import { resize } from 'motion-dom';
import { scrollInfo } from './track.mjs';
import { canUseNativeTimeline } from './utils/can-use-native-timeline.mjs';
import { getTimeline } from './utils/get-timeline.mjs';
import { offsetToViewTimelineRange } from './utils/offset-to-range.mjs';

function attachToAnimation(animation, options) {
    const { target, container, axis } = options;
    const range = target && offsetToViewTimelineRange(options.offset);
    /**
     * Use native timeline when:
     * - No target and no offset: ScrollTimeline
     * - Target with mappable offset: ViewTimeline with named range
     * - Otherwise: fall back to JS observe. A ScrollTimeline has no offset,
     *   so page offsets are applied by the JS timeline.
     */
    const native = canUseNativeTimeline(target) && (target ? !!range : !options.offset);
    const animations = new Map();
    const observed = new Set();
    let stopObserving;
    let reverse = false;
    /**
     * When an offset's second point comes first, its range is swapped and
     * the animation played backwards. The range is set after the direction,
     * as that's what realigns a running animation with its timeline. Chrome
     * skips that realignment when the range changes in the frame the
     * animation starts, leaving it offset for good, so it's replayed too.
     */
    const apply = (direction, waapi) => {
        const [start, end] = range.points;
        waapi.effect.updateTiming({
            direction: reverse
                ? direction === "normal"
                    ? "reverse"
                    : "alternate-reverse"
                : direction,
        });
        Object.assign(waapi, {
            rangeStart: reverse ? end : start,
            rangeEnd: reverse ? start : end,
        });
        waapi.play();
    };
    const stops = [
        animation.attachTimeline({
            /**
             * Read only by WAAPI animations, so values driven from JS don't
             * create a native timeline they won't use.
             */
            get timeline() {
                return native ? getTimeline(options) : undefined;
            },
            onAttach: range &&
                ((waapi) => {
                    const direction = waapi.effect.getTiming().direction;
                    animations.set(waapi, direction);
                    apply(direction, waapi);
                }),
            /**
             * Values driven from JS all track the offset with scrollInfo,
             * which measures once per frame for all of them.
             */
            observe: (valueAnimation) => {
                valueAnimation.pause();
                observed.add(valueAnimation);
                stopObserving || (stopObserving = scrollInfo((info) => {
                    observed.forEach((observedAnimation) => {
                        observedAnimation.time =
                            observedAnimation.iterationDuration *
                                info[axis].progress;
                    });
                }, options));
                return () => observed.delete(valueAnimation);
            },
        }),
    ];
    if (native && range) {
        const { a, b } = range;
        const length = axis === "y" ? "clientHeight" : "clientWidth";
        /**
         * Offsets like All only run forwards when the target is longer than
         * the container, so their direction is remeasured on resize.
         */
        const update = () => {
            if (reverse !==
                (reverse = a * target[length] + b * container[length] < 0)) {
                animations.forEach(apply);
            }
        };
        update();
        if (a * b < 0) {
            stops.push(resize(update), resize([target, container], update));
        }
    }
    return () => {
        stops.forEach((stop) => stop());
        stopObserving?.();
    };
}

export { attachToAnimation };
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