// Package coach decides which workouts the weather allows. The scoring is
// plain rules so the numbers are always right; the language model only
// explains the result and fills in the workout itself.
package coach

import (
	"fmt"
	"math"
	"slices"
	"time"

	"git.b0b.be/bdeb/workout-suggester/internal/routes"
	"git.b0b.be/bdeb/workout-suggester/internal/weather"
)

// Activity is something to do.
type Activity string

const (
	Any    Activity = ""
	Run    Activity = "run"
	Ride   Activity = "ride"
	Walk   Activity = "walk"
	Indoor Activity = "indoor"
)

// Outdoor lists the activities we score against the weather.
var Outdoor = []Activity{Run, Ride, Walk}

// Label is a human name with an emoji.
func (a Activity) Label() string {
	switch a {
	case Run:
		return "🏃 Run"
	case Ride:
		return "🚴 Ride"
	case Walk:
		return "🥾 Walk / hike"
	case Indoor:
		return "🏠 Indoor workout"
	}
	return "✨ Surprise me"
}

// Noun is the activity as a word for prompts.
func (a Activity) Noun() string {
	switch a {
	case Run:
		return "running"
	case Ride:
		return "cycling"
	case Walk:
		return "walking/hiking"
	case Indoor:
		return "an indoor workout (HIIT, bodyweight or gym)"
	}
	return "anything"
}

// RouteKind is the kind of signposted route that suits the activity.
func (a Activity) RouteKind() routes.Kind {
	if a == Ride {
		return routes.Bike
	}
	return routes.Foot
}

// Intensity is how hard the user wants to go.
type Intensity string

const (
	Easy     Intensity = "easy"
	Moderate Intensity = "moderate"
	Hard     Intensity = "hard"
)

// Request is what the user asked for.
type Request struct {
	Activity  Activity
	Intensity Intensity
	Minutes   int
	Note      string
}

// Score is how good the weather is for an activity, 0–100, with the reasons
// points were taken off.
type Score struct {
	Activity Activity
	Value    int
	Reasons  []string
}

// Verdict buckets a score.
func (s Score) Verdict() string {
	switch {
	case s.Value >= 75:
		return "great"
	case s.Value >= 50:
		return "fine"
	case s.Value >= 30:
		return "meh"
	}
	return "no"
}

// Later is a noticeably better window later today.
type Later struct {
	Start    time.Time
	Activity Activity
	Score    int
}

// Assessment is the full verdict for a request.
type Assessment struct {
	Scores   []Score // now, one per outdoor activity
	Pick     Activity
	Later    *Later
	TargetKm float64 // 0 for indoor
	Pace     string
}

// IndoorBelow is the best outdoor score under which we send people inside.
const IndoorBelow = 40

// Assess scores every outdoor activity for the user's time window and picks one.
func Assess(f weather.Forecast, req Request) Assessment {
	n := windowHours(f, req.Minutes)
	now := f.Hours[:min(n, len(f.Hours))]
	var a Assessment
	for _, act := range Outdoor {
		a.Scores = append(a.Scores, score(act, now))
	}
	a.Pick = pick(a.Scores, req)
	a.Later = later(f, req, n, a.Scores)
	a.TargetKm, a.Pace = target(a.Pick, req.Intensity, req.Minutes)
	return a
}

// ScoreOf returns the score for one activity.
func (a Assessment) ScoreOf(act Activity) Score {
	for _, s := range a.Scores {
		if s.Activity == act {
			return s
		}
	}
	return Score{Activity: act}
}

func windowHours(f weather.Forecast, minutes int) int {
	return max(1, int(math.Ceil(float64(f.Now.Time.Minute()+minutes)/60)))
}

func pick(scores []Score, req Request) Activity {
	if req.Activity == Indoor {
		return Indoor
	}
	byAct := map[Activity]int{}
	for _, s := range scores {
		byAct[s.Activity] = s.Value
	}
	if req.Activity != Any && byAct[req.Activity] >= 50 {
		return req.Activity
	}
	best, bestV := Indoor, -1
	for _, act := range Outdoor {
		v := byAct[act]
		if act == Walk { // a stroll is an easy workout
			v += map[Intensity]int{Easy: 5, Moderate: -10, Hard: -20}[req.Intensity]
		}
		if v > bestV {
			best, bestV = act, v
		}
	}
	if byAct[best] < IndoorBelow {
		return Indoor
	}
	return best
}

// later looks up to 12 hours ahead for a daylight window that is clearly
// better than now for the picked (or wanted) activity.
func later(f weather.Forecast, req Request, n int, nowScores []Score) *Later {
	acts := Outdoor
	if req.Activity != Any && req.Activity != Indoor {
		acts = []Activity{req.Activity}
	}
	bestNow := 0
	for _, s := range nowScores {
		if slices.Contains(acts, s.Activity) {
			bestNow = max(bestNow, s.Value)
		}
	}
	if bestNow >= 75 {
		return nil
	}
	for start := 1; start <= 12 && start+n <= len(f.Hours); start++ {
		win := f.Hours[start : start+n]
		if !win[0].IsDay {
			continue
		}
		for _, act := range acts {
			s := score(act, win)
			if s.Value >= 60 && s.Value >= bestNow+20 {
				return &Later{Start: win[0].Time, Activity: act, Score: s.Value}
			}
		}
	}
	return nil
}

// score applies simple, explainable rules to the worst hour in the window.
func score(act Activity, hours []weather.Hour) Score {
	var (
		maxPrecip, maxGust, maxWind float64
		minFeels, maxFeels          = math.Inf(1), math.Inf(-1)
		maxProb                     int
		thunder, ice, snow, fog     bool
		dark                        bool
	)
	for _, h := range hours {
		maxPrecip = max(maxPrecip, h.Precip)
		maxGust = max(maxGust, h.Gusts)
		maxWind = max(maxWind, h.Wind)
		minFeels = min(minFeels, h.Feels)
		maxFeels = max(maxFeels, h.Feels)
		maxProb = max(maxProb, h.PrecipProb)
		thunder = thunder || h.Code >= 95
		ice = ice || h.Code == 56 || h.Code == 57 || h.Code == 66 || h.Code == 67
		snow = snow || (h.Code >= 71 && h.Code <= 77) || h.Code == 85 || h.Code == 86
		fog = fog || h.Code == 45 || h.Code == 48
		dark = dark || !h.IsDay
	}

	s := Score{Activity: act, Value: 100}
	take := func(points int, why string) {
		if points > 0 {
			s.Value -= points
			s.Reasons = append(s.Reasons, why)
		}
	}
	// per activity: ride, run, walk
	by := func(ride, run, walk int) int {
		switch act {
		case Ride:
			return ride
		case Run:
			return run
		}
		return walk
	}

	if thunder {
		take(100, "thunderstorms: stay off open ground")
	}
	switch {
	case maxPrecip >= 2:
		take(by(70, 65, 65), fmt.Sprintf("heavy rain (up to %.1f mm/h)", maxPrecip))
	case maxPrecip >= 0.5:
		take(by(40, 30, 30), fmt.Sprintf("rain (up to %.1f mm/h)", maxPrecip))
	case maxPrecip >= 0.1:
		take(by(15, 5, 10), "light drizzle")
	case maxProb >= 60:
		take(10, fmt.Sprintf("%d%% chance of rain", maxProb))
	}
	switch {
	case maxGust >= 60:
		take(by(70, 40, 35), fmt.Sprintf("storm gusts up to %.0f km/h", maxGust))
	case maxGust >= 45:
		take(by(40, 15, 10), fmt.Sprintf("strong gusts up to %.0f km/h", maxGust))
	case maxGust >= 35:
		take(by(20, 5, 0), fmt.Sprintf("gusty, up to %.0f km/h", maxGust))
	}
	if maxWind >= 25 {
		take(by(15, 5, 0), fmt.Sprintf("steady %.0f km/h wind", maxWind))
	}
	switch {
	case minFeels < -5:
		take(by(50, 30, 35), fmt.Sprintf("bitter cold (feels like %.0f°C)", minFeels))
	case minFeels < 2:
		take(by(20, 5, 10), fmt.Sprintf("cold (feels like %.0f°C)", minFeels))
	}
	switch {
	case maxFeels > 30:
		take(by(15, 40, 20), fmt.Sprintf("hot (feels like %.0f°C)", maxFeels))
	case maxFeels > 26:
		take(by(5, 15, 5), fmt.Sprintf("warm (feels like %.0f°C)", maxFeels))
	}
	if ice {
		take(by(60, 40, 30), "freezing rain: slippery")
	} else if snow {
		take(by(50, 20, 10), "snow")
	}
	if fog {
		take(by(15, 5, 5), "fog: low visibility")
	}
	if dark {
		take(by(10, 5, 10), "dark: bring lights and something reflective")
	}
	s.Value = max(0, s.Value)
	return s
}

// target turns time and intensity into a distance at a sensible pace.
func target(act Activity, in Intensity, minutes int) (km float64, pace string) {
	i := map[Intensity]int{Easy: 0, Moderate: 1, Hard: 2}[in]
	h := float64(minutes) / 60
	switch act {
	case Run:
		minPerKm := []float64{6.5, 5.75, 5.0}[i]
		km = float64(minutes) / minPerKm
		pace = fmt.Sprintf("about %d:%02d min/km", int(minPerKm), int(math.Round((minPerKm-math.Floor(minPerKm))*60)))
	case Ride:
		kmh := []float64{18, 24, 28}[i]
		km = h * kmh
		pace = fmt.Sprintf("about %.0f km/h", kmh)
	case Walk:
		kmh := []float64{4.5, 5, 5.5}[i]
		km = h * kmh
		pace = fmt.Sprintf("about %.1f km/h", kmh)
	default:
		return 0, ""
	}
	return math.Round(km*2) / 2, pace
}