/**
 * SortableList — minimal HTML5 drag-and-drop hook for reorderable lists.
 *
 * Markup contract:
 *   <div phx-hook="SortableList" id="..." data-event="reorder_layers" data-group-key="schedule_id">
 *     <div data-id="<uuid>" draggable="true">...</div>
 *     <div data-id="<uuid>" draggable="true">...</div>
 *   </div>
 *
 * On drop, the hook pushes one event named by `data-event` with payload
 * `{ ordered_ids: [...] }` carrying the new order of every direct child
 * with a `data-id` attribute.
 *
 * No external dependency — uses native HTML5 drag-and-drop. Mirrors the
 * existing DeviceListReorder hook in style.
 */

export const SortableList = {
  draggedEl: null as HTMLElement | null,
  handleDragStart: null as ((e: DragEvent) => void) | null,
  handleDragEnd: null as ((e: DragEvent) => void) | null,
  handleDragOver: null as ((e: DragEvent) => void) | null,
  handleDrop: null as ((e: DragEvent) => void) | null,

  mounted(this: any) {
    const container: HTMLElement = this.el
    const eventName: string = container.dataset.event || "reorder"

    const itemFromTarget = (t: EventTarget | null): HTMLElement | null => {
      const el = t as HTMLElement | null
      return el ? (el.closest<HTMLElement>("[data-id]") || null) : null
    }

    const itemIsDirectChild = (item: HTMLElement | null): item is HTMLElement => {
      return !!item && item.parentElement === container
    }

    this.handleDragStart = (e: DragEvent) => {
      const item = itemFromTarget(e.target)
      if (!itemIsDirectChild(item) || item.getAttribute("draggable") !== "true") return
      this.draggedEl = item
      item.classList.add("opacity-50")
      e.dataTransfer!.effectAllowed = "move"
    }

    this.handleDragEnd = (_e: DragEvent) => {
      if (this.draggedEl) {
        this.draggedEl.classList.remove("opacity-50")
        this.draggedEl = null
      }
      container.querySelectorAll(".sortable-drop-target").forEach((el: Element) => {
        el.classList.remove("sortable-drop-target", "border-t-4", "border-b-4", "border-blue-500")
      })
    }

    this.handleDragOver = (e: DragEvent) => {
      e.preventDefault()
      if (!this.draggedEl) return

      const target = itemFromTarget(e.target)
      if (!itemIsDirectChild(target) || target === this.draggedEl) return

      const rect = target.getBoundingClientRect()
      const isBottomHalf = e.clientY > rect.top + rect.height / 2

      container.querySelectorAll(".sortable-drop-target").forEach((el: Element) => {
        el.classList.remove("sortable-drop-target", "border-t-4", "border-b-4", "border-blue-500")
      })
      target.classList.add(
        "sortable-drop-target",
        "border-blue-500",
        isBottomHalf ? "border-b-4" : "border-t-4"
      )
    }

    this.handleDrop = (e: DragEvent) => {
      e.preventDefault()
      if (!this.draggedEl) return

      const target = itemFromTarget(e.target)
      if (!itemIsDirectChild(target) || target === this.draggedEl) return

      const rect = target.getBoundingClientRect()
      const isBottomHalf = e.clientY > rect.top + rect.height / 2

      // Reorder DOM optimistically so the user sees the result
      // immediately; the server-side patch will reconcile.
      if (isBottomHalf) {
        container.insertBefore(this.draggedEl, target.nextSibling)
      } else {
        container.insertBefore(this.draggedEl, target)
      }

      const orderedIds = Array.from(
        container.querySelectorAll<HTMLElement>(":scope > [data-id]")
      ).map(el => el.dataset.id!)

      this.pushEvent(eventName, { ordered_ids: orderedIds })
    }

    container.addEventListener("dragstart", this.handleDragStart)
    container.addEventListener("dragend", this.handleDragEnd)
    container.addEventListener("dragover", this.handleDragOver)
    container.addEventListener("drop", this.handleDrop)
  },

  destroyed(this: any) {
    if (this.handleDragStart) this.el.removeEventListener("dragstart", this.handleDragStart)
    if (this.handleDragEnd) this.el.removeEventListener("dragend", this.handleDragEnd)
    if (this.handleDragOver) this.el.removeEventListener("dragover", this.handleDragOver)
    if (this.handleDrop) this.el.removeEventListener("drop", this.handleDrop)
    this.draggedEl = null
  }
}