fraiseql_core/cache/

key.rs

//! Cache key generation for query results.
//!
//! # Security Critical
//!
//! This module is **security-critical**. Cache keys MUST include variable values
//! to prevent data leakage between different users or requests. Incorrect key
//! generation could allow User A to see User B's cached data.
//!
//! # Key Composition
//!
//! Cache keys are generated from a single-pass ahash over:
//! 1. Query string bytes
//! 2. Recursively hashed variable values (canonical ordering)
//! 3. WHERE clause structure (hashed structurally, not via serde)
//! 4. Schema version string
//!
//! The hasher uses fixed seeds so that keys are deterministic across restarts.
//!
//! # Example
//!
//! ```rust
//! use fraiseql_core::cache::generate_cache_key;
//! use fraiseql_core::db::{WhereClause, WhereOperator};
//! use serde_json::json;
//!
//! // Two different users querying their own data
//! let key1 = generate_cache_key(
//!     "query { user(id: $id) { name } }",
//!     &json!({"id": "alice"}),
//!     None,
//!     "v1"
//! );
//!
//! let key2 = generate_cache_key(
//!     "query { user(id: $id) { name } }",
//!     &json!({"id": "bob"}),
//!     None,
//!     "v1"
//! );
//!
//! // Different variables MUST produce different keys (security requirement)
//! assert_ne!(key1, key2);
//! ```

use std::hash::{BuildHasher, Hash, Hasher};

use ahash::RandomState;
use serde_json::Value as JsonValue;

use crate::{
    db::{WhereOperator, where_clause::WhereClause},
    schema::{QueryDefinition, SqlProjectionHint},
};

// Fixed seeds for deterministic hashing across process restarts.
// These are arbitrary constants — changing them invalidates all cached entries.
const SEED_K0: u64 = 0x5241_4953_454F_4E31; // "RAISEON1"
const SEED_K1: u64 = 0x4652_4149_5345_514C; // "FRAISEQL"
const SEED_K2: u64 = 0x4341_4348_454B_4559; // "CACHEKEY"
const SEED_K3: u64 = 0x5632_5F43_4143_4845; // "V2_CACHE"

/// Create a new hasher from the fixed-seed `RandomState`.
fn new_hasher() -> impl Hasher {
    RandomState::with_seeds(SEED_K0, SEED_K1, SEED_K2, SEED_K3).build_hasher()
}

/// Generate cache key for query result.
///
/// # Security Critical
///
/// **DIFFERENT VARIABLE VALUES MUST PRODUCE DIFFERENT KEYS** to prevent data
/// leakage between users. This function feeds the full query, variables, WHERE
/// clause, and schema version into a single-pass ahash for a fast, deterministic
/// `u64` key.
///
/// # Key Composition
///
/// The cache key is a single ahash pass over:
/// ```text
/// ahash(
///   query_bytes          +
///   hash(variables)      +   ← recursive, canonical key ordering
///   hash(WHERE_clause)   +   ← structural, not serde-dependent
///   schema_version_bytes
/// )
/// ```
///
/// This ensures:
/// - Same query + variables = same key (cache hit)
/// - Different variables = different key (security)
/// - Different WHERE clauses = different key (correctness)
/// - Schema changes = different key (validity)
///
/// # Arguments
///
/// * `query` - GraphQL query string
/// * `variables` - Query variables from GraphQL request (optional)
/// * `where_clause` - WHERE filter from auto-params (optional)
/// * `schema_version` - Schema hash from `CompiledSchema`
///
/// # Returns
///
/// A `u64` cache key suitable for use as a hash-map key.
///
/// # Security Examples
///
/// ```rust
/// use fraiseql_core::cache::generate_cache_key;
/// use serde_json::json;
///
/// let query = "query getUser($id: ID!) { user(id: $id) { name } }";
///
/// // Different users MUST get different cache keys
/// let alice_key = generate_cache_key(query, &json!({"id": "alice"}), None, "v1");
/// let bob_key = generate_cache_key(query, &json!({"id": "bob"}), None, "v1");
/// assert_ne!(alice_key, bob_key, "Security: different variables must produce different keys");
///
/// // Same user MUST get same key (determinism)
/// let alice_key2 = generate_cache_key(query, &json!({"id": "alice"}), None, "v1");
/// assert_eq!(alice_key, alice_key2, "Determinism: same inputs must produce same key");
/// ```
#[must_use]
pub fn generate_cache_key(
    query: &str,
    variables: &JsonValue,
    where_clause: Option<&WhereClause>,
    schema_version: &str,
) -> u64 {
    let mut h = new_hasher();

    // Domain-separate the four sections with unique tags so that, e.g.,
    // a query ending with "v1" and an empty schema_version can never
    // collide with a shorter query and schema_version = "v1".
    h.write(b"q:");
    h.write(query.as_bytes());

    h.write(b"\0v:");
    hash_json_value(&mut h, variables);

    h.write(b"\0w:");
    if let Some(wc) = where_clause {
        h.write_u8(1);
        hash_where_clause(&mut h, wc);
    } else {
        h.write_u8(0);
    }

    h.write(b"\0s:");
    h.write(schema_version.as_bytes());

    h.finish()
}

/// Fast cache key for a view query — **zero heap allocations**.
///
/// Hashes `view + where_clause + limit + offset + schema_version` directly
/// without constructing an intermediate `String` or `serde_json::Value`.
/// Use this instead of [`generate_cache_key`] in the cache adapter hot path.
///
/// Domain tag `"v:"` separates these keys from projection keys (`"p:"`) and
/// generic query keys (`"q:"`), preventing cross-path collisions.
///
/// # Arguments
///
/// * `view` - Database view / table name
/// * `where_clause` - Optional WHERE filter (e.g. from RLS injection)
/// * `limit` - Optional row limit
/// * `offset` - Optional row offset
/// * `schema_version` - Schema hash from `CompiledSchema::content_hash()`
#[must_use]
pub fn generate_view_query_key(
    view: &str,
    where_clause: Option<&WhereClause>,
    limit: Option<u32>,
    offset: Option<u32>,
    schema_version: &str,
) -> u64 {
    let mut h = new_hasher();
    h.write(b"v:");
    h.write(view.as_bytes());
    h.write(b"\0w:");
    if let Some(wc) = where_clause {
        h.write_u8(1);
        hash_where_clause(&mut h, wc);
    } else {
        h.write_u8(0);
    }
    h.write(b"\0l:");
    match limit {
        Some(l) => {
            h.write_u8(1);
            h.write_u32(l);
        },
        None => h.write_u8(0),
    }
    h.write(b"\0o:");
    match offset {
        Some(o) => {
            h.write_u8(1);
            h.write_u32(o);
        },
        None => h.write_u8(0),
    }
    h.write(b"\0s:");
    h.write(schema_version.as_bytes());
    h.finish()
}

/// Fast cache key for a projection query — **zero heap allocations**.
///
/// Like [`generate_view_query_key`] but also hashes the projection template.
/// Domain tag `"p:"` separates these keys from plain view keys.
///
/// # Arguments
///
/// * `view` - Database view / table name
/// * `projection` - Optional SQL projection hint (column subset)
/// * `where_clause` - Optional WHERE filter
/// * `limit` - Optional row limit
/// * `offset` - Optional row offset
/// * `schema_version` - Schema hash from `CompiledSchema::content_hash()`
#[must_use]
pub fn generate_projection_query_key(
    view: &str,
    projection: Option<&SqlProjectionHint>,
    where_clause: Option<&WhereClause>,
    limit: Option<u32>,
    offset: Option<u32>,
    schema_version: &str,
) -> u64 {
    let mut h = new_hasher();
    h.write(b"p:");
    h.write(view.as_bytes());
    h.write(b"\0j:");
    match projection {
        Some(p) => {
            h.write_u8(1);
            h.write(p.projection_template.as_bytes());
        },
        None => h.write_u8(0),
    }
    h.write(b"\0w:");
    if let Some(wc) = where_clause {
        h.write_u8(1);
        hash_where_clause(&mut h, wc);
    } else {
        h.write_u8(0);
    }
    h.write(b"\0l:");
    match limit {
        Some(l) => {
            h.write_u8(1);
            h.write_u32(l);
        },
        None => h.write_u8(0),
    }
    h.write(b"\0o:");
    match offset {
        Some(o) => {
            h.write_u8(1);
            h.write_u32(o);
        },
        None => h.write_u8(0),
    }
    h.write(b"\0s:");
    h.write(schema_version.as_bytes());
    h.finish()
}

/// Recursively hash a `serde_json::Value` into the given hasher.
///
/// Object keys are sorted before hashing so that insertion order does not
/// affect the output (critical for variable-order independence).
fn hash_json_value(h: &mut impl Hasher, value: &JsonValue) {
    // Write a type discriminant so that `null`, `false`, `0`, `""`, `[]`, and `{}`
    // all produce distinct hashes.
    match value {
        JsonValue::Null => h.write_u8(0),
        JsonValue::Bool(b) => {
            h.write_u8(1);
            b.hash(h);
        },
        JsonValue::Number(n) => {
            h.write_u8(2);
            // Use the canonical string form so that 1.0 and 1 hash identically
            // when serde represents them the same way.
            h.write(n.to_string().as_bytes());
        },
        JsonValue::String(s) => {
            h.write_u8(3);
            h.write(s.as_bytes());
        },
        JsonValue::Array(arr) => {
            h.write_u8(4);
            h.write_usize(arr.len());
            for item in arr {
                hash_json_value(h, item);
            }
        },
        JsonValue::Object(map) => {
            h.write_u8(5);
            h.write_usize(map.len());
            // Sort keys for canonical ordering.
            let mut keys: Vec<&String> = map.keys().collect();
            keys.sort_unstable();
            for key in keys {
                h.write(key.as_bytes());
                hash_json_value(h, &map[key]);
            }
        },
    }
}

/// Hash a `WhereClause` tree structurally.
///
/// Uses discriminant tags and recursion so that structurally different clauses
/// always produce different hash contributions.
fn hash_where_clause(h: &mut impl Hasher, clause: &WhereClause) {
    match clause {
        WhereClause::Field {
            path,
            operator,
            value,
        } => {
            h.write_u8(b'F');
            h.write_usize(path.len());
            for segment in path {
                h.write(segment.as_bytes());
                h.write_u8(0); // separator
            }
            hash_where_operator(h, operator);
            hash_json_value(h, value);
        },
        WhereClause::And(clauses) => {
            h.write_u8(b'A');
            h.write_usize(clauses.len());
            for c in clauses {
                hash_where_clause(h, c);
            }
        },
        WhereClause::Or(clauses) => {
            h.write_u8(b'O');
            h.write_usize(clauses.len());
            for c in clauses {
                hash_where_clause(h, c);
            }
        },
        WhereClause::Not(inner) => {
            h.write_u8(b'N');
            hash_where_clause(h, inner);
        },
        // WhereClause is #[non_exhaustive]; unknown variants get a distinct tag
        // plus their Debug representation as a conservative fallback.
        _ => {
            h.write_u8(b'?');
            h.write(format!("{clause:?}").as_bytes());
        },
    }
}

/// Hash a `WhereOperator` by its `Debug` representation.
///
/// `WhereOperator` is `#[non_exhaustive]` with 40+ variants (including
/// `Extended(ExtendedOperator)`). Using the `Debug` string is stable across
/// refactors and automatically covers new variants without maintenance.
/// Hash a `WhereOperator` without allocating.
///
/// Uses `std::mem::discriminant` for the variant tag (zero-allocation).
/// For the `Extended(op)` variant which carries data, also hashes the
/// Debug representation of the inner operator (rare path, acceptable allocation).
fn hash_where_operator(h: &mut impl Hasher, op: &WhereOperator) {
    // discriminant is a fixed-size hashable value — no allocation
    std::mem::discriminant(op).hash(h);

    // Extended operators carry inner data that affects the hash.
    // All other variants are fully distinguished by their discriminant.
    if let WhereOperator::Extended(inner) = op {
        // Rare path: Extended operators are uncommon. The Debug allocation
        // here is acceptable because it only triggers for rich-filter queries.
        let inner_str = format!("{inner:?}");
        h.write(inner_str.as_bytes());
    }
}

/// Extract accessed views from query definition.
///
/// We track which database views/tables a query accesses for view-based
/// cache invalidation. When a mutation modifies a view, we can invalidate
/// all cached queries that read from that view.
///
/// # Current Scope
///
/// Currently extracts only the primary SQL source from the query definition.
/// Does not analyze:
/// - JOIN clauses (requires compiled SQL)
/// - Resolver chains (requires runtime context)
/// - Nested queries (requires query analyzer)
///
/// # Future Enhancements
///
/// - Extract views from JOIN clauses in compiled SQL
/// - Extract views from resolver chains
/// - Support for custom resolver view tracking
/// - Entity-level tracking (extract IDs from results)
///
/// # Arguments
///
/// * `query_def` - The compiled query definition from schema
///
/// # Returns
///
/// List of view/table names accessed by this query
///
/// # Examples
///
/// ```rust
/// use fraiseql_core::cache::extract_accessed_views;
/// use fraiseql_core::schema::QueryDefinition;
///
/// let query_def = QueryDefinition::new("users", "User")
///     .returning_list()
///     .with_sql_source("v_user");
///
/// let views = extract_accessed_views(&query_def);
/// assert_eq!(views, vec!["v_user"]);
/// ```
#[must_use]
pub fn extract_accessed_views(query_def: &QueryDefinition) -> Vec<String> {
    let mut views = Vec::new();

    // Add primary SQL source
    if let Some(sql_source) = &query_def.sql_source {
        views.push(sql_source.clone());
    }

    // Add developer-declared secondary views (JOINs, nested queries, etc.)
    // Required for correct invalidation when a query reads from multiple views.
    views.extend(query_def.additional_views.iter().cloned());

    views
}

/// Verify cache key generation is deterministic.
///
/// Used in testing to ensure cache hits work correctly.
/// Same inputs must always produce the same key.
///
/// # Arguments
///
/// * `query` - GraphQL query string
/// * `variables` - Query variables
/// * `schema_version` - Schema version hash
///
/// # Returns
///
/// `true` if two sequential key generations produce identical keys
#[cfg(test)]
#[must_use]
pub fn verify_deterministic(query: &str, variables: &JsonValue, schema_version: &str) -> bool {
    let key1 = generate_cache_key(query, variables, None, schema_version);
    let key2 = generate_cache_key(query, variables, None, schema_version);
    key1 == key2
}

#[cfg(test)]
mod tests {
    use std::collections::{HashMap, HashSet};

    use indexmap::IndexMap;
    use serde_json::json;

    use super::*;
    use crate::schema::CursorType;

    // ========================================================================
    // Security Tests (CRITICAL)
    // ========================================================================

    #[test]
    fn test_different_variables_produce_different_keys() {
        // SECURITY CRITICAL: Different variables MUST produce different keys
        // to prevent User A from seeing User B's cached data
        let query = "query getUser($id: ID!) { user(id: $id) { name email } }";

        let key_alice = generate_cache_key(query, &json!({"id": "alice"}), None, "v1");
        let key_bob = generate_cache_key(query, &json!({"id": "bob"}), None, "v1");

        assert_ne!(
            key_alice, key_bob,
            "SECURITY: Different variables MUST produce different cache keys"
        );
    }

    #[test]
    fn test_different_variable_values_produce_different_keys() {
        let query = "query getUsers($limit: Int!) { users(limit: $limit) { id } }";

        let key_10 = generate_cache_key(query, &json!({"limit": 10}), None, "v1");
        let key_20 = generate_cache_key(query, &json!({"limit": 20}), None, "v1");

        assert_ne!(
            key_10, key_20,
            "SECURITY: Different variable values MUST produce different keys"
        );
    }

    #[test]
    fn test_empty_vs_non_empty_variables() {
        let query = "query { users { id } }";

        let key_empty = generate_cache_key(query, &json!({}), None, "v1");
        let key_with_vars = generate_cache_key(query, &json!({"limit": 10}), None, "v1");

        assert_ne!(
            key_empty, key_with_vars,
            "Empty variables must produce different key than non-empty"
        );
    }

    #[test]
    fn test_variable_order_independence() {
        // Object keys are sorted before hashing, so insertion order should
        // not affect the result. serde_json's default Map is BTreeMap (sorted),
        // but we sort explicitly in hash_json_value to be safe regardless.
        let query = "query($a: Int, $b: Int) { users { id } }";

        let key1 = generate_cache_key(query, &json!({"a": 1, "b": 2}), None, "v1");
        let key2 = generate_cache_key(query, &json!({"a": 1, "b": 2}), None, "v1");

        assert_eq!(key1, key2, "Same variables must produce same key");
    }

    // ========================================================================
    // Determinism Tests
    // ========================================================================

    #[test]
    fn test_cache_key_deterministic() {
        // Same inputs must always produce same output
        let query = "query { users { id } }";
        let vars = json!({"limit": 10});

        let key1 = generate_cache_key(query, &vars, None, "v1");
        let key2 = generate_cache_key(query, &vars, None, "v1");

        assert_eq!(key1, key2, "Cache keys must be deterministic");
    }

    #[test]
    fn test_verify_deterministic_helper() {
        assert!(
            verify_deterministic("query { users }", &json!({}), "v1"),
            "Helper should verify determinism"
        );
    }

    // ========================================================================
    // WHERE Clause Tests
    // ========================================================================

    #[test]
    fn test_different_where_clauses_produce_different_keys() {
        let query = "query { users { id } }";

        let where1 = WhereClause::Field {
            path:     vec!["email".to_string()],
            operator: WhereOperator::Eq,
            value:    json!("alice@example.com"),
        };

        let where2 = WhereClause::Field {
            path:     vec!["email".to_string()],
            operator: WhereOperator::Eq,
            value:    json!("bob@example.com"),
        };

        let key1 = generate_cache_key(query, &json!({}), Some(&where1), "v1");
        let key2 = generate_cache_key(query, &json!({}), Some(&where2), "v1");

        assert_ne!(key1, key2, "Different WHERE clauses must produce different keys");
    }

    #[test]
    fn test_different_where_operators_produce_different_keys() {
        let query = "query { users { id } }";

        let where_eq = WhereClause::Field {
            path:     vec!["age".to_string()],
            operator: WhereOperator::Eq,
            value:    json!(30),
        };

        let where_gt = WhereClause::Field {
            path:     vec!["age".to_string()],
            operator: WhereOperator::Gt,
            value:    json!(30),
        };

        let key_eq = generate_cache_key(query, &json!({}), Some(&where_eq), "v1");
        let key_gt = generate_cache_key(query, &json!({}), Some(&where_gt), "v1");

        assert_ne!(key_eq, key_gt, "Different operators must produce different keys");
    }

    #[test]
    fn test_with_and_without_where_clause() {
        let query = "query { users { id } }";

        let where_clause = WhereClause::Field {
            path:     vec!["active".to_string()],
            operator: WhereOperator::Eq,
            value:    json!(true),
        };

        let key_without = generate_cache_key(query, &json!({}), None, "v1");
        let key_with = generate_cache_key(query, &json!({}), Some(&where_clause), "v1");

        assert_ne!(key_without, key_with, "Presence of WHERE clause must change key");
    }

    #[test]
    fn test_complex_where_clause() {
        let query = "query { users { id } }";

        let where_clause = WhereClause::And(vec![
            WhereClause::Field {
                path:     vec!["age".to_string()],
                operator: WhereOperator::Gte,
                value:    json!(18),
            },
            WhereClause::Field {
                path:     vec!["active".to_string()],
                operator: WhereOperator::Eq,
                value:    json!(true),
            },
        ]);

        // Should not panic; produces a valid u64.
        let _key = generate_cache_key(query, &json!({}), Some(&where_clause), "v1");
    }

    // ========================================================================
    // Schema Version Tests
    // ========================================================================

    #[test]
    fn test_different_schema_versions_produce_different_keys() {
        let query = "query { users { id } }";

        let key_v1 = generate_cache_key(query, &json!({}), None, "v1");
        let key_v2 = generate_cache_key(query, &json!({}), None, "v2");

        assert_ne!(key_v1, key_v2, "Different schema versions must produce different keys");
    }

    #[test]
    fn test_schema_version_invalidation() {
        // When schema changes, all cache keys change (automatic invalidation)
        let query = "query { users { id } }";

        let old_schema = "abc123";
        let new_schema = "def456";

        let key_old = generate_cache_key(query, &json!({}), None, old_schema);
        let key_new = generate_cache_key(query, &json!({}), None, new_schema);

        assert_ne!(key_old, key_new, "Schema changes should invalidate cache");
    }

    // ========================================================================
    // Collision Avoidance Test
    // ========================================================================

    #[test]
    fn test_no_collisions_in_sample() {
        // Generate a sample of cache keys from varied inputs and verify
        // that no two distinct inputs produce the same u64.
        let mut keys = HashSet::new();
        let mut count = 0u32;

        let queries = [
            "query { users { id } }",
            "query { posts { id } }",
            "query { users { id name } }",
            "query getUser($id: ID!) { user(id: $id) { name } }",
            "",
        ];
        let variable_sets: &[JsonValue] = &[
            json!({}),
            json!(null),
            json!({"id": 1}),
            json!({"id": 2}),
            json!({"id": "alice"}),
            json!({"limit": 10, "offset": 0}),
            json!({"filter": {"active": true}}),
        ];
        let schema_versions = ["v1", "v2", "abc123"];

        for query in &queries {
            for vars in variable_sets {
                for sv in &schema_versions {
                    let key = generate_cache_key(query, vars, None, sv);
                    keys.insert(key);
                    count += 1;
                }
            }
        }

        assert_eq!(
            keys.len(),
            count as usize,
            "Collision detected among {count} sample cache keys"
        );
    }

    // ========================================================================
    // Extract Views Tests
    // ========================================================================

    #[test]
    fn test_extract_accessed_views_with_sql_source() {
        use crate::schema::AutoParams;

        let query_def = QueryDefinition {
            name:                "users".to_string(),
            return_type:         "User".to_string(),
            returns_list:        true,
            nullable:            false,
            arguments:           vec![],
            sql_source:          Some("v_user".to_string()),
            description:         None,
            auto_params:         AutoParams {
                has_where:    true,
                has_order_by: false,
                has_limit:    true,
                has_offset:   false,
            },
            deprecation:         None,
            jsonb_column:        "data".to_string(),
            relay:               false,
            relay_cursor_column: None,
            relay_cursor_type:   CursorType::default(),
            inject_params:       IndexMap::default(),
            cache_ttl_seconds:   None,
            additional_views:    vec![],
            requires_role:       None,
            rest_path:           None,
            rest_method:         None,
            native_columns:      HashMap::new(),
        };

        let views = extract_accessed_views(&query_def);
        assert_eq!(views, vec!["v_user"]);
    }

    #[test]
    fn test_extract_accessed_views_without_sql_source() {
        use crate::schema::AutoParams;

        let query_def = QueryDefinition {
            name:                "customQuery".to_string(),
            return_type:         "Custom".to_string(),
            returns_list:        false,
            nullable:            false,
            arguments:           vec![],
            sql_source:          None, // No SQL source (custom resolver)
            description:         None,
            auto_params:         AutoParams {
                has_where:    false,
                has_order_by: false,
                has_limit:    false,
                has_offset:   false,
            },
            deprecation:         None,
            jsonb_column:        "data".to_string(),
            relay:               false,
            relay_cursor_column: None,
            relay_cursor_type:   CursorType::default(),
            inject_params:       IndexMap::default(),
            cache_ttl_seconds:   None,
            additional_views:    vec![],
            requires_role:       None,
            rest_path:           None,
            rest_method:         None,
            native_columns:      HashMap::new(),
        };

        let views = extract_accessed_views(&query_def);
        assert_eq!(views, Vec::<String>::new());
    }

    #[test]
    fn test_extract_accessed_views_with_additional_views() {
        use crate::schema::AutoParams;

        let query_def = QueryDefinition {
            name:                "usersWithPosts".to_string(),
            return_type:         "UserWithPosts".to_string(),
            returns_list:        true,
            nullable:            false,
            arguments:           vec![],
            sql_source:          Some("v_user_with_posts".to_string()),
            description:         None,
            auto_params:         AutoParams::default(),
            deprecation:         None,
            jsonb_column:        "data".to_string(),
            relay:               false,
            relay_cursor_column: None,
            relay_cursor_type:   CursorType::default(),
            inject_params:       IndexMap::default(),
            cache_ttl_seconds:   None,
            additional_views:    vec!["v_post".to_string(), "v_tag".to_string()],
            requires_role:       None,
            rest_path:           None,
            rest_method:         None,
            native_columns:      HashMap::new(),
        };

        let views = extract_accessed_views(&query_def);
        assert_eq!(views, vec!["v_user_with_posts", "v_post", "v_tag"]);
    }

    // ========================================================================
    // Edge Case Tests
    // ========================================================================

    #[test]
    fn test_empty_query_string() {
        // Should not panic; produces a valid u64.
        let _key = generate_cache_key("", &json!({}), None, "v1");
    }

    #[test]
    fn test_null_variables() {
        // Should not panic; produces a valid u64.
        let _key = generate_cache_key("query { users }", &json!(null), None, "v1");
    }

    #[test]
    fn test_large_variable_object() {
        let large_vars = json!({
            "filter": {
                "age": 30,
                "active": true,
                "tags": ["rust", "graphql", "database"],
                "metadata": {
                    "created_after": "2024-01-01",
                    "updated_before": "2024-12-31"
                }
            }
        });

        // Should not panic; produces a valid u64.
        let _key = generate_cache_key("query { users }", &large_vars, None, "v1");
    }

    #[test]
    fn test_special_characters_in_query() {
        let query = r#"query { user(email: "test@example.com") { name } }"#;
        // Should not panic; produces a valid u64.
        let _key = generate_cache_key(query, &json!({}), None, "v1");
    }
}