package common.network;

import java.io.IOException;
import java.util.Locale;

import okhttp3.Interceptor;
import okhttp3.Request;
import okhttp3.Response;

/**
 * Created by oleynikd on 6/9/16.
 */
public class AcceptLanguageHeaderInterceptor implements Interceptor {
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request originalRequest = chain.request();
        Request requestWithHeaders = originalRequest.newBuilder()
                .header("Accept-Language", localeToBcp47Language(Locale.getDefault()))
                .build();
        return chain.proceed(requestWithHeaders);
    }

    /*
     * From https://github.com/apache/cordova-plugin-globalization/blob/master/src/android/Globalization.java#L140
     * @Description: Returns a well-formed ITEF BCP 47 language tag representing
     * the locale identifier for the client's current locale
     *
     * @Return: String: The BCP 47 language tag for the current locale
     */
    private static String localeToBcp47Language(Locale loc) {
        final char SEP = '-';       // we will use a dash as per BCP 47
        String language = loc.getLanguage();
        String region = loc.getCountry();
        String variant = loc.getVariant();

        // special case for Norwegian Nynorsk since "NY" cannot be a variant as per BCP 47
        // this goes before the string matching since "NY" wont pass the variant checks
        if( language.equals("no") && region.equals("NO") && variant.equals("NY")){
            language = "nn";
            region = "NO";
            variant = "";
        }

        if( language.isEmpty() || !language.matches("\p{Alpha}{2,8}")){
            language = "und";       // Follow the Locale#toLanguageTag() implementation
            // which says to return "und" for Undetermined
        }else if(language.equals("iw")){
            language = "he";        // correct deprecated "Hebrew"
        }else if(language.equals("in")){
            language = "id";        // correct deprecated "Indonesian"
        }else if(language.equals("ji")){
            language = "yi";        // correct deprecated "Yiddish"
        }

        // ensure valid country code, if not well formed, it's omitted
        if (!region.matches("\p{Alpha}{2}|\p{Digit}{3}")) {
            region = "";
        }

        // variant subtags that begin with a letter must be at least 5 characters long
        if (!variant.matches("\p{Alnum}{5,8}|\p{Digit}\p{Alnum}{3}")) {
            variant = "";
        }

        StringBuilder bcp47Tag = new StringBuilder(language);
        if (!region.isEmpty()) {
            bcp47Tag.append(SEP).append(region);
        }
        if (!variant.isEmpty()) {
            bcp47Tag.append(SEP).append(variant);
        }

        return bcp47Tag.toString();
    }
}

private static final OkHttpClient client = new OkHttpClient.Builder()
            .addInterceptor(new AcceptLanguageHeaderInterceptor())
            .build();

Retrofit ret = new Retrofit.Builder()
                .client(new OkHttpClient.Builder()
                .addNetworkInterceptor(new Interceptor() {

                    @Override
                    public Response intercept(Chain chain) throws IOException {
                        Request.Builder builder = chain.request().newBuilder();

                        builder.addHeader("Accept-Language", "Your value");
                        Request request = builder.build();
                        Response response = chain.proceed(request);

                        return response;
                    }
                }).build())
                .build();

Locale.getDefault().getDisplayLanguage();

toLanguageTag
Added in API level 21
String toLanguageTag ()
Returns a well-formed IETF BCP 47 language tag representing this locale.

private class AcceptLanguageInterceptor(val locale: Locale) : Interceptor {

        @Throws(IOException::class)
        override fun intercept(chain: Interceptor.Chain): okhttp3.Response = chain.proceed(chain.request().newBuilder()
                .header("Accept-Language", locale.toLanguageTag())
                .build())
}