#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <ctype.h>
#include "cpu.h"

typedef enum {
	IMMED4,
	IMMED8,
	IMMEDHI,
	BCCDST,
	DCB,
	DCW,
	DCL
} reftype;

typedef struct {
	uint16_t address;
	reftype  type;
} reference;


typedef struct {
	char      *name;
	reference *references;
	size_t    num_references;
	size_t    reference_storage;
	uint16_t  address;
	uint8_t   valid;
} label;

typedef struct {
	label  *labels;
	size_t num_labels;
	size_t label_storage;
} label_meta;

typedef struct {
	int immed_min;
	int immed_max;
	uint16_t base;
	uint8_t  first_shift;
	uint8_t  second_shift;
	uint8_t  expected_args;
} inst_info;

label *add_label(label_meta *labels, char *name, uint16_t address, uint8_t valid)
{
	if (labels->num_labels == labels->label_storage) {
		labels->label_storage *= 2;
		labels->labels = realloc(labels->labels, sizeof(label) * labels->label_storage);
	}
	labels->labels[labels->num_labels].name = strdup(name);
	labels->labels[labels->num_labels].references = NULL;
	labels->labels[labels->num_labels].address = address;
	labels->labels[labels->num_labels].valid = valid;
	labels->num_labels++;
	return labels->labels + labels->num_labels - 1;
}

label *find_label(label_meta *meta, char *name)
{
	for (size_t i = 0; i < meta->num_labels; i++)
	{
		if (!strcmp(name, meta->labels[i].name)) {
			return meta->labels + i;
		}
	}
	return NULL;
}

uint16_t find_string_arr(char ** list, char *str, uint16_t num_entries)
{
	for (uint16_t i = 0; i < num_entries; i++)
	{
		if (!strcmp(list[i], str)) {
			return i;
		}
	}
	return num_entries;
}

inst_info find_mnemonic(char *mnemonic)
{
	uint16_t index = find_string_arr(mnemonics, mnemonic, SINGLE_SOURCE);
	inst_info ret;
	if (index < SINGLE_SOURCE) {
		ret.base = index;
		ret.first_shift = 4;
		if (index == LDIM || index == LDIMH) {
			ret.second_shift = 12;
			ret.expected_args = 2;
			ret.immed_min = -128;
			ret.immed_max = 256;
		} else {
			ret.second_shift = 8;
			ret.expected_args = 3;
			ret.immed_min = ret.immed_max = 0;
		}
		return ret;
	}
	index = find_string_arr(mnemonics_single_src, mnemonic, SINGLE_REG);
	if (index < SINGLE_REG) {
		ret.base = index << 4 | SINGLE_SOURCE;
		ret.first_shift = 8;
		ret.second_shift = 12;
		ret.expected_args = 2;
		if (index >= INI) {
			if (index >= ADDI) {
				ret.immed_min = -8;
				ret.immed_max = 8;
			} else {
				ret.immed_min = 0;
				ret.immed_max = 15;
			}
		} else {
			ret.immed_min = ret.immed_max = 0;
		}
		return ret;
	}
	index = find_string_arr(mnemonics_single_reg, mnemonic, SETENUM+1);
	if (index > SETENUM) {
		ret.base = 0xFFFF;
		return ret;
	}
	ret.base = index << 8 | SINGLE_REG << 4 | SINGLE_SOURCE;
	ret.immed_min = ret.immed_max = 0;
	ret.first_shift = 12;
	ret.second_shift = 0;
	ret.expected_args = 1;
	return ret;
}

void add_reference(label *label, uint16_t address, reftype type)
{
	if (!label->references) {
		label->reference_storage = 4;
		label->references = malloc(sizeof(reference) * label->reference_storage);
		label->num_references = 0;
	} else if (label->num_references == label->reference_storage) {
		label->reference_storage *= 2;
		label->references = realloc(label->references, sizeof(reference) * label->reference_storage);
	}
	
	label->references[label->num_references].address = address;
	label->references[label->num_references].type = type;
	label->num_references++;
}

char * get_arg(char **pos)
{
	char *linebuf = *pos;
	while (*linebuf && isspace(*linebuf) && *linebuf != ';')
	{
		linebuf++;
	}
	char * start = linebuf;
	char * end = start;
	while (*linebuf && *linebuf != ';' && *linebuf != ',')
	{
		if (!isspace(*linebuf)) {
			end = linebuf+1;
		}
		linebuf++;
	}
	if (start == end) {
		return NULL;
	}
	if (*end) {
		if (*linebuf == ',') {
			linebuf++;
		} else {
			linebuf = end;
		}
		*end = 0;
	}
	*pos = linebuf;
	return start;
}

void free_labels (label_meta *meta)
{
	for (size_t i = 0; i < meta->num_labels; i++)
	{
		free(meta->labels[i].name);
		if(meta->labels[i].references) {
			free(meta->labels[i].references);
		}
	}
	free(meta->labels);
}

int handle_dc(char size, char *linebuf, uint8_t *outbuf, uint16_t *pc, label_meta *meta)
{
	char *arg;
	long value;
	char *start = linebuf;
	char *orig = strdup(linebuf);
	int in_string = 0;
	while ((arg = in_string ? linebuf : get_arg(&linebuf)))
	{
		//TODO: actual error checking
		if (arg[0] == '$' || (arg[0] == '0' && arg[1] == 'x')) {
			value = strtol(arg[0] == '$' ? arg+1 : arg+2, NULL, 16);
		} else if (arg[0] >= '0' && arg[0] <= '9' || arg[0] == '-') {
			value = strtol(arg, NULL, 10);
		} else if (arg[0] == '"') {
			if (arg[1] == '"') {
				//emtpy string or end of string
				in_string = 0;
				continue;
			}
			if (arg[1] == '\\' && arg[2]) {
				switch(arg[2])
				{
				case 'n':
					value = '\n';
					break;
				case 't':
					value = '\t';
					break;
				case 'r':
					value = '\r';
					break;
				case '"':
				case '\\':
					value = arg[2];
					break;
				default:
					fprintf(stderr, "WARNING: Unrecognized escape char %c\n", arg[2]);
					value = arg[2];
					break;
				}
				arg++;
			} else {
				value = arg[1];
			}
			in_string = 1;
			arg[1] = '"';
			linebuf = arg+1;
			int len = strlen(linebuf);
			//undo termination done by get_arg
			linebuf[len] = orig[len + linebuf-start];
		} else {
			label *l = find_label(meta, arg);
			if (!l) {
				l = add_label(meta, arg, 0, 0);
			}
			if (l->valid) {
				value = l->address;
			} else {
				value = 0;
				add_reference(l, *pc, size == 'b' ? DCB : size == 'w' ? DCW : DCL);
			}
		}
		switch (size)
		{
		case 'b':
			if (value < -128 || value > 255) {
				fprintf(stderr, "WARNING: %s is too large to fit in a byte\n", arg);
			}
			if (*pc >= 48 * 1024) {
				fputs("ERROR: Hit end of ROM space\n", stderr);
				free(orig);
				return 0;
			}
			outbuf[(*pc)++] = value;
			break;
		case 'w':
			if (value < -32768 || value > 65535) {
				fprintf(stderr, "WARNING: %s is too large to fit in a word\n", arg);
			}
			if (*pc >= 48 * 1024 - 1) {
				fputs("ERROR: Hit end of ROM space\n", stderr);
				free(orig);
				return 0;
			}
			outbuf[(*pc)++] = value >> 8;
			outbuf[(*pc)++] = value;
			break;
		case 'l':
			if (*pc >= 48 * 1024 - 3) {
				fputs("ERROR: Hit end of ROM space\n", stderr);
				free(orig);
				return 0;
			}
			outbuf[(*pc)++] = value >> 24;
			outbuf[(*pc)++] = value >> 16;
			outbuf[(*pc)++] = value >> 8;
			outbuf[(*pc)++] = value;
			break;
		}
	}
	free(orig);
	return 1;
}

int process_arg(uint16_t *inst, char *arg, int arg_shift, int immed_min, int immed_max, label_meta *meta, uint16_t pc)
{
	long value;
	if (arg[0] == 'r' && arg[1] >= '0' && arg[1] <= '9' && (arg[2] == 0 || arg[3] == 0)) {
		//posible register
		value = strtol(arg+1, NULL, 10);
		if (value >= 0 && value < 16) {
			*inst |= value << arg_shift;
			return 1;
		}
	}
	if (!strcmp(arg, "pc")) {
		*inst |= REG_PC << arg_shift;
	}
	if (!strcmp(arg, "sr")) {
		*inst |= REG_SR << arg_shift;
	}
	if (immed_min == immed_max) {
		fprintf(stderr, "ERROR: Non-register argument %s where a register is required\n", arg);
		return 0;
	}
	
	//TODO: actual error checking
	if (arg[0] == '$' || (arg[0] == '0' && arg[1] == 'x')) {
		value = strtol(arg[0] == '$' ? arg+1 : arg+2, NULL, 16);
	} else if (arg[0] >= '0' && arg[0] <= '9' || arg[0] == '-') {
		value = strtol(arg, NULL, 10);
	} else {
		label *l = find_label(meta, arg);
		if (!l) {
			l = add_label(meta, arg, 0, 0);
		}
		if (l->valid) {
			value = l->address;
		} else {
			value = 0;
			add_reference(l, pc, (*inst & 0xF) == LDIMH ? IMMEDHI : (*inst & 0xF) == LDIM ? IMMED8 : IMMED4);
		}
	}
	if (value > immed_max || value < immed_min) {
		fprintf(stderr, "WARNING: %s is too big to fit in an %s\n", arg, (*inst & 0xF) <= LDIMH ? "byte" : "nibble");
	}
	if (immed_max == 8) {
		if (value == 8) {
			value = 0;
		}
		value &= 0xF;
	} else {
		value &= 0xFF;
	}
	*inst |= value << arg_shift;
	return 1;
}

char * condition_names[] = {
	"ra", "rn", "eq", "ne", "mi", "pl", "cs", "cc", "gr", "le"
};

int handle_bcc(char *cc, char *args, uint8_t *outbuf, uint16_t pc, label_meta *meta)
{
	uint16_t intcc = find_string_arr(condition_names, cc, COND_LEQ+1);
	if (intcc > COND_LEQ) {
		fprintf(stderr, "ERROR: Invalid condition code %s\n", cc);
		return 0;
	}
	char *dest = get_arg(&args);
	if (!dest) {
		fprintf(stderr, "ERROR: Missing argument to b%s\n", cc);
		return 0;
	}
	char *extra = get_arg(&args);
	if (extra) {
		fprintf(stderr, "ERROR: Extra argument %s to b%s\n", extra, cc);
	}
	label *l = find_label(meta, dest);
	if (!l) {
		l = add_label(meta, dest, 0, 0);
		add_reference(l, pc, BCCDST);
	}
	uint16_t dest_addr = l->valid ? l->address : pc + 4;
	if (dest_addr & 1) {
		fprintf(stderr, "ERROR: Label %s refers to odd address %X which is illegal for b%s\n", dest, dest_addr, cc);
		return 0;
	}
	int32_t diff = dest_addr - (pc + 4);
	if (diff < -512 || diff > 510) {
		fprintf(stderr, "ERROR: Label %s is out of range for b%s\n", dest, cc);
		return 0;
	}
	diff &= 0x1FE;
	uint16_t inst = BCC | diff << 3 | intcc << 12;
	outbuf[pc] = inst >> 8;
	outbuf[pc+1] = inst;
	return 1;
}

uint8_t assemble_file(FILE *input, FILE *output)
{
	//fixed size buffers are lame, but so are lines longer than 4K characters
	//this is good enough for the really simple first version
	char linebuf[4096];
	//maximum program size is 48KB
	uint8_t outbuf[48*1024];
	uint16_t pc = 0;
	
	size_t num_labels = 0;
	size_t label_storage = 1024;
	label_meta labels = {
		.labels = malloc(sizeof(label) * 1024),
		.label_storage = 1024,
		.num_labels = 0
	};
	int line = 0;
	
	while (fgets(linebuf, sizeof(linebuf), input) && pc < sizeof(outbuf)/sizeof(uint16_t))
	{
		line++;
		char *lname = NULL;
		char *cur = linebuf;
		if (!isspace(*cur)) {
			lname = cur;
			while(*cur && *cur != ':' && !isspace(*cur))
			{
				cur++;
			}
			if (*cur) {
				*cur = 0;
				cur++;
			}
		}
		while (*cur && isspace(*cur))
		{
			cur++;
		}
		if (!*cur || *cur == ';') {
			if (lname) {
				label *l = find_label(&labels, lname);
				if (l) {
					l->address = pc;
					l->valid = 1;
				} else {
					add_label(&labels, lname, pc, 1);
				}
			}
			continue;
		}
		char *mnemonic = cur;
		while (*cur && !isspace(*cur) && *cur != ';')
		{
			cur++;
		}
		if (!*cur || *cur == ';') {
			*cur = 0;
			fprintf(stderr, "Missing arguments to instruction %s on line %d\n", mnemonic, line);
			goto error;
		}
		*cur = 0;
		cur++;
		if (!strncmp(mnemonic, "dc.", 3) && (mnemonic[3] == 'b' || mnemonic[3] == 'w' || mnemonic[3] == 'l')) {
			if (mnemonic[3] != 'b' && pc & 1) {
				outbuf[pc] = 0;
				pc++;
			}
			if (lname) {
				label *l = find_label(&labels, lname);
				if (l) {
					l->address = pc;
					l->valid = 1;
				} else {
					add_label(&labels, lname, pc, 1);
				}
			}
			if (!handle_dc(mnemonic[3], cur, outbuf, &pc, &labels)) {
				goto error;
			}
			continue;
		}
		//automatically align to word boundary
		if (pc & 1) {
			outbuf[pc] = 0;
			pc++;
		}
		if (lname) {
			label *l = find_label(&labels, lname);
			if (l) {
				l->address = pc;
				l->valid = 1;
			} else {
				add_label(&labels, lname, pc, 1);
			}
		}
		if (mnemonic[0] == 'b' && strlen(mnemonic) == 3) {
			if (!handle_bcc(mnemonic + 1, cur, outbuf, pc, &labels)) {
				goto error;
			}
			pc+=2;
			continue;
		}
		char *firstarg = get_arg(&cur);
		
		if (!firstarg) {
			fprintf(stderr, "Missing arguments to instruction %s on line %d\n", mnemonic, line);
			goto error;
		}
		char *secondarg = get_arg(&cur);
		char *thirdarg;
		int num_args;
		if (secondarg) {
			thirdarg = get_arg(&cur);
			num_args = thirdarg ? 3 : 2;
		} else {
			thirdarg = NULL;
			num_args = 1;
		}
		
		inst_info inf = find_mnemonic(mnemonic);
		if (inf.base == 0xFFFF) {
			fprintf(stderr, "Invalid mnemonic %s on line %d\n", mnemonic, line);
			goto error;
		}
		if (inf.expected_args != num_args) {
			fprintf(stderr, "Instruction %s expects %d args, but %d were given on line %d\n", mnemonic, inf.expected_args, num_args, line);
			goto error;
		}
		
		uint16_t inst = inf.base;
		if (!process_arg(&inst, firstarg, inf.first_shift, inf.immed_min, inf.immed_max, &labels, pc)) {
			goto error;
		}
		if (secondarg) {
			if (!process_arg(&inst, secondarg, inf.second_shift, 0, 0, &labels, pc)) {
				goto error;
			}
			if (thirdarg) {
				if (!process_arg(&inst, thirdarg, inf.second_shift+4, 0, 0, &labels, pc)) {
					goto error;
				}
			}
		}
		outbuf[pc++] = inst >> 8;
		outbuf[pc++] = inst;
	}
	for (int i = 0; i < labels.num_labels; i++)
	{
		if (labels.labels[i].references) {
			if (!labels.labels[i].valid) {
				fprintf(stderr, "ERROR: label %s is used but not defined\n", labels.labels[i].name);
				goto error;
			}
			uint16_t address = labels.labels[i].address;
			for(reference *ref = labels.labels[i].references; 
			    ref < labels.labels[i].references + labels.labels[i].num_references;
				ref++
			)
			{
				//TODO: Warn when addresses don't fit
				switch(ref->type)
				{
				case IMMED4:
					if (address == 8) {
						address = 0;
					}
					outbuf[ref->address] |= address & 0xF;
					break;
				case IMMED8:
					outbuf[ref->address] |= (address & 0xF0) >> 4;
					outbuf[ref->address+1] |= (address & 0xF) << 4;
					break;
				case IMMEDHI:
					outbuf[ref->address] |= (address & 0xF000) >> 12;
					outbuf[ref->address+1] |= (address & 0xF00) >> 4; 
					break;
				case BCCDST: {
					if (address & 1) {
						fprintf(stderr, "ERROR: Label %s refers to odd address %X which is illegal for bcc\n", labels.labels[i].name, address);
						goto error;
					}
					int diff = address - (ref->address + 4);
					if (diff < -512 || diff > 510) {
						fprintf(stderr, "ERROR: Label %s has address %X which is out of range of bcc at %X\n", labels.labels[i].name, address, ref->address);
					}
					outbuf[ref->address] |= (diff & 0x1E0) >> 5;
					outbuf[ref->address+1] |= (diff & 0x01E) << 3;
					break;
				}
				case DCB:
					outbuf[ref->address] = address;
					break;
				case DCW:
					outbuf[ref->address] = address >> 8;
					outbuf[ref->address+1] = address;
					break;
				case DCL:
					outbuf[ref->address] = 0;
					outbuf[ref->address+1] = 0;
					outbuf[ref->address+2] = address >> 8;
					outbuf[ref->address+3] = address;
					break;
				}
			}
		}
	}
	if (pc == fwrite(outbuf, 1, pc, output)) {
		free_labels(&labels);
		return 1;
	}
	fputs("Error writing to output file\n", stderr);
error:
	free_labels(&labels);
	return 0;
}


int main(int argc, char ** argv)
{
	if (argc < 3) {
		fputs("Usage: asm INFILE OUTFILE\n", stderr);
		return 1;
	}
	FILE *infile = strcmp("-", argv[1]) ? fopen(argv[1], "r") : stdin;
	if (!infile) {
		fprintf(stderr, "Failed to open %s for reading\n", argv[1]);
		return 1;
	}
	FILE *outfile = strcmp("-", argv[2]) ? fopen(argv[2], "w") : stdout;
	if (!outfile) {
		fprintf(stderr, "Failed to open %s for writing\n", argv[2]);
		return 1;
	}
	int ret = assemble_file(infile, outfile);
	fclose(infile);
	fclose(outfile);
	return ret;
}