feat: src/useSubtasks.ts (#20)

Author: tapiwamakandigona

src/useSubtasks.ts

@@ -0,0 +1,68 @@
+import { useState, useCallback, useEffect } from "react";
+
+interface Subtask {
+  id: string;
+  text: string;
+  done: boolean;
+}
+
+type SubtaskMap = Record<string, Subtask[]>;
+
+/**
+ * Manage subtasks for todo items.
+ * Each todo can have unlimited subtasks with independent completion state.
+ */
+export function useSubtasks() {
+  const [subtasks, setSubtasks] = useState<SubtaskMap>(() => {
+    const saved = localStorage.getItem("subtasks");
+    return saved ? JSON.parse(saved) : {};
+  });
+
+  useEffect(() => {
+    localStorage.setItem("subtasks", JSON.stringify(subtasks));
+  }, [subtasks]);
+
+  const addSubtask = useCallback((todoId: string, text: string) => {
+    setSubtasks(prev => ({
+      ...prev,
+      [todoId]: [...(prev[todoId] || []), { id: crypto.randomUUID(), text, done: false }],
+    }));
+  }, []);
+
+  const toggleSubtask = useCallback((todoId: string, subtaskId: string) => {
+    setSubtasks(prev => ({
+      ...prev,
+      [todoId]: (prev[todoId] || []).map(s =>
+        s.id === subtaskId ? { ...s, done: !s.done } : s
+      ),
+    }));
+  }, []);
+
+  const deleteSubtask = useCallback((todoId: string, subtaskId: string) => {
+    setSubtasks(prev => ({
+      ...prev,
+      [todoId]: (prev[todoId] || []).filter(s => s.id !== subtaskId),
+    }));
+  }, []);
+
+  const getSubtasks = useCallback((todoId: string): Subtask[] => {
+    return subtasks[todoId] || [];
+  }, [subtasks]);
+
+  const getProgress = useCallback((todoId: string): { done: number; total: number; percentage: number } => {
+    const subs = subtasks[todoId] || [];
+    const done = subs.filter(s => s.done).length;
+    const total = subs.length;
+    return { done, total, percentage: total > 0 ? Math.round((done / total) * 100) : 0 };
+  }, [subtasks]);
+
+  const clearSubtasks = useCallback((todoId: string) => {
+    setSubtasks(prev => {
+      const copy = { ...prev };
+      delete copy[todoId];
+      return copy;
+    });
+  }, []);
+
+  return { addSubtask, toggleSubtask, deleteSubtask, getSubtasks, getProgress, clearSubtasks };
+}