zen/core/engine/src/lib.rs

//! # ZEN Engine
//!
//! ZEN Engine is business-friendly Open-Source Business Rules Engine (BRE) which executes decision
//! models according to the GoRules JSON Decision Model (JDM) standard. It's written in Rust and
//! provides native bindings for NodeJS and Python.
//!
//! # Usage
//!
//! To execute a simple decision using a Noop (default) loader you can use the code below.
//!
//! ```rust
//! use serde_json::json;
//! use zen_engine::DecisionEngine;
//! use zen_engine::model::DecisionContent;
//!
//! async fn evaluate() {
//!     let decision_content: DecisionContent = serde_json::from_str(include_str!("jdm_graph.json")).unwrap();
//!     let engine = DecisionEngine::default();
//!     let decision = engine.create_decision(decision_content.into());
//!
//!     let result = decision.evaluate(&json!({ "input": 12 })).await;
//! }
//! ```
//!
//! Alternatively, you may create decision indirectly without constructing the engine utilising
//! `Decision::from` function.
//!
//! # Loaders
//!
//! For more advanced use cases where you want to load multiple decisions and utilise graphs you
//! may use one of the following pre-made loaders:
//! - FilesystemLoader - with a given path as a root it tries to load a decision based on relative path
//! - MemoryLoader - works as a HashMap (key-value store)
//! - ClosureLoader - allows for definition of simple async callback function which takes key as a parameter
//! and returns an `Arc<DecisionContent>` instance
//! - NoopLoader - (default) fails to load decision, allows for usage of create_decision
//! (mostly existing for streamlining API across languages)
//!
//! ## Filesystem loader
//!
//! Assuming that you have a folder with decision models (.json files) which is located under /app/decisions,
//! you may use FilesystemLoader in the following way:
//!
//! ```rust
//! use serde_json::json;
//! use zen_engine::DecisionEngine;
//! use zen_engine::loader::{FilesystemLoader, FilesystemLoaderOptions};
//!
//! async fn evaluate() {
//!     let engine = DecisionEngine::new(FilesystemLoader::new(FilesystemLoaderOptions {
//!         root: "/app/decisions"
//!     }));
//!     
//!     let context = json!({ "customer": { "joinedAt": "2022-01-01" } });
//!     // If you plan on using it multiple times, you may cache JDM for minor performance gains
//!     // In case of bindings (in other languages, this increase is much greater)
//!     {
//!         let promotion_decision = engine.get_decision("commercial/promotion.json").await.unwrap();
//!         let result = promotion_decision.evaluate(&context).await.unwrap();
//!     }
//!     
//!     // Or on demand
//!     {
//!         let result = engine.evaluate("commercial/promotion.json", &context).await.unwrap();
//!     }
//! }
//!
//!
//! ```
//!
//! ## Custom loader
//! You may create a custom loader for zen engine by implementing `DecisionLoader` trait.
//! Here's an example of how MemoryLoader has been implemented.
//! ```rust
//! use std::collections::HashMap;
//! use std::sync::{Arc, RwLock};
//! use zen_engine::loader::{DecisionLoader, LoaderError, LoaderResponse};
//! use zen_engine::model::DecisionContent;
//!
//! #[derive(Debug, Default)]
//! pub struct MemoryLoader {
//!     memory_refs: RwLock<HashMap<String, Arc<DecisionContent>>>,
//! }
//!
//! impl MemoryLoader {
//!     pub fn add<K, D>(&self, key: K, content: D)
//!         where
//!             K: Into<String>,
//!             D: Into<DecisionContent>,
//!     {
//!         let mut mref = self.memory_refs.write().unwrap();
//!         mref.insert(key.into(), Arc::new(content.into()));
//!     }
//!
//!     pub fn get<K>(&self, key: K) -> Option<Arc<DecisionContent>>
//!         where
//!             K: AsRef<str>,
//!     {
//!         let mref = self.memory_refs.read().unwrap();
//!         mref.get(key.as_ref()).map(|r| r.clone())
//!     }
//!
//!     pub fn remove<K>(&self, key: K) -> bool
//!         where
//!             K: AsRef<str>,
//!     {
//!         let mut mref = self.memory_refs.write().unwrap();
//!         mref.remove(key.as_ref()).is_some()
//!     }
//! }
//!
//! impl DecisionLoader for MemoryLoader {
//! fn load<'a>(&'a self, key: &'a str) -> impl Future<Output = LoaderResponse> + 'a {
//!     async move {
//!         self.get(&key)
//!             .ok_or_else(|| LoaderError::NotFound(key.to_string()).into())
//!     }
//! }
//! ```

#![forbid(unsafe_code)]
#![deny(clippy::unwrap_used)]
#![allow(clippy::module_inception)]

mod config;
mod decision;
mod decision_graph;
mod engine;
pub mod error;
pub mod loader;
pub mod model;
pub mod nodes;
pub mod policy;
pub mod workspace;

pub const ENGINE_VERSION: &str = env!("CARGO_PKG_VERSION");

pub use config::ZEN_CONFIG;
pub use decision::Decision;
pub use decision_graph::{
    DecisionGraphResponse, DecisionGraphTrace, DecisionGraphValidationError, EvaluationTrace,
};
pub use engine::{
    DecisionEngine, EvaluationOptions, EvaluationSerializedOptions, EvaluationTraceKind,
};
pub use error::{CompileFailure, ContentKindError, EvaluationError};
pub use workspace::Workspace;
pub use zen_expression::Variable;