celers-protocol 0.2.0

//! Lazy deserialization for improved performance
//!
//! This module provides lazy deserialization capabilities where message bodies
//! and other large data structures are only deserialized when actually accessed.
//! This is particularly useful for:
//! - Large message bodies that may not always be needed
//! - Message routing/filtering scenarios where only headers are needed
//! - High-throughput scenarios where deserialization overhead matters
//!
//! # Examples
//!
//! ```
//! use celers_protocol::lazy::LazyMessage;
//! use uuid::Uuid;
//!
//! let task_id = Uuid::new_v4();
//! let json = format!(r#"{{"headers":{{"task":"tasks.add","id":"{}","lang":"rust"}},"properties":{{"delivery_mode":2}},"body":"e30=","content-type":"application/json","content-encoding":"utf-8"}}"#, task_id);
//!
//! // Parse only the headers initially
//! let msg = LazyMessage::from_json(json.as_bytes()).unwrap();
//!
//! // Headers are immediately available
//! assert_eq!(msg.task_name(), "tasks.add");
//!
//! // Body is only deserialized when accessed
//! let body = msg.body().unwrap();
//! ```

use serde::Deserialize;
use std::sync::{Arc, RwLock};
use uuid::Uuid;

/// Error type for lazy deserialization
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum LazyError {
    /// Deserialization failed
    DeserializationFailed(String),
    /// Invalid JSON
    InvalidJson(String),
    /// Body not available
    BodyNotAvailable,
}

impl std::fmt::Display for LazyError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            LazyError::DeserializationFailed(msg) => write!(f, "Deserialization failed: {}", msg),
            LazyError::InvalidJson(msg) => write!(f, "Invalid JSON: {}", msg),
            LazyError::BodyNotAvailable => write!(f, "Message body not available"),
        }
    }
}

impl std::error::Error for LazyError {}

/// Lazy-deserialized message body
///
/// The body is stored in raw form and only deserialized when accessed.
/// Uses interior mutability with `RwLock` to cache the deserialized value.
#[derive(Debug, Clone)]
pub struct LazyBody {
    /// Raw body bytes
    raw: Vec<u8>,
    /// Cached deserialized body
    cached: Arc<RwLock<Option<Vec<u8>>>>,
}

impl LazyBody {
    /// Create a new lazy body from raw bytes
    pub fn new(raw: Vec<u8>) -> Self {
        Self {
            raw,
            cached: Arc::new(RwLock::new(None)),
        }
    }

    /// Get the raw bytes without deserialization
    pub fn raw_bytes(&self) -> &[u8] {
        &self.raw
    }

    /// Get the body size in bytes
    #[inline]
    pub fn size(&self) -> usize {
        self.raw.len()
    }

    /// Deserialize the body (base64 decode)
    pub fn deserialize(&self) -> Result<Vec<u8>, LazyError> {
        // Check cache first
        {
            let cached = self.cached.read().expect("lock should not be poisoned");
            if let Some(body) = cached.as_ref() {
                return Ok(body.clone());
            }
        }

        // Deserialize and cache
        let decoded = base64::Engine::decode(&base64::engine::general_purpose::STANDARD, &self.raw)
            .map_err(|e| LazyError::DeserializationFailed(e.to_string()))?;

        let mut cached = self.cached.write().expect("lock should not be poisoned");
        *cached = Some(decoded.clone());

        Ok(decoded)
    }

    /// Check if body is already deserialized
    pub fn is_cached(&self) -> bool {
        self.cached
            .read()
            .expect("lock should not be poisoned")
            .is_some()
    }
}

/// Lazy-deserialized message
///
/// Headers and properties are eagerly deserialized (they're small),
/// but the body is lazily deserialized only when accessed.
#[derive(Debug, Clone)]
pub struct LazyMessage {
    /// Message headers (eagerly deserialized)
    pub headers: crate::MessageHeaders,

    /// Message properties (eagerly deserialized)
    pub properties: crate::MessageProperties,

    /// Lazy body
    body: LazyBody,

    /// Content type
    pub content_type: String,

    /// Content encoding
    pub content_encoding: String,
}

impl LazyMessage {
    /// Create a lazy message from JSON bytes
    ///
    /// This performs minimal deserialization - only headers and properties
    /// are parsed. The body remains in raw form until accessed.
    pub fn from_json(data: &[u8]) -> Result<Self, LazyError> {
        #[derive(Deserialize)]
        struct LazyMessageHelper {
            headers: crate::MessageHeaders,
            properties: crate::MessageProperties,
            #[serde(with = "serde_bytes_helper")]
            body: Vec<u8>,
            #[serde(rename = "content-type")]
            content_type: String,
            #[serde(rename = "content-encoding")]
            content_encoding: String,
        }

        let helper: LazyMessageHelper =
            serde_json::from_slice(data).map_err(|e| LazyError::InvalidJson(e.to_string()))?;

        Ok(Self {
            headers: helper.headers,
            properties: helper.properties,
            body: LazyBody::new(helper.body),
            content_type: helper.content_type,
            content_encoding: helper.content_encoding,
        })
    }

    /// Get the task ID
    pub fn task_id(&self) -> Uuid {
        self.headers.id
    }

    /// Get the task name
    pub fn task_name(&self) -> &str {
        &self.headers.task
    }

    /// Get the body size without deserializing
    pub fn body_size(&self) -> usize {
        self.body.size()
    }

    /// Check if body is already deserialized
    pub fn is_body_cached(&self) -> bool {
        self.body.is_cached()
    }

    /// Get raw body bytes without deserializing
    pub fn raw_body(&self) -> &[u8] {
        self.body.raw_bytes()
    }

    /// Get deserialized body (triggers deserialization if not cached)
    pub fn body(&self) -> Result<Vec<u8>, LazyError> {
        self.body.deserialize()
    }

    /// Check if message has ETA
    pub fn has_eta(&self) -> bool {
        self.headers.eta.is_some()
    }

    /// Check if message has expiration
    pub fn has_expires(&self) -> bool {
        self.headers.expires.is_some()
    }

    /// Check if message has parent
    pub fn has_parent(&self) -> bool {
        self.headers.parent_id.is_some()
    }

    /// Check if message has root
    pub fn has_root(&self) -> bool {
        self.headers.root_id.is_some()
    }

    /// Check if message has group
    pub fn has_group(&self) -> bool {
        self.headers.group.is_some()
    }

    /// Convert to fully deserialized message
    pub fn into_message(self) -> Result<crate::Message, LazyError> {
        Ok(crate::Message {
            headers: self.headers,
            properties: self.properties,
            body: self.body.deserialize()?,
            content_type: self.content_type,
            content_encoding: self.content_encoding,
        })
    }
}

// Helper for deserializing body as raw bytes
mod serde_bytes_helper {
    use serde::{Deserialize, Deserializer};

    pub fn deserialize<'de, D>(deserializer: D) -> Result<Vec<u8>, D::Error>
    where
        D: Deserializer<'de>,
    {
        let s = String::deserialize(deserializer)?;
        Ok(s.into_bytes())
    }
}

/// Lazy task arguments
///
/// Defers parsing of task arguments until they're actually needed.
#[derive(Debug, Clone)]
pub struct LazyTaskArgs {
    /// Raw JSON bytes
    raw: Vec<u8>,
    /// Cached parsed arguments
    cached: Arc<RwLock<Option<crate::TaskArgs>>>,
}

impl LazyTaskArgs {
    /// Create lazy task arguments from raw JSON
    pub fn new(raw: Vec<u8>) -> Self {
        Self {
            raw,
            cached: Arc::new(RwLock::new(None)),
        }
    }

    /// Get raw bytes
    pub fn raw_bytes(&self) -> &[u8] {
        &self.raw
    }

    /// Parse task arguments (cached)
    pub fn parse(&self) -> Result<crate::TaskArgs, LazyError> {
        // Check cache
        {
            let cached = self.cached.read().expect("lock should not be poisoned");
            if let Some(args) = cached.as_ref() {
                return Ok(args.clone());
            }
        }

        // Parse and cache
        let args: crate::TaskArgs = serde_json::from_slice(&self.raw)
            .map_err(|e| LazyError::DeserializationFailed(e.to_string()))?;

        let mut cached = self.cached.write().expect("lock should not be poisoned");
        *cached = Some(args.clone());

        Ok(args)
    }

    /// Check if arguments are cached
    pub fn is_cached(&self) -> bool {
        self.cached
            .read()
            .expect("lock should not be poisoned")
            .is_some()
    }
}

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

    #[test]
    fn test_lazy_body() {
        let raw = b"dGVzdCBkYXRh"; // base64 "test data"
        let body = LazyBody::new(raw.to_vec());

        assert_eq!(body.size(), raw.len());
        assert!(!body.is_cached());

        let decoded = body.deserialize().unwrap();
        assert_eq!(decoded, b"test data");
        assert!(body.is_cached());
    }

    #[test]
    fn test_lazy_message_from_json() {
        let task_id = Uuid::new_v4();
        let json = format!(
            r#"{{"headers":{{"task":"tasks.add","id":"{}","lang":"rust"}},"properties":{{"delivery_mode":2}},"body":"e30=","content-type":"application/json","content-encoding":"utf-8"}}"#,
            task_id
        );

        let msg = LazyMessage::from_json(json.as_bytes()).unwrap();

        assert_eq!(msg.task_name(), "tasks.add");
        assert_eq!(msg.task_id(), task_id);
        assert!(!msg.is_body_cached());

        let _body = msg.body().unwrap();
        assert!(msg.is_body_cached());
    }

    #[test]
    fn test_lazy_message_predicates() {
        let task_id = Uuid::new_v4();
        let json = format!(
            r#"{{"headers":{{"task":"tasks.test","id":"{}","lang":"rust","eta":"2024-12-31T23:59:59Z"}},"properties":{{"delivery_mode":2}},"body":"e30=","content-type":"application/json","content-encoding":"utf-8"}}"#,
            task_id
        );

        let msg = LazyMessage::from_json(json.as_bytes()).unwrap();

        assert!(msg.has_eta());
        assert!(!msg.has_expires());
        assert!(!msg.has_parent());
    }

    #[test]
    fn test_lazy_message_body_size() {
        let task_id = Uuid::new_v4();
        let json = format!(
            r#"{{"headers":{{"task":"tasks.test","id":"{}","lang":"rust"}},"properties":{{"delivery_mode":2}},"body":"dGVzdA==","content-type":"application/json","content-encoding":"utf-8"}}"#,
            task_id
        );

        let msg = LazyMessage::from_json(json.as_bytes()).unwrap();
        assert!(msg.body_size() > 0);
    }

    #[test]
    fn test_lazy_task_args() {
        let json = r#"{"args":[1,2,3],"kwargs":{"key":"value"}}"#;
        let lazy_args = LazyTaskArgs::new(json.as_bytes().to_vec());

        assert!(!lazy_args.is_cached());

        let args = lazy_args.parse().unwrap();
        assert_eq!(args.args.len(), 3);
        assert_eq!(args.kwargs.get("key").unwrap(), "value");

        assert!(lazy_args.is_cached());
    }

    #[test]
    fn test_lazy_error_display() {
        let err = LazyError::DeserializationFailed("test error".to_string());
        assert_eq!(err.to_string(), "Deserialization failed: test error");

        let err = LazyError::InvalidJson("bad json".to_string());
        assert_eq!(err.to_string(), "Invalid JSON: bad json");

        let err = LazyError::BodyNotAvailable;
        assert_eq!(err.to_string(), "Message body not available");
    }

    #[test]
    fn test_lazy_message_into_message() {
        let task_id = Uuid::new_v4();
        let json = format!(
            r#"{{"headers":{{"task":"tasks.test","id":"{}","lang":"rust"}},"properties":{{"delivery_mode":2}},"body":"dGVzdA==","content-type":"application/json","content-encoding":"utf-8"}}"#,
            task_id
        );

        let lazy_msg = LazyMessage::from_json(json.as_bytes()).unwrap();
        let msg = lazy_msg.into_message().unwrap();

        assert_eq!(msg.headers.task, "tasks.test");
        assert_eq!(msg.headers.id, task_id);
    }
}