#include "sedpp/Input.h"

#include <fstream>
#include <filesystem>
#include <iostream>
#include <sstream>
#include <stdexcept>

namespace sedpp {
namespace {

// Used for --follow-symlinks display names.  This follows the same bounded walk
// as in-place editing but leaves actual reading to the caller.
std::string followSymlinkName(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

InputLoader::InputLoader(const Options &options) : options_(options) {}

std::vector<Record> InputLoader::splitBuffer(const std::string &buffer,
                                             const std::string &fileName,
                                             std::uint64_t &globalLine) const {
  std::vector<Record> records;
  const char delimiter = options_.nullData ? '\0' : '\n';
  std::uint64_t fileLine = 0;

  // Split manually instead of using getline so NUL-delimited mode and missing
  // final delimiters are represented exactly.
  std::size_t start = 0;
  while (start < buffer.size()) {
    const std::size_t end = buffer.find(delimiter, start);
    Record record;
    record.text = buffer.substr(start, end == std::string::npos
                                           ? std::string::npos
                                           : end - start);
    record.hadDelimiter = end != std::string::npos;
    record.fileName = fileName.empty() ? "-" : fileName;
    record.lineNumber = ++globalLine;
    record.fileLineNumber = ++fileLine;
    records.push_back(std::move(record));
    if (end == std::string::npos) {
      break;
    }
    start = end + 1;
  }

  if (buffer.empty()) {
    // Empty files produce no sed cycles.
    return records;
  }

  if (!records.empty()) {
    // $ in --separate mode needs to know the final record in each file.
    records.back().lastInFile = true;
  }
  return records;
}

std::vector<Record> InputLoader::loadFile(const std::string &fileName) const {
  std::uint64_t globalLine = 0;
  if (fileName == "-") {
    // In single-file loading, stdin is treated as the whole input stream.
    std::ostringstream buffer;
    buffer << std::cin.rdbuf();
    auto records = splitBuffer(buffer.str(), "-", globalLine);
    if (!records.empty()) {
      records.back().lastOverall = true;
    }
    return records;
  }

  const std::string displayName =
      options_.followSymlinks ? followSymlinkName(fileName) : fileName;
  // Open the original argument even when --follow-symlinks is set; the resolved
  // name is for diagnostics/F command output, not for changing read semantics.
  std::ifstream input(fileName, std::ios::binary);
  if (!input) {
    throw std::runtime_error("can't read " + fileName);
  }
  std::ostringstream buffer;
  buffer << input.rdbuf();
  auto records = splitBuffer(buffer.str(), displayName, globalLine);
  if (!records.empty()) {
    records.back().lastOverall = true;
  }
  return records;
}

std::vector<Record> InputLoader::loadAll() const {
  std::vector<Record> all;
  std::uint64_t globalLine = 0;
  const std::vector<std::string> files =
      options_.inputFiles.empty() ? std::vector<std::string>{"-"}
                                  : options_.inputFiles;

  for (const std::string &fileName : files) {
    std::vector<Record> records;
    if (fileName == "-") {
      // GNU sed consumes stdin at the point "-" appears among input files.
      std::ostringstream buffer;
      buffer << std::cin.rdbuf();
      records = splitBuffer(buffer.str(), "-", globalLine);
    } else {
      const std::string displayName =
          options_.followSymlinks ? followSymlinkName(fileName) : fileName;
      std::ifstream input(fileName, std::ios::binary);
      if (!input) {
        throw std::runtime_error("can't read " + fileName);
      }
      std::ostringstream buffer;
      buffer << input.rdbuf();
      records = splitBuffer(buffer.str(), displayName, globalLine);
    }
    all.insert(all.end(), records.begin(), records.end());
  }

  if (!all.empty()) {
    // $ without --separate is only true for the final record of the combined
    // input stream.
    all.back().lastOverall = true;
  }
  return all;
}

} // namespace sedpp