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package Torello.HTML;

import Torello.Java.StringParse;
import Torello.Java.StrCmpr;

import Torello.Java.Additional.Ret2;

import java.net.URL;
import java.net.MalformedURLException;

class LinksResolve_KE
{
    static Ret2<URL, MalformedURLException> resolve(String src, final URL sourcePage)
    {
        if (sourcePage == null) throw new NullPointerException(
            "Though you may provide null to the partial-URL to dereference parameter, null " +
            "may not be passed to the Source-Page Parameter.  The purpose of the 'resolve' " +
            "operation is to resolve partial-URLs against a source-page (root) URL. " +
            "Therefore this is not allowed."
        );

        if (src == null) return null;

        src = src.trim();

        if (src.length() == 0) return null;

        String srcLC = src.toLowerCase();

        if (StrCmpr.startsWithXOR
                (srcLC, "tel:", "javascript:", "mailto:", "magnet:", "file:", "ftp:", "#"))

            return new Ret2<URL, MalformedURLException>
                (null, new MalformedURLException(
                    "InnerTag/Attribute begins with: " + src.substring(0, 1 + src.indexOf(":")) +
                    ", so it is not a hyper-link."
                ));


        // Includes the first few characters of the URL - for reporting/convenience. 
        // If this is an "image", the image-type & name will be included

        if (StrCmpr.startsWithXOR(srcLC, "data:", "blob:"))

            return new Ret2<URL, MalformedURLException>(null, new MalformedURLException(
                "InnerTag/Attribute begins with: " +
                ((src.length() > 25) ? src.substring(0, 25) : src) +
                ", not a URL."
            ));


        if (srcLC.startsWith("http://") || srcLC.startsWith("https://"))

            try
                { return new Ret2<URL, MalformedURLException>(new URL(src), null); }

            catch (MalformedURLException e)
                { return new Ret2<URL, MalformedURLException>(null, e); }


        if (src.startsWith("//") && (src.charAt(3) != '/'))

            try
            { 
                return new Ret2<URL, MalformedURLException>
                    (new URL(  sourcePage.getProtocol().toLowerCase() + ":" + src), null);
            }

            catch (MalformedURLException e)
                { return new Ret2<URL, MalformedURLException>(null, e); }


        if (src.startsWith("/"))

            try
            {
                return new Ret2<URL, MalformedURLException>(new URL(
                    sourcePage.getProtocol().toLowerCase() + "://" +
                    sourcePage.getHost().toLowerCase() +
                    src), null
                );
            }

            catch (MalformedURLException e)
                { return new Ret2<URL, MalformedURLException>(null, e); }


        if (src.startsWith("../"))
        {
            String  sourcePageStr   = sourcePage.toString();
            short   nLevels         = 0;

            do
                { nLevels++;  src = src.substring(3); }
            while (src.startsWith("../"));

            String  directory = StringParse.dotDotParentDirectory(sourcePage.toString(), nLevels);

            try
                { return new Ret2<URL, MalformedURLException>(new URL(directory + src), null); }

            catch (MalformedURLException e)
                { return new Ret2<URL, MalformedURLException>(null, e); }

            catch (Exception e)
            { 
                return new Ret2<URL, MalformedURLException>
                    (null,
                    new MalformedURLException(e.getClass().getCanonicalName() +
                    ":" + e.getMessage())
                    );
            }
        }


        String  root =
            sourcePage.getProtocol().toLowerCase() + "://" + 
            sourcePage.getHost().toLowerCase();

        String  path    = sourcePage.getPath().trim();
        int     pos     = StringParse.findLastFrontSlashPos(path);

        if (pos == -1) throw new StringIndexOutOfBoundsException(
            "The URL you have provided: " + sourcePage.toString() +
            " does not have a '/' front-slash character in it's path." +
            "Cannot proceed resolving relative-URL's without this."
        );

        path = path.substring(0, pos + 1);

        try
            { return new Ret2<URL, MalformedURLException>(new URL(root + path + src), null); }

        catch (MalformedURLException e)
            { return new Ret2<URL, MalformedURLException>(null, e); }
    }
}