Cut climb profile sections in the backend

The chart steps are computed in Go and shipped as finished sections, next to
the profile statistics the climb package already owns: climb.ProfileSections
cuts a Route at its widest bends under a ProfilePolicy, and
rideanalysis.MergeClimbProfile takes over the merge that lived in
web/climbs.go, so web only loads the attempt rides and maps the DTOs.

The payload carries sections instead of raw elevations, and the browser keeps
what needs the canvas: slope bands, labels, distance ticks and colours.
official-climb-profile-logic.ts and its tests are gone, replaced by
climb/profile_test.go and a page test reading the embedded profile JSON.

1 files changed, 113 insertions, 0 deletions

diff --git a/climb/profile_test.go b/climb/profile_test.go
new file mode 100644
index 0000000..1342916
--- /dev/null
+++ b/climb/profile_test.go
@@ -0,0 +1,113 @@
+package climb
+
+import (
+	"math"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// stretch describes one [lengthM, slopePercent] stretch of the buildProfile trace.
+type stretch struct {
+	lengthM      float64
+	slopePercent float64
+}
+
+// buildProfile lays out one recorded point every 50 m along the given stretches.
+func buildProfile(stretches ...stretch) Route {
+	route := Route{Distances: []float64{0}, Elevations: []float64{0}}
+	distanceM, elevationM := 0.0, 0.0
+	for _, stretch := range stretches {
+		pointCount := int(math.Round(stretch.lengthM / 50))
+		for index := 1; index <= pointCount; index++ {
+			stepM := stretch.lengthM * float64(index) / float64(pointCount)
+			route.Distances = append(route.Distances, distanceM+stepM)
+			route.Elevations = append(route.Elevations, elevationM+stepM*stretch.slopePercent/100)
+		}
+		distanceM += stretch.lengthM
+		elevationM += stretch.lengthM * stretch.slopePercent / 100
+	}
+	return route
+}
+
+func TestProfileSectionsKeepsShortRamp(t *testing.T) {
+	route := buildProfile(stretch{300, 4}, stretch{300, 12}, stretch{300, 4})
+
+	sections := route.ProfileSections(DefaultProfilePolicy())
+
+	require.Len(t, sections, 3)
+	assert.InDelta(t, 4, sections[0].SlopePercent, 0.01)
+	assert.InDelta(t, 12, sections[1].SlopePercent, 0.01)
+	assert.InDelta(t, 4, sections[2].SlopePercent, 0.01)
+	assert.InDelta(t, 300, sections[1].EndDistanceM-sections[1].StartDistanceM, 0.01)
+}
+
+func TestProfileSectionsCollapsesConstantSlope(t *testing.T) {
+	route := buildProfile(stretch{5000, 6})
+
+	sections := route.ProfileSections(DefaultProfilePolicy())
+
+	require.Len(t, sections, 1)
+	assert.InDelta(t, 6, sections[0].SlopePercent, 0.01)
+	assert.Zero(t, sections[0].StartDistanceM)
+	assert.InDelta(t, 5000, sections[0].EndDistanceM, 0.01)
+}
+
+func TestProfileSectionsReportsDescent(t *testing.T) {
+	route := buildProfile(stretch{2000, -5})
+
+	sections := route.ProfileSections(DefaultProfilePolicy())
+
+	require.Len(t, sections, 1)
+	assert.InDelta(t, -5, sections[0].SlopePercent, 0.01)
+}
+
+func TestProfileSectionsHonoursBudget(t *testing.T) {
+	route := Route{}
+	for index := 0; index <= 200; index++ {
+		distanceM := float64(index) * 50
+		route.Distances = append(route.Distances, distanceM)
+		route.Elevations = append(route.Elevations, distanceM*0.05+math.Sin(float64(index))*4)
+	}
+
+	sections := route.ProfileSections(DefaultProfilePolicy())
+
+	assert.Greater(t, len(sections), 10)
+	assert.LessOrEqual(t, len(sections), DefaultProfilePolicy().MaxSections)
+
+	budgeted := route.ProfileSections(ProfilePolicy{MaxSections: 5, MinBendM: 1, BendPerBaseStep: 0.01})
+	assert.LessOrEqual(t, len(budgeted), 5)
+}
+
+func TestProfileSectionsKeepsAbsoluteDistances(t *testing.T) {
+	route := buildProfile(stretch{2000, 8})
+	for index := range route.Distances {
+		route.Distances[index] += 5000
+	}
+
+	sections := route.ProfileSections(DefaultProfilePolicy())
+
+	require.Len(t, sections, 1)
+	assert.InDelta(t, 5000, sections[0].StartDistanceM, 0.01)
+	assert.InDelta(t, 7000, sections[0].EndDistanceM, 0.01)
+}
+
+func TestProfileSectionsReadsRouteSlice(t *testing.T) {
+	route := buildProfile(stretch{1000, 20}, stretch{1000, 8}, stretch{1000, 20})
+	start := 20
+	end := 40
+
+	sections := route.Slice(start, end).ProfileSections(DefaultProfilePolicy())
+
+	require.Len(t, sections, 1)
+	assert.InDelta(t, 8, sections[0].SlopePercent, 0.01)
+	assert.InDelta(t, route.Distances[start], sections[0].StartDistanceM, 0.01)
+	assert.InDelta(t, route.Distances[end], sections[0].EndDistanceM, 0.01)
+}
+
+func TestProfileSectionsRejectsShortRoute(t *testing.T) {
+	assert.Nil(t, Route{}.ProfileSections(DefaultProfilePolicy()))
+	assert.Nil(t, Route{Distances: []float64{0}, Elevations: []float64{0}}.ProfileSections(DefaultProfilePolicy()))
+	assert.Nil(t, Route{Distances: []float64{0, 10}, Elevations: []float64{0}}.ProfileSections(DefaultProfilePolicy()))
+}