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Spring Framework on Google Cloud Vision Module
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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.AnnotateFileResponse;
import com.google.cloud.vision.v1.AnnotateImageResponse;
import com.google.cloud.vision.v1.TextAnnotation;
import com.google.protobuf.InvalidProtocolBufferException;
import com.google.protobuf.util.JsonFormat;
import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

/** Represents a range of pages of the OCR content of a document. */
final class OcrPageRange {

  private static final Pattern OUTPUT_PAGE_PATTERN =
      Pattern.compile("output-(\\d+)-to-(\\d+)\\.json");

  private final Blob blob;

  private final int startPage;

  private final int endPage;

  private List pages = null;

  OcrPageRange(Blob blob) {
    Matcher matcher = OUTPUT_PAGE_PATTERN.matcher(blob.getName());
    boolean success = matcher.find();

    if (success) {
      this.blob = blob;
      this.startPage = Integer.parseInt(matcher.group(1));
      this.endPage = Integer.parseInt(matcher.group(2));
    } else {
      throw new IllegalArgumentException(
          "Cannot create a DocumentOcrResultSet with blob: "
              + blob.getName()
              + " Blob name does not contain suffix with the form: output-#-to-#.json");
    }
  }

  TextAnnotation getPage(int pageNumber) throws InvalidProtocolBufferException {
    if (pageNumber < startPage || pageNumber > endPage) {
      throw new IndexOutOfBoundsException(
          "Page number not found: "
              + pageNumber
              + ". Could not "
              + "find page in closest JSON output file: "
              + blob.getName());
    }

    int offsetIdx = pageNumber - startPage;
    return getPages().get(offsetIdx);
  }

  List getPages() throws InvalidProtocolBufferException {
    if (pages == null) {
      pages = parseJsonBlob(blob);
    }

    return pages;
  }

  public Blob getBlob() {
    return blob;
  }

  int getStartPage() {
    return startPage;
  }

  int getEndPage() {
    return endPage;
  }

  private static List parseJsonBlob(Blob blob)
      throws InvalidProtocolBufferException {

    AnnotateFileResponse.Builder annotateFileResponseBuilder = AnnotateFileResponse.newBuilder();
    String jsonContent = new String(blob.getContent(), StandardCharsets.UTF_8);
    JsonFormat.parser().ignoringUnknownFields().merge(jsonContent, annotateFileResponseBuilder);

    AnnotateFileResponse annotateFileResponse = annotateFileResponseBuilder.build();

    return annotateFileResponse.getResponsesList().stream()
        .map(AnnotateImageResponse::getFullTextAnnotation)
        .collect(Collectors.toList());
  }
}