refactor(ride,rideanalysis): replace magic numbers with named constants

2 files changed, 57 insertions, 18 deletions

diff --git a/ride/climb.go b/ride/climb.go
index 56e47c6..8852cbf 100644
--- a/ride/climb.go
+++ b/ride/climb.go
@@ -13,6 +13,41 @@ import (
 
 const ClimbDistanceMinimum = 500
 
+// Category is the difficulty class of a climb, ordered from easiest to
+// hardest.
+type Category int
+
+const (
+	CategoryNo Category = iota
+	CategoryFour
+	CategoryThree
+	CategoryTwo
+	CategoryOne
+	CategoryHC
+)
+
+type categoryInfo struct {
+	label    string
+	maxScore 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.
+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)},
+}
+
+// climbDetectionMinimumScore is the climb-detection score below which a
+// candidate segment is not reported as a climb.
+const climbDetectionMinimumScore = 35
+
 type Climb struct {
 	ride      Ride
 	rideStart int
@@ -80,7 +115,7 @@ func (climb Climb) String() string {
 	startDistance := climb.StartDistanceM()
 	endDistance := climb.EndDistanceM()
 	cotacol := climb.DifficultyScore()
-	body := fmt.Sprintf("%.1fkm-%.1fkm: %.1fkm at %.1f%% (%d pts - %s)", startDistance/1000, endDistance/1000, (endDistance-startDistance)/1000, Slope(climb.ride, climb.rideStart, climb.rideEnd)*100, int(cotacol), Category(cotacol))
+	body := fmt.Sprintf("%.1fkm-%.1fkm: %.1fkm at %.1f%% (%d pts - %s)", startDistance/1000, endDistance/1000, (endDistance-startDistance)/1000, Slope(climb.ride, climb.rideStart, climb.rideEnd)*100, int(cotacol), CategoryOf(cotacol))
 	if climb.Name == "" {
 		return body
 	}
@@ -105,21 +140,21 @@ func climbDetectionScore(r Ride, start, end int) float64 {
 	return math.Abs(dElevation) * dElevation / distance * 100.0 * 100.0 / 1000.0
 }
 
-func Category(cotacol float64) string {
-	switch {
-	case cotacol < 35:
-		return "NO"
-	case cotacol < 80:
-		return "Cat 4"
-	case cotacol < 180:
-		return "Cat 3"
-	case cotacol < 250:
-		return "Cat 2"
-	case cotacol < 600:
-		return "Cat 1"
-	default:
-		return "HC"
+func (c Category) String() string {
+	return categories[c].label
+}
+
+// CategoryOf returns the difficulty class of a Cotacol score.
+func CategoryOf(cotacol float64) Category {
+	best := CategoryHC
+	bestMax := math.Inf(+1)
+	for category, info := range categories {
+		if cotacol < info.maxScore && info.maxScore < bestMax {
+			best = category
+			bestMax = info.maxScore
+		}
 	}
+	return best
 }
 
 func bestClimbBetween(r Ride, start, end int) Climb {
@@ -170,7 +205,7 @@ func climbsBetween(r Ride, start, end int) []Climb {
 		return climbsBetween(r, start+1, end)
 	}
 	climb := bestClimbBetween(r, start, highest)
-	if climbDetectionScore(r, climb.rideStart, climb.rideEnd) >= 35 && climb.EndDistanceM()-climb.StartDistanceM() >= ClimbDistanceMinimum {
+	if climbDetectionScore(r, climb.rideStart, climb.rideEnd) >= climbDetectionMinimumScore && climb.EndDistanceM()-climb.StartDistanceM() >= ClimbDistanceMinimum {
 		slog.Debug("Found climb between", slog.Int("start", int(climb.StartDistanceM())), slog.Int("end", int(climb.EndDistanceM())))
 		climbs = append(climbs, climb)
 	}
diff --git a/ride/ride.go b/ride/ride.go
index 278880f..a10d8a2 100644
--- a/ride/ride.go
+++ b/ride/ride.go
@@ -230,6 +230,10 @@ func metricValue(point gpx.GPXPoint, name string) (*float64, error) {
 
 const CotacolAlgorithmVersion = "v1"
 
+// cotacolSegmentLengthM is the fixed length of the elevation segments the
+// Cotacol score is computed over.
+const cotacolSegmentLengthM = 100
+
 func Cotacol(ride Ride) float64 {
 	return difficultyScore(ride, 0, ride.Len()-1)
 }
@@ -245,8 +249,8 @@ func difficultyScore(r Ride, startIndex, endIndex int) float64 {
 	}
 	cotacol := 0.0
 	i := startIndex
-	for start := startDistance; start < lastDistance; start += 100 {
-		end := math.Min(start+100, lastDistance)
+	for start := startDistance; start < lastDistance; start += cotacolSegmentLengthM {
+		end := math.Min(start+cotacolSegmentLengthM, lastDistance)
 		for i < endIndex && r.DistanceM(i+1) <= start {
 			i++
 		}