/** @file

   Class for handling "views" of text. Views presume the memory for the buffer is managed
   elsewhere and allow efficient access to segments of the buffer without copies. Views are read
   only as the view doesn't own the memory. Along with generic buffer methods are specialized
   methods to support better string parsing, particularly token based parsing.

   This class is based on @c std::string_view and is easily and cheaply converted to and from that class.


   @section license License

   Licensed to the Apache Software Foundation (ASF) under one or more contributor license
   agreements.  See the NOTICE file distributed with this work for additional information regarding
   copyright ownership.  The ASF licenses this file to you 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

   http://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.
 */

#pragma once
#include <bitset>
#include <functional>
#include <iosfwd>
#include <memory.h>
#include <algorithm>
#include <string>
#include <string_view>
#include <limits>
#include <cstdint>

/** Compare views with ordering, ignoring case.
 *
 * @param lhs input view
 * @param rhs input view
 * @return The ordered comparison value.
 *
 * - -1 if @a lhs is less than @a rhs
 * -  1 if @a lhs is greater than @a rhs
 * -  0 if the views have identical content.
 *
 * If one view is the prefix of the other, the shorter view is less (first in the ordering).
 */
int strcasecmp(const std::string_view &lhs, const std::string_view &rhs);

/** Compare views with ordering.
 *
 * @param lhs input view
 * @param rhs input view
 * @return The ordered comparison value.
 *
 * - -1 if @a lhs is less than @a rhs
 * -  1 if @a lhs is greater than @a rhs
 * -  0 if the views have identical content.
 *
 * If one view is the prefix of the other, the shorter view is less (first in the ordering).
 *
 * @note For string views, there is no difference between @c strcmp and @c memcmp.
 * @see strcmp
 */
int memcmp(const std::string_view &lhs, const std::string_view &rhs);

/** Copy bytes.
 *
 * @param dst Destination buffer.
 * @param src Original string.
 * @return @a dest
 *
 * This is a convenience for
 * @code
 *   memcpy(dst, src.data(), size.size());
 * @endcode
 * Therefore @a dst must point at a buffer large enough to hold @a src. If this is not already
 * determined, then presuming @c DST_SIZE is the size of the buffer at @a dst
 * @code
 *   memcpy(dst, src.prefix(DST_SIZE));
 * @endcode
 *
 */
inline void *
memcpy(void *dst, const std::string_view &src)
{
  return memcpy(dst, src.data(), src.size());
}

/** Compare views with ordering.
 *
 * @param lhs input view
 * @param rhs input view
 * @return The ordered comparison value.
 *
 * - -1 if @a lhs is less than @a rhs
 * -  1 if @a lhs is greater than @a rhs
 * -  0 if the views have identical content.
 *
 * If one view is the prefix of the other, the shorter view is less (first in the ordering).
 *
 * @note For string views, there is no difference between @c strcmp and @c memcmp.
 * @see memcmp
 */
inline int
strcmp(const std::string_view &lhs, const std::string_view &rhs)
{
  return memcmp(lhs, rhs);
}

namespace ts
{
class TextView;

/** A read only view of contiguous piece of memory.

    A @c TextView does not own the memory to which it refers, it is simply a view of part of some
    (presumably) larger memory object. The purpose is to allow working in a read only way a specific
    part of the memory. A classic example for ATS is working with HTTP header fields and values
    which need to be accessed independently but preferably without copying. A @c TextView supports this style.

    @c TextView is based on an earlier classes @c ConstBuffer, @c StringView and influenced by @c
    Boost.string_ref and @c std::string_view. None of these were adequate for how use of @c
    ConstBuffer evolved with regard to text based manipulations. @c TextView is a super set of @c
    std::string_view (and therefore our local implementation, @std::string_view). It is designed to
    be a drop in replacement.

    @note To simplify the interface there is no constructor just a character pointer. Constructors require
    either a literal string or an explicit length. This avoid ambiguities which are much more annoying that
    explicitly calling @c strlen on a character pointer.
 */
class TextView : public std::string_view
{
  using self_type  = TextView;         ///< Self reference type.
  using super_type = std::string_view; ///< Parent type.

public:
  /// Default constructor (empty buffer).
  constexpr TextView();

  /** Construct from pointer and size.
   *
   * @param ptr String for the view.
   * @param n Length of string at @a ptr.
   *
   * If @a n is @c npos then @a ptr is presumed to be a C string and the length is computed from it.
   * In this case, if @a ptr is @c nullptr the length is zero, otherwise the length is that returned
   * by @c strlen(ptr).
   *
   * @note - @c strlen can't be called in a @a constexpr value therefore @a n must not be @c npos
   * in any @c constexpr definition.
   */
  constexpr TextView(const char *ptr, size_t n);

  /** Construct explicitly with a pointer and size.
   *
   * @param ptr String.
   * @param n Length
   *
   * If @a n is negative then @a ptr is presumed to be a C string the length is computed.
   * In this case, if @a ptr is  @c nullptr the length is zero, otherwise the length is that returned
   * by @c strlen(ptr).
   *
   * @note - @c strlen can't be called in a @a constexpr value therefore @a n must not be negative
   * in any @c constexpr definition.
   *
   * @internal This is also useful for cases where the integral type is already signed, to avoid
   * having to cast.
   */
  constexpr TextView(const char *ptr, int n);

  /** Construct from a half open range of two pointers.
      @note The byte at @start is in the view but the byte at @a end is not.
  */
  constexpr TextView(const char *start, ///< First byte in the view.
                     const char *end    ///< First byte not in the view.
  );

  /** Constructor from constant string.

      Construct directly from an array of characters. All elements of the array are
      included in the view unless the last element is nul, in which case it is elided.
      If this is inappropriate then a constructor with an explicit size should be used.

      @code
        TextView a("A literal string");
      @endcode
   */
  template <size_t N> constexpr TextView(const char (&s)[N]);

  /** Construct from nullptr.
      This implicitly makes the length 0.
  */
  constexpr TextView(std::nullptr_t);

  /// Construct from a @c std::string_view.
  constexpr TextView(super_type const &that);

  /// Construct from @c std::string, referencing the entire string contents.
  /// @internal Not all compilers make @c std::string methods called @c constexpr
  TextView(std::string const &str);

  /// Pointer to byte past the last byte in the view.
  const char *data_end() const;

  /// Assignment.
  self_type &operator                    =(super_type const &that);
  template <size_t N> self_type &operator=(const char (&s)[N]);
  self_type &operator                    =(const std::string &s);

  /// Explicitly set the view.
  self_type &assign(char const *ptr, size_t n);

  /// Explicitly set the view to the range [ @a b , @a e )
  self_type &assign(char const *b, char const *e);

  /// Explicitly set the view from a @c std::string
  self_type &assign(std::string const &s);

  /** Dereference operator.

      @note This allows the view to be used as if it were a character iterator to a null terminated
      string which is handy for several other STL interfaces.

      @return The first byte in the view, or a nul character if the view is empty.
  */
  /// @return The first byte in the view.
  char operator*() const;

  /** Shift the view to discard the first byte.
      @return @a this.
  */
  self_type &operator++();

  /// Shift the view to discard the first byte.
  /// @return A pre-increment copy of the view.
  self_type operator++(int);

  /** Shift the view to discard the leading @a n bytes.
      Equivalent to @c std::string_view::remove_prefix
      @return @a this
  */
  self_type &operator+=(size_t n);

  /// Check for empty view.
  /// @return @c true if the view has a zero pointer @b or size.
  bool operator!() const;

  /// Check for non-empty view.
  /// @return @c true if the view refers to a non-empty range of bytes.
  explicit operator bool() const;

  /// Clear the view (become an empty view).
  self_type &clear();

  /// Get the offset of the first character for which @a pred is @c true.
  template <typename F> size_t find_if(F const &pred) const;
  /// Get the offset of the last character for which @a pred is @c true.
  template <typename F> size_t rfind_if(F const &pred) const;

  /** Remove bytes that match @a c from the start of the view.
   */
  self_type &ltrim(char c);

  /** Remove bytes from the start of the view that are in @a delimiters.
   */
  self_type &ltrim(super_type const &delimiters);

  /** Remove bytes from the start of the view that are in @a delimiters.
      @internal This is needed to avoid collisions with the templated predicate style.
      @return @c *this
  */
  self_type &ltrim(const char *delimiters);

  /** Remove bytes from the start of the view for which @a pred is @c true.
      @a pred must be a functor taking a @c char argument and returning @c bool.
      @return @c *this
  */
  template <typename F> self_type &ltrim_if(F const &pred);

  /** Remove bytes that match @a c from the end of the view.
   */
  self_type &rtrim(char c);

  /** Remove bytes from the end of the view that are in @a delimiters.
   */
  self_type &rtrim(super_type const &delimiters);

  /** Remove bytes from the end of the view that are in @a delimiters.
      @internal This is needed to avoid collisions with the templated predicate style.
      @return @c *this
   */
  self_type &rtrim(const char *delimiters);

  /** Remove bytes from the start and end of the view for which @a pred is @c true.
      @a pred must be a functor taking a @c char argument and returning @c bool.
      @return @c *this
  */
  template <typename F> self_type &rtrim_if(F const &pred);

  /** Remove bytes that match @a c from the end of the view.
   */
  self_type &trim(char c);

  /** Remove bytes from the start and end of the view that are in @a delimiters.
   */
  self_type &trim(super_type const &delimiters);

  /** Remove bytes from the start and end of the view that are in @a delimiters.
      @internal This is needed to avoid collisions with the templated predicate style.
      @return @c *this
  */
  self_type &trim(const char *delimiters);

  /** Remove bytes from the start and end of the view for which @a pred is @c true.
      @a pred must be a functor taking a @c char argument and returning @c bool.
      @return @c *this
  */
  template <typename F> self_type &trim_if(F const &pred);

  /** Get the prefix of size @a n.

      If @a n is greater than the size the entire view is returned.

      @return A view of the prefix.
  */
  self_type prefix(size_t n) const;
  /// Convenience overload to avoid ambiguity for literal numbers.
  self_type prefix(int n) const;
  /** Get the prefix delimited by the first occurrence of the character @a c.

      If @a c is not found the entire view is returned.
      The delimiter character is not included in the returned view.

      @return A view of the prefix.
  */
  self_type prefix(char c) const;
  /** Get the prefix delimited by the first occurrence of a character in @a delimiters.

      If no such character is found the entire view is returned.
      The delimiter character is not included in the returned view.

      @return A view of the prefix.
  */
  self_type prefix(super_type const &delimiters) const;
  /** Get the prefix delimited by the first character for which @a pred is @c true.

      If no such character is found the entire view is returned
      The delimiter character is not included in the returned view.

      @return A view of the prefix.
  */
  template <typename F> self_type prefix_if(F const &pred) const;

  /// Overload to provide better return type.
  self_type &remove_prefix(size_t n);

  /// Remove the prefix delimited by the first occurrence of @a c.
  self_type &remove_prefix_at(char c);

  /// Remove the prefix delimited by the first occurrence of a character for which @a pred is @c true.
  template <typename F> self_type &remove_prefix_if(F const &pred);

  /** Split a prefix from the view on the character at offset @a n.

      The view is split in to two parts and the byte at offset @a n is discarded. @a this retains
      all data @b after offset @a n (equivalent to <tt>TextView::substr(n+1)</tt>). A new view
      containing the initial bytes up to but not including the byte at offset @a n is returned,
      (equivalent to <tt>TextView(0, n)</tt>).

      This is convenient when tokenizing.

      If @a n is larger than the size of the view no change is made and an empty buffer is
      returned. Therefore this method is most useful when checking for the presence of the delimiter
      is desirable, as the result of @c find methods can be passed directly to this method.

      @note This method and its overloads always remove the delimiter character.

      @code
        void f(TextView& text) {
          TextView token = text.get_prefix_at(text.find(delimiter));
          if (token) { // ... process token }
      @endcode

      @return The prefix bounded at offset @a n or an empty view if @a n is more than the view
      size.

      @see take_prefix_at
  */
  self_type split_prefix_at(size_t n);

  /// Convenience overload for literal numbers.
  self_type split_prefix_at(int n);
  /// Convenience overload, split on character.
  self_type split_prefix_at(char c);
  /// Convenience overload, split on delimiter set.
  self_type split_prefix_at(super_type const &delimiters);
  /// Convenience overload, split on predicate.
  template <typename F> self_type split_prefix_if(F const &pred);

  /** Split a prefix from the view on the character at offset @a n.

      The view is split in to two parts and the byte at offset @a n is discarded. @a this retains
      all data @b after offset @a n (equivalent to <tt>TextView::substr(n+1)</tt>). A new view
      containing the initial bytes up to but not including the byte at offset @a n is returned,
      (equivalent to <tt>TextView(0, n)</tt>).

      This is convenient when tokenizing.

      If @a n is larger than the view size then the entire view is removed and returned, leaving an
      empty view. Therefore if @this is not empty, a non-empty view is always returned. This is desirable
      if a non-empty return view is always wanted, regardless of whether a delimiter is present.

      @note This method and its overloads always remove the delimiter character.

      @code
      TextView text;
      while (text) {
        TextView token = text.take_prefix_at(text.find(delimiter));
        // token will always be non-empty because text was not empty.
      }
      @endcode

      @return The prefix bounded at offset @a n or the entire view if @a n is more than the view
      size.

      @see split_prefix_at
  */
  self_type take_prefix_at(size_t n);

  /// Convenience overload, extract on delimiter set.
  self_type take_prefix_at(char c);
  /// Convenience overload, extract on delimiter set.
  self_type take_prefix_at(super_type const &delimiters);
  /// Convenience overload, extract on predicate.
  template <typename F> self_type take_prefix_if(F const &pred);

  /** Get the last @a n characters of the view.

      @return A buffer that contains @a n characters at the end of the view.
  */
  self_type suffix(size_t n) const;

  /// Convenience overload to avoid ambiguity for literal numbers.
  self_type suffix(int n) const;
  /// Convenience overload for character.
  self_type suffix(char c) const;
  /// Convenience overload for delimiter set.
  self_type suffix(super_type const &delimiters) const;
  /// Convenience overload for delimiter set.
  self_type suffix(const char *delimiters) const;
  /// Get the prefix delimited by the first character for which @a pred is @c true.
  template <typename F> self_type suffix_if(F const &pred) const;

  /// Overload to provide better return type.
  self_type &remove_suffix(size_t n);

  /// Remove a suffix, delimited by the last occurrence of @c c.
  self_type &remove_suffix_at(char c);

  /// Remove a suffix, delimited by the last occurrence of a character for which @a pred is @c true.
  template <typename F> self_type &remove_suffix_if(F const &f);

  /** Split the view to get a suffix of size @a n.

      The view is split in to two parts, a suffix of size @a n and a remainder which is the original
      view less @a n + 1 characters at the end. That is, the character between the suffix and the
      remainder is discarded. This is equivalent to <tt>TextView::suffix(this->size()-n)</tt> and
      <tt>TextView::remove_suffix(this->size() - (n+1))</tt>.

      If @a n is equal to or larger than the size of the view the entire view is removed as the
      suffix.

      @return The suffix of size @a n.

      @see split_suffix_at
  */
  self_type split_suffix(size_t n);
  /// Convenience overload for literal integers.
  self_type split_suffix(int n);

  /** Split the view on the character at offset @a n.

      The view is split in to two parts and the byte at offset @a n is discarded. @a this retains
      all data @b before offset @a n (equivalent to <tt>TextView::prefix(this->size()-n-1)</tt>). A
      new view containing the trailing bytes after offset @a n is returned, (equivalent to
      <tt>TextView::suffix(n))</tt>).

      If @a n is larger than the size of the view no change is made and an empty buffer is
      returned. Therefore this method is most useful when checking for the presence of the delimiter
      is desirable, as the result of @c find methods can be passed directly to this method.

      @note This method and its overloads always remove the delimiter character.

      @return The suffix bounded at offset @a n or an empty view if @a n is more than the view
      size.
  */
  self_type split_suffix_at(size_t n);

  /// Convenience overload for literal integers.
  self_type split_suffix_at(int n);
  /// Convenience overload for character.
  self_type split_suffix_at(char c);
  /// Convenience overload for delimiter set.
  self_type split_suffix_at(super_type const &delimiters);
  /// Split the view on the last character for which @a pred is @c true.
  template <typename F> self_type split_suffix_if(F const &pred);

  /** Split the view on the character at offset @a n.

      The view is split in to two parts and the byte at offset @a n is discarded. @a this retains
      all data @b before offset @a n (equivalent to <tt>TextView::prefix(this->size()-n-1)</tt>). A
      new view containing the trailing bytes after offset @a n is returned, (equivalent to
      <tt>TextView::suffix(n))</tt>).

      If @a n is larger than the view size then the entire view is removed and returned, leaving an
      empty view. Therefore if @this is not empty, a non-empty view is always returned. This is desirable
      if a non-empty return view is always wanted, regardless of whether a delimiter is present.

      @note This method and its overloads always remove the delimiter character.

      @return The suffix bounded at offset @a n or the entire view if @a n is more than the view
      size.
  */
  self_type take_suffix_at(size_t n);

  /// Convenience overload for literal integers.
  self_type take_suffix_at(int n);
  /// Convenience overload for character.
  self_type take_suffix_at(char c);
  /// Convenience overload for delimiter set.
  self_type take_suffix_at(super_type const &delimiters);
  /// Split the view on the last character for which @a pred is @c true.
  template <typename F> self_type take_suffix_if(F const &pred);

  /** Prefix check.
      @return @c true if @a this is a prefix of @a that.
  */
  bool isPrefixOf(super_type const &that) const;

  /** Case ignoring prefix check.
      @return @c true if @a this is a prefix of @a that, ignoring case.
  */
  bool isNoCasePrefixOf(super_type const &that) const;

  // Functors for using this class in STL containers.
  /// Ordering functor, lexicographic comparison.
  struct LessThan {
    bool
    operator()(self_type const &lhs, self_type const &rhs)
    {
      return -1 == strcmp(lhs, rhs);
    }
  };
  /// Ordering functor, case ignoring lexicographic comparison.
  struct LessThanNoCase {
    bool
    operator()(self_type const &lhs, self_type const &rhs)
    {
      return -1 == strcasecmp(lhs, rhs);
    }
  };

  /// Specialized stream operator implementation.
  /// @note Use the standard stream operator unless there is a specific need for this, which is unlikely.
  /// @return The stream @a os.
  /// @internal Needed because @c std::ostream::write must be used and
  /// so alignment / fill have to be explicitly handled.
  template <typename Stream> Stream &stream_write(Stream &os, const TextView &b) const;

protected:
  /// Faster find on a delimiter set, taking advantage of supporting only ASCII.
  size_t search(super_type const &delimiters) const;
  /// Faster reverse find on a delimiter set, taking advantage of supporting only ASCII.
  size_t rsearch(super_type const &delimiters) const;

  /// Initialize a bit mask to mark which characters are in this view.
  static void init_delimiter_set(super_type const &delimiters, std::bitset<256> &set);
};

// Internal character conversion table.
// Converts a character to the numeric digit value, or negative if the character is not a valid digit.
extern const int8_t svtoi_convert[256];
;

/** Convert the text in @c TextView @a src to a numeric value.

    If @a parsed is non-null then the part of the string actually parsed is placed there.
    @a base sets the conversion base. This defaults to 10 with two special cases:

    - If the number starts with a literal '0' then it is treated as base 8.
    - If the number starts with the literal characters '0x' or '0X' then it is treated as base 16.
*/
intmax_t svtoi(TextView src, TextView *parsed = nullptr, int base = 0);

/** Convert the text in @c src to an unsigned numeric value.
 *
 * @tparam N The radix (must be  1..36)
 * @param src The source text. Updated during parsing.
 * @return The converted numeric value.
 *
 * This is a specialized function useful only where conversion performance is critical, or for some
 * other reason the numeric text has already been parsed out. The performance gains comes from
 * templating the divisor which enables the compiler to optimize the multiplication (e.g., for
 * powers of 2 shifts is used). It is used inside @c svtoi and @c svtou for the common cases of 8,
 * 10, and 16, therefore normally this isn't much more performant than @c svtoi. Because of this
 * only positive values are parsed. If determining the radix from the text or signed value parsing
 * is needed, used @c svtoi.
 *
 * @a src is updated in place by removing parsed characters. Parsing stops on the first invalid
 * digit, so any leading non-digit characters (e.g. whitespace) must already be removed. Overflow
 * is detected and the first digit that would overflow is not parsed, and the maximum value is
 * returned.
 */
template <uintmax_t N>
uintmax_t
svto_radix(ts::TextView &src)
{
  static_assert(0 < N && N <= 36, "Radix must be in the range 1..36");
  uintmax_t zret{0};
  uintmax_t v;
  while (src.size() && ((v = ts::svtoi_convert[static_cast<unsigned char>(*src)]) < N)) {
    auto n = zret * N + v;
    if (n < zret) { // overflow / wrap
      return std::numeric_limits<uintmax_t>::max();
    }
    zret = n;
    ++src;
  }
  return zret;
};

// ----------------------------------------------------------
// Inline implementations.

// === TextView Implementation ===
inline constexpr TextView::TextView() {}
inline constexpr TextView::TextView(const char *ptr, size_t n) : super_type(ptr, n == npos ? (ptr ? ::strlen(ptr) : 0) : n) {}
inline constexpr TextView::TextView(const char *ptr, int n) : super_type(ptr, n < 0 ? (ptr ? ::strlen(ptr) : 0) : n) {}
inline constexpr TextView::TextView(const char *start, const char *end) : super_type(start, end - start) {}
inline constexpr TextView::TextView(std::nullptr_t) : super_type(nullptr, 0) {}
inline TextView::TextView(std::string const &str) : super_type(str) {}
inline constexpr TextView::TextView(super_type const &that) : super_type(that) {}
template <size_t N> constexpr TextView::TextView(const char (&s)[N]) : super_type(s, s[N - 1] ? N : N - 1) {}

inline void
TextView::init_delimiter_set(super_type const &delimiters, std::bitset<256> &set)
{
  set.reset();
  for (char c : delimiters)
    set[static_cast<uint8_t>(c)] = true;
}

inline const char *
TextView::data_end() const
{
  return this->data() + this->size();
}

inline TextView &
TextView::clear()
{
  new (this) self_type();
  return *this;
}

inline char
TextView::operator*() const
{
  return this->empty() ? 0 : *(this->data());
}

inline bool
TextView::operator!() const
{
  return this->empty();
}

inline TextView::operator bool() const
{
  return !this->empty();
}

inline TextView &
TextView::operator++()
{
  this->remove_prefix(1);
  return *this;
}

inline TextView
TextView::operator++(int)
{
  self_type zret{*this};
  this->remove_prefix(1);
  return zret;
}

inline TextView &
TextView::operator+=(size_t n)
{
  this->remove_prefix(n);
  return *this;
}

template <size_t N>
inline TextView &
TextView::operator=(const char (&s)[N])
{
  return *this = self_type{s, s[N - 1] ? N : N - 1};
}

inline TextView &
TextView::operator=(super_type const &that)
{
  this->super_type::operator=(that);
  return *this;
}

inline TextView &
TextView::operator=(const std::string &s)
{
  this->super_type::operator=(s);
  return *this;
}

inline TextView &
TextView::assign(const std::string &s)
{
  *this = super_type(s);
  return *this;
}

inline TextView &
TextView::assign(char const *ptr, size_t n)
{
  *this = super_type(ptr, n == npos ? (ptr ? ::strlen(ptr) : 0) : n);
  return *this;
}

inline TextView &
TextView::assign(char const *b, char const *e)
{
  *this = super_type(b, e - b);
  return *this;
}

inline size_t
TextView::search(super_type const &delimiters) const
{
  std::bitset<256> valid;
  this->init_delimiter_set(delimiters, valid);

  for (const char *spot = this->data(), *limit = this->data_end(); spot < limit; ++spot)
    if (valid[static_cast<uint8_t>(*spot)])
      return spot - this->data();
  return npos;
}

inline size_t
TextView::rsearch(super_type const &delimiters) const
{
  std::bitset<256> valid;
  this->init_delimiter_set(delimiters, valid);

  for (const char *spot = this->data_end(), *limit = this->data(); spot > limit;)
    if (valid[static_cast<uint8_t>(*--spot)])
      return spot - this->data();
  return npos;
}

inline TextView
TextView::prefix(size_t n) const
{
  return self_type(this->data(), std::min(n, this->size()));
}

inline TextView
TextView::prefix(int n) const
{
  return this->prefix(static_cast<size_t>(n));
}

inline TextView
TextView::prefix(char c) const
{
  return this->prefix(this->find(c));
}

inline TextView
TextView::prefix(super_type const &delimiters) const
{
  return this->prefix(this->search(delimiters));
}

template <typename F>
inline TextView
TextView::prefix_if(F const &pred) const
{
  return this->prefix(this->find_if(pred));
}

inline TextView &
TextView::remove_prefix(size_t n)
{
  if (n > this->size()) {
    this->clear();
  } else {
    this->super_type::remove_prefix(n);
  }
  return *this;
}

inline TextView &
TextView::remove_prefix_at(char c)
{
  auto n = this->find(c);
  if (n == npos) {
    this->clear();
  } else {
    this->super_type::remove_prefix(n + 1);
  }
  return *this;
}

template <typename F>
TextView &
TextView::remove_prefix_if(F const &pred)
{
  auto n = this->find_if(pred);
  if (n == npos) {
    this->clear();
  } else {
    this->super_type::remove_prefix(n + 1);
  }
  return *this;
}

inline TextView
TextView::split_prefix_at(size_t n)
{
  self_type zret; // default to empty return.
  if (n < this->size()) {
    zret = this->prefix(n);
    this->remove_prefix(std::min(n + 1, this->size()));
  }
  return zret;
}

inline TextView
TextView::split_prefix_at(int n)
{
  return this->split_prefix_at(static_cast<size_t>(n));
}

inline TextView
TextView::split_prefix_at(char c)
{
  return this->split_prefix_at(this->find(c));
}

inline TextView
TextView::split_prefix_at(super_type const &delimiters)
{
  return this->split_prefix_at(this->search(delimiters));
}

template <typename F>
inline TextView
TextView::split_prefix_if(F const &pred)
{
  return this->split_prefix_at(this->find_if(pred));
}

inline TextView
TextView::take_prefix_at(size_t n)
{
  n              = std::min(n, this->size());
  self_type zret = this->prefix(n);
  this->remove_prefix(std::min(n + 1, this->size()));
  return zret;
}

inline TextView
TextView::take_prefix_at(char c)
{
  return this->take_prefix_at(this->find(c));
}

inline TextView
TextView::take_prefix_at(super_type const &delimiters)
{
  return this->take_prefix_at(this->search(delimiters));
}

template <typename F>
inline TextView
TextView::take_prefix_if(F const &pred)
{
  return this->take_prefix_at(this->find_if(pred));
}

inline TextView
TextView::suffix(size_t n) const
{
  n = std::min(n, this->size());
  return self_type(this->data_end() - n, n);
}

inline TextView
TextView::suffix(int n) const
{
  return this->suffix(static_cast<size_t>(n));
}

inline TextView
TextView::suffix(char c) const
{
  return this->suffix((this->size() - std::min(this->size(), this->rfind(c))) - 1);
}

inline TextView
TextView::suffix(super_type const &delimiters) const
{
  return this->suffix((this->size() - std::min(this->size(), this->rsearch(delimiters))) - 1);
}

template <typename F>
inline TextView
TextView::suffix_if(F const &pred) const
{
  return this->suffix((this->size() - std::min(this->size(), this->rfind_if(pred))) - 1);
}

inline TextView &
TextView::remove_suffix_at(char c)
{
  auto n = this->rfind(c);
  if (n == npos) {
    this->clear();
  } else {
    this->remove_suffix(this->size() - n);
  }
  return *this;
}

template <typename F>
TextView &
TextView::remove_suffix_if(F const &pred)
{
  auto n = this->rfind_if(pred);
  if (n == npos) {
    this->clear();
  } else {
    this->remove_suffix(this->size() - n);
  }
  return *this;
}

inline auto
TextView::remove_suffix(size_t n) -> self_type &
{
  if (n > this->size()) {
    this->clear();
  } else {
    this->super_type::remove_suffix(n);
  }
  return *this;
}

inline TextView
TextView::split_suffix(size_t n)
{
  self_type zret;
  n    = std::min(n, this->size());
  zret = this->suffix(n);
  this->remove_suffix(n + 1); // haha, saved by integer overflow!
  return zret;
}

inline TextView
TextView::split_suffix(int n)
{
  return this->split_suffix(static_cast<size_t>(n));
}

inline TextView
TextView::split_suffix_at(size_t n)
{
  self_type zret;
  if (n < this->size()) {
    n    = this->size() - n;
    zret = this->suffix(n - 1);
    this->remove_suffix(n);
  }
  return zret;
}

inline TextView
TextView::split_suffix_at(int n)
{
  return this->split_suffix_at(static_cast<size_t>(n));
}

inline TextView
TextView::split_suffix_at(char c)
{
  return this->split_suffix_at(this->rfind(c));
}

inline TextView
TextView::split_suffix_at(super_type const &delimiters)
{
  return this->split_suffix_at(this->rsearch(delimiters));
}

template <typename F>
inline TextView
TextView::split_suffix_if(F const &pred)
{
  return this->split_suffix_at(this->rfind_if(pred));
}

inline TextView
TextView::take_suffix_at(size_t n)
{
  self_type zret{*this};
  *this = zret.split_prefix_at(n);
  return zret;
}

inline TextView
TextView::take_suffix_at(int n)
{
  return this->take_suffix_at(static_cast<size_t>(n));
}

inline TextView
TextView::take_suffix_at(char c)
{
  return this->take_suffix_at(this->rfind(c));
}

inline TextView
TextView::take_suffix_at(super_type const &delimiters)
{
  return this->take_suffix_at(this->rsearch(delimiters));
}

template <typename F>
inline TextView
TextView::take_suffix_if(F const &pred)
{
  return this->take_suffix_at(this->rfind_if(pred));
}

template <typename F>
inline size_t
TextView::find_if(F const &pred) const
{
  for (const char *spot = this->data(), *limit = this->data_end(); spot < limit; ++spot)
    if (pred(*spot))
      return spot - this->data();
  return npos;
}

template <typename F>
inline size_t
TextView::rfind_if(F const &pred) const
{
  for (const char *spot = this->data_end(), *limit = this->data(); spot > limit;)
    if (pred(*--spot))
      return spot - this->data();
  return npos;
}

inline TextView &
TextView::ltrim(char c)
{
  this->remove_prefix(this->find_first_not_of(c));
  return *this;
}

inline TextView &
TextView::rtrim(char c)
{
  auto n = this->find_last_not_of(c);
  this->remove_suffix(this->size() - (n == npos ? 0 : n + 1));
  return *this;
}

inline TextView &
TextView::trim(char c)
{
  return this->ltrim(c).rtrim(c);
}

inline TextView &
TextView::ltrim(super_type const &delimiters)
{
  std::bitset<256> valid;
  this->init_delimiter_set(delimiters, valid);
  const char *spot;
  const char *limit;

  for (spot = this->data(), limit = this->data_end(); spot < limit && valid[static_cast<uint8_t>(*spot)]; ++spot)
    ;
  this->remove_prefix(spot - this->data());

  return *this;
}

inline TextView &
TextView::ltrim(const char *delimiters)
{
  return this->ltrim(std::string_view(delimiters));
}

inline TextView &
TextView::rtrim(const char *delimiters)
{
  return this->rtrim(std::string_view(delimiters));
}

inline TextView &
TextView::rtrim(super_type const &delimiters)
{
  std::bitset<256> valid;
  this->init_delimiter_set(delimiters, valid);
  const char *spot  = this->data_end();
  const char *limit = this->data();

  while (limit < spot-- && valid[static_cast<uint8_t>(*spot)])
    ;

  this->remove_suffix(this->data_end() - (spot + 1));
  return *this;
}

inline TextView &
TextView::trim(super_type const &delimiters)
{
  std::bitset<256> valid;
  this->init_delimiter_set(delimiters, valid);
  const char *spot;
  const char *limit;

  // Do this explicitly, so we don't have to initialize the character set twice.
  for (spot = this->data(), limit = this->data_end(); spot < limit && valid[static_cast<uint8_t>(*spot)]; ++spot)
    ;
  this->remove_prefix(spot - this->data());

  spot  = this->data_end();
  limit = this->data();
  while (limit < spot-- && valid[static_cast<uint8_t>(*spot)])
    ;
  this->remove_suffix(this->data_end() - (spot + 1));

  return *this;
}

inline TextView &
TextView::trim(const char *delimiters)
{
  return this->trim(std::string_view(delimiters));
}

template <typename F>
inline TextView &
TextView::ltrim_if(F const &pred)
{
  const char *spot;
  const char *limit;
  for (spot = this->data(), limit = this->data_end(); spot < limit && pred(*spot); ++spot)
    ;
  this->remove_prefix(spot - this->data());
  return *this;
}

template <typename F>
inline TextView &
TextView::rtrim_if(F const &pred)
{
  const char *spot  = this->data_end();
  const char *limit = this->data();
  while (limit < spot-- && pred(*spot))
    ;
  this->remove_suffix(this->data_end() - (spot + 1));
  return *this;
}

template <typename F>
inline TextView &
TextView::trim_if(F const &pred)
{
  return this->ltrim_if(pred).rtrim_if(pred);
}

inline bool
TextView::isPrefixOf(super_type const &that) const
{
  return this->size() <= that.size() && 0 == memcmp(this->data(), that.data(), this->size());
}

inline bool
TextView::isNoCasePrefixOf(super_type const &that) const
{
  return this->size() <= that.size() && 0 == strncasecmp(this->data(), that.data(), this->size());
}

template <typename Stream>
Stream &
TextView::stream_write(Stream &os, const TextView &b) const
{
  // Local function, avoids extra template work.
  static const auto stream_fill = [](Stream &os, size_t n) -> Stream & {
    static constexpr size_t pad_size = 8;
    typename Stream::char_type padding[pad_size];

    std::fill_n(padding, pad_size, os.fill());
    for (; n >= pad_size && os.good(); n -= pad_size)
      os.write(padding, pad_size);
    if (n > 0 && os.good())
      os.write(padding, n);
    return os;
  };

  const std::size_t w = os.width();
  if (w <= b.size()) {
    os.write(b.data(), b.size());
  } else {
    const std::size_t pad_size = w - b.size();
    const bool align_left      = (os.flags() & Stream::adjustfield) == Stream::left;
    if (!align_left && os.good())
      stream_fill(os, pad_size);
    if (os.good())
      os.write(b.data(), b.size());
    if (align_left && os.good())
      stream_fill(os, pad_size);
  }
  return os;
}

// Provide an instantiation for @c std::ostream as it's likely this is the only one ever used.
extern template std::ostream &TextView::stream_write(std::ostream &, const TextView &) const;

/** User literals for TextView.
 *
 * - _tv : TextView
 * - _sv : std::string_view
 */
namespace literals
{
  /** Literal constructor for @c ts::TextView.
   *
   * @param s The source string.
   * @param n Size of the source string.
   * @return A @c string_view
   *
   * @internal This is provided because the STL one does not support @c constexpr which seems
   * rather bizarre to me, but there it is. Update: this depends on the version of the compiler,
   * so hopefully someday this can be removed.
   */
  constexpr ts::TextView operator"" _tv(const char *s, size_t n) { return {s, n}; }
} // namespace literals

/** Functor for STL containers that need caseless comparisons of standard string types.
 *
 * For example a @c std::set of strings with caseless comparison would be
 *
 * @code
 * std::set<std::string, ts::caseless_compare> strings;
 * @endcode
 */
struct caseless_less_than {
  bool
  operator()(std::string_view const &lhs, std::string_view const &rhs) const
  {
    return strcasecmp(lhs, rhs) < 0;
  }
  bool
  operator()(TextView const &lhs, TextView const &rhs) const
  {
    return strcasecmp(lhs, rhs) < 0;
  }
  bool
  operator()(std::string const &lhs, std::string const &rhs) const
  {
    return strcasecmp(lhs, rhs) < 0;
  }
};

/** Functor for STL containers that need caseless equality of standard string types.
 *
 * For example a @c std::set of strings with caseless comparison would be
 *
 * @code
 * std::set<std::string, ts::caseless_compare> strings;
 * @endcode
 */
struct caseless_equal {
  bool
  operator()(std::string_view const &lhs, std::string_view const &rhs) const
  {
    return strcasecmp(lhs, rhs) == 0;
  }
  bool
  operator()(TextView const &lhs, TextView const &rhs) const
  {
    return strcasecmp(lhs, rhs) == 0;
  }
  bool
  operator()(std::string const &lhs, std::string const &rhs) const
  {
    return strcasecmp(lhs, rhs) == 0;
  }
};

} // namespace ts

namespace std
{
ostream &operator<<(ostream &os, const ts::TextView &b);

/* For interaction with specific STL interfaces, primarily std::filesystem. Along with the
 * dereference operator, this enables a @c TextView to act as a character iterator to a C string
 * even if the internal view is not nul terminated.
 * @note Putting these directly in the class doesn't seem to work.
 */
template <> struct iterator_traits<ts::TextView> {
  using value_type        = char;
  using pointer_type      = const char *;
  using reference_type    = const char &;
  using difference_type   = ssize_t;
  using iterator_category = forward_iterator_tag;
};

} // namespace std

// @c constexpr literal constructor for @c std::string_view
//
// For unknown reasons, this enables creating @c constexpr constructs using @c std::string_view while the
// standard one (""sv) does not.
//
// I couldn't think of any better place to put this, so it's here. At least @c TextView is strongly related
// to @c std::string_view.
constexpr std::string_view operator"" _sv(const char *s, size_t n)
{
  return {s, n};
}