Add a metadata system

internal/component/instances/meta.go

@@ -0,0 +1,204 @@
+package instances
+
+import (
+	"encoding/json"
+	"errors"
+
+	"github.com/FAU-CDI/wisski-distillery/internal/component/sql"
+	"github.com/FAU-CDI/wisski-distillery/internal/models"
+	"gorm.io/gorm"
+)
+
+// MetaKey represents a key for metadata.
+type MetaKey string
+
+// ErrMetadatumNotSet is returned by various [MetaStorage] functions when a metadatum is not set
+var ErrMetadatumNotSet = errors.New("metadatum not set")
+
+// MetaStorage manages some metadata.
+type MetaStorage interface {
+	// Get retrieves metadata with the provided key and deserializes the first one into target.
+	// If no metadatum exists, returns [ErrMetadatumNotSet].
+	Get(key MetaKey, target any) error
+
+	// GetAll receives all metadata with the provided keys.
+	// For each received value, the targets function is called with the current index, and total number of results.
+	// The function is intended to return a target for deserialization.
+	//
+	// When no metadatum exists, targets is not called, and nil error is returned.
+	GetAll(key MetaKey, targets func(index, total int) any) error
+
+	// Delete deletes all metadata with the provided key.
+	Delete(key MetaKey) error
+
+	// Set serializes value and stores it with the provided key.
+	// Any other metadata with the same key is deleted.
+	Set(key MetaKey, value any) error
+
+	// Add serializes values and stores each as associated with the provided key.
+	// Already existing metadata is left intact.
+	Add(key MetaKey, values ...any) error
+
+	// Purge removes all metadata, regardless of key.
+	Purge() error
+}
+
+// Metadata returns a system-wide [MetaStorage].
+func (instances *Instances) Metadata() MetaStorage {
+	return &storage{
+		SQL:  instances.SQL,
+		Slug: "", // not associated to any slug
+	}
+}
+
+// Metadata returns a [MetaStorage] that manages metadata related to this WissKI instance.
+// It will be automatically deleted once the instance is deleted.
+func (wisski *WissKI) Metadata() MetaStorage {
+	return &storage{
+		SQL:  wisski.instances.SQL,
+		Slug: wisski.Slug, // associated to this instance
+	}
+}
+
+// storage implements MetaStorage
+type storage struct {
+	SQL  *sql.SQL
+	Slug string
+}
+
+func (s *storage) Get(key MetaKey, target any) error {
+	table, err := s.SQL.QueryTable(true, models.MetadataTable)
+	if err != nil {
+		return err
+	}
+
+	// read the datum from the database
+	var datum models.Metadatum
+	status := table.Where(&models.Metadatum{Slug: s.Slug, Key: string(key)}).Order("pk DESC").Find(&datum)
+
+	// check if there was an error
+	if err := status.Error; err != nil {
+		return err
+	}
+
+	// check if e actually found it!
+	if status.RowsAffected == 0 {
+		return ErrMetadatumNotSet
+	}
+
+	// and do the unmarshaling!
+	return json.Unmarshal(datum.Value, target)
+}
+
+func (s *storage) GetAll(key MetaKey, target func(index, total int) any) error {
+	table, err := s.SQL.QueryTable(true, models.MetadataTable)
+	if err != nil {
+		return err
+	}
+
+	// read the datum from the database
+	var data []models.Metadatum
+	status := table.Where(&models.Metadatum{Slug: s.Slug, Key: string(key)}).Find(&data)
+
+	// check if there was an error
+	if err := status.Error; err != nil {
+		return err
+	}
+
+	// unpack all of them into the destination
+	for index, datum := range data {
+		err := json.Unmarshal(datum.Value, target(index, len(data)))
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (s *storage) Delete(key MetaKey) error {
+	table, err := s.SQL.QueryTable(true, models.MetadataTable)
+	if err != nil {
+		return err
+	}
+
+	// delete all the values
+	status := table.Where(&models.Metadatum{Slug: s.Slug, Key: string(key)}).Delete(&models.Metadatum{})
+	if err := status.Error; err != nil {
+		return err
+	}
+	return nil
+}
+
+func (s *storage) Set(key MetaKey, value any) error {
+	table, err := s.SQL.QueryTable(true, models.MetadataTable)
+	if err != nil {
+		return err
+	}
+
+	// marshal the value
+	bytes, err := json.Marshal(value)
+	if err != nil {
+		return err
+	}
+
+	return table.Transaction(func(tx *gorm.DB) error {
+		// delete the old values
+		status := tx.Where(&models.Metadatum{Slug: s.Slug, Key: string(key)}).Delete(&models.Metadatum{})
+		if err := status.Error; err != nil {
+			return err
+		}
+
+		// create the new item to insert
+		status = tx.Create(&models.Metadatum{
+			Key:   string(key),
+			Slug:  s.Slug,
+			Value: bytes,
+		})
+		if err := status.Error; err != nil {
+			return err
+		}
+
+		return nil
+	})
+}
+
+func (s *storage) Add(key MetaKey, values ...any) error {
+	table, err := s.SQL.QueryTable(true, models.MetadataTable)
+	if err != nil {
+		return err
+	}
+
+	return table.Transaction(func(tx *gorm.DB) error {
+		for _, value := range values {
+			bytes, err := json.Marshal(value)
+			if err != nil {
+				return err
+			}
+
+			// create the new item to insert
+			status := tx.Create(&models.Metadatum{
+				Key:   string(key),
+				Slug:  s.Slug,
+				Value: bytes,
+			})
+			if err := status.Error; err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+}
+
+func (s *storage) Purge() error {
+	table, err := s.SQL.QueryTable(true, models.MetadataTable)
+	if err != nil {
+		return err
+	}
+
+	status := table.Where("slug = ?", s.Slug).Delete(&models.Metadatum{})
+	if status.Error != nil {
+		return status.Error
+	}
+	return nil
+}