JSONParser.js

//Null Parser
function nullParser(input) {
    if (!input.startsWith('null')) return null
    return [null, input.slice(4)]
}
//Boolean Parser
function booleanParser(input){
    if (input.startsWith('true')) return [true,input.slice(4)]
    if (input.startsWith('false')) return [false,input.slice(5)]
    return null;
}

//Number Parser
function numberParser(input){
    let re=/^-?([1-9](\d)*|0)(\.(\d)+)?([eE][+-]?(\d)+)?/
    let n=input.match(re);
    // console.log(n)
    if(!n)return null
    return [Number(n[0]),input.slice(n[0].length)]
}
//String Parser
function StringParser(input){
    // console.log(input)
    input=input.trim()
    let a = new Set(['"', '\\', '/', 'b', 'f', 'n', 'r', 't', 'u']) 
    if(!(input.startsWith('"'))) return null;
    let i=1;
    while(input[i]!='"'){
        if(input.charCodeAt(i)===9||input.charCodeAt(i)===10) return null
        if(input[i]=='\\'){
            if(!a.has(input[i+1]))return null;
            i++;
        }
        i++
    }
    return [input.slice(1,i),input.slice(i+1)];
}


//Value Switch
function valueSelect(input){
    input=input.trim();
    return (nullParser(input)||booleanParser(input)||numberParser(input)||StringParser(input)||arrayParser(input)||objectParser(input))
}

//Array Parser
function arrayParser(input){
    let rem=input.trim();
    let arr=[]
    let val;
    if(!(input.startsWith('['))) return null;
    while(!(rem[0]==']')){
        rem=rem.slice(1).trim()
        if(rem[0]==']')break;
        val=valueSelect(rem)
        if(!val)return null
        rem=val[1].trim()
        arr.push(val[0])     //Push that value shit in the array
        if(rem[0]!==','&& rem[0]!==']')return null  //fail22
        if(rem[0]===','&& rem[1]===']')return null  //fail4
    }
    return [arr,rem.slice(1)]
}

//Object Parser
function objectParser(input){
    input=input.trim()
    let rem=input;
    let obj={}
    let key,val;
    // console.log(rem[1])
    if(!(/^{/.test(rem))) return null;
    while(!(rem[0]=='}')){
        rem=rem.slice(1).trim()
        if(rem[0]=='}')break;
        key=StringParser(rem)
        if(!key)return null
        rem=key[1].trim()
        if(rem[0]!=':')return null;
        val=valueSelect(rem.slice(1))
        if(!val)return null
        rem=val[1].trim()
        rem=rem.trim()
        obj[key[0]]=val[0];
        if(rem[0]===','&& rem[1]==='}')return null  //fail9

    }
    // console.log("input:",input)
    // console.log('rem:',rem)
    return [obj,rem.slice(1)]
    // return obj
}

// console.log(arrayParser('[1,2,3,4,5,6,7,8,69,"fffff"]'));

// console.log(objectParser('{"imped":34,"modiji":true},this is also a obje'));

// console.log(StringParser('"this is \"sparta \t hokage Omewa \" Mo sindeiru \u123f jutsu"well then i am god'));

// console.log(JSON.parse('"this is \" sparta \t hokage Omewa\" Mo sindeiru \u123f jutsu"'))
  
// console.log(numberParser('edc123'))

// JSONParser('{"hey":[1,2,3,4]}')
// StringParser("superduper")
// console.log(numberParser('2322asdf'))


function JSONParser (input) {
    // input = input.trim()
    // console.log("json Input;",input)
    const parsedValue = arrayParser(input) || objectParser(input)
    
    if (parsedValue === null ||parsedValue[1]!=='') { return 'Not a valid JSON input'}  //sec condition is for test case 7 and 8
    // console.log('Parsed:')
    // if((parsedValue[1])){return 'Not a JSON'}    //see fail 7 and 8 for reason of inserting this line
    return parsedValue[0]
  }

const fs = require('fs');
const { json } = require('stream/consumers');
// fail cases
for (let i = 1; i <= 33; i++) {
  if (i !== 18) {
    const data = fs.readFileSync(`./test/fail${i}.json`, 'utf8')
    console.log(`fail${i}:`, JSONParser(data))
  }
}

// pass cases
for (let i = 1; i <= 5; i++) {
  const data = fs.readFileSync(`./test/pass${i}.json`, 'utf8')
  console.log(`pass${i}:`, JSONParser(data))
}


// console.log(numberParser('12e'))
// console.log(arrayParser('[[[[[[[[[[[[[[[[[[["Not too deep"]]]]]]]]]]]]]]]]]]]'))
// const data = fs.readFileSync(`./test/pass4.json`, 'utf8')
// console.log(`pass`, JSONParser(data))

// let a=JSON.stringify({"google":"My war \n and hokage"})
// console.log(JSON.stringify({"google":"My war \n and hokage"}))
// console.log(`pass`, JSONParser(a))