cel-rust-wasm/src/lib.rs

use std::collections::HashMap;
use std::mem;
use std::slice;
use std::str;

use cel::{Context, Program, Value};
use serde_json;

#[unsafe(no_mangle)]
pub extern "C" fn allocation(n: usize) -> *mut u8 {
    mem::ManuallyDrop::new(Vec::with_capacity(n)).as_mut_ptr()
}

#[unsafe(no_mangle)]
pub unsafe extern "C" fn evaluate(s: *const u8) -> *mut u8 {
    unsafe {
        let length = u32::from_le_bytes(*(s as *const [u8; 4])) as usize;
        let input = slice::from_raw_parts(s.offset(4), length);
        let output = evaluate_buffers(input);
        mem::ManuallyDrop::new(output).as_mut_ptr()
    }
}

fn evaluate_buffers(input: &[u8]) -> Vec<u8> {
    let contents = str::from_utf8(input).unwrap();
    let result = evaluate_cel_with_context(contents);
    let success = result.is_ok();
    let message = result.unwrap_or_else(|e| e);
    let len = message.len();
    let mut buffer = Vec::with_capacity(len + 8);
    buffer.push(if success { 1 } else { 0 });
    buffer.extend(vec![0; 3]);
    buffer.extend_from_slice(&(len as u32).to_le_bytes());
    buffer.extend_from_slice(message.as_bytes());
    buffer
}

fn json_to_cel_value(json_value: &serde_json::Value) -> Value {
    match json_value {
        serde_json::Value::Null => Value::Null,
        serde_json::Value::Bool(b) => Value::Bool(*b),
        serde_json::Value::Number(n) => {
            if let Some(i) = n.as_i64() {
                Value::Int(i)
            } else if let Some(f) = n.as_f64() {
                Value::Float(f)
            } else {
                Value::Null
            }
        }
        serde_json::Value::String(s) => Value::String(s.clone().into()),
        serde_json::Value::Array(arr) => {
            let cel_vec: Vec<Value> = arr.iter().map(json_to_cel_value).collect();
            Value::List(cel_vec.into())
        }
        serde_json::Value::Object(obj) => {
            let mut cel_map = HashMap::new();
            for (key, value) in obj.iter() {
                cel_map.insert(key.clone(), json_to_cel_value(value));
            }
            Value::Map(cel_map.into())
        }
    }
}

fn evaluate_cel_with_context(content: &str) -> Result<String, String> {
    // Split the input to get expression and context
    let parts: Vec<&str> = content.split("\n---CONTEXT---\n").collect();
    let expression = parts[0].trim();
    let context_json = if parts.len() > 1 {
        parts[1].trim()
    } else {
        "{}"
    };

    // Parse the CEL expression
    let program = match Program::compile(expression) {
        Ok(prog) => prog,
        Err(e) => return Err(format!("Compilation error: {}", e)),
    };

    // Create context and add JSON values
    let mut context = Context::default();

    // Parse JSON context if provided and not empty
    if !context_json.is_empty() && context_json != "{}" {
        match serde_json::from_str::<serde_json::Value>(context_json) {
            Ok(json_value) => {
                if let serde_json::Value::Object(obj) = json_value {
                    for (key, value) in obj.iter() {
                        let cel_value = json_to_cel_value(value);
                        context
                            .add_variable(key, cel_value)
                            .map_err(|e| format!("Context error: {}", e))?;
                    }
                } else {
                    return Err("JSON context must be an object".to_string());
                }
            }
            Err(e) => return Err(format!("JSON parsing error: {}", e)),
        }
    }

    // Execute the program
    match program.execute(&context) {
        Ok(value) => Ok(format!("{:?}", value)),
        Err(e) => Err(format!("Execution error: {}", e)),
    }
}