feat(group): group service to create, update, and delete groups (#10455)

# Which Problems Are Solved

This PR adds API definition and backend implementation for GroupService
to manage user groups.

# How the Problems Are Solved
* API definition to create, update, retrieve, and delete groups is added
* Command-side implementation to create, update, and delete user groups
as part of the GroupV2 API is added

# Additional Changes
N/A

# Additional Context
- Related to #10089, #9702 (parent ticket)
- User contribution: https://github.com/zitadel/zitadel/pull/9428/files
- Additional functionalities to list/search user groups, add
permissions, manage users in groups, group scopes will be added in
subsequent PRs.
- Also needs documentation, which will be added once the entire feature
is available

---------

Co-authored-by: Livio Spring <[email protected]>

internal/command/group.go

@@ -0,0 +1,160 @@
+package command
+
+import (
+	"context"
+	"strings"
+
+	"github.com/zitadel/zitadel/internal/domain"
+	"github.com/zitadel/zitadel/internal/eventstore/v1/models"
+	repo "github.com/zitadel/zitadel/internal/repository/group"
+	"github.com/zitadel/zitadel/internal/telemetry/tracing"
+	"github.com/zitadel/zitadel/internal/zerrors"
+)
+
+type CreateGroup struct {
+	models.ObjectRoot
+
+	Name        string
+	Description string
+}
+
+func (g *CreateGroup) IsValid() error {
+	if strings.TrimSpace(g.Name) == "" {
+		return zerrors.ThrowInvalidArgument(nil, "GROUP-m177lN", "Errors.Group.InvalidName")
+	}
+	return nil
+}
+
+// CreateGroup creates a new user group in an organization
+func (c *Commands) CreateGroup(ctx context.Context, group *CreateGroup) (details *domain.ObjectDetails, err error) {
+	ctx, span := tracing.NewSpan(ctx)
+	defer func() { span.EndWithError(err) }()
+
+	// todo: check permissions
+
+	if err = group.IsValid(); err != nil {
+		return nil, err
+	}
+	if group.ResourceOwner == "" {
+		return nil, zerrors.ThrowInvalidArgument(nil, "CMDGRP-msc0Tt", "Errors.Group.MissingOrganizationID")
+	}
+	// check whether the organization where the group should be created exists
+	err = c.checkOrgExists(ctx, group.ResourceOwner)
+	if err != nil {
+		return nil, zerrors.ThrowPreconditionFailed(nil, "CMDGRP-j1mH8l", "Errors.Org.NotFound")
+	}
+
+	// create a unique group ID if not provided
+	if group.AggregateID == "" {
+		group.AggregateID, err = c.idGenerator.Next()
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// check if a group with the same ID already exists
+	groupWriteModel, err := c.getGroupWriteModelByID(ctx, group.AggregateID, group.ResourceOwner)
+	if err != nil {
+		return nil, err
+	}
+	if groupWriteModel.State.Exists() {
+		return nil, zerrors.ThrowAlreadyExists(nil, "CMDGRP-shRut3", "Errors.Group.AlreadyExists")
+	}
+
+	err = c.pushAppendAndReduce(ctx,
+		groupWriteModel,
+		repo.NewGroupAddedEvent(ctx,
+			GroupAggregateFromWriteModel(ctx, &groupWriteModel.WriteModel),
+			group.Name,
+			group.Description,
+		))
+	if err != nil {
+		return nil, err
+	}
+	return writeModelToObjectDetails(&groupWriteModel.WriteModel), nil
+}
+
+type UpdateGroup struct {
+	models.ObjectRoot
+
+	Name        *string
+	Description *string
+}
+
+func (g *UpdateGroup) IsValid() error {
+	if g.Name != nil && strings.TrimSpace(*g.Name) == "" {
+		return zerrors.ThrowInvalidArgument(nil, "GROUP-dUNd3r", "Errors.Group.InvalidName")
+	}
+	return nil
+}
+
+// UpdateGroup updates a user group in an organization
+func (c *Commands) UpdateGroup(ctx context.Context, groupUpdate *UpdateGroup) (details *domain.ObjectDetails, err error) {
+	ctx, span := tracing.NewSpan(ctx)
+	defer func() { span.EndWithError(err) }()
+
+	if err = groupUpdate.IsValid(); err != nil {
+		return nil, err
+	}
+
+	// todo: check permissions
+	existingGroup, err := c.getGroupWriteModelByID(ctx, groupUpdate.AggregateID, groupUpdate.ResourceOwner)
+	if err != nil {
+		return nil, err
+	}
+	if !existingGroup.State.Exists() {
+		return nil, zerrors.ThrowNotFound(nil, "CMDGRP-b33zly", "Errors.Group.NotFound")
+	}
+
+	changedEvent := existingGroup.NewChangedEvent(
+		ctx,
+		GroupAggregateFromWriteModel(ctx, &existingGroup.WriteModel),
+		groupUpdate.Name,
+		groupUpdate.Description,
+	)
+	if changedEvent == nil {
+		return writeModelToObjectDetails(&existingGroup.WriteModel), nil
+	}
+
+	err = c.pushAppendAndReduce(ctx,
+		existingGroup,
+		changedEvent)
+	if err != nil {
+		return nil, err
+	}
+	return writeModelToObjectDetails(&existingGroup.WriteModel), nil
+}
+
+// DeleteGroup deletes a user group from an organization
+func (c *Commands) DeleteGroup(ctx context.Context, groupID string) (details *domain.ObjectDetails, err error) {
+	ctx, span := tracing.NewSpan(ctx)
+	defer func() { span.EndWithError(err) }()
+
+	existingGroup, err := c.getGroupWriteModelByID(ctx, groupID, "")
+	if err != nil {
+		return nil, err
+	}
+	if !existingGroup.State.Exists() {
+		return writeModelToObjectDetails(&existingGroup.WriteModel), nil
+	}
+
+	err = c.pushAppendAndReduce(ctx,
+		existingGroup,
+		repo.NewGroupRemovedEvent(ctx,
+			GroupAggregateFromWriteModel(ctx, &existingGroup.WriteModel),
+			existingGroup.Name,
+		))
+	if err != nil {
+		return nil, err
+	}
+	return writeModelToObjectDetails(&existingGroup.WriteModel), nil
+}
+
+func (c *Commands) getGroupWriteModelByID(ctx context.Context, id, orgID string) (*GroupWriteModel, error) {
+	groupWriteModel := NewGroupWriteModel(id, orgID)
+	err := c.eventstore.FilterToQueryReducer(ctx, groupWriteModel)
+	if err != nil {
+		return nil, err
+	}
+	return groupWriteModel, nil
+}