gistfile1.txt

var topsort = function (hash) {
    let nodes = (Object.values(hash));
    let output = [];
    let seen = new Set();

    nodes.forEach(node => {
        if (!seen.has(node)) {
            dfs(node, seen, output)
        }
    })


    return output;
}

var dfs = function (node, seen, output) {
    seen.add(node)
    for(let i=0;i<node.next.length; i++) {
        let inner = node.next[i];
        if (!seen.has(inner)) {
            dfs(inner, seen, output)
        }
    }
    output.unshift(node.value)

}




//let dict = ["ab", "abx", "aby", "c", "cg", "db", "dc", "a"]
let dict = ["a", "bb", "ba"]



// confirm no circles
let rules = new Set()

var dostuff = function(dict) {
    console.log(dict)
    dict.map((word, i) => {
        if (word === '' && i !== 0) {
            throw new Error("illegal state")
        }
    })
    console.log(dict)
    // console.log(dict)
    for (let i=0;i<dict.length;i++) {
        let prevLetter = dict[i - 1] != undefined ? dict[i - 1][0] : undefined;
        let letter = dict[i] != undefined ? dict[i][0] : undefined;
        if (prevLetter !== undefined && letter !== undefined && prevLetter !== letter) {
            rules.add(`${prevLetter}${letter}`)
        }
    }

    let inner = Object.values(dict.reduce((acc, word) => {
        if (word.length === 0) {
            return acc
        }
        if (acc[word[0]] === undefined) {
            acc[word[0]] = [];
        }
        acc[word[0]].push(word.slice(1))
        return acc;
    }, {}));
    for (let i=0;i<inner.length;i++) {
        dostuff(inner[i])
    }

}

dostuff(dict)



let entries = Object.fromEntries(Array.from(new Set(dict.join("").split(""))).map(letter => ([letter, { value: letter, next: [] }])))
rules.forEach(rule => {
    entries[rule[0]].next.push(entries[rule[1]])
})

// todo check circular dep

var checkCircular = function(entry) {
    let visited = new Set();

    let _checkCircular = function(entry) {
        visited.add(entry)
        for(let i=0;i<entry.next.length;i++) {
            let edge = entry.next[i];
            if (!visited.has(edge)) {
                return true;
            }
            let isCircular = _checkCircular(edge);
            if (isCircular) {
                return true;
            }
        }
        return false;
    }

    return _checkCircular(entry);
}

console.log(rules)

Object.values(entries).forEach((item) => {
    if (checkCircular(item)) {
        throw new Error("circular")
    }
})

console.log('---')
console.log(topsort(entries).join(""))