// Package tawhiri implements the legacy Tawhiri-compatible HTTP endpoint
// (GET /api/v1/prediction). The request/response shapes match the original
// Cambridge University Spaceflight predictor for drop-in compatibility.
//
// Internally the handler builds an engine.Profile from query parameters and
// dispatches it through the same engine path as the new v2 endpoint.
package tawhiri

import (
	"context"
	"errors"
	"net/http"
	"time"

	"go.uber.org/zap"

	"predictor-refactored/internal/datasets"
	"predictor-refactored/internal/elevation"
	"predictor-refactored/internal/engine"
	"predictor-refactored/internal/metrics"
	api "predictor-refactored/pkg/rest"
)

// Handler implements api.Handler (the ogen-generated interface for
// performPrediction and readinessCheck).
type Handler struct {
	mgr     *datasets.Manager
	elev    *elevation.Dataset
	metrics metrics.Sink
	log     *zap.Logger
}

// New wires a 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}
}

// Compile-time check that Handler satisfies api.Handler.
var _ api.Handler = (*Handler)(nil)

// PerformPrediction runs the Tawhiri-style prediction.
func (h *Handler) PerformPrediction(ctx context.Context, params api.PerformPredictionParams) (*api.PredictionResponse, error) {
	field := h.mgr.Active()
	if field == nil {
		return nil, newError(http.StatusServiceUnavailable, "no dataset loaded, service is starting up")
	}

	// Parameters with Tawhiri defaults.
	profileKind := "standard_profile"
	if v, ok := params.Profile.Get(); ok {
		profileKind = string(v)
	}
	ascentRate := 5.0
	if v, ok := params.AscentRate.Get(); ok {
		ascentRate = v
	}
	burstAltitude := 28000.0
	if v, ok := params.BurstAltitude.Get(); ok {
		burstAltitude = v
	}
	descentRate := 5.0
	if v, ok := params.DescentRate.Get(); ok {
		descentRate = v
	}
	launchAlt := 0.0
	if v, ok := params.LaunchAltitude.Get(); ok {
		launchAlt = v
	}

	lng := params.LaunchLongitude
	if lng < 0 {
		lng += 360
	}

	launchTime := float64(params.LaunchDatetime.Unix())
	warnings := &engine.Warnings{}

	// Build the profile.
	var stageNames []string
	var prof engine.Profile
	switch profileKind {
	case "standard_profile":
		stageNames = []string{"ascent", "descent"}
		prof = engine.Profile{
			Direction: engine.Forward,
			Stages: []*engine.Propagator{
				{
					Name: "ascent",
					Step: 60,
					Model: engine.Sum(
						engine.ConstantRate(ascentRate),
						engine.WindTransport(field, warnings),
					),
					Constraints: []engine.Constraint{engine.MaxAltitude{Limit: burstAltitude, On: engine.ActionStop}},
				},
				{
					Name: "descent",
					Step: 60,
					Model: engine.Sum(
						engine.ParachuteDescent(descentRate),
						engine.WindTransport(field, warnings),
					),
					Constraints: descentConstraints(h.elev),
				},
			},
		}
	case "float_profile":
		floatAlt := 25000.0
		if v, ok := params.FloatAltitude.Get(); ok {
			floatAlt = v
		}
		stopTime := params.LaunchDatetime.Add(24 * time.Hour)
		if v, ok := params.StopDatetime.Get(); ok {
			stopTime = v
		}
		stageNames = []string{"ascent", "float"}
		prof = engine.Profile{
			Direction: engine.Forward,
			Stages: []*engine.Propagator{
				{
					Name: "ascent",
					Step: 60,
					Model: engine.Sum(
						engine.ConstantRate(ascentRate),
						engine.WindTransport(field, warnings),
					),
					Constraints: []engine.Constraint{engine.MaxAltitude{Limit: floatAlt, On: engine.ActionStop}},
				},
				{
					Name:        "float",
					Step:        60,
					Model:       engine.WindTransport(field, warnings),
					Constraints: []engine.Constraint{engine.MaxTime{Limit: float64(stopTime.Unix()), On: engine.ActionStop}},
				},
			},
		}
	default:
		return nil, newError(http.StatusBadRequest, "unknown profile: "+profileKind)
	}

	started := time.Now().UTC()
	results := prof.Run(launchTime, engine.State{Lat: params.LaunchLatitude, Lng: lng, Altitude: launchAlt})
	completed := time.Now().UTC()
	h.metrics.Prediction(profileKind, completed.Sub(started), nil)

	resp := &api.PredictionResponse{
		Metadata: api.PredictionResponseMetadata{
			StartDatetime:    started,
			CompleteDatetime: completed,
		},
	}

	for i, r := range results {
		stageName := "ascent"
		if i < len(stageNames) {
			stageName = stageNames[i]
		}
		stageEnum := api.PredictionResponsePredictionItemStageAscent
		switch stageName {
		case "descent":
			stageEnum = api.PredictionResponsePredictionItemStageDescent
		case "float":
			stageEnum = api.PredictionResponsePredictionItemStageFloat
		}
		traj := make([]api.PredictionResponsePredictionItemTrajectoryItem, 0, len(r.Points))
		for _, pt := range r.Points {
			ptLng := pt.Lng
			if ptLng > 180 {
				ptLng -= 360
			}
			traj = append(traj, api.PredictionResponsePredictionItemTrajectoryItem{
				Datetime:  time.Unix(int64(pt.Time), 0).UTC(),
				Latitude:  pt.Lat,
				Longitude: ptLng,
				Altitude:  pt.Altitude,
			})
		}
		resp.Prediction = append(resp.Prediction, api.PredictionResponsePredictionItem{
			Stage:      stageEnum,
			Trajectory: traj,
		})
	}

	resp.Request = api.NewOptPredictionResponseRequest(api.PredictionResponseRequest{
		Dataset:         api.NewOptString(field.Epoch().Format("2006-01-02T15:04:05Z")),
		LaunchLatitude:  api.NewOptFloat64(params.LaunchLatitude),
		LaunchLongitude: api.NewOptFloat64(params.LaunchLongitude),
		LaunchDatetime:  api.NewOptString(params.LaunchDatetime.Format(time.RFC3339)),
		LaunchAltitude:  params.LaunchAltitude,
	})

	if warns := warnings.ToMap(); len(warns) > 0 {
		resp.Warnings = api.NewOptPredictionResponseWarnings(api.PredictionResponseWarnings{})
	}

	h.log.Info("prediction complete",
		zap.String("profile", profileKind),
		zap.Int("stages", len(results)),
		zap.Duration("elapsed", completed.Sub(started)))

	return resp, nil
}

// descentConstraints returns the descent termination set: TerrainContact if an
// elevation dataset is loaded, MinAltitude(0) otherwise.
func descentConstraints(elev *elevation.Dataset) []engine.Constraint {
	if elev != nil {
		return []engine.Constraint{engine.TerrainContact{Provider: elev, On: engine.ActionStop}}
	}
	return []engine.Constraint{engine.MinAltitude{Limit: 0, On: engine.ActionStop}}
}

// ReadinessCheck reports whether a dataset is currently loaded.
func (h *Handler) ReadinessCheck(_ context.Context) (*api.ReadinessResponse, error) {
	resp := &api.ReadinessResponse{}
	if field := h.mgr.Active(); field != nil {
		resp.Status = api.ReadinessResponseStatusOk
		resp.DatasetTime = api.NewOptDateTime(field.Epoch())
	} else {
		resp.Status = api.ReadinessResponseStatusNotReady
		resp.ErrorMessage = api.NewOptString("no dataset loaded")
	}
	return resp, nil
}

// NewError implements the ogen Handler interface for unhandled errors.
func (h *Handler) NewError(_ context.Context, err error) *api.ErrorStatusCode {
	var statusErr *api.ErrorStatusCode
	if errors.As(err, &statusErr) {
		return statusErr
	}
	h.log.Error("unhandled error", zap.Error(err))
	return newError(http.StatusInternalServerError, err.Error())
}

func newError(status int, description string) *api.ErrorStatusCode {
	return &api.ErrorStatusCode{
		StatusCode: status,
		Response: api.Error{
			Error: api.ErrorError{
				Type:        http.StatusText(status),
				Description: description,
			},
		},
	}
}