diff --git a/assets/ts/customCursor.ts b/assets/ts/customCursor.ts
new file mode 100644
index 0000000..43cc50e
--- /dev/null
+++ b/assets/ts/customCursor.ts
@@ -0,0 +1,38 @@
+import { addActiveCallback } from './stage'
+
+let cursor: HTMLDivElement
+
+// create cursor
+cursor = document.createElement('div')
+cursor.className = 'cursor'
+cursor.classList.add('active')
+// create cursor inner
+const cursorInner = document.createElement('div')
+cursorInner.className = 'cursorInner'
+// append cursor inner to cursor
+cursor.append(cursorInner)
+
+function onMouse(e: MouseEvent) {
+  const x = e.clientX
+  const y = e.clientY
+  cursor.style.transform = `translate3d(${x}px, ${y}px, 0)`
+}
+
+export function initCustomCursor(): void {
+  // append cursor to main
+  document.getElementById('main')!.append(cursor)
+  // bind mousemove event to window
+  window.addEventListener('mousemove', onMouse)
+  // add active callback
+  addActiveCallback((active) => {
+    if (active) {
+      cursor.classList.add('active')
+    } else {
+      cursor.classList.remove('active')
+    }
+  })
+}
+
+export function setCustomCursor(text: string): void {
+  cursorInner.innerText = text
+}
diff --git a/assets/ts/dataFetch.ts b/assets/ts/dataFetch.ts
deleted file mode 100644
index 5a4e92c..0000000
--- a/assets/ts/dataFetch.ts
+++ /dev/null
@@ -1,14 +0,0 @@
-import { type ImageData } from './utils'
-
-// fetch images info from JSON
-const imageArrayElement = document.getElementById('images_info') as HTMLScriptElement
-const rawImagesInfo = imageArrayElement.textContent as string
-export const imagesInfo: ImageData[] = JSON.parse(rawImagesInfo).sort(
-  (a: ImageData, b: ImageData) => {
-    if (a.index < b.index) {
-      return -1
-    }
-    return 1
-  }
-)
-export const imagesLen: number = imagesInfo.length
diff --git a/assets/ts/desktop.ts b/assets/ts/desktop.ts
deleted file mode 100644
index daea4a3..0000000
--- a/assets/ts/desktop.ts
+++ /dev/null
@@ -1,165 +0,0 @@
-import { overlayEnable } from './overlay'
-import {
-  calcImageIndex,
-  center,
-  delay,
-  mouseToTransform,
-  pushIndex,
-  type position,
-  hideImage
-} from './utils'
-import { thresholdIndex, thresholdSensitivityArray } from './thresholdCtl'
-import { imgIndexSpanUpdate } from './indexDisp'
-import { imagesLen } from './dataFetch'
-import { imagesDivNodes as images } from './elemGen'
-
-// global index for "activated"
-export let globalIndex: number = 0
-// last position set as "activated"
-let last: position = { x: 0, y: 0 }
-export let trailingImageIndexes: number[] = []
-// only used in overlay disable, for storing positions temporarily
-export let transformCache: string[] = []
-// abort controller for enter overlay event listener
-let EnterOverlayClickAbCtl = new AbortController()
-// stack depth of images array
-export let stackDepth: number = 5
-export let lastStackDepth: number = 5
-
-export const addEnterOverlayEL = (e: HTMLImageElement): void => {
-  EnterOverlayClickAbCtl.abort()
-  EnterOverlayClickAbCtl = new AbortController()
-  e.addEventListener(
-    'click',
-    () => {
-      void enterOverlay()
-    },
-    {
-      passive: true,
-      once: true,
-      signal: EnterOverlayClickAbCtl.signal
-    }
-  )
-}
-
-// activate top image
-const activate = (index: number, mouseX: number, mouseY: number): void => {
-  addEnterOverlayEL(images[index])
-  if (stackDepth !== lastStackDepth) {
-    trailingImageIndexes.push(index)
-    refreshStack()
-    lastStackDepth = stackDepth
-  }
-  const indexesNum: number = pushIndex(
-    index,
-    trailingImageIndexes,
-    stackDepth,
-    images,
-    imagesLen
-  )
-  // set img position
-  images[index].style.transform = mouseToTransform(mouseX, mouseY, true, true)
-  images[index].dataset.status = 'null'
-  // reset z index
-  for (let i = indexesNum; i > 0; i--) {
-    images[trailingImageIndexes[i - 1]].style.zIndex = `${i}`
-  }
-  images[index].style.visibility = 'visible'
-  last = { x: mouseX, y: mouseY }
-}
-
-// Compare the current mouse position with the last activated position
-const distanceFromLast = (x: number, y: number): number => {
-  return Math.hypot(x - last.x, y - last.y)
-}
-
-// handle mouse move
-export const handleOnMove = (e: MouseEvent): void => {
-  // meet threshold
-  if (
-    distanceFromLast(e.clientX, e.clientY) >
-    window.innerWidth / thresholdSensitivityArray[thresholdIndex]
-  ) {
-    // calculate the actual index
-    const imageIndex = calcImageIndex(globalIndex, imagesLen)
-    // show top image and change index
-    activate(imageIndex, e.clientX, e.clientY)
-    imgIndexSpanUpdate(imageIndex + 1, imagesLen)
-    // self increment
-    globalIndexInc()
-  }
-}
-
-async function enterOverlay(): Promise<void> {
-  // stop images animation
-  window.removeEventListener('mousemove', handleOnMove)
-  // get index array length
-  const indexesNum: number = trailingImageIndexes.length
-  for (let i = 0; i < indexesNum; i++) {
-    // create image element
-    const e: HTMLImageElement = images[trailingImageIndexes[i]]
-    // cache images' position
-    transformCache.push(e.style.transform)
-    // set style for the images
-    if (i === indexesNum - 1) {
-      e.style.transitionDelay = `${0.1 * i + 0.2}s, ${0.1 * i + 0.2 + 0.5}s`
-      e.dataset.status = 'top'
-      center(e)
-    } else {
-      e.style.transitionDelay = `${0.1 * i}s`
-      e.dataset.status = 'trail'
-    }
-  }
-  // sleep
-  await delay(stackDepth * 100 + 100 + 1000)
-  // post process
-  for (let i = 0; i < indexesNum; i++) {
-    images[trailingImageIndexes[i]].style.transitionDelay = ''
-    if (i === indexesNum - 1) {
-      images[trailingImageIndexes[i]].dataset.status = 'overlay'
-    } else {
-      images[trailingImageIndexes[i]].style.visibility = 'hidden'
-    }
-  }
-  // Offset previous self increment of global index (by handleOnMove)
-  globalIndexDec()
-  // overlay init
-  overlayEnable()
-}
-
-// initialization
-export const trackMouseInit = (): void => {
-  window.addEventListener('mousemove', handleOnMove)
-}
-
-export const globalIndexDec = (): void => {
-  globalIndex--
-}
-
-export const globalIndexInc = (): void => {
-  globalIndex++
-}
-
-export const emptyTransformCache = (): void => {
-  transformCache = []
-}
-
-export const emptyTrailingImageIndexes = (): void => {
-  trailingImageIndexes = []
-}
-
-export const setStackDepth = (newStackDepth: number): void => {
-  if (stackDepth !== newStackDepth) {
-    lastStackDepth = stackDepth
-    stackDepth = newStackDepth
-  }
-}
-
-export const refreshStack = (): void => {
-  const l: number = trailingImageIndexes.length
-  if (stackDepth < lastStackDepth && l > stackDepth) {
-    const times: number = l - stackDepth
-    for (let i = 0; i < times; i++)
-      hideImage(images[trailingImageIndexes.shift() as number])
-  }
-}
diff --git a/assets/ts/elemGen.ts b/assets/ts/elemGen.ts
deleted file mode 100644
index 6b54071..0000000
--- a/assets/ts/elemGen.ts
+++ /dev/null
@@ -1,55 +0,0 @@
-import { imagesInfo, imagesLen } from './dataFetch'
-import { createImgElement } from './utils'
-
-// get components of overlay
-export let overlayCursor: HTMLDivElement
-export let cursorInnerContent: HTMLDivElement
-export let imagesDivNodes: NodeListOf<HTMLImageElement>
-
-const mainDiv = document.getElementById('main') as HTMLDivElement
-
-const passDesktopElements = (): void => {
-  overlayCursor = document
-    .getElementsByClassName('overlay_cursor')
-    .item(0) as HTMLDivElement
-  cursorInnerContent = document
-    .getElementsByClassName('cursor_innerText')
-    .item(0) as HTMLDivElement
-  imagesDivNodes = document.getElementsByClassName('imagesDesktop')[0]
-    .childNodes as NodeListOf<HTMLImageElement>
-}
-
-const passMobileElements = (): void => {
-  imagesDivNodes = document.getElementsByClassName('imagesMobile')[0]
-    .childNodes as NodeListOf<HTMLImageElement>
-}
-
-const createCursorDiv = (): HTMLDivElement => {
-  const cursorDiv: HTMLDivElement = document.createElement('div')
-  cursorDiv.className = 'overlay_cursor'
-  const innerTextDiv: HTMLDivElement = document.createElement('div')
-  innerTextDiv.className = 'cursor_innerText'
-  cursorDiv.appendChild(innerTextDiv)
-  return cursorDiv
-}
-
-export const createDesktopElements = (): void => {
-  mainDiv.appendChild(createCursorDiv())
-  const imagesDiv: HTMLDivElement = document.createElement('div')
-  imagesDiv.className = 'imagesDesktop'
-  for (let i = 0; i < imagesLen; i++) {
-    imagesDiv.appendChild(createImgElement(imagesInfo[i]))
-  }
-  mainDiv.appendChild(imagesDiv)
-  passDesktopElements()
-}
-
-export const createMobileElements = (): void => {
-  const imagesDiv: HTMLDivElement = document.createElement('div')
-  imagesDiv.className = 'imagesMobile'
-  for (let i = 0; i < imagesLen; i++) {
-    imagesDiv.appendChild(createImgElement(imagesInfo[i]))
-  }
-  mainDiv.appendChild(imagesDiv)
-  passMobileElements()
-}
diff --git a/assets/ts/imageCache.ts b/assets/ts/imageCache.ts
deleted file mode 100644
index 46320c3..0000000
--- a/assets/ts/imageCache.ts
+++ /dev/null
@@ -1,18 +0,0 @@
-import { imagesInfo, imagesLen } from './dataFetch'
-import { preloadImage, calcImageIndex } from './utils'
-
-let lastIndex: number = 0
-
-export const preloader = (index: number): void => {
-  if (lastIndex === index) {
-    for (let i: number = -2; i <= 1; i++)
-      preloadImage(imagesInfo[calcImageIndex(index + i, imagesLen)].url)
-  } else if (lastIndex > index) {
-    for (let i: number = 1; i <= 3; i++)
-      preloadImage(imagesInfo[calcImageIndex(index - i, imagesLen)].url)
-  } else {
-    for (let i: number = 1; i <= 3; i++)
-      preloadImage(imagesInfo[calcImageIndex(index + i, imagesLen)].url)
-  }
-  lastIndex = index
-}
diff --git a/assets/ts/indexDisp.ts b/assets/ts/indexDisp.ts
deleted file mode 100644
index e772230..0000000
--- a/assets/ts/indexDisp.ts
+++ /dev/null
@@ -1,17 +0,0 @@
-import { duper } from './utils'
-
-// update index of displaying image
-export const imgIndexSpanUpdate = (numOne: number, numTwo: number): void => {
-  // footer index number display module
-  const footerIndexDisp = document.getElementsByClassName('ftid')
-  const numOneString: string = duper(numOne)
-  const numTwoString: string = duper(numTwo)
-  for (let i: number = 0; i <= 7; i++) {
-    const footerIndex = footerIndexDisp[i] as HTMLSpanElement
-    if (i > 3) {
-      footerIndex.innerText = numTwoString[i - 4]
-    } else {
-      footerIndex.innerText = numOneString[i]
-    }
-  }
-}
diff --git a/assets/ts/main.ts b/assets/ts/main.ts
index 19b6283..2d58579 100644
--- a/assets/ts/main.ts
+++ b/assets/ts/main.ts
@@ -1,28 +1,13 @@
-import { createDesktopElements, createMobileElements } from './elemGen'
-import { imgIndexSpanUpdate } from './indexDisp'
-import { trackMouseInit } from './desktop'
-import { thresholdCtlInit } from './thresholdCtl'
-import { imagesLen } from './dataFetch'
-import { vwRefreshInit } from './overlay'
-import { preloader } from './imageCache'
-import { getDeviceType } from './utils'
-import { renderImages } from './mobile'
+import { initResources } from './resources'
+import { initState } from './state'
+import { initCustomCursor } from './customCursor'
+import { initNav } from './nav'
+import { initStage } from './stage'
+import { initStageNav } from './stageNav'
 
-const desktopInit = (): void => {
-  createDesktopElements()
-  preloader(0)
-  vwRefreshInit()
-  imgIndexSpanUpdate(0, imagesLen)
-  thresholdCtlInit()
-  trackMouseInit()
-}
-
-const mobileInit = (): void => {
-  createMobileElements()
-  vwRefreshInit()
-  imgIndexSpanUpdate(0, imagesLen)
-  renderImages()
-  console.log('mobile')
-}
-
-getDeviceType().desktop ? mobileInit() : desktopInit()
+initCustomCursor()
+const ijs = initResources()
+initState(ijs.length)
+initStage(ijs)
+initStageNav()
+initNav()
diff --git a/assets/ts/mobile.ts b/assets/ts/mobile.ts
deleted file mode 100644
index b3e93ee..0000000
--- a/assets/ts/mobile.ts
+++ /dev/null
@@ -1,24 +0,0 @@
-import { imagesDivNodes as images } from './elemGen'
-import { imagesLen } from './dataFetch'
-
-export const renderImages = (): void => {
-  images.forEach((img: HTMLImageElement, idx: number): void => {
-    const randomX: number = Math.floor(Math.random() * 35) + 2
-    let randomY: number
-
-    // random Y calculation
-    if (idx === 0) {
-      randomY = 68
-    } else if (idx === 1) {
-      randomY = 44
-    } else if (idx === imagesLen - 1) {
-      randomY = 100
-    } else {
-      randomY = Math.floor(Math.random() * 51) + 2
-    }
-
-    img.style.transform = `translate(${randomX}vw, -${randomY}%)`
-    img.style.marginTop = `${idx === 1 ? 70 : 0}vh`
-    img.style.visibility = 'visible'
-  })
-}
diff --git a/assets/ts/nav.ts b/assets/ts/nav.ts
new file mode 100644
index 0000000..6a8b235
--- /dev/null
+++ b/assets/ts/nav.ts
@@ -0,0 +1,59 @@
+import { getState, incThreshold, decThreshold } from './state'
+import { expand } from './utils'
+
+// threshold div
+const thresholdDiv = document
+  .getElementsByClassName('threshold')
+  .item(0) as HTMLDivElement
+
+// threshold nums span
+const thresholdDispNums = Array.from(
+  thresholdDiv.getElementsByClassName('num')
+) as HTMLSpanElement[]
+
+// threshold buttons
+const decButton = thresholdDiv
+  .getElementsByClassName('dec')
+  .item(0) as HTMLButtonElement
+const incButton = thresholdDiv
+  .getElementsByClassName('inc')
+  .item(0) as HTMLButtonElement
+
+// index div
+const indexDiv = document.getElementsByClassName('index').item(0) as HTMLDivElement
+
+// index nums span
+const indexDispNums = Array.from(
+  indexDiv.getElementsByClassName('num')
+) as HTMLSpanElement[]
+
+export function initNav() {
+  // init threshold text
+  updateThresholdText()
+  // init index text
+  updateIndexText()
+  // event listeners
+  decButton.addEventListener('click', () => decThreshold())
+  incButton.addEventListener('click', () => incThreshold())
+}
+
+// helper
+
+export function updateThresholdText(): void {
+  const thresholdValue: string = expand(getState().threshold)
+  thresholdDispNums.forEach((e: HTMLSpanElement, i: number) => {
+    e.innerText = thresholdValue[i]
+  })
+}
+
+export function updateIndexText(): void {
+  const indexValue: string = expand(getState().index + 1)
+  const indexLength: string = expand(getState().length)
+  indexDispNums.forEach((e: HTMLSpanElement, i: number) => {
+    if (i < 4) {
+      e.innerText = indexValue[i]
+    } else {
+      e.innerText = indexLength[i - 4]
+    }
+  })
+}
diff --git a/assets/ts/overlay.ts b/assets/ts/overlay.ts
deleted file mode 100644
index 544a013..0000000
--- a/assets/ts/overlay.ts
+++ /dev/null
@@ -1,204 +0,0 @@
-import { delay, center, calcImageIndex, mouseToTransform, pushIndex } from './utils'
-import {
-  handleOnMove,
-  globalIndex,
-  globalIndexDec,
-  globalIndexInc,
-  trailingImageIndexes,
-  transformCache,
-  emptyTransformCache,
-  emptyTrailingImageIndexes,
-  stackDepth,
-  addEnterOverlayEL
-} from './desktop'
-import { imagesLen } from './dataFetch'
-import { imgIndexSpanUpdate } from './indexDisp'
-import { overlayCursor, cursorInnerContent, imagesDivNodes as images } from './elemGen'
-
-let oneThird: number = Math.round(window.innerWidth / 3)
-
-// set cursor text
-const setCursorText = (text: string): void => {
-  cursorInnerContent.innerText = text
-}
-
-// overlay cursor event handler
-const setTextPos = (e: MouseEvent): void => {
-  overlayCursor.style.transform = mouseToTransform(e.clientX, e.clientY, false, true)
-}
-
-// disable listeners
-const disableListener = (): void => {
-  window.removeEventListener('mousemove', handleOverlayMouseMove)
-  overlayCursor.removeEventListener('click', handleOverlayClick)
-}
-
-// enable overlay
-export const overlayEnable = (): void => {
-  // show the overlay components
-  overlayCursor.style.zIndex = '21'
-  // set overlay event listeners
-  setListener()
-}
-
-// disable overlay
-export const overlayDisable = (): void => {
-  // hide the overlay components
-  overlayCursor.style.zIndex = '-1'
-  // set overlay cursor text content to none
-  setCursorText('')
-  // disable overlay event listeners
-  disableListener()
-}
-
-// handle close click
-async function handleCloseClick(): Promise<void> {
-  // disable overlay
-  overlayDisable()
-  // get length of indexes and empty indexes array
-  const indexesNum = trailingImageIndexes.length
-  emptyTrailingImageIndexes()
-  // prepare animation
-  for (let i: number = 0; i < indexesNum; i++) {
-    // get element from index and store the index
-    const index: number = calcImageIndex(globalIndex - i, imagesLen)
-    const e: HTMLImageElement = images[index]
-    trailingImageIndexes.unshift(index)
-    // set z index for the image element
-    e.style.zIndex = `${indexesNum - i - 1}`
-    // set different style for trailing and top image
-    if (i === 0) {
-      // set position
-      e.style.transform = transformCache[indexesNum - i - 1]
-      // set transition delay
-      e.style.transitionDelay = '0s, 0.7s'
-      // set status for css
-      e.dataset.status = 'resumeTop'
-    } else {
-      // set position
-      e.style.transform = transformCache[indexesNum - i - 1]
-      // set transition delay
-      e.style.transitionDelay = `${1.2 + 0.1 * i - 0.1}s`
-      // set status for css
-      e.dataset.status = 'resume'
-    }
-    // style process complete, show the image
-    e.style.visibility = 'visible'
-  }
-  // halt the function while animation is running
-  await delay(1200 + stackDepth * 100 + 100)
-  // add back enter overlay event listener to top image
-  addEnterOverlayEL(images[calcImageIndex(globalIndex, imagesLen)])
-  // clear unused status and transition delay
-  for (let i: number = 0; i < indexesNum; i++) {
-    const index: number = calcImageIndex(globalIndex - i, imagesLen)
-    images[index].dataset.status = 'null'
-    images[index].style.transitionDelay = ''
-  }
-  // Add back previous self increment of global index (by handleOnMove)
-  globalIndexInc()
-  // add back mousemove event listener
-  window.addEventListener('mousemove', handleOnMove, { passive: true })
-  // empty the position array cache
-  emptyTransformCache()
-}
-
-const handleSideClick = (CLD: boolean): void => {
-  // get last displayed image's index
-  const imgIndex: number = calcImageIndex(globalIndex, imagesLen)
-  // change global index and get current displayed image's index
-  CLD ? globalIndexInc() : globalIndexDec()
-  const currImgIndex: number = calcImageIndex(globalIndex, imagesLen)
-  // store current displayed image's index
-  CLD
-    ? pushIndex(
-        currImgIndex,
-        trailingImageIndexes,
-        stackDepth,
-        images,
-        imagesLen,
-        false,
-        false
-      )
-    : pushIndex(
-        currImgIndex,
-        trailingImageIndexes,
-        stackDepth,
-        images,
-        imagesLen,
-        true,
-        false
-      )
-  // hide last displayed image
-  images[imgIndex].style.visibility = 'hidden'
-  images[imgIndex].dataset.status = 'trail'
-  // process the image going to display
-  center(images[currImgIndex])
-  images[currImgIndex].dataset.status = 'overlay'
-  // process complete, show the image
-  images[currImgIndex].style.visibility = 'visible'
-  // change index display
-  imgIndexSpanUpdate(currImgIndex + 1, imagesLen)
-}
-
-// change text and position of overlay cursor
-const handleOverlayMouseMove = (e: MouseEvent): void => {
-  // set text position
-  setTextPos(e)
-  // set text content
-  if (e.clientX < oneThird) {
-    setCursorText('PREV')
-    overlayCursor.dataset.status = 'PREV'
-  } else if (e.clientX < oneThird * 2) {
-    setCursorText('CLOSE')
-    overlayCursor.dataset.status = 'CLOSE'
-  } else {
-    setCursorText('NEXT')
-    overlayCursor.dataset.status = 'NEXT'
-  }
-}
-
-const handleOverlayClick = (): void => {
-  switch (overlayCursor.dataset.status) {
-    case 'PREV':
-      handleSideClick(false)
-      break
-    case 'CLOSE':
-      void handleCloseClick()
-      break
-    case 'NEXT':
-      handleSideClick(true)
-      break
-  }
-}
-
-// set event listener
-const setListener = (): void => {
-  // add mouse move event listener (for overlay text cursor)
-  window.addEventListener('mousemove', handleOverlayMouseMove, { passive: true })
-  // add close/prev/next click event listener
-  overlayCursor.addEventListener('click', handleOverlayClick, { passive: true })
-}
-
-export const vwRefreshInit = (): void => {
-  window.addEventListener(
-    'resize',
-    () => {
-      // refresh value of one third
-      oneThird = Math.round(window.innerWidth / 3)
-      // reset footer height
-      const r = document.querySelector(':root') as HTMLStyleElement
-      if (window.innerWidth > 768) {
-        r.style.setProperty('--footer-height', '38px')
-      } else {
-        r.style.setProperty('--footer-height', '31px')
-      }
-      // recenter image (only in overlay)
-      if (
-        images[calcImageIndex(globalIndex, imagesLen)].dataset.status === 'overlay'
-      )
-        center(images[calcImageIndex(globalIndex, imagesLen)])
-    },
-    { passive: true }
-  )
-}
diff --git a/assets/ts/resources.ts b/assets/ts/resources.ts
new file mode 100644
index 0000000..4eb0b06
--- /dev/null
+++ b/assets/ts/resources.ts
@@ -0,0 +1,21 @@
+// data structure for images info
+export interface ImageJSON {
+  index: number
+  url: string
+  imgH: number
+  imgW: number
+  pColor: string
+  sColor: string
+}
+
+export function initResources(): ImageJSON[] {
+  const imagesJson = document.getElementById('imagesSource') as HTMLScriptElement
+  return JSON.parse(imagesJson.textContent as string).sort(
+    (a: ImageJSON, b: ImageJSON) => {
+      if (a.index < b.index) {
+        return -1
+      }
+      return 1
+    }
+  )
+}
diff --git a/assets/ts/stage.ts b/assets/ts/stage.ts
new file mode 100644
index 0000000..7d0ee37
--- /dev/null
+++ b/assets/ts/stage.ts
@@ -0,0 +1,217 @@
+import { incIndex, getState } from './state'
+import { gsap, Power3 } from 'gsap'
+import { ImageJSON } from './resources'
+
+export type HistoryItem = { i: number; x: number; y: number }
+
+let imgs: HTMLImageElement[] = []
+
+class CordHist {
+  private obj: HistoryItem[] = []
+
+  get(): HistoryItem[] {
+    return this.obj
+  }
+
+  set(e: HistoryItem[]): void {
+    this.obj = e
+    setPositions()
+  }
+}
+
+class IsOpen {
+  private obj = false
+
+  get(): boolean {
+    return this.obj
+  }
+
+  set(e: boolean): void {
+    this.obj = e
+    activeCallbacks.forEach((callback) => callback(getActive()))
+  }
+}
+
+let last = { x: 0, y: 0 }
+export let cordHist = new CordHist()
+export let isOpen = new IsOpen()
+let isAnimating = false
+let activeCallbacks: ((active: boolean) => void)[] = []
+
+// getter
+
+function getElTrail(): HTMLImageElement[] {
+  return cordHist.get().map((item) => imgs[item.i])
+}
+
+function getElTrailCurrent(): HTMLImageElement[] {
+  return getElTrail().slice(-getState().trailLength)
+}
+
+function getElTrailInactive(): HTMLImageElement[] {
+  const elTrailCurrent = getElTrailCurrent()
+  return elTrailCurrent.slice(0, elTrailCurrent.length - 1)
+}
+
+function getElCurrent(): HTMLImageElement {
+  const elTrail = getElTrail()
+  return elTrail[elTrail.length - 1]
+}
+
+export function getIsAnimating(): boolean {
+  return isAnimating
+}
+
+export function getActive(): boolean {
+  return isOpen.get() && !getIsAnimating()
+}
+
+// setter
+
+export function addActiveCallback(callback: (active: boolean) => void): void {
+  activeCallbacks.push(callback)
+}
+
+export function setIsAnimating(e: boolean): void {
+  isAnimating = e
+  activeCallbacks.forEach((callback) => callback(getActive()))
+}
+
+// main functions
+
+// on mouse
+function onMouse(e: MouseEvent): void {
+  if (isOpen.get() || getIsAnimating()) return
+  const cord = { x: e.clientX, y: e.clientY }
+  const travelDist = Math.hypot(cord.x - last.x, cord.y - last.y)
+
+  if (travelDist > getState().threshold) {
+    last = cord
+    incIndex()
+
+    const newHist = { i: getState().index, ...cord }
+    cordHist.set([...cordHist.get(), newHist].slice(-getState().length))
+  }
+}
+
+// set image position with gsap
+function setPositions(): void {
+  const elTrail = getElTrail()
+  if (!elTrail.length) return
+
+  gsap.set(elTrail, {
+    x: (i: number) => cordHist.get()[i].x - window.innerWidth / 2,
+    y: (i: number) => cordHist.get()[i].y - window.innerHeight / 2,
+    opacity: (i: number) =>
+      i + 1 + getState().trailLength <= cordHist.get().length ? 0 : 1,
+    zIndex: (i: number) => i,
+    scale: 0.6
+  })
+
+  if (isOpen.get()) {
+    gsap.set(imgs, { opacity: 0 })
+    gsap.set(getElCurrent(), { opacity: 1, x: 0, y: 0, scale: 1 })
+  }
+}
+
+// open image into navigation
+function expandImage(): void {
+  if (getIsAnimating()) return
+
+  isOpen.set(true)
+  setIsAnimating(true)
+
+  const tl = gsap.timeline()
+  // move down and hide trail inactive
+  tl.to(getElTrailInactive(), {
+    y: '+=20',
+    ease: Power3.easeIn,
+    stagger: 0.075,
+    duration: 0.3,
+    delay: 0.1,
+    opacity: 0
+  })
+  // current move to center
+  tl.to(getElCurrent(), {
+    x: 0,
+    y: 0,
+    ease: Power3.easeInOut,
+    duration: 0.7,
+    delay: 0.3
+  })
+  // current expand
+  tl.to(getElCurrent(), {
+    delay: 0.1,
+    scale: 1,
+    ease: Power3.easeInOut
+  })
+  // finished
+  tl.then(() => {
+    setIsAnimating(false)
+  })
+}
+
+// close navigation and back to stage
+export function minimizeImage(): void {
+  if (isAnimating) return
+
+  isOpen.set(false)
+  setIsAnimating(true)
+
+  const tl = gsap.timeline()
+  // shrink current
+  tl.to(getElCurrent(), {
+    scale: 0.6,
+    duration: 0.6,
+    ease: Power3.easeInOut
+  })
+  // move current to original position
+  tl.to(getElCurrent(), {
+    delay: 0.3,
+    duration: 0.7,
+    ease: Power3.easeInOut,
+    x: cordHist.get()[cordHist.get().length - 1].x - window.innerWidth / 2,
+    y: cordHist.get()[cordHist.get().length - 1].y - window.innerHeight / 2
+  })
+  // show trail inactive
+  tl.to(getElTrailInactive(), {
+    y: '-=20',
+    ease: Power3.easeOut,
+    stagger: -0.1,
+    duration: 0.3,
+    opacity: 1
+  })
+  // finished
+  tl.then(() => {
+    setIsAnimating(false)
+  })
+}
+
+// init
+
+export function initStage(ijs: ImageJSON[]): void {
+  createStage(ijs)
+  const stage = document.getElementsByClassName('stage').item(0) as HTMLDivElement
+  imgs = Array.from(stage.getElementsByTagName('img'))
+  stage.addEventListener('click', () => expandImage())
+  stage.addEventListener('keydown', () => expandImage())
+  window.addEventListener('mousemove', onMouse)
+}
+
+// hepler
+
+function createStage(ijs: ImageJSON[]): void {
+  // create container for images
+  const stage: HTMLDivElement = document.createElement('div')
+  stage.className = 'stage'
+  // append images to container
+  for (let ij of ijs) {
+    const e = document.createElement('img')
+    e.src = ij.url
+    e.height = ij.imgH
+    e.width = ij.imgW
+    e.alt = 'image'
+    stage.append(e)
+  }
+  document.getElementById('main')!.append(stage)
+}
diff --git a/assets/ts/stageNav.ts b/assets/ts/stageNav.ts
new file mode 100644
index 0000000..cba6d97
--- /dev/null
+++ b/assets/ts/stageNav.ts
@@ -0,0 +1,93 @@
+import { setCustomCursor } from './customCursor'
+import { decIndex, incIndex, getState } from './state'
+import { increment, decrement } from './utils'
+import {
+  cordHist,
+  isOpen,
+  getIsAnimating,
+  minimizeImage,
+  addActiveCallback
+} from './stage'
+
+type NavItem = (typeof navItems)[number]
+const navItems = ['prev', 'close', 'next'] as const
+
+// main functions
+
+function handleClick(type: NavItem) {
+  switch (type) {
+    case 'prev':
+      prevImage()
+      break
+    case 'close':
+      minimizeImage()
+      break
+    case 'next':
+      nextImage()
+      break
+  }
+}
+
+function handleKey(e: KeyboardEvent) {
+  if (isOpen.get() || getIsAnimating()) return
+  switch (e.key) {
+    case 'ArrowLeft':
+      prevImage()
+      break
+    case 'Escape':
+      minimizeImage()
+      break
+    case 'ArrowRight':
+      nextImage()
+      break
+  }
+}
+
+// init
+
+export function initStageNav() {
+  const navOverlay = document.createElement('div')
+  navOverlay.className = 'navOverlay'
+  for (let navItem of navItems) {
+    const overlay = document.createElement('div')
+    overlay.className = 'overlay'
+    overlay.addEventListener('click', () => handleClick(navItem))
+    overlay.addEventListener('keydown', () => handleClick(navItem))
+    overlay.addEventListener('mouseover', () => setCustomCursor(navItem))
+    overlay.addEventListener('focus', () => setCustomCursor(navItem))
+    navOverlay.append(overlay)
+  }
+  addActiveCallback((active) => {
+    if (active) {
+      navOverlay.classList.add('active')
+    } else {
+      navOverlay.classList.remove('active')
+    }
+  })
+  document.getElementById('main')!.append(navOverlay)
+  window.addEventListener('keydown', handleKey)
+}
+
+// hepler
+
+function nextImage() {
+  if (getIsAnimating()) return
+  cordHist.set(
+    cordHist.get().map((item) => {
+      return { ...item, i: increment(item.i, getState().length) }
+    })
+  )
+
+  incIndex()
+}
+
+function prevImage() {
+  if (getIsAnimating()) return
+  cordHist.set(
+    cordHist.get().map((item) => {
+      return { ...item, i: decrement(item.i, getState().length) }
+    })
+  )
+
+  decIndex()
+}
diff --git a/assets/ts/state.ts b/assets/ts/state.ts
new file mode 100644
index 0000000..4aebfe9
--- /dev/null
+++ b/assets/ts/state.ts
@@ -0,0 +1,68 @@
+import { increment, decrement } from './utils'
+import { updateIndexText, updateThresholdText } from './nav'
+
+const thresholds = [
+  { threshold: 20, trailLength: 20 },
+  { threshold: 40, trailLength: 10 },
+  { threshold: 80, trailLength: 5 },
+  { threshold: 140, trailLength: 5 },
+  { threshold: 200, trailLength: 5 }
+]
+
+const defaultState = {
+  index: -1,
+  length: 0,
+  threshold: thresholds[2].threshold,
+  trailLength: thresholds[2].trailLength
+}
+
+export type State = typeof defaultState
+
+let state = defaultState
+
+export function getState(): State {
+  // return a copy of state
+  return Object.create(
+    Object.getPrototypeOf(state),
+    Object.getOwnPropertyDescriptors(state)
+  )
+}
+
+export function initState(length: number): void {
+  state.length = length
+}
+
+export function setIndex(index: number): void {
+  state.index = index
+  updateIndexText()
+}
+
+export function incIndex(): void {
+  state.index = increment(state.index, state.length)
+  updateIndexText()
+}
+
+export function decIndex(): void {
+  state.index = decrement(state.index, state.length)
+  updateIndexText()
+}
+
+export function incThreshold(): void {
+  state = updateThreshold(state, 1)
+  updateThresholdText()
+}
+
+export function decThreshold(): void {
+  state = updateThreshold(state, -1)
+  updateThresholdText()
+}
+
+// helper
+
+function updateThreshold(state: State, inc: number): State {
+  const i = thresholds.findIndex((t) => state.threshold === t.threshold)
+  const newItems = thresholds[i + inc]
+  // out of range
+  if (!newItems) return state
+  return { ...state, ...newItems }
+}
diff --git a/assets/ts/thresholdCtl.ts b/assets/ts/thresholdCtl.ts
deleted file mode 100644
index 30f2a21..0000000
--- a/assets/ts/thresholdCtl.ts
+++ /dev/null
@@ -1,51 +0,0 @@
-import { duper } from './utils'
-import { setStackDepth } from './desktop'
-
-// get threshold display element
-const thresholdDisp = document.getElementsByClassName('thid').item(0) as HTMLSpanElement
-
-// threshold data
-const threshold: number[] = [0, 40, 80, 120, 160, 200]
-export const thresholdSensitivityArray: number[] = [100, 40, 18, 14, 9, 5]
-export let thresholdIndex: number = 2
-
-export const stackDepthArray: number[] = [15, 8, 5, 5, 5, 5]
-
-// update inner text of threshold display element
-const thresholdUpdate = (): void => {
-  thresholdDisp.innerText = duper(threshold[thresholdIndex])
-}
-
-const stackDepthUpdate = (): void => {
-  setStackDepth(stackDepthArray[thresholdIndex])
-}
-
-// threshold control initialization
-export const thresholdCtlInit = (): void => {
-  thresholdUpdate()
-  const dec = document.getElementById('thresholdDec') as HTMLButtonElement
-  dec.addEventListener(
-    'click',
-    function () {
-      if (thresholdIndex > 0) {
-        thresholdIndex--
-        thresholdUpdate()
-        stackDepthUpdate()
-      }
-    },
-    { passive: true }
-  )
-
-  const inc = document.getElementById('thresholdInc') as HTMLButtonElement
-  inc.addEventListener(
-    'click',
-    function () {
-      if (thresholdIndex < 5) {
-        thresholdIndex++
-        thresholdUpdate()
-        stackDepthUpdate()
-      }
-    },
-    { passive: true }
-  )
-}
diff --git a/assets/ts/utils.ts b/assets/ts/utils.ts
index 04da9fa..63743a6 100644
--- a/assets/ts/utils.ts
+++ b/assets/ts/utils.ts
@@ -1,145 +1,15 @@
-export interface ImageData {
-  index: string
-  url: string
-  imgH: string
-  imgW: string
-  pColor: string
-  sColor: string
+export function increment(num: number, length: number): number {
+  return (num + 1) % length
 }
 
-export interface position {
-  x: number
-  y: number
+export function decrement(num: number, length: number): number {
+  return (num + length - 1) % length
 }
 
-export interface deviceType {
-  mobile: boolean
-  tablet: boolean
-  desktop: boolean
-}
-
-// 0 to 0001, 25 to 0025
-export const duper = (num: number): string => {
+export function expand(num: number): string {
   return ('0000' + num.toString()).slice(-4)
 }
 
-export const mouseToTransform = (
-  x: number,
-  y: number,
-  centerCorrection: boolean = true,
-  accelerate: boolean = false
-): string => {
-  return `translate${accelerate ? '3d' : ''}(${
-    centerCorrection ? `calc(${x}px - 50%)` : `${x}px`
-  }, ${centerCorrection ? `calc(${y}px - 50%)` : `${y}px`}${accelerate ? ', 0' : ''})`
-}
-
-// eslint-disable-next-line @typescript-eslint/promise-function-async
-export function delay(ms: number): Promise<void> {
-  return new Promise((resolve) => setTimeout(resolve, ms))
-}
-
-// remove all event listeners from a node
-export const removeAllEventListeners = (e: Node): Node => {
-  return e.cloneNode(true)
-}
-
-// center top div
-export const center = (e: HTMLElement): void => {
-  const x: number = window.innerWidth / 2
-  let y: number
-  if (window.innerWidth > 768) {
-    y = (window.innerHeight - 38) / 2
-  } else {
-    y = (window.innerHeight - 31) / 2 + 31
-  }
-  e.style.transform = mouseToTransform(x, y)
-}
-
-export const createImgElement = (input: ImageData): HTMLImageElement => {
-  const img = document.createElement('img')
-  img.setAttribute('src', input.url)
-  img.setAttribute('alt', '')
-  img.setAttribute('height', input.imgH)
-  img.setAttribute('width', input.imgW)
-  img.style.visibility = 'hidden'
-  img.dataset.status = 'trail'
-  // img.style.backgroundImage = `linear-gradient(15deg, ${input.pColor}, ${input.sColor})`
-  return img
-}
-
-export const calcImageIndex = (index: number, imgCounts: number): number => {
-  if (index >= 0) {
-    return index % imgCounts
-  } else {
-    return (imgCounts + (index % imgCounts)) % imgCounts
-  }
-}
-
-export const preloadImage = (src: string): void => {
-  const cache = new Image()
-  cache.src = src
-}
-
-export const getDeviceType = (): deviceType => {
-  const ua: string = navigator.userAgent
-  const result: deviceType = { mobile: false, tablet: false, desktop: false }
-  if (/(tablet|ipad|playbook|silk)|(android(?!.*mobi))/i.test(ua)) {
-    result.mobile = true
-    result.tablet = true
-  } else if (
-    /Mobile|iP(hone|od)|Android|BlackBerry|IEMobile|Kindle|Silk-Accelerated|(hpw|web)OS|Opera M(obi|ini)/.test(
-      ua
-    )
-  ) {
-    result.mobile = true
-  } else result.desktop = true
-  return result
-}
-
-export const hideImage = (e: HTMLImageElement): void => {
-  e.style.visibility = 'hidden'
-  e.dataset.status = 'trail'
-}
-
-export const pushIndex = (
-  index: number,
-  indexesArray: number[],
-  stackDepth: number,
-  imagesArray: NodeListOf<HTMLImageElement>,
-  imagesArrayLen: number,
-  invertFlag: boolean = false,
-  autoHideFlag: boolean = true
-): number => {
-  let indexesNum: number = indexesArray.length
-  // create variable overflow to store the tail index
-  let overflow: number
-  if (!invertFlag) {
-    // if stack is full, push the tail index out and hide the image
-    if (indexesNum === stackDepth) {
-      // insert
-      indexesArray.push(index)
-      // pop out
-      overflow = indexesArray.shift() as number
-      // auto hide tail image
-      if (autoHideFlag) hideImage(imagesArray[overflow])
-    } else {
-      indexesArray.push(index)
-      indexesNum += 1
-    }
-  } else {
-    // if stack is full, push the tail index out and hide the image
-    if (indexesNum === stackDepth) {
-      // insert
-      indexesArray.unshift(calcImageIndex(index - stackDepth + 1, imagesArrayLen))
-      // pop out
-      overflow = indexesArray.pop() as number
-      // auto hide tail image
-      if (autoHideFlag) hideImage(imagesArray[overflow])
-    } else {
-      indexesArray.unshift(calcImageIndex(index - indexesNum + 1, imagesArrayLen))
-      indexesNum += 1
-    }
-  }
-  return indexesNum
+export function isMobile(): boolean {
+  return window.matchMedia('(hover: none)').matches
 }