package io;

import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.StringWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.apache.commons.io.Charsets;
import org.apache.commons.io.IOUtils;

/**
 * Performs an API Request.
 *
 * @author Peter Wu
 */
public abstract class AbstractRequester implements Requester {

    private static final String API_URL = "https://api.twitter.com/";

    @Override
    public Response getJSON(String resource)
            throws IOException, RateLimitException {
        HttpURLConnection conn = open(buildUrl(resource));
        try {
            preconnect(conn);
            JsonElement resp = getResponseAsJson(conn);

            if (resp.isJsonObject() && resp.getAsJsonObject().has("errors")) {
                /* print response to stderr for debugging */
                String errors = resp.getAsJsonObject().get("errors").toString();
                getLogger().log(Level.INFO, "Request failed: {0}", errors);
            }
            

            // TODO: what if there is an internal server error? Technically we
            // should always treat that as "don't know what the server thinks".
            if (conn.getResponseCode() != 200) {
                if (conn.getResponseCode() == 429) {
                    //TODO: wait for real time and not 15 minutes.
                    throw new RateLimitException(Integer.parseInt(conn.getHeaderField("X-Rate-Limit-Reset")));
                }
                // TODO: print more helpful details
                throw new IOException("Unexpected response code");
            }
            
            int rateLimit = Integer.parseInt(conn.getHeaderField("X-Rate-Limit-Limit"));
            int rateLimitRemaining = Integer.parseInt(conn.getHeaderField("X-Rate-Limit-Remaining"));
            int rateLimitReset = Integer.parseInt(conn.getHeaderField("X-Rate-Limit-Reset"));

            return new Response(resp, rateLimit, rateLimitRemaining, rateLimitReset);
        } finally {
            conn.disconnect();
        }
    }

    protected final URL buildUrl(String resource) throws IOException {
        String spec = API_URL;
        String[] split = resource.split("\\?", 2);
        boolean isPreV1;
        isPreV1 = resource.startsWith("oauth/") || resource.startsWith("oauth2/");
        if (!isPreV1 && !resource.startsWith("1")) {
            // manual inspection shows that at least oauth/ and oauth2/ do not
            // have a version prefixed. Do not add version if already given
            // (e.g. "1/account/rate_limit_status").
            spec += "1.1/";
        }
        // path part
        spec += split[0];
        if (!isPreV1) {
            // not sure about the history, but oauth{,2}/ don't have this.
            spec += ".json";
        }

        // append parameters after path
        if (split.length >= 2) {
            spec += "?" + split[1];
        }

        return new URL(spec);
    }

    /**
     * Opens a connection to the URL.
     *
     * @param url The URL to open a connection to.
     * @return a connection that can be used for sending requests.
     * @throws java.io.IOException on failure to open a connection.
     */
    protected final HttpURLConnection open(URL url) throws IOException {
        getLogger().log(Level.FINE, "Opening: {0}", url);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        // set default param: fail if no response within 5 seconds
        conn.setReadTimeout(5000);
        return conn;
    }

    /**
     * Reads the response body from a connection (in JSON format).
     *
     * @param conn An open connection to which a request was already made.
     * @return A JSON object as parsed from the response.
     * @throws java.io.IOException if the response cannot be retrieved or if the
     * response does not contain well-formed JSON.
     */
    protected final JsonElement getResponseAsJson(HttpURLConnection conn)
            throws IOException {
        StringWriter writer = new StringWriter();
        InputStream is;
        try {
            is = conn.getInputStream();
        } catch (FileNotFoundException ex) {
            /* 404 (FileNotFoundException) */
            is = conn.getErrorStream();
        }
        // this could happen if the URL was severly malformed
        if (is == null) {
            throw new IOException("Failed to fetch response");
        }
        IOUtils.copy(is, writer, Charsets.UTF_8);

        JsonParser parser = new JsonParser();
        return parser.parse(writer.toString());
    }

    /**
     * Prepare the request before it gets send.
     *
     * @param conn A connection for the request.
     * @throws java.io.IOException on failing to prepare the request.
     */
    protected abstract void preconnect(URLConnection conn)
            throws IOException;

    private Logger getLogger() {
        return Logger.getLogger(getClass().getName());
    }
}