// Hirschberg's algorithm
// http://en.wikipedia.org/wiki/Hirschberg%27s_algorithm

/**
 * @module zrender/core/arrayDiff
 * @author Yi Shen
 */

function defaultCompareFunc(a, b) {
    return a === b;
}

function createItem(cmd, idx, idx1) {
    var res = {
        // cmd explanation
        // '=': not change
        // '^': replace with a new item in second array. Unused temporary
        // '+': add a new item of second array
        // '-': del item in first array
        cmd: cmd,
        // Value index, use index in the first array
        // Except '+'. Adding a new item needs value in the second array
        idx: idx
    };
    // Replace need to know both two indices
    // if (cmd === '^') {
    //     res.idx1 = idx1;
    // }

    if (cmd === '=') {
        res.idx1 = idx1;
    }
    return res;
}

function append(out, cmd, idx, idx1) {
    out.push(createItem(cmd, idx, idx1));
}

var abs = Math.abs;
// Needleman-Wunsch score
function score(arr0, arr1, i0, i1, j0, j1, equal, memo) {
    var last;
    var invM = i0 > i1;
    var invN = j0 > j1;
    var m = abs(i1 - i0);
    var n = abs(j1 - j0);
    var i;
    var j;
    for (i = 0; i <= m; i++) {
        for (j = 0; j <= n; j++) {
            if (i === 0) {
                memo[j] = j;
            }
            else if (j === 0) {
                last = memo[j];
                memo[j] = i;
            }
            else {
                // memo[i-1][j-1] + same(arr0[i-1], arr1[j-1]) ? 0 : 1
                // Retained or replace
                var val0 = arr0[invM ? (i0 - i) : (i - 1 + i0)];
                var val1 = arr1[invN ? (j0 - j) : (j - 1 + j0)];
                // Because replace is add after remove actually
                // It has a higher score than removing or adding
                // TODO custom score function
                var score0 = last + (equal(val0, val1) ? 0 : 2);
                // memo[i-1][j] + 1
                // Remove arr0[i-1]
                var score1 = memo[j] + 1;
                // memo[i][j-1] + 1
                // Add arr1[j-1]
                var score2 = memo[j - 1] + 1;

                last = memo[j];
                memo[j] = score0 < score1 ? score0 : score1;
                score2 < memo[j] && (memo[j] = score2);
                // Math min of three parameters seems slow
                // memo[j] = Math.min(score0, score1, score2);
            }
        }
    }

    return memo;
}

function hirschberg(arr0, arr1, i0, i1, j0, j1, equal, score0, score1) {
    var out = [];
    var len0 = i1 - i0;
    var len1 = j1 - j0;
    var i;
    var j;
    if (!len0) {
        for (j = 0; j < len1; j++) {
            append(out, '+', j + j0);
        }
    }
    else if (!len1) {
        for (i = 0; i < len0; i++) {
            append(out, '-', i + i0);
        }
    }
    else if (len0 === 1) {
        var a = arr0[i0];
        var matched = false;
        for (j = 0; j < len1; j++) {
            if (equal(a, arr1[j + j0]) && !matched) {
                matched = true;
                // Equal and update use the index in first array
                append(out, '=', i0, j + j0);
            }
            else {
                // if (j === len1 - 1 && ! matched) {
                //     append(out, '^', i0, j + j0);
                // }
                // else {
                append(out, '+', j + j0);
                // }
            }
        }
        if (!matched) {
            append(out, '-', i0);
        }
    }
    else if (len1 === 1) {
        var b = arr1[j0];
        var matched = false;
        for (i = 0; i < len0; i++) {
            if (equal(b, arr0[i + i0]) && !matched) {
                matched = true;
                append(out, '=', i + i0, j0);
            }
            else {
                // if (i === len0 - 1 && ! matched) {
                //     append(out, '^', i + i0, j0);
                // }
                // else {
                append(out, '-', i + i0);
                // }
            }
        }
        if (!matched) {
            append(out, '+', j0);
        }
    }
    else {
        var imid = ((len0 / 2) | 0) + i0;

        score(arr0, arr1, i0, imid, j0, j1, equal, score0);
        score(arr0, arr1, i1, imid + 1, j1, j0, equal, score1);

        var min = Infinity;
        var jmid = 0;
        var sum;
        for (j = 0; j <= len1; j++) {
            sum = score0[j] + score1[len1 - j];
            if (sum < min) {
                min = sum;
                jmid = j;
            }
        }
        jmid += j0;

        out = hirschberg(arr0, arr1, i0, imid, j0, jmid, equal, score0, score1);
        var out1 = hirschberg(arr0, arr1, imid, i1, jmid, j1, equal, score0, score1);
        // Concat
        for (i = 0; i < out1.length; i++) {
            out.push(out1[i]);
        }
    }
    return out;
}

function arrayDiff(arr0, arr1, equal) {
    equal = equal || defaultCompareFunc;
    // Remove the common head and tail
    var i;
    var j;
    var len0 = arr0.length;
    var len1 = arr1.length;
    var lenMin = Math.min(len0, len1);
    var head = [];
    for (i = 0; i < lenMin; i++) {
        if (!equal(arr0[i], arr1[i])) {
            break;
        }
        append(head, '=', i, i);
    }

    for (j = 0; j < lenMin; j++) {
        if (!equal(arr0[len0 - j - 1], arr1[len1 - j - 1])) {
            break;
        }
    }

    if (len0 - j >= i || len1 - j >= i) {
        var middle = hirschberg(arr0, arr1, i, len0 - j, i, len1 - j, equal, [], []);
        for (i = 0; i < middle.length; i++) {
            head.push(middle[i]);
        }
        for (i = 0; i < j; i++) {
            append(head, '=', len0 - j + i, len1 - j + i);
        }
    }
    return head;
}

export default arrayDiff;