parent pointer tree to map

pptToMap.js

import R from "ramda";

const stringize = value => typeof value === "number" ? value + "" : value;

const orphanIds = R.compose(
    R.reduce((partial, pair) => [
        ...partial,
        pair[0],
        ...orphanIds(pair[1].children)
    ], []),
    R.toPairs()
);

// Update de-orphaned indices to reflect the location of their new parent
const updateOrphanIndices = (orphan, parentLocation) => indices => R.reduce(
    (partial, id) => R.over(R.lensProp(id), R.compose(
        R.concat(parentLocation),
        R.update(0, "children")
    ), partial),
    indices,
    orphanIds(orphan)
);

// Convert parent-pointer-tree to map
const resolve = R.reduce((partial, update) => {
    const id = stringize(update.id);
    const parent = stringize(update.parent);
    const {
        orphans,
        indices
    } = partial;

    const orphan = R.path([id, "children"], orphans) || {};
    const entry = R.compose(
        R.dissoc("parent"),
        R.dissoc("id"),
        R.assoc("children", orphan)
    )(update);

    const location = (parent === null) ? [] :
        indices[parent] || ["orphans", parent];

    return R.compose(
        R.over(R.lensProp("indices"), updateOrphanIndices(orphan, location)), // Update orphan indices
        R.dissocPath(["orphans", id ]), // Remove obsolete orphan entry
        R.assocPath(["indices", id], [ ...location, "children", id ]), // Assign new index
        R.assocPath([...location, "children", id], entry) // Attach to parent
    )(partial);
});


const x = resolve({
    children: {},
    orphans: {},
    indices: {}
}, [
    {
    	id: 5,
        x: "c5",
        parent: 2
    },
	{
    	id: 1,
        x: "a1",
        parent: null
    },
    {
    	id: 2,
        x: "b2",
        parent: 1
    },
    {
    	id: 3,
        x: "b3",
        parent: 1
    },
    {
    	id: 4,
        x: "c4",
        parent: 2
    }
]);

JSON.stringify(x, null, 4)