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Implementation of the Cloud platform abstraction for general-purpose connectivity on the SAP Cloud Platform (Cloud Foundry).

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/*
 * Copyright (c) 2020 SAP SE or an SAP affiliate company. All rights reserved.
 */

package com.sap.cloud.sdk.cloudplatform.connectivity;

import java.net.URI;

import javax.annotation.Nonnull;

import com.sap.cloud.sdk.cloudplatform.security.exception.TokenRequestFailedException;

import io.vavr.control.Try;

/**
 * Default strategy for replacing the subdomain of the XSUAA URL used to get access tokens for destinations. In this
 * strategy, the tenant specific subdomain (i.e. identity zone) of the XSUAA URL is replaced with the tenant specific
 * subdomain of the service that issued the user's JWT.
 */
public class DefaultSubdomainReplacer implements SubdomainReplacer
{
    /**
     * This function takes the issuer URL from the user's JWT and the XSUAA URL and returns a new XSUAA URL. In this
     * implementation, the XSUAA's tenant specific subdomain is replaced by the tenant specific subdomain of the service
     * that issued the user's JWT.
     *
     * @param issuerUrl
     *            The URL of the service that issued the user's JWT.
     * @param xsuaaUrl
     *            The URL of XSUAA instance that should be used to retrieve access tokens.
     * @return A new XSUAA URL.
     */
    @Override
    @Nonnull
    public URI replaceSubdomain( @Nonnull final String issuerUrl, @Nonnull final URI xsuaaUrl )
    {
        final String issuerSubdomain =
            Try.of(() -> new URI(issuerUrl)).map(this::parseSubdomain).getOrElseThrow(
                ex -> new TokenRequestFailedException("Unable to parse JWT issuer URL", ex));

        final String xsuaaSubdomain = parseSubdomain(xsuaaUrl);

        if( xsuaaSubdomain.equals(issuerSubdomain) ) {
            return xsuaaUrl;
        } else {
            return replace(xsuaaUrl, issuerSubdomain);
        }
    }

    private URI replace( @Nonnull final URI uri, @Nonnull final String subdomain )
        throws TokenRequestFailedException
    {
        return Try
            .of(
                () -> new URI(
                    uri.getScheme(),
                    null,
                    subdomain + uri.getHost().substring(uri.getHost().indexOf(".")),
                    uri.getPort(),
                    uri.getPath(),
                    null,
                    null))
            .getOrElseThrow(TokenRequestFailedException::new);
    }

    private String parseSubdomain( final URI uri )
        throws TokenRequestFailedException
    {
        final String host = uri.getHost();

        if( host == null || !host.contains(".") ) {
            throw new TokenRequestFailedException("Failed to determine subdomain: invalid host in URI '" + uri + "'.");
        }

        return host.split("\\.")[0];
    }
}