elusion 8.3.0

Elusion is a modern DataFrame / Data Engineering / Data Analysis library that combines the familiarity of DataFrame operations (like those in PySpark, Pandas, and Polars) with the power of SQL query building. It provides flexible query construction without enforcing strict operation ordering, enabling developers to write intuitive and maintainable data transformations.
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use crate::custom_error::cust_error::{ElusionError, ElusionResult};

/// Resolves a value that might be an env var name or a literal string.
/// If the value matches an existing env var, returns that.
/// Otherwise returns the value as-is (literal string).
/// Checks system env vars first, then .env file via dotenvy.
pub fn resolve_env_value(value: &str) -> ElusionResult<String> {
    // Load .env file if present - dotenvy is silent if .env doesn't exist
    let _ = dotenvy::dotenv();

    // Try system env var first
    match std::env::var(value) {
        Ok(resolved) => {
            println!("🔑 Resolved env var: {}", value);
            Ok(resolved)
        }
        Err(_) => {
            // Not an env var - treat as literal value
            Ok(value.to_string())
        }
    }
}

/// Resolve and fail fast if value is empty after resolution
pub fn resolve_required(key: &str, value: &str) -> ElusionResult<String> {
    let resolved = resolve_env_value(value)?;
    if resolved.trim().is_empty() {
        return Err(ElusionError::Custom(format!(
            "❌ Required config value '{}' is empty. Set it as an env var or in your .env file.",
            key
        )));
    }
    Ok(resolved)
}

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

    #[test]
    fn test_literal_value_returned_as_is() {
        let result = resolve_env_value("some_literal_value").unwrap();
        assert_eq!(result, "some_literal_value");
    }

    #[test]
    fn test_env_var_resolved() {
        std::env::set_var("TEST_ELUSION_KEY", "my_secret_value");
        let result = resolve_env_value("TEST_ELUSION_KEY").unwrap();
        assert_eq!(result, "my_secret_value");
        std::env::remove_var("TEST_ELUSION_KEY");
    }

    #[test]
    fn test_required_fails_on_empty_string() {
        let result = resolve_required("my_key", "");
        assert!(result.is_err());
    }

    #[test]
    fn test_required_returns_value_when_set() {
        std::env::set_var("TEST_REQUIRED_KEY", "real_value");
        let result = resolve_required("TEST_REQUIRED_KEY", "TEST_REQUIRED_KEY").unwrap();
        assert_eq!(result, "real_value");
        std::env::remove_var("TEST_REQUIRED_KEY");
    }
}