/*
 * Copyright (c) 1997, 2022, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */

package sun.security.x509;

import java.io.*;
import java.util.*;

import sun.security.util.*;

/**
 * Represent the GeneralSubtrees ASN.1 object.
 * <p>
 * The ASN.1 for this is
 * <pre>
 * GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree
 * </pre>
 *
 *
 * @author Amit Kapoor
 * @author Hemma Prafullchandra
 * @author Andreas Sterbenz
 */
public class GeneralSubtrees implements Cloneable, DerEncoder {

    private final List<GeneralSubtree> trees;

    // Private variables
    private static final int NAME_DIFF_TYPE = GeneralNameInterface.NAME_DIFF_TYPE;
    private static final int NAME_MATCH = GeneralNameInterface.NAME_MATCH;
    private static final int NAME_NARROWS = GeneralNameInterface.NAME_NARROWS;
    private static final int NAME_WIDENS = GeneralNameInterface.NAME_WIDENS;
    private static final int NAME_SAME_TYPE = GeneralNameInterface.NAME_SAME_TYPE;

    /**
     * The default constructor for the class.
     */
    public GeneralSubtrees() {
        trees = new ArrayList<>();
    }

    private GeneralSubtrees(GeneralSubtrees source) {
        trees = new ArrayList<>(source.trees);
    }

    /**
     * Create the object from the passed DER encoded form.
     *
     * @param val the DER encoded form of the same.
     */
    public GeneralSubtrees(DerValue val) throws IOException {
        this();
        if (val.tag != DerValue.tag_Sequence) {
            throw new IOException("Invalid encoding of GeneralSubtrees.");
        }
        while (val.data.available() != 0) {
            DerValue opt = val.data.getDerValue();
            GeneralSubtree tree = new GeneralSubtree(opt);
            add(tree);
        }
    }

    public GeneralSubtree get(int index) {
        return trees.get(index);
    }

    public void remove(int index) {
        trees.remove(index);
    }

    public void add(GeneralSubtree tree) {
        if (tree == null) {
            throw new NullPointerException();
        }
        trees.add(tree);
    }

    public boolean contains(GeneralSubtree tree) {
        if (tree == null) {
            throw new NullPointerException();
        }
        return trees.contains(tree);
    }

    public int size() {
        return trees.size();
    }

    public Iterator<GeneralSubtree> iterator() {
        return trees.iterator();
    }

    public List<GeneralSubtree> trees() {
        return trees;
    }

    public Object clone() {
        return new GeneralSubtrees(this);
    }

    /**
     * Return a printable string of the GeneralSubtree.
     */
    public String toString() {
        return "   GeneralSubtrees:\n" + trees + '\n';
    }

    /**
     * Encode the GeneralSubtrees.
     *
     * @param out the DerOutputStream to encode this object to.
     */
    @Override
    public void encode(DerOutputStream out) {
        DerOutputStream seq = new DerOutputStream();

        for (int i = 0, n = size(); i < n; i++) {
            get(i).encode(seq);
        }
        out.write(DerValue.tag_Sequence, seq);
    }

    /**
     * Compare two general subtrees by comparing the subtrees
     * of each.
     *
     * @param obj GeneralSubtrees to compare to this
     * @return true if match
     */
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof GeneralSubtrees other)) {
            return false;
        }
        return this.trees.equals(other.trees);
    }

    public int hashCode() {
        return trees.hashCode();
    }

    /**
     * Return the GeneralNameInterface form of the GeneralName in one of
     * the GeneralSubtrees.
     *
     * @param ndx index of the GeneralSubtree from which to obtain the name
     */
    private GeneralNameInterface getGeneralNameInterface(int ndx) {
        return getGeneralNameInterface(get(ndx));
    }

    private static GeneralNameInterface getGeneralNameInterface(GeneralSubtree gs) {
        GeneralName gn = gs.getName();
        return gn.getName();
    }

    /**
     * minimize this GeneralSubtrees by removing all redundant entries.
     * Internal method used by intersect and reduce.
     */
    private void minimize() {

        // Algorithm: compare each entry n to all subsequent entries in
        // the list: if any subsequent entry matches or widens entry n,
        // remove entry n. If any subsequent entries narrow entry n, remove
        // the subsequent entries.
        for (int i = 0; i < (size() - 1); i++) {
            GeneralNameInterface current = getGeneralNameInterface(i);
            boolean remove1 = false;

            /* compare current to subsequent elements */
            for (int j = i + 1; j < size(); j++) {
                GeneralNameInterface subsequent = getGeneralNameInterface(j);
                switch (current.constrains(subsequent)) {
                    case GeneralNameInterface.NAME_DIFF_TYPE:
                        /* not comparable; different name types; keep checking */
                        continue;
                    case GeneralNameInterface.NAME_MATCH:
                        /* delete one of the duplicates */
                        remove1 = true;
                        break;
                    case GeneralNameInterface.NAME_NARROWS:
                        /* subsequent narrows current */
                        /* remove narrower name (subsequent) */
                        remove(j);
                        j--; /* continue check with new subsequent */
                        continue;
                    case GeneralNameInterface.NAME_WIDENS:
                        /* subsequent widens current */
                        /* remove narrower name current */
                        remove1 = true;
                        break;
                    case GeneralNameInterface.NAME_SAME_TYPE:
                        /* keep both for now; keep checking */
                        continue;
                }
                break;
            } /* end of this pass of subsequent elements */

            if (remove1) {
                remove(i);
                i--; /* check the new i value */
            }

        }
    }

    /**
     * create a subtree containing an instance of the input
     * name type that widens all other names of that type.
     *
     * @param name GeneralNameInterface name
     * @return GeneralSubtree containing widest name of that type
     * @throws RuntimeException on error (should not occur)
     */
    private GeneralSubtree createWidestSubtree(GeneralNameInterface name) {
        try {
            GeneralName newName;
            switch (name.getType()) {
            case GeneralNameInterface.NAME_ANY:
                // Create new OtherName with same OID as baseName, but
                // empty value
                ObjectIdentifier otherOID = ((OtherName)name).getOID();
                newName = new GeneralName(new OtherName(otherOID, null));
                break;
            case GeneralNameInterface.NAME_RFC822:
                newName = new GeneralName(new RFC822Name(""));
                break;
            case GeneralNameInterface.NAME_DNS:
                newName = new GeneralName(new DNSName(""));
                break;
            case GeneralNameInterface.NAME_X400:
                newName = new GeneralName(new X400Address(null));
                break;
            case GeneralNameInterface.NAME_DIRECTORY:
                newName = new GeneralName(new X500Name(""));
                break;
            case GeneralNameInterface.NAME_EDI:
                newName = new GeneralName(new EDIPartyName(""));
                break;
            case GeneralNameInterface.NAME_URI:
                newName = new GeneralName(new URIName(""));
                break;
            case GeneralNameInterface.NAME_IP:
                newName = new GeneralName(new IPAddressName((byte[])null));
                break;
            case GeneralNameInterface.NAME_OID:
                newName = new GeneralName(new OIDName(""));
                break;
            default:
                throw new IOException
                    ("Unsupported GeneralNameInterface type: " + name.getType());
            }
            return new GeneralSubtree(newName, 0, -1);
        } catch (IOException e) {
            throw new RuntimeException("Unexpected error: " + e, e);
        }
    }

    /**
     * intersect this GeneralSubtrees with other.  This function
     * is used in merging permitted NameConstraints.  The operation
     * is performed as follows:
     * <ul>
     * <li>If a name in other narrows all names of the same type in this,
     *     the result will contain the narrower name and none of the
     *     names it narrows.
     * <li>If a name in other widens all names of the same type in this,
     *     the result will not contain the wider name.
     * <li>If a name in other does not share the same subtree with any name
     *     of the same type in this, then the name is added to the list
     *     of GeneralSubtrees returned.  These names should be added to
     *     the list of names that are specifically excluded.  The reason
     *     is that, if the intersection is empty, then no names of that
     *     type are permitted, and the only way to express this in
     *     NameConstraints is to include the name in excludedNames.
     * <li>If a name in this has no name of the same type in other, then
     *     the result contains the name in this.  No name of a given type
     *     means the name type is completely permitted.
     * <li>If a name in other has no name of the same type in this, then
     *     the result contains the name in other.  This means that
     *     the name is now constrained in some way, whereas before it was
     *     completely permitted.
     * </ul>
     *
     * @param other GeneralSubtrees to be intersected with this
     * @return  GeneralSubtrees to be merged with excluded; these are
     *          empty-valued name types corresponding to entries that were
     *          of the same type but did not share the same subtree between
     *          this and other. Returns null if no such.
     */
    public GeneralSubtrees intersect(GeneralSubtrees other) {

        if (other == null) {
            throw new NullPointerException("other GeneralSubtrees must not be null");
        }

        GeneralSubtrees newThis = new GeneralSubtrees();
        GeneralSubtrees newExcluded = null;

        // Step 1: If this is empty, just add everything in other to this and
        // return no new excluded entries
        if (size() == 0) {
            union(other);
            return null;
        }

        // Step 2: For ease of checking the subtrees, minimize them by
        // constructing versions that contain only the widest instance of
        // each type
        this.minimize();
        other.minimize();

        // Step 3: Check each entry in this to see whether we keep it or
        // remove it, and whether we add anything to newExcluded or newThis.
        // We keep an entry in this unless it is narrowed by all entries in
        // other.  We add an entry to newExcluded if there is at least one
        // entry of the same nameType in other, but this entry does
        // not share the same subtree with any of the entries in other.
        // We add an entry from other to newThis if there is no name of the
        // same type in this.
        for (int i = 0; i < size(); i++) {
            GeneralNameInterface thisEntry = getGeneralNameInterface(i);

            // Step 3a: If the widest name of this type in other narrows
            // thisEntry, remove thisEntry and add widest other to newThis.
            // Simultaneously, check for situation where there is a name of
            // this type in other, but no name in other matches, narrows,
            // or widens thisEntry.
            boolean sameType = false;
            for (int j = 0; j < other.size(); j++) {
                GeneralSubtree otherEntryGS = other.get(j);
                GeneralNameInterface otherEntry =
                    getGeneralNameInterface(otherEntryGS);
                switch (thisEntry.constrains(otherEntry)) {
                    case NAME_NARROWS:
                        remove(i);
                        i--;
                        newThis.add(otherEntryGS);
                        sameType = false;
                        break;
                    case NAME_SAME_TYPE:
                        sameType = true;
                        continue;
                    case NAME_MATCH:
                    case NAME_WIDENS:
                        sameType = false;
                        break;
                    case NAME_DIFF_TYPE:
                    default:
                        continue;
                }
                break;
            }

            // Step 3b: If sameType is still true, we have the situation
            // where there was a name of the same type as thisEntry in
            // other, but no name in other widened, matched, or narrowed
            // thisEntry.
            if (sameType) {

                // Step 3b.1: See if there are any entries in this and other
                // with this type that match, widen, or narrow each other.
                // If not, then we need to add a "widest subtree" of this
                // type to excluded.
                boolean intersection = false;
                for (int j = 0; j < size(); j++) {
                    GeneralNameInterface thisAltEntry = getGeneralNameInterface(j);

                    if (thisAltEntry.getType() == thisEntry.getType()) {
                        for (int k = 0; k < other.size(); k++) {
                            GeneralNameInterface othAltEntry =
                                other.getGeneralNameInterface(k);

                            int constraintType =
                                thisAltEntry.constrains(othAltEntry);
                            if (constraintType == NAME_MATCH ||
                                constraintType == NAME_WIDENS ||
                                constraintType == NAME_NARROWS) {
                                intersection = true;
                                break;
                            }
                        }
                    }
                }
                if (!intersection) {
                    if (newExcluded == null) {
                        newExcluded = new GeneralSubtrees();
                    }
                    GeneralSubtree widestSubtree =
                         createWidestSubtree(thisEntry);
                    if (!newExcluded.contains(widestSubtree)) {
                        newExcluded.add(widestSubtree);
                    }
                }

                // Step 3b.2: Remove thisEntry from this
                remove(i);
                i--;
            }
        }

        // Step 4: Add all entries in newThis to this
        if (newThis.size() > 0) {
            union(newThis);
        }

        // Step 5: Add all entries in other that do not have any entry of the
        // same type in this to this
        for (int i = 0; i < other.size(); i++) {
            GeneralSubtree otherEntryGS = other.get(i);
            GeneralNameInterface otherEntry = getGeneralNameInterface(otherEntryGS);
            boolean diffType = false;
            for (int j = 0; j < size(); j++) {
                GeneralNameInterface thisEntry = getGeneralNameInterface(j);
                switch (thisEntry.constrains(otherEntry)) {
                    case NAME_DIFF_TYPE:
                        diffType = true;
                        // continue to see if we find something later of the
                        // same type
                        continue;
                    case NAME_NARROWS:
                    case NAME_SAME_TYPE:
                    case NAME_MATCH:
                    case NAME_WIDENS:
                        diffType = false; // we found an entry of the same type
                        // break because we know we won't be adding it to
                        // this now
                        break;
                    default:
                        continue;
                }
                break;
            }
            if (diffType) {
                add(otherEntryGS);
            }
        }

        // Step 6: Return the newExcluded GeneralSubtrees
        return newExcluded;
    }

    /**
     * construct union of this GeneralSubtrees with other.
     *
     * @param other GeneralSubtrees to be united with this
     */
    public void union(GeneralSubtrees other) {
        if (other != null) {
            for (int i = 0, n = other.size(); i < n; i++) {
                add(other.get(i));
            }
            // Minimize this
            minimize();
        }
    }

    /**
     * reduce this GeneralSubtrees by contents of another.  This function
     * is used in merging excluded NameConstraints with permitted NameConstraints
     * to obtain a minimal form of permitted NameConstraints.  It is an
     * optimization, and does not affect correctness of the results.
     *
     * @param excluded GeneralSubtrees
     */
    public void reduce(GeneralSubtrees excluded) {
        if (excluded == null) {
            return;
        }
        for (int i = 0, n = excluded.size(); i < n; i++) {
            GeneralNameInterface excludedName = excluded.getGeneralNameInterface(i);
            for (int j = 0; j < size(); j++) {
                GeneralNameInterface permitted = getGeneralNameInterface(j);
                switch (excludedName.constrains(permitted)) {
                case GeneralNameInterface.NAME_DIFF_TYPE:
                    break;
                case GeneralNameInterface.NAME_MATCH:
                    remove(j);
                    j--;
                    break;
                case GeneralNameInterface.NAME_NARROWS:
                    /* permitted narrows excluded */
                    remove(j);
                    j--;
                    break;
                case GeneralNameInterface.NAME_WIDENS:
                    /* permitted widens excluded */
                    break;
                case GeneralNameInterface.NAME_SAME_TYPE:
                    break;
                }
            } /* end of this pass of permitted */
        } /* end of pass of excluded */
    }
}
