-- ============================================
-- PastPaper Master — 初始数据库 Schema
-- Version: 001
-- Date: 2025-03-11
-- ============================================

-- 启用必要的扩展
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";

-- ============================================
-- Table 1: papers — 上传的试卷
-- ============================================
CREATE TABLE papers (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  user_id UUID NOT NULL REFERENCES auth.users(id) ON DELETE CASCADE,

  -- 元信息（用户上传时填写）
  course_code TEXT NOT NULL,                -- "COMP2011"
  year INTEGER NOT NULL,                    -- 2024
  term TEXT NOT NULL CHECK (term IN ('fall', 'spring', 'summer')),
  exam_type TEXT NOT NULL CHECK (exam_type IN ('midterm', 'final', 'quiz')),

  -- 文件 (Supabase Storage)
  paper_file_url TEXT NOT NULL,             -- 试卷 PDF
  answer_file_url TEXT,                     -- 答案 PDF（可选）

  -- 处理状态
  status TEXT NOT NULL DEFAULT 'uploaded'
    CHECK (status IN ('uploaded', 'processing', 'ready', 'error')),
  error_message TEXT,                       -- 处理失败时的错误信息

  -- 提取的原始文本（缓存）
  paper_extracted_text TEXT,
  answer_extracted_text TEXT,

  -- 整卷概览（AI 生成）
  total_score INTEGER,
  question_count INTEGER,
  topics_summary JSONB,                     -- {"Linked List": 40, "Recursion": 30}
  difficulty_level TEXT CHECK (difficulty_level IN ('easy', 'medium', 'hard')),

  created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
  updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
);

-- ============================================
-- Table 2: paper_questions — 逐题数据
-- ============================================
CREATE TABLE paper_questions (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  paper_id UUID NOT NULL REFERENCES papers(id) ON DELETE CASCADE,

  -- 题目标识
  question_number TEXT NOT NULL,             -- "1", "1a", "2b"
  parent_question TEXT,                      -- 子题的父题号: "1a" → "1"
  display_order INTEGER NOT NULL,            -- 显示顺序

  -- 题目内容
  question_type TEXT NOT NULL
    CHECK (question_type IN ('mc', 'fill_blank', 'long_question')),
  question_text TEXT NOT NULL,               -- 题目原文
  score INTEGER,                             -- 分值
  page_number INTEGER,                       -- PDF 页码（左右联动）

  -- 选择题专用
  options JSONB,                             -- [{"label":"A","text":"..."},...]
  correct_option TEXT,                       -- "B"

  -- 填空题专用
  correct_answer TEXT,                       -- 正确答案
  accept_variants TEXT[],                    -- 等价表达 ["O(nlogn)","O(n log n)"]

  -- 答案 PDF 提取的原始答案（所有题型）
  raw_answer_text TEXT,

  -- 知识点标签
  topics TEXT[],                             -- ["Linked List","Pointer"]
  difficulty TEXT CHECK (difficulty IN ('easy', 'medium', 'hard')),

  -- AI 三件套（HTML + KaTeX）
  knowledge_reminder TEXT,                   -- 知识点 Reminder
  ai_hint TEXT,                              -- AI Hint
  solution TEXT,                             -- Solution（逐步 derivation）

  created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
  updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
);

-- ============================================
-- Table 3: user_attempts — 用户答题记录
-- Phase 4 实现，先建好表结构
-- ============================================
CREATE TABLE user_attempts (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  user_id UUID NOT NULL REFERENCES auth.users(id) ON DELETE CASCADE,
  question_id UUID NOT NULL REFERENCES paper_questions(id) ON DELETE CASCADE,

  -- 用户的作答
  attempt_type TEXT NOT NULL
    CHECK (attempt_type IN ('select', 'input', 'photo')),
  user_answer TEXT,                          -- 选项 / 输入的答案
  photo_url TEXT,                            -- 上传的照片
  photo_ocr_text TEXT,                       -- OCR 识别结果

  -- AI 判定
  is_correct BOOLEAN,
  feedback TEXT,                             -- HTML — 逐步错误分析
  error_at_step INTEGER,                     -- 第几步开始错

  -- 错题本
  in_error_book BOOLEAN NOT NULL DEFAULT false,
  mastered BOOLEAN NOT NULL DEFAULT false,

  created_at TIMESTAMPTZ NOT NULL DEFAULT now()
);

-- ============================================
-- 索引
-- ============================================
CREATE INDEX idx_papers_user ON papers(user_id);
CREATE INDEX idx_papers_course ON papers(course_code);
CREATE INDEX idx_papers_status ON papers(status);

CREATE INDEX idx_questions_paper ON paper_questions(paper_id);
CREATE INDEX idx_questions_type ON paper_questions(question_type);
CREATE INDEX idx_questions_topics ON paper_questions USING GIN(topics);

CREATE INDEX idx_attempts_user ON user_attempts(user_id);
CREATE INDEX idx_attempts_question ON user_attempts(question_id);
CREATE INDEX idx_attempts_errorbook ON user_attempts(user_id)
  WHERE in_error_book = true;

-- ============================================
-- RLS 策略
-- ============================================
ALTER TABLE papers ENABLE ROW LEVEL SECURITY;
ALTER TABLE paper_questions ENABLE ROW LEVEL SECURITY;
ALTER TABLE user_attempts ENABLE ROW LEVEL SECURITY;

-- papers: 用户只能看自己上传的（以后加公共库时再调整）
CREATE POLICY "Users can view own papers"
  ON papers FOR SELECT
  USING (auth.uid() = user_id);

CREATE POLICY "Users can insert own papers"
  ON papers FOR INSERT
  WITH CHECK (auth.uid() = user_id);

CREATE POLICY "Users can update own papers"
  ON papers FOR UPDATE
  USING (auth.uid() = user_id);

CREATE POLICY "Users can delete own papers"
  ON papers FOR DELETE
  USING (auth.uid() = user_id);

-- paper_questions: 跟随 paper 的权限
CREATE POLICY "Users can view questions of own papers"
  ON paper_questions FOR SELECT
  USING (
    EXISTS (
      SELECT 1 FROM papers
      WHERE papers.id = paper_questions.paper_id
      AND papers.user_id = auth.uid()
    )
  );

-- service_role 用于后端写入 questions（处理管线用）
-- 前端不直接写 questions，通过 API 触发后端处理

-- user_attempts: 用户只能看/写自己的
CREATE POLICY "Users can view own attempts"
  ON user_attempts FOR SELECT
  USING (auth.uid() = user_id);

CREATE POLICY "Users can insert own attempts"
  ON user_attempts FOR INSERT
  WITH CHECK (auth.uid() = user_id);

CREATE POLICY "Users can update own attempts"
  ON user_attempts FOR UPDATE
  USING (auth.uid() = user_id);

-- ============================================
-- updated_at 自动更新触发器
-- ============================================
CREATE OR REPLACE FUNCTION update_updated_at()
RETURNS TRIGGER AS $$
BEGIN
  NEW.updated_at = now();
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER papers_updated_at
  BEFORE UPDATE ON papers
  FOR EACH ROW EXECUTE FUNCTION update_updated_at();

CREATE TRIGGER questions_updated_at
  BEFORE UPDATE ON paper_questions
  FOR EACH ROW EXECUTE FUNCTION update_updated_at();

-- ============================================
-- Storage bucket
-- ============================================
-- 在 Supabase Dashboard 中手动创建 bucket: "papers"
-- 或通过 API 创建（后端初始化时处理）