#include <mercury/kernel/application.hpp>
#include <mercury/kernel/paging.hpp>

//TODO - scheduling.

namespace mercury::kernel::application {

  app_instance::app_instance() : state(app_state::paused) {

    framebuffer_vaddr = 0;

    uint64_t p3_paddr;
    uint64_t p2_paddr;

    uint64_t p4_vaddr;
    uint64_t p3_vaddr;
    uint64_t p2_vaddr;

    paging::map_new_kernel_page(p4_vaddr, p4_paddr);
    paging::map_new_kernel_page(p3_vaddr, p3_paddr);
    paging::map_new_kernel_page(p2_vaddr, p2_paddr);

    p4 = (uint64_t *)p4_vaddr;
    p3 = (uint64_t *)p3_vaddr;
    p2 = (uint64_t *)p2_vaddr;

    for (int i = 1; i < 511; ++i)
      p4[i] = 0;
    p4[511] = paging::kernel_p4e;
    p4[0] = paging::encode_pte(p3_paddr, true, true, true, false);

    for (int i = 1; i < 512; ++i)
      p3[i] = 0;
    p3[0] = paging::encode_pte(p2_paddr, true, true, true, false);

    for (int i = 0; i < 512; ++i)
      p2[i] = 0;

    p2es_to_free_on_exit = new bool[512];

  }

  app_instance::~app_instance() {

    for (int i = 1; i < 512; ++i)
      if (p2[i] != 0 && p2es_to_free_on_exit[i]) {
        uint64_t paddr = p2[i] & ~0x1fffffULL;
        paging::mark_pram_region_free(paddr, paddr + 0x200000);
      }

    delete[] p2es_to_free_on_exit;

    uint64_t p2_paddr = p3[0] & ~0x1fffffULL;
    paging::unmap_kernel_page((uint64_t)p2);
    paging::mark_pram_region_free(p2_paddr, p2_paddr + 4096);

    uint64_t p3_paddr = p4[0] & ~0x1fffffULL;
    paging::unmap_kernel_page((uint64_t)p3);
    paging::mark_pram_region_free(p3_paddr, p3_paddr + 4096);

    paging::unmap_kernel_page((uint64_t)p4);
    paging::mark_pram_region_free(p4_paddr, p4_paddr + 4096);

  }

  void app_instance::map_page(uint64_t vaddr, uint64_t paddr,
    bool write, bool execute, bool free_pram_on_exit
  ) {
    uint64_t i = vaddr / 0x200000;
    p2[i] = paging::encode_pte(paddr, true, write, execute, true);
    p2es_to_free_on_exit[i] = free_pram_on_exit;
  }

  uint64_t app_instance::get_free_vaddr_pages(uint64_t count) {
    uint64_t start = 1;
    uint64_t length = 0;
    while (start + length < 510) {
      if (length == count)
        return start * 0x200000;
      if (p2[start + length] == 0)
        ++length;
      else {
        start += length + 1;
        length = 0;
      }
    }
    //TODO: handle out of memory
    return 0;
  }

  void app_instance::create_stack() {
    uint64_t stack_paddr = paging::take_2mib_pram_page();
    map_page(0x3fe00000, stack_paddr, true, false, true);
    for (int i = 0; i < 512; ++i) {
      uint64_t vaddr = paging::find_unmapped_vram_region(1);
      paging::map_kernel_page(stack_paddr + 512 * i, vaddr, true, false);
      for (int j = 0; j < 4096 / 8; ++j)
        *(uint64_t *)(vaddr + j * 8) = 0;
      paging::unmap_kernel_page(vaddr);
    }
    saved_regs.rsp = 0x40000000;
  }

  void app_instance::set_instruction_pointer(uint64_t vaddr) {
    saved_regs.rip = vaddr;
  }

  uint64_t app_instance::count_mapped_vram_pages() {
    uint64_t count = 0;
    for (int i = 1; i < 512; ++i)
      if (p2[i] != 0)
        ++count;
    return count;
  }

  app_instance *running_app;

  static uint8_t correct_magic[16] = {
    0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01, 0x00,
    0x02, 0x00, 0x3e, 0x00, 0x01, 0x00, 0x00, 0x00
  };

#define READ(a, b, c) \
  { \
    storage::fs_result _result = file.read_file(a, b, c); \
    if (_result == storage::fs_result::device_error) \
      return create_app_result::device_error; \
    if (_result == storage::fs_result::fs_corrupt) \
      return create_app_result::fs_corrupt; \
  }

  struct load_info {
    uint64_t foffset;
    uint64_t fsize;
    uint64_t vaddr;
    uint64_t vpages;
    bool writable;
    bool executable;
  };

  create_app_result create_app(const vfile::vfile &file, app_instance *&out) {

    uint8_t magic[16];
    if (file.dir_entry.length < 64)
      return create_app_result::app_corrupt;
    READ(0, 8, magic)
    READ(16, 8, magic + 8)
    for (int i = 0; i < 16; ++i)
      if (magic[i] != correct_magic[i])
        return create_app_result::app_corrupt;

    uint64_t entry_point;
    uint64_t phead_start;
    uint16_t phead_entry_size;
    uint16_t phead_entry_count;

    READ(24, 8, &entry_point)
    READ(32, 8, &phead_start)
    READ(54, 2, &phead_entry_size)
    READ(56, 2, &phead_entry_count)

    if (file.dir_entry.length <
        phead_start + phead_entry_size * phead_entry_count)
      return create_app_result::app_corrupt;

    utility::vector<load_info> load_infos;

    for (uint16_t i = 0; i < phead_entry_count; ++i) {

      uint64_t entry_start = phead_start + phead_entry_size * i;

      uint32_t seg_type;
      READ(entry_start, 4, &seg_type)
      if (seg_type != 1)
        continue;

      uint64_t foffset;
      uint64_t vaddr;
      uint64_t fsize;
      uint64_t vsize;
      uint32_t flags;

      READ(entry_start + 8, 8, &foffset)
      READ(entry_start + 16, 8, &vaddr)
      READ(entry_start + 32, 8, &fsize)
      READ(entry_start + 40, 8, &vsize)
      READ(entry_start + 4, 4, &flags)

      if (vaddr & 0x1fffff)
        return create_app_result::app_corrupt;
      if (file.dir_entry.length < foffset + fsize)
        return create_app_result::app_corrupt;
      if (fsize > vsize)
        return create_app_result::app_corrupt;
      if (vaddr == 0)
        return create_app_result::app_corrupt;

      uint64_t vpages = (vsize - 1) / 0x200000 + 1;

      if (vaddr + vpages * 0x200000 > ((1 << 30) - (4 << 20)))
        return create_app_result::app_corrupt;

      load_info info = {
        .foffset = foffset,
        .fsize = fsize,
        .vaddr = vaddr,
        .vpages = vpages,
        .writable = (flags & 2) == 2,
        .executable = (flags & 1) == 1
      };
      load_infos.add_end(info);

    }

    out = new app_instance();

    for (unsigned i = 0; i < load_infos.count; ++i) {
      const auto &info = load_infos.buffer[i];
      for (uint64_t j = 0; j < info.vpages; ++j) {
        uint64_t paddr = paging::take_2mib_pram_page();
        out->map_page(info.vaddr + j * 0x200000, paddr,
          info.writable, info.executable, true);
        for (int k = 0; k < 512; ++k) {
          uint64_t offset_in_segment = j * 0x200000 + k * 4096;
          uint64_t kvaddr = paging::find_unmapped_vram_region(1);
          paging::map_kernel_page(paddr + k * 4096, kvaddr, true, false);
          storage::fs_result result = storage::fs_result::success;
          if (info.fsize > offset_in_segment) {
            if (info.fsize >= offset_in_segment + 4096)
              result = file.read_file(
                info.foffset + offset_in_segment, 4096, (void *)kvaddr);
            else {
              int to_read = info.fsize - offset_in_segment;
              result = file.read_file(
                info.foffset + offset_in_segment, to_read, (void *)kvaddr);
              uint8_t *blank = (uint8_t *)(kvaddr + to_read);
              for (int i = 0; i < 4096 - to_read; ++i)
                blank[i] = 0;
            }
          }
          else {
            uint8_t *blank = (uint8_t *)kvaddr;
            for (int i = 0; i < 4096; ++i)
              blank[i] = 0;
          }
          paging::unmap_kernel_page(kvaddr);
          if (result == storage::fs_result::device_error) {
            delete out;
            return create_app_result::device_error;
          }
          if (result == storage::fs_result::fs_corrupt) {
            delete out;
            return create_app_result::fs_corrupt;
          }
        }
      }
    }

    out->create_stack();
    out->set_instruction_pointer(entry_point);

    return create_app_result::success;

  }

}