MTU-Dining/app/src/main/java/com/thebrokenrail/mtudining/activity/task/TaskAdapter.java

package com.thebrokenrail.mtudining.activity.task;

import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.thebrokenrail.mtudining.widget.LoaderView;

/**
 * RecyclerView adapter for a given {@link Task}.
 */
public abstract class TaskAdapter<E, VH extends RecyclerView.ViewHolder> extends RecyclerView.Adapter<RecyclerView.ViewHolder> implements Task.Listener<E> {
    public static final int LOADER_TYPE = 1;
    public static final int DATA_TYPE = 0;

    /**
     * The task.
     */
    private final Task<E> task;

    /**
     * Current task status.
     */
    private Task.Status currentStatus;

    /**
     * Task result (or null if none).
     */
    private E result;

    /**
     * Get task result.
     * @return Task result
     */
    protected E getResult() {
        return result;
    }

    /**
     * Create adapter.
     * @param task The task
     */
    public TaskAdapter(Task<E> task) {
        // Setup Event Handling
        this.task = task;
        task.addListener(this);
    }

    /**
     * Call when activity is destroyed.
     */
    public void onDestroy() {
        // Stop Handling Events
        task.removeListener(this);
    }

    /**
     * Create view holder for item in task's result.
     * @param parent The view parent
     * @return The new view holder
     */
    protected abstract VH createItemViewHolder(@NonNull ViewGroup parent);

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        if (viewType == LOADER_TYPE) {
            // Loader
            LoaderView loader = new LoaderView(parent.getContext(), null);
            RecyclerView.LayoutParams layoutParams = new RecyclerView.LayoutParams(RecyclerView.LayoutParams.MATCH_PARENT, RecyclerView.LayoutParams.WRAP_CONTENT);
            loader.setLayoutParams(layoutParams);
            return new RecyclerView.ViewHolder(loader) {};
        } else if (viewType == DATA_TYPE) {
            // Data
            return createItemViewHolder(parent);
        } else {
            // Unknown
            throw new RuntimeException();
        }
    }

    /**
     * Bind view holder for item in task's result.
     * @param holder The view holder
     * @param position The item's position
     */
    protected abstract void bindDataViewHolder(@NonNull VH holder, int position);

    @SuppressWarnings({"unchecked"})
    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        int type = getItemViewType(position);
        if (type == LOADER_TYPE) {
            // Loader
            ((LoaderView) holder.itemView).setup(currentStatus == Task.Status.ERROR, task::start);
        } else if (type == DATA_TYPE) {
            // Data
            bindDataViewHolder((VH) holder, position);
        }
    }

    /**
     * Get size of task's dataset.
     * @return The size of the dataset
     */
    protected abstract int getDataSize();

    @Override
    public int getItemCount() {
        if (currentStatus != Task.Status.DONE) {
            // Only Loader
            return 1;
        } else {
            // Data Size
            return getDataSize();
        }
    }

    @Override
    public int getItemViewType(int position) {
        if (currentStatus != Task.Status.DONE && position == 0) {
            // Loader
            return LOADER_TYPE;
        } else {
            // Data
            return DATA_TYPE;
        }
    }

    @Override
    public void update(Task.Status status, E result) {
        int oldItemCount = getItemCount();
        // Store
        this.currentStatus = status;
        this.result = result;
        // Change UI
        if (status == Task.Status.IN_PROGRESS || status == Task.Status.NOT_STARTED) {
            // Show Progress Circle
            reloadUI(oldItemCount);
            // Start Task If Needed
            if (status == Task.Status.NOT_STARTED) {
                task.start();
            }
        } else if (status == Task.Status.ERROR) {
            // Show Error
            reloadUI(oldItemCount);
        } else {
            // Done
            reloadUI(oldItemCount);
        }
    }

    /**
     * Reload UI.
     */
    private void reloadUI(int oldItemCount) {
        // Remove Existing Items
        notifyItemRangeRemoved(0, oldItemCount);
        // Add Items
        notifyItemRangeInserted(0, getItemCount());
    }
}