Extract climb detection into a dedicated climb package

Move climb detection, slope, and Cotacol scoring out of ride into a new
climb package that operates on a geometry-only Route (distances, elevations,
coords). Ride embeds climb.Route and keeps its timing and telemetry columns.

- climb.Detect returns []DetectedClimb (Climb + ride-absolute Start).
- Climb owns its sliced geometry; indices are local, with Start reported at
  the detection boundary for absolute position.
- Detected bounds use core.Interval; freeRegions claim suppression fixed.
- ride no longer builds slices: ClimbFromDist/ClimbFromIndexes/climbFrom and
  ride.Climb/Interval/Range are removed; rideanalysis, mountain_pass MatchClimb,
  and web views are rewired to climb types.
- New internal/routetest builds climb.Route from the ride DSL; ridetest reuses
  it and adds timestamps and telemetry.
- Tests moved to climb (synthetic detection and difficulty) and kept in ride
  for GPX-example integration; ride.comparison detection coverage retained.
- mountain_pass.nearestCrossing now reuses geo.Nearest.

6 files changed, 475 insertions, 0 deletions

diff --git a/climb/climb.go b/climb/climb.go
new file mode 100644
index 0000000..2d764dd
--- /dev/null
+++ b/climb/climb.go
@@ -0,0 +1,87 @@
+package climb
+
+import (
+	"fmt"
+	"math"
+)
+
+const (
+	ClimbDistanceMinimum  = 500
+	ClimbSlopeMinimum     = 0.035
+	detectionMinimumScore = 35
+)
+
+type Category int
+
+const (
+	CategoryNo Category = iota
+	CategoryFour
+	CategoryThree
+	CategoryTwo
+	CategoryOne
+	CategoryHC
+)
+
+type categoryInfo struct {
+	label    string
+	minScore float64
+}
+
+var categories = map[Category]categoryInfo{
+	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},
+}
+
+func (c Category) String() string {
+	return categories[c].label
+}
+
+func CategoryOf(cotacol float64) Category {
+	best := CategoryNo
+	bestMin := math.Inf(-1)
+	found := false
+	for category, info := range categories {
+		if cotacol >= info.minScore && (!found || info.minScore > bestMin) {
+			best = category
+			bestMin = info.minScore
+			found = true
+		}
+	}
+	if !found {
+		// NaN reaches no floor; preserve the original switch default (HC).
+		return CategoryHC
+	}
+	return best
+}
+
+type Climb struct {
+	Route
+}
+
+func (climb Climb) String() string {
+	cotacol := climb.DifficultyScore()
+	return fmt.Sprintf("%.1fkm at %.1f%% (%d pts - %s)", climb.Distances[len(climb.Distances)-1]/1000, Slope(climb.Distances, climb.Elevations)*100, int(cotacol), CategoryOf(cotacol))
+}
+
+func (climb Climb) DifficultyScore() float64 {
+	return Cotacol(climb.Distances, climb.Elevations)
+}
+
+func (climb Climb) Top() (int, float64) {
+	top := 0
+	for i := 1; i < len(climb.Elevations); i++ {
+		if climb.Elevations[i] > climb.Elevations[top] {
+			top = i
+		}
+	}
+	return top, climb.Elevations[top]
+}
+
+func Slope(distances, elevations []float64) float64 {
+	end := len(distances) - 1
+	return (elevations[end] - elevations[0]) / (distances[end] - distances[0])
+}
diff --git a/climb/cotacol.go b/climb/cotacol.go
new file mode 100644
index 0000000..85b096b
--- /dev/null
+++ b/climb/cotacol.go
@@ -0,0 +1,48 @@
+package climb
+
+import "math"
+
+const (
+	CotacolAlgorithmVersion = "v1"
+	cotacolSegmentLengthM   = 100
+)
+
+func Cotacol(distances, elevations []float64) float64 {
+	startIndex, endIndex := 0, len(distances)-1
+	if endIndex-startIndex < 1 {
+		return 0
+	}
+	startDistance := distances[startIndex]
+	lastDistance := distances[endIndex]
+	if lastDistance <= startDistance {
+		return 0
+	}
+	cotacol := 0.0
+	i := startIndex
+	for start := startDistance; start < lastDistance; start += cotacolSegmentLengthM {
+		end := math.Min(start+cotacolSegmentLengthM, lastDistance)
+		for i < endIndex && distances[i+1] <= start {
+			i++
+		}
+		startElevation := interpolateElevation(distances, elevations, i, start)
+		for i < endIndex && distances[i+1] < end {
+			i++
+		}
+		endElevation := interpolateElevation(distances, elevations, i, end)
+		slope := (endElevation - startElevation) / (end - start)
+		if slope > 0 {
+			cotacol += (end - start) / 1000 * (slope * 100) * (slope * 100)
+		}
+	}
+	return cotacol
+}
+
+func interpolateElevation(distances, elevations []float64, i int, distance float64) float64 {
+	if i+1 >= len(distances) {
+		return elevations[i]
+	}
+	startDistance := distances[i]
+	endDistance := distances[i+1]
+	t := (distance - startDistance) / (endDistance - startDistance)
+	return elevations[i] + t*(elevations[i+1]-elevations[i])
+}
diff --git a/climb/detection.go b/climb/detection.go
new file mode 100644
index 0000000..1efe1c5
--- /dev/null
+++ b/climb/detection.go
@@ -0,0 +1,175 @@
+package climb
+
+import (
+	"log/slog"
+	"math"
+	"slices"
+
+	"github.com/martinlehoux/biking_home/core"
+	"github.com/martinlehoux/kagamigo/kcore"
+)
+
+type DetectedClimb struct {
+	Climb Climb
+	Start int
+}
+
+// returns the detected climbs but never a climb that overlaps a claimed range.
+func Detect(route Route, claimed []core.Interval, minSlope float64) []DetectedClimb {
+	distances, elevations, coords := route.Distances, route.Elevations, route.Coords
+	bounds := make([]core.Interval, 0)
+	for _, region := range freeRegions(0, len(distances)-1, claimed) {
+		bounds = append(bounds, climbsBetween(distances, elevations, core.NewInterval(region.Start, region.End), minSlope)...)
+	}
+	slices.SortFunc(bounds, func(a, b core.Interval) int { return a.Start - b.Start })
+	climbs := make([]DetectedClimb, 0, len(bounds))
+	for _, b := range bounds {
+		climbs = append(climbs, DetectedClimb{
+			Climb: Climb{Route: Route{
+				Distances:  distances[b.Start : b.End+1],
+				Elevations: elevations[b.Start : b.End+1],
+				Coords:     coords[b.Start : b.End+1],
+			}},
+			Start: b.Start,
+		})
+	}
+	return climbs
+}
+
+// freeRegions returns the maximal sub-ranges of [rStart, rEnd] that are not
+// covered by any claimed range, after discarding claims that fall outside.
+func freeRegions(rStart, rEnd int, claimed []core.Interval) []core.Interval {
+	valid := make([]core.Interval, 0, len(claimed))
+	for _, claim := range claimed {
+		// Discard claims outside the route or with a degenerate range.
+		if claim.Start < 0 || claim.End >= rEnd+1 || claim.Start >= claim.End {
+			continue
+		}
+		valid = append(valid, claim)
+	}
+	slices.SortFunc(valid, func(a, b core.Interval) int { return a.Start - b.Start })
+	regions := make([]core.Interval, 0, len(valid)+1)
+	current := rStart
+	for _, claim := range valid {
+		if claim.End < current {
+			continue
+		}
+		if claim.Start > current {
+			regions = append(regions, core.NewInterval(current, claim.Start-1))
+		}
+		if claim.End+1 > current {
+			current = claim.End + 1
+		}
+	}
+	if current <= rEnd {
+		regions = append(regions, core.NewInterval(current, rEnd))
+	}
+	return regions
+}
+
+// climbsBetween returns the detected climb bounds inside bounds from the
+// distance and elevation components.
+func climbsBetween(distances, elevations []float64, bounds core.Interval, minSlope float64) []core.Interval {
+	start, end := bounds.Start, bounds.End
+	climbs := []core.Interval{}
+	if distances[end]-distances[start] < ClimbDistanceMinimum {
+		return climbs
+	}
+	slog.Debug("Searching climbs between", slog.Int("start", int(distances[start])), slog.Int("end", int(distances[end])))
+	highest := start
+	for i := start; i <= end; i++ {
+		if elevations[i] > elevations[highest] {
+			highest = i
+		}
+	}
+	// TODO: Use descent to reduce recursion
+	if distances[highest]-distances[start] < ClimbDistanceMinimum {
+		return climbsBetween(distances, elevations, core.NewInterval(start+1, end), minSlope)
+	}
+	climb, found := bestClimbBetween(distances[start:highest+1], elevations[start:highest+1], minSlope)
+	if !found {
+		// No qualifying climb up to the top; only the part past it can hold climbs.
+		return climbsBetween(distances, elevations, core.NewInterval(highest, end), minSlope)
+	}
+	// bestClimbBetween returns an interval relative to its sliced input;
+	// re-anchor it into this slice's index space.
+	climbStart := start + climb.Start
+	climbEnd := start + climb.End
+	if climbDetectionScore(distances[climbStart:climbEnd+1], elevations[climbStart:climbEnd+1]) >= detectionMinimumScore && distances[climbEnd]-distances[climbStart] >= ClimbDistanceMinimum {
+		slog.Debug("Found climb between", slog.Int("start", int(distances[climbStart])), slog.Int("end", int(distances[climbEnd])))
+		climbs = append(climbs, core.NewInterval(climbStart, climbEnd))
+	}
+	climbs = append(climbs, climbsBetween(distances, elevations, core.NewInterval(start, climbStart), minSlope)...)
+	climbs = append(climbs, climbsBetween(distances, elevations, core.NewInterval(climbEnd, end), minSlope)...)
+
+	return climbs
+}
+
+func climbDetectionScore(distances, elevations []float64) float64 {
+	kcore.Assert(len(distances) > 0, "no points for climb detection")
+	end := len(distances) - 1
+	distance := distances[end] - distances[0]
+	if distance == 0 {
+		return 0
+	}
+	dElevation := elevations[end] - elevations[0]
+	return math.Abs(dElevation) * dElevation / distance * 100.0 * 100.0 / 1000.0
+}
+
+// bestClimbBetween returns the highest-scoring sub-interval of the segment
+// given by [0, len-1]; when that climb averages below minSlope, it instead
+// returns the best qualifying sub-segment (found=false when none exists). The
+// returned interval is relative to the start of the given (already sliced)
+// slices; callers add back their offset to recover absolute indices.
+func bestClimbBetween(distances, elevations []float64, minSlope float64) (core.Interval, bool) {
+	end := len(distances) - 1
+	kcore.Assert(end > 0, "empty points")
+
+	bestDetectionScore := climbDetectionScore(distances, elevations)
+	best := core.NewInterval(0, end)
+	for i := 0; i < end; i++ {
+		detectionScore := climbDetectionScore(distances[i:end], elevations[i:end])
+		if detectionScore > bestDetectionScore {
+			best.Start = i
+			bestDetectionScore = detectionScore
+		}
+	}
+	for i := end; i > best.Start; i-- {
+		detectionScore := climbDetectionScore(distances[best.Start:i+1], elevations[best.Start:i+1])
+		if detectionScore > bestDetectionScore {
+			best.End = i
+			bestDetectionScore = detectionScore
+		}
+	}
+	for i := best.Start; i < best.End; i++ {
+		detectionScore := climbDetectionScore(distances[i:best.End], elevations[i:best.End])
+		if detectionScore > bestDetectionScore {
+			best.Start = i
+			bestDetectionScore = detectionScore
+		}
+	}
+	kcore.Assert(best.Start < best.End, "empty climb")
+	if minSlope <= 0 || Slope(distances[best.Start:best.End+1], elevations[best.Start:best.End+1]) >= minSlope {
+		return best, true
+	}
+	// Classic best too gentle: re-segment into the best qualifying sub-segment.
+	bestDetectionScore = math.Inf(-1)
+	best = core.NewInterval(-1, -1)
+	for i := 0; i < end; i++ {
+		for j := i + 1; j <= end; j++ {
+			if Slope(distances[i:j+1], elevations[i:j+1]) < minSlope {
+				continue
+			}
+			detectionScore := climbDetectionScore(distances[i:j+1], elevations[i:j+1])
+			if detectionScore > bestDetectionScore {
+				bestDetectionScore = detectionScore
+				best.Start = i
+				best.End = j
+			}
+		}
+	}
+	if best.Start < 0 {
+		return core.Interval{}, false
+	}
+	return best, true
+}
diff --git a/climb/detection_test.go b/climb/detection_test.go
new file mode 100644
index 0000000..3c6a33b
--- /dev/null
+++ b/climb/detection_test.go
@@ -0,0 +1,84 @@
+package climb_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/martinlehoux/biking_home/climb"
+	"github.com/martinlehoux/biking_home/core"
+	"github.com/martinlehoux/biking_home/internal/routetest"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// describe renders a detected climb as the ride-style
+// "start-end: length at slope (pts - cat)" string, so positions are asserted.
+func describe(route climb.Route, detected climb.DetectedClimb) string {
+	seg := detected.Climb
+	startKm := route.Distances[detected.Start] / 1000
+	endKm := route.Distances[detected.Start+len(seg.Distances)-1] / 1000
+	lengthKm := (seg.Distances[len(seg.Distances)-1] - seg.Distances[0]) / 1000
+	slopePercent := climb.Slope(seg.Distances, seg.Elevations) * 100
+	pts := int(seg.DifficultyScore())
+	return fmt.Sprintf("%.1fkm-%.1fkm: %.1fkm at %.1f%% (%d pts - %s)", startKm, endKm, lengthKm, slopePercent, pts, climb.CategoryOf(seg.DifficultyScore()))
+}
+
+func TestClimbThenFalseFlat(t *testing.T) {
+	route := routetest.MustRoute("2km at 7% | 10km at 1%")
+	detected := climb.Detect(route, nil, climb.ClimbSlopeMinimum)
+
+	assert.Len(t, detected, 1)
+	assert.Equal(t, "0.0km-2.0km: 2.0km at 7.0% (98 pts - Cat 3)", describe(route, detected[0]))
+}
+
+func TestSmallClimbWithDescentInsideFalseFlat(t *testing.T) {
+	route := routetest.MustRoute("10km at 1% | 2km at 7% | 1km at -7% | 10km at 1%")
+	detected := climb.Detect(route, nil, climb.ClimbSlopeMinimum)
+
+	assert.Len(t, detected, 1)
+	assert.Equal(t, "10.0km-12.0km: 2.0km at 7.0% (98 pts - Cat 3)", describe(route, detected[0]))
+}
+
+func TestDetectClimbsSkipsMiddleClaim(t *testing.T) {
+	// A climb, a false flat giving a saddle, then a climb again. Claiming the
+	// saddle's descent base should leave both climbs detected separately.
+	route := routetest.MustRoute("2km at 7% | 1km at -7% | 2km at 7%")
+	detected := climb.Detect(route, []core.Interval{core.NewInterval(20, 20)}, climb.ClimbSlopeMinimum)
+
+	// No free region falls under the min distance except the two climbs.
+	assert.Len(t, detected, 2)
+	assert.Equal(t, "0.0km-2.0km: 2.0km at 7.0% (98 pts - Cat 3)", describe(route, detected[0]))
+	assert.Equal(t, "3.0km-5.0km: 2.0km at 7.0% (98 pts - Cat 3)", describe(route, detected[1]))
+}
+
+func TestDetectClimbsOverlappingClaimDropsClimb(t *testing.T) {
+	// Claiming the ascent region entirely swallows the climb.
+	route := routetest.MustRoute("2km at 7% | 20km at 0%")
+	detected := climb.Detect(route, []core.Interval{core.NewInterval(0, 40)}, climb.ClimbSlopeMinimum)
+	assert.Empty(t, detected)
+}
+
+func TestDetectClimbsIgnoresOutOfRangeClaim(t *testing.T) {
+	route := routetest.MustRoute("2km at 7% | 20km at 0%")
+	detected := climb.Detect(route, []core.Interval{core.NewInterval(-5, -1)}, climb.ClimbSlopeMinimum)
+	require.Len(t, detected, 1)
+	assert.Equal(t, "0.0km-2.0km: 2.0km at 7.0% (98 pts - Cat 3)", describe(route, detected[0]))
+}
+
+func TestDetectClimbsWithUnsortedClaimsDropsOverlappingClimb(t *testing.T) {
+	// Reproduces ride 6 Chemin des Lauriers bug: Detect must not depend on
+	// caller-provided order. Two official claims out of ID order (Bastides
+	// 2140-2627 before Lauriers 1215-1588) caused freeRegions to skip the
+	// earlier claim and leave the overlapping Cat 4 1352-1601 visible.
+	// Minimal reproduction: two climbs 0-2km and 3-5km separated by a descent.
+	route := routetest.MustRoute("2km at 7% | 1km at -7% | 2km at 7%")
+	// Both climbs claimed, but in reverse order (mimics ORDER BY id returning 30-50 before 0-20).
+	// Sorted input correctly yields 0 detected climbs.
+	sorted := []core.Interval{core.NewInterval(0, 20), core.NewInterval(30, 50)}
+	assert.Empty(t, climb.Detect(route, sorted, climb.ClimbSlopeMinimum))
+
+	unsorted := []core.Interval{core.NewInterval(30, 50), core.NewInterval(0, 20)}
+	detected := climb.Detect(route, unsorted, climb.ClimbSlopeMinimum)
+	// Before fix this fails: freeRegions skips {0,20} because 20 < 30 and returns 1 climb.
+	assert.Empty(t, detected, "unsorted claimed ranges must still suppress overlapping climbs — expected 0, got %v", detected)
+}
diff --git a/climb/difficulty_test.go b/climb/difficulty_test.go
new file mode 100644
index 0000000..92c0a74
--- /dev/null
+++ b/climb/difficulty_test.go
@@ -0,0 +1,72 @@
+package climb_test
+
+import (
+	"math"
+	"testing"
+
+	"github.com/martinlehoux/biking_home/climb"
+	"github.com/martinlehoux/biking_home/internal/routetest"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCotacolConstantClimb(t *testing.T) {
+	route := routetest.MustRoute("2km at 7%")
+	assert.InDelta(t, 98.0, climb.Cotacol(route.Distances, route.Elevations), 1e-9)
+}
+
+func TestCotacolIgnoresDescent(t *testing.T) {
+	route := routetest.MustRoute("2km at 7% | 2km at -7%")
+	assert.InDelta(t, 98.0, climb.Cotacol(route.Distances, route.Elevations), 1e-9)
+}
+
+func TestCotacolFlatIsZero(t *testing.T) {
+	route := routetest.MustRoute("5km at 0%")
+	assert.Zero(t, climb.Cotacol(route.Distances, route.Elevations))
+}
+
+func TestCotacolSteepShortCountsMore(t *testing.T) {
+	steep := routetest.MustRoute("0.5km at 14%")
+	long := routetest.MustRoute("1km at 7%")
+	assert.InDelta(t, 98.0, climb.Cotacol(steep.Distances, steep.Elevations), 1e-9)
+	assert.InDelta(t, 49.0, climb.Cotacol(long.Distances, long.Elevations), 1e-9)
+}
+
+func TestCotacolPrecisionInvariant(t *testing.T) {
+	coarse := routetest.MustRoute("3km at 5%")
+	fine := routetest.MustRoute("3km at 5%", routetest.Sampling(50))
+	assert.InDelta(t, climb.Cotacol(coarse.Distances, coarse.Elevations), climb.Cotacol(fine.Distances, fine.Elevations), 1e-9)
+}
+
+func TestCotacolClimbNotAtStart(t *testing.T) {
+	route := routetest.MustRoute("1km at 0% | 2km at 7%")
+	detected := climb.Detect(route, nil, climb.ClimbSlopeMinimum)
+	assert.Len(t, detected, 1)
+	assert.InDelta(t, 98.0, detected[0].Climb.DifficultyScore(), 1e-9)
+}
+
+func TestCategoryOfBoundaries(t *testing.T) {
+	cases := []struct {
+		score float64
+		want  climb.Category
+	}{
+		{-5, climb.CategoryNo},
+		{30, climb.CategoryNo},
+		{35, climb.CategoryFour}, // 35 is the first floor, not below it
+		{79, climb.CategoryFour},
+		{80, climb.CategoryThree},
+		{179, climb.CategoryThree},
+		{180, climb.CategoryTwo},
+		{249, climb.CategoryTwo},
+		{250, climb.CategoryOne},
+		{599, climb.CategoryOne},
+		{600, climb.CategoryHC},
+		{700, climb.CategoryHC},
+		{math.NaN(), climb.CategoryHC}, // reaches no floor, like the original switch default
+	}
+
+	for _, c := range cases {
+		assert.Equal(t, c.want, climb.CategoryOf(c.score), "score %v", c.score)
+	}
+	assert.Equal(t, "Cat 1", climb.CategoryOne.String())
+	assert.Equal(t, "NO", climb.CategoryNo.String())
+}
diff --git a/climb/route.go b/climb/route.go
new file mode 100644
index 0000000..80a9a43
--- /dev/null
+++ b/climb/route.go
@@ -0,0 +1,9 @@
+package climb
+
+import "github.com/jftuga/geodist"
+
+type Route struct {
+	Distances  []float64
+	Elevations []float64
+	Coords     []geodist.Coord
+}