#include "MessageHeaders.h"
#include <algorithm>
#include <cctype>

namespace mail {

   void splitMessage(const std::string &message, std::string &headerBlock, std::string &bodyBlock) {
      size_t split = message.find("\r\n\r\n");
      size_t skip = 4;
      if (split == std::string::npos) {
         split = message.find("\n\n");
         skip = 2;
      }
      if (split == std::string::npos) {
         headerBlock = message;
         bodyBlock = "";
      } else {
         headerBlock = message.substr(0, split);
         bodyBlock = message.substr(split + skip);
      }
   }

   std::vector<std::pair<std::string, std::string>> parseHeaderLines(const std::string &headerBlock) {
      std::vector<std::string> lines;
      size_t pos = 0;
      while (pos <= headerBlock.size()) {
         size_t next = headerBlock.find("\r\n", pos);
         size_t lineEnd = (next == std::string::npos) ? headerBlock.size() : next;
         lines.push_back(headerBlock.substr(pos, lineEnd - pos));
         if (next == std::string::npos)
            break;
         pos = next + 2;
      }

      std::vector<std::pair<std::string, std::string>> headers;
      for (const std::string &line : lines) {
         if (line.empty())
            continue;
         if ((line[0] == ' ' || line[0] == '\t') && !headers.empty()) {
            std::string continuation = line;
            size_t start = continuation.find_first_not_of(" \t");
            headers.back().second += " ";
            headers.back().second += (start == std::string::npos) ? "" : continuation.substr(start);
            continue;
         }
         size_t colon = line.find(':');
         if (colon == std::string::npos)
            continue;
         std::string name = line.substr(0, colon);
         std::string value = line.substr(colon + 1);
         size_t start = value.find_first_not_of(" \t");
         value = (start == std::string::npos) ? "" : value.substr(start);
         headers.push_back({name, value});
      }
      return headers;
   }

   std::string getHeader(const std::vector<std::pair<std::string, std::string>> &headers, const std::string &name) {
      for (const auto &header : headers) {
         if (header.first.size() != name.size())
            continue;
         bool match = true;
         for (size_t i = 0; i < name.size(); ++i)
            if (std::toupper((unsigned char)header.first[i]) != std::toupper((unsigned char)name[i])) {
               match = false;
               break;
            }
         if (match)
            return header.second;
      }
      return "";
   }

   namespace {

      std::string trim(const std::string &s) {
         size_t start = s.find_first_not_of(" \t\r\n");
         size_t end = s.find_last_not_of(" \t\r\n");
         if (start == std::string::npos)
            return "";
         return s.substr(start, end - start + 1);
      }

      std::string stripQuotes(const std::string &s) {
         std::string value = trim(s);
         if (value.size() >= 2 && value.front() == '"' && value.back() == '"')
            return value.substr(1, value.size() - 2);
         return value;
      }

      Address parseOneAddress(const std::string &text) {
         Address address;
         size_t lt = text.find('<');
         size_t gt = text.find('>');
         std::string addrPart;
         if (lt != std::string::npos && gt != std::string::npos && gt > lt) {
            address.name = stripQuotes(trim(text.substr(0, lt)));
            addrPart = text.substr(lt + 1, gt - lt - 1);
         } else {
            addrPart = text;
         }
         addrPart = trim(addrPart);
         size_t at = addrPart.find_last_of('@');
         if (at == std::string::npos) {
            address.mailbox = addrPart;
         } else {
            address.mailbox = addrPart.substr(0, at);
            address.host = addrPart.substr(at + 1);
         }
         return address;
      }

   }

   std::vector<Address> parseAddressList(const std::string &headerValue) {
      std::vector<Address> addresses;
      std::string current;
      bool inQuotes = false;
      int angleDepth = 0;
      for (char c : headerValue) {
         if (c == '"')
            inQuotes = !inQuotes;
         else if (!inQuotes && c == '<')
            ++angleDepth;
         else if (!inQuotes && c == '>' && angleDepth > 0)
            --angleDepth;
         if (c == ',' && !inQuotes && angleDepth == 0) {
            std::string piece = trim(current);
            if (!piece.empty())
               addresses.push_back(parseOneAddress(piece));
            current.clear();
            continue;
         }
         current += c;
      }
      std::string piece = trim(current);
      if (!piece.empty())
         addresses.push_back(parseOneAddress(piece));
      return addresses;
   }

   std::string imapQuoteOrNil(const std::string &value) {
      if (value.empty())
         return "NIL";
      std::string escaped;
      escaped.reserve(value.size() + 2);
      escaped += '"';
      for (char c : value) {
         if (c == '"' || c == '\\')
            escaped += '\\';
         if (c == '\r' || c == '\n')
            continue;
         escaped += c;
      }
      escaped += '"';
      return escaped;
   }

   namespace {

      std::string addressListToEnvelope(const std::vector<Address> &addresses) {
         if (addresses.empty())
            return "NIL";
         std::string result = "(";
         for (const Address &address : addresses) {
            result += "(" + imapQuoteOrNil(address.name) + " NIL " +
                      imapQuoteOrNil(address.mailbox) + " " + imapQuoteOrNil(address.host) + ")";
         }
         result += ")";
         return result;
      }

   }

   std::string buildEnvelope(const std::string &message) {
      std::string headerBlock, bodyBlock;
      splitMessage(message, headerBlock, bodyBlock);
      auto headers = parseHeaderLines(headerBlock);

      std::string date = getHeader(headers, "Date");
      std::string subject = getHeader(headers, "Subject");
      std::vector<Address> from = parseAddressList(getHeader(headers, "From"));
      std::string senderHeader = getHeader(headers, "Sender");
      std::vector<Address> sender = senderHeader.empty() ? from : parseAddressList(senderHeader);
      std::string replyToHeader = getHeader(headers, "Reply-To");
      std::vector<Address> replyTo = replyToHeader.empty() ? from : parseAddressList(replyToHeader);
      std::vector<Address> to = parseAddressList(getHeader(headers, "To"));
      std::vector<Address> cc = parseAddressList(getHeader(headers, "Cc"));
      std::vector<Address> bcc = parseAddressList(getHeader(headers, "Bcc"));
      std::string inReplyTo = getHeader(headers, "In-Reply-To");
      std::string messageId = getHeader(headers, "Message-ID");

      std::string envelope = "(";
      envelope += imapQuoteOrNil(date) + " ";
      envelope += imapQuoteOrNil(subject) + " ";
      envelope += addressListToEnvelope(from) + " ";
      envelope += addressListToEnvelope(sender) + " ";
      envelope += addressListToEnvelope(replyTo) + " ";
      envelope += addressListToEnvelope(to) + " ";
      envelope += addressListToEnvelope(cc) + " ";
      envelope += addressListToEnvelope(bcc) + " ";
      envelope += imapQuoteOrNil(inReplyTo) + " ";
      envelope += imapQuoteOrNil(messageId);
      envelope += ")";
      return envelope;
   }

}