fosk 0.2.0

In-memory SQL-like query engine and lightweight data store for testing and prototyping.
Documentation 
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use serde_json::Value;

use crate::{
    JsonPrimitive,
    parser::{
        aggregators_helper::{Accumulator, AggregateImpl},
        analyzer::{AnalysisContext, AnalyzerError},
        ast::Function,
    },
};

pub struct SumImpl;
impl AggregateImpl for SumImpl {
    fn name(&self) -> &'static str {
        "sum"
    }
    fn infer_type(
        &self,
        fun: &Function,
        ctx: &AnalysisContext,
    ) -> Result<(JsonPrimitive, bool), AnalyzerError> {
        // Reuse your analyzer logic: only numeric allowed; nullable true.
        if let Some(arg) = fun.args.first() {
            let (t, _n) = crate::parser::analyzer::TypeInference::infer_scalar(arg, ctx)?;
            match t {
                JsonPrimitive::Int => Ok((JsonPrimitive::Int, true)),
                JsonPrimitive::Float => Ok((JsonPrimitive::Float, true)),
                other => Err(AnalyzerError::FunctionArgMismatch {
                    name: fun.name.clone(),
                    expected: "numeric".into(),
                    got: vec![other],
                }),
            }
        } else {
            Err(AnalyzerError::FunctionArgMismatch {
                name: fun.name.clone(),
                expected: "SUM(arg)".into(),
                got: vec![],
            })
        }
    }
    fn create_accumulator(&self) -> Box<dyn Accumulator> {
        Box::new(SumAcc::Empty)
    }
}

// Track the concrete numeric kind seen first.
enum SumAcc {
    Empty,
    Int(i128),
    Float(f64),
}
impl Accumulator for SumAcc {
    fn update(&mut self, args: &[Value]) -> Result<(), AnalyzerError> {
        let [v] = args else {
            return Err(AnalyzerError::FunctionArgMismatch {
                name: "SUM".into(),
                expected: "SUM(expr)".into(),
                got: vec![],
            });
        };
        if matches!(v, Value::Null) {
            return Ok(());
        }

        match (&mut *self, v) {
            (SumAcc::Empty, Value::Number(n)) => {
                if let Some(i) = n.as_i64() {
                    *self = SumAcc::Int(i as i128);
                } else if let Some(f) = n.as_f64() {
                    *self = SumAcc::Float(f);
                } else {
                    return Err(AnalyzerError::Other("SUM got non numeric number".into()));
                }
            }
            (SumAcc::Int(acc), Value::Number(n)) => {
                if let Some(i) = n.as_i64() {
                    *acc += i as i128;
                } else if let Some(_f) = n.as_f64() {
                    return Err(AnalyzerError::Other(
                        "SUM received float for INT aggregation".into(),
                    ));
                } else {
                    return Err(AnalyzerError::Other("SUM got non numeric number".into()));
                }
            }
            (SumAcc::Float(acc), Value::Number(n)) => {
                if let Some(i) = n.as_i64() {
                    *acc += i as f64;
                } else if let Some(f) = n.as_f64() {
                    *acc += f;
                } else {
                    return Err(AnalyzerError::Other("SUM got non numeric number".into()));
                }
            }
            (_, other) => {
                return Err(AnalyzerError::Other(format!(
                    "SUM got non numeric arg: {:?}",
                    other
                )));
            }
        }
        Ok(())
    }
    fn finalize(&self) -> Value {
        match self {
            SumAcc::Empty => Value::Null, // SQL SUM over all NULLs -> NULL
            SumAcc::Int(i) => Value::Number(serde_json::Number::from(*i as i64)), // safe if your ints fit i64; otherwise customize
            SumAcc::Float(f) => serde_json::Number::from_f64(*f)
                .map(Value::Number)
                .unwrap_or(Value::Null),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::SumImpl;
    use crate::parser::aggregators_helper::AggregateImpl;
    use serde_json::json;

    #[test]
    fn accumulator_sums_ints_and_ignores_nulls() {
        let mut acc = SumImpl.create_accumulator();

        acc.update(&[json!(1)]).unwrap();
        acc.update(&[json!(null)]).unwrap();
        acc.update(&[json!(2)]).unwrap();

        assert_eq!(acc.finalize(), json!(3));
    }

    #[test]
    fn accumulator_sums_floats_and_ints_after_float_start() {
        let mut acc = SumImpl.create_accumulator();

        acc.update(&[json!(1.5)]).unwrap();
        acc.update(&[json!(2)]).unwrap();

        assert_eq!(acc.finalize(), json!(3.5));
    }

    #[test]
    fn accumulator_rejects_bad_arg_count_and_non_numeric_values() {
        let mut acc = SumImpl.create_accumulator();

        assert!(acc.update(&[]).is_err());
        assert!(acc.update(&[json!("bad")]).is_err());
    }

    #[test]
    fn accumulator_rejects_float_after_int_start() {
        let mut acc = SumImpl.create_accumulator();

        acc.update(&[json!(1)]).unwrap();

        assert!(acc.update(&[json!(1.5)]).is_err());
    }
}