/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsComponentManagerUtils.h"
#include "nsStreamConverterService.h"
#include "nsIComponentRegistrar.h"
#include "nsString.h"
#include "nsAtom.h"
#include "nsDeque.h"
#include "nsIInputStream.h"
#include "nsIStreamConverter.h"
#include "nsICategoryManager.h"
#include "nsXPCOM.h"
#include "nsISupportsPrimitives.h"
#include "nsTArray.h"
#include "nsServiceManagerUtils.h"
#include "nsISimpleEnumerator.h"
#include "mozilla/UniquePtr.h"

///////////////////////////////////////////////////////////////////
// Breadth-First-Search (BFS) algorithm state classes and types.

// Used to establish discovered verticies.
enum BFScolors { white, gray, black };

// BFS hashtable data class.
struct BFSTableData {
  nsCString key;
  BFScolors color;
  int32_t distance;
  mozilla::UniquePtr<nsCString> predecessor;

  explicit BFSTableData(const nsACString& aKey)
      : key(aKey), color(white), distance(-1) {}
};

////////////////////////////////////////////////////////////
// nsISupports methods
NS_IMPL_ISUPPORTS(nsStreamConverterService, nsIStreamConverterService)

////////////////////////////////////////////////////////////
// nsIStreamConverterService methods

////////////////////////////////////////////////////////////
// nsStreamConverterService methods

// Builds the graph represented as an adjacency list (and built up in
// memory using an nsObjectHashtable and nsCOMArray combination).
//
// :BuildGraph() consults the category manager for all stream converter
// CONTRACTIDS then fills the adjacency list with edges.
// An edge in this case is comprised of a FROM and TO MIME type combination.
//
// CONTRACTID format:
// @mozilla.org/streamconv;1?from=text/html&to=text/plain
// XXX curently we only handle a single from and to combo, we should repeat the
// XXX registration process for any series of from-to combos.
// XXX can use nsTokenizer for this.
//

nsresult nsStreamConverterService::BuildGraph() {
  nsresult rv;

  nsCOMPtr<nsICategoryManager> catmgr(
      do_GetService(NS_CATEGORYMANAGER_CONTRACTID, &rv));
  if (NS_FAILED(rv)) return rv;

  nsCOMPtr<nsISimpleEnumerator> entries;
  rv = catmgr->EnumerateCategory(NS_ISTREAMCONVERTER_KEY,
                                 getter_AddRefs(entries));
  if (NS_FAILED(rv)) return rv;

  // go through each entry to build the graph
  nsCOMPtr<nsISupports> supports;
  nsCOMPtr<nsISupportsCString> entry;
  rv = entries->GetNext(getter_AddRefs(supports));
  while (NS_SUCCEEDED(rv)) {
    entry = do_QueryInterface(supports);

    // get the entry string
    nsAutoCString entryString;
    rv = entry->GetData(entryString);
    if (NS_FAILED(rv)) return rv;

    // cobble the entry string w/ the converter key to produce a full
    // contractID.
    nsAutoCString contractID(NS_ISTREAMCONVERTER_KEY);
    contractID.Append(entryString);

    // now we've got the CONTRACTID, let's parse it up.
    rv = AddAdjacency(contractID.get());
    if (NS_FAILED(rv)) return rv;

    rv = entries->GetNext(getter_AddRefs(supports));
  }

  return NS_OK;
}

// XXX currently you can not add the same adjacency (i.e. you can't have
// multiple
// XXX stream converters registering to handle the same from-to combination.
// It's
// XXX not programatically prohibited, it's just that results are un-predictable
// XXX right now.
nsresult nsStreamConverterService::AddAdjacency(const char* aContractID) {
  nsresult rv;
  // first parse out the FROM and TO MIME-types.

  nsAutoCString fromStr, toStr;
  rv = ParseFromTo(aContractID, fromStr, toStr);
  if (NS_FAILED(rv)) return rv;

  // Each MIME-type is a vertex in the graph, so first lets make sure
  // each MIME-type is represented as a key in our hashtable.

  nsTArray<RefPtr<nsAtom>>* const fromEdges =
      mAdjacencyList.GetOrInsertNew(fromStr);

  mAdjacencyList.GetOrInsertNew(toStr);

  // Now we know the FROM and TO types are represented as keys in the hashtable.
  // Let's "connect" the verticies, making an edge.

  RefPtr<nsAtom> vertex = NS_Atomize(toStr);
  if (!vertex) return NS_ERROR_OUT_OF_MEMORY;

  NS_ASSERTION(fromEdges, "something wrong in adjacency list construction");
  if (!fromEdges) return NS_ERROR_FAILURE;

  // XXX(Bug 1631371) Check if this should use a fallible operation as it
  // pretended earlier.
  fromEdges->AppendElement(vertex);
  return NS_OK;
}

nsresult nsStreamConverterService::ParseFromTo(const char* aContractID,
                                               nsCString& aFromRes,
                                               nsCString& aToRes) {
  nsAutoCString ContractIDStr(aContractID);

  int32_t fromLoc = ContractIDStr.Find("from=");
  int32_t toLoc = ContractIDStr.Find("to=");
  if (-1 == fromLoc || -1 == toLoc) return NS_ERROR_FAILURE;

  fromLoc = fromLoc + 5;
  toLoc = toLoc + 3;

  nsAutoCString fromStr, toStr;

  ContractIDStr.Mid(fromStr, fromLoc, toLoc - 4 - fromLoc);
  ContractIDStr.Mid(toStr, toLoc, ContractIDStr.Length() - toLoc);

  aFromRes.Assign(fromStr);
  aToRes.Assign(toStr);

  return NS_OK;
}

using BFSHashTable = nsClassHashtable<nsCStringHashKey, BFSTableData>;

// nsObjectHashtable enumerator functions.

class CStreamConvDeallocator : public nsDequeFunctor<nsCString> {
 public:
  void operator()(nsCString* anObject) override { delete anObject; }
};

// walks the graph using a breadth-first-search algorithm which generates a
// discovered verticies tree. This tree is then walked up (from destination
// vertex, to origin vertex) and each link in the chain is added to an
// nsStringArray. A direct lookup for the given CONTRACTID should be made prior
// to calling this method in an attempt to find a direct converter rather than
// walking the graph.
nsresult nsStreamConverterService::FindConverter(
    const char* aContractID, nsTArray<nsCString>** aEdgeList) {
  nsresult rv;
  if (!aEdgeList) return NS_ERROR_NULL_POINTER;
  *aEdgeList = nullptr;

  // walk the graph in search of the appropriate converter.

  uint32_t vertexCount = mAdjacencyList.Count();
  if (0 >= vertexCount) return NS_ERROR_FAILURE;

  // Create a corresponding color table for each vertex in the graph.
  BFSHashTable lBFSTable;
  for (const auto& entry : mAdjacencyList) {
    const nsACString& key = entry.GetKey();
    MOZ_ASSERT(entry.GetWeak(), "no data in the table iteration");
    lBFSTable.InsertOrUpdate(key, mozilla::MakeUnique<BFSTableData>(key));
  }

  NS_ASSERTION(lBFSTable.Count() == vertexCount,
               "strmconv BFS table init problem");

  // This is our source vertex; our starting point.
  nsAutoCString fromC, toC;
  rv = ParseFromTo(aContractID, fromC, toC);
  if (NS_FAILED(rv)) return rv;

  BFSTableData* data = lBFSTable.Get(fromC);
  if (!data) {
    return NS_ERROR_FAILURE;
  }

  data->color = gray;
  data->distance = 0;
  auto* dtorFunc = new CStreamConvDeallocator();

  nsDeque grayQ(dtorFunc);

  // Now generate the shortest path tree.
  grayQ.Push(new nsCString(fromC));
  while (0 < grayQ.GetSize()) {
    nsCString* currentHead = (nsCString*)grayQ.PeekFront();
    nsTArray<RefPtr<nsAtom>>* data2 = mAdjacencyList.Get(*currentHead);
    if (!data2) return NS_ERROR_FAILURE;

    // Get the state of the current head to calculate the distance of each
    // reachable vertex in the loop.
    BFSTableData* headVertexState = lBFSTable.Get(*currentHead);
    if (!headVertexState) return NS_ERROR_FAILURE;

    int32_t edgeCount = data2->Length();

    for (int32_t i = 0; i < edgeCount; i++) {
      nsAtom* curVertexAtom = data2->ElementAt(i);
      auto* curVertex = new nsCString();
      curVertexAtom->ToUTF8String(*curVertex);

      BFSTableData* curVertexState = lBFSTable.Get(*curVertex);
      if (!curVertexState) {
        delete curVertex;
        return NS_ERROR_FAILURE;
      }

      if (white == curVertexState->color) {
        curVertexState->color = gray;
        curVertexState->distance = headVertexState->distance + 1;
        curVertexState->predecessor =
            mozilla::MakeUnique<nsCString>(*currentHead);
        grayQ.Push(curVertex);
      } else {
        delete curVertex;  // if this vertex has already been discovered, we
                           // don't want to leak it. (non-discovered vertex's
                           // get cleaned up when they're popped).
      }
    }
    headVertexState->color = black;
    nsCString* cur = (nsCString*)grayQ.PopFront();
    delete cur;
    cur = nullptr;
  }
  // The shortest path (if any) has been generated and is represented by the
  // chain of BFSTableData->predecessor keys. Start at the bottom and work our
  // way up.

  // first parse out the FROM and TO MIME-types being registered.

  nsAutoCString fromStr, toMIMEType;
  rv = ParseFromTo(aContractID, fromStr, toMIMEType);
  if (NS_FAILED(rv)) return rv;

  // get the root CONTRACTID
  nsAutoCString ContractIDPrefix(NS_ISTREAMCONVERTER_KEY);
  auto* shortestPath = new nsTArray<nsCString>();

  data = lBFSTable.Get(toMIMEType);
  if (!data) {
    // If this vertex isn't in the BFSTable, then no-one has registered for it,
    // therefore we can't do the conversion.
    delete shortestPath;
    return NS_ERROR_FAILURE;
  }

  while (data) {
    if (fromStr.Equals(data->key)) {
      // found it. We're done here.
      *aEdgeList = shortestPath;
      return NS_OK;
    }

    // reconstruct the CONTRACTID.
    // Get the predecessor.
    if (!data->predecessor) break;  // no predecessor
    BFSTableData* predecessorData = lBFSTable.Get(*data->predecessor);

    if (!predecessorData) break;  // no predecessor, chain doesn't exist.

    // build out the CONTRACTID.
    nsAutoCString newContractID(ContractIDPrefix);
    newContractID.AppendLiteral("?from=");

    newContractID.Append(predecessorData->key);

    newContractID.AppendLiteral("&to=");
    newContractID.Append(data->key);

    // Add this CONTRACTID to the chain.
    // XXX(Bug 1631371) Check if this should use a fallible operation as it
    // pretended earlier.
    shortestPath->AppendElement(newContractID);

    // move up the tree.
    data = predecessorData;
  }
  delete shortestPath;
  return NS_ERROR_FAILURE;  // couldn't find a stream converter or chain.
}

/////////////////////////////////////////////////////
// nsIStreamConverterService methods
NS_IMETHODIMP
nsStreamConverterService::CanConvert(const char* aFromType, const char* aToType,
                                     bool* _retval) {
  nsCOMPtr<nsIComponentRegistrar> reg;
  nsresult rv = NS_GetComponentRegistrar(getter_AddRefs(reg));
  if (NS_FAILED(rv)) return rv;

  nsAutoCString contractID;
  contractID.AssignLiteral(NS_ISTREAMCONVERTER_KEY "?from=");
  contractID.Append(aFromType);
  contractID.AppendLiteral("&to=");
  contractID.Append(aToType);

  // See if we have a direct match
  rv = reg->IsContractIDRegistered(contractID.get(), _retval);
  if (NS_FAILED(rv)) return rv;
  if (*_retval) return NS_OK;

  // Otherwise try the graph.
  rv = BuildGraph();
  if (NS_FAILED(rv)) return rv;

  nsTArray<nsCString>* converterChain = nullptr;
  rv = FindConverter(contractID.get(), &converterChain);
  *_retval = NS_SUCCEEDED(rv);

  delete converterChain;
  return NS_OK;
}

NS_IMETHODIMP
nsStreamConverterService::ConvertedType(const nsACString& aFromType,
                                        nsIChannel* aChannel,
                                        nsACString& aOutToType) {
  // first determine whether we can even handle this conversion
  // build a CONTRACTID
  nsAutoCString contractID;
  contractID.AssignLiteral(NS_ISTREAMCONVERTER_KEY "?from=");
  contractID.Append(aFromType);
  contractID.AppendLiteral("&to=*/*");
  const char* cContractID = contractID.get();

  nsresult rv;
  nsCOMPtr<nsIStreamConverter> converter(do_CreateInstance(cContractID, &rv));
  if (NS_SUCCEEDED(rv)) {
    return converter->GetConvertedType(aFromType, aChannel, aOutToType);
  }
  return rv;
}

NS_IMETHODIMP
nsStreamConverterService::Convert(nsIInputStream* aFromStream,
                                  const char* aFromType, const char* aToType,
                                  nsISupports* aContext,
                                  nsIInputStream** _retval) {
  if (!aFromStream || !aFromType || !aToType || !_retval) {
    return NS_ERROR_NULL_POINTER;
  }
  nsresult rv;

  // first determine whether we can even handle this conversion
  // build a CONTRACTID
  nsAutoCString contractID;
  contractID.AssignLiteral(NS_ISTREAMCONVERTER_KEY "?from=");
  contractID.Append(aFromType);
  contractID.AppendLiteral("&to=");
  contractID.Append(aToType);
  const char* cContractID = contractID.get();

  nsCOMPtr<nsIStreamConverter> converter(do_CreateInstance(cContractID, &rv));
  if (NS_FAILED(rv)) {
    // couldn't go direct, let's try walking the graph of converters.
    rv = BuildGraph();
    if (NS_FAILED(rv)) return rv;

    nsTArray<nsCString>* converterChain = nullptr;

    rv = FindConverter(cContractID, &converterChain);
    if (NS_FAILED(rv)) {
      // can't make this conversion.
      // XXX should have a more descriptive error code.
      return NS_ERROR_FAILURE;
    }

    int32_t edgeCount = int32_t(converterChain->Length());
    NS_ASSERTION(edgeCount > 0, "findConverter should have failed");

    // convert the stream using each edge of the graph as a step.
    // this is our stream conversion traversal.
    nsCOMPtr<nsIInputStream> dataToConvert = aFromStream;
    nsCOMPtr<nsIInputStream> convertedData;

    for (int32_t i = edgeCount - 1; i >= 0; i--) {
      const char* lContractID = converterChain->ElementAt(i).get();

      converter = do_CreateInstance(lContractID, &rv);

      if (NS_FAILED(rv)) {
        delete converterChain;
        return rv;
      }

      nsAutoCString fromStr, toStr;
      rv = ParseFromTo(lContractID, fromStr, toStr);
      if (NS_FAILED(rv)) {
        delete converterChain;
        return rv;
      }

      rv = converter->Convert(dataToConvert, fromStr.get(), toStr.get(),
                              aContext, getter_AddRefs(convertedData));
      dataToConvert = convertedData;
      if (NS_FAILED(rv)) {
        delete converterChain;
        return rv;
      }
    }

    delete converterChain;
    convertedData.forget(_retval);
  } else {
    // we're going direct.
    rv = converter->Convert(aFromStream, aFromType, aToType, aContext, _retval);
  }

  return rv;
}

NS_IMETHODIMP
nsStreamConverterService::AsyncConvertData(const char* aFromType,
                                           const char* aToType,
                                           nsIStreamListener* aListener,
                                           nsISupports* aContext,
                                           nsIStreamListener** _retval) {
  if (!aFromType || !aToType || !aListener || !_retval) {
    return NS_ERROR_NULL_POINTER;
  }

  nsresult rv;

  // first determine whether we can even handle this conversion
  // build a CONTRACTID
  nsAutoCString contractID;
  contractID.AssignLiteral(NS_ISTREAMCONVERTER_KEY "?from=");
  contractID.Append(aFromType);
  contractID.AppendLiteral("&to=");
  contractID.Append(aToType);
  const char* cContractID = contractID.get();

  nsCOMPtr<nsIStreamConverter> listener(do_CreateInstance(cContractID, &rv));
  if (NS_FAILED(rv)) {
    // couldn't go direct, let's try walking the graph of converters.
    rv = BuildGraph();
    if (NS_FAILED(rv)) return rv;

    nsTArray<nsCString>* converterChain = nullptr;

    rv = FindConverter(cContractID, &converterChain);
    if (NS_FAILED(rv)) {
      // can't make this conversion.
      // XXX should have a more descriptive error code.
      return NS_ERROR_FAILURE;
    }

    // aListener is the listener that wants the final, converted, data.
    // we initialize finalListener w/ aListener so it gets put at the
    // tail end of the chain, which in the loop below, means the *first*
    // converter created.
    nsCOMPtr<nsIStreamListener> finalListener = aListener;

    // convert the stream using each edge of the graph as a step.
    // this is our stream conversion traversal.
    int32_t edgeCount = int32_t(converterChain->Length());
    NS_ASSERTION(edgeCount > 0, "findConverter should have failed");
    for (int i = 0; i < edgeCount; i++) {
      const char* lContractID = converterChain->ElementAt(i).get();

      // create the converter for this from/to pair
      nsCOMPtr<nsIStreamConverter> converter(do_CreateInstance(lContractID));
      NS_ASSERTION(converter,
                   "graph construction problem, built a contractid that wasn't "
                   "registered");

      nsAutoCString fromStr, toStr;
      rv = ParseFromTo(lContractID, fromStr, toStr);
      if (NS_FAILED(rv)) {
        delete converterChain;
        return rv;
      }

      // connect the converter w/ the listener that should get the converted
      // data.
      rv = converter->AsyncConvertData(fromStr.get(), toStr.get(),
                                       finalListener, aContext);
      if (NS_FAILED(rv)) {
        delete converterChain;
        return rv;
      }

      // the last iteration of this loop will result in finalListener
      // pointing to the converter that "starts" the conversion chain.
      // this converter's "from" type is the original "from" type. Prior
      // to the last iteration, finalListener will continuously be wedged
      // into the next listener in the chain, then be updated.
      finalListener = converter;
    }
    delete converterChain;
    // return the first listener in the chain.
    finalListener.forget(_retval);
  } else {
    // we're going direct.
    rv = listener->AsyncConvertData(aFromType, aToType, aListener, aContext);
    listener.forget(_retval);
  }

  return rv;
}

nsresult NS_NewStreamConv(nsStreamConverterService** aStreamConv) {
  MOZ_ASSERT(aStreamConv != nullptr, "null ptr");
  if (!aStreamConv) return NS_ERROR_NULL_POINTER;

  RefPtr<nsStreamConverterService> conv = new nsStreamConverterService();
  conv.forget(aStreamConv);

  return NS_OK;
}