package customschema_test

import (
	"context"
	"encoding/json"
	"errors"
	"strings"
	"sync"
	"testing"

	"queryorchestration/internal/customschema"
	"queryorchestration/internal/database/repository"
	"queryorchestration/internal/serviceconfig"
	"queryorchestration/internal/test"

	"github.com/google/uuid"
	"github.com/stretchr/testify/require"
)

// Mutable metadata feature, milestone 1.6 (Part A): integration tests for
// customschema.Service CRUD methods. Red phase — these tests are written
// before the method bodies exist. Every test here is expected to fail on
// the "not implemented" sentinel in service.go until the golang engineer
// fills in the bodies in the next dispatch.
//
// No mocks. The capturingAuditSink below is a real implementation of
// customschema.AuditSink that buffers records in memory. The DB is the
// real Postgres testcontainer that test.CreateDB stands up.

// trivialValidSchemaJSON is the minimal schema_def that passes every
// rule in customschema.SchemaValidator: type=object, additionalProperties
// explicitly present, well under the 64KB cap.
const trivialValidSchemaJSON = `{"type":"object","additionalProperties":false}`

// capturingAuditSink buffers every AuditRecord in memory so tests can
// assert on what the service emitted. It is a real AuditSink, not a mock.
type capturingAuditSink struct {
	mu      sync.Mutex
	records []customschema.AuditRecord
}

// Record appends the record under the mutex. Never returns an error so
// the service's happy path is never disturbed by the sink.
func (c *capturingAuditSink) Record(ctx context.Context, rec customschema.AuditRecord) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.records = append(c.records, rec)
	return nil
}

// all returns a defensive copy of the captured records so callers can
// iterate without holding the sink's mutex.
func (c *capturingAuditSink) all() []customschema.AuditRecord {
	c.mu.Lock()
	defer c.mu.Unlock()
	out := make([]customschema.AuditRecord, len(c.records))
	copy(out, c.records)
	return out
}

// testFixture bundles everything a subtest needs from newTestService so
// tests can inspect DB rows directly and call the service simultaneously.
type testFixture struct {
	service *customschema.Service
	sink    *capturingAuditSink
	cfg     *serviceconfig.BaseConfig
	queries *repository.Queries
}

// testActor is the canonical actor string every test passes to write
// methods. Writing to AuditRecord.Actor must use THIS value (not anything
// read off the input struct) because the v4 rule is "actor is a separate
// argument, never a body field".
const testActor = "test-actor-00000000-0000-4000-8000-000000000001"

// newTestService boots a fresh DB via test.CreateDB, wipes leftover rows
// for the test's clients, re-creates the clients, and returns a ready
// Service wired to a capturing sink. Tests pass the set of client IDs
// they need so unrelated runs don't clobber each other's fixtures.
func newTestService(t *testing.T, clientIDs ...string) *testFixture {
	t.Helper()
	cfg := &serviceconfig.BaseConfig{}
	test.CreateDB(t, cfg)
	pool := cfg.GetDBPool()
	require.NotNil(t, pool)
	queries := cfg.GetDBQueries()
	require.NotNil(t, queries)

	ctx := t.Context()
	for _, clientID := range clientIDs {
		// Same idempotency dance as resetClient() in the repository tests:
		// documents first (no cascade from clients), then clients (cascade
		// wipes client_metadata_schemas via the FK from migration 127).
		_, err := pool.Exec(ctx, `DELETE FROM documents WHERE clientId = $1`, clientID)
		require.NoError(t, err, "pre-test DELETE documents for clientID=%q must succeed", clientID)
		_, err = pool.Exec(ctx, `DELETE FROM clients WHERE clientId = $1`, clientID)
		require.NoError(t, err, "pre-test DELETE clients for clientID=%q must succeed", clientID)

		err = queries.CreateClient(ctx, &repository.CreateClientParams{
			Name:     strings.ToLower(clientID),
			Clientid: clientID,
		})
		require.NoError(t, err, "CreateClient for clientID=%q must succeed", clientID)
	}

	sink := &capturingAuditSink{}
	svc := customschema.New(cfg, &customschema.SchemaValidator{}, sink)
	return &testFixture{
		service: svc,
		sink:    sink,
		cfg:     cfg,
		queries: queries,
	}
}

// TestService_CreateSchema covers the happy path and every documented
// rejection rule for CreateSchema (tracking lines 126–130).
func TestService_CreateSchema(t *testing.T) {
	if testing.Short() {
		t.SkipNow()
	}
	ctx := t.Context()
	const clientID = "TEST_SVC_CREATE_A"
	fx := newTestService(t, clientID)

	t.Run("happy_path_valid_schema", func(t *testing.T) {
		input := customschema.CreateSchemaInput{
			ClientID:    clientID,
			Name:        "happy_path",
			Description: "unit test schema",
			SchemaDef:   json.RawMessage(trivialValidSchemaJSON),
		}
		got, err := fx.service.CreateSchema(ctx, input, testActor)
		require.NoError(t, err)
		require.NotNil(t, got)
		require.NotEqual(t, uuid.Nil, got.ID, "ID must be assigned")
		require.Equal(t, clientID, got.ClientID)
		require.Equal(t, "happy_path", got.Name)
		require.Equal(t, 1, got.Version)
		require.Equal(t, "active", got.Status)
		require.False(t, got.CreatedAt.IsZero(), "CreatedAt must be populated")
		require.Equal(t, testActor, got.CreatedBy,
			"CreatedBy must be the actor arg, never a body field")

		// DB round-trip: the row must exist under this id.
		row, err := fx.queries.GetClientMetadataSchema(ctx, got.ID)
		require.NoError(t, err)
		require.Equal(t, clientID, row.ClientID)
		require.Equal(t, "happy_path", row.Name)
	})

	t.Run("writes_schema_create_audit_entry", func(t *testing.T) {
		// Seed a second schema (distinct name so the happy-path row above
		// does not collide with this one) and verify exactly one audit
		// entry was emitted for this subtest's write.
		before := len(fx.sink.all())
		input := customschema.CreateSchemaInput{
			ClientID:    clientID,
			Name:        "audit_entry_probe",
			Description: "",
			SchemaDef:   json.RawMessage(trivialValidSchemaJSON),
		}
		got, err := fx.service.CreateSchema(ctx, input, testActor)
		require.NoError(t, err)
		require.NotNil(t, got)

		records := fx.sink.all()
		require.Equal(t, before+1, len(records),
			"exactly one audit entry must be emitted by CreateSchema")
		last := records[len(records)-1]
		require.Equal(t, customschema.AuditActionSchemaCreate, last.Action)
		require.Equal(t, testActor, last.Actor)
		require.Equal(t, got.ID, last.ResourceID)
		// AuditRecord.ClientID is uuid.UUID, but client_metadata_schemas.client_id
		// is a varchar(255) Cognito-style identifier. This is a type mismatch
		// the team lead needs to resolve. For the red-phase test we simply
		// assert the schema's string ClientID is threaded into Details under
		// a well-known key so the engineer has freedom to pick either
		// Details.client_id_legacy or uuid.Nil in the ClientID column.
		if last.Details != nil {
			// If the engineer chose the Details route, assert the string
			// shows up there. If they chose uuid.Nil in ClientID, Details
			// may be nil — that's still acceptable for this red phase and
			// the assertion simply short-circuits.
			if v, ok := last.Details["client_id"]; ok {
				require.Equal(t, clientID, v,
					"Details.client_id must mirror the legacy varchar client id")
			}
		}
	})

	t.Run("rejects_invalid_json_schema", func(t *testing.T) {
		before := len(fx.sink.all())
		input := customschema.CreateSchemaInput{
			ClientID:  clientID,
			Name:      "invalid_json",
			SchemaDef: json.RawMessage("{this is not json"),
		}
		_, err := fx.service.CreateSchema(ctx, input, testActor)
		require.Error(t, err, "malformed JSON must be rejected")

		// No DB row written for this name.
		_, getErr := fx.queries.GetLatestSchemaByName(ctx, &repository.GetLatestSchemaByNameParams{
			ClientID: clientID,
			Name:     "invalid_json",
		})
		require.Error(t, getErr, "no row must exist for the rejected name")

		// No audit entry emitted.
		require.Equal(t, before, len(fx.sink.all()),
			"no audit entry must be emitted on validation failure")
	})

	t.Run("rejects_oversize_schema_def", func(t *testing.T) {
		// Build a JSON document whose length is strictly greater than
		// MaxSchemaDefinitionBytes. The validator rejects on strict >.
		var b strings.Builder
		b.WriteString(`{"type":"object","additionalProperties":false,"description":"`)
		padding := customschema.MaxSchemaDefinitionBytes + 1 - b.Len() - 2
		for i := 0; i < padding; i++ {
			b.WriteByte('x')
		}
		b.WriteString(`"}`)
		oversize := b.String()
		require.Greater(t, len(oversize), customschema.MaxSchemaDefinitionBytes,
			"test fixture must actually exceed the schema-definition ceiling")

		before := len(fx.sink.all())
		input := customschema.CreateSchemaInput{
			ClientID:  clientID,
			Name:      "oversize_probe",
			SchemaDef: json.RawMessage(oversize),
		}
		_, err := fx.service.CreateSchema(ctx, input, testActor)
		require.Error(t, err, "oversize schema_def must be rejected")

		_, getErr := fx.queries.GetLatestSchemaByName(ctx, &repository.GetLatestSchemaByNameParams{
			ClientID: clientID,
			Name:     "oversize_probe",
		})
		require.Error(t, getErr, "no row must exist for the rejected oversize schema")

		require.Equal(t, before, len(fx.sink.all()),
			"no audit entry must be emitted on oversize rejection")
	})

	t.Run("rejects_duplicate_name_at_version_1", func(t *testing.T) {
		const schemaName = "duplicate_name_probe"
		input := customschema.CreateSchemaInput{
			ClientID:  clientID,
			Name:      schemaName,
			SchemaDef: json.RawMessage(trivialValidSchemaJSON),
		}
		_, err := fx.service.CreateSchema(ctx, input, testActor)
		require.NoError(t, err, "first insert must succeed")

		before := len(fx.sink.all())
		_, err = fx.service.CreateSchema(ctx, input, testActor)
		require.Error(t, err,
			"second insert with same (client, name) must fail at the service layer")

		// Count rows for this (client, name). Should still be exactly one.
		var count int
		err = fx.cfg.GetDBPool().QueryRow(ctx,
			`SELECT COUNT(*) FROM client_metadata_schemas WHERE client_id = $1 AND name = $2`,
			clientID, schemaName,
		).Scan(&count)
		require.NoError(t, err)
		require.Equal(t, 1, count,
			"duplicate rejection must not write a second row")

		// No second audit entry (the first audit entry from the happy
		// call in this subtest is still there; the rejected call must
		// have emitted nothing).
		require.Equal(t, before, len(fx.sink.all()),
			"rejected duplicate must emit no audit entry")
	})
}

// TestService_GetSchema covers the GetSchema happy path and the 404
// sentinel (tracking lines 139–140).
func TestService_GetSchema(t *testing.T) {
	if testing.Short() {
		t.SkipNow()
	}
	ctx := t.Context()
	const clientID = "TEST_SVC_GET_A"
	fx := newTestService(t, clientID)

	t.Run("happy_path", func(t *testing.T) {
		// Seed directly via the repository (no need to exercise CreateSchema here).
		desc := "get-happy"
		row, err := fx.queries.CreateClientMetadataSchema(ctx, &repository.CreateClientMetadataSchemaParams{
			ClientID:    clientID,
			Name:        "get_happy",
			Description: &desc,
			SchemaDef:   []byte(trivialValidSchemaJSON),
			Version:     1,
			Status:      repository.SchemaStatusTypeActive,
			CreatedBy:   "seed-user",
		})
		require.NoError(t, err)
		require.NotNil(t, row)

		got, err := fx.service.GetSchema(ctx, row.ID)
		require.NoError(t, err)
		require.Equal(t, row.ID, got.Schema.ID)
		require.Equal(t, clientID, got.Schema.ClientID)
		require.Equal(t, "get_happy", got.Schema.Name)
		require.Equal(t, 1, got.Schema.Version)
		require.Equal(t, "active", got.Schema.Status)
		require.Equal(t, "seed-user", got.Schema.CreatedBy)
		// Freshly created schema has no bound documents.
		require.Equal(t, int64(0), got.DocumentCount)
		require.True(t, got.CanDelete)
	})

	t.Run("returns_not_found_sentinel", func(t *testing.T) {
		missing := uuid.New()
		_, err := fx.service.GetSchema(ctx, missing)
		require.Error(t, err)
		require.True(t, errors.Is(err, customschema.ErrSchemaNotFound),
			"GetSchema must wrap ErrSchemaNotFound on missing row, got: %v", err)
	})
}

// TestService_ListSchemas covers the filter matrix plus DocumentCount /
// CanDelete decoration (tracking lines 141–144).
func TestService_ListSchemas(t *testing.T) {
	if testing.Short() {
		t.SkipNow()
	}
	ctx := t.Context()
	const clientID = "TEST_SVC_LIST_A"
	fx := newTestService(t, clientID)

	// Shared fixture seeded once per top-level test run. Subtests that
	// mutate DocumentCount use their own distinct schema name.
	seedDirect := func(name string, version int32, status repository.SchemaStatusType) *repository.ClientMetadataSchema {
		desc := ""
		row, err := fx.queries.CreateClientMetadataSchema(ctx, &repository.CreateClientMetadataSchemaParams{
			ClientID:    clientID,
			Name:        name,
			Description: &desc,
			SchemaDef:   []byte(trivialValidSchemaJSON),
			Version:     version,
			Status:      status,
			CreatedBy:   "seed-user",
		})
		require.NoError(t, err)
		return row
	}
	seedDirect("alpha", 1, repository.SchemaStatusTypeActive)
	alphaV2 := seedDirect("alpha", 2, repository.SchemaStatusTypeActive)
	betaV1 := seedDirect("beta", 1, repository.SchemaStatusTypeActive)
	seedDirect("gamma", 1, repository.SchemaStatusTypeSuperseded)

	t.Run("default_filters_returns_active_latest", func(t *testing.T) {
		got, err := fx.service.ListSchemas(ctx, clientID, customschema.ListFilters{
			Limit:  100,
			Offset: 0,
		})
		require.NoError(t, err)

		// Build a (name, version) set for assertion.
		type tup struct {
			name    string
			version int
		}
		seen := map[tup]customschema.SchemaSummary{}
		for _, s := range got {
			seen[tup{s.Schema.Name, s.Schema.Version}] = s
		}
		require.Contains(t, seen, tup{"alpha", 2},
			"default filters must include alpha v2")
		require.Contains(t, seen, tup{"beta", 1},
			"default filters must include beta v1")
		require.NotContains(t, seen, tup{"alpha", 1},
			"default filters must collapse to MAX(version)")
		require.NotContains(t, seen, tup{"gamma", 1},
			"default filters must drop superseded rows")

		// Each summary from the fixture is unbound, so canDelete is true.
		require.Equal(t, int64(0), seen[tup{"alpha", 2}].DocumentCount)
		require.True(t, seen[tup{"alpha", 2}].CanDelete)
		require.Equal(t, int64(0), seen[tup{"beta", 1}].DocumentCount)
		require.True(t, seen[tup{"beta", 1}].CanDelete)
		_ = alphaV2
		_ = betaV1
	})

	t.Run("status_any_returns_all", func(t *testing.T) {
		got, err := fx.service.ListSchemas(ctx, clientID, customschema.ListFilters{
			StatusAny:          true,
			IncludeAllVersions: true,
			Limit:              100,
		})
		require.NoError(t, err)
		foundGamma := false
		for _, s := range got {
			if s.Schema.Name == "gamma" && s.Schema.Version == 1 {
				foundGamma = true
				require.Equal(t, "superseded", s.Schema.Status)
			}
		}
		require.True(t, foundGamma,
			"StatusAny+IncludeAllVersions must surface the superseded row")
	})

	t.Run("include_all_versions_returns_every_version", func(t *testing.T) {
		got, err := fx.service.ListSchemas(ctx, clientID, customschema.ListFilters{
			IncludeAllVersions: true,
			Limit:              100,
		})
		require.NoError(t, err)
		versions := map[int]bool{}
		for _, s := range got {
			if s.Schema.Name == "alpha" {
				versions[s.Schema.Version] = true
			}
		}
		require.True(t, versions[1], "alpha v1 must be returned when IncludeAllVersions=true")
		require.True(t, versions[2], "alpha v2 must be returned when IncludeAllVersions=true")
	})

	t.Run("document_count_drives_can_delete", func(t *testing.T) {
		// Dedicated schema + two bound documents so the fixture above is
		// not disturbed. Use the SAME client so the FK is satisfied.
		bound := seedDirect("bound_schema", 1, repository.SchemaStatusTypeActive)
		pool := fx.cfg.GetDBPool()
		doc1, err := fx.queries.CreateDocument(ctx, &repository.CreateDocumentParams{
			Clientid: clientID,
			Hash:     "svc_list_bound_doc_1",
		})
		require.NoError(t, err)
		_, err = pool.Exec(ctx,
			`UPDATE documents SET custom_schema_id = $1 WHERE id = $2`,
			bound.ID, doc1)
		require.NoError(t, err)
		doc2, err := fx.queries.CreateDocument(ctx, &repository.CreateDocumentParams{
			Clientid: clientID,
			Hash:     "svc_list_bound_doc_2",
		})
		require.NoError(t, err)
		_, err = pool.Exec(ctx,
			`UPDATE documents SET custom_schema_id = $1 WHERE id = $2`,
			bound.ID, doc2)
		require.NoError(t, err)

		got, err := fx.service.ListSchemas(ctx, clientID, customschema.ListFilters{
			Name:   "bound_schema",
			Limit:  100,
			Offset: 0,
		})
		require.NoError(t, err)
		require.Len(t, got, 1, "name filter must narrow to exactly one row")
		require.Equal(t, int64(2), got[0].DocumentCount)
		require.False(t, got[0].CanDelete, "CanDelete must be false when documents are bound")
	})

	t.Run("name_filter_narrows_results", func(t *testing.T) {
		// Name filter is EXACT match (the underlying query uses `name = $`,
		// not ILIKE). Asserted by the repository tests too; re-asserted here
		// at the service layer so handlers know they cannot pass a prefix.
		got, err := fx.service.ListSchemas(ctx, clientID, customschema.ListFilters{
			Name:  "alpha",
			Limit: 100,
		})
		require.NoError(t, err)
		for _, s := range got {
			require.Equal(t, "alpha", s.Schema.Name,
				"name filter must return only rows whose name matches exactly")
		}
	})
}

// TestService_DeleteSchema covers the retire-on-delete happy path, the
// audit entry, the in-use rejection, and the not-found sentinel
// (tracking lines 145–147).
func TestService_DeleteSchema(t *testing.T) {
	if testing.Short() {
		t.SkipNow()
	}
	ctx := t.Context()
	const clientID = "TEST_SVC_DELETE_A"
	fx := newTestService(t, clientID)

	seed := func(name string) *repository.ClientMetadataSchema {
		desc := ""
		row, err := fx.queries.CreateClientMetadataSchema(ctx, &repository.CreateClientMetadataSchemaParams{
			ClientID:    clientID,
			Name:        name,
			Description: &desc,
			SchemaDef:   []byte(trivialValidSchemaJSON),
			Version:     1,
			Status:      repository.SchemaStatusTypeActive,
			CreatedBy:   "seed-user",
		})
		require.NoError(t, err)
		return row
	}

	t.Run("happy_path_retires", func(t *testing.T) {
		schema := seed("delete_happy")
		err := fx.service.DeleteSchema(ctx, schema.ID, testActor)
		require.NoError(t, err)

		// Row must still exist with status=retired.
		reloaded, err := fx.queries.GetClientMetadataSchema(ctx, schema.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeRetired, reloaded.Status,
			"DeleteSchema must retire the row, not physically delete it")
	})

	t.Run("writes_schema_delete_audit_entry", func(t *testing.T) {
		schema := seed("delete_audit")
		before := len(fx.sink.all())
		err := fx.service.DeleteSchema(ctx, schema.ID, testActor)
		require.NoError(t, err)

		records := fx.sink.all()
		require.Equal(t, before+1, len(records),
			"exactly one audit entry must be emitted by DeleteSchema")
		last := records[len(records)-1]
		require.Equal(t, customschema.AuditActionSchemaDelete, last.Action)
		require.Equal(t, testActor, last.Actor)
		require.Equal(t, schema.ID, last.ResourceID)
	})

	t.Run("rejects_when_document_bound_returns_conflict", func(t *testing.T) {
		schema := seed("delete_in_use")
		doc, err := fx.queries.CreateDocument(ctx, &repository.CreateDocumentParams{
			Clientid: clientID,
			Hash:     "svc_delete_bound_doc",
		})
		require.NoError(t, err)
		_, err = fx.cfg.GetDBPool().Exec(ctx,
			`UPDATE documents SET custom_schema_id = $1 WHERE id = $2`,
			schema.ID, doc)
		require.NoError(t, err)

		before := len(fx.sink.all())
		err = fx.service.DeleteSchema(ctx, schema.ID, testActor)
		require.Error(t, err)
		require.True(t, errors.Is(err, customschema.ErrSchemaInUse),
			"DeleteSchema must wrap ErrSchemaInUse when a document is bound, got: %v", err)

		// Status must still be active — no state change on rejection.
		reloaded, err := fx.queries.GetClientMetadataSchema(ctx, schema.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeActive, reloaded.Status,
			"rejected delete must not mutate status")

		require.Equal(t, before, len(fx.sink.all()),
			"rejected delete must emit no audit entry")
	})

	t.Run("returns_not_found_on_missing_id", func(t *testing.T) {
		before := len(fx.sink.all())
		missing := uuid.New()
		err := fx.service.DeleteSchema(ctx, missing, testActor)
		require.Error(t, err)
		require.True(t, errors.Is(err, customschema.ErrSchemaNotFound),
			"DeleteSchema must wrap ErrSchemaNotFound on missing id, got: %v", err)
		require.Equal(t, before, len(fx.sink.all()),
			"missing-id delete must emit no audit entry")
	})
}

// TestService_CreateSchemaVersion is Part B of mutable-metadata milestone
// 1.6: integration tests for CreateSchemaVersion. Red phase — the stub in
// service.go returns errNotImplemented so every subtest below fails until
// the golang engineer fills in the body in the next dispatch.
//
// Tracking §1.6 lines 131-138 enumerate the rules this test codifies:
//
//	131 happy path produces v2
//	132 concurrency produces distinct versions
//	133 rejects when parent does not exist
//	134 non-active parent rejection (caller passed v1 while v2 is active)
//	135 retired parent rejection
//	136 active-parent invariant after every write
//	137 rejects invalid schema definition
//	138 writes schema.update audit entry
//
// Sentinel mapping decision (made by the test engineer for this dispatch,
// the golang engineer must match):
//
//   - ErrSchemaParentNotActive  -> parent row's status is not 'active' and
//     not 'retired' (typical: 'superseded').
//   - ErrSchemaParentRetired    -> parent row's status is 'retired'. More
//     specific than ErrSchemaParentNotActive so the handler layer can
//     surface a more actionable reason.
func TestService_CreateSchemaVersion(t *testing.T) {
	if testing.Short() {
		t.SkipNow()
	}
	ctx := t.Context()
	const clientID = "TEST_SVC_V"
	fx := newTestService(t, clientID)

	// seedV1 creates a fresh (clientID, name) lineage at version 1 via the
	// real CreateSchema code path so the test exercises the same insert
	// route the handler layer will take. Returns the new schema's id.
	seedV1 := func(t *testing.T, name string) *customschema.Schema {
		t.Helper()
		// Idempotency: wipe any leftover lineage rows under this name.
		_, err := fx.cfg.GetDBPool().Exec(ctx,
			`DELETE FROM client_metadata_schemas WHERE client_id = $1 AND name = $2`,
			clientID, name)
		require.NoError(t, err)
		got, err := fx.service.CreateSchema(ctx, customschema.CreateSchemaInput{
			ClientID:    clientID,
			Name:        name,
			Description: "seed v1",
			SchemaDef:   json.RawMessage(trivialValidSchemaJSON),
		}, testActor)
		require.NoError(t, err)
		require.NotNil(t, got)
		require.Equal(t, 1, got.Version)
		require.Equal(t, "active", got.Status)
		return got
	}

	// countRows returns the number of rows in client_metadata_schemas for
	// a (client, name) pair. Used by the "no row inserted" assertions.
	countRows := func(t *testing.T, name string) int {
		t.Helper()
		var n int
		err := fx.cfg.GetDBPool().QueryRow(ctx,
			`SELECT COUNT(*) FROM client_metadata_schemas WHERE client_id = $1 AND name = $2`,
			clientID, name).Scan(&n)
		require.NoError(t, err)
		return n
	}

	// countActiveRows returns the number of 'active' rows for a (client,
	// name) pair. Used by the active-parent invariant assertions.
	countActiveRows := func(t *testing.T, name string) int {
		t.Helper()
		var n int
		err := fx.cfg.GetDBPool().QueryRow(ctx,
			`SELECT COUNT(*) FROM client_metadata_schemas WHERE client_id = $1 AND name = $2 AND status = 'active'`,
			clientID, name).Scan(&n)
		require.NoError(t, err)
		return n
	}

	freshInput := func(desc string) customschema.CreateSchemaVersionInput {
		return customschema.CreateSchemaVersionInput{
			Description: desc,
			SchemaDef:   json.RawMessage(trivialValidSchemaJSON),
		}
	}

	t.Run("happy_path_produces_v2", func(t *testing.T) {
		v1 := seedV1(t, "invoice")

		got, err := fx.service.CreateSchemaVersion(ctx, v1.ID, freshInput("v2"), testActor)
		require.NoError(t, err)
		require.NotNil(t, got)
		require.Equal(t, 2, got.Version, "new row must land at version 2")
		require.Equal(t, "active", got.Status, "new row must be active")
		require.Equal(t, testActor, got.CreatedBy,
			"CreatedBy must be the actor arg, never a body field")
		require.NotEqual(t, v1.ID, got.ID, "v2 must have a distinct id from v1")

		// Parent should now be superseded.
		parent, err := fx.queries.GetClientMetadataSchema(ctx, v1.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeSuperseded, parent.Status,
			"parent v1 must transition to superseded inside the same tx")

		// New row should be active.
		child, err := fx.queries.GetClientMetadataSchema(ctx, got.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeActive, child.Status,
			"new v2 row must be active")
		require.Equal(t, int32(2), child.Version)
	})

	t.Run("rejects_parent_not_found", func(t *testing.T) {
		// Use a schema name that has no rows so the count assertion is
		// unambiguous. Count BEFORE the call and after to prove nothing
		// was inserted.
		const probeName = "ghost_parent"
		require.Equal(t, 0, countRows(t, probeName),
			"fixture precondition: no rows for probe lineage")

		missing := uuid.New()
		_, err := fx.service.CreateSchemaVersion(ctx, missing, freshInput("ghost"), testActor)
		require.Error(t, err)
		require.True(t, errors.Is(err, customschema.ErrSchemaNotFound),
			"missing parent must surface ErrSchemaNotFound, got: %v", err)

		// No row was inserted under the probe name — obvious because no
		// lineage row ever existed for it.
		require.Equal(t, 0, countRows(t, probeName),
			"missing-parent rejection must not insert any row")
	})

	t.Run("rejects_non_active_parent", func(t *testing.T) {
		v1 := seedV1(t, "alpha")
		// Supersede v1 by creating v2 from v1.
		v2, err := fx.service.CreateSchemaVersion(ctx, v1.ID, freshInput("alpha v2"), testActor)
		require.NoError(t, err)
		require.NotNil(t, v2)
		require.Equal(t, 2, v2.Version)

		// Now v1 is superseded. Calling CreateSchemaVersion with v1.ID
		// must be rejected with ErrSchemaParentNotActive.
		_, err = fx.service.CreateSchemaVersion(ctx, v1.ID, freshInput("should fail"), testActor)
		require.Error(t, err)
		require.True(t, errors.Is(err, customschema.ErrSchemaParentNotActive),
			"non-active parent must surface ErrSchemaParentNotActive, got: %v", err)

		// v2 is still active, v1 is still superseded, total rows still 2.
		v2reload, err := fx.queries.GetClientMetadataSchema(ctx, v2.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeActive, v2reload.Status,
			"v2 must remain active after rejection")
		v1reload, err := fx.queries.GetClientMetadataSchema(ctx, v1.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeSuperseded, v1reload.Status,
			"v1 must remain superseded after rejection")
		require.Equal(t, 2, countRows(t, "alpha"),
			"rejected call must not insert a third row")
	})

	t.Run("rejects_retired_parent", func(t *testing.T) {
		// The test engineer chose ErrSchemaParentRetired as the expected
		// sentinel here (more specific than ErrSchemaParentNotActive so
		// the handler layer can surface a more actionable reason). The
		// golang engineer must map retired parents to this sentinel.
		v1 := seedV1(t, "beta")

		// Retire v1 via the real DeleteSchema path.
		err := fx.service.DeleteSchema(ctx, v1.ID, testActor)
		require.NoError(t, err)

		_, err = fx.service.CreateSchemaVersion(ctx, v1.ID, freshInput("should fail"), testActor)
		require.Error(t, err)
		require.True(t, errors.Is(err, customschema.ErrSchemaParentRetired),
			"retired parent must surface ErrSchemaParentRetired, got: %v", err)

		// v1 is still retired, no new row inserted.
		v1reload, err := fx.queries.GetClientMetadataSchema(ctx, v1.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeRetired, v1reload.Status,
			"retired v1 must remain retired after rejection")
		require.Equal(t, 1, countRows(t, "beta"),
			"rejected call against retired parent must not insert a row")
	})

	t.Run("invalid_schema_definition_rejected", func(t *testing.T) {
		v1 := seedV1(t, "gamma")
		before := len(fx.sink.all())

		_, err := fx.service.CreateSchemaVersion(ctx, v1.ID, customschema.CreateSchemaVersionInput{
			Description: "malformed",
			SchemaDef:   json.RawMessage("{this is not json"),
		}, testActor)
		require.Error(t, err, "malformed schema_def must be rejected")

		// Parent is untouched, no new row inserted, no audit entry.
		v1reload, err := fx.queries.GetClientMetadataSchema(ctx, v1.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeActive, v1reload.Status,
			"parent must remain active after validation failure")
		require.Equal(t, 1, countRows(t, "gamma"),
			"validation failure must not insert a new row")
		require.Equal(t, before, len(fx.sink.all()),
			"validation failure must not emit an audit entry")
	})

	t.Run("writes_schema_update_audit_entry", func(t *testing.T) {
		// ResourceID choice: the new version's id. Justification: the
		// audit event is reporting "a new version landed", so the row
		// it names is the new version's id, not the (now superseded)
		// parent's id. The golang engineer must match this.
		v1 := seedV1(t, "delta")
		before := len(fx.sink.all())

		got, err := fx.service.CreateSchemaVersion(ctx, v1.ID, freshInput("delta v2"), testActor)
		require.NoError(t, err)
		require.NotNil(t, got)

		records := fx.sink.all()
		require.Equal(t, before+1, len(records),
			"exactly one audit entry must be emitted by CreateSchemaVersion")
		last := records[len(records)-1]
		require.Equal(t, customschema.AuditActionSchemaUpdate, last.Action,
			"audit action must be schema.update")
		require.Equal(t, testActor, last.Actor,
			"audit actor must be the actor arg, never a body field")
		require.Equal(t, got.ID, last.ResourceID,
			"audit ResourceID must name the new version's id, not the parent's id")
		require.Equal(t, clientID, last.ClientID,
			"audit ClientID must be the schema's varchar client id")
	})

	t.Run("active_parent_invariant_after_each_write", func(t *testing.T) {
		v1 := seedV1(t, "epsilon")

		// Three sequential calls produce v2 -> v3 -> v4. After each call
		// there must be exactly one active row for (clientID, epsilon).
		currentParentID := v1.ID
		for i := 0; i < 3; i++ {
			next, err := fx.service.CreateSchemaVersion(ctx, currentParentID, freshInput("epsilon step"), testActor)
			require.NoError(t, err, "sequential call %d must succeed", i+1)
			require.NotNil(t, next)
			require.Equal(t, i+2, next.Version, "sequential call %d must land at version %d", i+1, i+2)

			require.Equal(t, 1, countActiveRows(t, "epsilon"),
				"active-parent invariant must hold after sequential call %d", i+1)
			currentParentID = next.ID
		}

		// Total of 4 rows: v1/v2/v3 superseded, v4 active.
		require.Equal(t, 4, countRows(t, "epsilon"),
			"three sequential version creations plus v1 must produce 4 rows")

		// Verify the per-status breakdown via a direct DB count so the
		// test doesn't depend on ListSchemas filter semantics.
		var superseded int
		err := fx.cfg.GetDBPool().QueryRow(ctx,
			`SELECT COUNT(*) FROM client_metadata_schemas
             WHERE client_id = $1 AND name = 'epsilon' AND status = 'superseded'`,
			clientID).Scan(&superseded)
		require.NoError(t, err)
		require.Equal(t, 3, superseded,
			"exactly three rows must be superseded after the loop")
	})

	t.Run("active_parent_invariant_holds_after_rejection", func(t *testing.T) {
		v1 := seedV1(t, "zeta")
		v2, err := fx.service.CreateSchemaVersion(ctx, v1.ID, freshInput("zeta v2"), testActor)
		require.NoError(t, err)
		require.NotNil(t, v2)

		// Branching from v1 again must be rejected.
		_, err = fx.service.CreateSchemaVersion(ctx, v1.ID, freshInput("should fail"), testActor)
		require.Error(t, err)
		require.True(t, errors.Is(err, customschema.ErrSchemaParentNotActive),
			"branching from superseded v1 must surface ErrSchemaParentNotActive, got: %v", err)

		require.Equal(t, 1, countActiveRows(t, "zeta"),
			"active-parent invariant must still hold after rejection (exactly one active row)")

		v1reload, err := fx.queries.GetClientMetadataSchema(ctx, v1.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeSuperseded, v1reload.Status,
			"v1 must remain superseded after rejection")
		v2reload, err := fx.queries.GetClientMetadataSchema(ctx, v2.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeActive, v2reload.Status,
			"v2 must remain active after rejection")
		require.Equal(t, 2, countRows(t, "zeta"),
			"rejected call must not insert a third row")
	})

	t.Run("concurrency_produces_distinct_versions", func(t *testing.T) {
		// Race design: two goroutines fire CreateSchemaVersion against
		// the same (clientID, "eta") v1 parent. Tracking line 132 says
		// "concurrent calls produce distinct version numbers". The v4
		// implementation achieves this by the first committer winning
		// with v2, and the second committer seeing the (now superseded)
		// parent and failing cleanly with ErrSchemaParentNotActive (per
		// tracking line 134). The expected end state is exactly two
		// rows: v1 superseded + v2 active. No v3, no duplicate v2.
		//
		// NOTE ON REGIME: if a future version of the service implements
		// a retry path where the loser re-reads the lineage and promotes
		// itself to v3, this subtest must be relaxed to "both succeed
		// with versions (2, 3)". The current v4 plan explicitly does
		// NOT implement that retry path — winner/loser is the contract.
		// Do not assert a specific winner; either goroutine may win.
		v1 := seedV1(t, "eta")

		var (
			wg    sync.WaitGroup
			mu    sync.Mutex
			oks   []*customschema.Schema
			fails []error
		)
		wg.Add(2)
		for _, desc := range []string{"v2-racer-A", "v2-racer-B"} {
			desc := desc
			go func() {
				defer wg.Done()
				got, err := fx.service.CreateSchemaVersion(ctx, v1.ID, freshInput(desc), testActor)
				mu.Lock()
				defer mu.Unlock()
				if err != nil {
					fails = append(fails, err)
					return
				}
				oks = append(oks, got)
			}()
		}
		wg.Wait()

		require.Len(t, oks, 1,
			"exactly one goroutine must succeed (winner-takes-all); got %d winners", len(oks))
		require.Len(t, fails, 1,
			"exactly one goroutine must fail; got %d failures", len(fails))
		require.True(t, errors.Is(fails[0], customschema.ErrSchemaParentNotActive),
			"loser must fail with ErrSchemaParentNotActive, got: %v", fails[0])
		require.Equal(t, 2, oks[0].Version,
			"winner must land at version 2")
		require.Equal(t, "active", oks[0].Status,
			"winner row must be active")

		// End state: exactly two rows for eta — v1 superseded + v2 active.
		require.Equal(t, 2, countRows(t, "eta"),
			"concurrency must leave exactly two rows (v1 + v2); no v3 and no duplicate v2")
		require.Equal(t, 1, countActiveRows(t, "eta"),
			"active-parent invariant must hold after the race")

		v1reload, err := fx.queries.GetClientMetadataSchema(ctx, v1.ID)
		require.NoError(t, err)
		require.Equal(t, repository.SchemaStatusTypeSuperseded, v1reload.Status,
			"v1 must be superseded after the race")
	})
}