// Copyright 2017 The Abseil Authors.

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//      https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

#include "absl/strings/match.h"

#include <algorithm>

#include <cstddef>

#include <cstdint>

#include "absl/base/attributes.h"

#include "absl/base/config.h"

#include "absl/base/internal/endian.h"

#include "absl/base/optimization.h"

#include "absl/numeric/bits.h"

#include "absl/strings/ascii.h"

#include "absl/strings/internal/memutil.h"

#include "absl/strings/string_view.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

bool EqualsIgnoreCase(absl::string_view piece1,

                      absl::string_view piece2) noexcept {

  return (piece1.size() == piece2.size() &&

          0 == absl::strings_internal::memcasecmp(piece1.data(), piece2.data(),

                                                  piece1.size()));

  // memcasecmp uses absl::ascii_tolower().

}

namespace {

// For larger haystacks (n >= 256), Case-Insensitive Boyer-Moore-Horspool

// provides sub-linear O(N / M) average-case performance, although it still has

// O(N * M) theoretical worst-case scaling.

// Scans the haystack from left to right using a search window of size `m`.

// For each window offset, Horspool inspects the rightmost character of the

// window (`haystack[pos + m - 1]`) first, enabling multi-byte shifts when

// mismatches occur and reducing average search time to O(N / M).

ABSL_ATTRIBUTE_NOINLINE bool StrContainsIgnoreCaseBMH(

    absl::string_view haystack, absl::string_view needle) noexcept {

  const size_t n = haystack.size();

  const size_t m = needle.size();

  // Step 1: Initialize the 256-entry shift table.

  // Unknown characters default to full window shift of `m` bytes.

  size_t shift[256];

  for (size_t i = 0; i < 256; ++i) {

    shift[i] = m;

  }

  // Populate shift distances for needle[0..m-2]. Dual assignment for

  // ascii_tolower and ascii_toupper stores distance from rightmost occurrence

  // to end of needle.

  for (size_t i = 0; i < m - 1; ++i) {

    const unsigned char c = static_cast<unsigned char>(needle[i]);

    shift[static_cast<unsigned char>(absl::ascii_tolower(c))] = m - 1 - i;

    shift[static_cast<unsigned char>(absl::ascii_toupper(c))] = m - 1 - i;

  }

  // Step 2: Search loop across candidate window offsets.

  size_t pos = 0;

  while (pos <= n - m) {

    const unsigned char last_hay =

        static_cast<unsigned char>(haystack[pos + m - 1]);

    const unsigned char last_needle = static_cast<unsigned char>(needle[m - 1]);

    // Check 1: Inspect right-most character of window first.

    if (last_hay == last_needle ||

        absl::ascii_tolower(last_hay) == absl::ascii_tolower(last_needle)) {

      // Check 2: Pre-filter on first character of window.

      const unsigned char first_hay = static_cast<unsigned char>(haystack[pos]);

      const unsigned char first_needle = static_cast<unsigned char>(needle[0]);

      if (first_hay == first_needle ||

          absl::ascii_tolower(first_hay) == absl::ascii_tolower(first_needle)) {

        // Check 3: Compare interior (m - 2) bytes.

        if (EqualsIgnoreCase(haystack.substr(pos + 1, m - 2),

                             needle.substr(1, m - 2))) {

          return true;

        }

      }

    }

    // Advance window by shift distance determined by right-most haystack byte.

    pos += shift[last_hay];

  }

  return false;

}

}  // namespace

bool StrContainsIgnoreCase(absl::string_view haystack,

                           absl::string_view needle) noexcept {

  const size_t n = haystack.size();

  const size_t m = needle.size();

  if (m == 0) return true;

  if (n < m) return false;

  if (m == 1) return StrContainsIgnoreCase(haystack, needle[0]);

  // For short haystacks (n < 256) or small needles (m == 2), avoid the

  // initialization overhead of a 256-entry shift table. Instead, use a fast

  // first-and-last character prefilter before inspecting interior bytes.

  if (n < 256 || m == 2) {

    const char first_needle =

        absl::ascii_tolower(static_cast<unsigned char>(needle[0]));

    const char last_needle =

        absl::ascii_tolower(static_cast<unsigned char>(needle[m - 1]));

    for (size_t pos = 0; pos <= n - m; ++pos) {

      const unsigned char first_hay = static_cast<unsigned char>(haystack[pos]);

      if (absl::ascii_tolower(first_hay) != first_needle) continue;

      const unsigned char last_hay =

          static_cast<unsigned char>(haystack[pos + m - 1]);

      if (absl::ascii_tolower(last_hay) != last_needle) continue;

      if (m == 2 || EqualsIgnoreCase(haystack.substr(pos + 1, m - 2),

                                     needle.substr(1, m - 2))) {

        return true;

      }

    }

    return false;

  }

  return StrContainsIgnoreCaseBMH(haystack, needle);

}

bool StrContainsIgnoreCase(absl::string_view haystack,

                           char needle) noexcept {

  char upper_needle = absl::ascii_toupper(static_cast<unsigned char>(needle));

  char lower_needle = absl::ascii_tolower(static_cast<unsigned char>(needle));

  if (upper_needle == lower_needle) {

    return StrContains(haystack, needle);

  }

  if (haystack.size() < 64) {

    for (char c : haystack) {

      if (c == lower_needle || c == upper_needle) return true;

    }

    return false;

  }

  const char both_cstr[3] = {lower_needle, upper_needle, '\0'};

  return haystack.find_first_of(both_cstr) != absl::string_view::npos;

}

bool StartsWithIgnoreCase(absl::string_view text,

                          absl::string_view prefix) noexcept {

  return (text.size() >= prefix.size()) &&

         EqualsIgnoreCase(text.substr(0, prefix.size()), prefix);

}

bool EndsWithIgnoreCase(absl::string_view text,

                        absl::string_view suffix) noexcept {

  return (text.size() >= suffix.size()) &&

         EqualsIgnoreCase(text.substr(text.size() - suffix.size()), suffix);

}

absl::string_view FindLongestCommonPrefix(absl::string_view a,

                                          absl::string_view b) {

  const absl::string_view::size_type limit = std::min(a.size(), b.size());

  const char* const pa = a.data();

  const char* const pb = b.data();

  absl::string_view::size_type count = (unsigned) 0;

  if (ABSL_PREDICT_FALSE(limit < 8)) {

    while (ABSL_PREDICT_TRUE(count + 2 <= limit)) {

      uint16_t xor_bytes = absl::little_endian::Load16(pa + count) ^

                           absl::little_endian::Load16(pb + count);

      if (ABSL_PREDICT_FALSE(xor_bytes != 0)) {

        if (ABSL_PREDICT_TRUE((xor_bytes & 0xff) == 0)) ++count;

        return absl::string_view(pa, count);

      }

      count += 2;

    }

    if (ABSL_PREDICT_TRUE(count != limit)) {

      if (ABSL_PREDICT_TRUE(pa[count] == pb[count])) ++count;

    }

    return absl::string_view(pa, count);

  }

  do {

    uint64_t xor_bytes = absl::little_endian::Load64(pa + count) ^

                         absl::little_endian::Load64(pb + count);

    if (ABSL_PREDICT_FALSE(xor_bytes != 0)) {

      count += static_cast<uint64_t>(absl::countr_zero(xor_bytes) >> 3);

      return absl::string_view(pa, count);

    }

    count += 8;

  } while (ABSL_PREDICT_TRUE(count + 8 < limit));

  count = limit - 8;

  uint64_t xor_bytes = absl::little_endian::Load64(pa + count) ^

                       absl::little_endian::Load64(pb + count);

  if (ABSL_PREDICT_TRUE(xor_bytes != 0)) {

    count += static_cast<uint64_t>(absl::countr_zero(xor_bytes) >> 3);

    return absl::string_view(pa, count);

  }

  return absl::string_view(pa, limit);

}

absl::string_view FindLongestCommonSuffix(absl::string_view a,

                                          absl::string_view b) {

  const absl::string_view::size_type limit = std::min(a.size(), b.size());

  if (limit == 0) return absl::string_view();

  const char* pa = a.data() + a.size() - 1;

  const char* pb = b.data() + b.size() - 1;

  absl::string_view::size_type count = (unsigned) 0;

  while (count < limit && *pa == *pb) {

    --pa;

    --pb;

    ++count;

  }

  return absl::string_view(++pa, count);

}

ABSL_NAMESPACE_END

}  // namespace absl