Given a possibly invalid JSON content and a caret position, determines the structure path that leads to it

json-autocompletion.js

const filePath = "whole-genome.json";
const esprima = require("esprima");
const fs = require("fs");
const wholeGenome = fs.readFileSync(filePath, "utf8");

console.time("whole-genome");
console.time("tokenizer");
const tokens = esprima.tokenize(wholeGenome, {loc: true});
console.timeEnd("tokenizer");

const typing = {
    column: 42,
    row: 2236 + 2
};

const lastIndex = tokens.findIndex(t => {
    return t.loc.start.line === typing.row && t.loc.end.column <= typing.column;
});

const preceedingTokens = tokens.slice(0, lastIndex);

let braceBalance = 0;
let lastEntryBalance = 0;
const keyTrace = [];
let keyCandidate;


for (let i = (preceedingTokens.length - 2); i >= 0; i--) {
    const t = preceedingTokens[i];

    const isString = t.type === "String";
    const isPunctuator = t.type === "Punctuator";

    const isBlockOpen = t.value === "{" || t.value === "[";
    const isBlockClose = t.value === "}" || t.value === "]";


    const preceedsColon = preceedingTokens[i + 1].type === "Punctuator" && preceedingTokens[i + 1].value === ":";


    if (
        (isString && preceedsColon)
        || (isPunctuator && (isBlockOpen || isBlockClose ))
    ) {
    } else {
        continue;
    }

    if (isString && !keyCandidate && braceBalance === keyTrace.length) {
        keyCandidate = t.value;
    }

    if (isPunctuator && isBlockClose) {
        braceBalance--;
    }

    if (isPunctuator && isBlockOpen) {
        braceBalance++;

        if (braceBalance > 0 && braceBalance > lastEntryBalance) {
            keyTrace.push(keyCandidate);
            lastEntryBalance = braceBalance;
            keyCandidate = undefined;
        }

    }
}

console.timeEnd("whole-genome");