', 'taxes', 'total']);
+select col_type_is('numerus'::name, 'new_invoice_amount'::name, 'subtotal'::name, 'text');
+select col_type_is('numerus'::name, 'new_invoice_amount'::name, 'taxes'::name, 'text[]');
+select col_type_is('numerus'::name, 'new_invoice_amount'::name, 'total'::name, 'text');
+
+
+select *
+from finish();
+
+rollback;

test/parse_price.sql

@@ -5,7 +5,7 @@ reset client_min_messages;
 
 begin;
 
-select plan(36);
+select plan(42);
 
 set search_path to auth, numerus, public;
 
@@ -23,8 +23,12 @@ select is( parse_price('1.1', 2), 110 );
 select is( parse_price('1.1', 3), 1100 );
 select is( parse_price('0', 2), 0 );
 select is( parse_price('0', 3), 0 );
+select is( parse_price('-0', 2), 0 );
+select is( parse_price('-0', 3), 0 );
 select is( parse_price('0.01', 2), 1 );
 select is( parse_price('0.001', 3), 1 );
+select is( parse_price('-0.01', 2), -1 );
+select is( parse_price('-0.001', 3), -1 );
 select is( parse_price('0.1', 2), 10 );
 select is( parse_price('0.01', 3), 10 );
 select is( parse_price('1', 2), 100 );
@@ -33,6 +37,8 @@ select is( parse_price('10', 2), 1000 );
 select is( parse_price('1', 3), 1000 );
 select is( parse_price('23.23', 2), 2323 );
 select is( parse_price('23.23', 3), 23230 );
+select is( parse_price('-23.23', 2), -2323 );
+select is( parse_price('-23.23', 3), -23230 );
 select throws_ok( $$ select parse_price('234.234', 2) $$ );
 select is( parse_price('234.234', 3), 234234 );
 select throws_ok( $$ select parse_price('2345.2345', 2) $$ );

test/to_price.sql

@@ -5,7 +5,7 @@ reset client_min_messages;
 
 begin;
 
-select plan(23);
+select plan(29);
 
 set search_path to numerus, public;
 
@@ -23,6 +23,8 @@ select is( to_price(0, 2), '0.00' );
 select is( to_price(0, 3), '0.000' );
 select is( to_price(1, 2), '0.01' );
 select is( to_price(1, 3), '0.001' );
+select is( to_price(-1, 2), '-0.01' );
+select is( to_price(-1, 3), '-0.001' );
 select is( to_price(10, 2), '0.10' );
 select is( to_price(10, 3), '0.010' );
 select is( to_price(100, 2), '1.00' );
@@ -33,6 +35,10 @@ select is( to_price(12345678, 2), '123456.78' );
 select is( to_price(12345678, 3), '12345.678' );
 select is( to_price(12345678, 4), '1234.5678' );
 select is( to_price(12345678, 5), '123.45678' );
+select is( to_price(-12345678, 2), '-123456.78' );
+select is( to_price(-12345678, 3), '-12345.678' );
+select is( to_price(-12345678, 4), '-1234.5678' );
+select is( to_price(-12345678, 5), '-123.45678' );
 
 select *
 from finish();

verify/available_languages.sql

@@ -9,20 +9,23 @@ from language
 where lang_tag = 'und'
   and name = 'Undefined'
   and endonym = 'Undefined'
-  and not selectable;
+  and not selectable
+  and currency_pattern = '%[3]s%.[1]*[2]f';
 
 select 1 / count(*)
 from language
 where lang_tag = 'ca'
   and name = 'Catalan'
   and endonym = 'català'
-  and selectable;
+  and selectable
+  and currency_pattern = '%.[1]*[2]f %[3]s';
 
 select 1 / count(*)
 from language
 where lang_tag = 'es'
   and name = 'Spanish'
   and endonym = 'español'
-  and selectable;
+  and selectable
+  and currency_pattern = '%.[1]*[2]f %[3]s';
 
 rollback;

verify/compute_new_invoice_amount.sql

@@ -0,0 +1,7 @@
+-- Verify numerus:compute_new_invoice_amount on pg
+
+begin;
+
+select has_function_privilege('numerus.compute_new_invoice_amount(integer, numerus.new_invoice_product[])', 'execute');
+
+rollback;

verify/language.sql

@@ -6,6 +6,7 @@ select lang_tag
      , name
      , endonym
      , selectable
+     , currency_pattern
 from public.language
 where false;
 

verify/new_invoice_amount.sql

@@ -0,0 +1,7 @@
+-- Verify numerus:new_invoice_amount on pg
+
+begin;
+
+select pg_catalog.has_type_privilege('numerus.new_invoice_amount', 'usage');
+
+rollback;

web/template/invoices/new.gohtml

@@ -16,6 +16,7 @@
         <form method="POST" action="{{ companyURI "/invoices" }}">
             {{ csrfToken }}
 
+            {{ with .Form -}}
                 {{ template "select-field" .Customer }}
                 {{ template "input-field" .Number }}
                 {{ template "input-field" .Date }}
@@ -32,6 +33,26 @@
                         {{ template "select-field" .Tax }}
                     </fieldset>
                 {{- end }}
+            {{- end }}
+
+            <table>
+                <tbody>
+                <tr>
+                    <th scope="row">{{(pgettext "Subtotal" "title")}}</th>
+                    <td class="numeric">{{ .Subtotal | formatPrice }}</td>
+                </tr>
+                {{- range $tax := .Taxes }}
+                    <tr>
+                        <th scope="row">{{ index . 0 }}</th>
+                        <td class="numeric">{{ index . 1 | formatPrice }}</td>
+                    </tr>
+                {{- end }}
+                <tr>
+                    <th scope="row">{{(pgettext "Total" "title")}}</th>
+                    <td class="numeric">{{ .Total | formatPrice }}</td>
+                </tr>
+                </tbody>
+            </table>
 
             <fieldset>
                 <button formnovalidate name="action" value="products"

web/template/invoices/products.gohtml

@@ -49,7 +49,7 @@
                         <tr>
                             <td><input type="checkbox" name="id" id="new-product-id-{{$key}}" value="{{.Id}}"></td>
                             <td><label for="new-product-id-{{$key}}">{{ .Name }}</label></td>
-                            <td>{{ .Price | formatPrice }}</td>
+                            <td class="numeric">{{ .Price | formatPrice }}</td>
                         </tr>
                     {{- end }}
                 {{ else }}

web/template/products/index.gohtml

@@ -29,7 +29,7 @@
                 <tr>
                     <td></td>
                     <td><a href="{{ companyURI "/products/"}}{{ .Slug }}">{{ .Name }}</a></td>
-                    <td>{{ .Price | formatPrice }}</td>
+                    <td class="numeric">{{ .Price | formatPrice }}</td>
                 </tr>
             {{- end }}
         {{ else }}