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package org.apache.openjpa.example.gallery.constraint;

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

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;

import org.apache.openjpa.example.gallery.model.Image;
import org.apache.openjpa.example.gallery.model.ImageType;

/**
 * Simple check that an Image is consistent in type, name, and format.
 */
public class ImageValidator implements ConstraintValidator<ImageConstraint, Image> {
    private List<ImageType> allowedTypes = null;
    /**
     * Configure the constraint validator based on the image
     * types it should support.
     * @param constraint the constraint definition
     */
    public void initialize(ImageConstraint constraint) {
        allowedTypes = Arrays.asList(constraint.value());
    }

    /**
     * Validate a specified value.
     */
    public boolean isValid(Image value, ConstraintValidatorContext context) {
        if (value == null) {
            return true;
        }

        // All these fields will be pre-validated with @NotNull constraints
        // so they are safe to use without null checks.
        byte[] data = value.getData();
        String fileName = value.getFileName();
        ImageType type = value.getType();

        // Verify the GIF type is correct5correct, has the correct extension and
        // the data header is either GIF87 or GIF89
        if (allowedTypes.contains(ImageType.GIF) &&
            type == ImageType.GIF &&
            fileName.endsWith(".gif")) {
            if (data != null && data.length >= 6) {
                String gifHeader = new String(data, 0, 6);
                if (gifHeader.equalsIgnoreCase("GIF87a") ||
                     gifHeader.equalsIgnoreCase("GIF89a")) {
                    return true;
                }
            }
        }
        // Verify the JPEG type is correct, has the correct extension and
        // the data begins with SOI & ends with EOI markers
        if (allowedTypes.contains(ImageType.JPEG) &&
                value.getType() == ImageType.JPEG &&
                (fileName.endsWith(".jpg") ||
                 fileName.endsWith(".jpeg"))) {
            if (data.length >= 4 &&
                    data[0] == 0xff && data[1] == 0xd8 &&
                    data[data.length - 2] == 0xff &&
                    data[data.length - 1] == 0xd9) {
                return true;
            }
        }
        // Unknown file format
        return false;
    }
}