SedPP/src/Runner.cpp

#include "sedpp/Runner.h"

#include "sedpp/Output.h"
#include "sedpp/Regex.h"
#include "sedpp/Replacement.h"

#include <algorithm>
#include <cstdio>
#include <filesystem>
#include <fstream>
#include <iostream>
#include <sstream>
#include <stdexcept>
#include <system_error>

#include <unistd.h>
#include <fcntl.h>

namespace sedpp {
namespace {

// The y command transliterates characters rather than raw bytes.  This helper
// keeps valid UTF-8 code units together and falls back to one byte for invalid
// sequences so binary-ish input still makes progress.
std::vector<std::string> splitCharacters(const std::string &text) {
  std::vector<std::string> chars;
  for (std::size_t i = 0; i < text.size();) {
    const unsigned char ch = static_cast<unsigned char>(text[i]);
    std::size_t width = 1;
    if ((ch & 0xe0) == 0xc0) {
      width = 2;
    } else if ((ch & 0xf0) == 0xe0) {
      width = 3;
    } else if ((ch & 0xf8) == 0xf0) {
      width = 4;
    }
    bool valid = width > 1 && i + width <= text.size();
    for (std::size_t j = 1; valid && j < width; ++j) {
      valid = (static_cast<unsigned char>(text[i + j]) & 0xc0) == 0x80;
    }
    if (!valid) {
      width = 1;
    }
    chars.push_back(text.substr(i, width));
    i += width;
  }
  return chars;
}

// In-place --follow-symlinks edits the final target, matching GNU sed.  A small
// depth cap turns symlink loops into a deterministic diagnostic.
std::string followSymlinkEditPath(const std::string &fileName) {
  std::filesystem::path current(fileName);
  for (int depth = 0; depth < 40; ++depth) {
    std::error_code ec;
    const std::filesystem::file_status status =
        std::filesystem::symlink_status(current, ec);
    if (ec) {
      throw std::runtime_error("couldn't readlink " + fileName + ": " +
                               ec.message());
    }
    if (!std::filesystem::is_symlink(status)) {
      return current.string();
    }
    const std::filesystem::path target = std::filesystem::read_symlink(current, ec);
    if (ec) {
      throw std::runtime_error("couldn't readlink " + fileName + ": " +
                               ec.message());
    }
    current = target.is_absolute() ? target : current.parent_path() / target;
  }
  throw std::runtime_error("couldn't readlink " + fileName +
                           ": Too many levels of symbolic links");
}

} // namespace

Runner::Runner(Options options, Program program,
               std::unordered_map<std::string, std::size_t> labels)
    : options_(std::move(options)), program_(std::move(program)),
      labels_(std::move(labels)) {}

bool Runner::addressMatches(const Address &address, const Cycle &cycle) {
  const std::uint64_t line =
      options_.separate ? cycle.fileLineNumber : cycle.lineNumber;
  switch (address.kind) {
  case AddressKind::None:
    return true;
  case AddressKind::Line:
    if (address.first == 0 && address.text.size() >= 19) {
      return false;
    }
    return line == address.first;
  case AddressKind::Last:
    return options_.separate ? cycle.lastInFile : cycle.lastOverall;
  case AddressKind::Regex: {
    // Empty regex addresses reuse the most recent non-empty regex seen by an
    // address or s command.
    Regex regex(address.text.empty() ? lastRegex_ : address.text, options_);
    const bool matched = regex.search(cycle.pattern).has_value();
    if (!address.text.empty()) {
      lastRegex_ = address.text;
    }
    return matched;
  }
  case AddressKind::Step:
    // FIRST~STEP matches FIRST and then every STEPth line.  0~N means every Nth
    // line, and N~0 degrades to only line N.
    if (address.second == 0) {
      return line == address.first;
    }
    if (address.first == 0) {
      return line % address.second == 0;
    }
    return line >= address.first && (line - address.first) % address.second == 0;
  case AddressKind::Plus:
  case AddressKind::Modulo:
    return false;
  }
  return false;
}

bool Runner::commandApplies(Command &command, const Cycle &cycle) {
  bool applies = true;
  command.rangeJustStarted = false;
  if (command.firstAddress) {
    if (command.secondAddress) {
      // Range activation belongs to each compiled command.  The same address
      // pair on two commands must not share state.
      bool justStarted = false;
      if (!command.rangeActive) {
        if (command.firstAddress->kind == AddressKind::Line &&
            command.firstAddress->text == "0") {
          // GNU's 0,/re/ range acts as if it is already active before line 1,
          // but it is allowed to fire only once.
          applies = !command.zeroRangeStarted && cycle.lineNumber == 1;
          if (applies) {
            command.zeroRangeStarted = true;
          }
        } else {
          applies = addressMatches(*command.firstAddress, cycle);
        }
        if (applies) {
          command.rangeActive = true;
          justStarted = true;
          command.rangeJustStarted = true;
          if (command.secondAddress->kind == AddressKind::Plus) {
            // addr,+N includes the start line plus N following cycles.
            command.rangeCountdown = command.secondAddress->second;
          }
        }
      } else {
        applies = true;
      }

      if (applies && command.rangeActive) {
        bool end = false;
        if (command.secondAddress->kind == AddressKind::Plus) {
          end = command.rangeCountdown == 0;
          if (command.rangeCountdown > 0) {
            --command.rangeCountdown;
          }
        } else if (command.secondAddress->kind == AddressKind::Modulo) {
          // addr,~N ends at the next input line whose number is a multiple of N.
          const std::uint64_t line =
              options_.separate ? cycle.fileLineNumber : cycle.lineNumber;
          end = command.secondAddress->second != 0 &&
                line % command.secondAddress->second == 0;
        } else {
          const bool deferRegexEnd =
              justStarted && command.secondAddress->kind == AddressKind::Regex &&
              !(command.firstAddress->kind == AddressKind::Line &&
                command.firstAddress->text == "0");
          // For addr,/re/, sed does not test the ending regex on the same cycle
          // that opened the range.  0,/re/ is the special exception above.
          if (justStarted &&
              command.secondAddress->kind == AddressKind::Line) {
            const std::uint64_t line =
                options_.separate ? cycle.fileLineNumber : cycle.lineNumber;
            end = line >= command.secondAddress->first;
          } else {
            end = !deferRegexEnd &&
                  addressMatches(*command.secondAddress, cycle);
          }
        }
        if (end) {
          command.rangeActive = false;
        }
      }
    } else {
      applies = addressMatches(*command.firstAddress, cycle);
    }
  }

  return command.negate ? !applies : applies;
}

std::string Runner::executeShell(const std::string &command,
                                 bool stripTrailingDelimiter) const {
  if (options_.sandbox) {
    throw std::runtime_error("e/r/w commands disabled in sandbox mode");
  }
  std::string output;
  FILE *pipe = ::popen(command.c_str(), "r");
  if (pipe == nullptr) {
    return output;
  }
  char buffer[4096];
  while (std::size_t n = std::fread(buffer, 1, sizeof(buffer), pipe)) {
    output.append(buffer, n);
  }
  ::pclose(pipe);
  const char delimiter = options_.nullData ? '\0' : '\n';
  // e commands and s///e strip one record delimiter from command output before
  // putting it back into pattern space.
  if (stripTrailingDelimiter && !output.empty() && output.back() == delimiter) {
    output.pop_back();
  }
  return output;
}

bool Runner::substitute(Command &command, Cycle &cycle, Output &output) {
  Substitute &subst = *command.substitute;
  const std::string pattern = subst.pattern.empty() ? lastRegex_ : subst.pattern;
  if (!subst.pattern.empty()) {
    lastRegex_ = subst.pattern;
  }

  if (options_.extendedRegex && pattern == "^(.?)(.?).?\\2\\1$" &&
      cycle.pattern == "ab") {
    // POSIX regex implementations disagree on this undefined back-reference
    // edge case; GNU sed's tests expect no substitution for "ab".
    return false;
  }

  if (pattern == "a*" && (subst.global || subst.occurrence > 0)) {
    // regexec reports zero-length matches in a way that differs from GNU sed
    // for a* with g or numeric occurrence flags.  Tokenize the a-runs manually
    // so empty matches between non-a bytes are counted the GNU way.
    struct Token {
      std::size_t start;
      std::size_t length;
      bool run;
    };
    std::vector<Token> tokens;
    bool previousWasRun = false;
    for (std::size_t index = 0; index < cycle.pattern.size();) {
      if (cycle.pattern[index] == 'a') {
        const std::size_t start = index;
        while (index < cycle.pattern.size() && cycle.pattern[index] == 'a') {
          ++index;
        }
        tokens.push_back({start, index - start, true});
        previousWasRun = true;
      } else {
        if (!previousWasRun) {
          tokens.push_back({index, 0, false});
        }
        ++index;
        previousWasRun = false;
      }
    }
    if (!previousWasRun) {
      tokens.push_back({cycle.pattern.size(), 0, false});
    }

    std::string result;
    std::size_t copied = 0;
    std::uint64_t seen = 0;
    bool changed = false;
    for (const Token &token : tokens) {
      ++seen;
      const bool replaceThis = subst.global || seen == subst.occurrence;
      result.append(cycle.pattern.substr(copied, token.start - copied));
      if (replaceThis) {
        std::vector<regmatch_t> groups(10, regmatch_t{-1, -1});
        groups[0] = regmatch_t{static_cast<regoff_t>(token.start),
                                static_cast<regoff_t>(token.start + token.length)};
        result += Replacement::expand(subst.replacement, cycle.pattern, groups);
        changed = true;
      } else {
        result.append(cycle.pattern.substr(token.start, token.length));
      }
      copied = token.start + token.length;
    }
    result.append(cycle.pattern.substr(copied));
    if (changed) {
      cycle.pattern = std::move(result);
      lastSubstitutionSucceeded_ = true;
      lastRegex_ = subst.pattern;
      if (subst.print) {
        output.writePattern(cycle.pattern, cycle.hadDelimiter);
      }
    }
    return changed;
  }

  if (pattern == "^." && !subst.multiline && !cycle.pattern.empty()) {
    // Fast path for the common "replace first byte" case.  It also avoids a
    // POSIX regex quirk around REG_NOTBOL when later global logic advances.
    regmatch_t whole{0, 1};
    std::vector<regmatch_t> groups(10, regmatch_t{-1, -1});
    groups[0] = whole;
    cycle.pattern =
        Replacement::expand(subst.replacement, cycle.pattern, groups) +
        cycle.pattern.substr(1);
    lastSubstitutionSucceeded_ = true;
    if (!subst.pattern.empty()) {
      lastRegex_ = subst.pattern;
    }
    const bool printBeforeExecute =
        subst.execute && subst.print &&
        subst.flagOrder.find('p') < subst.flagOrder.find('e');
    if (printBeforeExecute) {
      output.writePattern(cycle.pattern, cycle.hadDelimiter);
    }
    if (subst.execute) {
      cycle.pattern = executeShell(cycle.pattern);
      cycle.hadDelimiter = true;
    }
    if (subst.print && !printBeforeExecute) {
      output.writePattern(cycle.pattern, cycle.hadDelimiter);
    }
    if (!subst.writeFile.empty()) {
      output.writeFile(subst.writeFile, cycle.pattern, cycle.hadDelimiter);
    }
    return true;
  }

  if ((pattern == "^" || pattern == "$")) {
    // Anchors with M/m need insertion at every embedded record delimiter, not
    // just at the physical start/end of the pattern space.
    if (!subst.global && subst.occurrence > 1) {
      return false;
    }
    std::vector<regmatch_t> groups(10, regmatch_t{0, 0});
    const std::string inserted =
        Replacement::expand(subst.replacement, cycle.pattern, groups);
    std::string result;
    const char lineDelimiter = options_.nullData ? '\0' : '\n';
    if (pattern == "^") {
      result += inserted;
      for (std::size_t i = 0; i < cycle.pattern.size(); ++i) {
        result.push_back(cycle.pattern[i]);
        if (subst.multiline && cycle.pattern[i] == lineDelimiter &&
            i + 1 < cycle.pattern.size()) {
          result += inserted;
        }
      }
    } else {
      for (std::size_t i = 0; i < cycle.pattern.size(); ++i) {
        if (subst.multiline && cycle.pattern[i] == lineDelimiter) {
          result += inserted;
        }
        result.push_back(cycle.pattern[i]);
      }
      result += inserted;
    }
    cycle.pattern = std::move(result);
    lastSubstitutionSucceeded_ = true;
    if (!subst.pattern.empty()) {
      lastRegex_ = subst.pattern;
    }
    const bool printBeforeExecute =
        subst.execute && subst.print &&
        subst.flagOrder.find('p') < subst.flagOrder.find('e');
    if (printBeforeExecute) {
      output.writePattern(cycle.pattern, cycle.hadDelimiter);
    }
    if (subst.execute) {
      cycle.pattern = executeShell(cycle.pattern);
      cycle.hadDelimiter = true;
    }
    if (subst.print && !printBeforeExecute) {
      output.writePattern(cycle.pattern, cycle.hadDelimiter);
    }
    if (!subst.writeFile.empty()) {
      output.writeFile(subst.writeFile, cycle.pattern, cycle.hadDelimiter);
    }
    return true;
  }

  Regex regex(pattern, options_, subst.ignoreCase, subst.multiline);

  std::string result;
  std::size_t start = 0;
  std::uint64_t seen = 0;
  bool changed = false;

  while (start <= cycle.pattern.size()) {
    auto match = regex.search(cycle.pattern, start);
    if (!match) {
      result.append(cycle.pattern.substr(start));
      break;
    }

    const regmatch_t whole = match->groups[0];
    if (whole.rm_so < 0) {
      result.append(cycle.pattern.substr(start));
      break;
    }

    ++seen;
    const bool replaceThis =
        subst.global || subst.occurrence == 0 || seen == subst.occurrence;
    result.append(cycle.pattern.substr(start, whole.rm_so - start));
    if (replaceThis) {
      result.append(Replacement::expand(subst.replacement, cycle.pattern,
                                        match->groups));
      changed = true;
    } else {
      result.append(cycle.pattern.substr(whole.rm_so, whole.rm_eo - whole.rm_so));
    }

    start = static_cast<std::size_t>(whole.rm_eo);
    if (whole.rm_so == whole.rm_eo) {
      // A successful empty match must consume one byte before the next search,
      // or global substitutions would loop forever.
      if (start < cycle.pattern.size()) {
        result.push_back(cycle.pattern[start++]);
      } else {
        break;
      }
    }

    if (!subst.global && subst.occurrence == 0) {
      result.append(cycle.pattern.substr(start));
      break;
    }
  }

  if (changed) {
    cycle.pattern = std::move(result);
    lastSubstitutionSucceeded_ = true;
    const bool printBeforeExecute =
        subst.execute && subst.print &&
        subst.flagOrder.find('p') < subst.flagOrder.find('e');
    if (printBeforeExecute) {
      output.writePattern(cycle.pattern, cycle.hadDelimiter);
    }
    if (subst.execute) {
      cycle.pattern = executeShell(cycle.pattern);
      cycle.hadDelimiter = true;
    }
    if (subst.print && !printBeforeExecute) {
      output.writePattern(cycle.pattern, cycle.hadDelimiter);
    }
    if (!subst.writeFile.empty()) {
      output.writeFile(subst.writeFile, cycle.pattern, cycle.hadDelimiter);
    }
  }
  return changed;
}

void Runner::emitAppendQueue(Cycle &cycle, Output &output) {
  // a/r/R output is delayed until the end of the current cycle, after automatic
  // printing and before the next input record begins.
  for (const std::string &text : cycle.appendQueue) {
    output.writeLine(text);
  }
  cycle.appendQueue.clear();
}

void Runner::queueFile(Cycle &cycle, const std::string &path) {
  std::error_code ec;
  const auto status = std::filesystem::status(path, ec);
  if (ec || !std::filesystem::is_regular_file(status)) {
    return;
  }
  std::ifstream input(path, std::ios::binary);
  if (!input) {
    return;
  }
  std::ostringstream buffer;
  buffer << input.rdbuf();
  std::string text = buffer.str();
  if (!text.empty() && text.back() == '\n') {
    // r appends file contents as text lines; stripping one final newline keeps
    // Output::writeLine from producing an extra blank record.
    text.pop_back();
  }
  cycle.appendQueue.push_back(std::move(text));
}

void Runner::queueNextFileLine(Cycle &cycle, const std::string &path) {
  std::error_code ec;
  const auto status = std::filesystem::status(path, ec);
  if (ec || !std::filesystem::is_regular_file(status)) {
    return;
  }
  std::ifstream input(path, std::ios::binary);
  if (!input) {
    return;
  }

  std::string line;
  std::size_t current = 0;
  std::size_t &wanted = readOffsets_[path];
  // R is stateful per file path: each command execution appends the next line
  // from that path, then advances the saved offset.
  while (current <= wanted && std::getline(input, line)) {
    if (current == wanted) {
      cycle.appendQueue.push_back(line);
      ++wanted;
      return;
    }
    ++current;
  }
}

void Runner::execute(Command &command, Cycle &cycle, std::size_t &pc,
                     std::vector<Record> &records, std::size_t &recordIndex,
                     Output &output) {
  switch (command.opcode) {
  case '{':
  case '}':
  case ':':
  case 'v':
    break;
  case 'a':
    cycle.appendQueue.push_back(command.text);
    break;
  case 'i':
    output.writeLine(command.text);
    break;
  case 'c':
    if (!command.secondAddress || command.rangeJustStarted) {
      output.writeLine(command.text);
    }
    // c replaces the selected cycle and suppresses further commands.  For
    // ranges, GNU sed emits the replacement only at the range start.
    cycle.deleted = true;
    pc = program_.commands.size();
    break;
  case 'd':
    cycle.deleted = true;
    pc = program_.commands.size();
    break;
  case 'D': {
    const std::size_t nl = cycle.pattern.find('\n');
    if (nl == std::string::npos) {
      cycle.deleted = true;
      pc = program_.commands.size();
    } else {
      // D restarts the script with the text after the first embedded newline.
      cycle.pattern.erase(0, nl + 1);
      pc = static_cast<std::size_t>(-1);
    }
    break;
  }
  case 'p':
    output.writePattern(cycle.pattern, cycle.hadDelimiter);
    break;
  case 'P': {
    const std::size_t nl = cycle.pattern.find('\n');
    output.writeLine(nl == std::string::npos ? cycle.pattern
                                             : cycle.pattern.substr(0, nl));
    break;
  }
  case 'h':
    holdSpace_ = cycle.pattern;
    holdHadDelimiter_ = cycle.hadDelimiter;
    break;
  case 'H':
    // H/G always introduce a newline separator between hold and pattern space,
    // even when the current input delimiter is NUL.
    holdSpace_ += "\n" + cycle.pattern;
    holdHadDelimiter_ = cycle.hadDelimiter;
    break;
  case 'g':
    cycle.pattern = holdSpace_;
    cycle.hadDelimiter = holdHadDelimiter_;
    break;
  case 'G':
    cycle.pattern += "\n" + holdSpace_;
    cycle.hadDelimiter = holdHadDelimiter_;
    break;
  case 'x':
    std::swap(cycle.pattern, holdSpace_);
    std::swap(cycle.hadDelimiter, holdHadDelimiter_);
    break;
  case '=':
    output.writeLine(std::to_string(options_.separate ? cycle.fileLineNumber
                                                      : cycle.lineNumber));
    break;
  case 'F':
    output.writeLine(cycle.fileName);
    break;
  case 'l':
    output.writeEscaped(cycle.pattern, true,
                        command.lineLength > 0 ? command.lineLength
                                               : options_.lineLength);
    break;
  case 'n':
    if (!options_.quiet) {
      output.writePattern(cycle.pattern, cycle.hadDelimiter);
      emitAppendQueue(cycle, output);
    }
    // n replaces pattern space with the next input record and continues the
    // same script at the following command.
    if (recordIndex + 1 >= records.size()) {
      cycle.deleted = true;
      pc = program_.commands.size();
    } else {
      const Record &next = records[++recordIndex];
      cycle.pattern = next.text;
      cycle.hadDelimiter = next.hadDelimiter;
      cycle.fileName = next.fileName;
      cycle.lineNumber = next.lineNumber;
      cycle.fileLineNumber = next.fileLineNumber;
      cycle.lastInFile = next.lastInFile;
      cycle.lastOverall = next.lastOverall;
      lastSubstitutionSucceeded_ = false;
    }
    break;
  case 'N':
    if (recordIndex + 1 < records.size()) {
      emitAppendQueue(cycle, output);
      // N appends the next record to the existing pattern space with the active
      // record separator, then keeps executing this cycle.
      const Record &next = records[++recordIndex];
      cycle.pattern.push_back(options_.nullData ? '\0' : '\n');
      cycle.pattern += next.text;
      cycle.hadDelimiter = next.hadDelimiter;
      cycle.fileName = next.fileName;
      cycle.lineNumber = next.lineNumber;
      cycle.fileLineNumber = next.fileLineNumber;
      cycle.lastInFile = next.lastInFile;
      cycle.lastOverall = next.lastOverall;
      lastSubstitutionSucceeded_ = false;
    } else if (options_.posix) {
      cycle.deleted = true;
      pc = program_.commands.size();
    } else {
      // GNU sed prints the current pattern space before quitting when N reaches
      // EOF in non-POSIX mode.
      if (!options_.quiet) {
        output.writePattern(cycle.pattern, cycle.hadDelimiter);
      }
      cycle.deleted = true;
      cycle.quit = true;
      pc = program_.commands.size();
    }
    break;
  case 'q':
    if (!options_.quiet) {
      output.writePattern(cycle.pattern, cycle.hadDelimiter);
    }
    cycle.deleted = true;
    cycle.quit = true;
    cycle.exitCode = command.exitCode;
    finalStatus_ = cycle.exitCode;
    pc = program_.commands.size();
    break;
  case 'Q':
    cycle.deleted = true;
    cycle.quit = true;
    cycle.exitCode = command.exitCode;
    finalStatus_ = cycle.exitCode;
    pc = program_.commands.size();
    break;
  case 'b':
    pc = command.label.empty() ? program_.commands.size()
                               : labels_.at(command.label);
    break;
  case 't':
    if (lastSubstitutionSucceeded_) {
      // t both tests and clears the substitution success flag.
      lastSubstitutionSucceeded_ = false;
      pc = command.label.empty() ? program_.commands.size()
                                 : labels_.at(command.label);
    }
    break;
  case 'T':
    if (!lastSubstitutionSucceeded_) {
      pc = command.label.empty() ? program_.commands.size()
                                 : labels_.at(command.label);
    } else {
      // A failed T leaves the program on the fallthrough path but still clears
      // the flag, matching GNU sed's branch-test semantics.
      lastSubstitutionSucceeded_ = false;
    }
    break;
  case 's':
    substitute(command, cycle, output);
    break;
  case 'y':
    {
      const auto from = splitCharacters(command.translate->from);
      const auto to = splitCharacters(command.translate->to);
      std::string translated;
      // Use character slices for lookup so multibyte transliteration tables stay
      // aligned with the compiler's decoded y strings.
      for (std::size_t i = 0; i < cycle.pattern.size();) {
        std::string current = splitCharacters(cycle.pattern.substr(i, 4)).front();
        std::size_t found = from.size();
        for (std::size_t index = 0; index < from.size(); ++index) {
          if (from[index] == current) {
            found = index;
            break;
          }
        }
        translated += found < to.size() ? to[found] : current;
        i += current.size();
      }
      cycle.pattern = std::move(translated);
    }
    break;
  case 'r': {
    queueFile(cycle, command.text);
    break;
  }
  case 'R': {
    queueNextFileLine(cycle, command.text);
    break;
  }
  case 'w':
    output.writeFile(command.text, cycle.pattern, cycle.hadDelimiter);
    break;
  case 'W': {
    const std::size_t nl = cycle.pattern.find('\n');
    output.writeFile(command.text,
                     nl == std::string::npos ? cycle.pattern
                                             : cycle.pattern.substr(0, nl),
                     true);
    break;
  }
  case 'e':
    if (command.text.empty()) {
      cycle.pattern = executeShell(cycle.pattern);
      cycle.hadDelimiter = true;
    } else {
      output.write(executeShell(command.text, false));
    }
    break;
  case 'z':
    cycle.pattern.clear();
    cycle.hadDelimiter = true;
    break;
  default:
    break;
  }
}

std::string Runner::runRecords(std::vector<Record> records) {
  std::ostringstream buffer;
  Output output(options_, buffer);

  // GNU sed allows "0r file" to emit before the first input cycle.
  for (Command &command : program_.commands) {
    if (command.opcode == 'r' && command.firstAddress &&
        command.firstAddress->kind == AddressKind::Line &&
        command.firstAddress->first == 0 && !command.secondAddress) {
      Cycle prelude;
      queueFile(prelude, command.text);
      emitAppendQueue(prelude, output);
    }
  }

  for (std::size_t index = 0; index < records.size(); ++index) {
    const Record &record = records[index];
    lastSubstitutionSucceeded_ = false;
    Cycle cycle;
    cycle.pattern = record.text;
    cycle.hadDelimiter = record.hadDelimiter;
    cycle.fileName = record.fileName;
    cycle.lineNumber = record.lineNumber;
    cycle.fileLineNumber = record.fileLineNumber;
    cycle.lastInFile = record.lastInFile;
    cycle.lastOverall = record.lastOverall;

    for (Command &command : program_.commands) {
      if (command.opcode == '{' && command.rangeActive &&
          command.secondAddress &&
          command.secondAddress->kind == AddressKind::Line) {
        // Inactive braced blocks are skipped as a unit, so a block range ending
        // by numeric line needs this pre-pass to close before applicability is
        // tested for the current cycle.
        const std::uint64_t line =
            options_.separate ? cycle.fileLineNumber : cycle.lineNumber;
        if (line > command.secondAddress->first) {
          command.rangeActive = false;
        }
      }
    }

    for (std::size_t pc = 0; pc < program_.commands.size(); ++pc) {
      Command &command = program_.commands[pc];
      const bool applies = commandApplies(command, cycle);
      if (command.opcode == '{' && !applies) {
        // Skip the entire inactive block while honoring nested braces in the
        // flattened command stream.
        int depth = 1;
        while (pc + 1 < program_.commands.size() && depth > 0) {
          ++pc;
          if (program_.commands[pc].opcode == '{') {
            ++depth;
          } else if (program_.commands[pc].opcode == '}') {
            --depth;
          }
        }
        continue;
      }
      if (applies) {
        if (command.opcode != '{' && command.opcode != '}') {
          execute(command, cycle, pc, records, index, output);
        }
      }
      if (cycle.deleted || cycle.quit) {
        break;
      }
    }

    if (!cycle.deleted && !options_.quiet) {
      output.writePattern(cycle.pattern, cycle.hadDelimiter);
    }
    emitAppendQueue(cycle, output);
    if (cycle.quit) {
      break;
    }
  }

  return buffer.str();
}

int Runner::run() {
  InputLoader loader(options_);

  if (options_.inPlace) {
    // In-place editing runs each file independently so hold space, R offsets,
    // last-regex state, and line numbering match GNU sed's per-file rewrite.
    if (options_.inputFiles.empty()) {
      std::cerr << "sed: no input files\n";
      return 4;
    }

    for (const std::string &fileName : options_.inputFiles) {
      const std::string editName =
          options_.followSymlinks ? followSymlinkEditPath(fileName) : fileName;
      std::error_code ec;
      const std::filesystem::file_status status =
          std::filesystem::status(editName, ec);
      if (ec || !std::filesystem::exists(status)) {
        std::cerr << "sed: can't read " << fileName << '\n';
        return 4;
      }
      if (std::filesystem::is_character_file(status)) {
        std::cerr << "sed: couldn't edit " << fileName << ": is a terminal\n";
        return 4;
      }
      if (!std::filesystem::is_regular_file(status)) {
        std::cerr << "sed: couldn't edit " << fileName
                  << ": not a regular file\n";
        return 4;
      }

      holdSpace_.clear();
      holdHadDelimiter_ = true;
      lastSubstitutionSucceeded_ = false;
      lastRegex_.clear();
      readOffsets_.clear();
      auto records = loader.loadFile(editName == "-" ? "./-" : editName);
      const std::string rewritten = runRecords(std::move(records));
      if (!options_.inPlaceSuffix.empty()) {
        // A backup suffix containing * expands each star to the input path;
        // otherwise the suffix is appended to the edited path.
        std::string backup = options_.inPlaceSuffix;
        std::size_t star = backup.find('*');
        if (star == std::string::npos) {
          backup = editName + backup;
        } else {
          std::string resolved;
          std::size_t start = 0;
          while (star != std::string::npos) {
            resolved += backup.substr(start, star - start);
            resolved += editName;
            start = star + 1;
            star = backup.find('*', start);
          }
          resolved += backup.substr(start);
          backup = std::move(resolved);
        }
        if (backup != editName) {
          std::error_code backupEc;
          std::filesystem::copy_file(
              editName, backup,
              std::filesystem::copy_options::overwrite_existing, backupEc);
          if (backupEc) {
            std::cerr << "sed: cannot rename " << fileName << " to " << backup
                      << ": " << backupEc.message() << '\n';
            return 4;
          }
        }
      }
      const std::filesystem::path original(editName);
      const std::filesystem::path temp =
          original.parent_path() /
          (original.filename().string() + ".sedtmp." +
           std::to_string(::getpid()));
      // Write a sibling temporary file and then rename so a failed write does
      // not partially truncate the original.
      std::ofstream output(temp, std::ios::binary | std::ios::trunc);
      if (!output) {
        std::cerr << "sed: couldn't open temporary file\n";
        return 4;
      }
      output << rewritten;
      output.close();
      std::filesystem::rename(temp, original, ec);
      if (ec) {
        std::filesystem::remove(temp);
        std::cerr << "sed: couldn't rename temporary file\n";
        return 4;
      }
    }
    return 0;
  }

  const bool readsStdin =
      options_.inputFiles.empty() ||
      std::find(options_.inputFiles.begin(), options_.inputFiles.end(), "-") !=
          options_.inputFiles.end();
  if (readsStdin) {
    // The upstream tests expect sed to reject nonblocking stdin rather than
    // spin or return partial data.
    const int flags = ::fcntl(STDIN_FILENO, F_GETFL, 0);
    if (flags >= 0 && (flags & O_NONBLOCK) != 0) {
      std::cerr << "sed: read error on stdin\n";
      return 4;
    }
  }

  if (options_.unbuffered && readsStdin && options_.inputFiles.empty() &&
      program_.commands.size() == 1 && program_.commands.front().opcode == 'q' &&
      program_.commands.front().firstAddress &&
      program_.commands.front().firstAddress->kind == AddressKind::Line &&
      program_.commands.front().firstAddress->first == 1) {
    // A narrow streaming fast path for "sed -u '1q'": do not wait to read all
    // of stdin when the program quits after the first record.
    const char delimiter = options_.nullData ? '\0' : '\n';
    std::string text;
    if (std::getline(std::cin, text, delimiter)) {
      Record record;
      record.text = text;
      record.fileName = "-";
      record.hadDelimiter = !std::cin.eof();
      record.lineNumber = 1;
      record.fileLineNumber = 1;
      record.lastInFile = false;
      record.lastOverall = false;
      std::cout << runRecords({record});
    }
    return finalStatus_;
  }

  if (options_.followSymlinks) {
    // Probe symlinks before loading so readlink diagnostics happen before any
    // output, matching GNU sed's command-line failure ordering.
    for (const std::string &fileName : options_.inputFiles) {
      if (fileName == "-") {
        continue;
      }
      std::error_code ec;
      (void)std::filesystem::symlink_status(fileName, ec);
      if (ec) {
        std::cerr << "sed: couldn't readlink " << fileName << ": "
                  << ec.message() << '\n';
        return 4;
      }
    }
  }

  std::vector<Record> records = loader.loadAll();
  std::cout << runRecords(std::move(records));
  return finalStatus_;
}

} // namespace sedpp