rpclibrary/src/Utils.ts

import * as uuidv4 from "uuid/v4"

import * as T from "./Types";
import * as I from "./Interfaces";

/**
 * Translate an RPC to RPCInfo for serialization.
 * @param rpc The RPC to transform
 * @param owner The owning RPC group's name
 * @param errorHandler The error handler to invoke when  something goes wrong
 * @param sesame optional sesame phrase to prepend before all RPC arguments 
 * @throws Error on RPC without name property
 */
export const rpcToRpcinfo = (socket: I.Socket, rpc : T.RPC<any, any>, owner: string, errorHandler: T.ErrorHandler, sesame?:T.SesameFunction):T.RpcInfo => {
    switch (typeof rpc){
        case  "object":
            if(rpc['call']){
                return {
                    owner: owner,
                    argNames: extractArgs(rpc['call']),
                    type: "Call",
                    name: rpc.name,
                    call: sesame?async (_sesame, ...args) => {if(sesame(_sesame)) return await rpc['call'].apply({}, args); socket.destroy()}:rpc['call'], // check & remove sesame 
                }
            }else{
                const generator = hookGenerator(<T.HookRPC<any, any>>rpc, errorHandler, sesame)
                return {
                    owner: owner,
                    argNames: extractArgs(generator(undefined)),
                    type: "Hook",
                    name: rpc.name,
                    generator: generator,
                }
            }
        case "function":
            if(!rpc.name) throw new Error(`
RPC did not provide a name. 
\nUse 'funtion name(..){ .. }' syntax instead.
\n
\n<------------OFFENDING RPC:
\n${rpc.toString()}
\n>------------OFFENDING RPC`)
            return {
                owner : owner,
                argNames: extractArgs(rpc),
                type: "Call",
                name: rpc.name,
                call: sesame?async (_sesame, ...args) => {if(sesame(_sesame)) return await rpc.apply({}, args); throw makeError(rpc.name)}:rpc, // check & remove sesame 
            }
    }
    throw new Error("Bad socketIORPC type "+ typeof rpc)
}

/**
 * Utility function to apply the RPCs of an {@link RPCExporter}.
 * @param socket The websocket (implementation: bsock) to hook on
 * @param exporter The exporter
 * @param makeUnique @default true Attach a suffix to RPC names
 */
export function rpcHooker(socket: I.Socket, exporter:I.RPCExporter<any, any>, errorHandler: T.ErrorHandler, sesame?:T.SesameFunction, makeUnique = true):T.ExtendedRpcInfo[]{
    const owner = exporter.name
    const RPCs = exporter.exportRPCs()

    return RPCs.map(rpc => rpcToRpcinfo(socket, rpc, owner, errorHandler, sesame))
    .map(info => {
        const suffix = makeUnique?"-"+uuidv4().substr(0,4):""
        const ret:any = info
        ret.uniqueName = info.name+suffix
        let rpcFunction = info.type === 'Hook'? info.generator(socket)
                                              : info.call

        socket.hook(ret.uniqueName, callGenerator(info.name, socket, rpcFunction, errorHandler))
        return ret
    })
}

/**
 * Decorate an RPC with the error handler
 * @param rpcFunction the function to decorate
 */
const callGenerator = (rpcName : string, socket: I.Socket, rpcFunction : T.AnyFunction, errorHandler: T.ErrorHandler) : T.AnyFunction => {
    const argsArr = extractArgs(rpcFunction)
    const args = argsArr.join(',')
    const argsStr = argsArr.map(stripAfterEquals).join(',')

    return eval(`async (`+args+`) => {
        try{
            return await rpcFunction(`+argsStr+`)
        }catch(e){
            errorHandler(socket)(e, rpcName, [`+args+`])
        }
    }`)
}

/**
 * Utility function to strip parameters like "a = 3" of their defaults
 * @param str The parameter to modify
 */
export function stripAfterEquals(str:string):string{
    return str.split("=")[0]
}

/**
 * Utility function to generate {@link HookFunction} from a RPC for backend
 * @param rpc The RPC to transform
 * @returns A {@link HookFunction}
 */
const hookGenerator = (rpc:T.HookRPC<any, any>, /*not unused!*/ errorHandler: T.ErrorHandler, sesameFn?: T.SesameFunction): T.HookInfo['generator'] => { 
    let argsArr = extractArgs(rpc.hook)
    argsArr.pop() //remove 'callback' from the end
    let callArgs = argsArr.join(',')

    const args = sesameFn?(['sesame', ...argsArr].join(','))
                         :callArgs

    callArgs = appendComma(callArgs, false)

    //note rpc.hook is the associated RPC, not a socket.hook
    return eval(`
    (clientSocket) => async (${args}) => {
        try{
            if(sesameFn && !sesameFn(sesame)) return
            const uuid = uuidv4()
            const res = await rpc.hook(${callArgs} (...cbargs) => {
                if(rpc.onCallback){
                    rpc.onCallback.apply({}, cbargs)
                }
                clientSocket.call.apply(clientSocket, [uuid, ...cbargs])
            })
            if(rpc.onClose){
                clientSocket.on('close', () => rpc.onClose(res, rpc))
            }
            return {'uuid': uuid, 'return': res}
        }catch(e){
            //can throw to pass exception to client or swallow to keep it local
            errorHandler(clientSocket)(e, ${rpc.name}, [${args}])
        }
    }`)
}

const makeError = (callName: string) => {
    return new Error("Call not found: "+callName+". ; Zone: <root> ; Task: Promise.then ; Value: Error: Call not found: "+callName)
}

/**
 * Extract a string list of parameters from a function
 * @param f The source function
 */
const extractArgs = (f:Function):string[] => {
    let fn:string
    fn = (fn = String(f)).substr(0, fn.indexOf(")")).substr(fn.indexOf("(")+1)
    return fn!==""?fn.split(',') : []
}


export function makeSesameFunction (sesame : T.SesameFunction | string) : T.SesameFunction {
    if(typeof sesame === 'function'){
        return sesame
    }

    return (testSesame : string) => {
        return testSesame === sesame 
    }
}


export function appendComma(s?:string, turnToString = true):string{
    if(turnToString)   
        return s?`'${s}',`:"" 
        return s?`${s},`:"" 
}


/**
 * Typescript incorrectly omits the function.name attribute for MethodDeclaration.
 * This was supposedly fixed (https://github.com/microsoft/TypeScript/issues/5611) but it still is the case.
 * This function sets the name value for all object members that are functions.
*/
export function fixNames(o:Object):void{
    Object.keys(o).forEach(key => {
        if(typeof o[key] === 'function' && !o[key].name){
            Object.defineProperty(o[key], 'name', {
                value: key
            })
        }
    })
}