package engine

import (
	"fmt"
	"math"
	"strings"
	"testing"
	"time"

	"predictor-refactored/internal/weather"
)

// noWind is a WindField that always returns zero wind.
type noWind struct{ epoch time.Time }

func (n noWind) Wind(_ float64, _, _, _ float64) (weather.Sample, error) {
	return weather.Sample{}, nil
}
func (n noWind) Epoch() time.Time { return n.epoch }
func (n noWind) Source() string   { return "test" }

// flatGround returns 0 metres everywhere.
type flatGround struct{}

func (flatGround) Elevation(_, _ float64) float64 { return 0 }

func TestConstantAscentToBurst(t *testing.T) {
	burst := 30000.0
	rate := 5.0

	ascend := &Propagator{
		Name:        "ascent",
		Step:        60,
		Model:       Sum(ConstantRate(rate), WindTransport(noWind{}, nil)),
		Constraints: []Constraint{Altitude{Op: OpGreaterEqual, Limit: burst, On: ActionStop}},
	}

	prof := Profile{Stages: []*Propagator{ascend}, Direction: Forward}
	results := prof.Run(0, State{Lat: 0, Lng: 0, Altitude: 0}, NewEventSink())

	if len(results) != 1 || results[0].Outcome != OutcomeStopped {
		t.Fatalf("expected one stopped stage, got %+v", results)
	}
	if results[0].ConstraintName == "" {
		t.Errorf("ConstraintName not populated")
	}
	if results[0].RefinedState.Altitude == 0 {
		t.Errorf("RefinedState not populated")
	}

	lastT, last := results[0].Path.Last()
	if math.Abs(last.Altitude-burst) > 5 {
		t.Errorf("burst altitude = %v, want within 5m of %v", last.Altitude, burst)
	}
	wantTime := burst / rate
	if math.Abs(lastT-wantTime) > 1 {
		t.Errorf("burst time = %v, want within 1s of %v", lastT, wantTime)
	}
}

func TestProfileWithFallback(t *testing.T) {
	burst := 1000.0
	rate := 5.0

	descent := &Propagator{
		Name:        "descent",
		Step:        60,
		Model:       ParachuteDescent(rate),
		Constraints: []Constraint{TerrainContact{Provider: flatGround{}, On: ActionStop}},
	}
	ascend := &Propagator{
		Name:        "ascent",
		Step:        60,
		Model:       ConstantRate(rate),
		Constraints: []Constraint{Altitude{Op: OpGreaterEqual, Limit: burst, On: ActionFallback}},
		Fallback:    descent,
	}

	prof := Profile{Stages: []*Propagator{ascend}, Direction: Forward}
	results := prof.Run(0, State{Altitude: 0}, NewEventSink())

	if len(results) != 2 {
		t.Fatalf("expected 2 results (ascent then descent fallback), got %d", len(results))
	}
	if results[0].Outcome != OutcomeFallback {
		t.Errorf("first outcome = %v, want OutcomeFallback", results[0].Outcome)
	}
	if results[1].Outcome != OutcomeStopped {
		t.Errorf("second outcome = %v, want OutcomeStopped", results[1].Outcome)
	}

	_, last := results[1].Path.Last()
	if math.Abs(last.Altitude) > 5 {
		t.Errorf("final altitude = %v, want within 5m of 0", last.Altitude)
	}
}

func TestReverseDirection(t *testing.T) {
	desc := &Propagator{
		Name:        "rewind",
		Step:        1,
		Model:       ConstantRate(-1),
		Constraints: []Constraint{Altitude{Op: OpGreaterEqual, Limit: 200, On: ActionStop}},
	}
	prof := Profile{Stages: []*Propagator{desc}, Direction: Reverse}
	results := prof.Run(0, State{Altitude: 100}, NewEventSink())

	lastT, last := results[0].Path.Last()
	if math.Abs(last.Altitude-200) > 1 {
		t.Errorf("reverse final altitude = %v, want ~200", last.Altitude)
	}
	if lastT >= 0 {
		t.Errorf("reverse final time = %v, want < 0", lastT)
	}
}

func TestPiecewiseRate(t *testing.T) {
	m := Piecewise([]RateSegment{
		{Until: 100, Rate: 5},
		{Until: 200, Rate: 3},
		{Until: math.Inf(1), Rate: 0},
	})

	if r := m(50, State{}); r.Vertical != 5 {
		t.Errorf("rate at t=50 = %v, want 5", r.Vertical)
	}
	if r := m(150, State{}); r.Vertical != 3 {
		t.Errorf("rate at t=150 = %v, want 3", r.Vertical)
	}
	if r := m(300, State{}); r.Vertical != 0 {
		t.Errorf("rate at t=300 = %v, want 0", r.Vertical)
	}
}

func TestPiecewiseReferenceResolution(t *testing.T) {
	// Build via the registry with propagator_start segments.
	spec := ModelSpec{
		Type: "piecewise",
		Segments: []PiecewiseSegmentSpec{
			{Until: 100, Rate: 5, Reference: "propagator_start"},
			{Until: 200, Rate: 3, Reference: "propagator_start"},
		},
	}
	built, err := BuildModel(spec, BuildDeps{})
	if err != nil {
		t.Fatalf("BuildModel: %v", err)
	}
	if built.Build == nil {
		t.Fatalf("expected lazy build for propagator_start references")
	}
	ctx := StageContext{ProfileStart: 1000, PropagatorStart: 5000}
	m := built.Build(ctx)
	// Until=100 from propagator_start=5000 → absolute 5100.
	if r := m(5050, State{}); r.Vertical != 5 {
		t.Errorf("rate at t=5050 = %v, want 5", r.Vertical)
	}
	if r := m(5150, State{}); r.Vertical != 3 {
		t.Errorf("rate at t=5150 = %v, want 3", r.Vertical)
	}
}

// fixedWind returns a constant wind sample.
type fixedWind struct{ u, v float64 }

func (w fixedWind) Wind(_ float64, _, _, _ float64) (weather.Sample, error) {
	return weather.Sample{U: w.u, V: w.v}, nil
}
func (fixedWind) Epoch() time.Time { return time.Unix(0, 0) }
func (fixedWind) Source() string   { return "test-fixed" }

func TestWindTransportPassesWindThroughUnchanged(t *testing.T) {
	// The wind field already gives a horizontal velocity, so the propagator
	// receives it verbatim. This replaces a test of the old deg/s conversion,
	// whose 1/cos(lat) factor is exactly what made the poles unusable.
	wind := WindTransport(fixedWind{u: 10, v: -4}, nil)

	for _, lat := range []float64{0, 45, 60, 89, 89.999} {
		r := wind(0, State{Lat: lat, Lng: 0, Altitude: 0})
		if r.East != 10 || r.North != -4 {
			t.Errorf("lat %g: rate = %+v, want East=10 North=-4", lat, r)
		}
		if r.Vertical != 0 {
			t.Errorf("lat %g: wind must not produce vertical motion, got %v", lat, r.Vertical)
		}
	}
}

// aboveModelWind reports AboveModel on every sample. Used to verify event emission.
type aboveModelWind struct{}

func (aboveModelWind) Wind(_ float64, _, _, _ float64) (weather.Sample, error) {
	return weather.Sample{AboveModel: true}, nil
}
func (aboveModelWind) Epoch() time.Time { return time.Unix(0, 0) }
func (aboveModelWind) Source() string   { return "above" }

func TestWindTransportEmitsAboveModel(t *testing.T) {
	sink := NewEventSink()
	wind := WindTransport(aboveModelWind{}, sink)
	for range 3 {
		_ = wind(0, State{})
	}
	events := sink.Snapshot()
	if len(events) != 1 || events[0].Type != "above_model" || events[0].Count != 3 {
		t.Errorf("expected one above_model event with count=3, got %+v", events)
	}
}

func TestNoTerminatorStopsAtStepCap(t *testing.T) {
	// A stage that ascends forever with no constraint must not loop endlessly;
	// the integrator's step backstop stops it and records a max_steps event.
	sink := NewEventSink()
	prof := Profile{
		Stages:    []*Propagator{{Name: "runaway", Step: 60, Model: ConstantRate(5)}},
		Direction: Forward,
	}
	results := prof.Run(0, State{}, sink)

	if results[0].Outcome != OutcomeContinued {
		t.Errorf("outcome = %v, want OutcomeContinued (step cap)", results[0].Outcome)
	}
	if results[0].Path.Len() != DefaultMaxSteps+1 {
		t.Errorf("path len = %d, want %d", results[0].Path.Len(), DefaultMaxSteps+1)
	}
	ev := sink.Snapshot()
	if len(ev) != 1 || ev[0].Type != "max_steps" {
		t.Errorf("expected a max_steps event, got %+v", ev)
	}
}

func TestPolygonInside(t *testing.T) {
	// Unit square at the equator.
	square := []PolygonVertex{
		{Lat: -1, Lng: -1},
		{Lat: -1, Lng: 1},
		{Lat: 1, Lng: 1},
		{Lat: 1, Lng: -1},
	}
	c := NewPolygon(square, PolygonInside, ActionStop, "")
	if !c.Violated(0, State{Lat: 0, Lng: 0}) {
		t.Errorf("origin should be inside the square")
	}
	if c.Violated(0, State{Lat: 5, Lng: 0}) {
		t.Errorf("(5, 0) should be outside the square")
	}
}

func TestPolygonOutsideAntimeridian(t *testing.T) {
	// A polygon centred near the antimeridian, spanning lng 170..-170
	// (i.e. lng 170..190 in [0, 360) form).
	poly := []PolygonVertex{
		{Lat: -10, Lng: 170},
		{Lat: -10, Lng: 190},
		{Lat: 10, Lng: 190},
		{Lat: 10, Lng: 170},
	}
	c := NewPolygon(poly, PolygonInside, ActionStop, "")
	// A point at the antimeridian.
	if !c.Violated(0, State{Lat: 0, Lng: 180}) {
		t.Errorf("(0, 180) should be inside the antimeridian polygon")
	}
	if c.Violated(0, State{Lat: 0, Lng: 0}) {
		t.Errorf("(0, 0) should be outside")
	}
}

// horizonWind has data up to horizon seconds and fails past it, the way a real
// dataset's time axis does (numerics.AxisError from Axis.Locate).
type horizonWind struct{ horizon float64 }

func (w horizonWind) Wind(t, _, _, _ float64) (weather.Sample, error) {
	if t > w.horizon {
		return weather.Sample{}, fmt.Errorf("hour=%v out of range", t/3600)
	}
	return weather.Sample{U: 10, V: 0}, nil
}
func (w horizonWind) Epoch() time.Time { return time.Unix(0, 0).UTC() }
func (w horizonWind) Source() string   { return "test" }

// TestWindSamplingFailureIsRecordedNotSwallowed pins the difference between an
// event and a failure.
//
// WindTransport used to discard the sampler's error and return a zero rate. A
// zero rate is indistinguishable from calm air, so a launch past the dataset's
// horizon integrated with no wind at all and produced a balloon that took off
// and landed on the same spot — returned as a successful forecast. An error from
// the sampler means there was no data, so the trajectory past that point is not
// a forecast and must not be presented as one.
func TestWindSamplingFailureIsRecordedNotSwallowed(t *testing.T) {
	sink := NewEventSink()
	ascend := &Propagator{
		Name:        "ascent",
		Step:        60,
		Model:       Sum(ConstantRate(5), WindTransport(horizonWind{horizon: 600}, sink)),
		Constraints: []Constraint{Altitude{Op: OpGreaterEqual, Limit: 30000, On: ActionStop}},
	}
	prof := Profile{Stages: []*Propagator{ascend}, Direction: Forward}
	prof.Run(0, State{Lat: 0, Lng: 0, Altitude: 0}, sink)

	err := sink.Err()
	if err == nil {
		t.Fatal("sink reports no failure; the sampling error was swallowed")
	}
	if !strings.Contains(err.Error(), "out of range") {
		t.Errorf("error %q does not carry the sampler's reason", err)
	}
}

// TestWindSamplingSuccessLeavesNoFailure keeps the check above from firing on
// healthy runs, which would turn every prediction into a 400.
func TestWindSamplingSuccessLeavesNoFailure(t *testing.T) {
	sink := NewEventSink()
	ascend := &Propagator{
		Name:        "ascent",
		Step:        60,
		Model:       Sum(ConstantRate(5), WindTransport(horizonWind{horizon: 1e9}, sink)),
		Constraints: []Constraint{Altitude{Op: OpGreaterEqual, Limit: 30000, On: ActionStop}},
	}
	prof := Profile{Stages: []*Propagator{ascend}, Direction: Forward}
	prof.Run(0, State{Lat: 0, Lng: 0, Altitude: 0}, sink)

	if err := sink.Err(); err != nil {
		t.Fatalf("healthy run reported a failure: %v", err)
	}
}

// TestAboveModelStaysNonFatal separates the two paths explicitly: extrapolating
// above the highest pressure level is a warning the caller may ignore, and must
// not become a hard failure.
func TestAboveModelStaysNonFatal(t *testing.T) {
	sink := NewEventSink()
	ascend := &Propagator{
		Name:        "ascent",
		Step:        60,
		Model:       Sum(ConstantRate(5), WindTransport(aboveModelWind{}, sink)),
		Constraints: []Constraint{Altitude{Op: OpGreaterEqual, Limit: 30000, On: ActionStop}},
	}
	prof := Profile{Stages: []*Propagator{ascend}, Direction: Forward}
	prof.Run(0, State{Lat: 0, Lng: 0, Altitude: 0}, sink)

	if err := sink.Err(); err != nil {
		t.Fatalf("above_model became a failure: %v", err)
	}
	if len(sink.Snapshot()) == 0 {
		t.Error("above_model event was not emitted")
	}
}

// TestEveryModelHonoursIncludeWind pins the promise ModelSpec.IncludeWind makes.
//
// buildConstantRate and buildParachuteDescent both took BuildDeps as `_` and
// returned a bare vertical model, so include_wind was accepted and discarded.
// Only buildPiecewise ever called maybeAddWind. POST /api/v2/prediction with the
// spec's own documented example therefore answered 200 with a trajectory that
// rose and fell on the spot — a wind-free forecast presented as a forecast.
//
// The loop over modelFactories is the part that matters going forward: a newly
// registered model type cannot be added without deciding here what include_wind
// does to it, which is exactly the step that was skipped before.
func TestEveryModelHonoursIncludeWind(t *testing.T) {
	cases := map[string]struct {
		spec      ModelSpec
		wantError bool
	}{
		"constant_rate":     {spec: ModelSpec{Type: "constant_rate", Rate: 5, IncludeWind: true}},
		"parachute_descent": {spec: ModelSpec{Type: "parachute_descent", SeaLevelRate: 5, IncludeWind: true}},
		"piecewise": {spec: ModelSpec{Type: "piecewise", IncludeWind: true,
			Segments: []PiecewiseSegmentSpec{{Until: math.Inf(1), Rate: 5}}}},
		// include_wind on the wind model itself would sum the wind into itself.
		// Refused rather than ignored: a silently doubled wind is a wrong forecast
		// that looks right.
		"wind": {spec: ModelSpec{Type: "wind", IncludeWind: true}, wantError: true},
	}

	for name := range modelFactories {
		if _, ok := cases[name]; !ok {
			t.Errorf("model %q is registered but has no include_wind case here", name)
		}
	}

	deps := BuildDeps{Wind: fixedWind{u: 10, v: -4}}
	for name, tc := range cases {
		t.Run(name, func(t *testing.T) {
			built, err := BuildModel(tc.spec, deps)
			if tc.wantError {
				if err == nil {
					t.Fatal("expected include_wind to be refused, got no error")
				}
				return
			}
			if err != nil {
				t.Fatalf("BuildModel: %v", err)
			}
			m := built.Model
			if built.Build != nil {
				m = built.Build(StageContext{})
			}
			rate := m(0, State{Lat: 0, Lng: 0, Altitude: 1000})
			if rate.East != 10 || rate.North != -4 {
				t.Errorf("include_wind ignored: east/north = %v/%v, want 10/-4", rate.East, rate.North)
			}
		})
	}
}

// TestIncludeWindWithoutAFieldIsRefused covers the other half of maybeAddWind,
// which returned the wind-free model when deps.Wind was nil. A request that asks
// for wind and cannot get it must fail, not quietly become a vertical drop.
func TestIncludeWindWithoutAFieldIsRefused(t *testing.T) {
	for _, typ := range []string{"constant_rate", "parachute_descent", "piecewise"} {
		t.Run(typ, func(t *testing.T) {
			spec := ModelSpec{Type: typ, Rate: 5, SeaLevelRate: 5, IncludeWind: true,
				Segments: []PiecewiseSegmentSpec{{Until: math.Inf(1), Rate: 5}}}
			if _, err := BuildModel(spec, BuildDeps{}); err == nil {
				t.Error("include_wind with no wind field was accepted")
			}
		})
	}
}