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package java.net;

import java.io.IOException;
import java.util.List;
import sun.security.util.SecurityConstants;

/**
 * Selects the proxy server to use, if any, when connecting to the
 * network resource referenced by a URL. A proxy selector is a
 * concrete sub-class of this class and is registered by invoking the
 * {@link java.net.ProxySelector#setDefault setDefault} method. The
 * currently registered proxy selector can be retrieved by calling
 * {@link java.net.ProxySelector#getDefault getDefault} method.
 *
 * <p> When a proxy selector is registered, for instance, a subclass
 * of URLConnection class should call the {@link #select select}
 * method for each URL request so that the proxy selector can decide
 * if a direct, or proxied connection should be used. The {@link
 * #select select} method returns an iterator over a collection with
 * the preferred connection approach.
 *
 * <p> If a connection cannot be established to a proxy (PROXY or
 * SOCKS) servers then the caller should call the proxy selector's
 * {@link #connectFailed connectFailed} method to notify the proxy
 * selector that the proxy server is unavailable. </p>
 *
 * <P>The default proxy selector does enforce a
 * <a href="doc-files/net-properties.html#Proxies">set of System Properties</a>
 * related to proxy settings.</P>
 *
 * @author Yingxian Wang
 * @author Jean-Christophe Collet
 * @since 1.5
 */
public abstract class ProxySelector {
 /**
 * The system wide proxy selector that selects the proxy server to
 * use, if any, when connecting to a remote object referenced by
 * an URL.
 *
 * @see #setDefault(ProxySelector)
 */
 private static ProxySelector theProxySelector;

 static {
 try {
 Class<?> c = Class.forName("sun.net.spi.DefaultProxySelector");
 if (c != null && ProxySelector.class.isAssignableFrom(c)) {
 @SuppressWarnings("deprecation")
 ProxySelector tmp = (ProxySelector) c.newInstance();
 theProxySelector = tmp;
 }
 } catch (Exception e) {
 theProxySelector = null;
 }
 }

 /**
 * Gets the system-wide proxy selector.
 *
 * @throws SecurityException
 * If a security manager has been installed and it denies
 * {@link NetPermission}{@code ("getProxySelector")}
 * @see #setDefault(ProxySelector)
 * @return the system-wide {@code ProxySelector}
 * @since 1.5
 */
 public static ProxySelector getDefault() {
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 sm.checkPermission(SecurityConstants.GET_PROXYSELECTOR_PERMISSION);
 }
 return theProxySelector;
 }

 /**
 * Sets (or unsets) the system-wide proxy selector.
 *
 * Note: non-standard protocol handlers may ignore this setting.
 *
 * @param ps The HTTP proxy selector, or
 * {@code null} to unset the proxy selector.
 *
 * @throws SecurityException
 * If a security manager has been installed and it denies
 * {@link NetPermission}{@code ("setProxySelector")}
 *
 * @see #getDefault()
 * @since 1.5
 */
 public static void setDefault(ProxySelector ps) {
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 sm.checkPermission(SecurityConstants.SET_PROXYSELECTOR_PERMISSION);
 }
 theProxySelector = ps;
 }

 /**
 * Selects all the applicable proxies based on the protocol to
 * access the resource with and a destination address to access
 * the resource at.
 * The format of the URI is defined as follow:
 * <UL>
 * <LI>http URI for http connections</LI>
 * <LI>https URI for https connections
 * <LI>{@code socket://host:port}<br>
 * for tcp client sockets connections</LI>
 * </UL>
 *
 * @param uri
 * The URI that a connection is required to
 *
 * @return a List of Proxies. Each element in the
 * the List is of type
 * {@link java.net.Proxy Proxy};
 * when no proxy is available, the list will
 * contain one element of type
 * {@link java.net.Proxy Proxy}
 * that represents a direct connection.
 * @throws IllegalArgumentException if the argument is null
 */
 public abstract List<Proxy> select(URI uri);

 /**
 * Called to indicate that a connection could not be established
 * to a proxy/socks server. An implementation of this method can
 * temporarily remove the proxies or reorder the sequence of
 * proxies returned by {@link #select(URI)}, using the address
 * and the IOException caught when trying to connect.
 *
 * @param uri
 * The URI that the proxy at sa failed to serve.
 * @param sa
 * The socket address of the proxy/SOCKS server
 *
 * @param ioe
 * The I/O exception thrown when the connect failed.
 * @throws IllegalArgumentException if either argument is null
 */
 public abstract void connectFailed(URI uri, SocketAddress sa, IOException ioe);

 /**
 * Returns a ProxySelector which uses the given proxy address for all HTTP
 * and HTTPS requests. If proxy is {@code null} then proxying is disabled.
 *
 * @param proxyAddress
 * The address of the proxy
 *
 * @return a ProxySelector
 *
 * @since 9
 */
 public static ProxySelector of(InetSocketAddress proxyAddress) {
 return new StaticProxySelector(proxyAddress);
 }

 static class StaticProxySelector extends ProxySelector {
 private static final List<Proxy> NO_PROXY_LIST = List.of(Proxy.NO_PROXY);
 final List<Proxy> list;

 StaticProxySelector(InetSocketAddress address){
 Proxy p;
 if (address == null) {
 p = Proxy.NO_PROXY;
 } else {
 p = new Proxy(Proxy.Type.HTTP, address);
 }
 list = List.of(p);
 }

 @Override
 public void connectFailed(URI uri, SocketAddress sa, IOException e) {
 /* ignore */
 }

 @Override
 public synchronized List<Proxy> select(URI uri) {
 String scheme = uri.getScheme().toLowerCase();
 if (scheme.equals("http") || scheme.equals("https")) {
 return list;
 } else {
 return NO_PROXY_LIST;
 }
 }
 }
}