/** @file

    Plugin to perform background fetches of certain content that would
    otherwise not be cached. For example, Range: requests / responses.

    @section license License

    Licensed to the Apache Software Foundation (ASF) under one
    or more contributor license agreements.  See the NOTICE file
    distributed with this work for additional information
    regarding copyright ownership.  The ASF licenses this file
    to you under the Apache License, Version 2.0 (the
    "License"); you may not use this file except in compliance
    with the License.  You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
*/
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cstdarg>

#include <string>
#include <iostream>
#include <unordered_map>
#include <cinttypes>
#include <string_view>
#include <array>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/un.h>

#include "ts/ts.h"
#include "ts/remap.h"
#include "background_fetch.h"
using OutstandingRequests = std::unordered_map<std::string, bool>;

namespace cache_fill_ns
{
DbgCtl dbg_ctl{PLUGIN_NAME};
}

///////////////////////////////////////////////////////////////////////////
// Remove a header (fully) from an TSMLoc / TSMBuffer. Return the number
// of fields (header values) we removed.
int
remove_header(TSMBuffer bufp, TSMLoc hdr_loc, const char *header, int len)
{
  TSMLoc field = TSMimeHdrFieldFind(bufp, hdr_loc, header, len);
  int    cnt   = 0;

  while (field) {
    TSMLoc tmp = TSMimeHdrFieldNextDup(bufp, hdr_loc, field);

    ++cnt;
    TSMimeHdrFieldDestroy(bufp, hdr_loc, field);
    TSHandleMLocRelease(bufp, hdr_loc, field);
    field = tmp;
  }

  return cnt;
}

///////////////////////////////////////////////////////////////////////////
// Set a header to a specific value. This will avoid going to through a
// remove / add sequence in case of an existing header.
// but clean.
static bool
set_header(TSMBuffer bufp, TSMLoc hdr_loc, const char *header, int len, const char *val, int val_len)
{
  if (!bufp || !hdr_loc || !header || len <= 0 || !val || val_len <= 0) {
    return false;
  }

  bool   ret       = false;
  TSMLoc field_loc = TSMimeHdrFieldFind(bufp, hdr_loc, header, len);

  if (!field_loc) {
    // No existing header, so create one
    if (TS_SUCCESS == TSMimeHdrFieldCreateNamed(bufp, hdr_loc, header, len, &field_loc)) {
      if (TS_SUCCESS == TSMimeHdrFieldValueStringSet(bufp, hdr_loc, field_loc, -1, val, val_len)) {
        TSMimeHdrFieldAppend(bufp, hdr_loc, field_loc);
        ret = true;
      }
      TSHandleMLocRelease(bufp, hdr_loc, field_loc);
    }
  } else {
    TSMLoc tmp   = nullptr;
    bool   first = true;

    while (field_loc) {
      tmp = TSMimeHdrFieldNextDup(bufp, hdr_loc, field_loc);
      if (first) {
        first = false;
        if (TS_SUCCESS == TSMimeHdrFieldValueStringSet(bufp, hdr_loc, field_loc, -1, val, val_len)) {
          ret = true;
        }
      } else {
        TSMimeHdrFieldDestroy(bufp, hdr_loc, field_loc);
      }
      TSHandleMLocRelease(bufp, hdr_loc, field_loc);
      field_loc = tmp;
    }
  }

  return ret;
}

///////////////////////////////////////////////////////////////////////////
// Dump a header on stderr, useful together with Dbg().
static void
dump_headers(TSMLoc hdr_loc)
{
  TSIOBuffer       output_buffer;
  TSIOBufferReader reader;
  TSIOBufferBlock  block;
  int64_t          block_avail;

  output_buffer = TSIOBufferCreate();
  reader        = TSIOBufferReaderAlloc(output_buffer);

  /* This will print  just MIMEFields and not the http request line */
  TSMimeHdrPrint(hdr_loc, output_buffer);

  /* We need to loop over all the buffer blocks, there can be more than 1 */
  block = TSIOBufferReaderStart(reader);
  do {
    const char *block_start = TSIOBufferBlockReadStart(block, reader, &block_avail);
    if (block_avail > 0) {
      Dbg(dbg_ctl, "Headers are:\n%.*s", static_cast<int>(block_avail), block_start);
    }
    TSIOBufferReaderConsume(reader, block_avail);
    block = TSIOBufferReaderStart(reader);
  } while (block && block_avail != 0);

  /* Free up the TSIOBuffer that we used to print out the header */
  TSIOBufferReaderFree(reader);
  TSIOBufferDestroy(output_buffer);
}

bool
BgFetchData::initialize(TSMBuffer request, TSMLoc req_hdr, TSHttpTxn txnp)
{
  struct sockaddr const *ip  = TSHttpTxnClientAddrGet(txnp);
  bool                   ret = false;

  TSAssert(TS_NULL_MLOC == hdr_loc);
  TSAssert(TS_NULL_MLOC == url_loc);

  if (ip) {
    if (ip->sa_family == AF_INET) {
      memcpy(&client_ip, ip, sizeof(sockaddr_in));
    } else if (ip->sa_family == AF_INET6) {
      memcpy(&client_ip, ip, sizeof(sockaddr_in6));
    } else if (ip->sa_family == AF_UNIX) {
      memcpy(&client_ip, ip, sizeof(sockaddr_un));
    } else {
      TSError("[%s] Unknown address family %d", PLUGIN_NAME, ip->sa_family);
      return false;
    }
  } else {
    TSError("[%s] Failed to get client host info", PLUGIN_NAME);
    return false;
  }

  hdr_loc = TSHttpHdrCreate(mbuf);
  if (TS_SUCCESS == TSHttpHdrCopy(mbuf, hdr_loc, request, req_hdr)) {
    TSMLoc p_url;

    // Now copy the pristine request URL into our MBuf
    if (TS_SUCCESS == TSHttpTxnPristineUrlGet(txnp, &request, &p_url)) {
      if (TS_SUCCESS == TSUrlClone(mbuf, request, p_url, &url_loc)) {
        TSMLoc c_url = TS_NULL_MLOC;
        int    len;
        char  *url = nullptr;

        // Get the cache key URL (for now), since this has better lookup behavior when using
        // e.g. the cachekey plugin.
        if (TS_SUCCESS == TSUrlCreate(request, &c_url)) {
          if (TS_SUCCESS == TSHttpTxnCacheLookupUrlGet(txnp, request, c_url)) {
            url = TSUrlStringGet(request, c_url, &len);
            TSHandleMLocRelease(request, TS_NULL_MLOC, c_url);
            Dbg(dbg_ctl, "Cache URL is %.*s", len, url);
          }
        }

        if (url) {
          _url.assign(url, len); // Save away the cache URL for later use when acquiring lock
          TSfree(static_cast<void *>(url));

          if (TS_SUCCESS == TSHttpHdrUrlSet(mbuf, hdr_loc, url_loc)) {
            // Make sure we have the correct Host: header for this request.
            const char *hostp = TSUrlHostGet(mbuf, url_loc, &len);

            if (set_header(mbuf, hdr_loc, TS_MIME_FIELD_HOST, TS_MIME_LEN_HOST, hostp, len)) {
              Dbg(dbg_ctl, "Set header Host: %.*s", len, hostp);
            }
            // Next, remove the Range headers and IMS (conditional) headers from the request
            for (auto const &header : FILTER_HEADERS) {
              if (remove_header(mbuf, hdr_loc, header.data(), header.size()) > 0) {
                Dbg(dbg_ctl, "Removed the %s header from request", header.data());
              }
            }
            ret = true;
          }
        }
      }
      TSHandleMLocRelease(request, TS_NULL_MLOC, p_url);
    }
  }

  return ret;
}

static int cont_bg_fetch(TSCont contp, TSEvent event, void *edata);

// Create, setup and schedule the background fetch continuation.
void
BgFetchData::schedule()
{
  TSAssert(nullptr == _cont);

  // Setup the continuation
  _cont = TSContCreate(cont_bg_fetch, TSMutexCreate());
  TSContDataSet(_cont, static_cast<void *>(this));

  // Initialize the VIO stuff (for the fetch)
  req_io_buf         = TSIOBufferCreate();
  req_io_buf_reader  = TSIOBufferReaderAlloc(req_io_buf);
  resp_io_buf        = TSIOBufferCreate();
  resp_io_buf_reader = TSIOBufferReaderAlloc(resp_io_buf);

  // Schedule
  TSContScheduleOnPool(_cont, 0, TS_THREAD_POOL_NET);
}

//////////////////////////////////////////////////////////////////////////////
// Continuation to perform a background fill of a URL. This is pretty
// expensive (memory allocations etc.), we could eliminate maybe the
// std::string, but I think it's fine for now.
static int
cont_bg_fetch(TSCont contp, TSEvent event, void * /* edata ATS_UNUSED */)
{
  BgFetchData *data = static_cast<BgFetchData *>(TSContDataGet(contp));
  int64_t      avail;

  switch (event) {
  case TS_EVENT_IMMEDIATE:
  case TS_EVENT_TIMEOUT:
    // Debug info for this particular bg fetch (put all debug in here please)
    if (dbg_ctl.on()) {
      char            buf[INET6_ADDRSTRLEN];
      const sockaddr *sockaddress = reinterpret_cast<const sockaddr *>(&data->client_ip);

      switch (sockaddress->sa_family) {
      case AF_INET:
        inet_ntop(AF_INET, &(((struct sockaddr_in *)sockaddress)->sin_addr), buf, INET_ADDRSTRLEN);
        Dbg(dbg_ctl, "Client IPv4 = %s", buf);
        break;
      case AF_INET6:
        inet_ntop(AF_INET6, &(((struct sockaddr_in6 *)sockaddress)->sin6_addr), buf, INET6_ADDRSTRLEN);
        Dbg(dbg_ctl, "Client IPv6 = %s", buf);
        break;
      default:
        TSError("[%s] Unknown address family %d", PLUGIN_NAME, sockaddress->sa_family);
        break;
      }
      Dbg(dbg_ctl, "Starting background fetch, replaying:");
      dump_headers(data->hdr_loc);
    }

    // Setup the NetVC for background fetch
    TSAssert(nullptr == data->vc);
    if ((data->vc = TSHttpConnectWithPluginId(reinterpret_cast<sockaddr *>(&data->client_ip), PLUGIN_NAME, 0)) != nullptr) {
      TSHttpHdrPrint(data->mbuf, data->hdr_loc, data->req_io_buf);
      // We never send a body with the request. ToDo: Do we ever need to support that ?
      TSIOBufferWrite(data->req_io_buf, "\r\n", 2);

      data->r_vio = TSVConnRead(data->vc, contp, data->resp_io_buf, INT64_MAX);
      data->w_vio = TSVConnWrite(data->vc, contp, data->req_io_buf_reader, TSIOBufferReaderAvail(data->req_io_buf_reader));
    } else {
      delete data;
      TSError("[%s] Failed to connect to internal process, major malfunction", PLUGIN_NAME);
    }
    break;

  case TS_EVENT_VCONN_WRITE_COMPLETE:
    // TSVConnShutdown(data->vc, 0, 1);
    // TSVIOReenable(data->w_vio);
    Dbg(dbg_ctl, "Write Complete");
    break;

  case TS_EVENT_VCONN_READ_READY:
    avail = TSIOBufferReaderAvail(data->resp_io_buf_reader);
    data->addBytes(avail);
    TSIOBufferReaderConsume(data->resp_io_buf_reader, avail);
    TSVIONDoneSet(data->r_vio, TSVIONDoneGet(data->r_vio) + avail);
    TSVIOReenable(data->r_vio);
    break;

  case TS_EVENT_VCONN_READ_COMPLETE:
  case TS_EVENT_VCONN_EOS:
  case TS_EVENT_VCONN_INACTIVITY_TIMEOUT:
  case TS_EVENT_ERROR:
    if (event == TS_EVENT_VCONN_INACTIVITY_TIMEOUT) {
      Dbg(dbg_ctl, "Encountered Inactivity Timeout");
      TSVConnAbort(data->vc, TS_VC_CLOSE_ABORT);
    } else {
      TSVConnClose(data->vc);
    }

    Dbg(dbg_ctl, "Closing down background transaction, event= %s(%d)", TSHttpEventNameLookup(event), event);
    avail = TSIOBufferReaderAvail(data->resp_io_buf_reader);
    data->addBytes(avail);
    TSIOBufferReaderConsume(data->resp_io_buf_reader, avail);
    TSVIONDoneSet(data->r_vio, TSVIONDoneGet(data->r_vio) + avail);

    // Close, release and cleanup
    data->vc = nullptr;
    delete data;
    break;

  default:
    Dbg(dbg_ctl, "Unhandled event: %s (%d)", TSHttpEventNameLookup(event), event);
    break;
  }

  return 0;
}
