#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <stdint.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <errno.h>
#include "emu.h"

#define RAM_BASE 0x10000000
#define RAM_TOP  0x10100000

#define BRK_TOP (RAM_TOP - 0x1000)

#define INIT_SP RAM_TOP
#define INIT_PC 0x08000054

/* Read/write macros */
#define READ_BYTE(BASE, ADDR) (BASE)[ADDR]
#define READ_WORD(BASE, ADDR) (((BASE)[ADDR]<<8) |			\
							  (BASE)[(ADDR)+1])
#define READ_LONG(BASE, ADDR) (((BASE)[ADDR]<<24) |			\
							  ((BASE)[(ADDR)+1]<<16) |		\
							  ((BASE)[(ADDR)+2]<<8) |		\
							  (BASE)[(ADDR)+3])

#define WRITE_BYTE(BASE, ADDR, VAL) (BASE)[ADDR] = (VAL)&0xff
#define WRITE_WORD(BASE, ADDR, VAL) (BASE)[ADDR] = ((VAL)>>8) & 0xff;		\
									(BASE)[(ADDR)+1] = (VAL)&0xff
#define WRITE_LONG(BASE, ADDR, VAL) (BASE)[ADDR] = ((VAL)>>24) & 0xff;		\
									(BASE)[(ADDR)+1] = ((VAL)>>16)&0xff;	\
									(BASE)[(ADDR)+2] = ((VAL)>>8)&0xff;		\
									(BASE)[(ADDR)+3] = (VAL)&0xff


static void emulated_syscall(void);

static unsigned char ram[RAM_TOP - RAM_BASE];
uint32_t brkbase = RAM_BASE;
uint32_t brkpos = RAM_BASE;
uint32_t entrypoint = RAM_BASE;

void fatal(char* fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	fprintf(stderr, "fatal: ");
	vfprintf(stderr, fmt, ap);
	fprintf(stderr, "\n");
	va_end(ap);

	exit(EXIT_FAILURE);
}

static uint32_t transform_address(uint32_t address)
{
	uint32_t a = address - RAM_BASE;
	if (a >= RAM_TOP)
		fatal("address 0x%x out of bounds", address);
	return a;
}

uint32_t read_long(uint32_t address)
{
	return READ_LONG(ram, transform_address(address));
}


uint32_t read_word(uint32_t address)
{
	return READ_WORD(ram, transform_address(address));
}

uint32_t read_byte(uint32_t address)
{
	return READ_BYTE(ram, transform_address(address));
}

void write_byte(uint32_t address, uint32_t value)
{
	WRITE_BYTE(ram, transform_address(address), value);
}

void write_word(uint32_t address, uint32_t value)
{
	WRITE_WORD(ram, transform_address(address), value);
}

void write_long(uint32_t address, uint32_t value)
{
	WRITE_LONG(ram, transform_address(address), value);
}

void system_call(uint8_t trapno)
{
	fatal("syscalls unimplemented");
}

static void load_program(FILE* fd)
{
	fseek(fd, 0, SEEK_SET);
	if (fread(ram, 1, 0x34, fd) != 0x34)
		fatal("couldn't read ELF header");
	
	uint32_t phoff = READ_LONG(ram, 0x1c);
	uint16_t phentsize = READ_WORD(ram, 0x2a);
	uint16_t phnum = READ_WORD(ram, 0x2c);
	entrypoint = READ_LONG(ram, 0x18);
	if ((phentsize != 0x20) || (phnum != 1))
		fatal("unsupported ELF file");

	fseek(fd, phoff, SEEK_SET);
	if (fread(ram, 1, phentsize, fd) != phentsize)
		fatal("couldn't read program header");

	uint32_t offset = READ_LONG(ram, 0x04);
	uint32_t vaddr = READ_LONG(ram, 0x08);
	uint32_t filesz = READ_LONG(ram, 0x10);
	uint32_t memsz = READ_LONG(ram, 0x14);
	brkbase = brkpos = vaddr + memsz;

	uint32_t vaddroffset = transform_address(vaddr);
	transform_address(vaddr + memsz); /* bounds check */
	memset(ram+vaddroffset, 0, memsz);
	fseek(fd, offset, SEEK_SET);
	if (fread(ram+vaddroffset, 1, filesz, fd) != filesz)
		fatal("couldn't read program data");
}

/* The main loop */
int main(int argc, char* argv[])
{
	if(argc != 2)
		fatal("syntax: emuppc <program file>");

	FILE* fd = fopen(argv[1], "rb");
	if (!fd)
		fatal("Unable to open %s", argv[1]);
	load_program(fd);
	fclose(fd);

	/* On entry, the Linux stack looks like this.
	 * 
	 * sp+..           NULL
     * sp+8+(4*argc)   env (X quads)
     * sp+4+(4*argc)   NULL
     * sp+4            argv (argc quads)
     * sp              argc
	 *
	 * We'll set it up with a bodgy stack frame with argc=0 just to keep the
	 * startup code happy.
	 */

	{
		uint32_t sp = INIT_SP;
		write_long(sp -= 4, 0);
		uint32_t envp = sp;
		write_long(sp -= 4, envp);
		write_long(sp -= 4, 0);
		unsigned long argv = sp;
		write_long(sp -= 4, argv);
		write_long(sp -= 4, 0);
		cpu.gpr[1] = sp;
		cpu.cia = entrypoint;
	}

	fatal("execution unimplemented");

	return 0;
}