'use strict';
// lineclip by mourner, https://github.com/mapbox/lineclip
// Cohen-Sutherland line clippign algorithm, adapted to efficiently
// handle polylines rather than just segments
function lineclip(points, bbox, result) {
    var len = points.length,
        codeA = bitCode(points[0], bbox),
        part = [],
        i, a, b, codeB, lastCode;
    if (!result) result = [];

    for (i = 1; i < len; i++) {
        a = points[i - 1];
        b = points[i];
        codeB = lastCode = bitCode(b, bbox);

        while (true) {
            if (!(codeA | codeB)) { // accept
                part.push(a);

                if (codeB !== lastCode) { // segment went outside
                    part.push(b);
                    if (i < len - 1) { // start a new line
                        result.push(part);
                        part = [];
                    }
                } else if (i === len - 1) {
                    part.push(b);
                }
                break;

            } else if (codeA & codeB) { // trivial reject
                break;
            } else if (codeA) { // a outside, intersect with clip edge
                a = intersect(a, b, codeA, bbox);
                codeA = bitCode(a, bbox);
            } else { // b outside
                b = intersect(a, b, codeB, bbox);
                codeB = bitCode(b, bbox);
            }
        }
        codeA = lastCode;
    }

    if (part.length) result.push(part);

    return result;
}

// Sutherland-Hodgeman polygon clipping algorithm
function polygonclip(points, bbox, secure = 0) {
    var result, edge, prev, prevInside, inter, i, p, inside;

    // clip against each side of the clip rectangle
    for (edge = 1; edge <= 8; edge *= 2) {
        result = [];
        prev = points[points.length-1];
        prevInside = !(bitCode(prev, bbox) & edge);

        for (i = 0; i < points.length; i++) {
            p = points[i];
            inside = !(bitCode(p, bbox) & edge);
            inter = inside !== prevInside; // segment goes through the clip window

            const pi = intersect(prev, p, edge, bbox);
            if (inter) result.push(pi); // add an intersection point
            if (secure && inter) result.push(pi, pi); // add additional intersection points to secure correct d3 curve
            if (inside) result.push(p); // add a point if it's inside

            prev = p;
            prevInside = inside;
        }
        points = result;
        if (!points.length) break;
    }
    //result.forEach(p => debug.append("circle").attr("cx", p[0]).attr("cy", p[1]).attr("r", .6).attr("fill", "red"));
    return result;
}

// intersect a segment against one of the 4 lines that make up the bbox
function intersect(a, b, edge, bbox) {
    return edge & 8 ? [a[0] + (b[0] - a[0]) * (bbox[3] - a[1]) / (b[1] - a[1]), bbox[3]] : // top
        edge & 4 ? [a[0] + (b[0] - a[0]) * (bbox[1] - a[1]) / (b[1] - a[1]), bbox[1]] : // bottom
        edge & 2 ? [bbox[2], a[1] + (b[1] - a[1]) * (bbox[2] - a[0]) / (b[0] - a[0])] : // right
        edge & 1 ? [bbox[0], a[1] + (b[1] - a[1]) * (bbox[0] - a[0]) / (b[0] - a[0])] : null; // left
}

// bit code reflects the point position relative to the bbox:
//         left  mid  right
//    top  1001  1000  1010
//    mid  0001  0000  0010
// bottom  0101  0100  0110
function bitCode(p, bbox) {
    var code = 0;

    if (p[0] < bbox[0]) code |= 1; // left
    else if (p[0] > bbox[2]) code |= 2; // right

    if (p[1] < bbox[1]) code |= 4; // bottom
    else if (p[1] > bbox[3]) code |= 8; // top

    return code;
}