const throttle = (fn, threshold = 160) => {
    let timeout;
    var start = +new Date;
    return function (...args) {
        let context = this, curTime = +new Date() - 0;
        //总是干掉事件回调
        window.clearTimeout(timeout);
        if (curTime - start >= threshold) {
            //只执行一部分方法，这些方法是在某个时间段内执行一次
            fn.apply(context, args);
            start = curTime;
        }
        else {
            //让方法在脱离事件后也能执行一次
            timeout = window.setTimeout(() => {
                //@ts-ignore
                fn.apply(this, args);
            }, threshold);
        }
    };
}

const eventMap = new Map<HTMLElement, Dragger>();

const defaultOptions = {
    inViewport: true
}

class Dragger {

    private _triggler: HTMLElement = null;
    private _container: HTMLElement = null;
    private _options: any = null;
    private _state: any = null;
    private _isFirst: boolean = true;
    private _style: string = null;

    constructor(triggler: HTMLElement, container: HTMLElement, dragInViewport: boolean) {
        this._triggler = triggler;
        this._container = container;
        this._options = Object.assign({}, defaultOptions, {
            inViewport: dragInViewport
        });
        this._state = {
            isInDrag: false,
            mX: 0, // mouse x
            mY: 0, // mouse y
            domStartX: 0, // on mousedown, the mouse x
            domStartY: 0, // on mousedown, the mouse y            
        }
    }

    getContainerPos() {
        const rect = this._container.getBoundingClientRect();
        return {
            left: rect.left,
            top: rect.top
        }
    }

    onMousedown = (e) => {
        const state = this._state;
        state.isInDrag = true;
        state.mX = e.clientX;
        state.mY = e.clientY;
        this._container.style.position = "absolute";
        const { left, top } = this.getContainerPos();

        if (this._isFirst) {

            state.domMaxY = document.documentElement.clientHeight
                - this._container.offsetHeight - 1;
            state.domMaxX = document.documentElement.clientWidth
                - this._container.offsetWidth - 1;

            this._container.style.left = left + 'px';
            this._container.style.top = top + 'px';

            if (!this._style) {
                this._style = this._container.getAttribute("style");
            }

            this._isFirst = false;
        }

        state.domStartX = left;
        state.domStartY = top;
    }

    onMouseup = (e) => {
        const state = this._state;

        state.isInDrag = false;

        const { left, top } = this.getContainerPos();
        state.domStartX = left;
        state.domStartY = top;
    }

    onMousemove = throttle((e) => {
        const state = this._state;
        if (state.isInDrag) {
            var nowX = e.clientX,
                nowY = e.clientY,
                disX = nowX - state.mX,
                disY = nowY - state.mY;

            var newDomX = state.domStartX + disX;
            var newDomY = state.domStartY + disY;
            if (this._options.inViewport) {
                if (newDomX < 0) {
                    newDomX = 0;
                }
                else if (newDomX > state.domMaxX) {
                    newDomX = state.domMaxX;
                }
                if (newDomY < 0) {
                    newDomY = 0;
                }
                else if (newDomY > state.domMaxY) {
                    newDomY = state.domMaxY;
                }
            }
            this._container.style.position = "absolute";
            this._container.style.margin = "0";
            this._container.style.paddingBottom = "0";
            this._container.style.left = newDomX + "px";
            this._container.style.top = newDomY + "px";
        }
    }, 60).bind(this)

    onResize = throttle((e) => {
        const state = this._state;

        state.domMaxY = document.documentElement.clientHeight
            - this._container.offsetHeight - 1;
        state.domMaxX = document.documentElement.clientWidth
            - this._container.offsetWidth - 1;
        state.domStartY = parseInt(this._container.style.top);
        state.domStartX = parseInt(this._container.style.left);
        if (state.domStartY > state.domMaxY) {
            if (state.domMaxY > 0) {
                this._container.style.top = state.domMaxY + "px";
            }
        }
        if (state.domStartX > state.domMaxX) {
            this._container.style.left = state.domMaxX + "px";
        }
    }, 60).bind(this)

    bindDrag() {
        const triggler = this._triggler;
        const options = this._options;

        triggler.addEventListener("mousedown", this.onMousedown, false);
        window.addEventListener("mouseup", this.onMouseup, false);
        document.addEventListener("mousemove", this.onMousemove);
        if (options.inViewport) {
            window.addEventListener("resize", this.onResize, false);
        }
    }

    unbindDrag() {
        const triggler = this._triggler;

        triggler.removeEventListener("mousedown", this.onMousedown, false);
        window.removeEventListener("mouseup", this.onMouseup, false);
        document.removeEventListener("mousemove", this.onMousemove);
        if (this._options.inViewport) {
            window.removeEventListener("resize", this.onResize, false);
        }
    }

    resetContainerStyle() {
        if (this._style !== null) {
            this._isFirst = true;
            this._container.setAttribute("style", this._style);
        }
    }
}

function enableDraggable(triggler: HTMLElement, container: HTMLElement, dragInViewport: boolean = true) {
    let dragger = eventMap.get(triggler);
    if (!dragger) {
        dragger = new Dragger(triggler, container, dragInViewport);
        eventMap.set(triggler, dragger);
    } 
    dragger.bindDrag();
}

function disableDraggable(triggler: HTMLElement) {
    const dragger = eventMap.get(triggler);
    if (dragger) {
        dragger.unbindDrag();
    }
}

function resetModalPosition(triggler: HTMLElement) {
    const dragger = eventMap.get(triggler);
    if (dragger) {
        dragger.resetContainerStyle();
    }
}

export { enableDraggable, disableDraggable, resetModalPosition };