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/*
 * Copyright 2017-2019 the original author or authors.
 *
 * Licensed 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
 *
 *      https://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.google.cloud.spring.vision;

import com.google.cloud.storage.Blob;
import com.google.cloud.vision.v1.TextAnnotation;
import com.google.protobuf.InvalidProtocolBufferException;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.TreeMap;

/** Represents the parsed OCR content for an document in the provided range of pages. */
public class DocumentOcrResultSet {

  private final TreeMap ocrPageRanges;

  private final int minPage;

  private final int maxPage;

  DocumentOcrResultSet(Collection pages) {
    this.ocrPageRanges = new TreeMap<>();

    for (Blob blob : pages) {
      OcrPageRange pageRange = new OcrPageRange(blob);
      ocrPageRanges.put(pageRange.getStartPage(), pageRange);
    }

    this.minPage = this.ocrPageRanges.firstEntry().getValue().getStartPage();
    this.maxPage = this.ocrPageRanges.lastEntry().getValue().getEndPage();
  }

  /**
   * Returns the minimum page number in the result set.
   *
   * @return the lowest page number in the result set.
   */
  public int getMinPage() {
    return this.minPage;
  }

  /**
   * Returns the maximum page number in the result set.
   *
   * @return the highest page number in the result set.
   */
  public int getMaxPage() {
    return this.maxPage;
  }

  /**
   * Retrieves the parsed OCR information of the page at index {@code pageNumber} of the document.
   * The page number must be a value between {@link DocumentOcrResultSet#getMinPage()} and {@link
   * DocumentOcrResultSet#getMaxPage()}.
   *
   * This returns a TextAnnotation object which is Google Cloud Vision's representation of a page
   * of a document. For more information on reading this object, see:
   * https://cloud.google.com/vision/docs/reference/rpc/google.cloud.vision.v1#google.cloud.vision.v1.TextAnnotation
   *
   * @param pageNumber the page number of the document
   * @return the {@link TextAnnotation} representing the page of the document
   * @throws InvalidProtocolBufferException if the OCR information for the page failed to be parsed
   */
  public TextAnnotation getPage(int pageNumber) throws InvalidProtocolBufferException {
    if (pageNumber < this.minPage || pageNumber > this.maxPage) {
      throw new IndexOutOfBoundsException("Page number out of bounds: " + pageNumber);
    }

    OcrPageRange pageRange = ocrPageRanges.floorEntry(pageNumber).getValue();
    return pageRange.getPage(pageNumber);
  }

  /**
   * Returns an {@link Iterator} over all the OCR pages of the document.
   *
   * @return iterator of {@link TextAnnotation} describing OCR content of each page in the document.
   */
  public Iterator getAllPages() {
    return new Iterator() {

      private final Iterator pageRangeIterator = ocrPageRanges.values().iterator();

      private int offset = 0;

      private List currentPageRange = Collections.emptyList();

      @Override
      public boolean hasNext() {
        return pageRangeIterator.hasNext() || offset < currentPageRange.size();
      }

      @Override
      public TextAnnotation next() {
        if (!hasNext()) {
          throw new NoSuchElementException("No more pages left in DocumentOcrResultSet.");
        }

        if (offset >= currentPageRange.size()) {
          OcrPageRange pageRange = pageRangeIterator.next();
          offset = 0;

          try {
            currentPageRange = pageRange.getPages();
          } catch (InvalidProtocolBufferException e) {
            throw new RuntimeException(
                "Failed to parse OCR output from JSON output file " + pageRange.getBlob().getName(),
                e);
          }
        }

        TextAnnotation result = currentPageRange.get(offset);
        offset++;
        return result;
      }
    };
  }
}