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

#include "memory/mm.h"
#include "process.h"
#include "scheduler.h"

#include <drivers/vga/vga.h>

#include <lib/print.h>

typedef struct registers {
    uint32_t gs, fs, es, ds;                           // Pushed manually
    uint32_t edi, esi, ebp, esp, ebx, edx, ecx, eax;   // Pushed by pusha
    uint32_t int_no, err_code;                         // Pushed manually
    uint32_t eip, cs, eflags, useresp, ss;             // Pushed automatically by CPU
} registers_t;


static int32_t sys_exit(int status) {
    asm volatile("cli");
    asm volatile("hlt");
    return 0;
}

static int32_t sys_write(int fd, const void* buf, size_t count) {
    if (fd == 1 || fd == 2) { // stdout or stderr
        const char* cbuf = (const char*)buf;
        for (size_t i = 0; i < count; i++) {
            vga_putchar(cbuf[i]); 
        }
        return count;
    }
    return -1;
}

static int32_t sys_read(int fd, void* buf, size_t count) {
    if (fd == 0) { // stdin
        char* cbuf = (char*)buf;
        size_t bytes_read = 0;
        while (bytes_read < count) {
            char c = 'r';
            cbuf[bytes_read++] = c;
            if (c == '\n') break;
        }
        return bytes_read;
    }
    return -1; 
}

static int32_t sys_open(const char* filename, int flags) {
    return -1; 
}

static int32_t sys_close(int fd) {
    return -1;
}

static int32_t sys_brk(uint32_t new_break) {
    process_t* current = current_task();

    if (new_break == 0) {
        return current->heap_end;
    }

    if (new_break < current->heap_end) {
        current->heap_end = new_break;
        return current->heap_end;
    }

    uint32_t page_start = (current->heap_end + 4095) & ~4095;
    uint32_t page_end   = (new_break + 4095) & ~4095;

    for (uint32_t addr = page_start; addr < page_end; addr += 4096) {
        // 1. Allocate a physical frame using your PMM (Physical Memory Manager)
        void* phys = p_alloc_frame();
        
        // 2. Map it into the current page directory using your VMM (Virtual Memory Manager)
        map_page(addr, (uint32_t)phys, PAGE_PRESENT | PAGE_WRITABLE | PAGE_USER);
    }

    current->heap_end = new_break;
    return current->heap_end;
}

int32_t syscall(registers_t* regs) {
    switch(regs->eax) {
        case 1: return sys_exit(regs->ebx);
        case 3: return sys_read(regs->ebx, (void*)regs->ecx, regs->edx);
        case 4: return sys_write(regs->ebx, (const void*)regs->ecx, regs->edx);
        case 5: return sys_open((const char*)regs->ebx, regs->ecx);
        case 6: return sys_close(regs->ebx);
        case 12: return sys_brk(regs->ebx);
        default:
            return -1;
    }
}