////////////////////////////////////////////////////////////////////////////////
/// @brief document request handler
///
/// @file
///
/// DISCLAIMER
///
/// Copyright 2014 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed 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.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Dr. Frank Celler
/// @author Copyright 2014, ArangoDB GmbH, Cologne, Germany
/// @author Copyright 2010-2013, triAGENS GmbH, Cologne, Germany
////////////////////////////////////////////////////////////////////////////////

#include "RestEdgeHandler.h"

#include "Basics/StringUtils.h"
#include "Basics/conversions.h"
#include "Basics/tri-strings.h"
#include "Cluster/ServerState.h"
#include "Cluster/ClusterInfo.h"
#include "Cluster/ClusterMethods.h"
#include "Rest/HttpRequest.h"
#include "VocBase/document-collection.h"
#include "VocBase/edge-collection.h"

using namespace std;
using namespace triagens::basics;
using namespace triagens::rest;
using namespace triagens::arango;

////////////////////////////////////////////////////////////////////////////////
/// @brief free a string if defined, nop otherwise
////////////////////////////////////////////////////////////////////////////////

#define FREE_STRING(zone, what)                                           \
  if (what != 0) {                                                        \
    TRI_Free(zone, what);                                                 \
    what = 0;                                                             \
  }
// -----------------------------------------------------------------------------
// --SECTION--                                      constructors and destructors
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief constructor
////////////////////////////////////////////////////////////////////////////////

RestEdgeHandler::RestEdgeHandler (HttpRequest* request)
  : RestDocumentHandler(request) {
}

// -----------------------------------------------------------------------------
// --SECTION--                                                 protected methods
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @startDocuBlock API_EDGE_CREATE
/// @brief creates an edge
///
/// @RESTHEADER{POST /_api/edge,Create edge}
///
/// @RESTBODYPARAM{edge-document,json,required}
/// A JSON representation of the edge document must be passed as the body of
/// the POST request. This JSON object may contain the edge's document key in
/// the *_key* attribute if needed.
///
/// @RESTQUERYPARAMETERS
///
/// @RESTQUERYPARAM{collection,string,required}
/// Creates a new edge in the collection identified by *collection* name.
///
/// @RESTQUERYPARAM{createCollection,boolean,optional}
/// If this parameter has a value of *true* or *yes*, then the collection is
/// created if it does not yet exist. Other values will be ignored so the
/// collection must be present for the operation to succeed.
///
/// **Note**: This flag is not supported in a cluster. Using it will result in an
/// error.
///
/// @RESTQUERYPARAM{waitForSync,boolean,optional}
/// Wait until the edge document has been synced to disk.
///
/// @RESTQUERYPARAM{from,string,required}
/// The document handle of the start point must be passed in *from* handle.
///
/// @RESTQUERYPARAM{to,string,required}
/// The document handle of the end point must be passed in *to* handle.
///
/// @RESTDESCRIPTION
/// Creates a new edge document in the collection named *collection*. A JSON
/// representation of the document must be passed as the body of the POST
/// request.
///
/// The *from* and *to* handles are immutable once the edge has been created.
///
/// In all other respects the method works like *POST /document*.
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{201}
/// is returned if the edge was created successfully and *waitForSync* was
/// *true*.
///
/// @RESTRETURNCODE{202}
/// is returned if the edge was created successfully and *waitForSync* was
/// *false*.
///
/// @RESTRETURNCODE{400}
/// is returned if the body does not contain a valid JSON representation of an
/// edge, or if the collection specified is not an edge collection.
/// The response body contains an error document in this case.
///
/// @RESTRETURNCODE{404}
/// is returned if the collection specified by *collection* is unknown.  The
/// response body contains an error document in this case.
///
/// @EXAMPLES
///
/// Create an edge and read it back:
///
/// @EXAMPLE_ARANGOSH_RUN{RestEdgeCreateEdge}
///     var Graph = require("org/arangodb/graph-blueprint").Graph;
///     var g = new Graph("graph", "vertices", "edges");
///     g.addVertex(1);
///     g.addVertex(2);
///     var url = "/_api/edge/?collection=edges&from=vertices/1&to=vertices/2";
///
///     var response = logCurlRequest("POST", url, { "name": "Emil" });
///
///     assert(response.code === 202);
///
///     logJsonResponse(response);
///     var body = response.body.replace(/\\/g, '');
///     var edge_id = JSON.parse(body)._id;
///     var response2 = logCurlRequest("GET", "/_api/edge/" + edge_id);
///
///     assert(response2.code === 200);
///
///     logJsonResponse(response2);
///     db._drop("edges");
///     db._drop("vertices");
///     db._graphs.remove("graph");
/// @END_EXAMPLE_ARANGOSH_RUN
/// @endDocuBlock
////////////////////////////////////////////////////////////////////////////////

bool RestEdgeHandler::createDocument () {
  vector<string> const& suffix = _request->suffix();

  if (suffix.size() != 0) {
    generateError(HttpResponse::BAD,
                  TRI_ERROR_HTTP_SUPERFLUOUS_SUFFICES,
                  "superfluous suffix, expecting " + EDGE_PATH + "?collection=<identifier>");
    return false;
  }

  // extract the from
  bool found;
  char const* from = _request->value("from", found);
  if (! found || *from == '\0') {
    generateError(HttpResponse::BAD,
                  TRI_ERROR_HTTP_BAD_PARAMETER,
                  "'from' is missing, expecting " + EDGE_PATH + "?collection=<identifier>&from=<from-handle>&to=<to-handle>");
    return false;
  }

  // extract the to
  char const* to = _request->value("to", found);

  if (! found || *to == '\0') {
    generateError(HttpResponse::BAD,
                  TRI_ERROR_HTTP_BAD_PARAMETER,
                  "'to' is missing, expecting " + EDGE_PATH + "?collection=<identifier>&from=<from-handle>&to=<to-handle>");
    return false;
  }

  // extract the cid
  const string& collection = _request->value("collection", found);

  if (! found || collection.empty()) {
    generateError(HttpResponse::BAD,
                  TRI_ERROR_ARANGO_COLLECTION_PARAMETER_MISSING,
                  "'collection' is missing, expecting " + DOCUMENT_PATH + "?collection=<identifier>");
    return false;
  }

  const bool waitForSync = extractWaitForSync();

  TRI_json_t* json = parseJsonBody();
  
  if (json == nullptr) {
    return false;
  }

  if (! TRI_IsArrayJson(json)) {
    TRI_FreeJson(TRI_UNKNOWN_MEM_ZONE, json);
    generateTransactionError(collection, TRI_ERROR_ARANGO_DOCUMENT_TYPE_INVALID);
    return false;
  }

  if (ServerState::instance()->isCoordinator()) {
    // json will be freed inside!
    return createDocumentCoordinator(collection, waitForSync, json, from, to);
  }

  if (! checkCreateCollection(collection, getCollectionType())) {
    TRI_FreeJson(TRI_UNKNOWN_MEM_ZONE, json);
    return false;
  }

  // find and load collection given by name or identifier
  SingleCollectionWriteTransaction<1> trx(new StandaloneTransactionContext(), _vocbase, collection);

  // .............................................................................
  // inside write transaction
  // .............................................................................

  int res = trx.begin();

  if (res != TRI_ERROR_NO_ERROR) {
    generateTransactionError(collection, res);
    TRI_FreeJson(TRI_UNKNOWN_MEM_ZONE, json);
    return false;
  }

  TRI_document_collection_t* document = trx.documentCollection();

  if (document->_info._type != TRI_COL_TYPE_EDGE) {
    // check if we are inserting with the EDGE handler into a non-EDGE collection
    generateError(HttpResponse::BAD, TRI_ERROR_ARANGO_COLLECTION_TYPE_INVALID);
    TRI_FreeJson(TRI_UNKNOWN_MEM_ZONE, json);
    return false;
  }

  const TRI_voc_cid_t cid = trx.cid();

  // edge
  TRI_document_edge_t edge;
  edge._fromCid = cid;
  edge._toCid   = cid;
  edge._fromKey = nullptr;
  edge._toKey   = nullptr;

  string wrongPart;
  // Note that in a DBserver in a cluster, the following call will
  // actually parse the first part of *from* as a cluster-wide
  // collection name, exactly as it is needed here!
  res = parseDocumentId(trx.resolver(), from, edge._fromCid, edge._fromKey);

  if (res != TRI_ERROR_NO_ERROR) {
    wrongPart = "'from'";
  }
  else {
    // Note that in a DBserver in a cluster, the following call will
    // actually parse the first part of *from* as a cluster-wide
    // collection name, exactly as it is needed here!
    res = parseDocumentId(trx.resolver(), to, edge._toCid, edge._toKey);

    if (res != TRI_ERROR_NO_ERROR) {
      wrongPart = "'to'";
    }
  }

  if (res != TRI_ERROR_NO_ERROR) {
    FREE_STRING(TRI_CORE_MEM_ZONE, edge._fromKey);
    FREE_STRING(TRI_CORE_MEM_ZONE, edge._toKey);

    TRI_FreeJson(TRI_UNKNOWN_MEM_ZONE, json);

    if (res == TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND) {
      generateError(HttpResponse::NOT_FOUND, res, wrongPart + " does not point to a valid collection");
    }
    else {
      generateError(HttpResponse::BAD, res, wrongPart + " is not a document handle");
    }
    return false;
  }

  // .............................................................................
  // inside write transaction
  // .............................................................................

  // will hold the result
  TRI_doc_mptr_copy_t mptr;
  res = trx.createEdge(&mptr, json, waitForSync, &edge);
  res = trx.finish(res);

  FREE_STRING(TRI_CORE_MEM_ZONE, edge._fromKey);
  FREE_STRING(TRI_CORE_MEM_ZONE, edge._toKey);
  TRI_FreeJson(TRI_UNKNOWN_MEM_ZONE, json);

  // .............................................................................
  // outside write transaction
  // .............................................................................

  if (res != TRI_ERROR_NO_ERROR) {
    generateTransactionError(collection, res);
    return false;
  }

  generateSaved(trx, cid, mptr);

  return true;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief creates a document (an edge), coordinator case in a cluster
////////////////////////////////////////////////////////////////////////////////

bool RestEdgeHandler::createDocumentCoordinator (string const& collname,
                                                 bool waitForSync,
                                                 TRI_json_t* json,
                                                 char const* from,
                                                 char const* to) {
  string const& dbname = _request->databaseName();

  triagens::rest::HttpResponse::HttpResponseCode responseCode;
  map<string, string> resultHeaders;
  string resultBody;

  int error = triagens::arango::createEdgeOnCoordinator(
            dbname, collname, waitForSync, json, from, to,
            responseCode, resultHeaders, resultBody);

  if (error != TRI_ERROR_NO_ERROR) {
    generateTransactionError(collname.c_str(), error);
    return false;
  }
  // Essentially return the response we got from the DBserver, be it
  // OK or an error:
  _response = createResponse(responseCode);
  triagens::arango::mergeResponseHeaders(_response, resultHeaders);
  _response->body().appendText(resultBody.c_str(), resultBody.size());
  return responseCode >= triagens::rest::HttpResponse::BAD;
}


////////////////////////////////////////////////////////////////////////////////
/// @startDocuBlock API_EDGE_READ
/// @brief reads a single edge
///
/// @RESTHEADER{GET /_api/edge/{document-handle}, Read edge}
///
/// @RESTURLPARAMETERS
///
/// @RESTURLPARAM{document-handle,string,required}
/// The handle of the edge document.
///
/// @RESTHEADERPARAMETERS
///
/// @RESTHEADERPARAM{If-None-Match,string,optional}
/// If the "If-None-Match" header is given, then it must contain exactly one
/// etag. The edge is returned if it has a different revision than the
/// given etag. Otherwise an *HTTP 304* is returned.
///
/// @RESTHEADERPARAM{If-Match,string,optional}
/// If the "If-Match" header is given, then it must contain exactly one
/// etag. The edge is returned if it has the same revision ad the
/// given etag. Otherwise a *HTTP 412* is returned. As an alternative
/// you can supply the etag in an attribute *rev* in the URL.
///
/// @RESTDESCRIPTION
/// Returns the edge identified by *document-handle*. The returned
/// edge contains a few special attributes:
///
/// - *_id* contains the document handle
///
/// - *_rev* contains the revision
///
/// - *_from* and *to* contain the document handles of the connected
///   vertex documents
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{200}
/// is returned if the edge was found
///
/// @RESTRETURNCODE{304}
/// is returned if the "If-None-Match" header is given and the edge has
/// the same version
///
/// @RESTRETURNCODE{404}
/// is returned if the edge or collection was not found
///
/// @RESTRETURNCODE{412}
/// is returned if a "If-Match" header or *rev* is given and the found
/// document has a different version. The response will also contain the found
/// document's current revision in the *_rev* attribute. Additionally, the
/// attributes *_id* and *_key* will be returned.
/// @endDocuBlock
////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////
/// @startDocuBlock API_EDGE_READ_ALL
/// @brief reads all edges from collection
///
/// @RESTHEADER{GET /_api/edge, Read all edges from collection}
///
/// @RESTQUERYPARAMETERS
///
/// @RESTQUERYPARAM{collection,string,required}
/// The name of the collection.
///
/// @RESTDESCRIPTION
/// Returns a list of all URI for all edges from the collection identified
/// by *collection*.
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{200}
/// All went good.
///
/// @RESTRETURNCODE{404}
/// The collection does not exist.
/// @endDocuBlock
////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////
/// @startDocuBlock API_EDGE_READ_HEAD
/// @brief reads a single edge head
///
/// @RESTHEADER{HEAD /_api/edge/{document-handle}, Read edge header}
///
/// @RESTURLPARAMETERS
///
/// @RESTURLPARAM{document-handle,string,required}
/// The handle of the edge document.
///
/// @RESTQUERYPARAMETERS
///
/// @RESTQUERYPARAM{rev,string,optional}
/// You can conditionally fetch an edge document based on a target revision id by
/// using the *rev* URL parameter.
///
/// @RESTHEADERPARAMETERS
///
/// @RESTHEADERPARAM{If-None-Match,string,optional}
/// If the "If-None-Match" header is given, then it must contain exactly one
/// etag. If the current document revision is different to the specified etag,
/// an *HTTP 200* response is returned. If the current document revision is
/// identical to the specified etag, then an *HTTP 304* is returned.
///
/// @RESTHEADERPARAM{If-Match,string,optional}
/// You can conditionally fetch an edge document based on a target revision id by
/// using the *if-match* HTTP header.
///
/// @RESTDESCRIPTION
/// Like *GET*, but only returns the header fields and not the body. You
/// can use this call to get the current revision of an edge document or check if
/// it was deleted.
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{200}
/// is returned if the edge document was found
///
/// @RESTRETURNCODE{304}
/// is returned if the "If-None-Match" header is given and the edge document has
/// same version
///
/// @RESTRETURNCODE{404}
/// is returned if the edge document or collection was not found
///
/// @RESTRETURNCODE{412}
/// is returned if a "If-Match" header or *rev* is given and the found
/// document has a different version. The response will also contain the found
/// document's current revision in the *etag* header.
/// @endDocuBlock
////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////
/// @startDocuBlock API_EDGE_REPLACE
/// @brief replaces an edge
///
/// @RESTHEADER{PUT /_api/edge/{document-handle},replaces an edge}
///
/// @RESTBODYPARAM{edge,json,required}
/// A JSON representation of the new edge data.
///
/// @RESTURLPARAMETERS
///
/// @RESTURLPARAM{document-handle,string,required}
/// The handle of the edge document.
///
/// @RESTQUERYPARAMETERS
///
/// @RESTQUERYPARAM{waitForSync,boolean,optional}
/// Wait until edge document has been synced to disk.
///
/// @RESTQUERYPARAM{rev,string,optional}
/// You can conditionally replace an edge document based on a target revision id by
/// using the *rev* URL parameter.
///
/// @RESTQUERYPARAM{policy,string,optional}
/// To control the update behavior in case there is a revision mismatch, you
/// can use the *policy* parameter (see below).
///
/// @RESTHEADERPARAMETERS
///
/// @RESTHEADERPARAM{If-Match,string,optional}
/// You can conditionally replace an edge document based on a target revision id by
/// using the *if-match* HTTP header.
///
/// @RESTDESCRIPTION
/// Completely updates (i.e. replaces) the edge document identified by *document-handle*.
/// If the edge document exists and can be updated, then a *HTTP 201* is returned
/// and the "ETag" header field contains the new revision of the edge document.
///
/// If the new edge document passed in the body of the request contains the
/// *document-handle* in the attribute *_id* and the revision in *_rev*,
/// these attributes will be ignored. Only the URI and the "ETag" header are
/// relevant in order to avoid confusion when using proxies. 
/// **Note**: The attributes
/// *_from* and *_to* of an edge are immutable and cannot be updated either.
///
/// Optionally, the URL parameter *waitForSync* can be used to force
/// synchronisation of the edge document replacement operation to disk even in case
/// that the *waitForSync* flag had been disabled for the entire collection.
/// Thus, the *waitForSync* URL parameter can be used to force synchronisation
/// of just specific operations. To use this, set the *waitForSync* parameter
/// to *true*. If the *waitForSync* parameter is not specified or set to
/// *false*, then the collection's default *waitForSync* behavior is
/// applied. The *waitForSync* URL parameter cannot be used to disable
/// synchronisation for collections that have a default *waitForSync* value
/// of *true*.
///
/// The body of the response contains a JSON object with the information about
/// the handle and the revision. The attribute *_id* contains the known
/// *document-handle* of the updated edge document, *_key* contains the key which 
/// uniquely identifies a document in a given collection, and the attribute *_rev*
/// contains the new document revision.
///
/// If the edge document does not exist, then a *HTTP 404* is returned and the
/// body of the response contains an error document.
///
/// There are two ways for specifying the targeted revision id for
/// conditional replacements (i.e. replacements that will only be executed if
/// the revision id found in the database matches the revision id specified
/// in the request):
/// - specifying the target revision in the *rev* URL query parameter
/// - specifying the target revision in the *if-match* HTTP header
///
/// Specifying a target revision is optional, however, if done, only one of the
/// described mechanisms must be used (either the *rev* URL parameter or the
/// *if-match* HTTP header).
/// Regardless which mechanism is used, the parameter needs to contain the target
/// revision id as returned in the *_rev* attribute of an edge document or
/// by an HTTP *etag* header.
///
/// For example, to conditionally replace an edge document based on a specific revision
/// id, you can use the following request:
///
/// - PUT /_api/document/*document-handle*?rev=*etag*
///
/// If a target revision id is provided in the request (e.g. via the *etag* value
/// in the *rev* URL query parameter above), ArangoDB will check that
/// the revision id of the edge document found in the database is equal to the target
/// revision id provided in the request. If there is a mismatch between the revision
/// id, then by default a *HTTP 412* conflict is returned and no replacement is
/// performed.
///
/// The conditional update behavior can be overriden with the *policy* URL query parameter:
///
/// - PUT /_api/document/*document-handle*?policy=*policy*
///
/// If *policy* is set to *error*, then the behavior is as before: replacements
/// will fail if the revision id found in the database does not match the target
/// revision id specified in the request.
///
/// If *policy* is set to *last*, then the replacement will succeed, even if the
/// revision id found in the database does not match the target revision id specified
/// in the request. You can use the *last* *policy* to force replacements.
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{201}
/// is returned if the edge document was replaced successfully and *waitForSync* was
/// *true*.
///
/// @RESTRETURNCODE{202}
/// is returned if the edge document was replaced successfully and *waitForSync* was
/// *false*.
///
/// @RESTRETURNCODE{400}
/// is returned if the body does not contain a valid JSON representation of an edge
/// document or if applied to a non-edge collection. The response body contains an
/// error document in this case.
///
/// @RESTRETURNCODE{404}
/// is returned if the collection or the edge document was not found
///
/// @RESTRETURNCODE{412}
/// is returned if a "If-Match" header or *rev* is given and the found
/// document has a different version. The response will also contain the found
/// document's current revision in the *_rev* attribute. Additionally, the
/// attributes *_id* and *_key* will be returned.
/// @endDocuBlock
////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////
/// @startDocuBlock API_EDGE_UPDATES
/// @brief updates an edge
///
/// @RESTHEADER{PATCH /_api/edge/{document-handle}, Patches edge}
///
/// @RESTBODYPARAM{document,json,required}
/// A JSON representation of the edge update.
///
/// @RESTURLPARAMETERS
///
/// @RESTURLPARAM{document-handle,string,required}
/// The handle of the edge document.
///
/// @RESTQUERYPARAMETERS
///
/// @RESTQUERYPARAM{keepNull,boolean,optional}
/// If the intention is to delete existing attributes with the patch command,
/// the URL query parameter *keepNull* can be used with a value of *false*.
/// This will modify the behavior of the patch command to remove any attributes
/// from the existing edge document that are contained in the patch document with an
/// attribute value of *null*.
///
/// @RESTQUERYPARAM{mergeObjects,boolean,optional}
/// Controls whether objects (not arrays) will be merged if present in both the
/// existing and the patch edge. If set to *false*, the value in the
/// patch edge will overwrite the existing edge's value. If set to
/// *true*, objects will be merged. The default is *true*.
///
/// @RESTQUERYPARAM{waitForSync,boolean,optional}
/// Wait until edge document has been synced to disk.
///
/// @RESTQUERYPARAM{rev,string,optional}
/// You can conditionally patch an edge document based on a target revision id by
/// using the *rev* URL parameter.
///
/// @RESTQUERYPARAM{policy,string,optional}
/// To control the update behavior in case there is a revision mismatch, you
/// can use the *policy* parameter.
///
/// @RESTHEADERPARAMETERS
///
/// @RESTHEADERPARAM{If-Match,string,optional}
/// You can conditionally patch an edge document based on a target revision id by
/// using the *if-match* HTTP header.
///
/// @RESTDESCRIPTION
/// Partially updates the edge document identified by *document-handle*.
/// The body of the request must contain a JSON document with the attributes
/// to patch (the patch document). All attributes from the patch document will
/// be added to the existing edge document if they do not yet exist, and overwritten
/// in the existing edge document if they do exist there.
///
/// Setting an attribute value to *null* in the patch document will cause a
/// value of *null* be saved for the attribute by default.
///
/// **Note**: Internal attributes such as *_key*, *_from* and *_to* are immutable
/// once set and cannot be updated.
///
/// Optionally, the URL parameter *waitForSync* can be used to force
/// synchronisation of the edge document update operation to disk even in case
/// that the *waitForSync* flag had been disabled for the entire collection.
/// Thus, the *waitForSync* URL parameter can be used to force synchronisation
/// of just specific operations. To use this, set the *waitForSync* parameter
/// to *true*. If the *waitForSync* parameter is not specified or set to
/// *false*, then the collection's default *waitForSync* behavior is
/// applied. The *waitForSync* URL parameter cannot be used to disable
/// synchronisation for collections that have a default *waitForSync* value
/// of *true*.
///
/// The body of the response contains a JSON object with the information about
/// the handle and the revision. The attribute *_id* contains the known
/// *document-handle* of the updated edge document, *_key* contains the key which 
/// uniquely identifies a document in a given collection, and the attribute *_rev*
/// contains the new document revision.
///
/// If the edge document does not exist, then a *HTTP 404* is returned and the
/// body of the response contains an error document.
///
/// You can conditionally update an edge document based on a target revision id by
/// using either the *rev* URL parameter or the *if-match* HTTP header.
/// To control the update behavior in case there is a revision mismatch, you
/// can use the *policy* parameter. This is the same as when replacing
/// edge documents (see replacing documents for details).
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{201}
/// is returned if the document was patched successfully and *waitForSync* was
/// *true*.
///
/// @RESTRETURNCODE{202}
/// is returned if the document was patched successfully and *waitForSync* was
/// *false*.
///
/// @RESTRETURNCODE{400}
/// is returned if the body does not contain a valid JSON representation or when
/// applied on an non-edge collection. The response body contains an error document
/// in this case.
///
/// @RESTRETURNCODE{404}
/// is returned if the collection or the edge document was not found
///
/// @RESTRETURNCODE{412}
/// is returned if a "If-Match" header or *rev* is given and the found
/// document has a different version. The response will also contain the found
/// document's current revision in the *_rev* attribute. Additionally, the
/// attributes *_id* and *_key* will be returned.
/// @endDocuBlock
////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////
/// @startDocuBlock API_EDGE_DELETE
/// @brief deletes an edge
///
/// @RESTHEADER{DELETE /_api/edge/{document-handle}, Deletes edge}
///
/// @RESTURLPARAMETERS
///
/// @RESTURLPARAM{document-handle,string,required}
/// Deletes the edge document identified by *document-handle*.
///
/// @RESTQUERYPARAMETERS
///
/// @RESTQUERYPARAM{rev,string,optional}
/// You can conditionally delete an edge document based on a target revision id by
/// using the *rev* URL parameter.
///
/// @RESTQUERYPARAM{policy,string,optional}
/// To control the update behavior in case there is a revision mismatch, you
/// can use the *policy* parameter. This is the same as when replacing edge
/// documents (see replacing edge documents for more details).
///
/// @RESTQUERYPARAM{waitForSync,boolean,optional}
/// Wait until edge document has been synced to disk.
///
/// @RESTHEADERPARAMETERS
///
/// @RESTHEADERPARAM{If-Match,string,optional}
/// You can conditionally delete an edge document based on a target revision id by
/// using the *if-match* HTTP header.
///
/// @RESTDESCRIPTION
/// The body of the response contains a JSON object with the information about
/// the handle and the revision. The attribute *_id* contains the known
/// *document-handle* of the deleted edge document, *_key* contains the key which 
/// uniquely identifies a document in a given collection, and the attribute *_rev*
/// contains the new document revision.
///
/// If the *waitForSync* parameter is not specified or set to
/// *false*, then the collection's default *waitForSync* behavior is
/// applied. The *waitForSync* URL parameter cannot be used to disable
/// synchronisation for collections that have a default *waitForSync* value
/// of *true*.
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{200}
/// is returned if the edge document was deleted successfully and *waitForSync* was
/// *true*.
///
/// @RESTRETURNCODE{202}
/// is returned if the edge document was deleted successfully and *waitForSync* was
/// *false*.
///
/// @RESTRETURNCODE{404}
/// is returned if the collection or the edge document was not found.
/// The response body contains an error document in this case.
///
/// @RESTRETURNCODE{412}
/// is returned if a "If-Match" header or *rev* is given and the found
/// document has a different version. The response will also contain the found
/// document's current revision in the *_rev* attribute. Additionally, the
/// attributes *_id* and *_key* will be returned.
/// @endDocuBlock
////////////////////////////////////////////////////////////////////////////////

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