motedb 0.1.4

//! Query execution engine

use crate::{Result, types::Row};
use std::sync::Arc;

/// Result iterator for streaming query results
pub struct ResultIterator {
    /// Internal buffer of rows
    rows: Vec<Row>,
    /// Current position
    pos: usize,
}

impl ResultIterator {
    /// Create a new result iterator
    pub fn new(rows: Vec<Row>) -> Self {
        Self { rows, pos: 0 }
    }
    
    /// Get next row
    pub fn next(&mut self) -> Option<&Row> {
        if self.pos < self.rows.len() {
            let row = &self.rows[self.pos];
            self.pos += 1;
            Some(row)
        } else {
            None
        }
    }
    
    /// Get total number of rows
    pub fn len(&self) -> usize {
        self.rows.len()
    }
    
    /// Check if empty
    pub fn is_empty(&self) -> bool {
        self.rows.is_empty()
    }
}

/// Volcano-style execution engine
/// Implements iterator-based query execution with push/pull model
pub struct ExecutionEngine {
    /// Maximum batch size for processing
    batch_size: usize,
}

impl ExecutionEngine {
    /// Create a new execution engine
    pub fn new() -> Result<Self> {
        Ok(Self {
            batch_size: 1000,
        })
    }
    
    /// Create with custom batch size
    pub fn with_batch_size(batch_size: usize) -> Result<Self> {
        Ok(Self { batch_size })
    }
    
    /// Execute a simple scan (placeholder for future query execution)
    #[allow(unused_variables)]
    pub fn execute_scan(&self, source: Arc<dyn Iterator<Item = Row>>) -> Result<ResultIterator> {
        // Future: Implement full scan with filters and projections
        Ok(ResultIterator::new(Vec::new()))
    }
    
    /// Get batch size
    pub fn batch_size(&self) -> usize {
        self.batch_size
    }
}

impl Default for ExecutionEngine {
    fn default() -> Self {
        Self::new().unwrap()
    }
}