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#include "unix/fcitx/surrounding_text_util.h"

#include <limits>
#include <string>
#include <fcitx/instance.h>
#include <fcitx/module/clipboard/fcitx-clipboard.h>

#ifdef InvokeFunction
#undef InvokeFunction
#endif

#include "absl/log/check.h"
#include "base/port.h"
#include "base/vlog.h"
#include "base/util.h"

namespace mozc {
namespace fcitx {

bool SurroundingTextUtil::GetSafeDelta(unsigned int from, unsigned int to, int32_t *delta) {
  DCHECK(delta);

  static_assert(sizeof(int64_t) >= sizeof(unsigned int),
                "int64 must be sufficient to store a unsigned int value.");
  static_assert(sizeof(int64_t) == sizeof(llabs(0)),
                "|llabs(0)| must returns a 64-bit integer.");
  const int64_t kInt32AbsMax =
      llabs(static_cast<int64_t>(std::numeric_limits<int32_t>::max()));
  const int64_t kInt32AbsMin =
      llabs(static_cast<int64_t>(std::numeric_limits<int32_t>::min()));
  const int64_t kInt32SafeAbsMax =
      std::min(kInt32AbsMax, kInt32AbsMin);

  const int64_t diff = static_cast<int64_t>(from) - static_cast<int64_t>(to);
  if (llabs(diff) > kInt32SafeAbsMax) {
    return false;
  }

  *delta = static_cast<int32_t>(diff);
  return true;
}

namespace {

// Moves |iter| with |skip_count| characters.
// Returns false if |iter| reaches to the end before skipping
// |skip_count| characters.
bool Skip(ConstChar32Iterator *iter, size_t skip_count) {
  for (size_t i = 0; i < skip_count; ++i) {
    if (iter->Done()) {
      return false;
    }
    iter->Next();
  }
  return true;
}

// Returns true if |prefix_iter| is the prefix of |iter|.
// Returns false if |prefix_iter| is an empty sequence.
// Otherwise returns false.
// This function receives ConstChar32Iterator as pointer because
// ConstChar32Iterator is defined as non-copyable.
bool StartsWith(ConstChar32Iterator *iter,
                ConstChar32Iterator *prefix_iter) {
  if (iter->Done() || prefix_iter->Done()) {
    return false;
  }

  while (true) {
    if (iter->Get() != prefix_iter->Get()) {
      return false;
    }
    prefix_iter->Next();
    if (prefix_iter->Done()) {
      return true;
    }
    iter->Next();
    if (iter->Done()) {
      return false;
    }
  }
}


// Returns true if |surrounding_text| contains |selected_text|
// from |cursor_pos| to |*anchor_pos|.
// Otherwise returns false.
bool SearchAnchorPosForward(
    const std::string &surrounding_text,
    const std::string &selected_text,
    size_t selected_chars_len,
    unsigned int cursor_pos,
    unsigned int *anchor_pos) {

  ConstChar32Iterator iter(surrounding_text);
  // Move |iter| to cursor pos.
  if (!Skip(&iter, cursor_pos)) {
    return false;
  }

  ConstChar32Iterator sel_iter(selected_text);
  if (!StartsWith(&iter, &sel_iter)) {
    return false;
  }
  *anchor_pos = cursor_pos + selected_chars_len;
  return true;
}

// Returns true if |surrounding_text| contains |selected_text|
// from |*anchor_pos| to |cursor_pos|.
// Otherwise returns false.
bool SearchAnchorPosBackward(
    const std::string &surrounding_text,
    const std::string &selected_text,
    size_t selected_chars_len,
    unsigned int cursor_pos,
    unsigned int *anchor_pos) {
  if (cursor_pos < selected_chars_len) {
    return false;
  }

  ConstChar32Iterator iter(surrounding_text);
  // Skip |iter| to (potential) anchor pos.
  const unsigned int skip_count = cursor_pos - selected_chars_len;
  DCHECK_LE(skip_count, cursor_pos);
  if (!Skip(&iter, skip_count)) {
    return false;
  }

  ConstChar32Iterator sel_iter(selected_text);
  if (!StartsWith(&iter, &sel_iter)) {
    return false;
  }
  *anchor_pos = cursor_pos - selected_chars_len;
  return true;
}

}  // namespace

bool SurroundingTextUtil::GetAnchorPosFromSelection(
    const std::string &surrounding_text,
    const std::string &selected_text,
    unsigned int cursor_pos,
    unsigned int *anchor_pos) {
  DCHECK(anchor_pos);

  if (surrounding_text.empty()) {
    return false;
  }

  if (selected_text.empty()) {
    return false;
  }

  const size_t selected_chars_len = Util::CharsLen(selected_text);

  if (SearchAnchorPosForward(surrounding_text, selected_text,
                             selected_chars_len,
                             cursor_pos, anchor_pos)) {
    return true;
  }

  return SearchAnchorPosBackward(surrounding_text, selected_text,
                                 selected_chars_len,
                                 cursor_pos, anchor_pos);
}

bool GetSurroundingText(FcitxInstance* instance,
                        SurroundingTextInfo *info) {
    FcitxInputContext* ic = FcitxInstanceGetCurrentIC(instance);
    if (!ic || !(ic->contextCaps & CAPACITY_SURROUNDING_TEXT)) {
        return false;
    }

    unsigned int cursor_pos = 0;
    unsigned int anchor_pos = 0;
    char* str = NULL;

    if (!FcitxInstanceGetSurroundingText(instance, ic, &str, &cursor_pos, &anchor_pos)) {
        return false;
    }

    const std::string surrounding_text(str);
    free(str);

    if (cursor_pos == anchor_pos) {
        const char* primary = NULL;

        if ((primary = FcitxClipboardGetPrimarySelection(instance, NULL)) != NULL) {
            unsigned int new_anchor_pos = 0;
            const std::string primary_text(primary);
            if (SurroundingTextUtil::GetAnchorPosFromSelection(
                surrounding_text, primary_text,
                cursor_pos, &new_anchor_pos)) {
                anchor_pos = new_anchor_pos;
            }
        }
    }

    if (!SurroundingTextUtil::GetSafeDelta(cursor_pos, anchor_pos,
                                           &info->relative_selected_length)) {
        LOG(ERROR) << "Too long text selection.";
        return false;
    }

    const size_t selection_start = std::min(cursor_pos, anchor_pos);
    const size_t selection_length = std::abs(info->relative_selected_length);
    info->preceding_text = std::string(Util::Utf8SubString(surrounding_text, 0, selection_start));
    info->selection_text = std::string(Util::Utf8SubString(surrounding_text, selection_start, selection_length));
    info->following_text = std::string(Util::Utf8SubString(surrounding_text, selection_start + selection_length));
    return true;
}

}  // namespace fcitx
}  // namespace mozc
