Tatycan

Tatycan grooms dogs and cats in Galapagar, on the edge of Madrid. The salon wanted what off-the-shelf tools wouldn’t give it: booking that understands breeds and sizes, records organized around pets rather than invoices, reminders that reach customers where they actually read them, and invoicing that satisfies Spain’s new digital-invoicing rules. So they asked for software of their own.

We built it as two small systems instead of one big one — and that separation is most of the story.

Keeping the halves apart is the design, not an accident. The public site cannot lose customer data because it never holds any; the CRM never has to trust input from the open internet. Behind the CRM, one background engine wakes every five minutes during salon hours and does three jobs: WhatsApp appointment reminders, booking confirmations, and the nightly tax paperwork. Each job claims its work atomically — the database itself guarantees a reminder can only be claimed once — so an overlapping or retried run can never message a customer twice.

Under VeriFactu (Royal Decree 1007/2023), invoicing software must produce tamper-evident records: every fiscal record carries a SHA-256 fingerprint of the record before it, forming a chain that cannot be edited without breaking. The CRM issues the day’s simplified invoices nightly, renders each record to the agency’s XML format, and submits it over a mutual-TLS connection. Once a visit is invoiced, its billing fields lock.

Two details we would defend anywhere: the chain re-checks its head inside the database write itself, so two invoices issued at the same moment cannot fork the chain; and the hash implementation is pinned to the tax agency’s published test vectors in the test suite, so conformance is a passing test rather than an opinion.