magic: refactor construction

1 files changed, 45 insertions, 3 deletions

diff --git a/cabinet/magic.cpp b/cabinet/magic.cpp
index f8d7337..96e212f 100644
--- a/cabinet/magic.cpp
+++ b/cabinet/magic.cpp
@@ -2,18 +2,60 @@
 
 #include <magic.h>
 
+#include <cerrno>
+#include <expected>
+#include <string_view>
+#include <system_error>
 #include <utility>
 
 namespace cab
 {
 
-  magic::magic(magic::flags flags)
-      : m_cookie{magic_open(std::to_underlying(flags))}
+  auto magic::open(magic::flags flags, std::string_view database) noexcept -> std::expected<magic, std::error_code>
+  {
+    auto cookie = magic_open(std::to_underlying(flags));
+    if (!cookie)
+    {
+      return std::unexpected{
+        std::error_code{errno, std::system_category()}
+      };
+    }
+
+    if (auto success = magic_load(cookie, database.data()); success < 0)
+    {
+      return std::unexpected{std::make_error_code(std::errc::invalid_argument)};
+    }
+
+    return magic{cookie};
+  }
+
+  magic::magic(::magic_t cookie) noexcept
+      : m_cookie{cookie}
+  {}
+
+  magic::magic(magic && other) noexcept
+      : m_cookie{std::exchange(other.m_cookie, nullptr)}
   {}
 
   magic::~magic()
   {
-    magic_close(m_cookie);
+    if (m_cookie)
+    {
+      magic_close(m_cookie);
+    }
+  }
+
+  auto magic::operator=(magic && other) noexcept -> magic &
+  {
+    std::swap(m_cookie, other.m_cookie);
+    return *this;
+  }
+
+  auto swap(magic & lhs, magic & rhs) noexcept -> void
+  {
+    auto temp = std::move(lhs);
+    lhs = std::move(rhs);
+    rhs = std::move(lhs);
   }
 
 }  // namespace cab