// vim: set ts=2 sw=2 et tw=80:

#include <cctype>
#include <arpa/inet.h>
#include <Magick++.h>
#include <sys/types.h>
#include <cstdint>
#include <sys/socket.h>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <unistd.h>
#include <pthread.h>
#include <iostream>
#include <map>
#include <vector>
#include <curl/curl.h>
#include <netdb.h>

using namespace std;

#define MAX_CLIENTS 128
#define BUFFER 8192

void* request_thread(void*);

// Do not kill process when socket connection is broken. Error is already
// handled
static void broken_pipe(int signo) {}

int sock_conn_d;

// Close socket when shutting down
static void sigint(int signo) {
  close(sock_conn_d);
  exit(0);
}

int main(int argc, char** argv) {
  signal(SIGPIPE, broken_pipe);
  Magick::InitializeMagick(*argv);

  if(argc < 3) {
    fprintf(stderr, "Give port and image_rotation\n");
    exit(255);
  }

  int sock_data_d;
  struct sockaddr_in server;

  if((sock_conn_d = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
    perror("server socket not created");
    exit(1);
  }

  memset(&server, 0, sizeof(server)); // zero the memory

  server.sin_family = AF_INET;
  server.sin_addr.s_addr = inet_addr("0.0.0.0");
  server.sin_port = htons(atoi(argv[1]));

  int reusePort = 1;
  setsockopt(sock_conn_d, SOL_SOCKET, SO_REUSEPORT, &reusePort,
      sizeof(reusePort));

  if(::bind(sock_conn_d, (struct sockaddr*)&server, sizeof(server)) == -1) {
    perror("server socket not bound");
    exit(2);
  }

  while(true) {
    if(listen(sock_conn_d, MAX_CLIENTS) != 0) {
      perror("cannot listen on socket");
      close(sock_conn_d);
      exit(3);
    }

    printf("listening...\n");

    struct sockaddr_in client;
    socklen_t client_len = sizeof(client);
    sock_data_d = accept(sock_conn_d, (struct sockaddr*)&client, &client_len);

    if(sock_data_d == -1) {
      perror("cannot accept client");
      close(sock_conn_d);
      exit(4);
    }

    int* fd = (int*) malloc(sizeof(int));
    if (!fd) {
      perror("thread creation failed");
      exit(1);
    }

    *fd = sock_data_d;

    pthread_t req;
    pthread_create(&req, NULL, request_thread, (void*) fd);
  }
}

bool empty_line(FILE* in) {
  char a = fgetc(in), b = fgetc(in);
  if (a == '\r' && b == '\n') {
    return true;
  } else {
    ungetc(b, in);
    ungetc(a, in);
    return false;
  }
}

bool parse_headers(FILE* in, map<string, string>& headers) {
  while(true) {
    // probe first two chars to see if body will start
    if (empty_line(in)) {
      break;
    }

    string header_name;
    char c;

    while((c = fgetc(in)) != ':') {
      if (c == EOF || c == '\r' || c == '\n' || !isascii(c)) {
        return false;
      } else {
        header_name += c;
      }
    }

    do {
      c = fgetc(in);
    } while(isspace(c) && c != '\n' && c != '\r');

    ungetc(c, in);

    string value = "";
    do {
      c = fgetc(in);
      value += c;
    } while(c != '\r');
    value.pop_back();
    fgetc(in); // \n

    headers[header_name] = value;
    cout << header_name << ": " << value << endl;
  }

  return true;
}

bool has_body(char* method) {
  return !strcmp(method, "POST") || !strcmp(method, "PUT");
}

bool is_chunk_start(char* buf) {
  char* i;
  for (i = buf; isdigit(*i); i++);
  if (*i != '\r') return false;
  i++;
  if (*i != '\n') return false;
  i++;
  return *i == '\0';
}

bool fetch_body(FILE* in, vector<uint8_t>& body,
    const map<string, string> headers) {
  bool chunked;
  size_t length, r = 0;

  auto p = headers.find("Content-Length");
  chunked = p == headers.end();

  if (!chunked) {
    length = atol(p->second.c_str());
  } else {
    auto q = headers.find("Transfer-Encoding");
    if (q == headers.end() || q->second != "chunked") {
      return false;
    }
  }

  if (!chunked) {
    // read Content-Length bytes
    uint8_t buf[8192];
    const size_t n = atol(p->second.c_str());
    for(size_t w = 0; w < n;) {
      ssize_t r = fread(buf, 1, (n - w) > 8192 ? 8192 : (n - w), in);
      if (r == -1) return false;
      body.insert(end(body), begin(buf), end(buf));
      w += r;
    }
  } else {
    // This was implemented before Prof. Carzaniga said chunked encoding is not
    // required. I am leaving this just because it is already done.
    // Read chunks and search for final chunk 0\r\n\r\n
    char buf[8193];
    bool chunk_start = true;

    while (true) {
      fgets(buf, 8193, in);

      if (!strcmp(buf, "0\r\n") && chunk_start) {
        break;
      }

      if (chunk_start && is_chunk_start(buf)) {
        continue;
      }

      body.insert(end(body), begin(buf), end(buf));
      body.pop_back();

      char b = body.back();
      body.pop_back();
      char a = body.back();
      body.pop_back();
      if (a != '\r' || b != '\n') {
        body.push_back(a);
        body.push_back(b);
      }

      size_t len = strlen(buf);
      chunk_start = len > 2 && buf[len-2] == '\r' && buf[len-1] == '\n';
    }

    body.insert(end(body), begin(buf), end(buf));
    body.push_back(fgetc(in)); // \r
    body.push_back(fgetc(in)); // \n
  }

  return true;
}

void send_error(FILE* in, FILE* out, const char* protocol, const int status,
    const string message) {
  const char* msg = message.c_str();

  fprintf(out, "%s %d %s\r\n", protocol, status, msg);
  fprintf(out, "Content-Type: text/html; charset=utf-8\r\n");
  fprintf(out, "Connection: close\r\n");

  cerr << status << ' ' << msg << endl;

  char message_buf[4096];
  message_buf[4095] = '\0';
  snprintf(message_buf, 4095, "<!DOCTYPE html>\n"
      "<html>\n"
      "  <head>\n"
      "    <meta charset=\"utf-8\"/>\n"
      "    <title>%s</title>\n"
      "  </head>\n"
      "  <body>\n"
      "    <h1>%s</h1>\n"
      "  </body>\n"
      "</html>\n", msg, msg);

  fprintf(out, "Content-Length: %lu\r\n\r\n", strlen(message_buf));
  fprintf(out, "%s", message_buf);

  fclose(in);
  fflush(out);
  fclose(out);
  pthread_exit(NULL);
}

bool set_curl_method(CURL* c, const char* method) {
  if (!strcmp(method, "GET")) {
    curl_easy_setopt(c, CURLOPT_HTTPGET, 1);
  } else if (!strcmp(method, "HEAD")) {
    curl_easy_setopt(c, CURLOPT_HTTPGET, 1);
    curl_easy_setopt(c, CURLOPT_NOBODY, 1);
  } else if (!strcmp(method, "POST")) {
    curl_easy_setopt(c, CURLOPT_POST, 1);
  } else if (!strcmp(method, "PUT")) {
    curl_easy_setopt(c, CURLOPT_PUT, 1);
  } else if (!strcmp(method, "DELETE")) {
    curl_easy_setopt(c, CURLOPT_CUSTOMREQUEST, "DELETE");
  } else {
    //TODO: implement CONNECT method
    return false;
  }

  return true;
}

struct buffer {
  size_t size;
  uint8_t* data;
};

void buffer_init(struct buffer* self) {
  self->size = 0;
  self->data = (uint8_t*) malloc(8192);
  if (self->data) {
    self->data[0] = 0;
  }
}

size_t write_buffer(void *ptr, size_t size, size_t nmemb,
    struct buffer* rbody) {
  size_t index = rbody->size;
  size_t n = size * nmemb;

  rbody->size += n;

  uint8_t* newdata = (uint8_t*) realloc(rbody->data, rbody->size + 1);

  if (!newdata) {
    perror("reallocation of body buffer failed");
    if (rbody->data) free(rbody->data);
    rbody->data = NULL;
    return 0;
  } else {
    rbody->data = newdata;
  }

  memcpy((rbody->data + index), ptr, n);
  rbody->data[rbody->size] = '\0';

  cout << "copy " << n << " size " << rbody->size << endl;

  return size * nmemb;
}

// Converts url in a zero-terminated string for the host name. Port is retured
// as integer, -1 on error
int find_host_port(char* url) {
  char* i = url;
  size_t c = 0;

  while (*i != ':' && *i != '\0') {
    if (c >= 256 || (!isalnum(*i) && *i != '-' && *i != '.')) return -1;
    i++;
    c++;
  }

  if (c == 0) return -1;

  *i = '\0';
  i++;
  if (*i == '\0') return 80;

  unsigned p;
  if (sscanf(i, "%5u", &p) == 1) {
    return p < 65536 ? p : 80;
  } else {
    return 80;
  }
}

struct forward {
  int in;
  int out;
};


bool total_write(uint8_t* data, size_t n, int out) {
  for(size_t w = 0; w < n;) {
    ssize_t written = write(out, data + w, n - w);
    if (written == -1) {
      return false;
    }
    w += written;
  }
  return true;
}

void* forwarder_thread(void* data) {
  struct forward* f = (struct forward*) data;
  const size_t BUF_SIZE = 65536;

  uint8_t buffer[BUF_SIZE];
  while (true) {
    size_t r = read(f->in, buffer, BUF_SIZE);

    if (r == 0) {
      break;
    }

    if (!total_write(buffer, r, f->out)) {
      cout << "Closing CONNECT forwaredr" << endl;
      return NULL;
    }
  }

  return NULL;
}

void handle_connect(FILE* in, FILE* out, const char* protocol, char* url,
    const int fd) {
  int port;
  if ((port = find_host_port(url)) == -1) {
    send_error(in, out, protocol, 500, "Hostname parse error");
  }

  int socketfd = socket(AF_INET, SOCK_STREAM, 0);
  if (socketfd == -1) {
    send_error(in, out, protocol, 500, "TCP socket connection error");
  }

  struct hostent *he = gethostbyname(url);
  if (!he) {
    send_error(in, out, protocol, 404, "Unknown host");
  }

  struct sockaddr_in locale;
  memset (&locale, 0, sizeof(struct sockaddr_in));

  locale.sin_family =	AF_INET;
  locale.sin_addr.s_addr	=	htonl(INADDR_ANY);
  locale.sin_port =	htons(0);

  if (::bind(socketfd, (struct sockaddr*) &locale, sizeof(locale)) == -1) {
    send_error(in, out, protocol, 500, "TCP socket connection error");
  }

  struct sockaddr_in remote;
  memset (&remote, 0, sizeof(struct sockaddr_in));

  remote.sin_family = he->h_addrtype;
  memmove(&remote.sin_addr, he->h_addr, he->h_length);
  remote.sin_port = htons((uint16_t) port);

  if (connect(socketfd, (struct sockaddr*) &remote, sizeof(remote)) == -1) {
    send_error(in, out, protocol, 500, "TCP socket connection error");
  }

  struct forward from = { .in = fd, .out = socketfd },
                 to = { .in = socketfd, .out = fd };


  fprintf(out, "%s %d %s\r\n\r\n", protocol, 200, "Connection established");
  fflush(out);

  cout << "Connection established" << endl;

  pthread_t ffrom;
  pthread_create(&ffrom, NULL, forwarder_thread, &from);

  forwarder_thread(&to);

  pthread_join(ffrom, NULL);
}

struct read_buffer {
  const vector<uint8_t>& body;
  size_t index;
};

static size_t read_buffer(void *dest, size_t size, size_t nmemb, void *userp)
{
  struct read_buffer *wt = (struct read_buffer*) userp;
  size_t buffer_size = size * nmemb;
  size_t remaining = wt->body.size() - wt->index;

  if (buffer_size == wt->body.size()) {
    return 0;
  }

  size_t chunk_len = remaining > buffer_size ? buffer_size : remaining;
  auto start = wt->body.begin() + wt->index;

  copy(start, start + chunk_len, (uint8_t*) dest);
  wt->index += chunk_len;
  return chunk_len;
}

void* request_thread(void* data) {
  int fd = *((int*) data);
  FILE* in = fdopen(dup(*((int*) data)), "r");
  FILE* out = fdopen(dup(*((int*) data)), "w");
  free(data);

  while (true) {

    char method[10];
    char url[8000];
    char protocol[10];
    map<string, string> headers;
    vector<uint8_t> body;

    if (fscanf(in, "%10s %8000s %10s\r\n", method, url, protocol) < 3) {
      send_error(in, out, protocol, 400, "Bad request line");
    }

    cout << "METHOD: " << method << " URL: " << url << " PROTOCOL: " << protocol
      << endl;

    if (!parse_headers(in, headers)) {
      send_error(in, out, protocol, 400, "Malformed header");
    }

    if (strncmp(url, "http", 4) && strcmp(method, "CONNECT")) {
      send_error(in, out, protocol, 400, "Request line must contain absolute"
          " URL (this is a proxy)");
    }

    cout << "BODY: " << endl;

    // check if Content-Length is present and read Content-Length bytes
    // check if Transfer-Encoding: chunked is present and wait for \r\n on a
    // line

    if (has_body(method)) {
      if (!fetch_body(in, body, headers)) {
        send_error(in, out, protocol, 411,
            "No Content-Length or Transfer-Encoding");
      }
    }

    cout << "PARSED" << endl;

    if (!strcmp(method, "CONNECT")) {
      handle_connect(in, out, protocol, url, fd);
      break;
    } else {
      struct buffer rhead;
      struct buffer rbody;
      buffer_init(&rhead);
      buffer_init(&rbody);

      if(!rhead.data || !rbody.data) {
        send_error(in, out, protocol, 500, "Failed to allocate response buffer");
      }

      CURL *curl;
      curl = curl_easy_init();

      if (!curl) {
        send_error(in, out, protocol, 500, "Cannot init CURL");
      }

      if (!set_curl_method(curl, method)) {
        send_error(in, out, protocol, 405, "Method not implemented");
      }

      curl_easy_setopt(curl, CURLOPT_URL, url);

      // Delete Proxy-Connection header
      {
        auto i = headers.find("Proxy-Connection");
        if (i != headers.end()) {
          headers.erase(i);
        }
      }

      struct curl_slist *chunk = NULL;
      for (auto i = headers.begin(); i != headers.end(); i++) {
        string header = i->first + ": " + i->second;
        chunk = curl_slist_append(chunk, header.c_str());
      }
      curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);

      if (has_body(method)) {
        struct read_buffer r = { .body = body, .index = 0 };
        curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_buffer);
        curl_easy_setopt(curl, CURLOPT_READDATA, &r);

        chunk = curl_slist_append(chunk, "Transfer-Encoding: chunked");
        chunk = curl_slist_append(chunk, "Expect:");
      }

      curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, write_buffer);
      curl_easy_setopt(curl, CURLOPT_HEADERDATA, &rhead);
      curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_buffer);
      curl_easy_setopt(curl, CURLOPT_WRITEDATA, &rbody);
      CURLcode res = curl_easy_perform(curl);
      if(res != CURLE_OK) {
        fprintf(stderr, "curl_easy_perform() failed: %s\n",
            curl_easy_strerror(res));
        send_error(in, out, protocol, 502, "Request to server failed");
      } else {
        char protocol_r[10];
        char message[8000];
        unsigned code;

        const char* image = NULL;
        const char* const PNG = "PNG";
        const char* const JPEG = "JPEG";

        {
          cout << "RESPONSE: " << endl;
          FILE* res_head = fmemopen(rhead.data, rhead.size, "r");

          fscanf(res_head, "%10s %3u %8000s\r\n", protocol_r, &code, message);

          cout << "STATUS: " << code << " PROTOCOL: " << protocol_r << endl;

          headers.empty();
          parse_headers(res_head, headers);

          auto a = headers.find("Content-Type");
          if (a != headers.end()) {
            if (a->second == "image/jpeg") image = JPEG;
            else if (a->second == "image/png") image = PNG;
          }
        }

        cout << "image: " << (image ? image : "NULL") << endl;


        if (image) {
          try {
            Magick::Blob my_blob(rbody.data, rbody.size);
            Magick::Blob output;

            Magick::Image to_rotate(my_blob);
            to_rotate.magick(image);
            to_rotate.flip();
            to_rotate.write(&output);

            cout << "IN" << endl << my_blob.length() << endl;
            cout << "OUT" << endl << output.length() << endl;

            fprintf(out, "%s %u %s\n", protocol_r, code, message);
            cout << protocol_r << ' ' << code << ' ' << message << endl;

            headers["Content-Length"] = to_string(output.length());
            for (auto i = headers.begin(); i != headers.end(); i++) {
              string header = i->first + ": " + i->second + "\r\n";
              fprintf(out, "%s\n", header.c_str());
              cout << header << endl;
            }
            fprintf(out, "\r\n");
            fflush(out);

            total_write((uint8_t*) output.data(), output.length(), fd);
          } catch (Magick::Exception &error) {
            send_error(in, out, protocol, 500, "Image conversion failed");
            fprintf(stderr, "I exit %s\n", error.what());
            break;
          } catch (std::exception &error) {
            send_error(in, out, protocol, 500, "Image conversion failed");
            fprintf(stderr, "I exit %s\n", error.what());
            break;
          }
        } else {
          total_write(rhead.data, rhead.size, fd);
          total_write(rbody.data, rbody.size, fd);
          fflush(out);
        }
      }

      curl_easy_cleanup(curl);
      curl_slist_free_all(chunk);
      free(rhead.data);
      free(rbody.data);
    }

    {
      auto i = headers.find("Connection");
      if (i != headers.end() && i->second == "close") {
        break;
      }
    }
  }

  cout << "closing data socket...\n";

  fclose(in);

  fflush(out);
  fclose(out);

  pthread_exit(NULL);
}