feat(backend): add sqlite migrations + app state + tests

backend/src/db/sqlite_db.cc

@@ -0,0 +1,135 @@
+#include "csp/db/sqlite_db.h"
+
+#include <stdexcept>
+#include <utility>
+
+namespace csp::db {
+
+namespace {
+
+void ThrowSqlite(int rc, sqlite3* db, const char* what) {
+  if (rc == SQLITE_OK) return;
+  const char* msg = db ? sqlite3_errmsg(db) : "";
+  throw std::runtime_error(std::string(what) + ": " + msg);
+}
+
+}  // namespace
+
+SqliteDb SqliteDb::OpenFile(const std::string& path) {
+  sqlite3* db = nullptr;
+  const int rc = sqlite3_open(path.c_str(), &db);
+  if (rc != SQLITE_OK) {
+    const char* msg = db ? sqlite3_errmsg(db) : "";
+    if (db) sqlite3_close(db);
+    throw std::runtime_error(std::string("sqlite3_open failed: ") + msg);
+  }
+  return SqliteDb(db);
+}
+
+SqliteDb SqliteDb::OpenMemory() {
+  sqlite3* db = nullptr;
+  const int rc = sqlite3_open(":memory:", &db);
+  ThrowSqlite(rc, db, "sqlite3_open(:memory:) failed");
+  return SqliteDb(db);
+}
+
+SqliteDb::~SqliteDb() {
+  if (db_) sqlite3_close(db_);
+}
+
+SqliteDb::SqliteDb(SqliteDb&& other) noexcept : db_(other.db_) {
+  other.db_ = nullptr;
+}
+
+SqliteDb& SqliteDb::operator=(SqliteDb&& other) noexcept {
+  if (this == &other) return *this;
+  if (db_) sqlite3_close(db_);
+  db_ = other.db_;
+  other.db_ = nullptr;
+  return *this;
+}
+
+void SqliteDb::Exec(const std::string& sql) {
+  char* err = nullptr;
+  const int rc = sqlite3_exec(db_, sql.c_str(), nullptr, nullptr, &err);
+  if (rc != SQLITE_OK) {
+    std::string msg = err ? err : "";
+    sqlite3_free(err);
+    ThrowSqlite(rc, db_, msg.c_str());
+  }
+}
+
+void ApplyMigrations(SqliteDb& db) {
+  // Keep it simple for MVP: apply the bundled init SQL.
+  // In later iterations we'll add a migrations table + incremental runner.
+  db.Exec("PRAGMA foreign_keys = ON;");
+
+  // 001_init.sql (embedded)
+  db.Exec(R"SQL(
+CREATE TABLE IF NOT EXISTS users (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  username TEXT NOT NULL UNIQUE,
+  password_salt TEXT NOT NULL,
+  password_hash TEXT NOT NULL,
+  rating INTEGER NOT NULL DEFAULT 0,
+  created_at INTEGER NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS sessions (
+  token TEXT PRIMARY KEY,
+  user_id INTEGER NOT NULL,
+  expires_at INTEGER NOT NULL,
+  created_at INTEGER NOT NULL,
+  FOREIGN KEY(user_id) REFERENCES users(id) ON DELETE CASCADE
+);
+
+CREATE TABLE IF NOT EXISTS problems (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  slug TEXT NOT NULL UNIQUE,
+  title TEXT NOT NULL,
+  statement_md TEXT NOT NULL,
+  difficulty INTEGER NOT NULL DEFAULT 1,
+  source TEXT NOT NULL DEFAULT "",
+  created_at INTEGER NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS problem_tags (
+  problem_id INTEGER NOT NULL,
+  tag TEXT NOT NULL,
+  PRIMARY KEY(problem_id, tag),
+  FOREIGN KEY(problem_id) REFERENCES problems(id) ON DELETE CASCADE
+);
+
+CREATE TABLE IF NOT EXISTS submissions (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  user_id INTEGER NOT NULL,
+  problem_id INTEGER NOT NULL,
+  language TEXT NOT NULL,
+  code TEXT NOT NULL,
+  status TEXT NOT NULL,
+  score INTEGER NOT NULL DEFAULT 0,
+  time_ms INTEGER NOT NULL DEFAULT 0,
+  memory_kb INTEGER NOT NULL DEFAULT 0,
+  created_at INTEGER NOT NULL,
+  FOREIGN KEY(user_id) REFERENCES users(id) ON DELETE CASCADE,
+  FOREIGN KEY(problem_id) REFERENCES problems(id) ON DELETE CASCADE
+);
+
+CREATE TABLE IF NOT EXISTS wrong_book (
+  user_id INTEGER NOT NULL,
+  problem_id INTEGER NOT NULL,
+  last_submission_id INTEGER,
+  note TEXT NOT NULL DEFAULT "",
+  updated_at INTEGER NOT NULL,
+  PRIMARY KEY(user_id, problem_id),
+  FOREIGN KEY(user_id) REFERENCES users(id) ON DELETE CASCADE,
+  FOREIGN KEY(problem_id) REFERENCES problems(id) ON DELETE CASCADE,
+  FOREIGN KEY(last_submission_id) REFERENCES submissions(id) ON DELETE SET NULL
+);
+
+CREATE INDEX IF NOT EXISTS idx_submissions_user_created_at ON submissions(user_id, created_at DESC);
+CREATE INDEX IF NOT EXISTS idx_submissions_problem_created_at ON submissions(problem_id, created_at DESC);
+  )SQL");
+}
+
+}  // namespace csp::db