Get as far as printing sector stats.

Storage/Disk/DiskImage/Formats/JFD.cpp

@@ -8,28 +8,82 @@
 
 #include "JFD.hpp"
 
+#include "Storage/Disk/Encodings/MFM/Constants.hpp"
+#include "Storage/Disk/Encodings/MFM/Encoder.hpp"
+#include "Storage/Disk/Encodings/MFM/Sector.hpp"
+
 using namespace Storage::Disk;
 
+uint32_t JFD::read32() const {
+	uint8_t bytes[4];
+	gzread(file_, bytes, 4);
+	return uint32_t(bytes[0] | (bytes[1] << 8) | (bytes[2] << 16) | (bytes[3] << 24));
+}
+
+uint8_t JFD::read8() const {
+	return uint8_t(gzgetc(file_));
+}
+
 JFD::JFD(const std::string &file_name) : file_name_(file_name) {
 	file_ = gzopen(file_name.c_str(), "rb");
 
+	// First four bytes: signature.
 	uint8_t signature[4];
 	constexpr uint8_t required_signature[4] = { 'J', 'F', 'D', 'I' };
 	gzread(file_, signature, sizeof(signature));
 	if(!std::equal(std::begin(signature), std::end(signature), std::begin(required_signature))) {
 		throw 1;
 	}
+
+	gzseek(file_, 24, SEEK_SET);
+	track_offset_ = read32();
+	sector_offset_ = read32();
+	data_offset_ = read32();
+	// TODO: grab delta tables, once I know how to parse them.
 }
 
 HeadPosition JFD::maximum_head_position() const {
-	return HeadPosition{};
+	return HeadPosition{
+		int((sector_offset_ - track_offset_) / (2 * sizeof(uint32_t)))
+	};
 }
 
 int JFD::head_count() const {
-	return 0;
+	return 2;
 }
 
-std::unique_ptr<Track> JFD::track_at_position(Track::Address) const {
+std::unique_ptr<Track> JFD::track_at_position(const Track::Address address) const {
+	const uint32_t offset = track_offset_ + uint32_t(address.head + address.position.as_int() * 2);
+
+	if(offset >= sector_offset_) {
+		return nullptr;
+	}
+	gzseek(file_, offset, SEEK_SET);
+
+	const uint32_t sector_begin = read32();
+	if(sector_begin == 0xffffffff) {
+		return nullptr;
+	}
+
+	std::vector<Storage::Encodings::MFM::Sector> sectors;
+	uint32_t sector = sector_begin;
+	while(sector < sector_offset_) {
+		gzseek(file_, sector_offset_ + sector, SEEK_SET);
+
+		const auto crc_size = read8();
+		const auto sector_number = read8();
+		const auto options_density = read8();
+		const auto time_ms = read8();
+		if(crc_size == 0xff && sector_number == 0xff && options_density == 0xff && time_ms == 0xff) {
+			break;
+		}
+
+		const auto data = read32();
+		printf("After %d ms, od %02x, sector %d, crc_size %02x, at %d\n", time_ms, options_density, sector_number, crc_size, data);
+
+		sector += 8;
+	}
+
 	return {};
 }
 

Storage/Disk/DiskImage/Formats/JFD.hpp

@@ -25,8 +25,14 @@ public:
 	bool represents(const std::string &) const;
 
 private:
-	gzFile file_;
 	std::string file_name_;
+	gzFile file_;
+	uint8_t read8() const;
+	uint32_t read32() const;
+
+	uint32_t track_offset_;
+	uint32_t sector_offset_;
+	uint32_t data_offset_;
 };
 
 }