Implement api/session/createproblem with self selecting problems

+const Participation = require("../../models/participation");
+const Session = require("../../models/session");
+const Group = require("../../models/group");
+const User = require("../../models/user");
+const mongoose = require("mongoose");
+
+const {ObjectId} = mongoose.Types;
+
 /* POST /api/session/createproblem/:how
 {   
-    problemList:[Number]
+    sessionId: ObjectId,
+    groupId: ObjectId,
+    problemList:[Number],
 }
 */
 exports.createProblem = async (ctx)=>{
     try{
+        let {sessionId,groupId,problemList} = ctx.request.body;
+        if(typeof(sessionId)==='string'){
+            sessionId=new ObjectId(sessionId);
+        }
+        if(typeof(groupId)==='string'){
+            groupId=new ObjectId(groupId);
+        }
+        if(typeof(problemList)==='string'){
+            problemList=JSON.parse(problemList);
+        }
+        const participation = await Participation.findOne({sessionId:sessionId,groupId:groupId});
+        const group = await Group.findById(groupId);
         const how=ctx.params.how;
         if(how==='self'){
-
+            let check = true;
+            for(let i=0;i<group.members.length;i++){
+                const user = await User.findById(group.members[i]);
+                console.log(user);
+                console.log(typeof(user.solvedBJ_date.solvedBJbyDATE));
+                let userProblemList = [];
+                for(let key in user.solvedBJ_date.solvedBJbyDATE){
+                    userProblemList.push(user.solvedBJ_date.solvedBJbyDATE[key]);
+                }
+                userProblemList=userProblemList.flat().map(elem=>elem.problem_number);
+                for(let j=0;j<problemList.length;j++){
+                    if(userProblemList.includes(problemList[j])){
+                        check = false;
+                        break;
+                    }
+                }
+            }
+            if(!check){
+                ctx.throw('그룹원이 이미 푼 문제는 등록할 수 없습니다.');
+                return;
+            }
+            else{
+                problemList.map(async problemNum=>await participation.addProblem({problemNum:problemNum,isSolved:false}));
+                ctx.body=participation.serialize(); 
+            }
         }
         else if(how==='recommend'){
-
+            //TODO
         }
     }
     catch(e){