feat: keep the materials index in sync and add bm:materials-reindex

- the materials admin syncs after create and update and removes after
  delete, once the save transaction commits (UseMaterialIndex, set at Boot)
- POST and PUT /api/v1/bm/materials sync after the transaction, DELETE
  removes the document (its statement has no primary key, so no callback)
- bm:materials-reindex [--fresh] [--if-configured] ensures the index and
  syncs every material; it refuses without an engine and runs nightly
  at 04:15 with --if-configured
- TestMaterialSearchAgainstDatabase (Postgres) is written for the final
  verification phase

controllers/materials_hooks_test.go

@@ -0,0 +1,81 @@
+package controllers
+
+import (
+	"context"
+	"slices"
+	"strconv"
+	"testing"
+
+	"git.golem15.com/jakub/sm-bm-plugin/models"
+	"gorm.io/gorm"
+)
+
+// recordingIndex records the after-commit calls of the materials admin.
+type recordingIndex struct {
+	calls []string
+	txs   []*gorm.DB
+}
+
+func (r *recordingIndex) SyncAfterCommit(_ context.Context, tx *gorm.DB, id uint) {
+	r.calls = append(r.calls, "sync "+itoa(id))
+	r.txs = append(r.txs, tx)
+}
+
+func (r *recordingIndex) RemoveAfterCommit(_ context.Context, tx *gorm.DB, id uint) {
+	r.calls = append(r.calls, "remove "+itoa(id))
+	r.txs = append(r.txs, tx)
+}
+
+func itoa(id uint) string { return strconv.FormatUint(uint64(id), 10) }
+
+func TestMaterialsAdminHooks(t *testing.T) {
+	t.Cleanup(func() { UseMaterialIndex(nil) })
+	var c materialsAdmin
+	ctx := context.Background()
+	m := &models.Material{ID: 7}
+
+	// No index installed: nothing to do, and no error.
+	UseMaterialIndex(nil)
+	for name, fn := range map[string]func(context.Context, any) error{"create": c.FormAfterCreate, "update": c.FormAfterUpdate, "delete": c.FormAfterDelete} {
+		if err := fn(ctx, m); err != nil {
+			t.Errorf("%s without an index: %v", name, err)
+		}
+	}
+
+	rec := &recordingIndex{}
+	UseMaterialIndex(rec)
+	if err := c.FormAfterCreate(ctx, m); err != nil {
+		t.Fatal(err)
+	}
+	if err := c.FormAfterUpdate(ctx, m); err != nil {
+		t.Fatal(err)
+	}
+	if err := c.FormAfterDelete(ctx, m); err != nil {
+		t.Fatal(err)
+	}
+	if want := []string{"sync 7", "sync 7", "remove 7"}; !slices.Equal(rec.calls, want) {
+		t.Errorf("calls = %v, want %v", rec.calls, want)
+	}
+	// Outside a cabana write there is no transaction: the index then runs
+	// at once (lagoon.AfterCommit with a nil handle).
+	for i, tx := range rec.txs {
+		if tx != nil {
+			t.Errorf("call %d got a transaction outside a write", i)
+		}
+	}
+
+	// A model of another type is an error and schedules nothing.
+	rec.calls = nil
+	for name, fn := range map[string]func(context.Context, any) error{"create": c.FormAfterCreate, "update": c.FormAfterUpdate, "delete": c.FormAfterDelete} {
+		if err := fn(ctx, &models.Course{ID: 7}); err == nil {
+			t.Errorf("%s with a course: no error", name)
+		}
+	}
+	var nilMaterial *models.Material
+	if err := c.FormAfterUpdate(ctx, nilMaterial); err == nil {
+		t.Error("update with a nil material: no error")
+	}
+	if len(rec.calls) != 0 {
+		t.Errorf("calls for a wrong model = %v", rec.calls)
+	}
+}