#include <aux/compiler.h>
#include <aux/elf.h>
#include <irq/irq.h>
#include <libk/align.h>
#include <libk/list.h>
#include <libk/std.h>
#include <libk/string.h>
#include <limine/requests.h>
#include <mm/liballoc.h>
#include <mm/pmm.h>
#include <proc/proc.h>
#include <rd/rd.h>
#include <sync/spin_lock.h>
#include <sys/debug.h>
#include <sys/mm.h>
#include <sys/sched.h>
#include <sys/smp.h>

#if defined(__x86_64__)
#include <amd64/intr_defs.h>
#endif

struct elf_aux {
  uint64_t entry;
  uint64_t phdr;
  uint64_t phent;
  uint64_t phnum;
};

static struct procw* procs;
static spin_lock_t procs_lock = SPIN_LOCK_INIT;

static bool proc_check_elf (uint8_t* elf) {
  if (!((elf[0] == 0x7F) && (elf[1] == 'E') && (elf[2] == 'L') && (elf[3] == 'F')))
    return false;
  return true;
}

void proc_map (struct proc* proc, uintptr_t start_paddr, uintptr_t start_vaddr, size_t pages,
               uint32_t flags) {
  struct proc_mapping* mapping = malloc (sizeof (*mapping));
  mapping->paddr = start_paddr;
  mapping->vaddr = start_vaddr;
  mapping->size = pages * PAGE_SIZE;

  flags &= ~MM_PD_LOCK; /* clear LOCK flag if present, because we lock manualy */

  spin_lock (&proc->pd.lock);

  linklist_append (struct proc_mapping*, proc->mappings, mapping);

  for (uintptr_t vpage = start_vaddr, ppage = start_paddr; vpage < start_vaddr + pages * PAGE_SIZE;
       vpage += PAGE_SIZE, ppage += PAGE_SIZE) {
    mm_map_page (&proc->pd, ppage, vpage, flags);
  }

  spin_unlock (&proc->pd.lock);
}

static struct elf_aux proc_load_segments (struct proc* proc, uint8_t* elf) {
  struct elf_aux aux;

  Elf64_Ehdr* ehdr = (Elf64_Ehdr*)elf;
  aux.entry = ehdr->e_entry;
  aux.phnum = ehdr->e_phnum;
  aux.phent = ehdr->e_phentsize;

  struct limine_hhdm_response* hhdm = limine_hhdm_request.response;

  for (uint64_t segment = 0; segment < ehdr->e_phnum; segment++) {
    Elf64_Phdr* phdr =
        (Elf64_Phdr*)((uintptr_t)elf + ehdr->e_phoff + (ehdr->e_phentsize * segment));

    switch (phdr->p_type) {
    case PT_PHDR: {
      aux.phdr = (uint64_t)phdr->p_vaddr;
    } break;
    case PT_LOAD: {
      uintptr_t v_addr = align_down (phdr->p_vaddr, PAGE_SIZE);
      uintptr_t off = phdr->p_vaddr - v_addr;

      size_t blks = div_align_up (phdr->p_memsz + off, PAGE_SIZE);

      uintptr_t p_addr = pmm_alloc (blks);
      if (p_addr == PMM_ALLOC_ERR)
        DEBUG ("pmm oom error while loading ELF segments! (tried to alloc %zu blks)\n", blks);

      memset ((void*)((uintptr_t)hhdm->offset + p_addr), 0, blks * PAGE_SIZE);
      memcpy ((void*)((uintptr_t)hhdm->offset + p_addr + off),
              (void*)((uintptr_t)elf + phdr->p_offset), phdr->p_filesz);

      uint32_t pg_flags = MM_PG_USER | MM_PG_PRESENT;
      if (phdr->p_flags & PF_W)
        pg_flags |= MM_PG_RW;

      proc_map (proc, p_addr, v_addr, blks, pg_flags);
    } break;
    }
  }

  return aux;
}

static struct proc* proc_spawn_rd (char* name) {
  struct rd_file* rd_file = rd_get_file (name);

  bool ok = proc_check_elf (rd_file->content);
  DEBUG ("ELF magic %s\n", (ok ? "OK" : "BAD"));

  if (!ok)
    return NULL;

  struct proc* proc = malloc (sizeof (*proc));
  if (proc == NULL)
    return NULL;

  memset (proc, 0, sizeof (*proc));

#if defined(__x86_64__)
  proc->pd.lock = SPIN_LOCK_INIT;
  proc->pd.cr3_paddr = mm_alloc_user_pd_phys ();
  if (proc->pd.cr3_paddr == 0) {
    free (proc);
    return NULL;
  }

  proc->pdata.syscall_stack = pmm_alloc (KSTACK_SIZE / PAGE_SIZE);
  if (proc->pdata.syscall_stack == PMM_ALLOC_ERR) {
    free (proc);
    return NULL;
  }

  proc->pdata.user_stack = pmm_alloc (USTACK_SIZE / PAGE_SIZE);
  if (proc->pdata.user_stack == PMM_ALLOC_ERR) {
    free (proc);
    pmm_free (proc->pdata.syscall_stack, USTACK_SIZE / PAGE_SIZE);
    return NULL;
  }

  uintptr_t user_stack = proc->pdata.user_stack;

  proc->pdata.syscall_stack += KSTACK_SIZE;
  proc->pdata.user_stack += USTACK_SIZE;

  proc_map (proc, user_stack, PROC_USTACK_TOP - USTACK_SIZE, USTACK_SIZE / PAGE_SIZE,
            MM_PG_USER | MM_PG_PRESENT | MM_PG_RW);

  struct elf_aux aux = proc_load_segments (proc, rd_file->content);

  proc->pdata.regs.ss = 0x20 | 0x03;
  proc->pdata.regs.rsp = (uint64_t)PROC_USTACK_TOP;
  proc->pdata.regs.rflags = 0x202;
  proc->pdata.regs.cs = 0x18 | 0x03;
  proc->pdata.regs.rip = aux.entry;
  proc->lock = SPIN_LOCK_INIT;
#endif

  return proc;
}

static void proc_register (struct proc* proc) {
  /* make available globally. */
  struct procw* procw = malloc (sizeof (*procw));
  if (procw == NULL)
    return;
  procw->proc = proc;
  proc->procw = procw;

  spin_lock (&procs_lock);

  spin_lock (&thiscpu->lock);

  linklist_append (struct procw*, procs, procw);
  linklist_append (struct proc*, thiscpu->proc_run_q, proc);

  if (thiscpu->proc_current == NULL)
    thiscpu->proc_current = proc;

  spin_unlock (&thiscpu->lock);

  spin_unlock (&procs_lock);
}

void proc_sched (void) {
  spin_lock (&thiscpu->lock);

  if (thiscpu->proc_run_q == NULL || thiscpu->proc_current == NULL) {
    goto done;
  }

  thiscpu->proc_current = thiscpu->proc_current->next;

  if (thiscpu->proc_current == NULL) {
    thiscpu->proc_current = thiscpu->proc_run_q;
  }

done:
  spin_unlock (&thiscpu->lock);

  if (thiscpu->proc_current != NULL) {
    do_sched (&thiscpu->proc_current->pdata.regs, &thiscpu->proc_current->pd);
  }

#if defined(__x86_64__)
  extern void amd64_spin (void);

  amd64_spin ();
#endif
}

void proc_kill (struct proc* proc) {
  spin_lock (&procs_lock);

  spin_lock (&thiscpu->lock);

  linklist_remove (struct procw*, procs, proc->procw);
  linklist_remove (struct proc*, thiscpu->proc_run_q, proc);

  if (thiscpu->proc_current == proc)
    thiscpu->proc_current = NULL;

  spin_unlock (&thiscpu->lock);

  spin_unlock (&procs_lock);

  /* clean up */
  free (proc->procw);
  free (proc);
}

static void proc_irq_sched (void* arg, void* regs) {
  (void)arg, (void)regs;
  proc_sched ();
}

void proc_init (void) {
  struct proc* init = proc_spawn_rd ("init.exe");
  proc_register (init);

#if defined(__x86_64__)
  irq_attach (&proc_irq_sched, NULL, SCHED_PREEMPT_TIMER, 0);
#endif

  do_sched (&init->pdata.regs, &init->pd);
}