From e8ddff0ee0d9475d0c178111468365b879ba35ba Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 21 Dec 2017 22:34:03 -0500
Subject: [PATCH] Makes a first, messy, attempt at serialising CAS files into
 audio.

---
 Storage/Tape/Formats/CAS.cpp | 84 ++++++++++++++++++++++++++++++++++--
 Storage/Tape/Formats/CAS.hpp |  9 ++++
 2 files changed, 89 insertions(+), 4 deletions(-)

diff --git a/Storage/Tape/Formats/CAS.cpp b/Storage/Tape/Formats/CAS.cpp
index edce11dd2..f6a2dd23b 100644
--- a/Storage/Tape/Formats/CAS.cpp
+++ b/Storage/Tape/Formats/CAS.cpp
@@ -8,21 +8,97 @@
 
 #include "CAS.hpp"
 
+#include <cstring>
+
 using namespace Storage::Tape;
 
+namespace  {
+	const uint8_t header_signature[8] = {0x1f, 0xa6, 0xde, 0xba, 0xcc, 0x13, 0x7d, 0x74};
+}
+
 CAS::CAS(const char *file_name) :
 	file_(file_name) {
+	file_.read(input_, sizeof(input_));
+	if(std::memcmp(input_, header_signature, sizeof(header_signature))) throw ErrorNotCAS;
 }
 
 bool CAS::is_at_end() {
-	return true;
+	return file_.eof();
 }
 
 void CAS::virtual_reset() {
-
+	file_.seek(0, SEEK_SET);
+	file_.read(input_, sizeof(input_));
+	phase_ = Phase::Header;
+	distance_into_phase_ = 0;
 }
 
 Tape::Pulse CAS::virtual_get_next_pulse() {
-	Pulse empty_pulse;
-	return empty_pulse;
+	Pulse pulse;
+	switch(phase_) {
+		case Phase::Gap: {
+			// Leave a fixed 0.5 second gap between blocks.
+			pulse.length.length = 2400;
+			pulse.length.clock_rate = 4800;
+			pulse.type = Pulse::Type::Zero;
+
+			if(!file_.eof()) phase_ = Phase::Header;
+		} break;
+
+		case Phase::Header: {
+			// 1 bits are two complete cycle at 2400 hz
+			pulse.length.length = 1;
+			pulse.length.clock_rate = 4800;
+			pulse.type = (distance_into_phase_&1) ? Pulse::Type::Low : Pulse::Type::High;
+
+			distance_into_phase_++;
+			if(distance_into_phase_ == 7936*4) {
+				distance_into_phase_ = 0;
+				phase_ = Phase::Bytes;
+
+				for(int c = 1; c < 8; c++) {
+					input_[c] = file_.get8();
+				}
+			}
+		} break;
+
+		case Phase::Bytes: {
+			unsigned int bit;
+			const int bit_offset = distance_into_phase_ >> 2;
+			switch(bit_offset) {
+				case 0:		bit = 0;									break;
+				default:	bit = (input_[0] >> (bit_offset - 1)) & 1;	break;
+				case 9:
+				case 10:	bit = 1;									break;
+			}
+
+			// 1 bits are two complete cycle at 2400 hz; 0 bits are one complete cycle at 1200 hz
+			pulse.length.length = 2 - bit;
+			pulse.length.clock_rate = 4800;
+			pulse.type = distance_into_phase_ ? Pulse::Type::High : Pulse::Type::Low;
+
+			int adder = 1;
+			if(!bit && ((distance_into_phase_&3) == 1)) adder = 3;
+			distance_into_phase_ = (distance_into_phase_ + adder) % (11 * 4);
+		} break;
+	}
+
+//	if(pulse.type == Pulse::Type::Zero) printf("\n---\n");
+//	else {
+//		if(pulse.length.length == 1) printf(".");
+//		else if(pulse.length.length == 2) printf("+");
+//		else printf("?");
+//	}
+
+	if(!distance_into_phase_ && phase_ == Phase::Bytes) {
+		std::memmove(input_, &input_[1], 7);
+		input_[7] = file_.get8();
+		if(!is_at_end()) {
+			if(!std::memcmp(input_, header_signature, sizeof(header_signature))) {
+				phase_ = Phase::Header;//Gap;
+			}
+		}
+	}
+
+	return pulse;
 }
diff --git a/Storage/Tape/Formats/CAS.hpp b/Storage/Tape/Formats/CAS.hpp
index 4b998e2b9..5aebffe72 100644
--- a/Storage/Tape/Formats/CAS.hpp
+++ b/Storage/Tape/Formats/CAS.hpp
@@ -39,6 +39,15 @@ class CAS: public Tape {
 
 		void virtual_reset();
 		Pulse virtual_get_next_pulse();
+
+		uint8_t input_[8] = {0, 0, 0, 0, 0, 0, 0, 0};
+
+		enum class Phase {
+			Header,
+			Bytes,
+			Gap
+		} phase_ = Phase::Header;
+		int distance_into_phase_ = 0;
 };
 
 }