// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.config.model.provision;

import com.yahoo.config.model.api.HostProvisioner;
import com.yahoo.config.provision.*;
import com.yahoo.vespa.model.container.Container;

import java.io.Reader;
import java.util.List;
import java.util.Optional;

/**
 * A host provisioner based on a hosts.xml file.
 * No state in this provisioner, i.e it does not know anything about the active
 * application if one exists. Pre-condition: A valid hosts file.
 *
 * @author hmusum
 */
public class HostsXmlProvisioner implements HostProvisioner {

    private final Hosts hosts;
    public static final String IMPLICIT_ADMIN_HOSTALIAS = "INTERNAL_VESPA_IMPLICIT_ADMIN";

    public HostsXmlProvisioner(Reader hosts) {
        this.hosts = Hosts.readFrom(hosts);
    }

    @Override
    public HostSpec allocateHost(String alias) {
        // Some special rules to allow no admin elements as well as container element without nodes.
        if (alias.equals(IMPLICIT_ADMIN_HOSTALIAS)) {
            if (hosts.asCollection().size() > 1) {
                throw new IllegalArgumentException("More than 1 host specified (" + hosts.asCollection().size() + ") and <admin> not specified");
            } else {
                return host2HostSpec(getFirstHost());
            }
        } else if (alias.equals(Container.SINGLENODE_CONTAINER_SERVICESPEC)) {
            return host2HostSpec(getFirstHost());
        }
        for (Host host : hosts.asCollection()) {
            if (host.aliases().contains(alias)) {
                return new HostSpec(host.hostname(), Optional.empty());
            }
        }
        throw new IllegalArgumentException("Unable to find host for alias '" + alias + "'");
    }

    /** Called when provisioning nodes using &lt;nodes count="..." */
    @Override
    public List<HostSpec> prepare(ClusterSpec cluster, Capacity quantity, ProvisionLogger logger) {
        throw new UnsupportedOperationException("Using <nodes count=\"...\"> is not supported when there is a " +
                                                "hosts.xml file. Remove hosts.xml to make this deployable on " +
                                                "Vespa Cloud and single-node self-hosted instances.");
    }

    private HostSpec host2HostSpec(Host host) {
        return new HostSpec(host.hostname(), Optional.empty());
    }

    private Host getFirstHost() {
        return hosts.asCollection().iterator().next();
    }

}