cloud-functions

        const functions = require('firebase-functions');
        const admin = require('firebase-admin');
        admin.initializeApp();

        exports.requestNotification=functions.database.ref('/Users/{userId}/Book_requests/{requestId}')
        .onCreate((snap, context) =>{
            const object=snap.val();
            const recevierId=context.params.userId;
            const requestId=context.params.requestId;
            const requesterId=object['requesterId'];
            const bookId=object['bookId'];

            const requesterRef=admin.database().ref('/Users/'+requesterId).once('value');
            const bookRef=admin.database().ref('/Books/'+bookId).once('value');
            const recieverRef=admin.database().ref('/Users/'+recevierId).once('value');

            return Promise.all([requesterRef,recieverRef,bookRef]).then((result=>{
                const requesterName=result[0].val()['name'];
                const reciverToken=result[1].val()['deviceToken'];
                const bookTitle=result[2].val()['title'];
                const recieverName=result[1].val()['name'];
                const requesterHistory='you have requested to '+recieverName+' for the book '+bookTitle;
                const recieverHistory=requesterName+' requests for the books named '+bookTitle;
                const historyRefRequester=admin.database().ref('/Users/'+requesterId+'/History/').push({
                    historyType:"request",
                    historyMsg:requesterHistory
                });
                const historyRefReciever=admin.database().ref('/Users/'+recevierId+'/History/').push({
                    historyType:"request",
                    historyMsg:recieverHistory
                });
                return Promise.all([historyRefRequester,historyRefReciever]).then((result=>{
                    const payload={
                        notification:{
                            title:" Book Request ",
                            body:requesterName+" wants one of your book named "+bookTitle
                        },
                        data:{
                            Type:"request"
                        }
                    }
                    return admin.messaging().sendToDevice(reciverToken,payload).catch((error=>{
                        console.log('error occured',error);
                    }));

                }))



            }))


        });

        exports.acceptNotification=functions.database.ref('/Users/{userId}/Book_requests/{requestId}')
        .onUpdate((change, context) =>{
            const updatedObj=change.after.val();
            const borrowerId=updatedObj['requesterId'];
            const requestId=context.params.requestId
            const lenderId =context.params.userId;
            const bookId=updatedObj['bookId'];
            const bookRef=admin.database().ref('/Books/'+bookId).once('value');
            const borrowerRef=admin.database().ref('/Users/'+borrowerId).once('value');
            const lenderRef=admin.database().ref('/Users/'+lenderId).once('value');

            return Promise.all([borrowerRef,lenderRef,bookRef]).then((result=>{
                const bookTitle=result[2].val()['title'];
                const borrowerName=result[0].val()['name'];
                const lenderName=result[1].val()['name'];
                const borrowerHistoy='your request for the book '+bookTitle+' has been accepted by '+lenderName;
                const lenderHistory='you have accepted '+borrowerName+' requests for the book'+bookTitle;
                const borrowerToken=result[0].val()['deviceToken'];
                const historyRefBorrower=admin.database().ref('/Users/'+borrowerId+'/History/').push({
                    historyType:"request accepted",
                    historyMsg:borrowerHistoy
                });
                const historyRefLender=admin.database().ref('/Users/'+lenderId+'/History/').push({
                    historyType:"request accepted",
                    historyMsg:lenderHistory
                });
                const updateBookStatus=admin.database().ref('/Books/'+bookId+'/').update({
                    status:'Not Available'
                });
                const originalBook=result[2].val();
                originalBook['borrowerId']=borrowerId;
                const deleteFromUserBookList=admin.database().ref('/Users/'+lenderId+'/Books/Available/'+bookId).remove();
                const requestDelete=admin.database().ref('/Users/'+lenderId+'/Book_requests/'+requestId).remove();
                const borrowedBookListRef=admin.database().ref('/Users/'+borrowerId+'/Books/Borrowed/'+bookId).set(originalBook);
                const lendBookListRef=admin.database().ref('/Users/'+lenderId+'/Books/Lend/'+bookId).set(originalBook);
                return Promise.all([historyRefBorrower,historyRefLender,updateBookStatus,borrowedBookListRef,lendBookListRef,deleteFromUserBookList,requestDelete]).then((result=>{
                    const payload={
                        notification:{
                            title:" Book Request Accepted ",
                            body:lenderName+" accepted your request for the book "+bookTitle
                        },
                        data:{
                            Type:"requestAccept"
                        }
                    }

                    return admin.messaging().sendToDevice(borrowerToken,payload).catch((error=>{
                        console.log("error occured in"+error);
                    }));
                }))


            }));



        });


        exports.returnRequestNotification=functions.database.ref('/Users/{recieverId}/Return_requests/{requestId}')
        .onCreate((snapshot,context)=>{
            const recevierId=context.params.recieverId;
            const requestId=context.params.requestId;
            const object=snapshot.val();
            const requesterName=object['requesterName'];
            const requesterId=object['requesterId'];
            const bookTitle=object['bookTitle'];
            const recieverRef=admin.database().ref('/Users/'+recevierId).once('value');
            return recieverRef.then((result=>{
                const recieverToken=result.val()['deviceToken'];
                const recieverName=result.val()['name'];
                const requesterHistory='you have requested to '+recieverName+' to return the book '+bookTitle;
                const recieverHistory=requesterName+' wants to return the book  '+bookTitle;
                const historyRefRequester=admin.database().ref('/Users/'+requesterId+'/History/').push({
                    historyType:"return request",
                    historyMsg:requesterHistory
                });
                const historyRefReciever=admin.database().ref('/Users/'+recevierId+'/History/').push({
                    historyType:"return request",
                    historyMsg:recieverHistory
                });

                return Promise.all([historyRefRequester,historyRefReciever]).then((result=>{
                        const payload={
                            notification:{
                                title:" Book Return Request ",
                                body:requesterName+" wants to return your book named "+bookTitle
                            },
                            data:{
                                Type:"returnRequest"
                            }
                    }

                    return admin.messaging().sendToDevice(recieverToken,payload).catch((error=>{
                        console.log("error occured in"+error);
                    }))

                }))

            }))

        })
        exports.acceptReturnRequestNotification=functions.database.ref('/Users/{recieverId}/Return_requests/{requestId}')
        .onUpdate((change,context)=>{
            const object=change.after.val();
            const recieverId=context.params.recieverId;
            const requestId=context.params.requestId;
            const requesterId=object['requesterId'];
            const bookId=object['bookId'];
            const bookTitle=object['bookTitle'];
            const requesterRef=admin.database().ref('/Users/'+requesterId).once('value');
            const recieverRef=admin.database().ref('/Users/'+recieverId).once('value');
            return Promise.all([requesterRef,recieverRef]).then((result=>{
                const requesterName=result[0].val()['name'];
                const requesterToken=result[0].val()['deviceToken'];
                const recieverName=result[1].val()['name'];
                const requesterHistoy='your return request for the book '+bookTitle+' has been accepted by '+recieverName;
                const recieverHistory='you have accepted return requests of '+requesterName+' for the book '+bookTitle;

                const historyRefRequester=admin.database().ref('/Users/'+requesterId+'/History/').push({
                    historyType:"return request accepted",
                    historyMsg:requesterHistoy
                });
                const historyRefReciever=admin.database().ref('/Users/'+recieverId+'/History/').push({
                    historyType:"return request accepted",
                    historyMsg:recieverHistory
                });
                const updateBookStatus=admin.database().ref('/Books/'+bookId+'/').update({
                    status:'Available'
                });


                return Promise.all([historyRefRequester,historyRefReciever,updateBookStatus])
                .then((result=>{
                const bookRef=admin.database().ref('/Books/'+bookId).once('value');
                return bookRef.then((result=>{
                   const bookObj=result.val();
                   bookObj['borrowerId']="";
                   const deleteFromlendList=admin.database().ref('/Users/'+recieverId+'/Books/Lend/'+bookId).remove();
                   const deleteFromBorrowList=admin.database().ref('/Users/'+requesterId+'/Books/Borrowed/'+bookId).remove();
                   const insertIntoAvailableList=admin.database().ref('/Users/'+recieverId+'/Books/Available/'+bookId).set(bookObj);
                   const deleteRequest=admin.database().ref('/Users/'+recieverId+'/Return_requests/'+requestId).remove();
                   return Promise.all([deleteFromlendList,deleteFromBorrowList,insertIntoAvailableList,deleteRequest])
                   .then((result=>{
                        const payload={
                        notification:{
                            title:"Return Book Request Accepted ",
                            body:recieverName+" accepted your return request for the book "+bookTitle
                        },
                        data:{
                            Type:"returnRequestAccept"
                        }
                    }

                    return admin.messaging().sendToDevice(requesterToken,payload).catch((error=>{
                        console.log(error);
                    }))

                   }))



                }))

                }))
            }))



        })

        exports.scheduledFunctionCrontab = functions.pubsub
        .schedule('50 19 * * *').onRun((context) => {
    console.log('This will be run every day at 19:50 AM UTC!');
});