refactor(config): add RampSchedule.CumulativePercent (631 C0)

internal/config/types.go

@@ -3,6 +3,7 @@ package config
 
 import (
 	"encoding/json"
+	"math"
 	"strings"
 	"time"
 
@@ -276,16 +277,22 @@ var PresetRampSchedules = map[string]RampSchedule{
 	},
 }
 
+// CumulativePercent is the share of the base (0..100) a ramp has bought once
+// step steps are complete: step*PercentPerStep capped at 100, and 100 for an
+// immediate schedule. It is the one definition of cumulative ramp progress.
+func (r *RampSchedule) CumulativePercent(step int) float64 {
+	if r.Type == "immediate" {
+		return 100
+	}
+	return math.Min(100, float64(step)*r.PercentPerStep)
+}
+
 // GetCurrentCoverage calculates the current effective coverage based on ramp progress.
 func (r *RampSchedule) GetCurrentCoverage(baseCoverage float64) float64 {
 	if r.Type == "immediate" {
-		return baseCoverage
-	}
-	completedPercent := float64(r.CurrentStep) * r.PercentPerStep
-	if completedPercent > 100 {
-		completedPercent = 100
+		return baseCoverage // base*100/100 is not exact in floating point
 	}
-	return baseCoverage * completedPercent / 100
+	return baseCoverage * r.CumulativePercent(r.CurrentStep) / 100
 }
 
 // GetNextPurchaseDate calculates when the next purchase step should occur.

internal/config/types_test.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"math"
 	"testing"
 	"time"
 
@@ -93,6 +94,46 @@ func TestRampSchedule_GetCurrentCoverage(t *testing.T) {
 	}
 }
 
+func TestRampSchedule_CumulativePercent(t *testing.T) {
+	weekly := RampSchedule{Type: "weekly", PercentPerStep: 25, TotalSteps: 4}
+	custom := RampSchedule{Type: "custom", PercentPerStep: 40, TotalSteps: 3}
+	tests := []struct {
+		name     string
+		schedule RampSchedule
+		step     int
+		expected float64
+	}{
+		{"immediate is always 100", RampSchedule{Type: "immediate"}, 0, 100},
+		{"weekly step 0", weekly, 0, 0},
+		{"weekly step 1", weekly, 1, 25},
+		{"weekly step 4", weekly, 4, 100},
+		{"custom 3x40 step 2", custom, 2, 80},
+		{"custom 3x40 step 3 clamps to 100", custom, 3, 100},
+		{"step beyond the ramp stays at 100", weekly, 9, 100},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.expected, tt.schedule.CumulativePercent(tt.step))
+		})
+	}
+}
+
+// GetCurrentCoverage must stay the base scaled by CumulativePercent at the
+// schedule's own CurrentStep, so the two cannot drift.
+func TestRampSchedule_GetCurrentCoverageUsesCumulativePercent(t *testing.T) {
+	s := RampSchedule{Type: "custom", PercentPerStep: 40, TotalSteps: 3, CurrentStep: 2}
+	assert.Equal(t, 80*s.CumulativePercent(2)/100, s.GetCurrentCoverage(80))
+}
+
+// An immediate schedule returns the base untouched: base*100/100 would turn
+// 0.1694 into 0.16939999999999997 and math.MaxFloat64 into +Inf.
+func TestRampSchedule_GetCurrentCoverageImmediateIsExact(t *testing.T) {
+	s := RampSchedule{Type: "immediate"}
+	for _, base := range []float64{0.1694, 80, math.MaxFloat64} {
+		assert.Equal(t, base, s.GetCurrentCoverage(base))
+	}
+}
+
 func TestRampSchedule_GetNextPurchaseDate(t *testing.T) {
 	now := time.Now()
 	startDate := time.Date(2024, 1, 1, 0, 0, 0, 0, time.UTC)