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.go

@@ -0,0 +1,77 @@
+package controllers
+
+import (
+	"context"
+	"errors"
+	"sync/atomic"
+
+	"git.golem15.com/golem15/summercms/modules/cabana"
+	"git.golem15.com/golem15/summercms/modules/pact"
+	"git.golem15.com/jakub/sm-bm-plugin/models"
+	"gorm.io/gorm"
+)
+
+var (
+	_ pact.FormAfterCreate = materialsAdmin{}
+	_ pact.FormAfterUpdate = materialsAdmin{}
+	_ pact.FormAfterDelete = materialsAdmin{}
+)
+
+// MaterialIndex keeps the materials search index current once a write
+// commits (classes.MaterialIndexer). Its calls never fail the write.
+type MaterialIndex interface {
+	SyncAfterCommit(ctx context.Context, tx *gorm.DB, id uint)
+	RemoveAfterCommit(ctx context.Context, tx *gorm.DB, id uint)
+}
+
+type materialIndexHolder struct{ ix MaterialIndex }
+
+var materialIndex atomic.Value
+
+// UseMaterialIndex installs the index the materials admin syncs after a
+// save or delete; nil turns the syncs off. Boot installs it, because the
+// generated controller value has no field to carry it.
+func UseMaterialIndex(ix MaterialIndex) {
+	materialIndex.Store(materialIndexHolder{ix: ix})
+}
+
+func installedMaterialIndex() MaterialIndex {
+	h, _ := materialIndex.Load().(materialIndexHolder)
+	return h.ix
+}
+
+// FormAfterCreate syncs the new material once the save transaction commits.
+func (materialsAdmin) FormAfterCreate(ctx context.Context, model any) error {
+	return materialAfterCommit(ctx, model, false)
+}
+
+// FormAfterUpdate syncs the material once the save transaction commits.
+func (materialsAdmin) FormAfterUpdate(ctx context.Context, model any) error {
+	return materialAfterCommit(ctx, model, false)
+}
+
+// FormAfterDelete removes the material's document once the delete commits.
+func (materialsAdmin) FormAfterDelete(ctx context.Context, model any) error {
+	return materialAfterCommit(ctx, model, true)
+}
+
+// materialAfterCommit schedules the index work of an admin save on the save
+// transaction. Only a model that is not a material is an error: the index
+// never fails a save.
+func materialAfterCommit(ctx context.Context, model any, remove bool) error {
+	m, ok := model.(*models.Material)
+	if !ok || m == nil {
+		return errors.New("materials admin: form model is not a material")
+	}
+	ix := installedMaterialIndex()
+	if ix == nil || m.ID == 0 {
+		return nil
+	}
+	tx, _ := cabana.TxFromContext(ctx)
+	if remove {
+		ix.RemoveAfterCommit(ctx, tx, m.ID)
+	} else {
+		ix.SyncAfterCommit(ctx, tx, m.ID)
+	}
+	return nil
+}