UrlBuilder.java

import com.google.common.base.Joiner;

import javax.annotation.Nonnull;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;
import java.util.Map;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Strings.isNullOrEmpty;

public class UrlBuilder
{
    public static URL parse(@Nonnull final String s)
    {
        try
        {
            return new URL(checkNotNull(s));
        }
        catch (final MalformedURLException e)
        {
            throw new RuntimeException(e);
        }
    }

    private static final int DEFAULT_PORT = -1;

    private final StringBuilder sb;

    public UrlBuilder()
    {
        this.sb = new StringBuilder(512);
    }

    @Nonnull
    private URL build()
    {
        try
        {
            return new URL(UrlBuilder.this.sb.toString());
        }
        catch (MalformedURLException e)
        {
            throw new RuntimeException(e);
        }
    }

    @Nonnull
    public Authority scheme(@Nonnull final String scheme)
    {
        this.sb.append(checkNotNull(scheme)).append("://");
        return new Authority() {

            @Nonnull
            @Override
            public URL build()
            {
                return UrlBuilder.this.build();
            }

            @Nonnull
            @Override
            public Builder fragment(@Nonnull final String fragment)
            {
                return new Fragment() {
                    @Nonnull
                    @Override
                    public Builder fragment(@Nonnull String fragment)
                    {
                        if (!isNullOrEmpty(fragment))
                        {
                            UrlBuilder.this.sb.append("#").append(fragment);
                        }
                        return this;
                    }
                    @Nonnull
                    @Override
                    public URL build()
                    {
                        return UrlBuilder.this.build();
                    }
                };
            }

            @Nonnull
            @Override
            public Query path(@Nonnull final List<String> path)
            {
                return this.path(Joiner.on('/').join(path));
            }

            @Nonnull
            @Override
            public Query path(@Nonnull final String path)
            {
                checkArgument(!path.startsWith("//"), "%s is not a valid path, path can not start with //", path);
                if (!isNullOrEmpty(path))
                {
                    UrlBuilder.this.sb.append(path);
                }
                return new Query() {

                    @Nonnull
                    @Override
                    public Fragment query(@Nonnull final Map<String, String> query)
                    {
                        return query(query, "&");
                    }

                    @Nonnull
                    @Override
                    public Fragment query(@Nonnull final Map<String, String> query, @Nonnull final String separator)
                    {
                        final String q = Joiner.on(separator).withKeyValueSeparator("=").join(checkNotNull(query));
                        if (!isNullOrEmpty(q))
                        {
                            UrlBuilder.this.sb.append("?").append(q);
                        }
                        return this;
                    }

                    @Nonnull
                    @Override
                    public Builder fragment(@Nonnull final String fragment)
                    {
                        if (!isNullOrEmpty(fragment))
                        {
                            UrlBuilder.this.sb.append("#").append(fragment);
                        }
                        return this;
                    }

                    @Nonnull
                    @Override
                    public URL build()
                    {
                        return UrlBuilder.this.build();
                    }
                };
            }

            @Nonnull
            @Override
            public Host userInfo(@Nonnull final String userName)
            {
                return this.userInfo(userName, "");
            }

            @Nonnull
            @Override
            public Host userInfo(@Nonnull final String userName, @Nonnull final String password)
            {
                if (!isNullOrEmpty(userName))
                {
                    UrlBuilder.this.sb.append(userName);
                    if (!isNullOrEmpty(password))
                    {
                        UrlBuilder.this.sb.append(":").append(password);
                    }
                    UrlBuilder.this.sb.append("@");
                }
                return this;
            }

            @Nonnull
            public Path host(@Nonnull final String hostName)
            {
                return host(hostName, DEFAULT_PORT);
            }

            @Nonnull
            public Path host(@Nonnull final String hostName, final int port)
            {
                if (!isNullOrEmpty(hostName))
                {
                    UrlBuilder.this.sb.append(hostName);
                    if (port > DEFAULT_PORT)
                    {
                        checkArgument(port >= 1 && port <= 65535, "%s is out of bounds, port must be between 1 - 65535", port);
                        UrlBuilder.this.sb.append(":").append(port);
                    }
                }
                return new Path() {

                    @Nonnull
                    @Override
                    public Query path(@Nonnull final List<String> path)
                    {
                        return this.path(Joiner.on('/').join(path));
                    }

                    @Nonnull
                    @Override
                    public Query path(@Nonnull final String path)
                    {
                        checkArgument(!path.startsWith("//"), "%s is not a valid path, path can not start with //", path);
                        if (!isNullOrEmpty(path))
                        {
                            UrlBuilder.this.sb.append(path);
                        }
                        return new Query() {

                            @Nonnull
                            @Override
                            public Fragment query(@Nonnull final Map<String, String> query)
                            {
                                return query(query, "&");
                            }

                            @Nonnull
                            @Override
                            public Fragment query(@Nonnull final Map<String, String> query, @Nonnull final String separator)
                            {
                                final String q = Joiner.on(separator).withKeyValueSeparator("=").join(checkNotNull(query));
                                if (!isNullOrEmpty(q))
                                {
                                    UrlBuilder.this.sb.append("?").append(q);
                                }
                                return this;
                            }

                            @Nonnull
                            @Override
                            public Builder fragment(@Nonnull final String fragment)
                            {
                                if (!isNullOrEmpty(fragment))
                                {
                                    UrlBuilder.this.sb.append("#").append(fragment);
                                }
                                return this;
                            }

                            @Nonnull
                            @Override
                            public URL build()
                            {
                                return UrlBuilder.this.build();
                            }
                        };
                    }

                    @Nonnull
                    @Override
                    public Builder fragment(@Nonnull final String fragment)
                    {
                        if (!isNullOrEmpty(fragment))
                        {
                            UrlBuilder.this.sb.append("#").append(fragment);
                        }
                        return this;
                    }

                    @Nonnull
                    @Override
                    public URL build()
                    {
                        return UrlBuilder.this.build();
                    }
                };
            }
        };
    }

    public interface Scheme
    {
        @Nonnull
        public Authority scheme(@Nonnull final String scheme);
    }

    public interface Authority extends Host
    {
        @Nonnull
        public Host userInfo(@Nonnull final String userName);
        @Nonnull
        public Host userInfo(@Nonnull final String userName, @Nonnull final String password);
    }

    public interface Host extends Path
    {
        @Nonnull
        public Path host(@Nonnull final String hostName);
        @Nonnull
        public Path host(@Nonnull final String hostName, final int port);
    }

    public interface Path extends Fragment
    {
        @Nonnull
        public Query path(@Nonnull final String path);
        @Nonnull
        public Query path(@Nonnull final List<String> path);
    }

    public interface Query extends Fragment
    {
        @Nonnull
        public Fragment query(@Nonnull final Map<String,String> query);
        @Nonnull
        public Fragment query(@Nonnull final Map<String,String> query, @Nonnull final String separator);
    }

    public interface Fragment extends Builder
    {
        @Nonnull
        public Builder fragment(@Nonnull final String fragment);
    }

    public interface Builder
    {
        @Nonnull
        public URL build();
    }
}