#include "vga.h"
#include <string.h>

static_assert(sizeof(VGA::Entry) == 2);

VGA::VGA(vga_color fg, vga_color bg, uint32_t address) : color_fg(fg), color_bg(bg) {
  buffer = reinterpret_cast<Entry*>(address);

  // clear buffer
  for (size_t y = 0; y < max_rows; y++) {
    for (size_t x = 0; x < max_columns; x++) {
      const size_t index = y * max_columns + x;
      buffer[index].c = ' ';
      buffer[index].fg = color_fg;
      buffer[index].bg = color_bg;
    }
  }

  enable_cursor(14, 15);
  update_cursor();
}

void VGA::set_color(vga_color fg, vga_color bg) {
  color_fg = fg;
  color_bg = bg;
  for (size_t y = 0; y < max_rows; y++) {
    for (size_t x = 0; x < max_columns; x++) {
      const size_t index = y * max_columns + x;
      buffer[index].fg = color_fg;
      buffer[index].bg = color_bg;
    }
  }
}

void VGA::enable_cursor(uint8_t start, uint8_t end) {
  p_3d4.write(0x0a);
  p_3d5.write((p_3d5.read() & 0xc0) | start);

  p_3d4.write(0x0b);
  p_3d5.write((p_3d5.read() & 0xe0) | end);
}
void VGA::disable_cursor() {
  p_3d4.write(0x0a);
  p_3d5.write(0x20);
}
void VGA::update_cursor() {
  const uint16_t pos = row * max_columns + column;

  p_3d4.write(0x0f);
  p_3d5.write(static_cast<uint8_t>(pos & 0xff));

  p_3d4.write(0x0e);
  p_3d5.write(static_cast<uint8_t>((pos >> 8) & 0xff));
}

void VGA::write(char c) {
  switch (c) {
    case '\n':
      column = 0;
      ++row;
      break;
    default: {
      const size_t index = row * max_columns + column;
      buffer[index].c = c;
      ++column;
    }
  }

  if (column == max_columns) {
    column = 0;
    ++row;
  }

  if (row == max_rows) {
    // scroll up - move rows 1~25 up by one
    for (size_t y = 1; y < max_rows; y++) {
      const auto prev_y = y - 1;
      for (size_t x = 0; x < max_columns; ++x) {
        const auto prev = prev_y * max_columns + x;
        const auto idx = y * max_columns + x;
        buffer[prev] = buffer[idx];
      }
    }
    --row;
  }
}

void VGA::write(ViewIterator& iter) {
  while (iter) {
    write(iter.next());
  }
}