package fitness

import (
	"fmt"
	"testing"
	"time"

	"github.com/tegwick/fluid-core/internal/contract"
)

func f64(v float64) *float64 { return &v }

func obs(metric string, rev contract.RevisionID, value float64, samples int) Observation {
	return Observation{Metric: metric, Revision: rev, Value: value, Samples: samples}
}

// specsFromBlueprint mirrors the section 33 worked example: requests per task
// must drop, latency must not regress past its guardrail.
func specsFromBlueprint() []MetricSpec {
	return []MetricSpec{
		{Name: MetricRequestsPerTask, Role: RolePrimary, Direction: Lower, Target: f64(1.2)},
		{Name: MetricP95LatencyMS, Role: RoleGuardrail, Direction: Lower, Threshold: f64(315)},
		{Name: MetricErrorRate, Role: RoleGuardrail, Direction: Lower, Threshold: f64(0.01)},
	}
}

func TestSucceedsWhenTargetsMetAndGuardrailsHold(t *testing.T) {
	e := NewEvaluator()

	eval := e.Evaluate("R-1", "R-2", Window{Start: time.Now().Add(-time.Hour)}, specsFromBlueprint(),
		[]Observation{
			obs(MetricRequestsPerTask, "R-1", 2.7, 400),
			obs(MetricRequestsPerTask, "R-2", 1.15, 400),
			obs(MetricP95LatencyMS, "R-1", 300, 400),
			obs(MetricP95LatencyMS, "R-2", 302, 400),
			obs(MetricErrorRate, "R-1", 0.008, 400),
			obs(MetricErrorRate, "R-2", 0.007, 400),
		})

	if eval.Verdict != VerdictSucceeded {
		t.Fatalf("verdict = %s, reasons %v", eval.Verdict, eval.Reasons)
	}

	primary := eval.PrimaryResults()
	if len(primary) != 1 {
		t.Fatalf("primary metrics = %d, want 1", len(primary))
	}
	if primary[0].TargetMet == nil || !*primary[0].TargetMet {
		t.Error("primary target not marked as met")
	}
	if primary[0].Delta >= 0 {
		t.Errorf("delta = %v, expected a reduction", primary[0].Delta)
	}
}

// TestGuardrailDominatesPrimarySuccess is the section 48.5 protection: a
// candidate that hit its target while regressing a guardrail has traded
// something it was told not to.
func TestGuardrailDominatesPrimarySuccess(t *testing.T) {
	e := NewEvaluator()

	eval := e.Evaluate("R-1", "R-2", Window{}, specsFromBlueprint(), []Observation{
		obs(MetricRequestsPerTask, "R-1", 2.7, 400),
		obs(MetricRequestsPerTask, "R-2", 1.05, 400), // target smashed
		obs(MetricP95LatencyMS, "R-1", 300, 400),
		obs(MetricP95LatencyMS, "R-2", 980, 400), // and latency ruined
		obs(MetricErrorRate, "R-1", 0.008, 400),
		obs(MetricErrorRate, "R-2", 0.009, 400),
	})

	if eval.Verdict != VerdictGuardrailBreached {
		t.Fatalf("verdict = %s, want GUARDRAIL_BREACHED; reasons %v", eval.Verdict, eval.Reasons)
	}
	if len(eval.Reasons) == 0 {
		t.Error("a breach was reported with no reason")
	}

	var latency *MetricResult
	for i, m := range eval.GuardrailResults() {
		if m.Name == MetricP95LatencyMS {
			latency = &eval.GuardrailResults()[i]
		}
	}
	if latency == nil || latency.GuardrailBreached == nil || !*latency.GuardrailBreached {
		t.Error("the breached guardrail is not marked as breached")
	}
}

func TestFailsWhenPrimaryTargetMissed(t *testing.T) {
	e := NewEvaluator()

	eval := e.Evaluate("R-1", "R-2", Window{}, specsFromBlueprint(), []Observation{
		obs(MetricRequestsPerTask, "R-1", 2.7, 400),
		obs(MetricRequestsPerTask, "R-2", 2.6, 400), // barely moved
		obs(MetricP95LatencyMS, "R-1", 300, 400),
		obs(MetricP95LatencyMS, "R-2", 301, 400),
		obs(MetricErrorRate, "R-1", 0.008, 400),
		obs(MetricErrorRate, "R-2", 0.008, 400),
	})

	if eval.Verdict != VerdictFailed {
		t.Fatalf("verdict = %s, want FAILED", eval.Verdict)
	}
	if len(eval.Reasons) == 0 || eval.Reasons[0] == "" {
		t.Error("failure reported without saying which target was missed")
	}
}

// TestUnderpoweredIsInconclusiveNotSuccessful: promoting on three requests is
// promoting on noise.
func TestUnderpoweredIsInconclusiveNotSuccessful(t *testing.T) {
	e := NewEvaluator()

	eval := e.Evaluate("R-1", "R-2", Window{}, specsFromBlueprint(), []Observation{
		obs(MetricRequestsPerTask, "R-1", 2.7, 3),
		obs(MetricRequestsPerTask, "R-2", 1.0, 2),
		obs(MetricP95LatencyMS, "R-1", 300, 3),
		obs(MetricP95LatencyMS, "R-2", 290, 2),
		obs(MetricErrorRate, "R-1", 0.0, 3),
		obs(MetricErrorRate, "R-2", 0.0, 2),
	})

	if eval.Verdict != VerdictInconclusive {
		t.Fatalf("verdict = %s, want INCONCLUSIVE on tiny samples", eval.Verdict)
	}
	for _, m := range eval.PrimaryResults() {
		if !m.Underpowered {
			t.Error("a two-sample comparison was not marked underpowered")
		}
	}
}

// TestMissingMeasurementIsNotZero: defaulting an absent metric to zero would
// read as a dramatic change that never happened.
func TestMissingMeasurementIsNotZero(t *testing.T) {
	e := NewEvaluator()

	eval := e.Evaluate("R-1", "R-2", Window{}, specsFromBlueprint(), []Observation{
		obs(MetricRequestsPerTask, "R-1", 2.7, 400),
		// no candidate measurement at all
		obs(MetricP95LatencyMS, "R-1", 300, 400),
		obs(MetricP95LatencyMS, "R-2", 300, 400),
		obs(MetricErrorRate, "R-1", 0.008, 400),
		obs(MetricErrorRate, "R-2", 0.008, 400),
	})

	if eval.Verdict == VerdictSucceeded {
		t.Fatal("a missing primary measurement produced a success verdict")
	}
	for _, m := range eval.PrimaryResults() {
		if m.Current != 0 && m.Baseline != 0 {
			continue
		}
		if !m.Underpowered {
			t.Error("an absent measurement was not flagged")
		}
	}
}

func TestNoPrimaryMetricIsInconclusive(t *testing.T) {
	e := NewEvaluator()
	eval := e.Evaluate("R-1", "R-2", Window{}, []MetricSpec{
		{Name: MetricErrorRate, Role: RoleGuardrail, Direction: Lower, Threshold: f64(0.05)},
	}, []Observation{
		obs(MetricErrorRate, "R-1", 0.01, 400),
		obs(MetricErrorRate, "R-2", 0.01, 400),
	})

	if eval.Verdict != VerdictInconclusive {
		t.Errorf("verdict = %s, want INCONCLUSIVE with no primary metric", eval.Verdict)
	}
}

func TestPrimaryWithoutTargetCannotPass(t *testing.T) {
	e := NewEvaluator()
	eval := e.Evaluate("R-1", "R-2", Window{}, []MetricSpec{
		{Name: MetricRequestsPerTask, Role: RolePrimary, Direction: Lower}, // no target
	}, []Observation{
		obs(MetricRequestsPerTask, "R-1", 2.7, 400),
		obs(MetricRequestsPerTask, "R-2", 1.0, 400),
	})

	if eval.Verdict == VerdictSucceeded {
		t.Error("a primary metric with no declared target was treated as met")
	}
}

func TestHigherIsBetterDirection(t *testing.T) {
	e := NewEvaluator()
	eval := e.Evaluate("R-1", "R-2", Window{}, []MetricSpec{
		{Name: MetricSuccessRate, Role: RolePrimary, Direction: Higher, Target: f64(0.99)},
		{Name: MetricSuccessRate + "_guard", Role: RoleGuardrail, Direction: Higher, Threshold: f64(0.95)},
	}, []Observation{
		obs(MetricSuccessRate, "R-1", 0.97, 400),
		obs(MetricSuccessRate, "R-2", 0.995, 400),
		obs(MetricSuccessRate+"_guard", "R-1", 0.97, 400),
		obs(MetricSuccessRate+"_guard", "R-2", 0.96, 400),
	})

	if eval.Verdict != VerdictSucceeded {
		t.Errorf("verdict = %s, reasons %v", eval.Verdict, eval.Reasons)
	}
}

func TestEvaluationIsDeterministic(t *testing.T) {
	e := NewEvaluator()
	specs := specsFromBlueprint()
	observations := []Observation{
		obs(MetricRequestsPerTask, "R-1", 2.7, 400),
		obs(MetricRequestsPerTask, "R-2", 2.6, 400),
		obs(MetricP95LatencyMS, "R-1", 300, 400),
		obs(MetricP95LatencyMS, "R-2", 999, 400),
		obs(MetricErrorRate, "R-1", 0.008, 400),
		obs(MetricErrorRate, "R-2", 0.5, 400),
	}

	first := e.Evaluate("R-1", "R-2", Window{}, specs, observations)
	for i := 0; i < 50; i++ {
		again := e.Evaluate("R-1", "R-2", Window{}, specs, observations)
		if again.Verdict != first.Verdict || len(again.Reasons) != len(first.Reasons) {
			t.Fatal("evaluation varied between runs")
		}
		for j := range first.Reasons {
			if again.Reasons[j] != first.Reasons[j] {
				t.Fatalf("reason order varied: %q vs %q", first.Reasons[j], again.Reasons[j])
			}
		}
		for j := range first.Metrics {
			if again.Metrics[j].Name != first.Metrics[j].Name {
				t.Fatal("metric order varied between runs")
			}
		}
	}
}

func TestMeasurerDerivesRequestsPerTask(t *testing.T) {
	m := NewMeasurer()
	now := time.Date(2026, 9, 5, 8, 0, 0, 0, time.UTC)

	var events []contract.FluidTelemetry
	// R-1: three calls per task. R-2: one.
	for c := 0; c < 10; c++ {
		chain := fmt.Sprintf("chain-%d", c)
		for i := 0; i < 3; i++ {
			events = append(events, telemetry("R-1", fmt.Sprintf("c-%d", c), chain, now, 120, false))
		}
		events = append(events, telemetry("R-2", fmt.Sprintf("c-%d", c), chain+"-b", now, 130, false))
	}

	observations := m.Measure(events, Window{Start: now.Add(-time.Hour)})

	got := map[contract.RevisionID]float64{}
	for _, o := range observations {
		if o.Metric == MetricRequestsPerTask {
			got[o.Revision] = o.Value
		}
	}
	if got["R-1"] != 3 {
		t.Errorf("R-1 requests per task = %v, want 3", got["R-1"])
	}
	if got["R-2"] != 1 {
		t.Errorf("R-2 requests per task = %v, want 1", got["R-2"])
	}
}

func TestMeasurerRespectsWindow(t *testing.T) {
	m := NewMeasurer()
	now := time.Date(2026, 9, 5, 8, 0, 0, 0, time.UTC)

	events := []contract.FluidTelemetry{
		telemetry("R-1", "c-1", "old", now.AddDate(0, 0, -10), 100, false),
		telemetry("R-1", "c-1", "new", now, 100, false),
	}

	// Only events inside the window may count, or the comparison is not
	// reproducible from its recorded period.
	observations := m.Measure(events, Window{Start: now.Add(-time.Hour)})
	for _, o := range observations {
		if o.Metric == MetricErrorRate && o.Samples != 1 {
			t.Errorf("samples = %d, want 1; events outside the window were counted", o.Samples)
		}
	}
}

func TestMeasurerComputesErrorRate(t *testing.T) {
	m := NewMeasurer()
	now := time.Date(2026, 9, 5, 8, 0, 0, 0, time.UTC)

	var events []contract.FluidTelemetry
	for i := 0; i < 8; i++ {
		events = append(events, telemetry("R-1", "c-1", fmt.Sprintf("ch-%d", i), now, 100, false))
	}
	for i := 0; i < 2; i++ {
		events = append(events, telemetry("R-1", "c-1", fmt.Sprintf("er-%d", i), now, 100, true))
	}

	for _, o := range m.Measure(events, Window{}) {
		if o.Metric == MetricErrorRate && o.Value != 0.2 {
			t.Errorf("error rate = %v, want 0.2", o.Value)
		}
		if o.Metric == MetricSuccessRate && o.Value != 0.8 {
			t.Errorf("success rate = %v, want 0.8", o.Value)
		}
	}
}

func telemetry(rev contract.RevisionID, consumer, chain string, at time.Time, latency float64, isError bool) contract.FluidTelemetry {
	r := rev
	l := latency
	status := int64(200)
	ev := contract.FluidTelemetry{
		ID:          fmt.Sprintf("tl-%s-%s", consumer, chain),
		OccurredAt:  at,
		Kind:        contract.FluidTelemetryKindRequest,
		ConsumerRef: consumer,
		Revision:    &r,
		Sequence:    &contract.FluidTelemetrySequence{ChainID: chain},
		Request:     &contract.FluidTelemetryRequest{Route: "/v1/x", Method: "GET", Status: &status, LatencyMS: &l},
	}
	if isError {
		ev.Kind = contract.FluidTelemetryKindError
		ev.Error = &contract.FluidTelemetryError{Class: contract.FluidTelemetryErrorClassBackendFailure}
	}
	return ev
}