package api

import (
	"net/http"
	"sort"
	"strconv"

	"github.com/go-chi/chi/v5"

	"geniusrun/backend/internal/store"
)

type progressionPoint struct {
	Date       string  `json:"date"`
	ActivityID int64   `json:"activity_id"`
	Value      float64 `json:"value"`
}

func metricValue(metric string, a store.Activity) (float64, bool) {
	switch metric {
	case "pace":
		if a.AvgSpeedMps == nil || *a.AvgSpeedMps <= 0 {
			return 0, false
		}
		return 1000 / *a.AvgSpeedMps, true
	case "hr":
		if a.AvgHR == nil {
			return 0, false
		}
		return *a.AvgHR, true
	case "vo2max":
		if a.VO2MaxValue == nil {
			return 0, false
		}
		return *a.VO2MaxValue, true
	case "aerobic_te":
		if a.AerobicTrainingEffect == nil {
			return 0, false
		}
		return *a.AerobicTrainingEffect, true
	case "anaerobic_te":
		if a.AnaerobicTrainingEffect == nil {
			return 0, false
		}
		return *a.AnaerobicTrainingEffect, true
	case "efficiency_factor":
		// Speed per heartbeat: how much ground each beat covers, on average.
		// A rising trend at similar effort/HR over time is a classic sign of
		// improving aerobic fitness, independent of pace/HR shown alone.
		// Scaled by 1000 (m/s per bpm is otherwise a tiny fraction like
		// 0.02, hard to read/compare at a glance).
		if a.AvgSpeedMps == nil || a.AvgHR == nil || *a.AvgHR <= 0 {
			return 0, false
		}
		return (*a.AvgSpeedMps / *a.AvgHR) * 1000, true
	default:
		return 0, false
	}
}

// handleProgression returns a time series of the requested metric for every
// activity currently assigned to a workout kind, for progression charts.
func (s *Server) handleProgression(w http.ResponseWriter, r *http.Request) {
	kindID, err := strconv.ParseInt(chi.URLParam(r, "kindID"), 10, 64)
	if err != nil {
		writeError(w, http.StatusBadRequest, "invalid workout kind id")
		return
	}
	metric := r.URL.Query().Get("metric")
	if metric == "" {
		metric = "pace"
	}
	from, to := r.URL.Query().Get("from"), r.URL.Query().Get("to")

	assignments, err := s.DB.AssignmentsForKind(r.Context(), kindID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	points := []progressionPoint{}
	for _, a := range assignments {
		activity, ok, err := s.DB.GetActivity(r.Context(), a.ActivityID)
		if err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		if !ok {
			continue
		}
		if from != "" && activity.StartTimeUTC < from {
			continue
		}
		if to != "" && activity.StartTimeUTC > to+" 23:59:59" {
			continue
		}
		value, ok := metricValue(metric, activity)
		if !ok {
			continue
		}
		points = append(points, progressionPoint{Date: activity.StartTimeUTC, ActivityID: activity.ID, Value: value})
	}

	sort.Slice(points, func(i, j int) bool { return points[i].Date < points[j].Date })
	writeJSON(w, http.StatusOK, points)
}