import _underscore from "underscore";
import _libJsdiff from "../lib/jsdiff";

var _module_ = {
    exports: {}
};

var exports = _module_.exports;
const jsdiff = _libJsdiff;
const _ = _underscore;

const statusFor = function(chunk) {
    if (chunk.added) {
        return "added";
    } else if (chunk.removed) {
        return "removed";
    } else {
        return "unchanged";
    }
};

// Turn a chunk (which contains an array of values and a status)
// into an array of values, each with the same status
const splitUpChunk = chunk => _.map(chunk.value, value => {
    return {
        value: value,
        status: statusFor(chunk),
    };
});

// Apply `fn` to every element in `lst` and then concatenate all the results
// http://clojuredocs.org/clojure_core/clojure.core/mapcat
const mapcat = function(lst, fn) {
    return _.flatten(_.map(lst, fn), true /* only flatten one level */);
};

// > ArrayDiff.diff([1,2,3], [2,3,4]);
// = [{ "value": [1],
//      "removed": true },
//    { "value": [2, 3] },
//    { "value": [4],
//      "added": true }]
const ArrayDiff = new jsdiff.Diff();
ArrayDiff.tokenize = array => _.map(array, elem => [elem]);
// The default is `+` for string concatenation, which doesn't work for array
// concatenation.
ArrayDiff.join = (a, b) => a.concat(b);
// By default jsDiff uses ===
ArrayDiff.equals = _.isEqual;

// Take the output of jsdiff's function (which concatenates adjacent entries)
// and make it just one entry per chunk
// > flattenChunks([{ "value": [1],
//                    "removed": true },
//                  { "value": [2, 3] },
//                  { "value": [4],
//                    "added": true }])
// = [{ "value":1, "status":"removed"},
//    { "value":2, "status":"unchanged"},
//    { "value":3, "status":"unchanged"},
//    { "value":4, "status":"added"}]
const flattenChunks = chunks => mapcat(chunks, splitUpChunk);

// Take two arrays and create a diff for them. The result is two arrays of
// objects, one for the things that should be included in a 'before', and one
// for 'after'
const stringArrayDiff = function(a, b) {
    const diffResult = ArrayDiff.diff(a, b);
    const flattened = flattenChunks(diffResult);

    return {
        before: _.filter(flattened, entry => entry.status !== "added"),
        after: _.filter(flattened, entry => entry.status !== "removed"),
    };
};

_module_.exports = stringArrayDiff;
export default _module_.exports;