feat(domain): add entities and json helpers for sqlite schema

backend/CMakeLists.txt

@@ -14,10 +14,13 @@ add_library(csp_core
   src/app_state.cc
   src/services/crypto.cc
   src/services/auth_service.cc
+  src/domain/enum_strings.cc
+  src/domain/json.cc
 )
 
 target_include_directories(csp_core PUBLIC
   ${CMAKE_CURRENT_SOURCE_DIR}/include
+  /usr/include/jsoncpp
 )
 
 target_link_libraries(csp_core PUBLIC
@@ -60,6 +63,7 @@ add_executable(csp_tests
   tests/sqlite_db_test.cc
   tests/auth_service_test.cc
   tests/auth_http_test.cc
+  tests/domain_test.cc
 )
 
 target_include_directories(csp_tests PRIVATE

backend/include/csp/domain/entities.h

@@ -0,0 +1,84 @@
+#pragma once
+
+#include <cstdint>
+#include <optional>
+#include <string>
+
+namespace csp::domain {
+
+// Notes:
+// - All *_at fields use Unix timestamp seconds (int64).
+// - id fields match SQLite INTEGER PRIMARY KEY AUTOINCREMENT (int64).
+
+struct User {
+  int64_t id = 0;
+  std::string username;
+  std::string password_salt;
+  std::string password_hash;
+  int32_t rating = 0;
+  int64_t created_at = 0;
+};
+
+struct Session {
+  std::string token;  // PK
+  int64_t user_id = 0;
+  int64_t expires_at = 0;
+  int64_t created_at = 0;
+};
+
+struct Problem {
+  int64_t id = 0;
+  std::string slug;
+  std::string title;
+  std::string statement_md;
+  int32_t difficulty = 1;
+  std::string source;
+  int64_t created_at = 0;
+};
+
+struct ProblemTag {
+  int64_t problem_id = 0;
+  std::string tag;
+};
+
+enum class SubmissionStatus {
+  Pending,
+  Compiling,
+  Running,
+  AC,
+  WA,
+  TLE,
+  MLE,
+  RE,
+  CE,
+  Unknown,
+};
+
+// MVP: only C++ is supported.
+enum class Language {
+  Cpp,
+  Unknown,
+};
+
+struct Submission {
+  int64_t id = 0;
+  int64_t user_id = 0;
+  int64_t problem_id = 0;
+  Language language = Language::Cpp;
+  std::string code;
+  SubmissionStatus status = SubmissionStatus::Pending;
+  int32_t score = 0;
+  int32_t time_ms = 0;
+  int32_t memory_kb = 0;
+  int64_t created_at = 0;
+};
+
+struct WrongBookItem {
+  int64_t user_id = 0;
+  int64_t problem_id = 0;
+  std::optional<int64_t> last_submission_id;
+  std::string note;
+  int64_t updated_at = 0;
+};
+
+}  // namespace csp::domain

backend/include/csp/domain/enum_strings.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include "csp/domain/entities.h"
+
+#include <string>
+
+namespace csp::domain {
+
+// String mapping for persistence/API.
+
+std::string ToString(SubmissionStatus s);
+SubmissionStatus SubmissionStatusFromString(const std::string& s);
+
+std::string ToString(Language l);
+Language LanguageFromString(const std::string& s);
+
+}  // namespace csp::domain

backend/include/csp/domain/json.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include "csp/domain/entities.h"
+#include "csp/domain/enum_strings.h"
+
+#include <json/json.h>
+
+namespace csp::domain {
+
+// These helpers are intended for API responses.
+// IMPORTANT: They intentionally exclude sensitive fields (password_salt/password_hash).
+
+Json::Value ToPublicJson(const User& u);
+Json::Value ToJson(const Problem& p);
+Json::Value ToJson(const Submission& s);
+Json::Value ToJson(const WrongBookItem& w);
+
+}  // namespace csp::domain

backend/src/domain/enum_strings.cc

@@ -0,0 +1,74 @@
+#include "csp/domain/enum_strings.h"
+
+#include <algorithm>
+
+namespace csp::domain {
+
+namespace {
+
+std::string Upper(std::string s) {
+  std::transform(s.begin(), s.end(), s.begin(), [](unsigned char c) {
+    return static_cast<char>(std::toupper(c));
+  });
+  return s;
+}
+
+}  // namespace
+
+std::string ToString(SubmissionStatus s) {
+  switch (s) {
+    case SubmissionStatus::Pending:
+      return "Pending";
+    case SubmissionStatus::Compiling:
+      return "Compiling";
+    case SubmissionStatus::Running:
+      return "Running";
+    case SubmissionStatus::AC:
+      return "AC";
+    case SubmissionStatus::WA:
+      return "WA";
+    case SubmissionStatus::TLE:
+      return "TLE";
+    case SubmissionStatus::MLE:
+      return "MLE";
+    case SubmissionStatus::RE:
+      return "RE";
+    case SubmissionStatus::CE:
+      return "CE";
+    case SubmissionStatus::Unknown:
+    default:
+      return "Unknown";
+  }
+}
+
+SubmissionStatus SubmissionStatusFromString(const std::string& s) {
+  const auto u = Upper(s);
+  if (u == "PENDING") return SubmissionStatus::Pending;
+  if (u == "COMPILING") return SubmissionStatus::Compiling;
+  if (u == "RUNNING") return SubmissionStatus::Running;
+  if (u == "AC") return SubmissionStatus::AC;
+  if (u == "WA") return SubmissionStatus::WA;
+  if (u == "TLE") return SubmissionStatus::TLE;
+  if (u == "MLE") return SubmissionStatus::MLE;
+  if (u == "RE") return SubmissionStatus::RE;
+  if (u == "CE") return SubmissionStatus::CE;
+  return SubmissionStatus::Unknown;
+}
+
+std::string ToString(Language l) {
+  switch (l) {
+    case Language::Cpp:
+      return "cpp";
+    case Language::Unknown:
+    default:
+      return "unknown";
+  }
+}
+
+Language LanguageFromString(const std::string& s) {
+  const auto u = Upper(s);
+  if (u == "CPP" || u == "C++" || u == "CXX") return Language::Cpp;
+  return Language::Unknown;
+}
+
+}  // namespace csp::domain

backend/src/domain/json.cc

@@ -0,0 +1,54 @@
+#include "csp/domain/json.h"
+
+namespace csp::domain {
+
+Json::Value ToPublicJson(const User& u) {
+  Json::Value j;
+  j["id"] = Json::Int64(u.id);
+  j["username"] = u.username;
+  j["rating"] = u.rating;
+  j["created_at"] = Json::Int64(u.created_at);
+  return j;
+}
+
+Json::Value ToJson(const Problem& p) {
+  Json::Value j;
+  j["id"] = Json::Int64(p.id);
+  j["slug"] = p.slug;
+  j["title"] = p.title;
+  j["statement_md"] = p.statement_md;
+  j["difficulty"] = p.difficulty;
+  j["source"] = p.source;
+  j["created_at"] = Json::Int64(p.created_at);
+  return j;
+}
+
+Json::Value ToJson(const Submission& s) {
+  Json::Value j;
+  j["id"] = Json::Int64(s.id);
+  j["user_id"] = Json::Int64(s.user_id);
+  j["problem_id"] = Json::Int64(s.problem_id);
+  j["language"] = ToString(s.language);
+  j["status"] = ToString(s.status);
+  j["score"] = s.score;
+  j["time_ms"] = s.time_ms;
+  j["memory_kb"] = s.memory_kb;
+  j["created_at"] = Json::Int64(s.created_at);
+  return j;
+}
+
+Json::Value ToJson(const WrongBookItem& w) {
+  Json::Value j;
+  j["user_id"] = Json::Int64(w.user_id);
+  j["problem_id"] = Json::Int64(w.problem_id);
+  if (w.last_submission_id.has_value()) {
+    j["last_submission_id"] = Json::Int64(*w.last_submission_id);
+  } else {
+    j["last_submission_id"] = Json::nullValue;
+  }
+  j["note"] = w.note;
+  j["updated_at"] = Json::Int64(w.updated_at);
+  return j;
+}
+
+}  // namespace csp::domain

backend/tests/domain_test.cc

@@ -0,0 +1,29 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include "csp/domain/enum_strings.h"
+#include "csp/domain/json.h"
+
+TEST_CASE("enum string mapping") {
+  REQUIRE(csp::domain::ToString(csp::domain::SubmissionStatus::AC) == "AC");
+  REQUIRE(csp::domain::SubmissionStatusFromString("ac") ==
+          csp::domain::SubmissionStatus::AC);
+  REQUIRE(csp::domain::LanguageFromString("cpp") == csp::domain::Language::Cpp);
+}
+
+TEST_CASE("domain json serialization hides secrets") {
+  csp::domain::User u;
+  u.id = 1;
+  u.username = "alice";
+  u.password_salt = "salt";
+  u.password_hash = "hash";
+  u.rating = 10;
+  u.created_at = 100;
+
+  auto j = csp::domain::ToPublicJson(u);
+  REQUIRE(j.isMember("id"));
+  REQUIRE(j.isMember("username"));
+  REQUIRE(j.isMember("rating"));
+  REQUIRE(j.isMember("created_at"));
+  REQUIRE_FALSE(j.isMember("password_salt"));
+  REQUIRE_FALSE(j.isMember("password_hash"));
+}