package v2

import (
	"encoding/json"
	"fmt"
	"net/http"
	"time"

	"go.uber.org/zap"

	"predictor-refactored/internal/datasets"
	"predictor-refactored/internal/elevation"
	"predictor-refactored/internal/engine"
	"predictor-refactored/internal/metrics"
)

// Handler serves POST /api/v2/prediction.
type Handler struct {
	mgr     *datasets.Manager
	elev    *elevation.Dataset
	metrics metrics.Sink
	log     *zap.Logger
}

// New wires a v2 Handler.
func New(mgr *datasets.Manager, elev *elevation.Dataset, sink metrics.Sink, log *zap.Logger) *Handler {
	if log == nil {
		log = zap.NewNop()
	}
	if sink == nil {
		sink = metrics.Noop()
	}
	return &Handler{mgr: mgr, elev: elev, metrics: sink, log: log}
}

func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		writeError(w, http.StatusMethodNotAllowed, "use POST")
		return
	}

	var req PredictionRequest
	dec := json.NewDecoder(r.Body)
	dec.DisallowUnknownFields()
	if err := dec.Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid request body: "+err.Error())
		return
	}

	if err := validateRequest(req); err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}

	field := h.mgr.Active()
	if field == nil {
		writeError(w, http.StatusServiceUnavailable, "no dataset loaded, service is starting up")
		return
	}

	// Normalize longitude to [0, 360) for internal use.
	lng := req.Launch.Longitude
	if lng < 0 {
		lng += 360
	}

	warnings := &engine.Warnings{}
	var terrain engine.TerrainProvider
	if h.elev != nil {
		terrain = h.elev
	}

	prof, err := buildProfile(req, field, terrain, warnings)
	if err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}

	started := time.Now().UTC()
	results := prof.Run(float64(req.Launch.Time.Unix()), engine.State{
		Lat:      req.Launch.Latitude,
		Lng:      lng,
		Altitude: req.Launch.Altitude,
	})
	completed := time.Now().UTC()
	h.metrics.Prediction("v2", completed.Sub(started), nil)

	resp := PredictionResponse{
		Stages:      make([]StageResult, 0, len(results)),
		StartedAt:   started,
		CompletedAt: completed,
		Dataset: DatasetInfo{
			Source: field.Source(),
			Epoch:  field.Epoch(),
		},
	}
	for _, r := range results {
		stage := StageResult{
			Name:    r.Propagator,
			Outcome: outcomeString(r.Outcome),
		}
		if r.Constraint != nil {
			stage.Constraint = r.Constraint.Name()
		}
		stage.Trajectory = make([]TrajectoryPoint, len(r.Points))
		for i, pt := range r.Points {
			ptLng := pt.Lng
			if ptLng > 180 {
				ptLng -= 360
			}
			stage.Trajectory[i] = TrajectoryPoint{
				Time:      time.Unix(int64(pt.Time), 0).UTC(),
				Latitude:  pt.Lat,
				Longitude: ptLng,
				Altitude:  pt.Altitude,
			}
		}
		resp.Stages = append(resp.Stages, stage)
	}
	if warns := warnings.ToMap(); len(warns) > 0 {
		resp.Warnings = warns
	}

	h.log.Info("v2 prediction complete",
		zap.Int("stages", len(results)),
		zap.Duration("elapsed", completed.Sub(started)))
	writeJSON(w, http.StatusOK, resp)
}

func validateRequest(req PredictionRequest) error {
	if req.Launch.Latitude < -90 || req.Launch.Latitude > 90 {
		return fmt.Errorf("launch.latitude must be in [-90, 90]")
	}
	if req.Launch.Longitude < -180 || req.Launch.Longitude >= 360 {
		return fmt.Errorf("launch.longitude must be in [-180, 360)")
	}
	if len(req.Profile) == 0 {
		return fmt.Errorf("profile must contain at least one stage")
	}
	for i, s := range req.Profile {
		if s.Name == "" {
			return fmt.Errorf("profile[%d].name is required", i)
		}
		if s.Model.Type == "" {
			return fmt.Errorf("profile[%d].model.type is required", i)
		}
	}
	return nil
}

func outcomeString(o engine.Outcome) string {
	switch o {
	case engine.OutcomeStopped:
		return "stopped"
	case engine.OutcomeFallback:
		return "fallback"
	default:
		return "continued"
	}
}

func writeError(w http.ResponseWriter, status int, description string) {
	writeJSON(w, status, ErrorResponse{Error: ErrorBody{
		Type:        http.StatusText(status),
		Description: description,
	}})
}

func writeJSON(w http.ResponseWriter, status int, body any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(body)
}