readb 0.4.1

A simple, efficient, and modular embedded read-first key-value database in Rust.
Documentation 
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use crate::cache::Key;
use crate::default_persist;
use crate::index_table::IndexTable;
use bincode::deserialize_from;
use fs2::FileExt;
use std::collections::BTreeMap;
use std::fs::{File, OpenOptions};
use std::io::BufReader;
use std::path::PathBuf;

#[repr(C)]
pub struct BTreeMapIndexTable {
    table: BTreeMap<String, Key>,
    file_path: PathBuf,
}

impl BTreeMapIndexTable {
    pub fn new(path: PathBuf) -> anyhow::Result<Self> {
        let file = OpenOptions::new()
            .read(true)
            .write(true)
            .create(true)
            .open(&path)?;

        // Lock the file
        file.lock_exclusive()?;

        let reader = BufReader::new(&file);
        let table: BTreeMap<String, Key> = match deserialize_from(reader) {
            Ok(table) => table,
            Err(_) => BTreeMap::new(),
        };

        // Remember to unlock the file when done
        file.unlock()?;

        Ok(Self {
            table,
            file_path: path,
        })
    }

    pub fn new_default(path: PathBuf) -> anyhow::Result<Self> {
        Ok(Self {
            table: BTreeMap::new(),
            file_path: path,
        })
    }
}

impl IndexTable for BTreeMapIndexTable {
    fn get(&self, key: &str) -> Option<Key> {
        self.table.get(key).copied()
    }

    fn insert(&mut self, key: &str, value: Key) -> anyhow::Result<()> {
        self.table.insert(key.to_string(), value);
        Ok(())
    }

    fn delete(&mut self, key: &str) -> anyhow::Result<()> {
        self.table.remove(key);
        Ok(())
    }

    fn load(&mut self) -> anyhow::Result<()> {
        let file = File::open(&self.file_path)?;

        // Lock the file
        file.lock_exclusive()?;

        let reader = BufReader::new(&file);
        self.table = match deserialize_from(reader) {
            Ok(table) => table,
            Err(_) => BTreeMap::new(),
        };

        // Remember to unlock the file when done
        file.unlock()?;

        Ok(())
    }

    fn persist(&self) -> anyhow::Result<()> {
        default_persist!(self, self.file_path.clone(), self.table);
        Ok(())
    }

    #[cfg(test)]
    fn index_type(&self) -> &str {
        "btree"
    }

    fn all_key_values(&self) -> Vec<(String, Key)> {
        self.table.iter().map(|(k, v)| (k.clone(), *v)).collect()
    }

    fn replace_all(&mut self, key_values: Vec<(String, Key)>) -> anyhow::Result<()> {
        self.table = key_values.into_iter().collect();
        Ok(())
    }

    #[cfg(feature = "write")]
    fn snapshot(&self) -> Box<dyn IndexTable> {
        Box::new(Self {
            table: self.table.clone(),
            file_path: self.file_path.clone(),
        })
    }
}

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

    #[test]
    fn test_insert_and_get() -> anyhow::Result<()> {
        // Setup - create a temporary directory
        let temp_dir = tempfile::tempdir()?;
        let index_path = temp_dir.path().join("index.bin");

        // Create a new index table
        let mut index_table = BTreeMapIndexTable::new(index_path.clone())?;

        // Test - insert an item
        let key = "test";
        let value = 123;
        index_table.insert(key, (value, 0)).unwrap();

        // Assert - get returns the correct value
        assert_eq!(index_table.get(&key), Some((value, 0)));

        // Test - persist to disk
        index_table.persist()?;

        // Assert - load from disk
        let mut loaded_table = BTreeMapIndexTable::new(index_path)?;
        loaded_table.load()?;
        assert_eq!(loaded_table.get(&key), Some((value, 0)));

        // Cleanup
        temp_dir.close()?;

        Ok(())
    }
}