#include "types.h"
#include "defs.h"
#include "param.h"
#include "memlayout.h"
#include "mmu.h"
#include "proc.h"
#include "x86.h"
#include "syscall.h"

// User code makes a system call with INT T_SYSCALL.
// System call number in %eax.
// Arguments on the stack, from the user call to the C
// library system call function. The saved user %esp points
// to a saved program counter, and then the first argument.

// Fetch the int at addr from the current process.
int fetchint(uint addr, int *ip)
{
    struct proc *curproc = myproc();

    if (addr >= curproc->sz || addr + 4 > curproc->sz)
        return -1;
    *ip = *(int *)(addr);
    return 0;
}

// Fetch the nul-terminated string at addr from the current process.
// Doesn't actually copy the string - just sets *pp to point at it.
// Returns length of string, not including nul.
int fetchstr(uint addr, char **pp)
{
    char *s, *ep;
    struct proc *curproc = myproc();

    if (addr >= curproc->sz)
        return -1;
    *pp = (char *)addr;
    ep = (char *)curproc->sz;
    for (s = *pp; s < ep; s++)
    {
        if (*s == 0)
            return s - *pp;
    }
    return -1;
}

// Fetch the nth 32-bit system call argument.
int argint(int n, int *ip)
{
    return fetchint((myproc()->tf->esp) + 4 + 4 * n, ip);
}

// Fetch the nth word-sized system call argument as a pointer
// to a block of memory of size bytes.  Check that the pointer
// lies within the process address space.
int argptr(int n, char **pp, int size)
{
    int i;
    struct proc *curproc = myproc();

    if (argint(n, &i) < 0)
        return -1;
    if (size < 0 || (uint)i >= curproc->sz || (uint)i + size > curproc->sz)
        return -1;
    *pp = (char *)i;
    return 0;
}

// Fetch the nth word-sized system call argument as a string pointer.
// Check that the pointer is valid and the string is nul-terminated.
// (There is no shared writable memory, so the string can't change
// between this check and being used by the kernel.)
int argstr(int n, char **pp)
{
    int addr;
    if (argint(n, &addr) < 0)
        return -1;
    return fetchstr(addr, pp);
}

extern int sys_chdir(void);
extern int sys_close(void);
extern int sys_dup(void);
extern int sys_exec(void);
extern int sys_exit(void);
extern int sys_fork(void);
extern int sys_fstat(void);
extern int sys_getpid(void);
extern int sys_kill(void);
extern int sys_link(void);
extern int sys_mkdir(void);
extern int sys_mknod(void);
extern int sys_open(void);
extern int sys_pipe(void);
extern int sys_read(void);
extern int sys_sbrk(void);
extern int sys_sleep(void);
extern int sys_unlink(void);
extern int sys_wait(void);
extern int sys_waitx(void);
extern int sys_write(void);
extern int sys_uptime(void);
extern int sys_set_priority(void);
extern int sys_ps(void);

static int (*syscalls[])(void) = {
    [SYS_fork] sys_fork,
    [SYS_exit] sys_exit,
    [SYS_wait] sys_wait,
    [SYS_waitx] sys_waitx,
    [SYS_pipe] sys_pipe,
    [SYS_read] sys_read,
    [SYS_kill] sys_kill,
    [SYS_exec] sys_exec,
    [SYS_fstat] sys_fstat,
    [SYS_chdir] sys_chdir,
    [SYS_dup] sys_dup,
    [SYS_getpid] sys_getpid,
    [SYS_sbrk] sys_sbrk,
    [SYS_sleep] sys_sleep,
    [SYS_uptime] sys_uptime,
    [SYS_open] sys_open,
    [SYS_write] sys_write,
    [SYS_mknod] sys_mknod,
    [SYS_unlink] sys_unlink,
    [SYS_link] sys_link,
    [SYS_mkdir] sys_mkdir,
    [SYS_close] sys_close,
    [SYS_set_priority] sys_set_priority,
    [SYS_ps] sys_ps,
};

void syscall(void)
{
    int num;
    struct proc *curproc = myproc();

    num = curproc->tf->eax;
    if (num > 0 && num < NELEM(syscalls) && syscalls[num])
    {
        curproc->tf->eax = syscalls[num]();
    }
    else
    {
        cprintf("%d %s: unknown sys call %d\n",
                curproc->pid, curproc->name, num);
        curproc->tf->eax = -1;
    }
}
