csp/backend/src/services/solution_access_service.cc

#include "csp/services/solution_access_service.h"

#include <sqlite3.h>

#include <chrono>
#include <ctime>
#include <stdexcept>
#include <string>

namespace csp::services {

namespace {

constexpr int kViewCost = 2;

int64_t NowSec() {
  using namespace std::chrono;
  return duration_cast<seconds>(system_clock::now().time_since_epoch()).count();
}

void CheckSqlite(int rc, sqlite3* db, const char* what) {
  if (rc == SQLITE_OK || rc == SQLITE_ROW || rc == SQLITE_DONE) return;
  throw std::runtime_error(std::string(what) + ": " + sqlite3_errmsg(db));
}

std::string ColText(sqlite3_stmt* stmt, int col) {
  const unsigned char* txt = sqlite3_column_text(stmt, col);
  return txt ? reinterpret_cast<const char*>(txt) : std::string();
}

std::string BuildDayKeyChina(int64_t ts_sec) {
  const std::time_t shifted = static_cast<std::time_t>(ts_sec + 8 * 3600);
  std::tm tm {};
  gmtime_r(&shifted, &tm);
  char buf[16] = {0};
  std::strftime(buf, sizeof(buf), "%Y-%m-%d", &tm);
  return std::string(buf);
}

int QueryRating(sqlite3* db, int64_t user_id) {
  sqlite3_stmt* stmt = nullptr;
  const char* sql = "SELECT rating FROM users WHERE id=?";
  CheckSqlite(sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr), db,
              "prepare query rating");
  CheckSqlite(sqlite3_bind_int64(stmt, 1, user_id), db, "bind user_id");
  if (sqlite3_step(stmt) != SQLITE_ROW) {
    sqlite3_finalize(stmt);
    throw std::runtime_error("user not found");
  }
  const int rating = sqlite3_column_int(stmt, 0);
  sqlite3_finalize(stmt);
  return rating;
}

int QueryDailyUsage(sqlite3* db, int64_t user_id, const std::string& day_key) {
  sqlite3_stmt* stmt = nullptr;
  const char* sql =
      "SELECT COUNT(1) FROM problem_solution_view_logs WHERE user_id=? AND day_key=?";
  CheckSqlite(sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr), db,
              "prepare query daily usage");
  CheckSqlite(sqlite3_bind_int64(stmt, 1, user_id), db, "bind user_id");
  CheckSqlite(sqlite3_bind_text(stmt, 2, day_key.c_str(), -1, SQLITE_TRANSIENT), db,
              "bind day_key");
  CheckSqlite(sqlite3_step(stmt), db, "step query daily usage");
  const int used = sqlite3_column_int(stmt, 0);
  sqlite3_finalize(stmt);
  return used;
}

void InsertViewLog(sqlite3* db,
                   int64_t user_id,
                   int64_t problem_id,
                   const std::string& day_key,
                   int64_t viewed_at,
                   bool charged,
                   int cost) {
  sqlite3_stmt* stmt = nullptr;
  const char* sql =
      "INSERT INTO problem_solution_view_logs(user_id,problem_id,day_key,viewed_at,charged,cost,created_at) "
      "VALUES(?,?,?,?,?,?,?)";
  CheckSqlite(sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr), db,
              "prepare insert solution view log");
  CheckSqlite(sqlite3_bind_int64(stmt, 1, user_id), db, "bind user_id");
  CheckSqlite(sqlite3_bind_int64(stmt, 2, problem_id), db, "bind problem_id");
  CheckSqlite(sqlite3_bind_text(stmt, 3, day_key.c_str(), -1, SQLITE_TRANSIENT), db,
              "bind day_key");
  CheckSqlite(sqlite3_bind_int64(stmt, 4, viewed_at), db, "bind viewed_at");
  CheckSqlite(sqlite3_bind_int(stmt, 5, charged ? 1 : 0), db, "bind charged");
  CheckSqlite(sqlite3_bind_int(stmt, 6, cost), db, "bind cost");
  CheckSqlite(sqlite3_bind_int64(stmt, 7, viewed_at), db, "bind created_at");
  CheckSqlite(sqlite3_step(stmt), db, "insert solution view log");
  sqlite3_finalize(stmt);
}

void DeductRating(sqlite3* db, int64_t user_id, int cost) {
  sqlite3_stmt* stmt = nullptr;
  const char* sql = "UPDATE users SET rating=rating-? WHERE id=?";
  CheckSqlite(sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr), db,
              "prepare deduct rating");
  CheckSqlite(sqlite3_bind_int(stmt, 1, cost), db, "bind cost");
  CheckSqlite(sqlite3_bind_int64(stmt, 2, user_id), db, "bind user_id");
  CheckSqlite(sqlite3_step(stmt), db, "deduct rating");
  sqlite3_finalize(stmt);
}

}  // namespace

SolutionViewChargeResult SolutionAccessService::ConsumeSolutionView(
    int64_t user_id,
    int64_t problem_id) {
  if (user_id <= 0 || problem_id <= 0) {
    throw std::runtime_error("invalid user_id/problem_id");
  }

  sqlite3* db = db_.raw();
  const int64_t now = NowSec();
  const std::string day_key = BuildDayKeyChina(now);

  db_.Exec("BEGIN IMMEDIATE");
  bool committed = false;
  try {
    SolutionViewChargeResult result;
    result.day_key = day_key;
    result.viewed_at = now;

    const int used_before = QueryDailyUsage(db, user_id, day_key);
    result.daily_used_count = used_before;
    const int rating_before = QueryRating(db, user_id);
    result.rating_before = rating_before;

    if (used_before <= 0) {
      result.daily_free = true;
      result.charged = false;
      result.cost = 0;
      result.rating_after = rating_before;
    } else {
      if (rating_before < kViewCost) {
        result.granted = false;
        result.charged = false;
        result.cost = kViewCost;
        result.rating_after = rating_before;
        result.deny_reason = "rating not enough";
        db_.Exec("ROLLBACK");
        return result;
      }
      result.daily_free = false;
      result.charged = true;
      result.cost = kViewCost;
      result.rating_after = rating_before - kViewCost;
      DeductRating(db, user_id, kViewCost);
    }

    InsertViewLog(db,
                  user_id,
                  problem_id,
                  day_key,
                  now,
                  result.charged,
                  result.cost);
    result.daily_used_count = used_before + 1;

    db_.Exec("COMMIT");
    committed = true;
    return result;
  } catch (...) {
    if (!committed) {
      try {
        db_.Exec("ROLLBACK");
      } catch (...) {
      }
    }
    throw;
  }
}

SolutionViewStats SolutionAccessService::QueryUserProblemViewStats(
    int64_t user_id,
    int64_t problem_id) {
  SolutionViewStats stats;
  if (user_id <= 0 || problem_id <= 0) return stats;

  sqlite3* db = db_.raw();
  sqlite3_stmt* stmt = nullptr;
  const char* sql =
      "SELECT COUNT(1),COALESCE(SUM(cost),0),MAX(viewed_at) "
      "FROM problem_solution_view_logs WHERE user_id=? AND problem_id=?";
  CheckSqlite(sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr), db,
              "prepare query solution view stats");
  CheckSqlite(sqlite3_bind_int64(stmt, 1, user_id), db, "bind user_id");
  CheckSqlite(sqlite3_bind_int64(stmt, 2, problem_id), db, "bind problem_id");

  CheckSqlite(sqlite3_step(stmt), db, "step query solution view stats");
  stats.total_views = sqlite3_column_int(stmt, 0);
  stats.total_cost = sqlite3_column_int(stmt, 1);
  if (sqlite3_column_type(stmt, 2) != SQLITE_NULL) {
    stats.last_viewed_at = sqlite3_column_int64(stmt, 2);
  }
  stats.has_viewed = stats.total_views > 0;
  sqlite3_finalize(stmt);
  return stats;
}

}  // namespace csp::services