package com.limegroup.gnutella.malware;

import java.io.File;
import java.util.HashSet;
import java.util.Locale;
import java.util.Set;

import org.limewire.core.settings.FilterSettings;
import org.limewire.inject.LazySingleton;
import org.limewire.util.FileUtils;

import eu.medsea.mimeutil.MimeException;
import eu.medsea.mimeutil.MimeUtil;

/**
 * Compares the mime type(s) of a file to its extension to ensure that, if
 * the mime type indicates a dangerous file type, the extension indicates
 * the same file type. See FileExtensionEncoder for the defined types. 
 */
@LazySingleton
class FileExtensionChecker implements DangerousFileChecker {

    private final DangerousFileType[] fileTypes;

    FileExtensionChecker() {
        DangerousFileType[] ft;
        try {
            String setting = FilterSettings.DANGEROUS_FILE_TYPES.get();
            ft = FileExtensionEncoder.decodeSetting(setting);
        } catch(IllegalArgumentException e) {
            ft = new DangerousFileType[0];
        }
        fileTypes = ft;
    }

    /**
     * Returns the number of dangerous file types the checker knows about.
     * Package access for testing.
     */
    protected int getNumKnownTypes() {
        return fileTypes.length;
    }

    /**
     * Returns true if the file's mime type indicates a dangerous type
     * but the extension does not.
     */
    @Override
    public boolean isDangerous(File file) {
        Set<String> types = new HashSet<String>();
        try {
            // The returned objects are MimeTypes - get their String values
            for(Object o : MimeUtil.getMimeTypes(file)) {
                types.add(o.toString());
            }
        } catch(MimeException e) {
            return false;
        }
        // Get the extension (empty if there's no extension)
        String ext = FileUtils.getFileExtension(file).toLowerCase(Locale.US);
        // Check each dangerous file type against the file's mime type(s)
        for(DangerousFileType type : fileTypes) {
            if(types.contains(type.mimeType)) {
                boolean extensionMatchesType = false;
                for(String allowed : type.extensions) {
                    if(ext.equals(allowed)) {
                        extensionMatchesType = true;
                        break;
                    }
                }
                return !extensionMatchesType;
            }
        }
        return false;
    }
}