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

constexpr uint8_t vga_entry_color(VGA::vga_color fg, VGA::vga_color bg) {
  return fg | bg << 4;
}

constexpr uint16_t vga_entry(unsigned char uc, uint8_t color) {
  return (uint16_t)uc | (uint16_t)color << 8;
}

VGA::VGA(vga_color fg, vga_color bg, uint32_t address) {
  color = vga_entry_color(fg, bg);
  buffer = (uint16_t*)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] = vga_entry(' ', color);
    }
  }
}

void VGA::write(char c) {
  switch (c) {
    case '\n':
      column = 0;
      ++row;
      break;
    default: {
      const size_t index = row * max_columns + column;
      buffer[index] = vga_entry(c, (color == 0) ? this->color : color);
      ++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());
  }
}