rustrails-record 0.1.2

use std::cell::RefCell;
use std::sync::Arc;

use rustrails_support::cache::{CacheOptions, CacheStore, MemoryStore};
use serde_json::Value;

thread_local! {
    static QUERY_CACHE_SCOPE: RefCell<Vec<QueryCacheScope>> = const { RefCell::new(Vec::new()) };
}

#[derive(Clone)]
struct QueryCacheScope {
    cache: QueryCache,
    bypass_depth: usize,
}

/// Per-request query cache backed by [`MemoryStore`].
#[derive(Clone, Debug)]
pub struct QueryCache {
    store: Arc<MemoryStore>,
}

impl QueryCache {
    /// Creates an empty query cache.
    #[must_use]
    pub fn new() -> Self {
        Self {
            store: Arc::new(MemoryStore::new()),
        }
    }

    /// Computes the cache key for an SQL statement and bind values.
    #[must_use]
    pub fn cache_key(sql: &str, binds: &[Value]) -> String {
        let binds = match serde_json::to_string(binds) {
            Ok(serialized) => serialized,
            Err(_) => "[]".to_owned(),
        };
        format!("{sql}::{binds}")
    }

    /// Runs `f` with an isolated request-scoped query cache.
    pub fn with_request_scope<F, R>(&self, f: F) -> R
    where
        F: FnOnce() -> R,
    {
        QUERY_CACHE_SCOPE.with(|scope| {
            scope.borrow_mut().push(QueryCacheScope {
                cache: QueryCache::new(),
                bypass_depth: 0,
            });
        });

        struct Guard;
        impl Drop for Guard {
            fn drop(&mut self) {
                QUERY_CACHE_SCOPE.with(|scope| {
                    scope.borrow_mut().pop();
                });
            }
        }

        let _guard = Guard;
        f()
    }

    /// Reads a cached query result or computes and stores it.
    pub fn fetch<F>(&self, sql: &str, binds: &[Value], loader: F) -> Value
    where
        F: FnOnce() -> Value,
    {
        let key = Self::cache_key(sql, binds);

        if let Some((cache, bypassed)) = current_scope() {
            if bypassed {
                return loader();
            }
            return cache.store.fetch(&key, CacheOptions::default(), loader);
        }

        self.store.fetch(&key, CacheOptions::default(), loader)
    }

    /// Clears cached query results after a write operation.
    pub fn execute_write<F, R>(&self, operation: F) -> R
    where
        F: FnOnce() -> R,
    {
        let result = operation();
        if let Some((cache, _)) = current_scope() {
            cache.store.clear();
        } else {
            self.store.clear();
        }
        result
    }

    /// Executes `f` while bypassing the current request cache.
    pub fn uncached<F, R>(f: F) -> R
    where
        F: FnOnce() -> R,
    {
        QUERY_CACHE_SCOPE.with(|scope| {
            if let Some(current) = scope.borrow_mut().last_mut() {
                current.bypass_depth += 1;
            }
        });

        struct Guard;
        impl Drop for Guard {
            fn drop(&mut self) {
                QUERY_CACHE_SCOPE.with(|scope| {
                    if let Some(current) = scope.borrow_mut().last_mut() {
                        current.bypass_depth = current.bypass_depth.saturating_sub(1);
                    }
                });
            }
        }

        let _guard = Guard;
        f()
    }
}

impl Default for QueryCache {
    fn default() -> Self {
        Self::new()
    }
}

fn current_scope() -> Option<(QueryCache, bool)> {
    QUERY_CACHE_SCOPE.with(|scope| {
        scope
            .borrow()
            .last()
            .map(|scope| (scope.cache.clone(), scope.bypass_depth > 0))
    })
}

#[cfg(test)]
mod tests {
    use std::sync::atomic::{AtomicUsize, Ordering};

    use serde_json::json;

    use super::QueryCache;

    #[test]
    fn cache_key_depends_on_sql_and_binds() {
        let first = QueryCache::cache_key("SELECT 1", &[json!(1)]);
        let second = QueryCache::cache_key("SELECT 1", &[json!(2)]);
        assert_ne!(first, second);
    }

    #[test]
    fn fetch_uses_cached_value_within_request_scope() {
        let cache = QueryCache::new();
        let calls = AtomicUsize::new(0);

        cache.with_request_scope(|| {
            let first = cache.fetch("SELECT * FROM users WHERE id = ?", &[json!(1)], || {
                calls.fetch_add(1, Ordering::SeqCst);
                json!({"id": 1})
            });
            let second = cache.fetch("SELECT * FROM users WHERE id = ?", &[json!(1)], || {
                calls.fetch_add(1, Ordering::SeqCst);
                json!({"id": 2})
            });

            assert_eq!(first, second);
        });

        assert_eq!(calls.load(Ordering::SeqCst), 1);
    }

    #[test]
    fn request_scopes_are_isolated() {
        let cache = QueryCache::new();
        let calls = AtomicUsize::new(0);

        cache.with_request_scope(|| {
            let _ = cache.fetch("SELECT 1", &[], || {
                calls.fetch_add(1, Ordering::SeqCst);
                json!(1)
            });
        });
        cache.with_request_scope(|| {
            let _ = cache.fetch("SELECT 1", &[], || {
                calls.fetch_add(1, Ordering::SeqCst);
                json!(1)
            });
        });

        assert_eq!(calls.load(Ordering::SeqCst), 2);
    }

    #[test]
    fn uncached_bypasses_request_cache() {
        let cache = QueryCache::new();
        let calls = AtomicUsize::new(0);

        cache.with_request_scope(|| {
            let _ = cache.fetch("SELECT 1", &[], || {
                calls.fetch_add(1, Ordering::SeqCst);
                json!(1)
            });
            let _ = QueryCache::uncached(|| {
                cache.fetch("SELECT 1", &[], || {
                    calls.fetch_add(1, Ordering::SeqCst);
                    json!(2)
                })
            });
        });

        assert_eq!(calls.load(Ordering::SeqCst), 2);
    }

    #[test]
    fn execute_write_invalidates_current_scope() {
        let cache = QueryCache::new();
        let calls = AtomicUsize::new(0);

        cache.with_request_scope(|| {
            let _ = cache.fetch("SELECT 1", &[], || {
                calls.fetch_add(1, Ordering::SeqCst);
                json!(1)
            });
            cache.execute_write(|| ());
            let _ = cache.fetch("SELECT 1", &[], || {
                calls.fetch_add(1, Ordering::SeqCst);
                json!(1)
            });
        });

        assert_eq!(calls.load(Ordering::SeqCst), 2);
    }

    #[test]
    fn execute_write_invalidates_non_scoped_cache() {
        let cache = QueryCache::new();
        let calls = AtomicUsize::new(0);

        let _ = cache.fetch("SELECT 1", &[], || {
            calls.fetch_add(1, Ordering::SeqCst);
            json!(1)
        });
        cache.execute_write(|| ());
        let _ = cache.fetch("SELECT 1", &[], || {
            calls.fetch_add(1, Ordering::SeqCst);
            json!(1)
        });

        assert_eq!(calls.load(Ordering::SeqCst), 2);
    }
}