BaseAdapter.kt

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.annotation.LayoutRes
import androidx.core.content.ContextCompat
import androidx.databinding.DataBindingUtil
import androidx.databinding.ViewDataBinding
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.ListAdapter
import androidx.recyclerview.widget.RecyclerView
import kotlinx.coroutines.*

/**
 * By extending this base adapter you have to provide 2 predicate parameters:
 *
 * @param itemSimilarity: a predicate to check for item similarity.
 *  ```
{ oldItem, newItem -> oldItem.id == newItem.id },

```
 * @param contentSimilarity: a predicate to check for content similarity.
 * ```
{ oldItem, newItem -> oldItem == newItem }
```
 *
 */
abstract class BaseAdapter<T>(
        private val itemSimilarity: (T, T) -> Boolean,
        private val contentSimilarity: (T, T) -> Boolean) : ListAdapter<T, BaseAdapter<T>.DataBindingViewHolder>(object : DiffUtil.ItemCallback<T>() {
    override fun areContentsTheSame(oldItem: T, newItem: T) = contentSimilarity.invoke(oldItem, newItem)
    override fun areItemsTheSame(oldItem: T, newItem: T) = itemSimilarity.invoke(oldItem, newItem)
}) {

    var onItemClicked: ((item: T, view: View, position: Int) -> Unit)? = null
    var onItemLongClicked: ((item: T, view: View, position: Int) -> Boolean)? = null
    var onItemSelected: ((position: Int) -> Unit)? = null
    var onClearSelections: (() -> Unit)? = null
    var onSelectAll: ((list: IntRange) -> Unit)? = null
    val selectedItems = mutableListOf<Int>()
    var isInSelectMode = false
        set(value) {
            field = value
            notifyDataSetChanged()
        }

    private val scope = CoroutineScope(Dispatchers.Main)

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) = DataBindingViewHolder(
            DataBindingUtil.inflate(
                    LayoutInflater.from(parent.context),
                    viewType,
                    parent,
                    false
            )
    )

    override fun onBindViewHolder(holder: DataBindingViewHolder, position: Int) =
            holder.bind(getItem(position), position, position in selectedItems)

    @LayoutRes
    abstract override fun getItemViewType(position: Int): Int

    fun clearAllSelectedItems() {
        val currentItems = selectedItems.toList()
        selectedItems.clear()
        onClearSelections?.invoke()
        scope.launch {
            currentItems.forEach {
                delay(2)
                notifyItemChanged(it)
            }
        }
    }

    fun selectAll() = currentList.indices.let {
        onSelectAll?.invoke(it)
        selectedItems.addAll(it)
        scope.launch {
            it.forEach {
                delay(2)
                notifyItemChanged(it)
            }
        }
    }

    inner class DataBindingViewHolder(private val binding: ViewDataBinding) : RecyclerView.ViewHolder(binding.root) {
        fun bind(item: T, position: Int, isSelected: Boolean) {
            binding.apply {
                setVariable(BR.item, item)
                executePendingBindings()

                root.apply {
                    if (!isInSelectMode) {
                        root.setBackgroundColor(ContextCompat.getColor(context, R.color.white))
                    } else {
                        if (isSelected) root.setBackgroundColor(ContextCompat.getColor(context, R.color.fine_red))
                        else root.setBackgroundColor(ContextCompat.getColor(context, R.color.white))
                    }

                    setOnClickListener {
                        /**
                         * Does not select mock items
                         */
                        if (isInSelectMode) {
                            onItemSelected?.invoke(adapterPosition)
                            if (isSelected) {
                                selectedItems.remove(adapterPosition)
                                notifyItemChanged(position)
                            } else {
                                selectedItems.add(adapterPosition)
                                notifyItemChanged(position)
                            }
                        } else onItemClicked?.invoke(item, this, adapterPosition)
                    }
                    setOnLongClickListener {
                        return@setOnLongClickListener onItemLongClicked?.invoke(item, this, adapterPosition)
                                ?: return@setOnLongClickListener true
                    }
                }
            }
        }
    }
}