#include "arch/context_switching/main.hpp"

#include "arch/boot/pointers.hpp"
#include "arch/context_switching/syscall_handler.hpp"
#include "arch/exception_handling/assert.hpp"
#include "arch/kernel/cpu/call.hpp"
#include "arch/kernel/cpu/control_register.hpp"
#include "arch/kernel/cpu/if.hpp"
#include "arch/kernel/cpu/segment_register.hpp"
#include "arch/kernel/cpu/tr.hpp"
#include "arch/video/vga/text.hpp"

namespace teachos::arch::context_switching
{
  namespace
  {
    constexpr interrupt_descriptor_table::segment_selector KERNEL_CODE_SEGMENT_SELECTOR{
        1U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
    constexpr kernel::cpu::far_pointer KERNEL_CODE_POINTER{&kernel::cpu::reload_data_segment_registers,
                                                           KERNEL_CODE_SEGMENT_SELECTOR};
    constexpr context_switching::interrupt_descriptor_table::segment_selector USER_CODE_SEGMENT_SELECTOR{
        3U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
    constexpr context_switching::interrupt_descriptor_table::segment_selector USER_DATA_SEGMENT_SELECTOR{
        4U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};

    auto reload_global_descriptor_table_register() -> void { kernel::cpu::call(KERNEL_CODE_POINTER); }

  }  // namespace

  auto initialize_descriptor_tables() -> descriptor_tables
  {
    static bool initalized = false;

    if (!initalized)
    {
      kernel::cpu::clear_interrupt_flag();

      segment_descriptor_table::update_global_descriptor_table_register();
      interrupt_descriptor_table::update_interrupt_descriptor_table_register();

      reload_global_descriptor_table_register();
      segment_descriptor_table::update_task_state_segment_register();

      kernel::cpu::set_interrupt_flag();
      initalized = true;
    }

    descriptor_tables tables = {segment_descriptor_table::get_or_create_global_descriptor_table(),
                                interrupt_descriptor_table::get_or_create_interrupt_descriptor_table()};
    return tables;
  }

  auto user_mode_main() -> void
  {
    kernel::cpu::validate_segment_registers(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR);

    asm volatile("SYSCALL");

    video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black);
  }

  auto switch_to_user_mode() -> void
  {
    switch_context(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR, user_mode_main);
  }

  auto switch_context(interrupt_descriptor_table::segment_selector data_segment,
                      interrupt_descriptor_table::segment_selector code_segment, void (*return_function)()) -> void
  {
    (void)initialize_descriptor_tables();
    kernel::cpu::set_data_segment_registers(data_segment);
    kernel::cpu::set_code_segment_register(data_segment, code_segment, reinterpret_cast<uint64_t>(return_function));
  }

  auto setup_syscall() -> void
  {
    uint64_t handler = reinterpret_cast<uint64_t>(syscall_handler);
    asm volatile(
        /* Write syscall_handler pointer in IA32_LSTAR MSR */
        "mov $0xC0000082, %%ecx\n" /* IA32_LSTAR MSR */
        "mov %[syscall_handler], %%rax"
        "mov %[syscall_handler], %%rdx"
        "shr $32, %%rdx\n"
        "wrmsr\n"

        /* Write RFLAGS Mask in IA32_LSTAR MSR */
        "mov $0xC0000084, %%ecx\n" /* IA32_FMASK MSR */
        "mov $0x0, %%rax\n"        /* RFLAGS Mask lower 32 bits */
        "mov $0x0, %%rdx\n"        /* RFLAGS Mask upper 32 bits */
        "wrmsr\n"

        /* Write kernel code segment offset in IA32_STAR MSR */
        "mov $0xC0000081, %%ecx\n" /* IA32_STAR MSR */
        "mov $0x10, %%rax\n"       /* kernel code segment offset lower 32 bits */
        "mov $0x0, %%rdx\n"        /* kernel code segment offset upper 32 bits */
        "wrmsr\n"

        /* Set SCE bit in MSR_EFER (enabling syscall instruction)*/
        "mov $0xC0000080, %%ecx\n"
        "rdmsr\n"
        "or $0x1, %%eax\n"
        "wrmsr"
        : /* no output from call */
        : [syscall_handler] "r"(handler));
  }

}  // namespace teachos::arch::context_switching