string_utils.cpp

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/*******************************************************************\
 
Module:
 
Author: Daniel Poetzl
 
\*******************************************************************/
 
#include "string_utils.h"
#include "exception_utils.h"
#include "invariant.h"
 
#include <algorithm>
#include <cctype>
#include <iomanip>

std::string strip_string(std::string_view s)
{
  auto pred=[](char c){ return std::isspace(c); };
 
  std::string_view::const_iterator left =
    std::find_if_not(s.begin(), s.end(), pred);
  if(left==s.end())
    return "";
 
  std::size_t i = std::distance(s.begin(), left);
 
  std::string_view::const_reverse_iterator right =
    std::find_if_not(s.rbegin(), s.rend(), pred);
  std::size_t j = std::distance(right, s.rend()) - 1;
 
  // copy happens here; this could return a view in the future
  return std::string{s.substr(i, (j - i + 1))};
}
 
void split_string(
  std::string_view s,
  char delim,
  std::vector<std::string> &result,
  bool strip,
  bool remove_empty)
{
  PRECONDITION(result.empty());
  // delim can't be a space character if using strip
  PRECONDITION(!std::isspace(delim) || !strip);
 
  if(s.empty())
  {
    if(!remove_empty)
      result.push_back("");
    return;
  }
 
  std::size_t n = s.length();
  INVARIANT(n > 0, "Empty string case should already be handled");
 
  std::size_t start = 0;
  std::size_t i;
 
  for(i=0; i<n; i++)
  {
    if(s[i]==delim)
    {
      // result owns std::strings rather than string_views: callers
      // routinely pass a temporary as `s` (e.g. some_function()
      // returning std::string), so the input may not outlive the
      // result.
      std::string new_s = std::string{s.substr(start, i - start)};
 
      if(strip)
        new_s=strip_string(new_s);
 
      if(!remove_empty || !new_s.empty())
        result.push_back(std::move(new_s));
 
      start=i+1;
    }
  }
 
  // result owns std::strings rather than string_views: see the
  // comment above the first push_back in the loop.
  std::string new_s = std::string{s.substr(start, n - start)};
 
  if(strip)
    new_s=strip_string(new_s);
 
  if(!remove_empty || !new_s.empty())
    result.push_back(std::move(new_s));
 
  if(!remove_empty && result.empty())
    result.push_back("");
}
 
void split_string(
  std::string_view s,
  char delim,
  std::string &left,
  std::string &right,
  bool strip)
{
  // delim can't be a space character if using strip
  PRECONDITION(!std::isspace(delim) || !strip);
 
  std::vector<std::string> result = split_string(s, delim, strip);
 
  if(result.size() != 2)
  {
    throw deserialization_exceptiont{
      "expected string '" + std::string{s} +
      "' to contain two substrings "
      "delimited by " +
      delim + " but has " + std::to_string(result.size())};
  }
 
  left=result[0];
  right=result[1];
}
 
std::vector<std::string>
split_string(std::string_view s, char delim, bool strip, bool remove_empty)
{
  std::vector<std::string> result;
  split_string(s, delim, result, strip, remove_empty);
  return result;
}
 
std::string trim_from_last_delimiter(std::string_view s, const char delim)
{
  std::string result;
  const size_t index=s.find_last_of(delim);
  if(index!=std::string::npos)
    result=s.substr(0, index);
  return result;
}
 
std::string escape(std::string_view s)
{
  std::string result;
 
  for(std::size_t i=0; i<s.size(); i++)
  {
    if(s[i]=='\\' || s[i]=='"')
      result+='\\';
 
    result+=s[i];
  }
 
  return result;
}
 
std::string escape_non_alnum(std::string_view to_escape)
{
  std::ostringstream escaped;
  for(auto &ch : to_escape)
  {
    // `ch` may have a negative value in the case of utf-8 encodings of
    // characters above unicode code point 127. The following line maps these
    // negative values to positive values in the 128-255 range, using a
    // `static_cast`. This is neccessary in order to avoid undefined behaviour
    // in `isalnum`. The positive values are then stored in an integer using a
    // widening initialisation so that the stream insertion operator prints them
    // as numbers rather than characters.
    const int uch{static_cast<unsigned char>(ch)};
    if(ch == '_')
      escaped << "__";
    else if(isalnum(uch))
      escaped << ch;
    else
      escaped << '_' << std::hex << std::setfill('0') << std::setw(2) << uch;
  }
  return escaped.str();
}
 
std::string capitalize(std::string_view s)
{
  if(s.empty())
    return std::string{};
  std::string capitalized = std::string{s}; // copy
  capitalized[0] = toupper(capitalized[0]);
  return capitalized;
}
 
std::string wrap_line(
  const std::string &line,
  const std::size_t left_margin,
  const std::size_t width)
{
  return wrap_line(line.cbegin(), line.cend(), left_margin, width);
}
 
std::string wrap_line(
  std::string::const_iterator left,
  std::string::const_iterator right,
  const std::size_t left_margin,
  const std::size_t width)
{
  PRECONDITION(left_margin < width);
 
  const std::size_t column_width = width - left_margin;
  const std::string margin(left_margin, ' ');
 
  auto distance = std::distance(left, right);
  CHECK_RETURN(distance > 0);
 
  std::string result;
 
  if(static_cast<std::size_t>(distance) <= column_width)
  {
    result.append(margin);
    result.append(left, right);
 
    return result;
  }
 
  auto it_line_begin = left;
 
  do
  {
    // points to the first character past the current column
    auto it = it_line_begin + column_width;
 
    auto rit_r = std::reverse_iterator<decltype(it)>(it) - 1;
    auto rit_l = rit_r + column_width;
 
    auto rit_space = std::find(rit_r, rit_l, ' ');
 
    if(rit_space != rit_l)
    {
      auto it_space = rit_space.base() - 1;
      CHECK_RETURN(*it_space == ' ');
 
      result.append(margin);
      result.append(it_line_begin, it_space);
      result.append("\n");
 
      it_line_begin = it_space + 1;
    }
    else
    {
      // we have not found a space, thus cannot wrap this line
      result.clear();
      result.append(left, right);
 
      return result;
    }
  } while(static_cast<std::size_t>(std::distance(it_line_begin, right)) >
          column_width);
 
  result.append(margin);
  result.append(it_line_begin, right);
 
  return result;
}