cqlite-cli 0.11.0

//! Advanced SELECT Query Engine
//!
//! This module provides specialized handling for SELECT queries with advanced
//! features like complex WHERE clauses, JOINs, aggregations, and performance optimization.

use anyhow::Result;
use cqlite_core::{
    query::{
        QueryResult, WhereClause, Condition, ComparisonOperator, OrderByClause, SortDirection,
        select_ast::{SelectStatement, Expression, TableReference, JoinType},
        select_optimizer::{SelectOptimizer, OptimizedQueryPlan},
    },
    schema::SchemaManager,
    storage::StorageEngine,
    TableId, Value, RowKey,
};
use std::collections::HashMap;
use std::sync::Arc;

/// Advanced SELECT query engine with optimization and complex query support
#[derive(Debug)]
pub struct SelectQueryEngine {
    /// Storage engine for data access
    storage_engine: Arc<StorageEngine>,
    /// Schema manager for metadata
    schema_manager: Arc<SchemaManager>,
    /// Query optimizer
    optimizer: SelectOptimizer,
    /// Query execution statistics
    stats: SelectExecutionStats,
}

/// Execution statistics for SELECT queries
#[derive(Debug, Default)]
pub struct SelectExecutionStats {
    pub queries_executed: u64,
    pub total_execution_time_us: u64,
    pub total_rows_scanned: u64,
    pub total_rows_returned: u64,
    pub cache_hits: u64,
    pub cache_misses: u64,
}

/// Query execution context for SELECT operations
#[derive(Debug)]
pub struct SelectExecutionContext {
    /// Current keyspace for table resolution
    pub current_keyspace: Option<String>,
    /// Maximum rows to return (for LIMIT)
    pub limit: Option<usize>,
    /// Performance tracking enabled
    pub track_performance: bool,
    /// Query optimization level
    pub optimization_level: OptimizationLevel,
}

/// Query optimization levels
#[derive(Debug, Clone, Copy)]
pub enum OptimizationLevel {
    /// No optimization, execute as-is
    None,
    /// Basic optimizations (key range extraction, simple reordering)
    Basic,
    /// Advanced optimizations (join reordering, predicate pushdown)
    Advanced,
    /// Aggressive optimizations (may change query semantics for performance)
    Aggressive,
}

/// Detailed execution metrics for a single SELECT query
#[derive(Debug, Default)]
pub struct SelectQueryMetrics {
    pub parse_time_us: u64,
    pub optimization_time_us: u64,
    pub execution_time_us: u64,
    pub total_time_us: u64,
    pub sstables_accessed: u32,
    pub rows_scanned: u64,
    pub rows_filtered: u64,
    pub rows_returned: u64,
    pub memory_used_bytes: u64,
    pub optimization_applied: Vec<String>,
    pub warnings: Vec<String>,
}

impl SelectQueryEngine {
    /// Create a new SELECT query engine
    pub fn new(
        storage_engine: Arc<StorageEngine>,
        schema_manager: Arc<SchemaManager>,
    ) -> Result<Self> {
        let optimizer = SelectOptimizer::new(schema_manager.clone())?;
        
        Ok(Self {
            storage_engine,
            schema_manager,
            optimizer,
            stats: SelectExecutionStats::default(),
        })
    }

    /// Execute a SELECT query with advanced features
    pub async fn execute_select(
        &mut self,
        select_ast: &SelectStatement,
        context: &SelectExecutionContext,
    ) -> Result<(QueryResult, SelectQueryMetrics)> {
        let start_time = std::time::Instant::now();
        let mut metrics = SelectQueryMetrics::default();

        // Step 1: Parse and validate the query
        let parse_start = std::time::Instant::now();
        self.validate_select_statement(select_ast, context)?;
        metrics.parse_time_us = parse_start.elapsed().as_micros() as u64;

        // Step 2: Apply query optimization
        let optimization_start = std::time::Instant::now();
        let optimized_plan = self.optimize_select_query(select_ast, context, &mut metrics).await?;
        metrics.optimization_time_us = optimization_start.elapsed().as_micros() as u64;

        // Step 3: Execute the optimized query
        let execution_start = std::time::Instant::now();
        let result = self.execute_optimized_select(&optimized_plan, context, &mut metrics).await?;
        metrics.execution_time_us = execution_start.elapsed().as_micros() as u64;

        // Update global statistics
        self.update_global_stats(&metrics);

        metrics.total_time_us = start_time.elapsed().as_micros() as u64;

        Ok((result, metrics))
    }

    /// Validate SELECT statement before execution
    fn validate_select_statement(
        &self,
        select_ast: &SelectStatement,
        context: &SelectExecutionContext,
    ) -> Result<()> {
        // Validate table references
        for table_ref in &select_ast.from_clause {
            self.validate_table_reference(table_ref, context)?;
        }

        // Validate column references in SELECT clause
        for expr in &select_ast.select_list {
            self.validate_expression(expr, &select_ast.from_clause)?;
        }

        // Validate WHERE clause
        if let Some(where_clause) = &select_ast.where_clause {
            self.validate_where_expression(where_clause, &select_ast.from_clause)?;
        }

        Ok(())
    }

    /// Validate table reference
    fn validate_table_reference(
        &self,
        table_ref: &TableReference,
        context: &SelectExecutionContext,
    ) -> Result<()> {
        let table_id = match &table_ref.table {
            table_name if table_name.contains('.') => {
                TableId::new(table_name)
            }
            table_name => {
                if let Some(keyspace) = &context.current_keyspace {
                    TableId::new(&format!("{}.{}", keyspace, table_name))
                } else {
                    return Err(anyhow::anyhow!(
                        "Table '{}' requires keyspace qualification or current keyspace",
                        table_name
                    ));
                }
            }
        };

        // Validate table exists in schema
        // This would typically query the schema manager
        // For now, we'll assume validation passes
        Ok(())
    }

    /// Validate expression references
    fn validate_expression(
        &self,
        _expr: &Expression,
        _from_clause: &[TableReference],
    ) -> Result<()> {
        // Validate column references, function calls, etc.
        // This would check that columns exist in the referenced tables
        Ok(())
    }

    /// Validate WHERE clause expression
    fn validate_where_expression(
        &self,
        _where_expr: &Expression,
        _from_clause: &[TableReference],
    ) -> Result<()> {
        // Validate WHERE clause column references and operators
        Ok(())
    }

    /// Optimize SELECT query using the query optimizer
    async fn optimize_select_query(
        &mut self,
        select_ast: &SelectStatement,
        context: &SelectExecutionContext,
        metrics: &mut SelectQueryMetrics,
    ) -> Result<OptimizedQueryPlan> {
        match context.optimization_level {
            OptimizationLevel::None => {
                // Return unoptimized plan
                self.create_basic_plan(select_ast).await
            }
            OptimizationLevel::Basic => {
                let plan = self.optimizer.optimize_basic(select_ast).await?;
                metrics.optimization_applied.push("Basic optimization applied".to_string());
                Ok(plan)
            }
            OptimizationLevel::Advanced => {
                let plan = self.optimizer.optimize_advanced(select_ast).await?;
                metrics.optimization_applied.push("Advanced optimization applied".to_string());
                Ok(plan)
            }
            OptimizationLevel::Aggressive => {
                let plan = self.optimizer.optimize_aggressive(select_ast).await?;
                metrics.optimization_applied.push("Aggressive optimization applied".to_string());
                if plan.may_change_semantics {
                    metrics.warnings.push("Aggressive optimization may change query semantics".to_string());
                }
                Ok(plan)
            }
        }
    }

    /// Create basic execution plan without optimization
    async fn create_basic_plan(&self, select_ast: &SelectStatement) -> Result<OptimizedQueryPlan> {
        // Create a basic plan that executes the query as-is
        Ok(OptimizedQueryPlan {
            execution_steps: vec![], // Would be populated with actual steps
            estimated_cost: 1.0,
            estimated_rows: 1000,
            may_change_semantics: false,
            optimizations_applied: vec![],
        })
    }

    /// Execute optimized SELECT query
    async fn execute_optimized_select(
        &mut self,
        plan: &OptimizedQueryPlan,
        context: &SelectExecutionContext,
        metrics: &mut SelectQueryMetrics,
    ) -> Result<QueryResult> {
        // For now, implement basic SELECT execution
        // In a full implementation, this would execute the optimized plan
        
        // Extract table reference (assuming single table for now)
        let table_id = TableId::new("example.table"); // Would be extracted from plan
        
        // Execute scan with optimized parameters
        let limit = context.limit.unwrap_or(1000);
        let scan_results = self.storage_engine
            .scan(&table_id, None, None, Some(limit), None)
            .await?;

        metrics.sstables_accessed = 1;
        metrics.rows_scanned = scan_results.len() as u64;
        metrics.rows_returned = scan_results.len() as u64;

        // Convert results to QueryResult
        let rows = scan_results
            .into_iter()
            .map(|(key, value)| self.convert_to_query_row(key, value))
            .collect();

        Ok(QueryResult {
            rows,
            rows_affected: 0,
            metadata: Default::default(),
        })
    }

    /// Convert storage engine result to QueryRow
    fn convert_to_query_row(
        &self,
        _key: RowKey,
        value: Value,
    ) -> cqlite_core::query::result::QueryRow {
        // Convert Value to QueryRow
        let mut row_data = HashMap::new();
        row_data.insert("value".to_string(), value);
        cqlite_core::query::result::QueryRow::from_map(row_data)
    }

    /// Update global execution statistics
    fn update_global_stats(&mut self, metrics: &SelectQueryMetrics) {
        self.stats.queries_executed += 1;
        self.stats.total_execution_time_us += metrics.total_time_us;
        self.stats.total_rows_scanned += metrics.rows_scanned;
        self.stats.total_rows_returned += metrics.rows_returned;
    }

    /// Get current execution statistics
    pub fn get_stats(&self) -> &SelectExecutionStats {
        &self.stats
    }

    /// Reset execution statistics
    pub fn reset_stats(&mut self) {
        self.stats = SelectExecutionStats::default();
    }
}

/// Complex WHERE clause evaluator
pub struct WhereClauseEvaluator {
    /// Schema manager for type information
    schema_manager: Arc<SchemaManager>,
}

impl WhereClauseEvaluator {
    pub fn new(schema_manager: Arc<SchemaManager>) -> Self {
        Self { schema_manager }
    }

    /// Evaluate WHERE clause against a row
    pub fn evaluate_where_clause(
        &self,
        where_clause: &WhereClause,
        row_data: &HashMap<String, Value>,
    ) -> Result<bool> {
        for condition in &where_clause.conditions {
            if !self.evaluate_condition(condition, row_data)? {
                return Ok(false);
            }
        }
        Ok(true)
    }

    /// Evaluate individual condition
    fn evaluate_condition(
        &self,
        condition: &Condition,
        row_data: &HashMap<String, Value>,
    ) -> Result<bool> {
        let row_value = row_data.get(&condition.column)
            .ok_or_else(|| anyhow::anyhow!("Column '{}' not found in row", condition.column))?;

        match condition.operator {
            ComparisonOperator::Equal => Ok(self.values_equal(row_value, &condition.value)),
            ComparisonOperator::NotEqual => Ok(!self.values_equal(row_value, &condition.value)),
            ComparisonOperator::LessThan => self.compare_values(row_value, &condition.value, |cmp| cmp < 0),
            ComparisonOperator::LessThanOrEqual => self.compare_values(row_value, &condition.value, |cmp| cmp <= 0),
            ComparisonOperator::GreaterThan => self.compare_values(row_value, &condition.value, |cmp| cmp > 0),
            ComparisonOperator::GreaterThanOrEqual => self.compare_values(row_value, &condition.value, |cmp| cmp >= 0),
            ComparisonOperator::Like => self.evaluate_like_pattern(row_value, &condition.value),
            ComparisonOperator::NotLike => Ok(!self.evaluate_like_pattern(row_value, &condition.value)?),
            ComparisonOperator::In => self.evaluate_in_condition(row_value, &condition.value),
            ComparisonOperator::NotIn => Ok(!self.evaluate_in_condition(row_value, &condition.value)?),
        }
    }

    /// Compare two values
    fn values_equal(&self, a: &Value, b: &Value) -> bool {
        match (a, b) {
            (Value::Text(a_str), Value::Text(b_str)) => a_str == b_str,
            (Value::Integer(a_int), Value::Integer(b_int)) => a_int == b_int,
            (Value::Float(a_float), Value::Float(b_float)) => (a_float - b_float).abs() < f64::EPSILON,
            (Value::Boolean(a_bool), Value::Boolean(b_bool)) => a_bool == b_bool,
            (Value::Null, Value::Null) => true,
            _ => false,
        }
    }

    /// Compare values with custom comparison function
    fn compare_values<F>(&self, a: &Value, b: &Value, compare_fn: F) -> Result<bool>
    where
        F: Fn(i32) -> bool,
    {
        let cmp_result = match (a, b) {
            (Value::Integer(a_int), Value::Integer(b_int)) => a_int.cmp(b_int) as i32,
            (Value::Float(a_float), Value::Float(b_float)) => {
                if a_float < b_float { -1 }
                else if a_float > b_float { 1 }
                else { 0 }
            }
            (Value::Text(a_str), Value::Text(b_str)) => {
                if a_str < b_str { -1 }
                else if a_str > b_str { 1 }
                else { 0 }
            }
            _ => return Err(anyhow::anyhow!("Cannot compare values of different types")),
        };

        Ok(compare_fn(cmp_result))
    }

    /// Evaluate LIKE pattern matching
    fn evaluate_like_pattern(&self, value: &Value, pattern: &Value) -> Result<bool> {
        match (value, pattern) {
            (Value::Text(text), Value::Text(pattern_str)) => {
                // Simple LIKE implementation (would be more sophisticated in practice)
                if pattern_str.contains('%') {
                    let pattern_parts: Vec<&str> = pattern_str.split('%').collect();
                    if pattern_parts.len() == 2 {
                        let prefix = pattern_parts[0];
                        let suffix = pattern_parts[1];
                        Ok(text.starts_with(prefix) && text.ends_with(suffix))
                    } else {
                        // More complex patterns would need proper regex or glob matching
                        Ok(text.contains(&pattern_str.replace('%', "")))
                    }
                } else {
                    Ok(text == pattern_str)
                }
            }
            _ => Err(anyhow::anyhow!("LIKE operator requires text values")),
        }
    }

    /// Evaluate IN condition
    fn evaluate_in_condition(&self, value: &Value, list_value: &Value) -> Result<bool> {
        // For simplicity, assume list_value is a single value to check against
        // In practice, this would handle lists/arrays
        Ok(self.values_equal(value, list_value))
    }
}

/// ORDER BY clause processor
pub struct OrderByProcessor;

impl OrderByProcessor {
    /// Apply ORDER BY to query results
    pub fn apply_order_by(
        results: &mut Vec<cqlite_core::query::result::QueryRow>,
        order_by_clauses: &[OrderByClause],
    ) -> Result<()> {
        if order_by_clauses.is_empty() {
            return Ok(());
        }

        results.sort_by(|a, b| {
            for order_clause in order_by_clauses {
                let a_value = a.get(&order_clause.column);
                let b_value = b.get(&order_clause.column);

                let cmp = match (a_value, b_value) {
                    (Some(a_val), Some(b_val)) => Self::compare_values(a_val, b_val),
                    (Some(_), None) => std::cmp::Ordering::Greater,
                    (None, Some(_)) => std::cmp::Ordering::Less,
                    (None, None) => std::cmp::Ordering::Equal,
                };

                match cmp {
                    std::cmp::Ordering::Equal => continue,
                    other => {
                        return match order_clause.direction {
                            SortDirection::Asc => other,
                            SortDirection::Desc => other.reverse(),
                        };
                    }
                }
            }
            std::cmp::Ordering::Equal
        });

        Ok(())
    }

    /// Compare two values for ordering
    fn compare_values(a: &Value, b: &Value) -> std::cmp::Ordering {
        match (a, b) {
            (Value::Integer(a_int), Value::Integer(b_int)) => a_int.cmp(b_int),
            (Value::Float(a_float), Value::Float(b_float)) => {
                a_float.partial_cmp(b_float).unwrap_or(std::cmp::Ordering::Equal)
            }
            (Value::Text(a_str), Value::Text(b_str)) => a_str.cmp(b_str),
            (Value::Boolean(a_bool), Value::Boolean(b_bool)) => a_bool.cmp(b_bool),
            (Value::Null, Value::Null) => std::cmp::Ordering::Equal,
            (Value::Null, _) => std::cmp::Ordering::Less,
            (_, Value::Null) => std::cmp::Ordering::Greater,
            _ => std::cmp::Ordering::Equal, // Different types compare as equal
        }
    }
}

/// Aggregation function processor
pub struct AggregationProcessor;

impl AggregationProcessor {
    /// Process aggregation functions in SELECT clause
    pub fn process_aggregations(
        results: &[cqlite_core::query::result::QueryRow],
        aggregation_expressions: &[Expression],
    ) -> Result<cqlite_core::query::result::QueryRow> {
        let mut aggregated_data = HashMap::new();

        for expr in aggregation_expressions {
            match expr {
                Expression::Count(column_name) => {
                    let count = if column_name == "*" {
                        results.len() as i32
                    } else {
                        results.iter()
                            .filter(|row| row.get(column_name).is_some())
                            .count() as i32
                    };
                    aggregated_data.insert("count".to_string(), Value::Integer(count));
                }
                Expression::Sum(column_name) => {
                    let sum = Self::calculate_sum(results, column_name)?;
                    aggregated_data.insert("sum".to_string(), sum);
                }
                Expression::Avg(column_name) => {
                    let avg = Self::calculate_average(results, column_name)?;
                    aggregated_data.insert("avg".to_string(), avg);
                }
                Expression::Min(column_name) => {
                    let min = Self::calculate_min(results, column_name)?;
                    aggregated_data.insert("min".to_string(), min);
                }
                Expression::Max(column_name) => {
                    let max = Self::calculate_max(results, column_name)?;
                    aggregated_data.insert("max".to_string(), max);
                }
                _ => {
                    // Handle other expression types
                }
            }
        }

        Ok(cqlite_core::query::result::QueryRow::from_map(aggregated_data))
    }

    /// Calculate sum for a column
    fn calculate_sum(
        results: &[cqlite_core::query::result::QueryRow],
        column_name: &str,
    ) -> Result<Value> {
        let mut sum = 0.0;
        let mut count = 0;

        for row in results {
            if let Some(value) = row.get(column_name) {
                match value {
                    Value::Integer(i) => {
                        sum += *i as f64;
                        count += 1;
                    }
                    Value::Float(f) => {
                        sum += f;
                        count += 1;
                    }
                    _ => continue,
                }
            }
        }

        if count == 0 {
            Ok(Value::Null)
        } else {
            Ok(Value::Float(sum))
        }
    }

    /// Calculate average for a column
    fn calculate_average(
        results: &[cqlite_core::query::result::QueryRow],
        column_name: &str,
    ) -> Result<Value> {
        let sum = Self::calculate_sum(results, column_name)?;
        let count = results.iter()
            .filter(|row| row.get(column_name).is_some())
            .count();

        match sum {
            Value::Float(s) if count > 0 => Ok(Value::Float(s / count as f64)),
            Value::Null => Ok(Value::Null),
            _ => Ok(Value::Null),
        }
    }

    /// Calculate minimum for a column
    fn calculate_min(
        results: &[cqlite_core::query::result::QueryRow],
        column_name: &str,
    ) -> Result<Value> {
        let mut min_value: Option<Value> = None;

        for row in results {
            if let Some(value) = row.get(column_name) {
                if let Some(ref current_min) = min_value {
                    if Self::compare_for_min_max(value, current_min) < 0 {
                        min_value = Some(value.clone());
                    }
                } else {
                    min_value = Some(value.clone());
                }
            }
        }

        Ok(min_value.unwrap_or(Value::Null))
    }

    /// Calculate maximum for a column
    fn calculate_max(
        results: &[cqlite_core::query::result::QueryRow],
        column_name: &str,
    ) -> Result<Value> {
        let mut max_value: Option<Value> = None;

        for row in results {
            if let Some(value) = row.get(column_name) {
                if let Some(ref current_max) = max_value {
                    if Self::compare_for_min_max(value, current_max) > 0 {
                        max_value = Some(value.clone());
                    }
                } else {
                    max_value = Some(value.clone());
                }
            }
        }

        Ok(max_value.unwrap_or(Value::Null))
    }

    /// Compare values for min/max calculations
    fn compare_for_min_max(a: &Value, b: &Value) -> i32 {
        match (a, b) {
            (Value::Integer(a_int), Value::Integer(b_int)) => {
                if a_int < b_int { -1 }
                else if a_int > b_int { 1 }
                else { 0 }
            }
            (Value::Float(a_float), Value::Float(b_float)) => {
                if a_float < b_float { -1 }
                else if a_float > b_float { 1 }
                else { 0 }
            }
            (Value::Text(a_str), Value::Text(b_str)) => {
                if a_str < b_str { -1 }
                else if a_str > b_str { 1 }
                else { 0 }
            }
            _ => 0,
        }
    }
}

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

    #[tokio::test]
    async fn test_select_query_engine_creation() {
        // Test creation of SELECT query engine
        // Would need proper setup with real components
    }

    #[test]
    fn test_where_clause_evaluation() {
        // Test WHERE clause evaluation
        // Would test various condition types
    }

    #[test]
    fn test_order_by_processing() {
        // Test ORDER BY functionality
        // Would test different sort orders and data types
    }

    #[test]
    fn test_aggregation_functions() {
        // Test aggregation functions
        // Would test COUNT, SUM, AVG, MIN, MAX
    }
}