vrl 0.32.0

use crate::compiler::prelude::*;

fn to_syslog_level(value: Value) -> Resolved {
    let value = value.try_integer()?;
    // Severity levels: https://en.wikipedia.org/wiki/Syslog#Severity_level
    let level = match value {
        0 => "emerg",
        1 => "alert",
        2 => "crit",
        3 => "err",
        4 => "warning",
        5 => "notice",
        6 => "info",
        7 => "debug",
        _ => return Err(format!("severity level {value} not valid").into()),
    };
    Ok(level.into())
}

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

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

    fn usage(&self) -> &'static str {
        r#"Converts the `value`, a Syslog [severity level](https://en.wikipedia.org/wiki/Syslog#Severity_level), into its corresponding keyword, i.e. 0 into `"emerg"`, 1 into `"alert"`, etc."#
    }

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

    fn internal_failure_reasons(&self) -> &'static [&'static str] {
        &[
            "`value` isn't a valid Syslog [severity level](https://en.wikipedia.org/wiki/Syslog#Severity_level).",
        ]
    }

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

    fn parameters(&self) -> &'static [Parameter] {
        const PARAMETERS: &[Parameter] = &[Parameter::required(
            "value",
            kind::INTEGER,
            "The severity level.",
        )];
        PARAMETERS
    }

    fn examples(&self) -> &'static [Example] {
        &[
            example! {
                title: "Coerce to a Syslog level",
                source: "to_syslog_level!(5)",
                result: Ok("notice"),
            },
            example! {
                title: "invalid",
                source: "to_syslog_level!(500)",
                result: Err(
                    r#"function call error for "to_syslog_level" at (0:21): severity level 500 not valid"#,
                ),
            },
        ]
    }

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

        Ok(ToSyslogLevelFn { value }.as_expr())
    }
}

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

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

        to_syslog_level(value)
    }

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

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

    test_function![
        to_syslog_level => ToSyslogLevel;

        emergency {
            args: func_args![value: value!(0)],
            want: Ok(value!("emerg")),
            tdef: TypeDef::bytes().fallible(),
        }

        alert {
            args: func_args![value: value!(1)],
            want: Ok(value!("alert")),
            tdef: TypeDef::bytes().fallible(),
        }

        critical {
            args: func_args![value: value!(2)],
            want: Ok(value!("crit")),
            tdef: TypeDef::bytes().fallible(),
        }

        error {
            args: func_args![value: value!(3)],
            want: Ok(value!("err")),
            tdef: TypeDef::bytes().fallible(),
        }

        warning {
            args: func_args![value: value!(4)],
            want: Ok(value!("warning")),
            tdef: TypeDef::bytes().fallible(),
        }

        notice {
            args: func_args![value: value!(5)],
            want: Ok(value!("notice")),
            tdef: TypeDef::bytes().fallible(),
        }

        informational {
            args: func_args![value: value!(6)],
            want: Ok(value!("info")),
            tdef: TypeDef::bytes().fallible(),
        }

        debug {
            args: func_args![value: value!(7)],
            want: Ok(value!("debug")),
            tdef: TypeDef::bytes().fallible(),
        }

        invalid_severity_next_int {
            args: func_args![value: value!(8)],
            want: Err("severity level 8 not valid"),
            tdef: TypeDef::bytes().fallible(),
        }

        invalid_severity_larger_int {
            args: func_args![value: value!(475)],
            want: Err("severity level 475 not valid"),
            tdef: TypeDef::bytes().fallible(),
        }

        invalid_severity_negative_int {
            args: func_args![value: value!(-1)],
            want: Err("severity level -1 not valid"),
            tdef: TypeDef::bytes().fallible(),
        }
    ];
}