(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
    typeof define === 'function' && define.amd ? define(factory) :
      (global.animal = factory());
}(this, (function () {
  'use strict';

  // --- Utils ---
  const isArr = (a) => Array.isArray(a);
  const isStr = (s) => typeof s === 'string';
  const isFunc = (f) => typeof f === 'function';
  const isNil = (v) => v === undefined || v === null;
  const isSVG = (el) => el instanceof SVGElement;
  
  const toArray = (targets) => {
    if (isArr(targets)) return targets;
    if (isStr(targets)) return Array.from(document.querySelectorAll(targets));
    if (targets instanceof NodeList) return Array.from(targets);
    if (targets instanceof Element || targets instanceof Window) return [targets];
    return [];
  };

  const $ = (targets) => toArray(targets);

  const UNITLESS_KEYS = ['opacity', 'scale', 'scaleX', 'scaleY', 'scaleZ', 'zIndex', 'fontWeight', 'strokeDashoffset', 'strokeDasharray', 'strokeWidth'];

  const getUnit = (val, prop) => {
    if (UNITLESS_KEYS.includes(prop)) return '';
    const split = /[+-]?\d*\.?\d+(?:\.\d+)?(?:[eE][+-]?\d+)?(%|px|pt|em|rem|in|cm|mm|ex|ch|pc|vw|vh|vmin|vmax|deg|rad|turn)?$/.exec(val);
    return split ? split[1] : undefined;
  };

  // --- Spring Physics (Simplified) ---
  // Returns an array of [time, value] or just value for WAAPI linear easing
  function spring({ stiffness = 100, damping = 10, mass = 1, velocity = 0, precision = 0.01 } = {}) {
    const values = [];
    let t = 0;
    const timeStep = 1 / 60; // 60fps simulation
    let current = 0;
    let v = velocity;
    const target = 1;

    let running = true;
    while (running && t < 10) { // Safety break at 10s
      const fSpring = -stiffness * (current - target);
      const fDamper = -damping * v;
      const a = (fSpring + fDamper) / mass;
      
      v += a * timeStep;
      current += v * timeStep;
      
      values.push(current);
      t += timeStep;

      if (Math.abs(current - target) < precision && Math.abs(v) < precision) {
        running = false;
      }
    }
    if (values[values.length - 1] !== 1) values.push(1);
    
    return values;
  }

  // --- WAAPI Core ---
  const TRANSFORMS = ['translateX', 'translateY', 'translateZ', 'rotate', 'rotateX', 'rotateY', 'rotateZ', 'scale', 'scaleX', 'scaleY', 'scaleZ', 'skew', 'skewX', 'skewY', 'perspective', 'x', 'y'];
  
  const ALIASES = {
    x: 'translateX',
    y: 'translateY',
    z: 'translateZ'
  };

  // Basic rAF loop for non-WAAPI props or fallback
  class RafEngine {
    constructor() {
      this.animations = [];
      this.tick = this.tick.bind(this);
      this.running = false;
    }
    add(anim) {
      this.animations.push(anim);
      if (!this.running) {
        this.running = true;
        requestAnimationFrame(this.tick);
      }
    }
    remove(anim) {
      this.animations = this.animations.filter(a => a !== anim);
    }
    tick(t) {
      const now = t;
      this.animations = this.animations.filter(anim => {
        return anim.tick(now); // return true to keep
      });
      if (this.animations.length) {
        requestAnimationFrame(this.tick);
      } else {
        this.running = false;
      }
    }
  }
  const rafEngine = new RafEngine();

  // --- Main Animation Logic ---
  function animate(targets, params) {
    const elements = toArray(targets);
    const { 
      duration = 1000, 
      delay = 0, 
      easing = 'ease-out', 
      direction = 'normal', 
      fill = 'forwards',
      loop = 1,
      endDelay = 0,
      autoplay = true,
      update, // callback
      begin, // callback
      complete // callback
    } = params;

    const animatableProps = {};
    const waapiProps = {};
    const jsProps = {};
    let isSpring = false;
    let springValues = null;

    if (typeof easing === 'object' && !Array.isArray(easing)) {
        isSpring = true;
        springValues = spring(easing);
    }

    Object.keys(params).forEach(key => {
      if (['duration', 'delay', 'easing', 'direction', 'fill', 'loop', 'endDelay', 'autoplay', 'update', 'begin', 'complete'].includes(key)) return;
      
      let prop = ALIASES[key] || key;
      const isTransform = TRANSFORMS.includes(prop) || TRANSFORMS.includes(key);
      const isCss = !isTransform && (key === 'opacity' || key === 'filter'); // Simplified check
      
      const val = params[key];
      
      if (isTransform || isCss) {
        waapiProps[key] = val;
      } else {
        jsProps[key] = val;
      }
    });

    // Create animations but don't play if autoplay is false
    const animations = [];

    const promises = elements.map(el => {
      // 1. WAAPI Animation
      let waapiAnim = null;
      let waapiPromise = Promise.resolve();
      
      if (Object.keys(waapiProps).length > 0) {
        
        const generateFrames = (propValues) => {
            if (isSpring && springValues) {
                return springValues.map(v => {
                    const frame = {};
                    Object.keys(propValues).forEach(k => {
                        const targetVal = parseFloat(propValues[k]);
                        const unit = getUnit(propValues[k], k) || (k.startsWith('rotate') ? 'deg' : (UNITLESS_KEYS.includes(k) ? '' : 'px'));
                        
                        let startVal = 0;
                        if (k.startsWith('scale')) startVal = 1;
                        if (k === 'opacity') startVal = parseFloat(getComputedStyle(el).opacity);
                        
                        if (Array.isArray(propValues[k])) {
                             startVal = parseFloat(propValues[k][0]);
                             const endVal = parseFloat(propValues[k][1]);
                             const current = startVal + (endVal - startVal) * v;
                             frame[k] = current + unit;
                        } else {
                             const endVal = targetVal;
                             const current = startVal + (endVal - startVal) * v;
                             frame[k] = current + unit;
                        }
                    });
                    return frame;
                });
            } else {
                const frame0 = {};
                const frame1 = {};
                
                Object.keys(propValues).forEach(k => {
                   let val = propValues[k];
                   if (Array.isArray(val)) {
                       frame0[k] = val[0];
                       frame1[k] = val[1];
                   } else {
                       frame1[k] = val;
                   }
                });
                return [frame0, frame1]; 
            }
        };

        let rawFrames = generateFrames(waapiProps);
        
        const finalFrames = rawFrames.map(f => {
            const final = {};
            let transformStr = '';
            Object.keys(f).forEach(k => {
                const isT = TRANSFORMS.includes(ALIASES[k] || k);
                if (isT) {
                    let key = ALIASES[k] || k;
                    if (key === 'x') key = 'translateX';
                    if (key === 'y') key = 'translateY';
                    if (key === 'z') key = 'translateZ';
                    
                    let val = f[k];
                    if (typeof val === 'number') {
                        if (key.startsWith('scale')) {
                            val = val + '';
                        } else if (key.startsWith('rotate') || key.startsWith('skew')) {
                            val = val + 'deg';
                        } else {
                            val = val + 'px';
                        }
                    }
                    transformStr += `${key}(${val}) `;
                } else {
                    final[k] = f[k];
                }
            });
            if (transformStr) final.transform = transformStr.trim();
            return final;
        });

        if (Object.keys(finalFrames[0]).length === 0) finalFrames.shift();

        const opts = {
            duration: isSpring ? (springValues.length * 1000 / 60) : duration,
            delay,
            fill,
            iterations: loop,
            easing: isSpring ? 'linear' : easing 
        };

        const animation = el.animate(finalFrames, opts);
        if (!autoplay) animation.pause();
        waapiAnim = animation;
        waapiPromise = animation.finished;
        animations.push(waapiAnim);
      }

      // 2. JS Animation (Fallback / Attributes)
      let jsPromise = Promise.resolve();
      if (Object.keys(jsProps).length > 0) {
          jsPromise = new Promise(resolve => {
             // For JS engine to support manual seek/scroll, we need to structure it differently.
             // But for this lite version, we focus on WAAPI for scroll linking.
             // JS fallback will just run normally if autoplay.
             if (!autoplay) return; // JS engine simplified doesn't support pause/seek easily yet

             const startTime = performance.now() + delay;
             const initialValues = {};
             
             // Setup
             Object.keys(jsProps).forEach(k => {
                 if (k === 'scrollTop' || k === 'scrollLeft') {
                     initialValues[k] = el[k];
                 } else if (k in el.style) {
                     initialValues[k] = parseFloat(el.style[k]) || 0; 
                 } else if (isSVG(el) && el.hasAttribute(k)) {
                     initialValues[k] = parseFloat(el.getAttribute(k)) || 0;
                 } else {
                     initialValues[k] = 0; 
                 }
             });

             const tick = (now) => {
                 if (now < startTime) return true;
                 const elapsed = now - startTime;
                 let progress = Math.min(elapsed / duration, 1);
                 
                 Object.keys(jsProps).forEach(k => {
                    const target = jsProps[k];
                    let start = initialValues[k];
                    let end = isArr(target) ? target[1] : target;
                    if (isArr(target)) start = target[0];
                    
                    const val = start + (end - start) * progress;
                    
                    if (k === 'scrollTop' || k === 'scrollLeft') {
                        el[k] = val;
                    } else if (k in el.style) {
                        el.style[k] = val; 
                    } else if (isSVG(el)) {
                        const attr = k.replace(/[A-Z]/g, m => '-' + m.toLowerCase());
                        el.setAttribute(attr, val);
                    } else {
                        el[k] = val; 
                    }
                    if (update) update({ target: el, progress, value: val });
                 });

                 if (progress < 1) return true;
                 if (complete) complete(el);
                 resolve();
                 return false;
             };
             
             rafEngine.add({ tick });
          });
      }

      return Promise.all([waapiPromise, jsPromise]);
    });

    const masterPromise = Promise.all(promises);
    masterPromise.then = (fn) => Promise.all(promises).then(fn);
    
    // Attach animations to promise for external control (like scroll)
    masterPromise.animations = animations;
    return masterPromise;
  }

  // --- SVG Draw ---
  function svgDraw(targets, params = {}) {
     const elements = toArray(targets);
     elements.forEach(el => {
         if (!isSVG(el)) return;
         const len = el.getTotalLength ? el.getTotalLength() : 0;
         el.style.strokeDasharray = len;
         el.style.strokeDashoffset = len; 
         
         animate(el, {
             strokeDashoffset: [len, 0],
             ...params
         });
     });
  }

  // --- In View ---
  function inViewAnimate(targets, params, options = {}) {
      const elements = toArray(targets);
      const observer = new IntersectionObserver((entries) => {
          entries.forEach(entry => {
              if (entry.isIntersecting) {
                  animate(entry.target, params);
                  if (options.once !== false) observer.unobserve(entry.target);
              }
          });
      }, { threshold: options.threshold || 0.1 });
      
      elements.forEach(el => observer.observe(el));
  }
  
  // --- Scroll Linked ---
  function scroll(animationPromise, options = {}) {
      // options: container (default window), range [start, end] (default viewport logic)
      const container = options.container || window;
      const target = options.target || document.body; // Element to track for progress
      // If passing an animation promise, we control its WAAPI animations
      
      const anims = animationPromise.animations || [];
      if (!anims.length) return;

      const updateScroll = () => {
          let progress = 0;
          
          if (container === window) {
              const scrollY = window.scrollY;
              const winH = window.innerHeight;
              const docH = document.body.scrollHeight;
              
              // Simple progress: how far down the page (0 to 1)
              // Or element based?
              // Motion One defaults to element entering view.
              
              if (options.target) {
                  const rect = options.target.getBoundingClientRect();
                  const start = winH; 
                  const end = -rect.height;
                  // progress 0 when rect.top == start (just entering)
                  // progress 1 when rect.top == end (just left)
                  
                  const totalDistance = start - end;
                  const currentDistance = start - rect.top;
                  progress = currentDistance / totalDistance;
              } else {
                  // Whole page scroll
                  progress = scrollY / (docH - winH);
              }
          }
          
          // Clamp
          progress = Math.max(0, Math.min(1, progress));
          
          anims.forEach(anim => {
             if (anim.effect) {
                 const dur = anim.effect.getComputedTiming().duration;
                 anim.currentTime = dur * progress;
             }
          });
      };

      window.addEventListener('scroll', updateScroll);
      updateScroll(); // Initial
      
      return () => window.removeEventListener('scroll', updateScroll);
  }

  // --- Timeline ---
  function timeline(defaults = {}) {
      const realTimeApi = {
          currentTime: 0,
          add: (targets, params, offset) => {
               const animParams = { ...defaults, ...params };
               let start = realTimeApi.currentTime;
               
               if (offset !== undefined) {
                  if (isStr(offset) && offset.startsWith('-=')) start -= parseFloat(offset.slice(2));
                  else if (isStr(offset) && offset.startsWith('+=')) start += parseFloat(offset.slice(2));
                  else if (typeof offset === 'number') start = offset; 
               }
               
               if (start <= 0) {
                   animate(targets, animParams);
               } else {
                   setTimeout(() => {
                       animate(targets, animParams);
                   }, start);
               }
               
               const dur = animParams.duration || 1000;
               realTimeApi.currentTime = Math.max(realTimeApi.currentTime, start + dur);
               return realTimeApi;
          }
      };
      return realTimeApi;
  }

  return {
    animate,
    timeline,
    svgDraw,
    inViewAnimate,
    spring,
    scroll,
    $
  };

})));