#include "vm.h"
#include "stdio.h"
#include "stdarg.h"
#include "string.h"


// Number of scratch items for opcodes to use as working space.
// Depends on VM implementation so it's declared here.
#define WORKING_SIZE  4


typedef void (*VMOpCodeT)(VMContextT *context);


void copyItem(PairT *item, PairT *source);
void op_add(VMContextT *context);
void op_boc(VMContextT *context);
void op_exe(VMContextT *context);
void op_jmp(VMContextT *context);
void op_hlt(VMContextT *context);
void op_pop(VMContextT *context);
void op_puc(VMContextT *context);
void op_puv(VMContextT *context);
void op_sub(VMContextT *context);
void readItemFromPC(VMContextT *context, PairT *item);
void setStringFormat(PairT *item, char *format, ...);


static VMOpCodeT opcodes[OPCODE_LAST];


void copyItem(PairT *item, PairT *source) {
	vmSetItem(item, source->text, &source->value);
}


void op_add(VMContextT *context) {
	bool isString0;
	bool isString1;

	vmPop(context, &context->working[0]);
	vmPop(context, &context->working[1]);
	isString0 = !vmIsItemNumber(&context->working[0]);
	isString1 = !vmIsItemNumber(&context->working[1]);

	// Both operands need to be numbers to result in a number.
	if (isString0 || isString1) {
		// Are both strings?
		if (isString0 && isString1) {
			setStringFormat(&context->working[2], "%s%s", context->working[0].text, context->working[1].text);
		} else {
			// Is the first a string?
			if (isString0) {
				setStringFormat(&context->working[2], "%s%d", context->working[0].text, context->working[1].value);
			} else {
				setStringFormat(&context->working[2], "%d%s", context->working[0].value, context->working[1].text);
			}
		}
		context->working[2].value = (jint16)strlen(context->working[2].text);
	} else {
		// Number
		context->working[2].value = context->working[0].value + context->working[1].value;
	}

	vmPush(context, &context->working[2]);
}


void op_boc(VMContextT *context) {
	bool isNumber0;
	bool isNumber2;
	int  result;

	vmPop(context, &context->working[0]); // arg1
	vmPop(context, &context->working[1]); // compairson
	vmPop(context, &context->working[2]); // arg2
	vmPop(context, &context->working[3]); // target pc
	isNumber0 = vmIsItemNumber(&context->working[0]);
	isNumber2 = vmIsItemNumber(&context->working[2]);

	// Both Numbers?
	if (isNumber0 && isNumber2) {
		switch (context->working[1].value) {
			case 0:  // =
				if (context->working[0].value == context->working[2].value) {
					context->private.pc = (juint16)context->working[3].value;
				}
				break;

			case 1:  // !
				if (context->working[0].value != context->working[2].value) {
					context->private.pc = (juint16)context->working[3].value;
				}
				break;

			case 2:  // <
				if (context->working[0].value < context->working[2].value) {
					context->private.pc = (juint16)context->working[3].value;
				}
				break;

			case 3:  // >
				if (context->working[0].value > context->working[2].value) {
					context->private.pc = (juint16)context->working[3].value;
				}
				break;
		}
	} else {
		// Which side is a number?
		if (isNumber0) {
			setStringFormat(&context->working[2], "%d", context->working[2].value);
		} else {
			setStringFormat(&context->working[0], "%d", context->working[0].value);
		}
		result = strcmp(context->working[0].text, context->working[2].text);
		switch (context->working[1].value) {
			case 0:  // =
				if (result == 0) {
					context->private.pc = (juint16)context->working[3].value;
				}
				break;

			case 1:  // !
				if (result != 0) {
					context->private.pc = (juint16)context->working[3].value;
				}
				break;

			case 2:  // <
				if (result < 0) {
					context->private.pc = (juint16)context->working[3].value;
				}
				break;

			case 3:  // >
				if (result > 0) {
					context->private.pc = (juint16)context->working[3].value;
				}
				break;
		}
	}
}


void op_exe(VMContextT *context) {
	vmPop(context, &context->working[0]); // Arg count
	vmPop(context, &context->working[1]); // Function number
	context->private.functions[context->working[1].value](context, (juint16)(context->working[0].value) - 1);
}


void op_jmp(VMContextT *context) {
	vmPop(context, &context->working[0]);
	//printf("Jumping to %04x\n", (juint16)context->working[0].value);
	context->private.pc = (juint16)context->working[0].value;
}


void op_hlt(VMContextT *context) {
	(void)(context);
	// We don't actually need to do anything for HLT.
}


void op_pop(VMContextT *context) {
	readItemFromPC(context, &context->working[0]);
	vmPop(context, &context->working[1]);
	copyItem(&context->private.variables[context->working[0].value], &context->working[1]);
}


void op_puc(VMContextT *context) {
	readItemFromPC(context, &context->working[0]);
	vmPush(context, &context->working[0]);
}


void op_puv(VMContextT *context) {
	readItemFromPC(context, &context->working[0]);
	vmPush(context, &context->private.variables[context->working[0].value]);
}


void op_sub(VMContextT *context) {
	vmPop(context, &context->working[0]);
	vmPop(context, &context->working[1]);

	// Number
	context->working[2].value = context->working[0].value - context->working[1].value;

	vmPush(context, &context->working[2]);
}


void readItemFromPC(VMContextT *context, PairT *item) {
	byte b1;
	byte b2;
	int  y;

	//printf("Reading item at offset %04x - %02x\n", context->private.pc + context->private.headerBytes, context->private.memory[context->private.pc]);

	// Get the length/value of this item
	b1 = context->private.memory[context->private.pc++];
	b2 = context->private.memory[context->private.pc++];
#ifdef JOEY_BIG_ENDIAN
	item->value = (jint16)((b1 << 8) + b2);
#else
	item->value = (jint16)((b2 << 8) + b1);
#endif

	// If this is a zero, it's a number.  If it's not, it's a string
	if (context->private.memory[context->private.pc] > 0) {
		if (item->allocated < item->value + 1) {
			item->text = (char *)jlRealloc(item->text, (size_t)(item->value + 1));
			item->allocated = item->value + 1;
		}
		for (y=0; y<item->value; y++) {
			item->text[y] = (char)context->private.memory[context->private.pc++];
		}
		item->text[y] = 0;
	} else {
		context->private.pc++;
		item->text[0] = 0;
	}

	//printf("Ending read (inclusive) at offset %04x - %02x\n", context->private.pc + context->private.headerBytes - 1, context->private.memory[context->private.pc - 1]);
}


void vmSetItem(PairT *item, char *text, jint16 *value) {
	juint16 len;

	if ((text != 0) && (text[0] != 0)) {
		len = (juint16)strlen(text) + 1;
		if (item->allocated < len) {
			item->text = (char *)jlRealloc(item->text, len);
			item->allocated = (jint16)len;
		}
		strcpy(item->text, text);
		item->value = (jint16)len - 1;
	} else {
		if (item->text != 0) {
			item->text[0] = 0;
		}
	}

	if (value != 0) {
		item->value = *value;
	}
}


#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wformat-nonliteral"
void setStringFormat(PairT *item, char *format, ...) {
	int     len;
	va_list args;

	// Do we have a buffer at all?
	if (item->allocated == 0) {
		item->text = (char *)jlMalloc(16 * sizeof(char));
		item->allocated = 16;
	}
	// Attempt to write formatted string into buffer.
	va_start(args, format);
	len = vsnprintf(item->text, (unsigned long)item->allocated, format, args);
	va_end(args);
	// Did it succeed?
	if (len >= item->allocated) {
		// Nope!  Allocate more memory and do it again.
		item->text = (char *)jlRealloc(item->text, (unsigned long)len);
		item->allocated = (jint16)len;
		va_start(args, format);
		len = vsnprintf(item->text, (unsigned long)item->allocated, format, args);
		va_end(args);
	}
}
#pragma GCC diagnostic pop


bool vmAddFunction(VMContextT *context, VMFuncT function) {
	context->private.functionCount++;
	context->private.functions = (VMFuncT *)jlRealloc(context->private.functions, sizeof(VMFuncT) * context->private.functionCount);
	context->private.functions[context->private.functionCount - 1] = function;
	return true;
}


bool vmCreate(VMContextT *context) {
	juint16 x;

	// This can be redundant but it doesn't hurt anything.
	opcodes[OPCODE_ADD - 1] = op_add;
	opcodes[OPCODE_BOC - 1] = op_boc;
	opcodes[OPCODE_EXE - 1] = op_exe;
	opcodes[OPCODE_JMP - 1] = op_jmp;
	opcodes[OPCODE_HLT - 1] = op_hlt;
	opcodes[OPCODE_POP - 1] = op_pop;
	opcodes[OPCODE_PUC - 1] = op_puc;
	opcodes[OPCODE_PUV - 1] = op_puv;
	opcodes[OPCODE_SUB - 1] = op_sub;

	context->private.sp          = 0;
	context->private.pc          = 0;
	context->private.headerBytes = 0;

	// Stack
	context->private.stack      = 0;
	context->private.stackCount = 0;

	// All variables
	context->private.variables = 0;
	context->private.variablesCount = 0;

	// Native function pointers
	context->private.functions     = 0;
	context->private.functionCount = 0;

	// Program space
	context->private.memory      = 0;
	context->private.programSize = 0;

	// Exported Labels
	context->private.labels     = 0;
	context->private.labelCount = 0;

	// Exported Variables
	context->private.variableTable      = 0;
	context->private.variableTableCount = 0;

	// Working RAM
	context->working = (PairT *)jlMalloc(sizeof(PairT) * WORKING_SIZE);
	for (x=0; x<WORKING_SIZE; x++) {
		context->working[x].text      = 0;
		context->working[x].allocated = 0;
		context->working[x].value     = 0;
	}

	return true;
}


bool vmDestroy(VMContextT *context) {

	juint16 x;

	// Working RAM
	for (x=0; x<WORKING_SIZE; x++) {
		jlFree(context->working[x].text);
	}
	jlFree(context->working);

	// Program space
	jlFree(context->private.memory);

	// Native function pointers
	jlFree(context->private.functions);

	// Label Jump Table
	for (x=0; x<context->private.labelCount; x++) {
		jlFree(context->private.labels[x].text);
	}
	jlFree(context->private.labels);

	// Exported Varaibles Index
	for (x=0; x<context->private.variableTableCount; x++) {
		jlFree(context->private.variableTable[x].text);
	}
	jlFree(context->private.variableTable);

	// All variables
	for (x=0; x<context->private.variablesCount; x++) {
		jlFree(context->private.variables[x].text);
	}
	jlFree(context->private.variables);

	// Stack
	for (x=0; x<context->private.stackCount; x++) {
		jlFree(context->private.stack[x].text);
	}
	jlFree(context->private.stack);

	return true;
}


bool vmGetPCIndex(VMContextT *context, char *label, juint16 *pc) {
	juint16 x;
	bool    result = false;

	for (x=0; x<context->private.labelCount; x++) {
		if (strcmp(context->private.labels[x].text, label) == 0) {
			*pc = context->private.labels[x].value;
			result = true;
			break;
		}
	}

	return result;
}


bool vmGetVariable(VMContextT *context, char *name, PairT *item) {
	juint16 x;

	item = NULL;

	if (vmGetVariableIndex(context, name, &x)) {
		*item = context->private.variables[x];
	}

	return (item != NULL);
}


bool vmGetVariableIndex(VMContextT *context, char *name, juint16 *index) {
	juint16 x;

	for (x=0; x<context->private.variableTableCount; x++) {
		if (strcmp(context->private.variableTable[x].text, name) == 0) {
			*index = context->private.variableTable[x].value;
			return true;
		}
	}

	return false;
}


bool vmIsItemNumber(PairT *item) {
	return (item->text == 0) || (item->text[0] == 0);
}


bool vmLoad(VMContextT *context, char *filename) {

	char     temp[4];
	FILE    *binFile;
	juint16  tempUnsigned;
	juint16  x;
	juint16  y;
	int      length;

	binFile = fopen(filename, "rb");
	if (!binFile) {
		return false;
	}

	// Get file size for later
	fseek(binFile, 0, SEEK_END);
	length = (int)ftell(binFile);
	fseek(binFile, 0, SEEK_SET);

	// Read header & Version Number
	fread(temp, 4, 1, binFile);
	if ((temp[0] != 'D') || (temp[1] != 'B') || (temp[2] != 'L') || (temp[3] != 0)) {
		fclose(binFile);
		return false;
	}

	// Read exported label entries
	fread(&tempUnsigned, sizeof(juint16), 1, binFile);
#ifdef JOEY_BIG_ENDIAN
	context->private.labelCount = jlByteSwap(tempUnsigned);
#else
	context->private.labelCount = tempUnsigned;
#endif
	context->private.labels = (UPairT *)jlMalloc(sizeof(UPairT) * context->private.labelCount);
	for (x=0; x<context->private.labelCount; x++) {
		fread(&tempUnsigned, sizeof(juint16), 1, binFile);  // Address of label
#ifdef JOEY_BIG_ENDIAN
		context->private.labels[x].value = jlByteSwap(tempUnsigned);
#else
		context->private.labels[x].value = tempUnsigned;
#endif
		y = (juint16)fgetc(binFile);  // Length of label name
		// Label Name
		context->private.labels[x].text = (char *)jlMalloc((y + 1) * sizeof(char));
		fread(context->private.labels[x].text, sizeof(char), y, binFile);
		context->private.labels[x].text[y] = 0;
		context->private.labels[x].allocated = (jint16)(y + 1);
	}

	// Read exported variable entries
	fread(&tempUnsigned, sizeof(juint16), 1, binFile);
#ifdef JOEY_BIG_ENDIAN
	context->private.variableTableCount = jlByteSwap(tempUnsigned);
#else
	context->private.variableTableCount = tempUnsigned;
#endif
	context->private.variableTable = (UPairT *)jlMalloc(sizeof(UPairT) * context->private.variableTableCount);
	for (x=0; x<context->private.variableTableCount; x++) {
		fread(&tempUnsigned, sizeof(juint16), 1, binFile);
#ifdef JOEY_BIG_ENDIAN
		context->private.variableTable[x].value = jlByteSwap(tempUnsigned);
#else
		context->private.variableTable[x].value = tempUnsigned;
#endif
		y = (juint16)fgetc(binFile);  // Length of variable name
		// Variable Name
		context->private.variableTable[x].text = (char *)jlMalloc((y + 1) * sizeof(char));
		fread(context->private.variableTable[x].text, sizeof(char), y, binFile);
		context->private.variableTable[x].text[y] = 0;
		context->private.variableTable[x].allocated = (jint16)(y + 1);
	}

	// Read total variable count
	fread(&tempUnsigned, sizeof(juint16), 1, binFile);
#ifdef JOEY_BIG_ENDIAN
	context->private.variablesCount = jlByteSwap(tempUnsigned);
#else
	context->private.variablesCount = tempUnsigned;
#endif
	context->private.variables = (PairT *)jlMalloc(sizeof(PairT) * context->private.variablesCount);
	for (x=0; x<context->private.variablesCount; x++) {
		context->private.variables->text      = 0;
		context->private.variables->allocated = 0;
		context->private.variables->value     = 0;
	}

	// Record position in file for debugging purposes
	context->private.headerBytes = (juint16)ftell(binFile);
	//printf("PC offset is %04x\n", context->private.headerBytes);

	// Read program byte stream
	context->private.programSize = (juint16)(length - ftell(binFile));
	context->private.memory = (byte *)jlMalloc(sizeof(byte) * context->private.programSize);
	fread(context->private.memory, sizeof(char) * context->private.programSize, 1, binFile);

	fclose(binFile);

	return true;
}


bool vmPop(VMContextT *context, PairT *item) {
	if (context->private.sp > 0) {
		context->private.sp--;
		copyItem(item, &context->private.stack[context->private.sp]);
		return true;
	}
	return false;
}


bool vmPush(VMContextT *context, PairT *item) {
	// Grow stack if needed.
	if (context->private.sp + 1 > context->private.stackCount) {
		context->private.stackCount = context->private.sp + 1;
		context->private.stack = (PairT *)jlRealloc(context->private.stack, sizeof(PairT) * context->private.stackCount);
		context->private.stack[context->private.sp].text      = 0;
		context->private.stack[context->private.sp].allocated = 0;
		context->private.stack[context->private.sp].value     = 0;
	}
	copyItem(&context->private.stack[context->private.sp], item);
	context->private.sp++;
	return true;
}


bool vmSetPC(VMContextT *context, char *label) {
	juint16 pc;
	bool    result = false;

	if (label == NULL) {
		context->private.pc = 0;
		result = true;
	} else {
		if (vmGetPCIndex(context, label, &pc)) {
			context->private.pc = pc;
			result = true;
		}
	}

	return result;
}


bool vmSetPCByIndex(VMContextT *context, juint16 index) {
	context->private.pc = index;  // Currently, the PC is the index we return
	return true;
}


bool vmSetVariable(VMContextT *context, char *name, PairT *item) {
	PairT *target = NULL;
	if (vmGetVariable(context, name, target)) {
		copyItem(target, item);
		return true;
	}
	return false;
}


bool vmSetVariableByIndex(VMContextT *context, jint16 index, PairT *item) {
	copyItem(&context->private.variables[index], item);
	return true;
}


bool vmStep(VMContextT *context) {
	byte opcode = context->private.memory[context->private.pc++];
	//printf("Fetched opcode at file offset %04x (PC %04x):  %02x\n", context->private.pc + context->private.headerBytes - 1, context->private.pc - 1, opcode);
	opcodes[opcode - 1](context);
	return (opcode != OPCODE_HLT);
}


bool vmRun(VMContextT *context) {
	while (vmStep(context))
		;
	return true;
}