Add turso db branch command (#1024)

The `turso db create --from-db` syntax is awkward and not discoverable.
Let's add a `turso db branch` command for better DX (but keep the create
variant too).

Author: penberg

README.md

@@ -85,6 +85,12 @@ Or you can specify the name of the database with:
 turso db create <database name>
 ```
 
+To create a branch from an existing database, run:
+
+```bash
+turso db branch <source-database> <target-database>
+```
+
 ### Start SQL shell
 
 You can start an interactive SQL shell similar to `sqlite3` with:

internal/cmd/db_branch.go

@@ -0,0 +1,81 @@
+package cmd
+
+import (
+	"errors"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+var branchTimestampFlag string
+
+func init() {
+	dbCmd.AddCommand(dbBranchCmd)
+	addGroupFlag(dbBranchCmd)
+	addLocationFlag(dbBranchCmd, "Location ID. If no ID is specified, primary location of the destination group is used by default.")
+	addRemoteEncryptionCipherFlag(dbBranchCmd)
+	addRemoteEncryptionKeyFlag(dbBranchCmd)
+	dbBranchCmd.Flags().StringVar(&branchTimestampFlag, "timestamp", "", "Set a point in time in the past to copy data from the source database. Must be in RFC3339 format like '2023-09-29T10:16:13-03:00'")
+}
+
+var dbBranchCmd = &cobra.Command{
+	Use:               "branch <source-database> <target-database>",
+	Short:             "Create a branch from an existing database.",
+	Args:              cobra.ExactArgs(2),
+	ValidArgsFunction: dbBranchArgs,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		cmd.SilenceUsage = true
+		sourceName := args[0]
+
+		client, err := authedTursoClient()
+		if err != nil {
+			return err
+		}
+		sourceDB, err := getDatabase(client, sourceName, true)
+		if err != nil {
+			return err
+		}
+
+		targetName, err := resolveBranchTargetName(args)
+		if err != nil {
+			return err
+		}
+
+		prevFromDB := fromDBFlag
+		prevTimestamp := timestampFlag
+		prevGroup := groupFlag
+		defer func() {
+			fromDBFlag = prevFromDB
+			timestampFlag = prevTimestamp
+			groupFlag = prevGroup
+		}()
+
+		fromDBFlag = sourceName
+		timestampFlag = branchTimestampFlag
+		if groupFlag == "" && sourceDB.Group != "" {
+			groupFlag = sourceDB.Group
+		}
+
+		return CreateDatabase(targetName)
+	},
+}
+
+func dbBranchArgs(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+	if len(args) == 0 {
+		return dbNameArg(cmd, args, toComplete)
+	}
+	return noFilesArg(cmd, args, toComplete)
+}
+
+func resolveBranchTargetName(args []string) (string, error) {
+	targetName := args[1]
+
+	targetName = strings.TrimSpace(targetName)
+	if targetName == "" {
+		return "", errors.New("branch name cannot be empty")
+	}
+	if targetName == args[0] {
+		return "", errors.New("branch name must be different from source database name")
+	}
+	return targetName, nil
+}