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#include "win32/base/surrogate_pair_observer.h"

#include "absl/base/optimization.h"
#include "win32/base/keyboard.h"

namespace mozc {
namespace win32 {
namespace {

// TODO(yukawa): Move this to util.cc.
char32_t SurrogatePairToCodepoint(wchar_t high, wchar_t low) {
  return (((high - 0xD800) & 0x3FF) << 10) + ((low - 0xDC00) & 0x3FF) + 0x10000;
}

}  // namespace

SurrogatePairObserver::SurrogatePairObserver()
    : state_(INITIAL_STATE), surrogate_high_(L'\0'), surrogate_low_(L'\0') {}

SurrogatePairObserver::ClientAction SurrogatePairObserver::OnTestKeyEvent(
    const VirtualKey &virtual_key, bool is_keydown) {
  return OnKeyEvent(virtual_key, is_keydown, true);
}

SurrogatePairObserver::ClientAction SurrogatePairObserver::OnKeyEvent(
    const VirtualKey &virtual_key, bool is_keydown) {
  return OnKeyEvent(virtual_key, is_keydown, false);
}

SurrogatePairObserver::ClientAction SurrogatePairObserver::OnKeyEvent(
    const VirtualKey &virtual_key, bool is_keydown, bool is_test_key) {
  switch (state_) {
    case INITIAL_STATE: {
      if ((virtual_key.virtual_key() != VK_PACKET)) {
        return ClientAction(DO_DEFAULT_ACTION, 0);
      }
      const wchar_t ucs2 = virtual_key.wide_char();
      if (IS_HIGH_SURROGATE(ucs2)) {
        if (is_keydown) {
          if (!is_test_key) {
            surrogate_high_ = ucs2;
            state_ = WAIT_FOR_SURROGATE_HIGH_UP;
          }
          return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
        }
        // Ignore orhpaned key-up of high surrogate.
        return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
      }
      if (IS_LOW_SURROGATE(ucs2)) {
        // Ignore orhpaned key-up/down of low surrogate.
        return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
      }
      return ClientAction(DO_DEFAULT_ACTION_WITH_RETURNED_UCS4, ucs2);
    }
    case WAIT_FOR_SURROGATE_HIGH_UP: {
      if ((virtual_key.virtual_key() != VK_PACKET)) {
        return ClientAction(DO_DEFAULT_ACTION, 0);
      }
      const wchar_t ucs2 = virtual_key.wide_char();
      if (IS_HIGH_SURROGATE(ucs2)) {
        if (is_keydown) {
          if (!is_test_key) {
            surrogate_high_ = ucs2;
            state_ = WAIT_FOR_SURROGATE_HIGH_UP;
          }
          return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
        }
        if (ucs2 != surrogate_high_) {
          // Ignore orhpaned key-up of high surrogate.
          return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
        }
        if (!is_test_key) {
          state_ = WAIT_FOR_SURROGATE_LOW_DOWM;
        }
        return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
      }
      if (IS_LOW_SURROGATE(ucs2)) {
        if (is_keydown) {
          const char32_t codepoint =
              SurrogatePairToCodepoint(surrogate_high_, ucs2);
          if (!is_test_key) {
            surrogate_low_ = ucs2;
            state_ = WAIT_FOR_SURROGATE_LOW_UP;
          }
          return ClientAction(DO_DEFAULT_ACTION_WITH_RETURNED_UCS4, codepoint);
        }
        // Ignore orhpaned key-up of low surrogate.
        return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
      }
      return ClientAction(DO_DEFAULT_ACTION_WITH_RETURNED_UCS4, ucs2);
    }
    case WAIT_FOR_SURROGATE_LOW_DOWM: {
      if ((virtual_key.virtual_key() != VK_PACKET)) {
        return ClientAction(DO_DEFAULT_ACTION, 0);
      }
      const wchar_t ucs2 = virtual_key.wide_char();
      if (IS_HIGH_SURROGATE(ucs2)) {
        if (is_keydown) {
          if (!is_test_key) {
            surrogate_high_ = ucs2;
            state_ = WAIT_FOR_SURROGATE_HIGH_UP;
          }
          return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
        }
        // Ignore orhpaned key-up of high surrogate.
        return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
      }
      if (IS_LOW_SURROGATE(ucs2)) {
        if (is_keydown) {
          const char32_t codepoint =
              SurrogatePairToCodepoint(surrogate_high_, ucs2);
          if (!is_test_key) {
            surrogate_low_ = ucs2;
            state_ = WAIT_FOR_SURROGATE_LOW_UP;
          }
          return ClientAction(DO_DEFAULT_ACTION_WITH_RETURNED_UCS4, codepoint);
        }
        // Ignore orhpaned key-up of low surrogate.
        return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
      }
      if (!is_test_key) {
        state_ = INITIAL_STATE;
        surrogate_high_ = L'\0';
        surrogate_low_ = L'\0';
      }
      return ClientAction(DO_DEFAULT_ACTION_WITH_RETURNED_UCS4, ucs2);
    }
    case WAIT_FOR_SURROGATE_LOW_UP: {
      if ((virtual_key.virtual_key() != VK_PACKET)) {
        return ClientAction(DO_DEFAULT_ACTION, 0);
      }
      const wchar_t ucs2 = virtual_key.wide_char();
      if (IS_HIGH_SURROGATE(ucs2)) {
        if (is_keydown) {
          if (!is_test_key) {
            surrogate_high_ = ucs2;
            state_ = WAIT_FOR_SURROGATE_HIGH_UP;
          }
          return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
        }
        // Ignore orhpaned key-up of high surrogate.
        return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
      }
      if (IS_LOW_SURROGATE(ucs2)) {
        if (is_keydown) {
          // Ignore orhpaned key-down of low surrogate.
          return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
        }
        if (surrogate_low_ != ucs2) {
          // Ignore orhpaned key-up of low surrogate.
          return ClientAction(CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER, 0);
        }
        const char32_t codepoint =
            SurrogatePairToCodepoint(surrogate_high_, surrogate_low_);
        if (!is_test_key) {
          state_ = INITIAL_STATE;
          surrogate_high_ = L'\0';
          surrogate_low_ = L'\0';
        }
        return ClientAction(DO_DEFAULT_ACTION_WITH_RETURNED_UCS4, codepoint);
      }
      if (!is_test_key) {
        state_ = INITIAL_STATE;
        surrogate_high_ = L'\0';
        surrogate_low_ = L'\0';
      }
      return ClientAction(DO_DEFAULT_ACTION_WITH_RETURNED_UCS4, ucs2);
    }
    default:
      ABSL_UNREACHABLE();
  }
}

}  // namespace win32
}  // namespace mozc
