/* ###
 * IP: GHIDRA
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package ghidra.app.plugin.assembler.sleigh.expr;

import java.util.Map;
import java.util.Set;

import ghidra.app.plugin.assembler.sleigh.sem.*;
import ghidra.app.plugin.processors.sleigh.expression.LeftShiftExpression;
import ghidra.util.Msg;

/**
 * Solves expressions of the form {@code A << B}
 */
public class LeftShiftExpressionSolver extends AbstractBinaryExpressionSolver<LeftShiftExpression> {

	public LeftShiftExpressionSolver() {
		super(LeftShiftExpression.class);
	}

	@Override
	public MaskedLong compute(MaskedLong lval, MaskedLong rval) {
		return lval.shiftLeft(rval);
	}

	@Override
	public MaskedLong computeLeft(MaskedLong rval, MaskedLong goal) throws SolverException {
		return goal.invShiftLeft(rval);
	}

	@Override
	public MaskedLong computeRight(MaskedLong lval, MaskedLong goal) throws SolverException {
		long acc = 0;
		long bit = 1;
		for (int i = 0; i < 64; i++) {
			if (lval.shiftLeft(i).agrees(goal)) {
				acc |= bit;
			}
			bit <<= 1;
		}
		if (Long.bitCount(acc) == 1) {
			return MaskedLong.fromLong(Long.numberOfTrailingZeros(acc));
		}
		throw new SolverException(
			"Cannot solve for the left shift amount: " + goal + " = " + lval + " << L");
	}

	@Override
	protected AssemblyResolution solveTwoSided(AbstractAssemblyResolutionFactory<?, ?> factory,
			LeftShiftExpression exp, MaskedLong goal, Map<String, Long> vals,
			AssemblyResolvedPatterns cur, Set<SolverHint> hints, String description)
			throws NeedsBackfillException, SolverException {
		// Do not guess the same parameter recursively
		if (hints.contains(DefaultSolverHint.GUESSING_LEFT_SHIFT_AMOUNT)) {
			// NOTE: Nested left shifts ought to be written as a left shift by a sum
			return super.solveTwoSided(factory, exp, goal, vals, cur, hints, description);
		}
		// Count the number of zeros to the right, and consider this the maximum shift value
		// Any higher shift amount would produce too many zeros to the right
		int maxShift = Long.numberOfTrailingZeros(goal.val);
		// Without making assumptions about the maximum value of the left side, we cannot make
		// use of the leading zero count, at least AFAIK. Maybe to better restrict the max???
		Set<SolverHint> hintsWithLShift =
			SolverHint.with(hints, DefaultSolverHint.GUESSING_LEFT_SHIFT_AMOUNT);
		if (maxShift == 64) {
			// If the goal is 0s, then any shift will do, so long as the shifted value is 0
			try {
				// NB. goal is already 0s, so just use it as subgoal for lhs of shift
				AssemblyResolution lres = solver.solve(factory, exp.getLeft(), goal, vals, cur,
					hintsWithLShift, description);
				if (lres.isError()) {
					throw new SolverException("Solving left:=0 failed");
				}
				// If this works, then the rhs can have any value, so nothing to solve for
				return lres;
			}
			catch (SolverException | UnsupportedOperationException e) {
				Msg.trace(this, "Trying left:=0 in shift resulted in " + e);
				// Fall through to the guessing method
			}
		}
		for (int shift = maxShift; shift >= 0; shift--) {
			try {
				MaskedLong reqr = MaskedLong.fromLong(shift);
				MaskedLong reql = computeLeft(reqr, goal);

				AssemblyResolution lres = solver.solve(factory, exp.getLeft(), reql, vals, cur,
					hintsWithLShift, description);
				if (lres.isError()) {
					throw new SolverException("Solving left failed");
				}
				AssemblyResolution rres =
					solver.solve(factory, exp.getRight(), reqr, vals, cur, hints, description);
				if (rres.isError()) {
					throw new SolverException("Solving right failed");
				}
				AssemblyResolvedPatterns lsol = (AssemblyResolvedPatterns) lres;
				AssemblyResolvedPatterns rsol = (AssemblyResolvedPatterns) rres;
				AssemblyResolvedPatterns sol = lsol.combine(rsol);
				if (sol == null) {
					throw new SolverException(
						"Left and right solutions conflict for shift=" + shift);
				}
				return sol;
			}
			catch (SolverException | UnsupportedOperationException e) {
				Msg.trace(this, "Shift of " + shift + " resulted in " + e);
				// try the next
			}
		}
		return super.solveTwoSided(factory, exp, goal, vals, cur, hints, description);
	}
}
