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

use crate::prelude::*;
use nu_engine::run_block;
use nu_engine::WholeStreamCommand;
use nu_errors::ShellError;
use nu_protocol::{
    hir::CapturedBlock, hir::ExternalRedirection, ColumnPath, Primitive, ReturnSuccess, Signature,
    SyntaxShape, UntaggedValue, Value,
};

use nu_value_ext::{as_string, ValueExt};

pub struct Command;

impl WholeStreamCommand for Command {
    fn name(&self) -> &str {
        "empty?"
    }

    fn signature(&self) -> Signature {
        Signature::build("empty?")
            .rest(
                SyntaxShape::ColumnPath,
                "the names of the columns to check emptiness",
            )
            .named(
                "block",
                SyntaxShape::Block,
                "an optional block to replace if empty",
                Some('b'),
            )
    }

    fn usage(&self) -> &str {
        "Check for empty values."
    }

    fn run_with_actions(&self, args: CommandArgs) -> Result<ActionStream, ShellError> {
        is_empty(args)
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Check if a value is empty",
                example: "echo '' | empty?",
                result: Some(vec![UntaggedValue::boolean(true).into()]),
            },
            Example {
                description: "more than one column",
                example: "echo [[meal size]; [arepa small] [taco '']] | empty? meal size",
                result: Some(
                    vec![
                        UntaggedValue::row(indexmap! {
                                "meal".to_string() => Value::from(false),
                                "size".to_string() => Value::from(false),
                        })
                        .into(),
                        UntaggedValue::row(indexmap! {
                                "meal".to_string() => Value::from(false),
                                "size".to_string() => Value::from(true),
                        })
                        .into(),
                    ],
                ),
            },Example {
                description: "use a block if setting the empty cell contents is wanted",
                example: "echo [[2020/04/16 2020/07/10 2020/11/16]; ['' [27] [37]]] | empty? 2020/04/16 -b { [33 37] }",
                result: Some(
                    vec![
                        UntaggedValue::row(indexmap! {
                                "2020/04/16".to_string() => UntaggedValue::table(&[UntaggedValue::int(33).into(), UntaggedValue::int(37).into()]).into(),
                                "2020/07/10".to_string() => UntaggedValue::table(&[UntaggedValue::int(27).into()]).into(),
                                "2020/11/16".to_string() => UntaggedValue::table(&[UntaggedValue::int(37).into()]).into(),
                        })
                        .into(),
                    ],
                ),
            },
        ]
    }
}

fn is_empty(args: CommandArgs) -> Result<ActionStream, ShellError> {
    let tag = args.call_info.name_tag.clone();
    let context = args.context.clone();
    let block: Option<CapturedBlock> = args.get_flag("block")?;
    let columns: Vec<ColumnPath> = args.rest(0)?;

    let input = args.input;

    if input.is_empty() {
        let stream =
            vec![UntaggedValue::Primitive(Primitive::Nothing).into_value(&tag)].into_iter();

        return Ok(InputStream::from_stream(stream)
            .map(move |input| {
                let columns = vec![];

                match process_row(&context, input, &block, columns) {
                    Ok(s) => s,
                    Err(e) => ActionStream::one(Err(e)),
                }
            })
            .flatten()
            .into_action_stream());
    }

    Ok(input
        .map(move |input| {
            let columns = columns.clone();

            match process_row(&context, input, &block, columns) {
                Ok(s) => s,
                Err(e) => ActionStream::one(Err(e)),
            }
        })
        .flatten()
        .into_action_stream())
}

fn process_row(
    context: &EvaluationContext,
    input: Value,
    default_block: &Option<CapturedBlock>,
    column_paths: Vec<ColumnPath>,
) -> Result<ActionStream, ShellError> {
    let mut out = Arc::new(None);
    let results = Arc::make_mut(&mut out);

    if let Some(default_block) = &*default_block {
        let for_block = input.clone();
        let input_stream = vec![Ok(for_block)].into_iter().into_input_stream();

        context.scope.enter_scope();
        context.scope.add_vars(&default_block.captured.entries);
        if let Some((arg, _)) = default_block.block.params.positional.first() {
            context.scope.add_var(arg.name(), input.clone());
        }

        let stream = run_block(
            &default_block.block,
            &*context,
            input_stream,
            ExternalRedirection::Stdout,
        );
        context.scope.exit_scope();

        let mut stream = stream?;
        *results = Some({
            let values = stream.drain_vec();

            let errors = context.get_errors();

            if let Some(error) = errors.first() {
                return Err(error.clone());
            }

            if values.len() == 1 {
                let value = values
                    .get(0)
                    .ok_or_else(|| ShellError::unexpected("No value."))?;

                Value {
                    value: value.value.clone(),
                    tag: input.tag.clone(),
                }
            } else if values.is_empty() {
                UntaggedValue::nothing().into_value(&input.tag)
            } else {
                UntaggedValue::table(&values).into_value(&input.tag)
            }
        });
    }

    match input {
        Value {
            value: UntaggedValue::Row(ref r),
            ref tag,
        } => {
            if column_paths.is_empty() {
                Ok(ActionStream::one(ReturnSuccess::value({
                    let is_empty = input.is_empty();

                    if default_block.is_some() {
                        if is_empty {
                            results
                                .clone()
                                .unwrap_or_else(|| UntaggedValue::boolean(true).into_value(tag))
                        } else {
                            input.clone()
                        }
                    } else {
                        UntaggedValue::boolean(is_empty).into_value(tag)
                    }
                })))
            } else {
                let mut obj = input.clone();

                for column in column_paths.clone() {
                    let path = UntaggedValue::Primitive(Primitive::ColumnPath(column.clone()))
                        .into_value(tag);
                    let data = r.get_data(&as_string(&path)?).borrow().clone();
                    let is_empty = data.is_empty();

                    let default = if default_block.is_some() {
                        if is_empty {
                            results
                                .clone()
                                .unwrap_or_else(|| UntaggedValue::boolean(true).into_value(tag))
                        } else {
                            data.clone()
                        }
                    } else {
                        UntaggedValue::boolean(is_empty).into_value(tag)
                    };

                    if let Ok(value) =
                        obj.swap_data_by_column_path(&column, Box::new(move |_| Ok(default)))
                    {
                        obj = value;
                    }
                }

                Ok(ActionStream::one(ReturnSuccess::value(obj)))
            }
        }
        other => Ok(ActionStream::one(ReturnSuccess::value({
            if other.is_empty() {
                results
                    .clone()
                    .unwrap_or_else(|| UntaggedValue::boolean(true).into_value(other.tag))
            } else {
                UntaggedValue::boolean(false).into_value(other.tag)
            }
        }))),
    }
}