akar-function 0.1.2

Function registry and expression evaluation for the Akar embedded graph database
Documentation 
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use crate::registry::*;
use crate::scalar::comparison::compare_values;
use akar_common::types::Value;

// ==================== Utility ====================

pub(crate) fn evaluate_utility(op: UtilityOp, args: &[Value]) -> Result<Value, String> {
    match op {
        UtilityOp::Coalesce | UtilityOp::IfNull => {
            for arg in args {
                if !matches!(arg, Value::Null) {
                    return Ok(arg.clone());
                }
            }
            Ok(Value::Null)
        }
        UtilityOp::TypeOf => {
            if args.is_empty() {
                return Ok(Value::String("NULL".into()));
            }
            Ok(Value::String(format!("{:?}", args[0].logical_type())))
        }
        UtilityOp::NullIf => {
            if args.len() < 2 {
                return Err("NULLIF requires 2 arguments".into());
            }
            if args[0] == args[1] {
                Ok(Value::Null)
            } else {
                Ok(args[0].clone())
            }
        }
        UtilityOp::Size => {
            if args.is_empty() {
                return Err("SIZE requires 1 argument".into());
            }
            match &args[0] {
                Value::List(v) => Ok(Value::Int64(v.len() as i64)),
                Value::String(s) => Ok(Value::Int64(s.len() as i64)),
                Value::Map(v) => Ok(Value::Int64(v.len() as i64)),
                Value::Null => Ok(Value::Null),
                _ => Err(format!("SIZE does not support type {:?}", args[0].logical_type())),
            }
        }
        UtilityOp::Error => {
            if args.is_empty() {
                return Err("ERROR requires 1 argument".into());
            }
            match &args[0] {
                Value::String(s) => Err(s.clone()),
                Value::Null => Err("user-triggered error".into()),
                other => Err(format!("{:?}", other)),
            }
        }
        UtilityOp::PgIsReady => Ok(Value::Bool(true)),
        UtilityOp::Greatest => {
            if args.is_empty() {
                return Err("GREATEST requires at least one argument".into());
            }
            let mut result = Value::Null;
            for arg in args {
                if matches!(arg, Value::Null) {
                    continue;
                }
                if matches!(result, Value::Null) {
                    result = arg.clone();
                } else if compare_values(arg, &result)?.is_gt() {
                    result = arg.clone();
                }
            }
            Ok(result)
        }
        UtilityOp::Least => {
            if args.is_empty() {
                return Err("LEAST requires at least one argument".into());
            }
            let mut result = Value::Null;
            for arg in args {
                if matches!(arg, Value::Null) {
                    continue;
                }
                if matches!(result, Value::Null) {
                    result = arg.clone();
                } else if compare_values(arg, &result)?.is_lt() {
                    result = arg.clone();
                }
            }
            Ok(result)
        }
        UtilityOp::ConstantOrNull => {
            if args.len() < 2 {
                return Err("CONSTANT_OR_NULL requires 2 arguments".into());
            }
            if matches!(args[0], Value::Null) || matches!(args[1], Value::Null) {
                Ok(Value::Null)
            } else {
                Ok(args[0].clone())
            }
        }
    }
}