/*
 * @author  xamidev <xamidev@riseup.net>
 * @brief   Process linked list implementation
 * @license GPL-3.0-only
 */

#include <stddef.h>
#include "process.h"
#include "mem/heap/kheap.h"
#include "kernel.h"
#include "string/string.h"
#include "mem/gdt/gdt.h"
#include "config.h"
#include "io/serial/serial.h"

#include "io/term/flanterm.h"
extern struct flanterm_context* ft_ctx;

struct process_t* processes_list;
struct process_t* current_process;

extern uint64_t *kernel_pml4;

size_t next_free_pid = 0;

void process_init()
{
    processes_list = NULL;
    current_process = NULL;
}

// Only for debug
void process_display_list(struct process_t* processes_list)
{
    int process_view_id = 0;
    struct process_t* tmp = processes_list;
    while (tmp != NULL)
    {
        DEBUG("{%d: %p} -> ", process_view_id, tmp);
        tmp = tmp->next;
        process_view_id++;
    }
    DEBUG("NULL");
}

struct process_t* process_create(char* name, void(*function)(void*), void* arg)
{
/*     CLEAR_INTERRUPTS; */
    struct process_t* proc = (struct process_t*)kmalloc(sizeof(struct process_t));
    
    struct cpu_status_t* ctx = (struct cpu_status_t*)kmalloc(sizeof(struct cpu_status_t));

    // No more memory?
    if (!proc) return NULL;
    if (!ctx) return NULL;

    strncpy(proc->name, name, PROCESS_NAME_MAX);
    proc->pid = next_free_pid++;
    proc->status = READY;

    uint64_t* stack_top = (uint64_t*)kalloc_stack();
    // push return address to the stack so when "ret" hits we jmp to exit instead of idk what
    // stack grows DOWNWARDS!!
    *(--stack_top) = (uint64_t)process_exit;

    proc->context = ctx;
    proc->context->iret_ss = KERNEL_DATA_SEGMENT; // process will live in kernel mode
    proc->context->iret_rsp = (uint64_t)stack_top;
    proc->context->iret_flags = 0x202; //bit 2 and 9 set (Interrupt Flag)
    proc->context->iret_cs = KERNEL_CODE_SEGMENT;
    proc->context->iret_rip = (uint64_t)function; // beginning of executable code
    proc->context->rdi = (uint64_t)arg; // 1st arg is in rdi (as per x64 calling convention)
    proc->context->rbp = 0; 

    // Kernel PML4 as it already maps code/stack (when switching to userland we'll have to change that)
    proc->root_page_table = kernel_pml4;

    proc->next = 0;

    process_add(&processes_list, proc);

/*     SET_INTERRUPTS; */
    return proc;
}

void process_add(struct process_t** processes_list, struct process_t* process)
{
    if (!process) return;
    process->next = NULL;

    if (*processes_list == NULL)
    {
        // List is empty
        *processes_list = process;
        return;
    }

    struct process_t* tmp = *processes_list;
    while (tmp->next != NULL)
    {
        tmp = tmp->next;
    }
    // We're at last process before NULL
    tmp->next = process;
    // process->next = NULL;
}

void process_delete(struct process_t** processes_list, struct process_t* process)
{
    if (!processes_list || !*processes_list || !process) return;

    if (*processes_list == process)
    {
        // process to delete is at head
        *processes_list = process->next;
        process->next = NULL;
        kfree(process);
        return;
    }

    struct process_t* tmp = *processes_list;
    while (tmp->next && tmp->next != process)
    {
        tmp = tmp->next;
    }

    if (tmp->next == NULL)
    {
        // Didn't find the process
        return;
    }

    // We're at process before the one we want to delete
    tmp->next = process->next;
    process->next = NULL;
    kfree(process);
}

struct process_t* process_get_next(struct process_t* process)
{
    if (!process) return NULL;
    return process->next;
}

// Will be used to clean up resources (if any, when we implement it)
// Just mark as DEAD then idle. Scheduler will delete process at next timer interrupt % quantum.
void process_exit()
{
    DEBUG("Exiting from process '%s'", current_process->name);
    CLEAR_INTERRUPTS;
    if (current_process)
    {
        current_process->status = DEAD;
    }
    SET_INTERRUPTS;
    
    //outb(0x20, 0x20);
    for (;;)
    {
        asm("hlt");
    }
}