feat: add collections management and study coach features

- Implemented collection repository with CRUD operations for user collections.
- Created routes for managing collections, including listing, creating, updating, and deleting collections.
- Added sharing functionality for exams, allowing users to share and clone exams.
- Developed a study coach service that analyzes exam results and provides study tips based on weak areas.
- Introduced frontend components for managing collections, sharing exams, and displaying study coach insights.
- Enhanced user experience with loading states and error handling in shared components.

backend/src/repositories/examRepo.ts

@@ -8,6 +8,12 @@ export interface DbExam {
   exam_json: string
   created_at: number
   updated_at: number
+  share_token: string | null
+  is_public: number
+  is_favorite: number
+  tags: string | null
+  share_mode: string | null
+  cloned_from_share_token: string | null
 }
 
 export interface ExamListItem {
@@ -17,14 +23,18 @@ export interface ExamListItem {
   created_at: number
   updated_at: number
   question_count: number
+  share_token: string | null
+  is_favorite: number
+  tags: string
+  collection_id: number | null
 }
 
-export function createExam(userId: number, title: string, subtitle: string | null, examJson: string): { id: number } {
+export function createExam(userId: number, title: string, subtitle: string | null, examJson: string, tagsJson: string = '[]'): { id: number } {
   const db = getDb()
   const result = db.prepare(`
-    INSERT INTO saved_exams (user_id, title, subtitle, exam_json)
-    VALUES (?, ?, ?, ?)
-  `).run(userId, title, subtitle, examJson)
+    INSERT INTO saved_exams (user_id, title, subtitle, exam_json, tags)
+    VALUES (?, ?, ?, ?, ?)
+  `).run(userId, title, subtitle, examJson, tagsJson)
   return { id: result.lastInsertRowid as number }
 }
 
@@ -36,16 +46,24 @@ export function getExamById(id: number, userId: number): DbExam | undefined {
 export function listExamsByUser(userId: number): ExamListItem[] {
   const db = getDb()
   return db.prepare(`
-    SELECT id, title, subtitle, created_at, updated_at,
+    SELECT id, title, subtitle, created_at, updated_at, share_token, is_favorite, tags, collection_id,
            json_array_length(json_extract(exam_json, '$.questions')) AS question_count
     FROM saved_exams
     WHERE user_id = ?
-    ORDER BY updated_at DESC
+    ORDER BY is_favorite DESC, updated_at DESC
   `).all(userId) as ExamListItem[]
 }
 
-export function updateExam(id: number, userId: number, title: string, subtitle: string | null, examJson: string): boolean {
+export function updateExam(id: number, userId: number, title: string, subtitle: string | null, examJson: string, tagsJson: string | null = null): boolean {
   const db = getDb()
+  if (tagsJson !== null) {
+    const result = db.prepare(`
+      UPDATE saved_exams
+      SET title = ?, subtitle = ?, exam_json = ?, tags = ?, updated_at = unixepoch()
+      WHERE id = ? AND user_id = ?
+    `).run(title, subtitle, examJson, tagsJson, id, userId)
+    return result.changes > 0
+  }
   const result = db.prepare(`
     UPDATE saved_exams
     SET title = ?, subtitle = ?, exam_json = ?, updated_at = unixepoch()
@@ -65,3 +83,106 @@ export function countExams(): number {
   const row = db.prepare('SELECT COUNT(*) AS cnt FROM saved_exams').get() as { cnt: number }
   return row.cnt
 }
+
+export function setShareToken(id: number, userId: number, token: string, mode: string = 'clone'): boolean {
+  const db = getDb()
+  const result = db.prepare(`
+    UPDATE saved_exams
+    SET share_token = ?, is_public = 1, share_mode = ?, updated_at = unixepoch()
+    WHERE id = ? AND user_id = ?
+  `).run(token, mode, id, userId)
+  return result.changes > 0
+}
+
+export function clearShareToken(id: number, userId: number): boolean {
+  const db = getDb()
+  const result = db.prepare(`
+    UPDATE saved_exams
+    SET share_token = NULL, is_public = 0, share_mode = 'clone', updated_at = unixepoch()
+    WHERE id = ? AND user_id = ?
+  `).run(id, userId)
+  return result.changes > 0
+}
+
+export function getExamByShareToken(token: string): DbExam | undefined {
+  const db = getDb()
+  return db.prepare('SELECT * FROM saved_exams WHERE share_token = ? AND is_public = 1').get(token) as DbExam | undefined
+}
+
+export function setShareMode(id: number, userId: number, mode: string): boolean {
+  const db = getDb()
+  const result = db.prepare(`
+    UPDATE saved_exams
+    SET share_mode = ?, updated_at = unixepoch()
+    WHERE id = ? AND user_id = ?
+  `).run(mode, id, userId)
+  return result.changes > 0
+}
+
+export function cloneExam(userId: number, sourceExam: DbExam, shareToken: string): { id: number } {
+  const db = getDb()
+  const parsed = JSON.parse(sourceExam.exam_json)
+  parsed.id = undefined
+  const result = db.prepare(`
+    INSERT INTO saved_exams (user_id, title, subtitle, exam_json, cloned_from_share_token)
+    VALUES (?, ?, ?, ?, ?)
+  `).run(userId, sourceExam.title + ' (copy)', sourceExam.subtitle, JSON.stringify(parsed), shareToken)
+  return { id: result.lastInsertRowid as number }
+}
+
+export interface ClonedExamItem {
+  id: number
+  title: string
+  subtitle: string | null
+  created_at: number
+  updated_at: number
+  question_count: number
+  cloned_from_share_token: string
+}
+
+export function listClonedExams(userId: number): ClonedExamItem[] {
+  const db = getDb()
+  return db.prepare(`
+    SELECT id, title, subtitle, created_at, updated_at, cloned_from_share_token,
+           json_array_length(json_extract(exam_json, '$.questions')) AS question_count
+    FROM saved_exams
+    WHERE user_id = ? AND cloned_from_share_token IS NOT NULL
+    ORDER BY updated_at DESC
+  `).all(userId) as ClonedExamItem[]
+}
+
+export function setFavorite(id: number, userId: number, isFavorite: boolean): boolean {
+  const db = getDb()
+  const result = db.prepare(`
+    UPDATE saved_exams
+    SET is_favorite = ?, updated_at = unixepoch()
+    WHERE id = ? AND user_id = ?
+  `).run(isFavorite ? 1 : 0, id, userId)
+  return result.changes > 0
+}
+
+export function getExamRawJson(id: number, userId: number): { title: string; exam_json: string } | undefined {
+  const db = getDb()
+  return db.prepare('SELECT title, exam_json FROM saved_exams WHERE id = ? AND user_id = ?').get(id, userId) as { title: string; exam_json: string } | undefined
+}
+
+export function duplicateOwnExam(userId: number, sourceExam: DbExam): { id: number } {
+  const db = getDb()
+  const parsed = JSON.parse(sourceExam.exam_json)
+  parsed.id = undefined
+  const result = db.prepare(`
+    INSERT INTO saved_exams (user_id, title, subtitle, exam_json, tags)
+    VALUES (?, ?, ?, ?, ?)
+  `).run(userId, sourceExam.title + ' (copy)', sourceExam.subtitle, JSON.stringify(parsed), sourceExam.tags ?? '[]')
+  return { id: result.lastInsertRowid as number }
+}
+
+export function setExamCollection(id: number, userId: number, collectionId: number | null): boolean {
+  const db = getDb()
+  const result = db.prepare(`
+    UPDATE saved_exams
+    SET collection_id = ?, updated_at = unixepoch()
+    WHERE id = ? AND user_id = ?
+  `).run(collectionId, id, userId)
+  return result.changes > 0
+}