Reapply "feat(loyalty): EnakPoint & EnakCoin" (#32)

This reverts commit 4e24f9bbb0.

internal/processor/earning_reversal_test.go

@@ -0,0 +1,25 @@
+package processor
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"apskel-pos-be/internal/entities"
+	"apskel-pos-be/internal/repository"
+)
+
+func TestEarningReversalTarget(t *testing.T) {
+	earn := entities.WalletTransaction{Amount: 875, Metadata: entities.Metadata{"basis": 87500.0}}
+	target := func(order repository.EarningOrder) int64 { return earningReversalTarget(&order, earn) }
+
+	assert.Equal(t, int64(0), target(repository.EarningOrder{}), "nothing refunded, nothing to take")
+	assert.Equal(t, int64(875), target(repository.EarningOrder{IsVoid: true}), "void takes everything")
+	assert.Equal(t, int64(200), target(repository.EarningOrder{RefundAmount: 20000}), "floor(875 × 20000 / 87500)")
+	assert.Equal(t, int64(299), target(repository.EarningOrder{RefundAmount: 29999.99}), "floor, not round")
+	assert.Equal(t, int64(875), target(repository.EarningOrder{RefundAmount: 87500}))
+	assert.Equal(t, int64(875), target(repository.EarningOrder{RefundAmount: 96250}), "a refund including tax cannot take more than was earned")
+
+	noBasis := entities.WalletTransaction{Amount: 10, Metadata: entities.Metadata{}}
+	assert.Equal(t, int64(10), earningReversalTarget(&repository.EarningOrder{RefundAmount: 1}, noBasis), "without a basis any refund takes it all")
+}