// 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"
	"predictor-refactored/internal/weather"
	api "predictor-refactored/pkg/rest"
)

// Handler implements api.Handler (ogen-generated interface).
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}
}

var _ api.Handler = (*Handler)(nil)

// PerformPrediction runs the Tawhiri-style prediction.
func (h *Handler) PerformPrediction(_ 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")
	}

	profileKind := optString(params.Profile, "standard_profile")
	ascentRate := optFloat(params.AscentRate, 5.0)
	burstAltitude := optFloat(params.BurstAltitude, 28000.0)
	descentRate := optFloat(params.DescentRate, 5.0)
	launchAlt := optFloat(params.LaunchAltitude, 0.0)

	lng := params.LaunchLongitude
	if lng < 0 {
		lng += 360
	}
	launchTime := float64(params.LaunchDatetime.Unix())

	events := engine.NewEventSink()

	var stageNames []string
	var prof engine.Profile
	switch profileKind {
	case "standard_profile":
		stageNames = []string{"ascent", "descent"}
		prof = standardProfile(field, h.elev, events, ascentRate, burstAltitude, descentRate)
	case "float_profile":
		floatAlt := optFloat(params.FloatAltitude, 25000.0)
		stopTime := params.LaunchDatetime.Add(24 * time.Hour)
		if v, ok := params.StopDatetime.Get(); ok {
			stopTime = v
		}
		stageNames = []string{"ascent", "float"}
		prof = floatProfile(field, events, ascentRate, floatAlt, stopTime)
	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}, events)
	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]
		}
		resp.Prediction = append(resp.Prediction, buildPredictionItem(stageName, r))
	}

	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 ev := events.Snapshot(); len(ev) > 0 {
		// Preserve the OpenAPI-defined Warnings shape (open object).
		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
}

// standardProfile constructs the ascent → descent profile.
func standardProfile(field weather.WindField, elev *elevation.Dataset, events *engine.EventSink, ascentRate, burstAltitude, descentRate float64) engine.Profile {
	wind := engine.WindTransport(field, events)
	descentTerm := []engine.Constraint{engine.Altitude{Op: engine.OpLessEqual, Limit: 0, On: engine.ActionStop}}
	if elev != nil {
		descentTerm = []engine.Constraint{engine.TerrainContact{Provider: elev, On: engine.ActionStop}}
	}
	return engine.Profile{
		Direction: engine.Forward,
		Stages: []*engine.Propagator{
			{
				Name:        "ascent",
				Step:        60,
				Model:       engine.Sum(engine.ConstantRate(ascentRate), wind),
				Constraints: []engine.Constraint{engine.Altitude{Op: engine.OpGreaterEqual, Limit: burstAltitude, On: engine.ActionStop}},
			},
			{
				Name:        "descent",
				Step:        60,
				Model:       engine.Sum(engine.ParachuteDescent(descentRate), wind),
				Constraints: descentTerm,
			},
		},
	}
}

// floatProfile constructs the ascent → float profile.
func floatProfile(field weather.WindField, events *engine.EventSink, ascentRate, floatAlt float64, stopTime time.Time) engine.Profile {
	wind := engine.WindTransport(field, events)
	return engine.Profile{
		Direction: engine.Forward,
		Stages: []*engine.Propagator{
			{
				Name:        "ascent",
				Step:        60,
				Model:       engine.Sum(engine.ConstantRate(ascentRate), wind),
				Constraints: []engine.Constraint{engine.Altitude{Op: engine.OpGreaterEqual, Limit: floatAlt, On: engine.ActionStop}},
			},
			{
				Name:        "float",
				Step:        60,
				Model:       wind,
				Constraints: []engine.Constraint{engine.Time{Op: engine.OpGreater, Limit: float64(stopTime.Unix()), On: engine.ActionStop}},
			},
		},
	}
}

func buildPredictionItem(stageName string, r engine.Result) api.PredictionResponsePredictionItem {
	var stageEnum api.PredictionResponsePredictionItemStage
	switch stageName {
	case "descent":
		stageEnum = api.PredictionResponsePredictionItemStageDescent
	case "float":
		stageEnum = api.PredictionResponsePredictionItemStageFloat
	default:
		stageEnum = api.PredictionResponsePredictionItemStageAscent
	}
	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,
		})
	}
	return api.PredictionResponsePredictionItem{Stage: stageEnum, Trajectory: traj}
}

// 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,
			},
		},
	}
}

// optString returns the option's value if set, else fallback.
func optString[T ~string](o interface {
	Get() (T, bool)
}, fallback string) string {
	if v, ok := o.Get(); ok {
		return string(v)
	}
	return fallback
}

// optFloat returns the option's float64 value if set, else fallback.
func optFloat(o api.OptFloat64, fallback float64) float64 {
	if v, ok := o.Get(); ok {
		return v
	}
	return fallback
}