const MOBILE_MEDIA = '(max-width: 767.98px)'
const KEYBOARD_GAP_PX = 16
const SCROLL_RETRY_MS = [0, 90, 220, 420, 640]

let started = false
let activeField: HTMLElement | null = null
let blurTimer = 0

function isMobileLayout(): boolean {
  return window.matchMedia(MOBILE_MEDIA).matches
}

function getKeyboardInset(): number {
  const vv = window.visualViewport
  if (!vv) return 0
  return Math.max(0, Math.round(window.innerHeight - vv.height - vv.offsetTop))
}

function getVisibleViewportBottom(): number {
  const vv = window.visualViewport
  return vv ? vv.offsetTop + vv.height : window.innerHeight
}

function syncViewportVars(hasFocusedField: boolean) {
  const vv = window.visualViewport
  const inset = getKeyboardInset()

  document.documentElement.style.setProperty('--app-keyboard-inset', `${inset}px`)

  if (vv) {
    document.documentElement.style.setProperty('--app-visual-viewport-height', `${Math.round(vv.height)}px`)
    document.documentElement.style.setProperty('--app-visual-viewport-offset-top', `${Math.round(vv.offsetTop)}px`)
  }

  if (hasFocusedField && inset > 0) {
    document.documentElement.dataset.keyboardOpen = 'true'
    return
  }

  if (!hasFocusedField) {
    delete document.documentElement.dataset.keyboardOpen
    document.documentElement.style.setProperty('--app-keyboard-inset', '0px')
  }
}

function resolveEditableTarget(node: EventTarget | null): HTMLElement | null {
  if (!(node instanceof HTMLElement)) return null

  const field = node.closest('input, textarea, select, [contenteditable="true"]')
  if (!(field instanceof HTMLElement)) return null

  if (field instanceof HTMLInputElement) {
    if (field.disabled || field.readOnly || field.type === 'hidden') return null
  }

  if (field instanceof HTMLTextAreaElement) {
    if (field.disabled || field.readOnly) return null
  }

  if (field instanceof HTMLSelectElement && field.disabled) return null

  return field
}

function findScrollableAncestor(el: HTMLElement): HTMLElement | null {
  let node: HTMLElement | null = el.parentElement

  while (node && node !== document.body && node !== document.documentElement) {
    const style = window.getComputedStyle(node)
    const overflowY = style.overflowY
    const scrollable = overflowY === 'auto' || overflowY === 'scroll' || overflowY === 'overlay'

    if (scrollable && node.scrollHeight > node.clientHeight + 1) {
      return node
    }

    node = node.parentElement
  }

  return null
}

function ensureFieldVisible(field: HTMLElement) {
  if (!isMobileLayout()) return

  syncViewportVars(true)

  const rect = field.getBoundingClientRect()
  const visibleBottom = getVisibleViewportBottom() - KEYBOARD_GAP_PX
  const scrollParent = findScrollableAncestor(field)

  if (rect.bottom > visibleBottom) {
    const delta = rect.bottom - visibleBottom
    if (scrollParent) {
      scrollParent.scrollTop += delta
    } else {
      window.scrollBy({top: delta, left: 0, behavior: 'auto'})
    }
  }

  if (rect.top < KEYBOARD_GAP_PX && scrollParent) {
    scrollParent.scrollTop += rect.top - KEYBOARD_GAP_PX
  }

  field.scrollIntoView({block: 'nearest', inline: 'nearest', behavior: 'auto'})
}

function scheduleEnsureVisible(field: HTMLElement) {
  SCROLL_RETRY_MS.forEach((delay) => {
    window.setTimeout(() => {
      const active = resolveEditableTarget(document.activeElement)
      if (!active || active !== field) return
      ensureFieldVisible(field)
    }, delay)
  })
}

function onFocusIn(event: FocusEvent) {
  if (!isMobileLayout()) return

  const field = resolveEditableTarget(event.target)
  if (!field) return

  activeField = field
  window.clearTimeout(blurTimer)
  scheduleEnsureVisible(field)
}

function onFocusOut() {
  window.clearTimeout(blurTimer)
  blurTimer = window.setTimeout(() => {
    const next = resolveEditableTarget(document.activeElement)
    activeField = next

    if (!next) {
      syncViewportVars(false)
      return
    }

    syncViewportVars(true)
    scheduleEnsureVisible(next)
  }, 120)
}

function onViewportChange() {
  if (!isMobileLayout()) return

  syncViewportVars(Boolean(activeField))

  const active = resolveEditableTarget(document.activeElement) ?? activeField
  if (!active) return

  activeField = active
  ensureFieldVisible(active)
}

/** موبایل: با باز شدن کیبورد، فیلد فوکوس‌شده بالای کیبورد دیده شود. */
export function initMobileInputKeyboardScroll() {
  if (typeof window === 'undefined' || started) return
  started = true

  document.addEventListener('focusin', onFocusIn, true)
  document.addEventListener('focusout', onFocusOut, true)
  window.visualViewport?.addEventListener('resize', onViewportChange, {passive: true})
  window.visualViewport?.addEventListener('scroll', onViewportChange, {passive: true})

  if (import.meta.hot) {
    import.meta.hot.dispose(() => {
      started = false
      document.removeEventListener('focusin', onFocusIn, true)
      document.removeEventListener('focusout', onFocusOut, true)
      window.visualViewport?.removeEventListener('resize', onViewportChange)
      window.visualViewport?.removeEventListener('scroll', onViewportChange)
    })
  }
}