Copyright (c) 2008, 2012 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
    Connexta, LLC - evaluation cache implementation
/*******************************************************************************
 * Copyright (c) 2008, 2012 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Connexta, LLC - evaluation cache implementation
 *******************************************************************************/
package org.eclipse.osgi.internal.permadmin;

import java.security.Permission;
import java.security.PermissionCollection;
import java.util.Enumeration;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.eclipse.osgi.internal.permadmin.SecurityRow.Decision;
import org.osgi.service.condpermadmin.Condition;

public class SecurityTable extends PermissionCollection {
	private static final long serialVersionUID = -1800193310096318060L;
	static final int GRANTED = 0x0001;
	static final int DENIED = 0x0002;
	static final int ABSTAIN = 0x0004;
	static final int POSTPONED = 0x0008;

	private static final int MUTABLE = 0x0016;

	private final SecurityRow[] rows;
	private final SecurityAdmin securityAdmin;

	private final transient Map<EvaluationCacheKey, Integer> evaluationCache = new ConcurrentHashMap<>(10000);

	public SecurityTable(SecurityAdmin securityAdmin, SecurityRow[] rows) {
		if (rows == null)
			throw new NullPointerException("rows cannot be null!!"); //$NON-NLS-1$
		this.rows = rows;
		this.securityAdmin = securityAdmin;
	}

	boolean isEmpty() {
		return rows.length == 0;
	}

	int evaluate(BundlePermissions bundlePermissions, Permission permission) {
		if (bundlePermissions == null) {
			return ABSTAIN;
		}
		EvaluationCacheKey evaluationCacheKey = new EvaluationCacheKey(bundlePermissions, permission);
		if (isEmpty()) {
			evaluationCache.put(evaluationCacheKey, ABSTAIN);
			return ABSTAIN;
		}

		//can't short-circuit early, so try cache
		Integer result = evaluationCache.get(evaluationCacheKey);
		boolean hasMutable = false;
		if (result != null) {
			hasMutable = (result & MUTABLE) == MUTABLE;
			if (!hasMutable) {
				return result;
			}
		}
		//cache miss or has mutable rows
		boolean postponed = false;
		Decision[] results = new Decision[rows.length];
		int immediateDecisionIdx = -1;
		// evaluate each row
		for (int i = 0; i < rows.length && immediateDecisionIdx == -1; i++) {
			if (result == null) {
				//check all conditions for any that are mutable, this will turn off the cache
				hasMutable |= checkMutable(bundlePermissions, evaluationCacheKey, rows[i]);
			}
			try {
				results[i] = rows[i].evaluate(bundlePermissions, permission);
			} catch (Exception e) {
				// TODO log?
				results[i] = SecurityRow.DECISION_ABSTAIN;
			}
			if ((results[i].decision & ABSTAIN) == ABSTAIN)
				continue; // ignore this row and continue to next row
			if ((results[i].decision & POSTPONED) == POSTPONED) {
				// row is postponed; we can no longer return quickly on a denied decision
				postponed = true;
				continue; // continue to next row
			}
			if (!postponed) {
				// no postpones encountered yet; we can return the decision quickly
				if (!hasMutable) {
					evaluationCache.put(evaluationCacheKey, results[i].decision);
				}
				return results[i].decision; // return GRANTED or DENIED
			}
			// got an immediate answer; but it is after a postponed condition.
			// no need to process the rest of the rows
			immediateDecisionIdx = i;
		}
		Integer immediateDecision = handlePostponedConditions(evaluationCacheKey, hasMutable, postponed, results, immediateDecisionIdx);
		if (immediateDecision != null)
			return immediateDecision;
		int finalDecision = postponed ? POSTPONED : ABSTAIN;
		if (!hasMutable && (finalDecision & POSTPONED) != POSTPONED) {
			evaluationCache.put(evaluationCacheKey, finalDecision);
		}
		return finalDecision;
	}

	private boolean checkMutable(BundlePermissions bundlePermissions, EvaluationCacheKey evaluationCacheKey, SecurityRow row) {
		Condition[] conditions = row.getConditions(bundlePermissions);
		if (conditions != null) {
			for (Condition condition : conditions) {
				if (condition != null && condition.isMutable()) {
					evaluationCache.put(evaluationCacheKey, MUTABLE);
					return true;
				}
			}
		}
		return false;
	}

	private Integer handlePostponedConditions(EvaluationCacheKey evaluationCacheKey, boolean hasMutable, boolean postponed, Decision[] results, int immediateDecisionIdx) {
		if (postponed) {
			int immediateDecision = immediateDecisionIdx < 0 ? DENIED : results[immediateDecisionIdx].decision;
			// iterate over all postponed conditions;
			// if they all provide the same decision as the immediate decision then return the immediate decision
			boolean allSameDecision = true;
			int i = immediateDecisionIdx < 0 ? results.length - 1 : immediateDecisionIdx - 1;
			for (; i >= 0 && allSameDecision; i--) {
				if ((results[i].decision & POSTPONED) == POSTPONED) {
					if ((results[i].decision & immediateDecision) == 0)
						allSameDecision = false;
					else
						results[i] = SecurityRow.DECISION_ABSTAIN; // we can clear postpones with the same decision as the immediate
				}
			}
			if (allSameDecision) {
				if (!hasMutable) {
					evaluationCache.put(evaluationCacheKey, immediateDecision);
				}
				return immediateDecision;
			}

			// we now are forced to postpone; we need to also remember the postponed decisions and
			// the immediate decision if there is one.
			EquinoxSecurityManager equinoxManager = securityAdmin.getSupportedSecurityManager();
			if (equinoxManager == null) {
				// TODO this is really an error condition.
				// This should never happen.  We checked for a supported manager when the row was postponed
				if (!hasMutable) {
					evaluationCache.put(evaluationCacheKey, ABSTAIN);
				}
				return ABSTAIN;
			}
			equinoxManager.addConditionsForDomain(results);
		}
		return null;
	}

	void clearEvaluationCache() {
		evaluationCache.clear();
	}

	SecurityRow getRow(int i) {
		return rows.length <= i || i < 0 ? null : rows[i];
	}

	SecurityRow getRow(String name) {
		for (SecurityRow row : rows) {
			if (name.equals(row.getName())) {
				return row;
			}
		}
		return null;
	}

	SecurityRow[] getRows() {
		return rows;
	}

	String[] getEncodedRows() {
		String[] encoded = new String[rows.length];
		for (int i = 0; i < rows.length; i++)
			encoded[i] = rows[i].getEncoded();
		return encoded;
	}

	@Override
	public void add(Permission permission) {
		throw new SecurityException();
	}

	@Override
	public Enumeration<Permission> elements() {
		return BundlePermissions.EMPTY_ENUMERATION;
	}

	@Override
	public boolean implies(Permission permission) {
		return (evaluate(null, permission) & SecurityTable.GRANTED) != 0;
	}
}