oglimmer/lunchy

package de.oglimmer.lunchy.web.servlet;

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.concurrent.ExecutionException;

import javax.servlet.jsp.JspContext;
import javax.servlet.jsp.PageContext;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.SneakyThrows;
import lombok.extern.slf4j.Slf4j;

import org.apache.commons.lang3.RandomStringUtils;

import com.google.common.base.Charsets;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.hash.Hashing;
import com.google.common.io.Files;

import de.oglimmer.lunchy.services.LunchyVersion;

@Slf4j
@Data
@AllArgsConstructor
class ReloadHash {

    private static final String PARAMETER_NAME = "cacheBuster";

    private static LoadingCache<ReloadHash, String> hashCache = CacheBuilder.newBuilder().build(new CacheLoader<ReloadHash, String>() {
        public String load(ReloadHash key) {
            return calcHash(key);
        }
    });

    private String src;
    private JspContext jspContext;

    public String getReloadHashParameter() {
        return getConcatChar() + PARAMETER_NAME + "=" + getHashValue();
    }

    private String getHashValue() {
        try {
            return LunchyVersion.INSTANCE.isRunsOnDev() ? RandomStringUtils.randomAlphanumeric(8) : hashCache.get(this);
        } catch (ExecutionException e) {
            log.warn("Failed to get cached value for ReloadHash");
            return calcHash(this);
        }
    }

    private char getConcatChar() {
        return src.contains("?") ? '&' : '?';
    }

    @SneakyThrows(value = IOException.class)
    private static String calcHash(ReloadHash data) {
        PageContext pageContext = (PageContext) data.getJspContext();
        String fullQualFileName = pageContext.getRequest().getServletContext().getRealPath(data.getSrc());
        String content = Files.toString(new File(fullQualFileName), Charsets.UTF_8);
        return Hashing.murmur3_32().hashString(content, Charset.defaultCharset()).toString();
    }
}