vrl 0.32.0

use super::util;
use crate::compiler::prelude::*;

fn is_nullish(value: &Value) -> bool {
    util::is_nullish(value)
}

#[derive(Clone, Copy, Debug)]
pub struct IsNullish;

impl Function for IsNullish {
    fn identifier(&self) -> &'static str {
        "is_nullish"
    }

    fn usage(&self) -> &'static str {
        r#"Determines whether `value` is nullish. Returns `true` if the specified `value` is `null`, an empty string, a string containing only whitespace, or the string `"-"`. Returns `false` otherwise."#
    }

    fn category(&self) -> &'static str {
        Category::Type.as_ref()
    }

    fn return_kind(&self) -> u16 {
        kind::BOOLEAN
    }

    fn return_rules(&self) -> &'static [&'static str] {
        &[
            "Returns `true` if `value` is `null`.",
            "Returns `true` if `value` is `\"-\"`.",
            "Returns `true` if `value` is whitespace as defined by [Unicode `White_Space` property](https://en.wikipedia.org/wiki/Unicode_character_property#Whitespace).",
            "Returns `false` if `value` is anything else.",
        ]
    }

    fn notices(&self) -> &'static [&'static str] {
        &[indoc! {r#"
            This function behaves inconsistently: it returns `false` for empty arrays (`[]`) and
            objects (`{}`), but `true` for empty strings (`""`) and `null`.
        "#}]
    }

    fn parameters(&self) -> &'static [Parameter] {
        const PARAMETERS: &[Parameter] = &[Parameter::required(
            "value",
            kind::ANY,
            "The value to check for nullishness, for example, a useless value.",
        )];
        PARAMETERS
    }

    fn examples(&self) -> &'static [Example] {
        &[
            example! {
                title: "Null detection (blank string)",
                source: r#"is_nullish("")"#,
                result: Ok("true"),
            },
            example! {
                title: "Null detection (dash string)",
                source: r#"is_nullish("-")"#,
                result: Ok("true"),
            },
            example! {
                title: "Null detection (whitespace)",
                source: "is_nullish(\"\n  \n\")",
                result: Ok("true"),
            },
            example! {
                title: "Null",
                source: "is_nullish(null)",
                result: Ok("true"),
            },
        ]
    }

    fn compile(
        &self,
        _state: &state::TypeState,
        _ctx: &mut FunctionCompileContext,
        arguments: ArgumentList,
    ) -> Compiled {
        let value = arguments.required("value");
        Ok(IsNullishFn { value }.as_expr())
    }
}

#[derive(Clone, Debug)]
struct IsNullishFn {
    value: Box<dyn Expression>,
}

impl FunctionExpression for IsNullishFn {
    fn resolve(&self, ctx: &mut Context) -> Resolved {
        let value = self.value.resolve(ctx)?;
        Ok(is_nullish(&value).into())
    }

    fn type_def(&self, _: &state::TypeState) -> TypeDef {
        TypeDef::boolean().infallible()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::value;
    test_function![
        is_nullish => IsNullish;

        empty_string {
            args: func_args![value: value!("")],
            want: Ok(value!(true)),
            tdef: TypeDef::boolean().infallible(),
        }

        single_space_string {
            args: func_args![value: value!(" ")],
            want: Ok(value!(true)),
            tdef: TypeDef::boolean().infallible(),
        }

        multi_space_string {
            args: func_args![value: value!("     ")],
            want: Ok(value!(true)),
            tdef: TypeDef::boolean().infallible(),
        }

        newline_string {
            args: func_args![value: value!("\n")],
            want: Ok(value!(true)),
            tdef: TypeDef::boolean().infallible(),
        }

        carriage_return_string {
            args: func_args![value: value!("\r")],
            want: Ok(value!(true)),
            tdef: TypeDef::boolean().infallible(),
        }

        dash_string {
            args: func_args![value: value!("-")],
            want: Ok(value!(true)),
            tdef: TypeDef::boolean().infallible(),
        }

        null {
            args: func_args![value: value!(null)],
            want: Ok(value!(true)),
            tdef: TypeDef::boolean().infallible(),
        }

        non_empty_string {
            args: func_args![value: value!("hello world")],
            want: Ok(value!(false)),
            tdef: TypeDef::boolean().infallible(),
        }

        // Shows that a non-string/null literal returns false
        integer {
            args: func_args![value: value!(427)],
            want: Ok(value!(false)),
            tdef: TypeDef::boolean().infallible(),
        }

        // Shows that a non-literal type returns false
        array {
            args: func_args![value: value!([1, 2, 3])],
            want: Ok(value!(false)),
            tdef: TypeDef::boolean().infallible(),
        }
    ];
}