package ride

import (
	"fmt"
	"log/slog"
	"math"
	"slices"
	"time"

	"github.com/jftuga/geodist"
	"github.com/martinlehoux/kagamigo/kcore"
)

const ClimbDistanceMinimum = 500

// ClimbSlopeMinimum is the minimum average slope (ratio) of a detected climb;
// gentler regions are re-segmented into their qualifying steeper parts.
const ClimbSlopeMinimum = 0.035

// 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
	minScore float64
}

// 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", 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
// candidate segment is not reported as a climb.
const climbDetectionMinimumScore = 35

type Climb struct {
	distances  []float64
	elevations []float64
	coords     []geodist.Coord
	timestamps []time.Time
	rideStart  int
	rideEnd    int
	Name       string
}

func (climb Climb) Duration() time.Duration {
	return climb.timestamps[climb.rideEnd].Sub(climb.timestamps[climb.rideStart])
}

func (climb Climb) Speed() float64 {
	return (climb.EndDistanceM() - climb.StartDistanceM()) / climb.Duration().Seconds()
}

func (climb Climb) StartIndex() int { return climb.rideStart }

func (climb Climb) EndIndex() int { return climb.rideEnd }

func (climb Climb) StartDistanceM() float64 {
	return climb.distances[climb.rideStart]
}

func (climb Climb) EndDistanceM() float64 {
	return climb.distances[climb.rideEnd]
}

func (climb Climb) StartCoord() geodist.Coord {
	return climb.coords[climb.rideStart]
}

func (climb Climb) EndCoord() geodist.Coord {
	return climb.coords[climb.rideEnd]
}

func (climb Climb) PointCoord(index int) geodist.Coord {
	kcore.Assert(index >= climb.rideStart && index <= climb.rideEnd, "point is outside climb")
	return climb.coords[index]
}

// TopIndex returns the highest point inside the climb, used as the crest anchor.
func (climb Climb) TopIndex() int {
	top := climb.rideStart
	for i := climb.rideStart; i <= climb.rideEnd; i++ {
		if climb.elevations[i] > climb.elevations[top] {
			top = i
		}
	}
	return top
}

func (climb Climb) TopDistanceM() float64 {
	return climb.distances[climb.TopIndex()]
}

func (climb Climb) TopElevationM() float64 {
	return climb.elevations[climb.TopIndex()]
}

func (climb Climb) TopCoord() geodist.Coord {
	return climb.coords[climb.TopIndex()]
}

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.distances, climb.elevations, climb.rideStart, climb.rideEnd)*100, int(cotacol), CategoryOf(cotacol))
	if climb.Name == "" {
		return body
	}
	return climb.Name + ": " + body
}

func (climb Climb) DifficultyScore() float64 {
	return difficultyScore(climb.distances, climb.elevations, climb.rideStart, climb.rideEnd)
}

func Slope(distances, elevations []float64, start, end int) float64 {
	return (elevations[end] - elevations[start]) / (distances[end] - distances[start])
}

func climbDetectionScore(distances, elevations []float64, start, end int) float64 {
	kcore.Assert(end > start, "no points for climb detection")
	distance := distances[end] - distances[start]
	if distance == 0 {
		return 0
	}
	dElevation := elevations[end] - elevations[start]
	return math.Abs(dElevation) * dElevation / distance * 100.0 * 100.0 / 1000.0
}

func (c Category) String() string {
	return categories[c].label
}

// CategoryOf returns the difficulty class of a Cotacol score: the category
// with the highest floor the score reaches.
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 interval struct {
	start int
	end   int
}

// bestClimbBetween returns the highest-scoring climb in [start, end]; when
// that climb averages below minSlope, it instead returns the best qualifying
// sub-segment (found=false when none exists).
func bestClimbBetween(distances, elevations []float64, start, end int, minSlope float64) (interval, bool) {
	kcore.Assert(end > start, "empty points")

	bestDetectionScore := climbDetectionScore(distances, elevations, start, end)
	bestStart := start
	for i := start; i < end; i++ {
		detectionScore := climbDetectionScore(distances, elevations, i, end)
		if detectionScore > bestDetectionScore {
			bestStart = i
			bestDetectionScore = detectionScore
		}
	}
	bestEnd := end
	for i := end; i > bestStart; i-- {
		detectionScore := climbDetectionScore(distances, elevations, bestStart, i)
		if detectionScore > bestDetectionScore {
			bestEnd = i
			bestDetectionScore = detectionScore
		}
	}
	for i := bestStart; i < bestEnd; i++ {
		detectionScore := climbDetectionScore(distances, elevations, i, bestEnd)
		if detectionScore > bestDetectionScore {
			bestStart = i
			bestDetectionScore = detectionScore
		}
	}
	kcore.Assert(bestStart < bestEnd, "empty climb")
	if minSlope <= 0 || Slope(distances, elevations, bestStart, bestEnd) >= minSlope {
		return interval{bestStart, bestEnd}, true
	}
	// Classic best too gentle: re-segment into the best qualifying sub-segment.
	bestDetectionScore = math.Inf(-1)
	bestStart, bestEnd = -1, -1
	for i := start; i < end; i++ {
		for j := i + 1; j <= end; j++ {
			if Slope(distances, elevations, i, j) < minSlope {
				continue
			}
			detectionScore := climbDetectionScore(distances, elevations, i, j)
			if detectionScore > bestDetectionScore {
				bestDetectionScore = detectionScore
				bestStart, bestEnd = i, j
			}
		}
	}
	if bestStart < 0 {
		return interval{}, false
	}
	return interval{bestStart, bestEnd}, true
}

// climbsBetween returns the detected climb bounds in [start, end] from the
// distance and elevation components.
func climbsBetween(distances, elevations []float64, start, end int, minSlope float64) []interval {
	climbs := []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, start+1, end, minSlope)
	}
	climb, found := bestClimbBetween(distances, elevations, start, highest, minSlope)
	if !found {
		// No qualifying climb up to the top; only the part past it can hold climbs.
		return climbsBetween(distances, elevations, highest, end, minSlope)
	}
	if climbDetectionScore(distances, elevations, climb.start, climb.end) >= climbDetectionMinimumScore && distances[climb.end]-distances[climb.start] >= ClimbDistanceMinimum {
		slog.Debug("Found climb between", slog.Int("start", int(distances[climb.start])), slog.Int("end", int(distances[climb.end])))
		climbs = append(climbs, climb)
	}
	climbs = append(climbs, climbsBetween(distances, elevations, start, climb.start, minSlope)...)
	climbs = append(climbs, climbsBetween(distances, elevations, climb.end, end, minSlope)...)

	return climbs
}

type Range struct {
	Start int
	End   int
}

func isValidClaim(claim Range, routeLen int) bool {
	return claim.Start >= 0 && claim.End < routeLen && claim.Start < claim.End
}

// 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 []Range) []Range {
	valid := make([]Range, 0, len(claimed))
	for _, claim := range claimed {
		if !isValidClaim(claim, rEnd+1) {
			continue
		}
		valid = append(valid, claim)
	}
	slices.SortFunc(valid, func(a, b Range) int { return a.Start - b.Start })
	regions := make([]Range, 0, len(valid)+1)
	current := rStart
	for _, claim := range valid {
		if claim.End < current {
			continue
		}
		if claim.Start > current {
			regions = append(regions, Range{Start: current, End: claim.Start - 1})
		}
		if claim.End+1 > current {
			current = claim.End + 1
		}
	}
	if current <= rEnd {
		regions = append(regions, Range{Start: current, End: rEnd})
	}
	return regions
}

// returns the detected climbs of the whole ride, but never a climb that overlaps
// a claimed range.
func (ride *Ride) DetectClimbs(claimed []Range, minSlope float64) []Climb {
	bounds := make([]interval, 0)
	for _, region := range freeRegions(0, ride.Len()-1, claimed) {
		bounds = append(bounds, climbsBetween(ride.distances, ride.elevations, region.Start, region.End, minSlope)...)
	}
	slices.SortFunc(bounds, func(a, b interval) int { return a.start - b.start })
	climbs := make([]Climb, 0, len(bounds))
	for _, b := range bounds {
		climbs = append(climbs, climbFromBounds(ride, b))
	}
	return climbs
}

func climbFromBounds(ride *Ride, b interval) Climb {
	return Climb{
		distances:  ride.distances,
		elevations: ride.elevations,
		coords:     ride.coords,
		timestamps: ride.timestamps,
		rideStart:  b.start,
		rideEnd:    b.end,
	}
}