package runtime

import (
	"errors"
	"testing"

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

const testInterface contract.InterfaceID = "hall-publishing"

// descriptor builds a minimal routable revision descriptor.
func descriptor(id contract.RevisionID, state contract.RevisionState, cohorts ...contract.CohortID) contract.Revision {
	d := contract.Revision{
		SchemaVersion: "0.1",
		ID:            id,
		Interface:     testInterface,
		State:         state,
		Contract: contract.RevisionContract{
			Type:   contract.RevisionContractTypeOpenapi,
			Digest: contract.Digest("sha256:" + zeros(64)),
		},
		Runtime: contract.RevisionRuntime{Upstream: "http://adapter:8080"},
		Intent:  contract.RevisionIntent{Version: "IEI-1"},
		Policy: contract.RevisionPolicy{
			Compatibility: contract.RevisionPolicyCompatibilityAdditive,
			SecurityCheck: contract.RevisionPolicySecurityCheckPassed,
		},
	}
	if len(cohorts) > 0 {
		d.Routing = &contract.RevisionRouting{EligibleCohorts: cohorts}
	}
	return d
}

func zeros(n int) string {
	b := make([]byte, n)
	for i := range b {
		b[i] = '0'
	}
	return string(b)
}

func policyWith(defaultRev contract.RevisionID, gen int64, rules ...contract.RoutingPolicyRulesItem) contract.RoutingPolicy {
	return contract.RoutingPolicy{
		SchemaVersion:   "0.1",
		Interface:       testInterface,
		Generation:      gen,
		DefaultRevision: defaultRev,
		Rules:           rules,
	}
}

func newFixture(t *testing.T, revs ...contract.Revision) *Registry {
	t.Helper()
	reg := NewRegistry(testInterface)
	for _, r := range revs {
		if err := reg.PutRevision(r); err != nil {
			t.Fatalf("PutRevision(%s): %v", r.ID, err)
		}
	}
	return reg
}

func TestResolvePrecedence(t *testing.T) {
	reg := newFixture(t,
		descriptor("R-1", contract.RevisionStateStable),
		descriptor("R-2", contract.RevisionStateExperiment),
		descriptor("R-3", contract.RevisionStateCandidate),
	)
	if err := reg.PutPolicy(policyWith("R-1", 1)); err != nil {
		t.Fatal(err)
	}

	res := NewResolver(reg, true)

	t.Run("explicit wins", func(t *testing.T) {
		got, err := res.Resolve(Request{ExplicitRevision: "R-3", BoundRevision: "R-2"})
		if err != nil {
			t.Fatal(err)
		}
		if got.Revision != "R-3" {
			t.Errorf("got %s, want R-3", got.Revision)
		}
		if got.Reason != contract.FluidTelemetryResolutionReasonExplicitRevision {
			t.Errorf("reason = %s", got.Reason)
		}
	})

	t.Run("bound contract beats default", func(t *testing.T) {
		got, err := res.Resolve(Request{BoundRevision: "R-2"})
		if err != nil {
			t.Fatal(err)
		}
		if got.Revision != "R-2" || got.Reason != contract.FluidTelemetryResolutionReasonBoundContract {
			t.Errorf("got %s via %s, want R-2 via bound_contract", got.Revision, got.Reason)
		}
	})

	t.Run("falls through to stable default", func(t *testing.T) {
		got, err := res.Resolve(Request{})
		if err != nil {
			t.Fatal(err)
		}
		if got.Revision != "R-1" || got.Reason != contract.FluidTelemetryResolutionReasonStableDefault {
			t.Errorf("got %s via %s, want R-1 via stable_default", got.Revision, got.Reason)
		}
	})

	t.Run("explicit disabled is ignored", func(t *testing.T) {
		strict := NewResolver(reg, false)
		got, err := strict.Resolve(Request{ExplicitRevision: "R-3"})
		if err != nil {
			t.Fatal(err)
		}
		if got.Revision != "R-1" {
			t.Errorf("got %s, want the default R-1 when pinning is disabled", got.Revision)
		}
	})
}

func TestUnroutableRevisionsAreRefused(t *testing.T) {
	reg := newFixture(t,
		descriptor("R-1", contract.RevisionStateStable),
		descriptor("R-created", contract.RevisionStateCreated),
		descriptor("R-retired", contract.RevisionStateRetired),
	)
	failed := descriptor("R-insecure", contract.RevisionStateStable)
	failed.Policy.SecurityCheck = contract.RevisionPolicySecurityCheckFailed
	if err := reg.PutRevision(failed); err != nil {
		t.Fatal(err)
	}
	if err := reg.PutPolicy(policyWith("R-1", 1)); err != nil {
		t.Fatal(err)
	}
	res := NewResolver(reg, true)

	for _, id := range []contract.RevisionID{"R-created", "R-retired", "R-insecure"} {
		if _, err := res.Resolve(Request{ExplicitRevision: id}); err == nil {
			t.Errorf("resolving %s should have been refused", id)
		} else if !errors.Is(err, ErrRevisionNotRoutable) {
			t.Errorf("resolving %s: got %v, want ErrRevisionNotRoutable", id, err)
		}
	}
}

func TestBoundRevisionDegradesToDefault(t *testing.T) {
	// A consumer pinned to a revision that has since retired should keep being
	// served rather than start failing.
	reg := newFixture(t,
		descriptor("R-1", contract.RevisionStateStable),
		descriptor("R-old", contract.RevisionStateRetired),
	)
	if err := reg.PutPolicy(policyWith("R-1", 1)); err != nil {
		t.Fatal(err)
	}

	got, err := NewResolver(reg, false).Resolve(Request{BoundRevision: "R-old"})
	if err != nil {
		t.Fatalf("a retired binding should degrade, not fail: %v", err)
	}
	if got.Revision != "R-1" {
		t.Errorf("got %s, want R-1", got.Revision)
	}
}

func TestCohortEligibility(t *testing.T) {
	reg := newFixture(t,
		descriptor("R-1", contract.RevisionStateStable),
		descriptor("R-2", contract.RevisionStateExperiment, "coding-agents"),
	)
	if err := reg.PutPolicy(policyWith("R-1", 1)); err != nil {
		t.Fatal(err)
	}

	if err := reg.CheckRoutable("R-2", "coding-agents"); err != nil {
		t.Errorf("eligible cohort refused: %v", err)
	}
	if err := reg.CheckRoutable("R-2", "partner-integrations"); err == nil {
		t.Error("ineligible cohort accepted")
	}
}

func TestAllocationIsStickyAndProportional(t *testing.T) {
	reg := newFixture(t,
		descriptor("R-1", contract.RevisionStateStable),
		descriptor("R-2", contract.RevisionStateExperiment),
	)
	exp := contract.ExperimentID("E-1")
	rule := contract.RoutingPolicyRulesItem{
		Experiment: &exp,
		Allocation: map[string]contract.UnitInterval{"R-1": 0.9, "R-2": 0.1},
	}
	if err := reg.PutPolicy(policyWith("R-1", 1, rule)); err != nil {
		t.Fatal(err)
	}
	res := NewResolver(reg, false)

	// Stickiness: the same consumer must resolve identically every time.
	first, err := res.Resolve(Request{ConsumerRef: "consumer-42"})
	if err != nil {
		t.Fatal(err)
	}
	for i := 0; i < 50; i++ {
		again, err := res.Resolve(Request{ConsumerRef: "consumer-42"})
		if err != nil {
			t.Fatal(err)
		}
		if again.Revision != first.Revision {
			t.Fatalf("assignment drifted: %s then %s", first.Revision, again.Revision)
		}
	}

	// Proportionality: roughly a tenth of consumers should see the candidate.
	const n = 4000
	candidate := 0
	for i := 0; i < n; i++ {
		got, err := res.Resolve(Request{ConsumerRef: consumerName(i)})
		if err != nil {
			t.Fatal(err)
		}
		if got.Revision == "R-2" {
			candidate++
		}
		if got.Experiment == nil || *got.Experiment != exp {
			t.Fatalf("experiment not recorded on resolution for consumer %d", i)
		}
	}
	share := float64(candidate) / n
	if share < 0.07 || share > 0.13 {
		t.Errorf("candidate share %.3f, want approximately 0.10", share)
	}
}

func consumerName(i int) string {
	digits := "0123456789"
	out := []byte("consumer-")
	if i == 0 {
		return string(append(out, '0'))
	}
	var rev []byte
	for i > 0 {
		rev = append(rev, digits[i%10])
		i /= 10
	}
	for j := len(rev) - 1; j >= 0; j-- {
		out = append(out, rev[j])
	}
	return string(out)
}

func TestStalePolicyRefused(t *testing.T) {
	reg := newFixture(t, descriptor("R-1", contract.RevisionStateStable))
	if err := reg.PutPolicy(policyWith("R-1", 5)); err != nil {
		t.Fatal(err)
	}
	if err := reg.PutPolicy(policyWith("R-1", 4)); !errors.Is(err, ErrStalePolicy) {
		t.Errorf("older generation accepted: %v", err)
	}
	if err := reg.PutPolicy(policyWith("R-1", 5)); !errors.Is(err, ErrStalePolicy) {
		t.Errorf("equal generation accepted: %v", err)
	}
	if err := reg.PutPolicy(policyWith("R-1", 6)); err != nil {
		t.Errorf("newer generation refused: %v", err)
	}
}

func TestWrongInterfaceRefused(t *testing.T) {
	reg := NewRegistry(testInterface)
	other := descriptor("R-1", contract.RevisionStateStable)
	other.Interface = "some-other-api"
	if err := reg.PutRevision(other); !errors.Is(err, ErrWrongInterface) {
		t.Errorf("foreign descriptor accepted: %v", err)
	}
}