module;

#include <sqlite3.h>

export module routemon:sqlite3;

import std;
import :util;

namespace routemon::sqlite3 {

class mutex_guard
{
  explicit mutex_guard(::sqlite3_mutex* mut) noexcept : mut_{mut}
  {
    ::sqlite3_mutex_enter(mut_);
  }

  friend auto
  do_guarded(::sqlite3_mutex* mut, std::invocable<mutex_guard const&> auto f)
      -> decltype(f(std::declval<mutex_guard const&>()));

public:
  mutex_guard(mutex_guard const&) = delete;
  ~mutex_guard() { ::sqlite3_mutex_leave(mut_); }

private:
  ::sqlite3_mutex* mut_;
};

auto do_guarded(::sqlite3_mutex* mut, std::invocable<mutex_guard const&> auto f)
    -> decltype(f(std::declval<mutex_guard const&>()))
{
  return f(mutex_guard{mut});
}

auto do_guarded(::sqlite3* dbc, std::invocable<mutex_guard const&> auto f)
    -> decltype(f(std::declval<mutex_guard const&>()))
{
  return do_guarded(::sqlite3_db_mutex(dbc), f);
}

class error : public std::exception
{
  int code_;
  std::string message_;

public:
  explicit error(mutex_guard const&, int code, ::sqlite3* dbc)
    : code_{code}, message_{::sqlite3_errmsg(dbc)}
  {
  }

  explicit error(int code) : code_{code}, message_{::sqlite3_errstr(code)} {}

  [[nodiscard]] auto what() const noexcept -> char const* override
  {
    return message_.c_str();
  }

  [[nodiscard]] auto code() const noexcept -> int { return code_; }
};

template <class T, template <class U> concept C>
concept optional_of = requires {
  typename T::value_type;
  requires std::same_as<T, std::optional<typename T::value_type>>;
  requires C<typename T::value_type>;
};

template <class T>
concept scannable_prim = std::same_as<T, std::string> || std::same_as<T, double>
                         || std::same_as<T, std::int64_t>;

template <class T>
concept scannable = scannable_prim<T> || optional_of<T, scannable_prim>;

class statement
{
  ::sqlite3_stmt* stmt_;

public:
  explicit statement(::sqlite3_stmt* stmt) : stmt_{stmt} {}
  statement(statement const&) = delete;
  statement(statement&& s) noexcept
  {
    stmt_ = s.stmt_;
    s.stmt_ = nullptr;
  }
  ~statement() { ::sqlite3_finalize(stmt_); }
  auto get() -> ::sqlite3_stmt* { return stmt_; }
};

class row_reader
{
  statement stmt_;

  explicit row_reader(statement stmt) : stmt_{std::move(stmt)} {}

  friend class connection;

  void scan(int col, std::string& s)
  {
    if (::sqlite3_column_type(stmt_.get(), col) != SQLITE_TEXT)
      throw std::invalid_argument{"invalid type for scan"};
    unsigned char const* chs = ::sqlite3_column_text(stmt_.get(), col);
    auto size = util::size_from_int(::sqlite3_column_bytes(stmt_.get(), col));
    if (!size.has_value())
      throw std::logic_error{"unexpected negative amount of bytes in column"};
    s = std::string{reinterpret_cast<char const*>(chs), *size};
  }

  void scan(int col, double& v)
  {
    if (::sqlite3_column_type(stmt_.get(), col) != SQLITE_FLOAT)
      throw std::invalid_argument{"invalid type for scan"};
    v = ::sqlite3_column_double(stmt_.get(), col);
  }

  void scan(int col, std::int64_t& v)
  {
    if (::sqlite3_column_type(stmt_.get(), col) != SQLITE_INTEGER)
      throw std::invalid_argument{"invalid type for scan"};
    v = ::sqlite3_column_int64(stmt_.get(), col);
  }

  void scan(int col, optional_of<scannable> auto& v)
  {
    if (::sqlite3_column_type(stmt_.get(), col) == SQLITE_NULL)
    {
      v.reset();
    }
    else
    {
      typename std::remove_cvref_t<decltype(v)>::value_type tmp;
      scan(col, tmp);
      v = std::move(tmp);
    }
  }

public:
  auto next() -> bool
  {
    ::sqlite3* dbc = ::sqlite3_db_handle(stmt_.get());
    return do_guarded(
        dbc,
        [&](auto const& guard) -> bool
        {
          auto const s = ::sqlite3_step(stmt_.get());
          if (s == SQLITE_ROW)
            return true;
          if (s == SQLITE_DONE)
            return false;
          throw error{guard, s, dbc};
        });
  }

  auto scan(scannable auto&... args) -> void
  {
    auto const ncols = util::size_from_int(::sqlite3_data_count(stmt_.get()));
    if (!ncols.has_value())
      throw std::logic_error{"got unexpected negative amount of columns"};
    if (sizeof...(args) > *ncols)
      throw std::invalid_argument{
        "more scanning arguments provided than columns in result set"
      };
    auto col = 0;
    (..., scan(col++, args));
  }

  auto scan_single(scannable auto&... args) -> void
  {
    if (!next())
      throw std::logic_error{"no row in result set"};
    scan(args...);
    if (next())
    {
      throw std::logic_error{"more than one row in result set"};
    }
  }
};

class binder
{
  statement& stmt_;

  explicit binder(statement& stmt) : stmt_{stmt} {}

  friend class connection;

public:
  auto text(std::string const& param_name, std::string_view str) -> void
  {
    int const i =
        ::sqlite3_bind_parameter_index(stmt_.get(), param_name.c_str());
    if (i == 0)
      throw std::invalid_argument{std::format(
          "bind: no parameter with name {} found", param_name)};
    auto str_size = util::int_from_size(str.size());
    if (!str_size.has_value())
      throw std::invalid_argument{"bind: provided text is too long"};
    if (auto s = ::sqlite3_bind_text(
            stmt_.get(), i, str.data(), *str_size, SQLITE_TRANSIENT);
        s != SQLITE_OK)
    {
      throw error{s};
    }
  }

  static auto noop(binder&) -> void {}
};

export class connection
{
  ::sqlite3* dbc_;
  ::sqlite3_mutex* mut_;

  explicit connection(::sqlite3* dbc) : dbc_{dbc}, mut_{::sqlite3_db_mutex(dbc)}
  {
  }

  friend auto open(std::string const& filename) -> connection;

public:
  connection(connection const&) = delete;
  connection(connection&& c) noexcept
  {
    dbc_ = c.dbc_;
    mut_ = c.mut_;
    c.dbc_ = nullptr;
    c.mut_ = nullptr;
  }

  [[nodiscard]] auto query(
      std::string const& sql,
      std::function<void(binder&)> const& bf = binder::noop) -> row_reader
  {
    ::sqlite3_stmt* pstmt = nullptr;
    char const* sql_tail = nullptr;
    auto sql_size = util::int_from_size(sql.size());
    if (!sql_size.has_value()
        || *sql_size >= std::numeric_limits<int>::max() - 1)
      throw std::invalid_argument{"provided input text too large"};
    do_guarded(
        mut_,
        [&](auto const& guard) -> void
        {
          if (auto s = ::sqlite3_prepare_v2(
                  dbc_, sql.data(), *sql_size + 1, &pstmt, &sql_tail);
              s != SQLITE_OK)
          {
            if (pstmt != nullptr)
            {
              // Use contract_assert when having a compiler with
              // contracts available
              ::sqlite3_finalize(pstmt);
              throw std::logic_error{
                "expected stmt to be null after failed preparation"
              };
            }
            throw error{guard, s, dbc_};
          }
        });
    if (!pstmt)
      throw std::invalid_argument{"provided input text contains no SQL"};
    auto stmt = statement{pstmt};
    if (sql_tail && std::strlen(sql_tail) > 0)
      throw std::invalid_argument{
        "provided input text contains more than one SQL statement"
      };
    auto b = binder{stmt};
    bf(b);
    return row_reader{std::move(stmt)};
  }

  auto exec(
      std::string const& sql,
      std::function<void(binder&)> const& bf = binder::noop) -> void
  {
    auto reader = query(sql, bf);
    while (reader.next())
      ;
  }

  ~connection() { std::ignore = ::sqlite3_close(std::exchange(dbc_, nullptr)); }
};

export auto open(std::string const& filename) -> connection
{
  ::sqlite3* dbc = nullptr;
  auto s = ::sqlite3_open_v2(
      filename.c_str(), &dbc,
      SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE | SQLITE_OPEN_FULLMUTEX
          | SQLITE_OPEN_EXRESCODE,
      nullptr);
  if (s != SQLITE_OK)
  {
    if (dbc)
    {
      do_guarded(
          dbc, [&](auto const& guard) -> void { throw error{guard, s, dbc}; });
    }
    else
    {
      throw error{s};
    }
  }
  return connection{dbc};
}

} // namespace routemon::sqlite3