membase 0.2.1

Ultra-high performance async runtime with fast task cycling, lock-free scheduling, and zero-overhead performance
Documentation 
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//! Index implementation for columnar database.

use std::collections::{HashMap, HashSet};
use std::path::{Path, PathBuf};

use crate::error::Result;
use crate::columnar::column::Column;

/// Index types supported by the columnar database.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum IndexType {
    /// B-tree index
    BTree,
    
    /// Hash index
    Hash,
    
    /// Bitmap index
    Bitmap,
    
    /// Inverted index
    Inverted,
}

/// An index on a column.
pub struct Index {
    /// Column name
    column_name: String,
    
    /// Index type
    index_type: IndexType,
    
    /// Base directory for index files
    _base_dir: PathBuf,
    
    /// Index data (simplified for this example)
    /// In a real implementation, this would be a more sophisticated data structure
    data: HashMap<Vec<u8>, Vec<u64>>,
}

impl Index {
    /// Create a new index.
    pub fn new(column_name: &str, index_type: IndexType, base_dir: &str) -> Self {
        let base_path = Path::new(base_dir).join(format!("index_{}", column_name));
        
        Index {
            column_name: column_name.to_string(),
            index_type,
            _base_dir: base_path,
            data: HashMap::new(),
        }
    }
    
    /// Build the index from a column.
    pub fn build(&mut self, column: &Column) -> Result<()> {
        // Clear existing data
        self.data.clear();
        
        // Build the index
        for i in 0..column.row_count() {
            if let Some(value) = column.get_bytes(i) {
                let entry = self.data.entry(value.to_vec()).or_insert_with(Vec::new);
                entry.push(i);
            }
        }

        // In a real implementation, we would write the index to disk
        // For this example, we'll keep it in memory
        
        Ok(())
    }
    
    /// Look up rows by value.
    pub fn lookup(&self, value: &[u8]) -> Option<&[u64]> {
        self.data.get(value).map(|v| v.as_slice())
    }
    
    /// Look up rows by range.
    pub fn lookup_range(&self, start: &[u8], end: &[u8]) -> Vec<u64> {
        let mut result = HashSet::new();
        
        for (key, rows) in &self.data {
            // Convert key to &[u8] for comparison
            if key.as_slice() >= start && key.as_slice() <= end {
                result.extend(rows);
            }
        }
        
        let mut vec: Vec<u64> = result.into_iter().collect();
        vec.sort();
        vec
    }
    
    /// Get the column name.
    pub fn column_name(&self) -> &str {
        &self.column_name
    }
    
    /// Get the index type.
    pub fn index_type(&self) -> IndexType {
        self.index_type
    }
    
    /// Get the number of distinct values in the index.
    pub fn cardinality(&self) -> usize {
        self.data.len()
    }
    
    /// Get the total number of entries in the index.
    pub fn entry_count(&self) -> usize {
        self.data.values().map(|v| v.len()).sum()
    }
}