XPlor/libs/dsl/reverseeval.cpp

#include "reverseeval.h"

InverseChain ReverseEvaluator::analyzeExpression(const Expr& expr, const QString& targetField) {
    Q_UNUSED(targetField);
    InverseChain chain;
    chain.canInvert = analyzeRecursive(expr, chain);

    if (!chain.canInvert && chain.reason.isEmpty()) {
        chain.reason = "Expression structure not supported for inversion";
    }

    return chain;
}

bool ReverseEvaluator::analyzeRecursive(const Expr& expr, InverseChain& chain) {
    // Case 1: Simple variable reference - this is the source field
    if (isVariable(expr)) {
        chain.sourceField = getVariableName(expr);
        return true;
    }

    // Case 2: Literal value - not invertible (no source to modify)
    if (isConstant(expr)) {
        chain.reason = "Expression is a constant with no source field";
        return false;
    }

    // Case 3: Unary operations
    if (std::holds_alternative<Expr::Unary>(expr.node)) {
        const auto& unary = std::get<Expr::Unary>(expr.node);

        if (unary.op == "-") {
            // -x → apply negate operation
            if (!analyzeRecursive(*unary.rhs, chain)) {
                return false;
            }
            chain.operations.append({InvertOp::Negate, 0});
            return true;
        }
        else if (unary.op == "~") {
            // ~x → bitwise not is self-inverse, but not in InvertOp
            chain.reason = "Bitwise NOT inversion not implemented";
            return false;
        }
        else if (unary.op == "!") {
            // !x → not invertible (boolean conversion loses information)
            chain.reason = "Logical NOT is not invertible (boolean conversion)";
            return false;
        }
    }

    // Case 4: Binary operations
    if (std::holds_alternative<Expr::Binary>(expr.node)) {
        const auto& binary = std::get<Expr::Binary>(expr.node);

        bool leftIsVar = !isConstant(*binary.lhs);
        bool rightIsVar = !isConstant(*binary.rhs);

        // If both sides are non-constant, we can't invert (multiple sources)
        if (leftIsVar && rightIsVar) {
            chain.reason = "Expression has multiple variable sources";
            return false;
        }

        // If both sides are constant, nothing to invert
        if (!leftIsVar && !rightIsVar) {
            chain.reason = "Expression has no variable sources";
            return false;
        }

        // Get the constant value
        qint64 constVal;
        const Expr* varExpr;
        bool constOnRight;

        if (leftIsVar) {
            constVal = getConstantValue(*binary.rhs);
            varExpr = binary.lhs.get();
            constOnRight = true;
        } else {
            constVal = getConstantValue(*binary.lhs);
            varExpr = binary.rhs.get();
            constOnRight = false;
        }

        // First, recurse into the variable side
        if (!analyzeRecursive(*varExpr, chain)) {
            return false;
        }

        // Now add the inverse operation based on the binary operator
        const QString& op = binary.op;

        if (op == "+") {
            // x = y + c → y = x - c
            // x = c + y → y = x - c (same inverse)
            chain.operations.append({InvertOp::Sub, constVal});
            return true;
        }
        else if (op == "-") {
            if (constOnRight) {
                // x = y - c → y = x + c
                chain.operations.append({InvertOp::Add, constVal});
            } else {
                // x = c - y → y = c - x
                chain.operations.append({InvertOp::SubFrom, constVal});
            }
            return true;
        }
        else if (op == "*") {
            // x = y * c → y = x / c
            if (constVal == 0) {
                chain.reason = "Cannot invert multiplication by zero";
                return false;
            }
            chain.operations.append({InvertOp::Div, constVal});
            return true;
        }
        else if (op == "/") {
            if (constOnRight) {
                // x = y / c → y = x * c
                chain.operations.append({InvertOp::Mul, constVal});
            } else {
                // x = c / y → y = c / x
                chain.reason = "Division with constant on left is not supported";
                return false;
            }
            return true;
        }
        else if (op == "%") {
            chain.reason = "Modulo operation is not invertible (infinite solutions)";
            return false;
        }
        else if (op == "<<") {
            if (constOnRight) {
                // x = y << c → y = x >> c
                chain.operations.append({InvertOp::Shr, constVal});
            } else {
                chain.reason = "Left shift with constant on left is not supported";
                return false;
            }
            return true;
        }
        else if (op == ">>") {
            if (constOnRight) {
                // x = y >> c → y = x << c
                chain.operations.append({InvertOp::Shl, constVal});
            } else {
                chain.reason = "Right shift with constant on left is not supported";
                return false;
            }
            return true;
        }
        else if (op == "&") {
            chain.reason = "Bitwise AND is not invertible (bits masked out are lost)";
            return false;
        }
        else if (op == "|") {
            chain.reason = "Bitwise OR is not invertible (cannot determine original bits)";
            return false;
        }
        else if (op == "^") {
            // x = y ^ c → y = x ^ c (XOR is its own inverse!)
            chain.operations.append({InvertOp::BitXor, constVal});
            return true;
        }
        else if (op == "==" || op == "!=" || op == "<" || op == "<=" ||
                 op == ">" || op == ">=" || op == "&&" || op == "||") {
            chain.reason = "Comparison/logical operations are not invertible";
            return false;
        }
        else {
            chain.reason = QString("Unknown binary operator: %1").arg(op);
            return false;
        }
    }

    // Case 5: Function calls - generally not invertible
    if (std::holds_alternative<Expr::Call>(expr.node)) {
        chain.reason = "Function calls are not invertible";
        return false;
    }

    // Case 6: Member access (x.field)
    if (std::holds_alternative<Expr::Member>(expr.node)) {
        chain.reason = "Member access expressions are not invertible";
        return false;
    }

    // Case 7: Pipe operations
    if (std::holds_alternative<Expr::Pipe>(expr.node)) {
        chain.reason = "Pipe expressions are not invertible";
        return false;
    }

    chain.reason = "Unknown expression type";
    return false;
}

qint64 ReverseEvaluator::computeInverse(const InverseChain& chain, qint64 editedValue) const {
    if (!chain.canInvert) {
        return editedValue; // Can't invert, return as-is
    }

    qint64 result = editedValue;

    // Apply operations in order (they were added in the order they need to be applied)
    for (const auto& op_pair : chain.operations) {
        result = applyInverseOp(result, op_pair.first, op_pair.second);
    }

    return result;
}

QVariant ReverseEvaluator::computeInverse(const InverseChain& chain, const QVariant& editedValue) const {
    return QVariant::fromValue(computeInverse(chain, editedValue.toLongLong()));
}

qint64 ReverseEvaluator::applyInverseOp(qint64 value, InvertOp op, qint64 operand) const {
    switch (op) {
        case InvertOp::Identity:
            return value;

        case InvertOp::Add:
            return value + operand;

        case InvertOp::Sub:
            return value - operand;

        case InvertOp::SubFrom:
            // For x = c - y, inverse is y = c - x
            return operand - value;

        case InvertOp::Mul:
            return value * operand;

        case InvertOp::Div:
            if (operand == 0) return value; // Avoid division by zero
            return value / operand;

        case InvertOp::Shl:
            return value << operand;

        case InvertOp::Shr:
            return value >> operand;

        case InvertOp::Negate:
            return -value;

        case InvertOp::BitAnd:
        case InvertOp::BitOr:
        case InvertOp::Modulo:
            // These are non-invertible, should never be called
            return value;

        case InvertOp::BitXor:
            // XOR is self-inverse
            return value ^ operand;
    }

    return value;
}

bool ReverseEvaluator::isInvertible(const Expr& expr) const {
    InverseChain chain;
    return const_cast<ReverseEvaluator*>(this)->analyzeRecursive(expr, chain);
}

QString ReverseEvaluator::whyNotInvertible(const Expr& expr) const {
    InverseChain chain;
    if (const_cast<ReverseEvaluator*>(this)->analyzeRecursive(expr, chain)) {
        return QString(); // It is invertible
    }
    return chain.reason;
}

bool ReverseEvaluator::isConstant(const Expr& expr) const {
    return std::holds_alternative<Expr::Int>(expr.node) ||
           std::holds_alternative<Expr::String>(expr.node);
}

qint64 ReverseEvaluator::getConstantValue(const Expr& expr) const {
    if (std::holds_alternative<Expr::Int>(expr.node)) {
        return std::get<Expr::Int>(expr.node).v;
    }
    return 0;
}

bool ReverseEvaluator::isVariable(const Expr& expr) const {
    return std::holds_alternative<Expr::Var>(expr.node);
}

QString ReverseEvaluator::getVariableName(const Expr& expr) const {
    if (std::holds_alternative<Expr::Var>(expr.node)) {
        return std::get<Expr::Var>(expr.node).name;
    }
    return QString();
}