package com.btr.proxy.selector.pac;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.Proxy;
import java.net.URISyntaxException;
import java.net.URL;

import com.btr.proxy.util.Logger;
import com.btr.proxy.util.Logger.LogLevel;
import com.btr.proxy.util.MiscUtil;

/*****************************************************************************
 * Script source that will load the content of a PAC file from an webserver.
 * The script content is cached once it was downloaded. 
 *
 * @author Bernd Rosstauscher (proxyvole@rosstauscher.de) Copyright 2009
 ****************************************************************************/

public class UrlPacScriptSource implements PacScriptSource {
	
	private static final int DEFAULT_CONNECT_TIMEOUT = 1 * 1000; // seconds
	private static final int DEFAULT_READ_TIMEOUT = 2 * 1000; // seconds
	public static final String OVERRIDE_CONNECT_TIMEOUT = "com.btr.proxy.url.connectTimeout";
	public static final String OVERRIDE_READ_TIMEOUT = "com.btr.proxy.url.readTimeout";
	
	private final String scriptUrl;
	private String scriptContent;
	private long expireAtMillis;
	
	/*************************************************************************
	 * Constructor
	 * @param url the URL to download the script from.
	 ************************************************************************/
	
	public UrlPacScriptSource(String url) {
		super();
		this.expireAtMillis = 0;
		this.scriptUrl = url;
	}

	/*************************************************************************
	 * getScriptContent
	 * @see com.btr.proxy.selector.pac.PacScriptSource#getScriptContent()
	 ************************************************************************/

	public synchronized String getScriptContent() throws IOException {
		if (this.scriptContent == null || 
				(this.expireAtMillis > 0 
						&& this.expireAtMillis > System.currentTimeMillis())) {
			try {
				if (this.scriptUrl.startsWith("file:/") || this.scriptUrl.indexOf(":/") == -1) {
					this.scriptContent = readPacFileContent(this.scriptUrl);
				} else {
					this.scriptContent = downloadPacContent(this.scriptUrl);
				}
			} catch (IOException e) {
				Logger.log(getClass(), LogLevel.ERROR, "Loading script failed from: {0} with error {1}", this.scriptUrl, e);
				this.scriptContent = "";
				throw e;
			}
		}
		return this.scriptContent;
	}
	
	/*************************************************************************
	 * Reads a PAC script from a local file.
	 * @param scriptUrl
	 * @return the content of the script file.
	 * @throws IOException 
	 * @throws URISyntaxException 
	 ************************************************************************/
	
	private String readPacFileContent(String scriptUrl) throws IOException {
		try {
			File file = null;
			if (scriptUrl.indexOf(":/") == -1) {
				file = new File(scriptUrl);
			} else {
				file = new File(new URL(scriptUrl).toURI());
			}
			BufferedReader r = new BufferedReader(new FileReader(file));
			StringBuilder result = new StringBuilder();
			try {
				String line; 
				while ((line = r.readLine()) != null) {
					result.append(line).append("\n");
				}
			} finally {
				r.close();
			} 
			return result.toString();
		} catch (Exception e) {
			Logger.log(getClass(), LogLevel.ERROR, "File reading error.", e);
			throw new IOException(e.getMessage());
		}
	}

	/*************************************************************************
	 * Downloads the script from a webserver.
	 * @param url the URL to the script file.
	 * @return the script content.
	 * @throws IOException on read error.
	 ************************************************************************/
	
	private String downloadPacContent(String url) throws IOException {
		if (url == null) {
			throw new IOException("Invalid PAC script URL: null");
		}

		setPacProxySelectorEnabled(false);
		
		HttpURLConnection con = null;
		try {
			con = setupHTTPConnection(url);
			if (con.getResponseCode() != 200) {
				throw new IOException("Server returned: "+con.getResponseCode()+" "+con.getResponseMessage());
			}
			// Read expire date.
			this.expireAtMillis = con.getExpiration();

			BufferedReader r = getReader(con);
			String result = readAllContent(r);
			r.close();
			return result;
		} finally {
			setPacProxySelectorEnabled(true);
			if (con != null) {
				con.disconnect();
			}
		}
	}

	/*************************************************************************
	 * Enables/disables the PAC proxy selector while we download to prevent recursion.
	 * See issue: 26 in the change tracker.
	 ************************************************************************/
	
	private void setPacProxySelectorEnabled(boolean enable) {
		PacProxySelector.setEnabled(enable);
	}

	/*************************************************************************
	 * Reads the whole content available into a String.
	 * @param r to read from.
	 * @return the complete PAC file content.
	 * @throws IOException
	 ************************************************************************/
	
	private String readAllContent(BufferedReader r) throws IOException {
		StringBuilder result = new StringBuilder();
		String line; 
		while ((line = r.readLine()) != null) {
			result.append(line).append("\n");
		}
		return result.toString();
	}

	/*************************************************************************
	 * Build a BufferedReader around the open HTTP connection.
	 * @param con to read from
	 * @return the BufferedReader.
	 * @throws UnsupportedEncodingException
	 * @throws IOException
	 ************************************************************************/
	
	private BufferedReader getReader(HttpURLConnection con)
			throws UnsupportedEncodingException, IOException {
		String charsetName = parseCharsetFromHeader(con.getContentType());
		BufferedReader r = new BufferedReader(new InputStreamReader(con.getInputStream(), charsetName));
		return r;
	}

	/*************************************************************************
	 * Configure the connection to download from.
	 * @param url to get the pac file content from
	 * @return a HTTPUrlConnecion to this url.
	 * @throws IOException
	 * @throws MalformedURLException
	 ************************************************************************/
	
	private HttpURLConnection setupHTTPConnection(String url)
			throws IOException, MalformedURLException {
		HttpURLConnection con = (HttpURLConnection) new URL(url).openConnection(Proxy.NO_PROXY);
		con.setConnectTimeout(getTimeOut(OVERRIDE_CONNECT_TIMEOUT, DEFAULT_CONNECT_TIMEOUT));
        con.setReadTimeout(getTimeOut(OVERRIDE_READ_TIMEOUT, DEFAULT_READ_TIMEOUT));
		con.setInstanceFollowRedirects(true);
		con.setRequestProperty("accept", "application/x-ns-proxy-autoconfig, */*;q=0.8");
		return con;
	}
	
	/*************************************************************************
	 * Gets the timeout value from a property or uses the given default value if
	 * the property cannot be parsed.
	 * @param overrideProperty the property to define the timeout value in milliseconds
	 * @param defaultValue the default timeout value in milliseconds.
	 * @return the value to use.
	 ************************************************************************/
	
	protected int getTimeOut(String overrideProperty, int defaultValue) {
		int timeout = defaultValue; 
		String prop = System.getProperty(overrideProperty);
		if (prop != null && prop.trim().length() > 0) {
			try {
				timeout = MiscUtil.parseInt(prop.trim());
			} catch (NumberFormatException e) {
				Logger.log(getClass(), LogLevel.DEBUG, "Invalid override property : {0}={1}", overrideProperty, prop);
				// In this case use the default value.
			}
		}
		return timeout;
	}

	/*************************************************************************
	 * Response Content-Type could be something like this:   
	 *    application/x-ns-proxy-autoconfig; charset=UTF-8
	 * @param contentType header field.
	 * @return the extracted charset if set else a default charset.
	 ************************************************************************/
	
	String parseCharsetFromHeader(String contentType) {
		String result = "ISO-8859-1";
		if (contentType != null) {
			String[] paramList = contentType.split(";");
			for (String param : paramList) {
				if (param.toLowerCase().trim().startsWith("charset") && param.indexOf("=") != -1) {
					result = param.substring(param.indexOf("=")+1).trim();
				}
			}
		}
		return result;
	}

	/***************************************************************************
	 * @see java.lang.Object#toString()
	 **************************************************************************/
	@Override
	public String toString() {
		return this.scriptUrl;
	}

	/*************************************************************************
	 * isScriptValid
	 * @see com.btr.proxy.selector.pac.PacScriptSource#isScriptValid()
	 ************************************************************************/
	
	public boolean isScriptValid() {
		try {
			String script = getScriptContent();
			if (script == null || script.trim().length() == 0) {
				Logger.log(getClass(), LogLevel.DEBUG, "PAC script is empty. Skipping script!");
				return false;
			}
			if (script.indexOf("FindProxyForURL") == -1) {
				Logger.log(getClass(), LogLevel.DEBUG, "PAC script entry point FindProxyForURL not found. Skipping script!");
				return false;
			}
			return true;
		} catch (IOException e) {
			Logger.log(getClass(), LogLevel.DEBUG, "File reading error: {0}", e);
			return false;
		}
	}
	
}