Make FileView more type-safe.

1 files changed, 86 insertions, 14 deletions

diff --git a/c/data.h b/c/data.h
index 2cc4c14..a93b256 100644
--- a/c/data.h
+++ b/c/data.h
@@ -1,15 +1,21 @@
 #ifndef DATA_H
 #define DATA_H
 
+#include <stdexcept>
+
 #include "pl.h"
 #include "util.h"
 #include "wcharptr.h"
+#include "win.h"
+
+/* The structs ending with A are written as-is to disk. As such, they
+ * should be regarded as immutable. If the format needs to be changed
+ * in the future, then new structs ending with B should be added. */
 
-/* ElvDataA and DlvDataA are written as-is to disk; note the careful
- * alignment. As such, they should be regarded as immutable. If the
- * format needs to be changed in the future, then new structs called
- * ElvDataB and DlvDataB should be added. */
+/* Note that unsigned chars are 1-byte-aligned, wchar_t are
+ * 2-byte-aligned and ints are 4-byte-aligned (on x86 Windows). */
 
+/* Basic episode data presented in episode list view. */
 struct ElvDataA
 {
 	unsigned char version = 'a';
@@ -21,6 +27,7 @@ struct ElvDataA
 	wchar_t title[128] = {0};
 };
 
+/* Extra episode data presented in data list view. */
 struct DlvDataA
 {
 	wchar_t date[32] = {0};
@@ -30,21 +37,86 @@ struct DlvDataA
 	wchar_t wiki[192] = {0};
 };
 
+/* Variable template for obtaining the version of a given struct. */
+template <typename T>
+constexpr inline unsigned char Version = T{}.version;
+
+template <typename T, typename = void>
+constexpr inline bool HasVersion = false;
+
+template <typename T>
+constexpr inline bool HasVersion<T, std::void_t<typename T::version>> = true;
+
+/* FileView objects manage a memory-mapped file. The view buffer may
+ * be treated as an array of a given type T. Note that reading and
+ * writing a view can throw structured exceptions. We ignore these. */
+template <typename T>
 struct FileView
 {
-	FileView(const wchar_t* filename, size_t cb);
-	~FileView();
-	inline operator unsigned char*() { return view; }
-	inline operator ElvDataA*() { return reinterpret_cast<ElvDataA*>(view); }
+	FileView(const wchar_t* filename, size_t c_) : c(c_)
+	{
+		hf = CreateFile(filename, GENERIC_READ|GENERIC_WRITE,
+		    0, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+		if (hf == INVALID_HANDLE_VALUE) {
+			if (GetLastError() == ERROR_FILE_NOT_FOUND) {
+				hf = CreateFile(filename, GENERIC_READ|GENERIC_WRITE,
+				    0, nullptr, CREATE_NEW, FILE_ATTRIBUTE_NORMAL, nullptr);
+				if (hf == INVALID_HANDLE_VALUE)
+					throw Win32Error{};
+			} else
+				throw Win32Error{};
+		}
+
+		LARGE_INTEGER cbMap;
+		cbMap.QuadPart = c*sizeof(T);
+		hm = CreateFileMapping(hf, nullptr, PAGE_READWRITE,
+		    cbMap.HighPart, cbMap.LowPart, nullptr);
+		if (!hm)
+			throw Win32Error{};
+
+		view = reinterpret_cast<T*>(MapViewOfFile(hm, FILE_MAP_ALL_ACCESS, 0, 0, 0));
+		if (!view)
+			throw Win32Error{};
+	}
+
+	~FileView()
+	{
+		FlushViewOfFile(view, 0);
+		UnmapViewOfFile(view);
+		CloseHandle(hm);
+		CloseHandle(hf);
+	}
+
+	/* Access element by index, performing bounds check and, if
+	 * applicable for T, version validation. */
+	T& At(size_t i)
+	{
+		if (i >= c)
+			throw std::out_of_range("index larger than buffer");
+
+		T& t = view[i];
+
+		if constexpr (HasVersion<T>)
+			if (t.version != Version<T>)
+				throw std::runtime_error("invalid struct version");
+
+		/* TODO: Use a custom exception type that informs the
+		 * user of possible data corruption. */
+
+		return t;
+	}
+
+	inline operator T*() noexcept
+	{
+		return view;
+	}
+
 	HANDLE hf;
 	HANDLE hm;
-	unsigned char* view;
-	/* TODO: Handle exceptions on read and write... */
+	T* view;
+	size_t c;
 };
-
-void Write(unsigned char* buf, const ElvDataA& e);
-ElvDataA* Read(unsigned char* buf);
-
+	
 inline int FromWeb(const int iEp, ElvDataA& e, DlvDataA& d) noexcept
 {
 	WcharPtr title, wiki, date, source, hint;