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package co.easimart;

import java.util.Arrays;
import java.util.List;

import bolts.Continuation;
import bolts.Task;

/** package */ class OfflineObjectStore implements EasimartObjectStore {

  private static  Task migrate(
      final EasimartObjectStore from, final EasimartObjectStore to) {
    return from.getAsync().onSuccessTask(new Continuation>() {
      @Override
      public Task then(Task task) throws Exception {
        final T object = task.getResult();
        if (object == null) {
          return task;
        }

        return Task.whenAll(Arrays.asList(
            from.deleteAsync(),
            to.setAsync(object)
        )).continueWith(new Continuation() {
          @Override
          public T then(Task task) throws Exception {
            return object;
          }
        });
      }
    });
  }

  private final String className;
  private final String pinName;
  private final EasimartObjectStore legacy;

  public OfflineObjectStore(Class clazz, String pinName, EasimartObjectStore legacy) {
    this(EasimartObject.getClassName(clazz), pinName, legacy);
  }

  public OfflineObjectStore(String className, String pinName, EasimartObjectStore legacy) {
    this.className = className;
    this.pinName = pinName;
    this.legacy = legacy;
  }

  @Override
  public Task setAsync(final T object) {
    return EasimartObject.unpinAllInBackground(pinName).continueWithTask(new Continuation>() {
      @Override
      public Task then(Task task) throws Exception {
        return object.pinInBackground(pinName, false);
      }
    });
  }

  @Override
  public Task getAsync() {
    // We need to set `ignoreACLs` since we can't use ACLs without the current user.
    EasimartQuery query = EasimartQuery.getQuery(className)
        .fromPin(pinName)
        .ignoreACLs();
    return query.findInBackground().onSuccessTask(new Continuation, Task>() {
      @Override
      public Task then(Task> task) throws Exception {
        List results = task.getResult();
        if (results != null) {
          if (results.size() == 1) {
            return Task.forResult(results.get(0));
          } else {
            return EasimartObject.unpinAllInBackground(pinName).cast();
          }
        }
        return Task.forResult(null);
      }
    }).onSuccessTask(new Continuation>() {
      @Override
      public Task then(Task task) throws Exception {
        T ldsObject = task.getResult();
        if (ldsObject != null) {
          return task;
        }

        return migrate(legacy, OfflineObjectStore.this).cast();
      }
    });
  }

  @Override
  public Task existsAsync() {
    // We need to set `ignoreACLs` since we can't use ACLs without the current user.
    EasimartQuery query = EasimartQuery.getQuery(className)
        .fromPin(pinName)
        .ignoreACLs();
    return query.countInBackground().onSuccessTask(new Continuation>() {
      @Override
      public Task then(Task task) throws Exception {
        boolean exists = task.getResult() == 1;
        if (exists) {
          return Task.forResult(true);
        }
        return legacy.existsAsync();
      }
    });
  }

  @Override
  public Task deleteAsync() {
    final Task ldsTask = EasimartObject.unpinAllInBackground(pinName);
    return Task.whenAll(Arrays.asList(
        legacy.deleteAsync(),
        ldsTask
    )).continueWithTask(new Continuation>() {
      @Override
      public Task then(Task task) throws Exception {
        // We only really care about the result of unpinning.
        return ldsTask;
      }
    });
  }
}