#include "Negotiate.hpp"

#include <cctype>

namespace molo::example::fw {

namespace {

std::string trim(std::string s) {
  while (!s.empty() && (s.front() == ' ' || s.front() == '\t')) s.erase(s.begin());
  while (!s.empty() && (s.back() == ' ' || s.back() == '\t')) s.pop_back();
  return s;
}

}  // namespace

std::string negotiate(const std::string& accept,
                      const std::vector<std::string>& available) {
  if (available.empty()) throw HttpError(500, "no_offers", "no offers");
  if (accept.empty()) return available.front();
  struct Range {
    std::string type;
    double q = 1.0;
  };
  std::vector<Range> ranges;
  std::size_t start = 0;
  while (start < accept.size()) {
    std::size_t comma = accept.find(',', start);
    if (comma == std::string::npos) comma = accept.size();
    std::string part = trim(accept.substr(start, comma - start));
    std::size_t semi = part.find(';');
    Range r{trim(part.substr(0, semi)), 1.0};
    if (semi != std::string::npos) {
      std::string params = part.substr(semi + 1);
      std::size_t q = params.find("q=");
      if (q != std::string::npos) {
        try {
          r.q = std::stod(params.substr(q + 2));
        } catch (...) {
          r.q = 1.0;
        }
      }
    }
    ranges.push_back(r);
    start = comma + 1;
  }
  std::string best;
  double best_q = -1.0;
  for (const auto& a : available) {
    for (const auto& r : ranges) {
      bool hit = r.type == "*/*" || r.type == a;
      if (!hit) {
        std::size_t slash = a.find('/');
        std::string wild = slash == std::string::npos
                               ? "*/*"
                               : a.substr(0, slash) + "/*";
        hit = r.type == wild;
      }
      if (hit && r.q > best_q) {
        best_q = r.q;
        best = a;
      }
    }
  }
  if (best.empty() || best_q <= 0.0)
    throw HttpError(406, "not_acceptable", "no acceptable format");
  return best;
}

}  // namespace molo::example::fw