Support pagination when single index query

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/tx/PagedIdHolder.java → hugegraph-core/src/main/java/com/baidu/hugegraph/backend/page/IdHolder.java

@@ -17,90 +17,81 @@
  * under the License.
  */
 
-package com.baidu.hugegraph.backend.tx;
+package com.baidu.hugegraph.backend.page;
 
 import java.util.Set;
 import java.util.function.Supplier;
 
 import com.baidu.hugegraph.backend.id.Id;
 import com.baidu.hugegraph.backend.query.Query;
-import com.baidu.hugegraph.exception.NotSupportException;
-import com.baidu.hugegraph.iterator.Metadatable;
 import com.baidu.hugegraph.util.E;
 
-public final class PagedIdHolder implements IdHolder, Metadatable {
+public final class IdHolder {
 
     private final Query query;
-    private final Supplier<PagedIds> idsFetcher;
+    private final Supplier<PageIds> idsFetcher;
+    private boolean exhausted;
 
-    private int limit;
     private Set<Id> ids;
-    private String page;
-    private boolean finished;
 
-    public PagedIdHolder(Query query, Supplier<PagedIds> idsFetcher) {
+    /**
+     * For non-paged situation
+     */
+    public IdHolder(Set<Id> ids) {
+        this.query = null;
+        this.idsFetcher = null;
+        this.exhausted = false;
+        this.ids = ids;
+    }
+
+    /**
+     * For paged situation
+     */
+    public IdHolder(Query query, Supplier<PageIds> idsFetcher) {
         E.checkArgument(query.paging(),
                         "Query '%s' must carry the page info in paged mode",
                         query);
         this.query = query;
         this.idsFetcher = idsFetcher;
+        this.exhausted = false;
         this.ids = null;
-        this.page = query.page();
-        this.finished = false;
-    }
-
-    public int limit() {
-        return this.limit;
     }
 
-    public void limit(int limit) {
-        this.limit = limit;
+    public void merge(Set<Id> ids) {
+        this.ids.addAll(ids);
     }
 
-    public String page() {
-        return this.page;
+    public Set<Id> ids() {
+        E.checkNotNull(this.ids, "ids");
+        return this.ids;
     }
 
-    public void page(String page) {
-        this.page = page;
+    public int size() {
+        if (this.ids == null) {
+            return 0;
+        }
+        return this.ids.size();
     }
 
-    public void resetPage() {
-        this.page = "";
+    public boolean paging() {
+        return this.idsFetcher != null;
     }
 
-    public Set<Id> fetchFromBackend() {
-        if (this.finished) {
+    public PageIds fetchNext(String page, long pageSize) {
+        if (this.exhausted) {
             return null;
         }
 
-        this.query.page(this.page);
-        this.query.limit(this.limit);
+        this.query.page(page);
+        this.query.limit(pageSize);
 
-        PagedIds result = this.idsFetcher.get();
+        PageIds result = this.idsFetcher.get();
         this.ids = result.ids();
-        this.page = result.page();
 
         assert this.ids != null;
-        if (this.ids.size() != this.query.limit() || this.page == null) {
-            this.finished = true;
-        }
-        return this.ids;
-    }
-
-    @Override
-    public int size() {
-        if (this.ids == null) {
-            return 0;
-        }
-        return this.ids.size();
-    }
-
-    @Override
-    public Object metadata(String meta, Object... args) {
-        if ("page".equals(meta)) {
-            return this.page;
+        if (this.ids.size() != this.query.limit() || result.page() == null) {
+            this.exhausted = true;
         }
-        throw new NotSupportException("Invalid meta '%s'", meta);
+        return result;
     }
 }

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/page/IdHolderList.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2017 HugeGraph Authors
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with this
+ * work for additional information regarding copyright ownership. The ASF
+ * licenses this file to You under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+package com.baidu.hugegraph.backend.page;
+
+import java.util.ArrayList;
+import java.util.Collection;
+
+import com.baidu.hugegraph.util.E;
+
+public final class IdHolderList extends ArrayList<IdHolder> {
+
+    private final boolean paging;
+
+    public IdHolderList(boolean paging) {
+        this.paging = paging;
+    }
+
+    public boolean paging() {
+        return this.paging;
+    }
+
+    @Override
+    public boolean add(IdHolder holder) {
+        E.checkArgument(this.paging == holder.paging(),
+                        "The IdHolder to be linked must be " +
+                        "IdHolder in paging mode");
+        if (this.paging || this.isEmpty()) {
+            super.add(holder);
+        } else {
+            assert this.size() == 1;
+            IdHolder self = this.get(0);
+            assert !self.paging();
+            self.merge(holder.ids());
+        }
+        return true;
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends IdHolder> idHolders) {
+        for (IdHolder idHolder : idHolders) {
+            this.add(idHolder);
+        }
+        return true;
+    }
+
+    public int idsSize() {
+        if (this.paging || this.isEmpty()) {
+            return 0;
+        } else {
+            assert this.size() == 1;
+            return this.get(0).size();
+        }
+    }
+}

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/page/PageEntryIterator.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2017 HugeGraph Authors
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with this
+ * work for additional information regarding copyright ownership. The ASF
+ * licenses this file to You under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+package com.baidu.hugegraph.backend.page;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+import com.baidu.hugegraph.backend.store.BackendEntry;
+import com.baidu.hugegraph.exception.NotSupportException;
+import com.baidu.hugegraph.iterator.Metadatable;
+import com.baidu.hugegraph.util.E;
+
+public class PageEntryIterator implements Iterator<BackendEntry>, Metadatable {
+
+    private final QueryList queries;
+    private final long pageSize;
+    private QueryList.PageIterator results;
+    private PageState pageState;
+    private long remaining;
+
+    public PageEntryIterator(QueryList queries, long pageSize) {
+        this.queries = queries;
+        this.pageSize = pageSize;
+        this.results = QueryList.PageIterator.EMPTY;
+        this.pageState = this.parsePageState();
+        this.remaining = queries.parent().limit();
+    }
+
+    private PageState parsePageState() {
+        String page = this.queries.parent().page();
+        PageState pageState = PageState.fromString(page);
+        E.checkState(pageState.offset() < this.queries.total(),
+                     "Invalid page '%s' with an offset '%s' exceeds " +
+                     "the size of IdHolderList", page, pageState.offset());
+        return pageState;
+    }
+
+    @Override
+    public boolean hasNext() {
+        if (this.results.iterator().hasNext()) {
+            return true;
+        }
+        return this.fetch();
+    }
+
+    private boolean fetch() {
+        if (this.remaining <= 0 ||
+            this.pageState.offset() >= this.queries.total()) {
+            return false;
+        }
+
+        long pageSize = this.remaining < this.pageSize ?
+                        this.remaining : this.pageSize;
+        this.results = this.queries.fetchNext(this.pageState, pageSize);
+        assert this.results != null;
+
+        if (this.results.iterator().hasNext()) {
+            if (results.page() == null) {
+                this.pageState.increase();
+            } else {
+                this.pageState.page(this.results.page());
+            }
+            return true;
+        } else {
+            this.pageState.increase();
+            return this.fetch();
+        }
+    }
+
+    @Override
+    public BackendEntry next() {
+        if (!this.results.iterator().hasNext() && !this.hasNext()) {
+            throw new NoSuchElementException();
+        }
+        BackendEntry entry = this.results.iterator().next();
+        this.remaining--;
+        return entry;
+    }
+
+    @Override
+    public Object metadata(String meta, Object... args) {
+        if ("page".equals(meta)) {
+            if (this.pageState.offset() >= this.queries.total()) {
+                return null;
+            }
+            return this.pageState.toString();
+        }
+        throw new NotSupportException("Invalid meta '%s'", meta);
+    }
+}

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/tx/PagedIds.java → hugegraph-core/src/main/java/com/baidu/hugegraph/backend/page/PageIds.java

@@ -17,18 +17,18 @@
  * under the License.
  */
 
-package com.baidu.hugegraph.backend.tx;
+package com.baidu.hugegraph.backend.page;
 
 import java.util.Set;
 
 import com.baidu.hugegraph.backend.id.Id;
 
-public final class PagedIds {
+public final class PageIds {
 
     private final Set<Id> ids;
     private final String page;
 
-    public PagedIds(Set<Id> ids, String page) {
+    public PageIds(Set<Id> ids, String page) {
         this.ids = ids;
         this.page = page;
     }

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/tx/PageState.java → hugegraph-core/src/main/java/com/baidu/hugegraph/backend/page/PageState.java

@@ -17,7 +17,7 @@
  * under the License.
  */
 
-package com.baidu.hugegraph.backend.tx;
+package com.baidu.hugegraph.backend.page;
 
 import java.util.Base64;
 
@@ -26,22 +26,33 @@
 import com.baidu.hugegraph.util.Bytes;
 import com.baidu.hugegraph.util.E;
 
-public class PageState {
+public final class PageState {
 
-    private final int offset;
-    private final String page;
+    public static final String PAGE_NONE = "";
+
+    private int offset;
+    private String page;
 
     public PageState(int offset, String page) {
-        E.checkArgument(offset >= 0, "The offset must >= 0");
+        E.checkArgument(offset >= 0, "The offset must be >= 0");
         E.checkNotNull(page, "page");
         this.offset = offset;
         this.page = page;
     }
 
+    public void increase() {
+        this.offset++;
+        this.page = PAGE_NONE;
+    }
+
     public int offset() {
         return this.offset;
     }
 
+    public void page(String page) {
+        this.page = page;
+    }
+
     public String page() {
         return this.page;
     }