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

package com.thebrokenrail.mtudining.activity.task;

import android.view.View;
import android.view.ViewGroup;

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

import com.thebrokenrail.mtudining.R;
import com.thebrokenrail.mtudining.widget.LoaderView;

/**
 * RecyclerView adapter for a given {@link Task}.
 */
public abstract class TaskAdapter<E> extends RecyclerView.Adapter<RecyclerView.ViewHolder> implements Task.Listener<E> {
    public static final int LOADER_TYPE = 1;
    public static final int ITEM_TYPE = 0;
    public static final int HEADER_TYPE = 2;

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

    /**
     * Create view for header.
     * @param parent The view parent
     * @return The new view
     */
    protected View createHeader(@NonNull ViewGroup parent) {
        // Just Create Margin
        View view = new View(parent.getContext());
        int margin = parent.getResources().getDimensionPixelSize(R.dimen.margin);
        RecyclerView.LayoutParams layoutParams = new RecyclerView.LayoutParams(RecyclerView.LayoutParams.MATCH_PARENT, margin);
        view.setLayoutParams(layoutParams);
        return view;
    }

    @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 == ITEM_TYPE) {
            // Data
            return new RecyclerView.ViewHolder(createItemView(parent)) {};
        } else if (viewType == HEADER_TYPE) {
            // Header
            return new RecyclerView.ViewHolder(createHeader(parent)) {};
        } else {
            // Unknown
            throw new RuntimeException();
        }
    }

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

    /**
     * Bind view for header.
     * @param view The view
     */
    protected void bindHeader(View view) {
    }

    @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 == ITEM_TYPE) {
            // Data
            bindItemView(holder.itemView, position);
        } else if (type == HEADER_TYPE) {
            // Header
            bindHeader(holder.itemView);
        }
    }

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

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

    /**
     * Get position of first non-header element.
     * @return Element position
     */
    public int getFirstElementPosition() {
        return 1;
    }

    @Override
    public int getItemViewType(int position) {
        if (currentStatus != Task.Status.DONE && position == getFirstElementPosition()) {
            // Loader
            return LOADER_TYPE;
        } else if (position == 0) {
            // Header
            return HEADER_TYPE;
        } else {
            // Item
            return ITEM_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.
     * @param oldItemCount Amount of visible items before UI change
     */
    protected void reloadUI(int oldItemCount) {
        // Reload Header Without Animation
        notifyItemChanged(0, new Object()); // https://stackoverflow.com/a/45590003
        // Remove Existing Items
        notifyItemRangeRemoved(1, oldItemCount - 1);
        // Add Items
        notifyItemRangeInserted(1, getItemCount() - 1);
    }

    /**
     * Get task.
     * @return The task
     */
    public Task<E> getTask() {
        return task;
    }
}