Although it is possible to just print the invoice from the browser, many
people will not even try an assume that they can not create a PDF for
the invoice.
I thought of using Groff or TeX to create the PDF, but it would mean
maintaining two templates in two different systems (HTML and whatever i
would use), and would probably look very different, because i do not
know Groff or TeX that well.
I wish there was a way to tell the browser to print to PDF, and it can
be done, but only with the Chrome Protocol to a server-side running
Chrome instance. This works, but i would need a Chrome running as a
daemon.
I also wrote a Qt application that uses QWebEngine to print the PDF,
much like wkhtmltopdf, but with support for more recent HTML and CSS
standards. Unfortunately, Qt 6.4’s embedded Chromium does not follow
break-page-inside as well as WeasyPrint does.
To use WeasyPrint, at first i wanted to reach the same URL as the user,
passing the cookie to WeasyPrint so that i can access the same invoice
as the user, something that can be done with wkhtmltopdf, but WeasyPrint
does not have such option. I did it with a custom Python script, but
then i need to package and install that script, that is not that much
work, but using the Debian-provided script is even less work, and less
likely to drift when WeasyPrint changes API.
Also, it is unnecessary to do a network round-trip from Go to Python
back to Go, because i can already write the invoice HTML as is to
WeasyPrint’s stdin.
I am planning to use WeasyPrint to “generate PDF” from the same HTML
that the user view, but it seems that it does not support flex’s gap
and some other properties that i had to change to work in both user
agents.
I also moved the invoice’s “footer” inside the last product’s body
because i do not want the footer to be a “widow”.
Had to group name and description rows in tbody because i do not want
to break them on pagination.
I also could not use tfoot for subtotal, taxes, and total because then
they appear on every page.
The disclaimer should appear only at the very bottom of the last page,
but i do not know how to do that; using position fixed shows it on
every page.
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
They are not functions because i need to join them with the main
invoice relation, and although possible is a bit more awkward with
functions.
The taxes have their own relation because i will need them grouped by
their name in the PDF, so it will probably be a select for that
relation.
When updating the product list, i forgot to change the index in the
product field’s names and, therefore, i created invoices with only the
products until the first gap.
I have moved everything into a different file, even though it is related
to “db”, because it was starting to get a bit ugly.
Apparently i was doing too much work and had to read the code to
understand what i was supposed to do, because pgtypes’ documentation,
as all other projects from the same author, is almost non-existent.
I needed to add binary encoding function for the new_invoice_product
type, and currently it is not correct: i hardcoded the OID values, but
they are going to be different on a different database.
They are to complete the invoice, so it can be in an invalid date, but
we do not want to force people to finish all required inputs before they
can add products or update quantities, do we?
Now had to add the empty option label for customer in all cases, because
it could be empty, although that should be done regardless in case
someone has a browser that does not validate fields.
I am going to add similar functions for invoices, as i will need to
add the taxes for their products and their own taxes, thus the Go code
will begin to be “too much work” and i feel better if that is in
PL/pgSQL.
If i have these functions for invoices, there is no point on having to
do almost the same work, albeit less, for products.
I have seen that pgx has the CollectRows function to do the same job as
that function. I can not use CollectRows because it uses generics and
requires Go 1.18, but i have adopted the same nomenclature they use.
Apparently, url.Values.Has and math.MaxInt was added to Go 1.17,
but on Debian Bullseye there is only Go 1.16. I do not want to
install a new version of Go to the server unless there is an
overwhelming reason, and a couple of methods are not. Thus, now i use
Go 1.16 too on my development machine, to avoid situations like this.
It seems that we do not agree en whether the IRPF tax should be
something of the product or the contact, so we decided to make the
product have multiple taxes, just in case, and if only one is needed,
then users can just select one; no need to limit to one.
This is not yet necessary, but the empty label is because i do not want
to select a default tax for products—at least, not without a setting for
it.
Since i need to add the required attribute now to select, because
otherwise the browser would allow sending that empty value, i did not
want to do it unconditionally, just in case.
I do not want to use floats in the Go lang application, because it is
not supposed to do anything with these values other than to print and
retrieve them from the user; all computations will be performed by
PostgreSQL in cents.
That means i have to “convert” from the price format that users expect
to see (e.g., 1.234,56) to cents (e.g., 123456) and back when passing
data between Go and PostgreSQL, and that conversion depends on the
currency’s decimal places.
At first i did everything in Go, but saw that i would need to do it in
a loop when retrieving the list of products, and immediately knew it was
a mistake—i needed a PL/pgSQL function for that.
I still need to convert from string to float, however, when printing the
value to the user. Because the string representation is in C, but i
need to format it according to the locale with golang/x/text. That
package has the information of how to correctly format numbers, but it
is in an internal package that i can not use, and numbers.Digit only
accepts numeric types, not a string.
Our company is a kind-of contact, although it does not appear in the
contact section, thus i could embed the contact form inside the tax
details form to reuse all the common fields.
I implemented the Valuer and Scanner interfaces to InputField and
SelectField for better passing values between the database and Go. I
had a conflict with the Value name and renamed the struct member to Val.
I also had to change the attributes array to be of type
template.HTMLAttr or html/template would replace `form="newtax"`
attribute to `zgotmplz="newtax"` because it deems it “unsafe”. I do
not like having to use template.HTMLAttr when assigning values, but
i do not know what else i can do now.
I was worried that i was repeating the AddInputErrors function for each
form, because they were basically the same. I could create a Form type
and make all forms embed it, but i realized that with a separate
validator i would have cleaner validation functions and would not need
the Valid field in the form that i am using only for that method.
Similar to the profile form, the login form now parses and validates
itself, with the InputField structs that the templates expect.
I realized that i was doing more work than necessary when parsing fields
fro the profile form because i was repeating the operation and the field
name, so now it is a function of InputField.
This time i needed extra attributes for the login form. I am not sure
that the Go source code needs to know about HTML attributes, but it was
the easiest way to pass them to the template.
This is just to set the correct `lang` attribute on the HTML, so that
text readers can do its job and the `(optional)` suffix of labels gets
the correct ”translation”.
Let’s start first with a non-fancy validation method with just if
conditionals instead of bringing yet another complicated library. I
hope i do not regret it.
I wanted to move all the input field to a template because all that
gobbledygook with the .input div and repeating the label in the
placeholder was starting to annoy me. Now with error messages was even
more concerning.
I did not know whether the label should be a part of the input fields
or something that the template should do. At the end i decided that
it makes more sense to be part of the input field because in the error
messages i use that same label, thus the template does not have a say
in that, and, besides, it was just easier to write the template.
The same with the error messages: i’ve seen frameworks that have a map
with the field’s id/name to the error slice, but then it would be
a bit harder to write the template.
I added AddError functions instead of just using append inside the
validator function, and have a local variable for whether it all went
OK, because i was worried that i would leave out the `ok = false`
in some conditions.
I had started writing “constructors” functions for InputField and
SelectField, but then had to add other methods to change the required
field and who knows what else, and in the end it was easier to just
construct the field inline.
I have been thinking about that, and it does not make that much sense to
have the titles in the Go source anymore: most of them are static text
that i have to remember to set in the controller each time, and when
the time come i have to face a dynamic title i am sure i will manage
with only the template capabilities—worst comes worst, i can always
define a function.
On the other hand, there is no way i can define a template without its
title and i know that everytime that template is used, no matter what
controller rendered it, it will always have that title.
This is not necessary per se, but it makes my life easier because that
way i know which company the user was when she went to its profile and
can “return” back in the menu and future nav items.
jordi fita mas