ProgressRecyclerAdapter

import android.support.v7.widget.RecyclerView
import android.view.View
import android.view.ViewGroup
import android.widget.ProgressBar
import android.widget.RelativeLayout

abstract class ProgressRecyclerAdapter<T : RecyclerView.ViewHolder> : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
    companion object {
        private val VIEW_PROGRESS = 11
    }

    var isProgress: Boolean = false
        set(value) {
            if (field == value) {
                return
            }

            field = value
            if (value) {
                notifyItemInserted(getOriginalItemCount())
            } else {
                notifyItemRemoved(getOriginalItemCount())
            }
        }

    final override fun getItemCount(): Int = getOriginalItemCount() + if (isProgress) 1 else 0

    final override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder =
            when (viewType) {
                VIEW_PROGRESS -> {
                    val layout = RelativeLayout(parent.context).apply {
                        val padding = parent.context.resources.getDimensionPixelSize(R.dimen.spacing)
                        setPadding(padding, padding, padding, padding)
                    }

                    val layoutParams = RelativeLayout.LayoutParams(progressWidth, progressHeight).apply {
                        addRule(RelativeLayout.CENTER_IN_PARENT, RelativeLayout.TRUE)
                    }

                    layout.addView(ProgressBar(parent.context), layoutParams)
                    ProgressViewHolder(layout)
                }
                else -> onCreateOriginalViewHolder(parent, viewType)
            }

    abstract val progressWidth: Int

    abstract val progressHeight: Int

    final override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        if (isProgress && position == getOriginalItemCount()) {
            return
        }

        onBindOriginalViewHolder(holder as T, position)
    }

    final override fun getItemViewType(position: Int): Int = if (getOriginalItemCount() == position) VIEW_PROGRESS else getOriginalItemViewType(position)

    abstract fun getOriginalItemCount(): Int

    abstract fun onCreateOriginalViewHolder(parent: ViewGroup, viewType: Int): T

    abstract fun onBindOriginalViewHolder(holder: T, position: Int)

    open fun getOriginalItemViewType(position: Int): Int = 0

    class ProgressViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView)
}