Make moving todo commits more robust

pkg/utils/rebaseTodo.go

@@ -1,11 +1,18 @@
 package utils
 
 import (
+	"fmt"
 	"os"
+	"strings"
 
 	"github.com/fsmiamoto/git-todo-parser/todo"
+	"github.com/samber/lo"
 )
 
+func equalShas(a, b string) bool {
+	return strings.HasPrefix(a, b) || strings.HasPrefix(b, a)
+}
+
 func ReadRebaseTodoFile(fileName string) ([]todo.Todo, error) {
 	f, err := os.Open(fileName)
 	if err != nil {
@@ -32,3 +39,70 @@ func WriteRebaseTodoFile(fileName string, todos []todo.Todo) error {
 	}
 	return err
 }
+
+func MoveTodoDown(fileName string, sha string, action todo.TodoCommand) error {
+	todos, err := ReadRebaseTodoFile(fileName)
+	if err != nil {
+		return err
+	}
+	rearrangedTodos, err := moveTodoDown(todos, sha, action)
+	if err != nil {
+		return err
+	}
+	return WriteRebaseTodoFile(fileName, rearrangedTodos)
+}
+
+func MoveTodoUp(fileName string, sha string, action todo.TodoCommand) error {
+	todos, err := ReadRebaseTodoFile(fileName)
+	if err != nil {
+		return err
+	}
+	rearrangedTodos, err := moveTodoUp(todos, sha, action)
+	if err != nil {
+		return err
+	}
+	return WriteRebaseTodoFile(fileName, rearrangedTodos)
+}
+
+func moveTodoDown(todos []todo.Todo, sha string, action todo.TodoCommand) ([]todo.Todo, error) {
+	rearrangedTodos, err := moveTodoUp(lo.Reverse(todos), sha, action)
+	return lo.Reverse(rearrangedTodos), err
+}
+
+func moveTodoUp(todos []todo.Todo, sha string, action todo.TodoCommand) ([]todo.Todo, error) {
+	_, sourceIdx, ok := lo.FindIndexOf(todos, func(t todo.Todo) bool {
+		// Comparing just the sha is not enough; we need to compare both the
+		// action and the sha, as the sha could appear multiple times (e.g. in a
+		// pick and later in a merge)
+		return t.Command == action && equalShas(t.Commit, sha)
+	})
+
+	if !ok {
+		// Should never happen
+		return []todo.Todo{}, fmt.Errorf("Todo %s not found in git-rebase-todo", sha)
+	}
+
+	// The todos are ordered backwards compared to our model commits, so
+	// actually move the commit _down_ in the todos slice (i.e. towards
+	// the end of the slice)
+
+	// Find the next todo that we show in lazygit's commits view (skipping the rest)
+	_, skip, ok := lo.FindIndexOf(todos[sourceIdx+1:], isRenderedTodo)
+
+	if !ok {
+		// We expect callers to guard against this
+		return []todo.Todo{}, fmt.Errorf("Destination position for moving todo is out of range")
+	}
+
+	destinationIdx := sourceIdx + 1 + skip
+
+	rearrangedTodos := MoveElement(todos, sourceIdx, destinationIdx)
+
+	return rearrangedTodos, nil
+}
+
+// We render a todo in the commits view if it's a commit or if it's an
+// update-ref. We don't render label, reset, or comment lines.
+func isRenderedTodo(t todo.Todo) bool {
+	return t.Commit != "" || t.Command == todo.UpdateRef
+}