PHP booking form with server-side validation and invoicing

01Summary

1. A booking form in plain PHP (5 files, 243 lines) validates every field on the server.
2. Each confirmed booking gets an invoice with net, 10% tax and a due date, and a slot can never be booked twice.
3. 24 of 24 automated tests pass.

Each confirmed booking gets an invoice with net, 10% tax and a due date, and a slot can never be booked twice.

Key point, computed from the sample files

02The scenario

In this scenario bookings arrive by email, two people sometimes get the same slot, and invoices are typed up later.

03Issues in the data

04How I approached it

• A booking form for 3 services with server-side validation of every field (name, email, weekday date from tomorrow, half-hour slots, quantity, notes).
• CSRF token and a hidden honeypot field against spam.
• SQLite storage with a unique rule on service, date and time, so a slot can only be booked once.
• Invoice numbering (INV-year-0001), 10% tax calculated in cents and a 14-day due date.
• A test script with 24 tests.

05How this applies to your business

1. Assess and designMap the current process, size the gaps from your own data, agree the design and a written scope.
2. Build and testBuild in your own tools with the checks built in, then run real cases end to end.
3. Document and hand overSOPs, a walkthrough and a handover, so your team runs it without me.

06Controls and checks

07What the files show

• tests/run_tests.php reports 24 of 24 tests passed (output included in the download).
• Run locally with php -S and checked in a browser: invalid input, a confirmed booking and a refused second booking (screenshots below).
• Impossible dates such as 31 November are rejected.

08Risks and how the build handles them

09Appendix: files

A. Screenshots of the deliverable

localhost:8000/book.php

Exhibit 8: Booking confirmed with invoice INV-2026-0001: line, net, 10% tax and total calculated server-side

Source: sample files

localhost:8000/book.php

Exhibit 9: The same form after an invalid submission, with a message beside each field that failed validation

Source: sample files

localhost:8000/book.php

Exhibit 10: A second booking for the same service, date and time is refused because the slot is already taken

Source: sample files

    public static function fromBooking(array $b, int $seq, DateTimeImmutable $issued): array
    {
        $svc = Validator::SERVICES[$b['service']];
        $unitCents = (int)round($svc['price'] * 100);
        $netCents = $unitCents * (int)$b['qty'];
        $taxCents = (int)round($netCents * self::TAX_RATE);
        return [
            'number' => sprintf('INV-%s-%04d', $issued->format('Y'), $seq),
            'issued' => $issued->format('Y-m-d'),
            'due'    => $issued->modify('+14 days')->format('Y-m-d'),
            'customer' => $b['name'], 'email' => $b['email'],
            'lines'  => [[
                'desc' => $svc['label'] . ' on ' . $b['date'] . ' at ' . $b['time'],
                'qty' => (int)$b['qty'], 'unit' => $unitCents / 100, 'net' => $netCents / 100,
            ]],
            'net' => $netCents / 100, 'tax' => $taxCents / 100, 'gross' => ($netCents + $taxCents) / 100,
        ];
    }

B. Downloadable files

Sample build: realistic data, built to show how I'd handle this work. Names are placeholders and no client data is used.