feat(store): add problem editor state management

- Create problem-editor store with Zustand
- Manage editor state including problem, language, value and path
- Implement localStorage persistence for editor content
- Provide utility functions for language and value retrieval

src/stores/problem-editor.ts

@@ -0,0 +1,91 @@
+import { create } from "zustand";
+import type { editor } from "monaco-editor";
+import { LANGUAGES } from "@/config/language";
+import { Language, type Template } from "@/generated/client";
+
+type Problem = {
+  problemId: string;
+  templates: Template[];
+};
+
+type ProblemEditorState = {
+  problem: Problem | null;
+  language: Language;
+  value: string;
+  path: string;
+  editor: editor.IStandaloneCodeEditor | null;
+};
+
+type ProblemEditorAction = {
+  setProblem: (problemId: string, templates: Template[]) => void;
+  setLanguage: (language: Language) => void;
+  setValue: (value: string) => void;
+  setPath: (path: string) => void;
+  setEditor: (editor: editor.IStandaloneCodeEditor) => void;
+};
+
+type ProblemEditorStore = ProblemEditorState & ProblemEditorAction;
+
+export const useProblemEditorStore = create<ProblemEditorStore>((set, get) => ({
+  problem: null,
+  language: Language.c,
+  value: "",
+  path: "",
+  editor: null,
+  setProblem: (problemId, templates) => {
+    const language = getLanguage(problemId);
+    const value = getValue(problemId, language, templates);
+    const path = getPath(problemId, language);
+    set({ problem: { problemId, templates }, language, value, path });
+  },
+  setLanguage: (newLanguage) => {
+    const { problem, language, value } = get();
+    if (problem) {
+      localStorage.setItem(`${problem.problemId}_${language}`, value);
+      localStorage.setItem(`${problem.problemId}_language`, newLanguage);
+    }
+    localStorage.setItem("global_language", newLanguage);
+    const newValue = problem
+      ? getValue(problem.problemId, newLanguage, problem.templates)
+      : "";
+    const newPath = problem ? getPath(problem.problemId, newLanguage) : "";
+    set({ language: newLanguage, value: newValue, path: newPath });
+  },
+  setValue: (value) => {
+    const { problem, language } = get();
+    if (problem) {
+      localStorage.setItem(`${problem.problemId}_${language}`, value);
+    }
+    set({ value });
+  },
+  setPath: (path) => set({ path }),
+  setEditor: (editor) => set({ editor }),
+}));
+
+const getStoredItem = <T extends string>(
+  key: string,
+  validValues?: T[]
+): T | null => {
+  const stored = localStorage.getItem(key);
+  return stored && (!validValues || validValues.includes(stored as T))
+    ? (stored as T)
+    : null;
+};
+
+const getLanguage = (problemId: string): Language =>
+  getStoredItem(`${problemId}_language`, LANGUAGES) ??
+  getStoredItem("global_language", LANGUAGES) ??
+  Language.c;
+
+const getValue = (
+  problemId: string,
+  language: Language,
+  templates: Template[]
+): string =>
+  getStoredItem(`${problemId}_${language}`) ??
+  templates.find((t) => t.language === language)?.content ??
+  "";
+
+export const getPath = (problemId: string, language: Language) => {
+  return `file:///${problemId}/main.${language}`;
+};