text: import {dispatch} from "d3-dispatch";
  import {dragDisable, dragEnable} from "d3-drag";
  import {interpolateZoom} from "d3-interpolate";
  import {event, customEvent, select, mouse, touch} from "d3-selection";
  import {interrupt} from "d3-transition";
  import constant from "./constant.js";
  import ZoomEvent from "./event.js";
  import {Transform, identity} from "./transform.js";
  import noevent, {nopropagation} from "./noevent.js";
  
  // Ignore right-click, since that should open the context menu.
  function defaultFilter() {
    return !event.ctrlKey && !event.button;
  }
  
  function defaultExtent() {
    var e = this;
    if (e instanceof SVGElement) {
      e = e.ownerSVGElement || e;
      if (e.hasAttribute("viewBox")) {
        e = e.viewBox.baseVal;
        return [[e.x, e.y], [e.x + e.width, e.y + e.height]];
      }
      return [[0, 0], [e.width.baseVal.value, e.height.baseVal.value]];
    }
    return [[0, 0], [e.clientWidth, e.clientHeight]];
  }
  
  function defaultTransform() {
    return this.__zoom || identity;
  }
  
  function defaultWheelDelta() {
    return -event.deltaY * (event.deltaMode === 1 ? 0.05 : event.deltaMode ? 1 : 0.002);
  }
  
  function defaultTouchable() {
    return navigator.maxTouchPoints || ("ontouchstart" in this);
  }
  
  function defaultConstrain(transform, extent, translateExtent) {
    var dx0 = transform.invertX(extent[0][0]) - translateExtent[0][0],
        dx1 = transform.invertX(extent[1][0]) - translateExtent[1][0],
        dy0 = transform.invertY(extent[0][1]) - translateExtent[0][1],
        dy1 = transform.invertY(extent[1][1]) - translateExtent[1][1];
    return transform.translate(
      dx1 > dx0 ? (dx0 + dx1) / 2 : Math.min(0, dx0) || Math.max(0, dx1),
      dy1 > dy0 ? (dy0 + dy1) / 2 : Math.min(0, dy0) || Math.max(0, dy1)
    );
  }
  
  export default function() {
    var filter = defaultFilter,
        extent = defaultExtent,
        constrain = defaultConstrain,
        wheelDelta = defaultWheelDelta,
        touchable = defaultTouchable,
        scaleExtent = [0, Infinity],
        translateExtent = [[-Infinity, -Infinity], [Infinity, Infinity]],
        duration = 250,
        interpolate = interpolateZoom,
        listeners = dispatch("start", "zoom", "end"),
        touchstarting,
        touchending,
        touchDelay = 500,
        wheelDelay = 150,
        clickDistance2 = 0;
  
    function zoom(selection) {
      selection
          .property("__zoom", defaultTransform)
          .on("wheel.zoom", wheeled)
          .on("mousedown.zoom", mousedowned)
          .on("dblclick.zoom", dblclicked)
        .filter(touchable)
          .on("touchstart.zoom", touchstarted)
          .on("touchmove.zoom", touchmoved)
          .on("touchend.zoom touchcancel.zoom", touchended)
          .style("touch-action", "none")
          .style("-webkit-tap-highlight-color", "rgba(0,0,0,0)");
    }
  
    zoom.transform = function(collection, transform, point) {
      var selection = collection.selection ? collection.selection() : collection;
      selection.property("__zoom", defaultTransform);
      if (collection !== selection) {
        schedule(collection, transform, point);
      } else {
        selection.interrupt().each(function() {
          gesture(this, arguments)
              .start()
              .zoom(null, typeof transform === "function" ? transform.apply(this, arguments) : transform)
              .end();
        });
      }
    };
  
    zoom.scaleBy = function(selection, k, p) {
      zoom.scaleTo(selection, function() {
        var k0 = this.__zoom.k,
            k1 = typeof k === "function" ? k.apply(this, arguments) : k;
        return k0 * k1;
      }, p);
    };
  
    zoom.scaleTo = function(selection, k, p) {
      zoom.transform(selection, function() {
        var e = extent.apply(this, arguments),
            t0 = this.__zoom,
            p0 = p == null ? centroid(e) : typeof p === "function" ? p.apply(this, arguments) : p,
            p1 = t0.invert(p0),
            k1 = typeof k === "function" ? k.apply(this, arguments) : k;
        return constrain(translate(scale(t0, k1), p0, p1), e, translateExtent);
      }, p);
    };
  
    zoom.translateBy = function(selection, x, y) {
      zoom.transform(selection, function() {
        return constrain(this.__zoom.translate(
          typeof x === "function" ? x.apply(this, arguments) : x,
          typeof y === "function" ? y.apply(this, arguments) : y
        ), extent.apply(this, arguments), translateExtent);
      });
    };
  
    zoom.translateTo = function(selection, x, y, p) {
      zoom.transform(selection, function() {
        var e = extent.apply(this, arguments),
            t = this.__zoom,
            p0 = p == null ? centroid(e) : typeof p === "function" ? p.apply(this, arguments) : p;
        return constrain(identity.translate(p0[0], p0[1]).scale(t.k).translate(
          typeof x === "function" ? -x.apply(this, arguments) : -x,
          typeof y === "function" ? -y.apply(this, arguments) : -y
        ), e, translateExtent);
      }, p);
    };
  
    function scale(transform, k) {
      k = Math.max(scaleExtent[0], Math.min(scaleExtent[1], k));
      return k === transform.k ? transform : new Transform(k, transform.x, transform.y);
    }
  
    function translate(transform, p0, p1) {
      var x = p0[0] - p1[0] * transform.k, y = p0[1] - p1[1] * transform.k;
      return x === transform.x && y === transform.y ? transform : new Transform(transform.k, x, y);
    }
  
    function centroid(extent) {
      return [(+extent[0][0] + +extent[1][0]) / 2, (+extent[0][1] + +extent[1][1]) / 2];
    }
  
    function schedule(transition, transform, point) {
      transition
          .on("start.zoom", function() { gesture(this, arguments).start(); })
          .on("interrupt.zoom end.zoom", function() { gesture(this, arguments).end(); })
          .tween("zoom", function() {
            var that = this,
                args = arguments,
                g = gesture(that, args),
                e = extent.apply(that, args),
                p = point == null ? centroid(e) : typeof point === "function" ? point.apply(that, args) : point,
                w = Math.max(e[1][0] - e[0][0], e[1][1] - e[0][1]),
                a = that.__zoom,
                b = typeof transform === "function" ? transform.apply(that, args) : transform,
                i = interpolate(a.invert(p).concat(w / a.k), b.invert(p).concat(w / b.k));
            return function(t) {
              if (t === 1) t = b; // Avoid rounding error on end.
              else { var l = i(t), k = w / l[2]; t = new Transform(k, p[0] - l[0] * k, p[1] - l[1] * k); }
              g.zoom(null, t);
            };
          });
    }
  
    function gesture(that, args, clean) {
      return (!clean && that.__zooming) || new Gesture(that, args);
    }
  
    function Gesture(that, args) {
      this.that = that;
      this.args = args;
      this.active = 0;
      this.extent = extent.apply(that, args);
      this.taps = 0;
    }
  
    Gesture.prototype = {
      start: function() {
        if (++this.active === 1) {
          this.that.__zooming = this;
          this.emit("start");
        }
        return this;
      },
      zoom: function(key, transform) {
        if (this.mouse && key !== "mouse") this.mouse[1] = transform.invert(this.mouse[0]);
        if (this.touch0 && key !== "touch") this.touch0[1] = transform.invert(this.touch0[0]);
        if (this.touch1 && key !== "touch") this.touch1[1] = transform.invert(this.touch1[0]);
        this.that.__zoom = transform;
        this.emit("zoom");
        return this;
      },
      end: function() {
        if (--this.active === 0) {
          delete this.that.__zooming;
          this.emit("end");
        }
        return this;
      },
      emit: function(type) {
        customEvent(new ZoomEvent(zoom, type, this.that.__zoom), listeners.apply, listeners, [type, this.that, this.args]);
      }
    };
  
    function wheeled() {
      if (!filter.apply(this, arguments)) return;
      var g = gesture(this, arguments),
          t = this.__zoom,
          k = Math.max(scaleExtent[0], Math.min(scaleExtent[1], t.k * Math.pow(2, wheelDelta.apply(this, arguments)))),
          p = mouse(this);
  
      // If the mouse is in the same location as before, reuse it.
      // If there were recent wheel events, reset the wheel idle timeout.
      if (g.wheel) {
        if (g.mouse[0][0] !== p[0] || g.mouse[0][1] !== p[1]) {
          g.mouse[1] = t.invert(g.mouse[0] = p);
        }
        clearTimeout(g.wheel);
      }
  
      // If this wheel event won’t trigger a transform change, ignore it.
      else if (t.k === k) return;
  
      // Otherwise, capture the mouse point and location at the start.
      else {
        g.mouse = [p, t.invert(p)];
        interrupt(this);
        g.start();
      }
  
      noevent();
      g.wheel = setTimeout(wheelidled, wheelDelay);
      g.zoom("mouse", constrain(translate(scale(t, k), g.mouse[0], g.mouse[1]), g.extent, translateExtent));
  
      function wheelidled() {
        g.wheel = null;
        g.end();
      }
    }
  
    function mousedowned() {
      if (touchending || !filter.apply(this, arguments)) return;
      var g = gesture(this, arguments, true),
          v = select(event.view).on("mousemove.zoom", mousemoved, true).on("mouseup.zoom", mouseupped, true),
          p = mouse(this),
          x0 = event.clientX,
          y0 = event.clientY;
  
      dragDisable(event.view);
      nopropagation();
      g.mouse = [p, this.__zoom.invert(p)];
      interrupt(this);
      g.start();
  
      function mousemoved() {
        noevent();
        if (!g.moved) {
          var dx = event.clientX - x0, dy = event.clientY - y0;
          g.moved = dx * dx + dy * dy > clickDistance2;
        }
        g.zoom("mouse", constrain(translate(g.that.__zoom, g.mouse[0] = mouse(g.that), g.mouse[1]), g.extent, translateExtent));
      }
  
      function mouseupped() {
        v.on("mousemove.zoom mouseup.zoom", null);
        dragEnable(event.view, g.moved);
        noevent();
        g.end();
      }
    }
  
    function dblclicked() {
      if (!filter.apply(this, arguments)) return;
      var t0 = this.__zoom,
          p0 = mouse(this),
          p1 = t0.invert(p0),
          k1 = t0.k * (event.shiftKey ? 0.5 : 2),
          t1 = constrain(translate(scale(t0, k1), p0, p1), extent.apply(this, arguments), translateExtent);
  
      noevent();
      if (duration > 0) select(this).transition().duration(duration).call(schedule, t1, p0);
      else select(this).call(zoom.transform, t1);
    }
  
    function touchstarted() {
      if (!filter.apply(this, arguments)) return;
      var touches = event.touches,
          n = touches.length,
          g = gesture(this, arguments, event.changedTouches.length === n),
          started, i, t, p;
  
      nopropagation();
      for (i = 0; i < n; ++i) {
        t = touches[i], p = touch(this, touches, t.identifier);
        p = [p, this.__zoom.invert(p), t.identifier];
        if (!g.touch0) g.touch0 = p, started = true, g.taps = 1 + !!touchstarting;
        else if (!g.touch1 && g.touch0[2] !== p[2]) g.touch1 = p, g.taps = 0;
      }
  
      if (touchstarting) touchstarting = clearTimeout(touchstarting);
  
      if (started) {
        if (g.taps < 2) touchstarting = setTimeout(function() { touchstarting = null; }, touchDelay);
        interrupt(this);
        g.start();
      }
    }
  
    function touchmoved() {
      if (!this.__zooming) return;
      var g = gesture(this, arguments),
          touches = event.changedTouches,
          n = touches.length, i, t, p, l;
  
      noevent();
      if (touchstarting) touchstarting = clearTimeout(touchstarting);
      g.taps = 0;
      for (i = 0; i < n; ++i) {
        t = touches[i], p = touch(this, touches, t.identifier);
        if (g.touch0 && g.touch0[2] === t.identifier) g.touch0[0] = p;
        else if (g.touch1 && g.touch1[2] === t.identifier) g.touch1[0] = p;
      }
      t = g.that.__zoom;
      if (g.touch1) {
        var p0 = g.touch0[0], l0 = g.touch0[1],
            p1 = g.touch1[0], l1 = g.touch1[1],
            dp = (dp = p1[0] - p0[0]) * dp + (dp = p1[1] - p0[1]) * dp,
            dl = (dl = l1[0] - l0[0]) * dl + (dl = l1[1] - l0[1]) * dl;
        t = scale(t, Math.sqrt(dp / dl));
        p = [(p0[0] + p1[0]) / 2, (p0[1] + p1[1]) / 2];
        l = [(l0[0] + l1[0]) / 2, (l0[1] + l1[1]) / 2];
      }
      else if (g.touch0) p = g.touch0[0], l = g.touch0[1];
      else return;
      g.zoom("touch", constrain(translate(t, p, l), g.extent, translateExtent));
    }
  
    function touchended() {
      if (!this.__zooming) return;
      var g = gesture(this, arguments),
          touches = event.changedTouches,
          n = touches.length, i, t;
  
      nopropagation();
      if (touchending) clearTimeout(touchending);
      touchending = setTimeout(function() { touchending = null; }, touchDelay);
      for (i = 0; i < n; ++i) {
        t = touches[i];
        if (g.touch0 && g.touch0[2] === t.identifier) delete g.touch0;
        else if (g.touch1 && g.touch1[2] === t.identifier) delete g.touch1;
      }
      if (g.touch1 && !g.touch0) g.touch0 = g.touch1, delete g.touch1;
      if (g.touch0) g.touch0[1] = this.__zoom.invert(g.touch0[0]);
      else {
        g.end();
        // If this was a dbltap, reroute to the (optional) dblclick.zoom handler.
        if (g.taps === 2) {
          var p = select(this).on("dblclick.zoom");
          if (p) p.apply(this, arguments);
        }
      }
    }
  
    zoom.wheelDelta = function(_) {
      return arguments.length ? (wheelDelta = typeof _ === "function" ? _ : constant(+_), zoom) : wheelDelta;
    };
  
    zoom.filter = function(_) {
      return arguments.length ? (filter = typeof _ === "function" ? _ : constant(!!_), zoom) : filter;
    };
  
    zoom.touchable = function(_) {
      return arguments.length ? (touchable = typeof _ === "function" ? _ : constant(!!_), zoom) : touchable;
    };
  
    zoom.extent = function(_) {
      return arguments.length ? (extent = typeof _ === "function" ? _ : constant([[+_[0][0], +_[0][1]], [+_[1][0], +_[1][1]]]), zoom) : extent;
    };
  
    zoom.scaleExtent = function(_) {
      return arguments.length ? (scaleExtent[0] = +_[0], scaleExtent[1] = +_[1], zoom) : [scaleExtent[0], scaleExtent[1]];
    };
  
    zoom.translateExtent = function(_) {
      return arguments.length ? (translateExtent[0][0] = +_[0][0], translateExtent[1][0] = +_[1][0], translateExtent[0][1] = +_[0][1], translateExtent[1][1] = +_[1][1], zoom) : [[translateExtent[0][0], translateExtent[0][1]], [translateExtent[1][0], translateExtent[1][1]]];
    };
  
    zoom.constrain = function(_) {
      return arguments.length ? (constrain = _, zoom) : constrain;
    };
  
    zoom.duration = function(_) {
      return arguments.length ? (duration = +_, zoom) : duration;
    };
  
    zoom.interpolate = function(_) {
      return arguments.length ? (interpolate = _, zoom) : interpolate;
    };
  
    zoom.on = function() {
      var value = listeners.on.apply(listeners, arguments);
      return value === listeners ? zoom : value;
    };
  
    zoom.clickDistance = function(_) {
      return arguments.length ? (clickDistance2 = (_ = +_) * _, zoom) : Math.sqrt(clickDistance2);
    };
  
    return zoom;
  }
  