refactor(ride): express category thresholds as inclusive min scores

2 files changed, 49 insertions, 16 deletions

diff --git a/ride/climb.go b/ride/climb.go
index 8852cbf..29a4dcf 100644
--- a/ride/climb.go
+++ b/ride/climb.go
@@ -28,20 +28,19 @@ const (
 
 type categoryInfo struct {
 	label    string
-	maxScore float64
+	minScore float64
 }
 
-// categories describes each Category: its display label and the exclusive
-// Cotacol score ceiling it applies to. A score at or above CategoryOne's
-// ceiling is Hors Catégorie.
+// categories describes each Category: its display label and the inclusive
+// Cotacol score floor at which it starts applying. A score at or above
+// CategoryOne's floor is Hors Catégorie; CategoryNo has no floor.
 var categories = map[Category]categoryInfo{
-	CategoryNo:    {label: "NO", maxScore: 35},
-	CategoryFour:  {label: "Cat 4", maxScore: 80},
-	CategoryThree: {label: "Cat 3", maxScore: 180},
-	CategoryTwo:   {label: "Cat 2", maxScore: 250},
-	CategoryOne:   {label: "Cat 1", maxScore: 600},
-	// Hors Catégorie has no ceiling.
-	CategoryHC: {label: "HC", maxScore: math.Inf(+1)},
+	CategoryNo:    {label: "NO", minScore: math.Inf(-1)},
+	CategoryFour:  {label: "Cat 4", minScore: 35},
+	CategoryThree: {label: "Cat 3", minScore: 80},
+	CategoryTwo:   {label: "Cat 2", minScore: 180},
+	CategoryOne:   {label: "Cat 1", minScore: 250},
+	CategoryHC:    {label: "HC", minScore: 600},
 }
 
 // climbDetectionMinimumScore is the climb-detection score below which a
@@ -144,16 +143,23 @@ func (c Category) String() string {
 	return categories[c].label
 }
 
-// CategoryOf returns the difficulty class of a Cotacol score.
+// CategoryOf returns the difficulty class of a Cotacol score: the category
+// with the highest floor the score reaches.
 func CategoryOf(cotacol float64) Category {
-	best := CategoryHC
-	bestMax := math.Inf(+1)
+	best := CategoryNo
+	bestMin := math.Inf(-1)
+	found := false
 	for category, info := range categories {
-		if cotacol < info.maxScore && info.maxScore < bestMax {
+		if cotacol >= info.minScore && (!found || info.minScore > bestMin) {
 			best = category
-			bestMax = info.maxScore
+			bestMin = info.minScore
+			found = true
 		}
 	}
+	if !found {
+		// NaN reaches no floor; preserve the original switch default (HC).
+		return CategoryHC
+	}
 	return best
 }
 
diff --git a/ride/difficulty_test.go b/ride/difficulty_test.go
index 142ac0a..5773376 100644
--- a/ride/difficulty_test.go
+++ b/ride/difficulty_test.go
@@ -1,6 +1,7 @@
 package ride_test
 
 import (
+	"math"
 	"testing"
 
 	"github.com/martinlehoux/biking_home/ride"
@@ -48,6 +49,32 @@ func TestCotacolClimbNotAtStart(t *testing.T) {
 	assert.InDelta(t, 98.0, climbs[0].DifficultyScore(), 1e-9)
 }
 
+func TestCategoryOfBoundaries(t *testing.T) {
+	cases := []struct {
+		score float64
+		want  ride.Category
+	}{
+		{-5, ride.CategoryNo},
+		{30, ride.CategoryNo},
+		{35, ride.CategoryFour}, // 35 is the first floor, not below it
+		{79, ride.CategoryFour},
+		{80, ride.CategoryThree},
+		{179, ride.CategoryThree},
+		{180, ride.CategoryTwo},
+		{249, ride.CategoryTwo},
+		{250, ride.CategoryOne},
+		{599, ride.CategoryOne},
+		{600, ride.CategoryHC},
+		{700, ride.CategoryHC},
+		{math.NaN(), ride.CategoryHC}, // reaches no floor, like the original switch default
+	}
+	for _, c := range cases {
+		assert.Equal(t, c.want, ride.CategoryOf(c.score), "score %v", c.score)
+	}
+	assert.Equal(t, "Cat 1", ride.CategoryOne.String())
+	assert.Equal(t, "NO", ride.CategoryNo.String())
+}
+
 func TestCotacolHautacamClimbfinderReference(t *testing.T) {
 	r, err := ride.ParseFile(parser, "../examples/2022-07-21.Pogacar.gpx")
 	assert.NoError(t, err)