pandrs 0.3.0

//! Expression Tree System for JIT Optimization
//!
//! This module provides an expression tree representation for complex operations
//! that enables advanced optimizations like common subexpression elimination,
//! algebraic simplification, and vectorization.

use crate::core::error::{Error, Result};
use crate::optimized::jit::types::{JitNumeric, NumericValue, TypedVector};
use std::collections::{HashMap, HashSet};
use std::fmt;
use std::hash::{Hash, Hasher};
use std::sync::Arc;

/// Expression tree node representing a computation
#[derive(Debug, Clone, PartialEq)]
pub enum ExpressionNode {
    /// Constant value
    Constant(NumericValue),
    /// Variable (input parameter)
    Variable {
        name: String,
        var_type: String,
        index: usize,
    },
    /// Array access
    ArrayAccess {
        array: Box<ExpressionNode>,
        index: Box<ExpressionNode>,
    },
    /// Binary operation
    BinaryOp {
        left: Box<ExpressionNode>,
        right: Box<ExpressionNode>,
        operator: BinaryOperator,
    },
    /// Unary operation
    UnaryOp {
        operand: Box<ExpressionNode>,
        operator: UnaryOperator,
    },
    /// Function call
    FunctionCall {
        function: String,
        arguments: Vec<ExpressionNode>,
    },
    /// Reduction operation (sum, mean, etc.)
    Reduction {
        array: Box<ExpressionNode>,
        operation: ReductionOperation,
        axis: Option<usize>,
    },
    /// Conditional expression
    Conditional {
        condition: Box<ExpressionNode>,
        true_expr: Box<ExpressionNode>,
        false_expr: Box<ExpressionNode>,
    },
}

/// Binary operators
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum BinaryOperator {
    Add,
    Subtract,
    Multiply,
    Divide,
    Modulo,
    Power,
    Equal,
    NotEqual,
    LessThan,
    LessThanOrEqual,
    GreaterThan,
    GreaterThanOrEqual,
    LogicalAnd,
    LogicalOr,
    BitwiseAnd,
    BitwiseOr,
    BitwiseXor,
}

/// Unary operators
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum UnaryOperator {
    Negate,
    LogicalNot,
    BitwiseNot,
    Abs,
    Sqrt,
    Sin,
    Cos,
    Tan,
    Log,
    Exp,
    Floor,
    Ceil,
    Round,
}

/// Reduction operations
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ReductionOperation {
    Sum,
    Product,
    Mean,
    Min,
    Max,
    Count,
    Any,
    All,
    Variance,
    StandardDeviation,
}

impl fmt::Display for BinaryOperator {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            BinaryOperator::Add => write!(f, "+"),
            BinaryOperator::Subtract => write!(f, "-"),
            BinaryOperator::Multiply => write!(f, "*"),
            BinaryOperator::Divide => write!(f, "/"),
            BinaryOperator::Modulo => write!(f, "%"),
            BinaryOperator::Power => write!(f, "**"),
            BinaryOperator::Equal => write!(f, "=="),
            BinaryOperator::NotEqual => write!(f, "!="),
            BinaryOperator::LessThan => write!(f, "<"),
            BinaryOperator::LessThanOrEqual => write!(f, "<="),
            BinaryOperator::GreaterThan => write!(f, ">"),
            BinaryOperator::GreaterThanOrEqual => write!(f, ">="),
            BinaryOperator::LogicalAnd => write!(f, "&&"),
            BinaryOperator::LogicalOr => write!(f, "||"),
            BinaryOperator::BitwiseAnd => write!(f, "&"),
            BinaryOperator::BitwiseOr => write!(f, "|"),
            BinaryOperator::BitwiseXor => write!(f, "^"),
        }
    }
}

impl fmt::Display for UnaryOperator {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            UnaryOperator::Negate => write!(f, "-"),
            UnaryOperator::LogicalNot => write!(f, "!"),
            UnaryOperator::BitwiseNot => write!(f, "~"),
            UnaryOperator::Abs => write!(f, "abs"),
            UnaryOperator::Sqrt => write!(f, "sqrt"),
            UnaryOperator::Sin => write!(f, "sin"),
            UnaryOperator::Cos => write!(f, "cos"),
            UnaryOperator::Tan => write!(f, "tan"),
            UnaryOperator::Log => write!(f, "log"),
            UnaryOperator::Exp => write!(f, "exp"),
            UnaryOperator::Floor => write!(f, "floor"),
            UnaryOperator::Ceil => write!(f, "ceil"),
            UnaryOperator::Round => write!(f, "round"),
        }
    }
}

impl Hash for ExpressionNode {
    fn hash<H: Hasher>(&self, state: &mut H) {
        std::mem::discriminant(self).hash(state);
        match self {
            ExpressionNode::Constant(value) => {
                value.type_name().hash(state);
                // Hash the numeric value as bits
                value.to_f64().to_bits().hash(state);
            }
            ExpressionNode::Variable {
                name,
                var_type,
                index,
            } => {
                name.hash(state);
                var_type.hash(state);
                index.hash(state);
            }
            ExpressionNode::ArrayAccess { array, index } => {
                array.hash(state);
                index.hash(state);
            }
            ExpressionNode::BinaryOp {
                left,
                right,
                operator,
            } => {
                left.hash(state);
                right.hash(state);
                operator.hash(state);
            }
            ExpressionNode::UnaryOp { operand, operator } => {
                operand.hash(state);
                operator.hash(state);
            }
            ExpressionNode::FunctionCall {
                function,
                arguments,
            } => {
                function.hash(state);
                for arg in arguments {
                    arg.hash(state);
                }
            }
            ExpressionNode::Reduction {
                array,
                operation,
                axis,
            } => {
                array.hash(state);
                operation.hash(state);
                axis.hash(state);
            }
            ExpressionNode::Conditional {
                condition,
                true_expr,
                false_expr,
            } => {
                condition.hash(state);
                true_expr.hash(state);
                false_expr.hash(state);
            }
        }
    }
}

/// Expression tree for representing complex computations
#[derive(Debug, Clone)]
pub struct ExpressionTree {
    /// Root node of the expression tree
    pub root: ExpressionNode,
    /// Variable definitions
    pub variables: HashMap<String, VariableInfo>,
    /// Expression metadata
    pub metadata: ExpressionMetadata,
}

/// Information about a variable in the expression
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct VariableInfo {
    /// Variable name
    pub name: String,
    /// Data type
    pub data_type: String,
    /// Shape (for arrays)
    pub shape: Option<Vec<usize>>,
    /// Whether this variable is mutable
    pub is_mutable: bool,
}

/// Metadata about an expression tree
#[derive(Debug, Clone)]
pub struct ExpressionMetadata {
    /// Estimated computational complexity
    pub complexity: u64,
    /// Whether the expression is vectorizable
    pub is_vectorizable: bool,
    /// Whether the expression is parallelizable
    pub is_parallelizable: bool,
    /// Memory usage estimate in bytes
    pub estimated_memory_usage: usize,
    /// Optimization opportunities
    pub optimizations: Vec<OptimizationOpportunity>,
}

/// Optimization opportunity identified in the expression
#[derive(Debug, Clone)]
pub struct OptimizationOpportunity {
    /// Type of optimization
    pub optimization_type: OptimizationType,
    /// Description of the optimization
    pub description: String,
    /// Estimated performance improvement (0.0 to 1.0)
    pub estimated_improvement: f64,
    /// Node path where optimization can be applied
    pub node_path: Vec<usize>,
}

/// Types of optimizations that can be applied
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum OptimizationType {
    CommonSubexpressionElimination,
    ConstantFolding,
    AlgebraicSimplification,
    LoopFusion,
    Vectorization,
    MemoryLayoutOptimization,
    BranchElimination,
    StrengthReduction,
}

impl ExpressionTree {
    /// Create a new expression tree
    pub fn new(root: ExpressionNode) -> Self {
        let mut tree = Self {
            root,
            variables: HashMap::new(),
            metadata: ExpressionMetadata {
                complexity: 0,
                is_vectorizable: false,
                is_parallelizable: false,
                estimated_memory_usage: 0,
                optimizations: Vec::new(),
            },
        };

        tree.analyze();
        tree
    }

    /// Add a variable definition
    pub fn add_variable(
        &mut self,
        name: String,
        data_type: String,
        shape: Option<Vec<usize>>,
        is_mutable: bool,
    ) {
        let var_info = VariableInfo {
            name: name.clone(),
            data_type,
            shape,
            is_mutable,
        };
        self.variables.insert(name, var_info);
    }

    /// Analyze the expression tree for optimization opportunities
    pub fn analyze(&mut self) {
        self.calculate_complexity();
        self.analyze_vectorization();
        self.analyze_parallelization();
        self.estimate_memory_usage();
        self.find_optimizations();
    }

    /// Calculate computational complexity
    fn calculate_complexity(&mut self) {
        self.metadata.complexity = self.calculate_node_complexity(&self.root);
    }

    /// Calculate complexity of a node and its children
    fn calculate_node_complexity(&self, node: &ExpressionNode) -> u64 {
        match node {
            ExpressionNode::Constant(_) => 1,
            ExpressionNode::Variable { .. } => 1,
            ExpressionNode::ArrayAccess { array, index } => {
                self.calculate_node_complexity(array) + self.calculate_node_complexity(index) + 2
            }
            ExpressionNode::BinaryOp {
                left,
                right,
                operator,
            } => {
                let left_complexity = self.calculate_node_complexity(left);
                let right_complexity = self.calculate_node_complexity(right);
                let op_complexity = match operator {
                    BinaryOperator::Add | BinaryOperator::Subtract => 1,
                    BinaryOperator::Multiply => 2,
                    BinaryOperator::Divide => 5,
                    BinaryOperator::Power => 10,
                    _ => 1,
                };
                left_complexity + right_complexity + op_complexity
            }
            ExpressionNode::UnaryOp { operand, operator } => {
                let operand_complexity = self.calculate_node_complexity(operand);
                let op_complexity = match operator {
                    UnaryOperator::Negate | UnaryOperator::LogicalNot => 1,
                    UnaryOperator::Abs => 2,
                    UnaryOperator::Sqrt => 5,
                    UnaryOperator::Sin | UnaryOperator::Cos | UnaryOperator::Tan => 10,
                    UnaryOperator::Log | UnaryOperator::Exp => 8,
                    _ => 3,
                };
                operand_complexity + op_complexity
            }
            ExpressionNode::FunctionCall { arguments, .. } => {
                let args_complexity: u64 = arguments
                    .iter()
                    .map(|arg| self.calculate_node_complexity(arg))
                    .sum();
                args_complexity + 10 // Function call overhead
            }
            ExpressionNode::Reduction {
                array, operation, ..
            } => {
                let array_complexity = self.calculate_node_complexity(array);
                let reduction_complexity = match operation {
                    ReductionOperation::Sum | ReductionOperation::Count => 1,
                    ReductionOperation::Mean => 2,
                    ReductionOperation::Min | ReductionOperation::Max => 1,
                    ReductionOperation::Variance | ReductionOperation::StandardDeviation => 10,
                    _ => 5,
                };
                array_complexity * reduction_complexity
            }
            ExpressionNode::Conditional {
                condition,
                true_expr,
                false_expr,
            } => {
                let condition_complexity = self.calculate_node_complexity(condition);
                let true_complexity = self.calculate_node_complexity(true_expr);
                let false_complexity = self.calculate_node_complexity(false_expr);
                condition_complexity + true_complexity.max(false_complexity) + 2
            }
        }
    }

    /// Analyze whether the expression can be vectorized
    fn analyze_vectorization(&mut self) {
        self.metadata.is_vectorizable = self.is_node_vectorizable(&self.root);
    }

    /// Check if a node can be vectorized
    fn is_node_vectorizable(&self, node: &ExpressionNode) -> bool {
        match node {
            ExpressionNode::Constant(_) => true,
            ExpressionNode::Variable { .. } => true,
            ExpressionNode::ArrayAccess { .. } => true,
            ExpressionNode::BinaryOp {
                left,
                right,
                operator,
            } => {
                let vectorizable_ops = [
                    BinaryOperator::Add,
                    BinaryOperator::Subtract,
                    BinaryOperator::Multiply,
                    BinaryOperator::Divide,
                ];
                vectorizable_ops.contains(operator)
                    && self.is_node_vectorizable(left)
                    && self.is_node_vectorizable(right)
            }
            ExpressionNode::UnaryOp { operand, operator } => {
                let vectorizable_ops = [
                    UnaryOperator::Negate,
                    UnaryOperator::Abs,
                    UnaryOperator::Sqrt,
                ];
                vectorizable_ops.contains(operator) && self.is_node_vectorizable(operand)
            }
            ExpressionNode::Reduction { .. } => true, // Reductions are naturally vectorizable
            _ => false, // Function calls and conditionals may not be vectorizable
        }
    }

    /// Analyze whether the expression can be parallelized
    fn analyze_parallelization(&mut self) {
        self.metadata.is_parallelizable = self.is_node_parallelizable(&self.root);
    }

    /// Check if a node can be parallelized
    fn is_node_parallelizable(&self, node: &ExpressionNode) -> bool {
        match node {
            ExpressionNode::Constant(_) => true,
            ExpressionNode::Variable { .. } => true,
            ExpressionNode::ArrayAccess { .. } => true,
            ExpressionNode::BinaryOp { left, right, .. } => {
                self.is_node_parallelizable(left) && self.is_node_parallelizable(right)
            }
            ExpressionNode::UnaryOp { operand, .. } => self.is_node_parallelizable(operand),
            ExpressionNode::Reduction { .. } => true, // Reductions can be parallelized
            ExpressionNode::FunctionCall { arguments, .. } => {
                // Function calls can be parallelized if all arguments are parallelizable
                // and the function is pure (side-effect free)
                arguments.iter().all(|arg| self.is_node_parallelizable(arg))
            }
            ExpressionNode::Conditional { .. } => false, // Conditionals typically can't be parallelized
        }
    }

    /// Estimate memory usage of the expression
    fn estimate_memory_usage(&mut self) {
        self.metadata.estimated_memory_usage = self.estimate_node_memory(&self.root);
    }

    /// Estimate memory usage of a node
    fn estimate_node_memory(&self, node: &ExpressionNode) -> usize {
        match node {
            ExpressionNode::Constant(_) => 8, // Assume 8 bytes per constant
            ExpressionNode::Variable { var_type, .. } => {
                // Estimate based on type and shape
                let base_size = match var_type.as_str() {
                    "f64" => 8,
                    "f32" => 4,
                    "i64" => 8,
                    "i32" => 4,
                    _ => 8,
                };

                if let Some(var_info) = self.variables.get(&format!("{}", var_type)) {
                    if let Some(shape) = &var_info.shape {
                        let total_elements: usize = shape.iter().product();
                        base_size * total_elements
                    } else {
                        base_size
                    }
                } else {
                    base_size
                }
            }
            ExpressionNode::ArrayAccess { array, index } => {
                self.estimate_node_memory(array) + self.estimate_node_memory(index)
            }
            ExpressionNode::BinaryOp { left, right, .. } => {
                self.estimate_node_memory(left) + self.estimate_node_memory(right) + 8
            }
            ExpressionNode::UnaryOp { operand, .. } => self.estimate_node_memory(operand) + 8,
            ExpressionNode::FunctionCall { arguments, .. } => {
                arguments
                    .iter()
                    .map(|arg| self.estimate_node_memory(arg))
                    .sum::<usize>()
                    + 64
            }
            ExpressionNode::Reduction { array, .. } => {
                self.estimate_node_memory(array) + 64 // Extra space for reduction state
            }
            ExpressionNode::Conditional {
                condition,
                true_expr,
                false_expr,
            } => {
                self.estimate_node_memory(condition)
                    + self
                        .estimate_node_memory(true_expr)
                        .max(self.estimate_node_memory(false_expr))
            }
        }
    }

    /// Find optimization opportunities in the expression tree
    fn find_optimizations(&mut self) {
        self.metadata.optimizations.clear();
        let root_clone = self.root.clone();
        self.find_node_optimizations(&root_clone, &mut Vec::new());
    }

    /// Find optimizations for a specific node
    fn find_node_optimizations(&mut self, node: &ExpressionNode, path: &mut Vec<usize>) {
        // Look for constant folding opportunities
        if self.can_constant_fold(node) {
            self.metadata.optimizations.push(OptimizationOpportunity {
                optimization_type: OptimizationType::ConstantFolding,
                description: "Constant expression can be pre-computed".to_string(),
                estimated_improvement: 0.2,
                node_path: path.clone(),
            });
        }

        // Look for algebraic simplifications
        if self.can_algebraic_simplify(node) {
            self.metadata.optimizations.push(OptimizationOpportunity {
                optimization_type: OptimizationType::AlgebraicSimplification,
                description: "Expression can be algebraically simplified".to_string(),
                estimated_improvement: 0.15,
                node_path: path.clone(),
            });
        }

        // Look for vectorization opportunities
        if self.metadata.is_vectorizable && self.can_vectorize(node) {
            self.metadata.optimizations.push(OptimizationOpportunity {
                optimization_type: OptimizationType::Vectorization,
                description: "Operation can be vectorized with SIMD instructions".to_string(),
                estimated_improvement: 0.4,
                node_path: path.clone(),
            });
        }

        // Recursively analyze child nodes
        match node {
            ExpressionNode::ArrayAccess { array, index } => {
                path.push(0);
                self.find_node_optimizations(array, path);
                path.pop();
                path.push(1);
                self.find_node_optimizations(index, path);
                path.pop();
            }
            ExpressionNode::BinaryOp { left, right, .. } => {
                path.push(0);
                self.find_node_optimizations(left, path);
                path.pop();
                path.push(1);
                self.find_node_optimizations(right, path);
                path.pop();
            }
            ExpressionNode::UnaryOp { operand, .. } => {
                path.push(0);
                self.find_node_optimizations(operand, path);
                path.pop();
            }
            ExpressionNode::FunctionCall { arguments, .. } => {
                for (i, arg) in arguments.iter().enumerate() {
                    path.push(i);
                    self.find_node_optimizations(arg, path);
                    path.pop();
                }
            }
            ExpressionNode::Reduction { array, .. } => {
                path.push(0);
                self.find_node_optimizations(array, path);
                path.pop();
            }
            ExpressionNode::Conditional {
                condition,
                true_expr,
                false_expr,
            } => {
                path.push(0);
                self.find_node_optimizations(condition, path);
                path.pop();
                path.push(1);
                self.find_node_optimizations(true_expr, path);
                path.pop();
                path.push(2);
                self.find_node_optimizations(false_expr, path);
                path.pop();
            }
            _ => {} // Constants and variables don't have children
        }
    }

    /// Check if a node can be constant folded
    fn can_constant_fold(&self, node: &ExpressionNode) -> bool {
        match node {
            ExpressionNode::BinaryOp { left, right, .. } => {
                matches!(**left, ExpressionNode::Constant(_))
                    && matches!(**right, ExpressionNode::Constant(_))
            }
            ExpressionNode::UnaryOp { operand, .. } => {
                matches!(**operand, ExpressionNode::Constant(_))
            }
            _ => false,
        }
    }

    /// Check if a node can be algebraically simplified
    fn can_algebraic_simplify(&self, node: &ExpressionNode) -> bool {
        match node {
            ExpressionNode::BinaryOp {
                left,
                right,
                operator,
            } => {
                // Look for patterns like x + 0, x * 1, x * 0, etc.
                match operator {
                    BinaryOperator::Add => {
                        self.is_zero_constant(left) || self.is_zero_constant(right)
                    }
                    BinaryOperator::Multiply => {
                        self.is_zero_constant(left)
                            || self.is_zero_constant(right)
                            || self.is_one_constant(left)
                            || self.is_one_constant(right)
                    }
                    BinaryOperator::Power => {
                        self.is_zero_constant(right) || self.is_one_constant(right)
                    }
                    _ => false,
                }
            }
            _ => false,
        }
    }

    /// Check if a node can be vectorized
    fn can_vectorize(&self, node: &ExpressionNode) -> bool {
        // For now, simple heuristic: vectorize arithmetic operations on arrays
        match node {
            ExpressionNode::BinaryOp { operator, .. } => {
                matches!(
                    operator,
                    BinaryOperator::Add
                        | BinaryOperator::Subtract
                        | BinaryOperator::Multiply
                        | BinaryOperator::Divide
                )
            }
            ExpressionNode::UnaryOp { operator, .. } => {
                matches!(
                    operator,
                    UnaryOperator::Negate | UnaryOperator::Abs | UnaryOperator::Sqrt
                )
            }
            _ => false,
        }
    }

    /// Check if a node is a zero constant
    fn is_zero_constant(&self, node: &ExpressionNode) -> bool {
        match node {
            ExpressionNode::Constant(value) => value.to_f64() == 0.0,
            _ => false,
        }
    }

    /// Check if a node is a one constant
    fn is_one_constant(&self, node: &ExpressionNode) -> bool {
        match node {
            ExpressionNode::Constant(value) => value.to_f64() == 1.0,
            _ => false,
        }
    }

    /// Generate optimized expression tree
    pub fn optimize(&self) -> Result<ExpressionTree> {
        let mut optimized_root = self.root.clone();

        // Apply optimizations in order of importance
        optimized_root = self.apply_constant_folding(optimized_root)?;
        optimized_root = self.apply_algebraic_simplification(optimized_root)?;
        optimized_root = self.apply_common_subexpression_elimination(optimized_root)?;

        let mut optimized_tree = ExpressionTree::new(optimized_root);
        optimized_tree.variables = self.variables.clone();

        Ok(optimized_tree)
    }

    /// Apply constant folding optimization
    fn apply_constant_folding(&self, node: ExpressionNode) -> Result<ExpressionNode> {
        match node {
            ExpressionNode::BinaryOp {
                left,
                right,
                operator,
            } => {
                let left = self.apply_constant_folding(*left)?;
                let right = self.apply_constant_folding(*right)?;

                if let (ExpressionNode::Constant(l_val), ExpressionNode::Constant(r_val)) =
                    (&left, &right)
                {
                    // Evaluate the constant expression
                    let result = self.evaluate_binary_constant_op(l_val, r_val, operator)?;
                    Ok(ExpressionNode::Constant(result))
                } else {
                    Ok(ExpressionNode::BinaryOp {
                        left: Box::new(left),
                        right: Box::new(right),
                        operator,
                    })
                }
            }
            ExpressionNode::UnaryOp { operand, operator } => {
                let operand = self.apply_constant_folding(*operand)?;

                if let ExpressionNode::Constant(val) = &operand {
                    let result = self.evaluate_unary_constant_op(val, operator)?;
                    Ok(ExpressionNode::Constant(result))
                } else {
                    Ok(ExpressionNode::UnaryOp {
                        operand: Box::new(operand),
                        operator,
                    })
                }
            }
            _ => Ok(node), // Other node types don't need constant folding
        }
    }

    /// Apply algebraic simplification
    fn apply_algebraic_simplification(&self, node: ExpressionNode) -> Result<ExpressionNode> {
        match node {
            ExpressionNode::BinaryOp {
                left,
                right,
                operator,
            } => {
                let left = self.apply_algebraic_simplification(*left)?;
                let right = self.apply_algebraic_simplification(*right)?;

                // Apply simplification rules
                match operator {
                    BinaryOperator::Add => {
                        if self.is_zero_constant(&left) {
                            return Ok(right);
                        }
                        if self.is_zero_constant(&right) {
                            return Ok(left);
                        }
                    }
                    BinaryOperator::Multiply => {
                        if self.is_zero_constant(&left) || self.is_zero_constant(&right) {
                            return Ok(ExpressionNode::Constant(NumericValue::F64(0.0)));
                        }
                        if self.is_one_constant(&left) {
                            return Ok(right);
                        }
                        if self.is_one_constant(&right) {
                            return Ok(left);
                        }
                    }
                    BinaryOperator::Power => {
                        if self.is_zero_constant(&right) {
                            return Ok(ExpressionNode::Constant(NumericValue::F64(1.0)));
                        }
                        if self.is_one_constant(&right) {
                            return Ok(left);
                        }
                    }
                    _ => {}
                }

                Ok(ExpressionNode::BinaryOp {
                    left: Box::new(left),
                    right: Box::new(right),
                    operator,
                })
            }
            _ => Ok(node),
        }
    }

    /// Apply common subexpression elimination
    fn apply_common_subexpression_elimination(
        &self,
        node: ExpressionNode,
    ) -> Result<ExpressionNode> {
        // This is a simplified implementation - a full CSE would require
        // building a hash table of all subexpressions and their frequencies
        Ok(node)
    }

    /// Evaluate a binary operation on constants
    fn evaluate_binary_constant_op(
        &self,
        left: &NumericValue,
        right: &NumericValue,
        operator: BinaryOperator,
    ) -> Result<NumericValue> {
        let l_val = left.to_f64();
        let r_val = right.to_f64();

        let result = match operator {
            BinaryOperator::Add => l_val + r_val,
            BinaryOperator::Subtract => l_val - r_val,
            BinaryOperator::Multiply => l_val * r_val,
            BinaryOperator::Divide => {
                if r_val == 0.0 {
                    return Err(Error::InvalidOperation("Division by zero".to_string()));
                }
                l_val / r_val
            }
            BinaryOperator::Power => l_val.powf(r_val),
            _ => {
                return Err(Error::NotImplemented(format!(
                    "Constant evaluation for {:?}",
                    operator
                )))
            }
        };

        Ok(NumericValue::F64(result))
    }

    /// Evaluate a unary operation on a constant
    fn evaluate_unary_constant_op(
        &self,
        operand: &NumericValue,
        operator: UnaryOperator,
    ) -> Result<NumericValue> {
        let val = operand.to_f64();

        let result = match operator {
            UnaryOperator::Negate => -val,
            UnaryOperator::Abs => val.abs(),
            UnaryOperator::Sqrt => {
                if val < 0.0 {
                    return Err(Error::InvalidOperation(
                        "Square root of negative number".to_string(),
                    ));
                }
                val.sqrt()
            }
            UnaryOperator::Sin => val.sin(),
            UnaryOperator::Cos => val.cos(),
            UnaryOperator::Tan => val.tan(),
            UnaryOperator::Log => {
                if val <= 0.0 {
                    return Err(Error::InvalidOperation(
                        "Logarithm of non-positive number".to_string(),
                    ));
                }
                val.ln()
            }
            UnaryOperator::Exp => val.exp(),
            UnaryOperator::Floor => val.floor(),
            UnaryOperator::Ceil => val.ceil(),
            UnaryOperator::Round => val.round(),
            _ => {
                return Err(Error::NotImplemented(format!(
                    "Constant evaluation for {:?}",
                    operator
                )))
            }
        };

        Ok(NumericValue::F64(result))
    }

    /// Convert the expression tree to a human-readable string
    pub fn to_string(&self) -> String {
        self.node_to_string(&self.root)
    }

    /// Convert a node to a string representation
    fn node_to_string(&self, node: &ExpressionNode) -> String {
        match node {
            ExpressionNode::Constant(value) => format!("{}", value.to_f64()),
            ExpressionNode::Variable { name, .. } => name.clone(),
            ExpressionNode::ArrayAccess { array, index } => {
                format!(
                    "{}[{}]",
                    self.node_to_string(array),
                    self.node_to_string(index)
                )
            }
            ExpressionNode::BinaryOp {
                left,
                right,
                operator,
            } => {
                format!(
                    "({} {} {})",
                    self.node_to_string(left),
                    operator,
                    self.node_to_string(right)
                )
            }
            ExpressionNode::UnaryOp { operand, operator } => {
                format!("{}({})", operator, self.node_to_string(operand))
            }
            ExpressionNode::FunctionCall {
                function,
                arguments,
            } => {
                let args: Vec<String> = arguments
                    .iter()
                    .map(|arg| self.node_to_string(arg))
                    .collect();
                format!("{}({})", function, args.join(", "))
            }
            ExpressionNode::Reduction {
                array,
                operation,
                axis,
            } => {
                let axis_str = if let Some(axis) = axis {
                    format!(", axis={})", axis)
                } else {
                    ")".to_string()
                };
                format!("{:?}({}{}", operation, self.node_to_string(array), axis_str)
            }
            ExpressionNode::Conditional {
                condition,
                true_expr,
                false_expr,
            } => {
                format!(
                    "if {} then {} else {}",
                    self.node_to_string(condition),
                    self.node_to_string(true_expr),
                    self.node_to_string(false_expr)
                )
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_expression_creation() {
        let x = ExpressionNode::Variable {
            name: "x".to_string(),
            var_type: "f64".to_string(),
            index: 0,
        };

        let constant = ExpressionNode::Constant(NumericValue::F64(2.0));

        let expr = ExpressionNode::BinaryOp {
            left: Box::new(x),
            right: Box::new(constant),
            operator: BinaryOperator::Multiply,
        };

        let tree = ExpressionTree::new(expr);
        assert!(tree.metadata.complexity > 0);
    }

    #[test]
    fn test_constant_folding() {
        let left = ExpressionNode::Constant(NumericValue::F64(2.0));
        let right = ExpressionNode::Constant(NumericValue::F64(3.0));

        let expr = ExpressionNode::BinaryOp {
            left: Box::new(left),
            right: Box::new(right),
            operator: BinaryOperator::Add,
        };

        let tree = ExpressionTree::new(expr);
        let optimized = tree.optimize().expect("operation should succeed");

        // Should have folded to a constant 5.0
        if let ExpressionNode::Constant(value) = optimized.root {
            assert_eq!(value.to_f64(), 5.0);
        } else {
            panic!("Expected constant folded result");
        }
    }

    #[test]
    fn test_algebraic_simplification() {
        let x = ExpressionNode::Variable {
            name: "x".to_string(),
            var_type: "f64".to_string(),
            index: 0,
        };

        let zero = ExpressionNode::Constant(NumericValue::F64(0.0));

        let expr = ExpressionNode::BinaryOp {
            left: Box::new(x.clone()),
            right: Box::new(zero),
            operator: BinaryOperator::Add,
        };

        let tree = ExpressionTree::new(expr);
        let optimized = tree.optimize().expect("operation should succeed");

        // Should have simplified to just x
        if let ExpressionNode::Variable { name, .. } = optimized.root {
            assert_eq!(name, "x");
        } else {
            panic!("Expected simplified result to be just variable x");
        }
    }

    #[test]
    fn test_expression_string_representation() {
        let x = ExpressionNode::Variable {
            name: "x".to_string(),
            var_type: "f64".to_string(),
            index: 0,
        };

        let constant = ExpressionNode::Constant(NumericValue::F64(2.0));

        let expr = ExpressionNode::BinaryOp {
            left: Box::new(x),
            right: Box::new(constant),
            operator: BinaryOperator::Multiply,
        };

        let tree = ExpressionTree::new(expr);
        let string_repr = tree.to_string();

        assert_eq!(string_repr, "(x * 2)");
    }
}