#include <stdint.h>
#include <stddef.h>

typedef int _PDCLIB_fd_t;

static inline int32_t inline_syscall(uint32_t num, uint32_t arg1, uint32_t arg2, uint32_t arg3) {
    int32_t ret;
    asm volatile (
        "int $0x80"
        : "=a" (ret)
        : "a" (num), "b" (arg1), "c" (arg2), "d" (arg3)
        : "memory"
    );
    return ret;
}

void _exit(int status) {
    inline_syscall(1, (uint32_t)status, 0, 0);
    while(1) { asm volatile("hlt"); }
}

void _PDCLIB_exit(int status) {
    _exit(status);
}

int _PDCLIB_read(_PDCLIB_fd_t fd, void *buf, size_t count) {
    int32_t ret = inline_syscall(3, (uint32_t)fd, (uint32_t)buf, (uint32_t)count);
    if (ret < 0) {
        return 0;
    }
    return ret;
}

int _PDCLIB_write(_PDCLIB_fd_t fd, const void *buf, size_t count) {
    int32_t ret = inline_syscall(4, (uint32_t)fd, (uint32_t)buf, (uint32_t)count);
    if (ret < 0) {
        return 0; 
    }
    return ret;
}

_PDCLIB_fd_t _PDCLIB_open(const char *filename, unsigned int mode) {
    _PDCLIB_fd_t fd;
    fd = inline_syscall(5, (uint32_t)filename, (uint32_t)mode, 0);
    return fd;
}

int _PDCLIB_close(_PDCLIB_fd_t fd) {
    return inline_syscall(6, (uint32_t)fd, 0, 0);
}

void * _PDCLIB_allocpages( size_t n ) {
    // 1. Get the current page break
    uint32_t current_break = inline_syscall(12, 0, 0, 0);
    if (current_break == (uint32_t)-1) {
        return NULL;
    }

    // 2. PDCLib requests memory in multiples of PAGES (typically 4096 bytes)
    uint32_t new_break = current_break + (n * 4096);

    // 3. Request kernel to move the break
    uint32_t result = inline_syscall(12, new_break, 0, 0);
    if (result != new_break) {
        return NULL; // Allocation failed
    }

    // Return the start of the newly allocated region
    return (void *)current_break;
}

int _PDCLIB_remove(const char *filename) { return -1; }
int _PDCLIB_rename(const char *old, const char *new) { return -1; }
long _PDCLIB_lseek(_PDCLIB_fd_t fd, long offset, int whence) { return -1; }

int open(const char *pathname, int flags, ...) {
    _PDCLIB_fd_t fd = _PDCLIB_open(pathname, (unsigned int)flags);
    return fd;
}

int read(int fd, void *buf, size_t count) {
    _PDCLIB_fd_t file_desc =  fd;
    return _PDCLIB_read(file_desc, buf, count);
}

int write(int fd, const void *buf, size_t count) {
    return _PDCLIB_write(fd, buf, count);
}

int close(int fd) {
    _PDCLIB_fd_t file_desc = fd;
    return _PDCLIB_close(file_desc);
}

void * sbrk(intptr_t increment) {
    uint32_t current_break = inline_syscall(12, 0, 0, 0);
    if (current_break == (uint32_t)-1) {
        return (void *)-1;
    }

    if (increment == 0) {
         return (void *)current_break; 
    }

    uint32_t new_break = (uint32_t)((intptr_t)current_break + increment);
    
    uint32_t result = inline_syscall(12, new_break, 0, 0);
    
    if (result == new_break) {
        return (void *)current_break; 
    }

    return (void *)-1;
}