Plugin Pipeline Demo

This example shows how multiple plugins compose into a billing calculation pipeline with priority-based execution.

Running the Example

go run ./examples/plugin-pipeline-demo/

Plugin Setup

Four plugins are registered with different priorities:

Priority	Plugin	Type	Action
0	audit-log	InvoiceLifecycleHook	Logs calculation flow
500	coupon	DiscountHook	10% coupon discount
500	loyalty-discount	DiscountHook	5% loyalty discount
900	tax	TaxHook	10% consumption tax

Calculation Pipeline

For a ¥10,000/month contract:

1. [AuditLog] BeforeCalculation (logs start)
2. Subtotal:             ¥10,000
3. [Coupon] -10%:        -¥1,000
4. [Loyalty] -5%:        -¥500
5. After discounts:      ¥8,500
6. [Tax] +10%:           +¥850
7. Total:                ¥9,350
8. [AuditLog] AfterCalculation (logs result)

Custom Plugin Example

The demo includes a custom loyaltyDiscountPlugin:

type loyaltyDiscountPlugin struct {
    priority int
}

func (p *loyaltyDiscountPlugin) CalculateDiscount(ctx *plugin.CalculationContext) (shared.Money, error) {
    rate := new(big.Rat).SetFrac64(5, 100) // 5%
    discount := ctx.Subtotal().Multiply(rate)
    ctx.RecordDiscount(plugin.AppliedDiscount{
        PluginName: "loyalty-discount",
        Code:       "LOYALTY5",
        Amount:     discount,
    })
    return discount, nil
}

Key Takeaways

• Plugins execute in priority order (lower number = higher priority)
• Multiple DiscountHooks stack — each applies to the original subtotal
• Tax is calculated on the post-discount amount
• InvoiceLifecycleHook provides before/after visibility into the pipeline