FileVault Subscription Billing System

Pricing that depends on usage

The monthly amount changes with the file count, so the tier boundaries and per-file costs must be applied the same way every time a price is calculated.

Keeping money logic testable

When pricing is mixed with payment API calls, every test needs a payment provider. Pricing has to be verifiable on its own.

Rules before charges

Invalid inputs or misconfigured tiers must be caught before a billing operation runs, not after a customer is charged.

• PHP/Laravel service architecture
• Dynamic monthly pricing calculations
• File-count-based pricing tiers
• Cost-per-file calculation logic
• Stripe billing integration
• Monthly recurring billing workflows
• Pricing validation and business rules
• Billing configuration and maintainable service design

Pricing is calculated first and passed to billing as a finished result. Billing never works out prices itself.

1. 1

   File count

   The number of stored files for the billing period is the input.

2. 2

   Tier resolution

   The count is matched against configured tier boundaries.

3. 3

   Price calculation

   Cost per file and the monthly total are calculated by a pure pricing service.

4. 4

   Validation

   The result is checked against business rules before it moves on.

5. 5

   Billing

   A separate billing service takes the validated result and handles the Stripe recurring charge.

Pricing is a calculation, billing is a side effect

The pricing service takes a file count and tier configuration and returns a result without calling external services. It can be unit-tested with plain inputs, and billing code only consumes its output.

Tiers as configuration

Tier boundaries and per-file costs live in configuration rather than scattered conditionals, so changing a price does not mean changing control flow.

Validate before charging

Pricing results are validated against business rules before any Stripe operation, so bad input fails early and clearly.

final class PricingCalculator
{
    public function __construct(private TierTable $tiers) {}

    public function quote(int $fileCount): PriceQuote
    {
        if ($fileCount < 0) {
            throw new InvalidArgumentException('File count cannot be negative.');
        }

        $tier = $this->tiers->forFileCount($fileCount);

        return new PriceQuote(
            fileCount: $fileCount,
            tier: $tier->name,
            costPerFileCents: $tier->costPerFileCents,
            monthlyTotalCents: $fileCount * $tier->costPerFileCents,
        );
    }
}

// Billing consumes the quote. It never calculates prices itself.
$quote = $pricing->quote($account->fileCount());
$billing->chargeMonthly($account, $quote);