nushell/crates/nu-command/src/commands/lines.rs

use crate::prelude::*;
use nu_engine::WholeStreamCommand;
use nu_errors::ShellError;
use nu_protocol::{Primitive, ReturnSuccess, Signature, UntaggedValue, Value};
use parking_lot::Mutex;

pub struct Lines;

#[async_trait]
impl WholeStreamCommand for Lines {
    fn name(&self) -> &str {
        "lines"
    }

    fn signature(&self) -> Signature {
        Signature::build("lines")
    }

    fn usage(&self) -> &str {
        "Split single string into rows, one per line."
    }

    async fn run(&self, args: CommandArgs) -> Result<OutputStream, ShellError> {
        lines(args).await
    }

    fn examples(&self) -> Vec<Example> {
        vec![Example {
            description: "Split multi-line string into lines",
            example: r#"^echo "two\nlines" | lines"#,
            result: None,
        }]
    }
}

fn ends_with_line_ending(st: &str) -> bool {
    let mut temp = st.to_string();
    let last = temp.pop();
    if let Some(c) = last {
        c == '\n'
    } else {
        false
    }
}

async fn lines(args: CommandArgs) -> Result<OutputStream, ShellError> {
    let leftover_string = Arc::new(Mutex::new(String::new()));
    let args = args.evaluate_once().await?;
    let tag = args.name_tag();
    let name_span = tag.span;

    let eos = futures::stream::iter(vec![
        UntaggedValue::Primitive(Primitive::EndOfStream).into_untagged_value()
    ]);

    Ok(args
        .input
        .chain(eos)
        .filter_map(move |item| {
            let leftover_string = leftover_string.clone();
            async move {
                match item {
                    Value {
                        value: UntaggedValue::Primitive(Primitive::String(st)),
                        ..
                    } => {
                        let mut leftover_string = leftover_string.lock();

                        let mut buffer = leftover_string.clone();
                        buffer.push_str(&st);

                        let mut lines: Vec<String> =
                            buffer.lines().map(|x| x.to_string()).collect();

                        leftover_string.clear();

                        if !ends_with_line_ending(&st) {
                            if let Some(last) = lines.pop() {
                                leftover_string.push_str(&last);
                            }
                        }

                        if !lines.is_empty() {
                            let success_lines: Vec<_> = lines
                                .iter()
                                .map(|x| {
                                    ReturnSuccess::value(
                                        UntaggedValue::string(x).into_untagged_value(),
                                    )
                                })
                                .collect();

                            Some(futures::stream::iter(success_lines))
                        } else {
                            None
                        }
                    }
                    Value {
                        value: UntaggedValue::Primitive(Primitive::EndOfStream),
                        ..
                    } => {
                        let st = (&*leftover_string).lock().clone();
                        if !st.is_empty() {
                            Some(futures::stream::iter(vec![ReturnSuccess::value(
                                UntaggedValue::string(st).into_untagged_value(),
                            )]))
                        } else {
                            None
                        }
                    }
                    Value {
                        tag: value_span, ..
                    } => Some(futures::stream::iter(vec![Err(
                        ShellError::labeled_error_with_secondary(
                            "Expected a string from pipeline",
                            "requires string input",
                            name_span,
                            "value originates from here",
                            value_span,
                        ),
                    )])),
                }
            }
        })
        .flatten()
        .to_output_stream())
}

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

    #[test]
    fn examples_work_as_expected() -> Result<(), ShellError> {
        use crate::examples::test as test_examples;

        test_examples(Lines {})
    }
}