Refactor all the image writing stuff into a ImageWriter subclass hierarchy with

a factory based on extension.

lib/imagewriter/imgimagewriter.cc

@@ -0,0 +1,62 @@
+#include "globals.h"
+#include "image.h"
+#include "flags.h"
+#include "dataspec.h"
+#include "sector.h"
+#include "sectorset.h"
+#include "imagewriter/imagewriter.h"
+#include "fmt/format.h"
+#include <algorithm>
+#include <iostream>
+#include <fstream>
+
+class ImgImageWriter : public ImageWriter
+{
+public:
+	ImgImageWriter(const SectorSet& sectors, const ImageSpec& spec):
+		ImageWriter(sectors, spec)
+	{}
+
+	void writeImage()
+	{
+		unsigned numCylinders = spec.cylinders;
+		unsigned numHeads = spec.heads;
+		unsigned numSectors = spec.sectors;
+		unsigned numBytes = spec.bytes;
+
+		size_t headSize = numSectors * numBytes;
+		size_t trackSize = headSize * numHeads;
+
+		std::cout << fmt::format("{} tracks, {} heads, {} sectors, {} bytes per sector, {} kB total",
+						numCylinders, numHeads,
+						numSectors, numBytes,
+						numCylinders * trackSize / 1024)
+				<< std::endl;
+
+		std::ofstream outputFile(spec.filename, std::ios::out | std::ios::binary);
+		if (!outputFile.is_open())
+			Error() << "cannot open output file";
+
+		for (int track = 0; track < numCylinders; track++)
+		{
+			for (int head = 0; head < numHeads; head++)
+			{
+				for (int sectorId = 0; sectorId < numSectors; sectorId++)
+				{
+					const auto& sector = sectors.get(track, head, sectorId);
+					if (sector)
+					{
+						outputFile.seekp(sector->logicalTrack*trackSize + sector->logicalSide*headSize + sector->logicalSector*numBytes, std::ios::beg);
+						outputFile.write((const char*) sector->data.cbegin(), sector->data.size());
+					}
+				}
+			}
+		}
+	}
+};
+
+std::unique_ptr<ImageWriter> ImageWriter::createImgImageWriter(
+	const SectorSet& sectors, const ImageSpec& spec)
+{
+    return std::unique_ptr<ImageWriter>(new ImgImageWriter(sectors, spec));
+}