feat(KAN-32): add hierarchical acceptance criteria checklist

resources/js/lib/acceptance-criteria.ts

@@ -5,6 +5,76 @@ import type {
 
 const MAX_INDENT_LEVEL = 8;
 
+export const canIndentAcceptanceCriterion = (
+    items: AcceptanceCriteriaModel,
+    index: number,
+): boolean => {
+    const item = items[index];
+    const previous = items[index - 1];
+    if (!item || !previous || item.indent > previous.indent) {
+        return false;
+    }
+    return items
+        .slice(index, acceptanceCriteriaSubtreeEnd(items, index))
+        .every((descendant) => descendant.indent < MAX_INDENT_LEVEL);
+};
+
+const acceptanceCriteriaSubtreeEnd = (
+    items: AcceptanceCriteriaModel,
+    index: number,
+): number => {
+    let end = index + 1;
+    while (end < items.length && items[end].indent > items[index].indent) {
+        end++;
+    }
+    return end;
+};
+
+export const indentAcceptanceCriterion = (
+    items: AcceptanceCriteriaModel,
+    index: number,
+    direction: 1 | -1,
+): AcceptanceCriteriaModel => {
+    if (
+        !items[index] ||
+        (direction === 1
+            ? !canIndentAcceptanceCriterion(items, index)
+            : items[index].indent === 0)
+    ) {
+        return items;
+    }
+    const end = acceptanceCriteriaSubtreeEnd(items, index);
+    return items.map((item, position) =>
+        position >= index && position < end
+            ? { ...item, indent: item.indent + direction }
+            : item,
+    );
+};
+
+/** Remove only the selected criterion, promoting its children without losing them. */
+export const removeAcceptanceCriterion = (
+    items: AcceptanceCriteriaModel,
+    index: number,
+): AcceptanceCriteriaModel => {
+    if (!items[index]) {
+        return items;
+    }
+    const end = acceptanceCriteriaSubtreeEnd(items, index);
+    return items.flatMap((item, position) =>
+        position === index
+            ? []
+            : [
+                  {
+                      ...item,
+                      indent:
+                          position > index && position < end
+                              ? item.indent - 1
+                              : item.indent,
+                  },
+              ],
+    );
+};
+
 export type AcceptanceCriteriaEditorState = {
     checklist: string;
 };