nushell/crates/nu-command/src/filters/last.rs

use nu_engine::CallExt;

use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{PipelineData, ShellError, Signature, SyntaxShape, Value};
//use nu_protocol::{IntoPipelineData, PipelineData, ShellError, Signature, SyntaxShape, Value};

#[derive(Clone)]
pub struct Last;

impl Command for Last {
    fn name(&self) -> &str {
        "last"
    }

    fn signature(&self) -> Signature {
        Signature::build("last").optional(
            "rows",
            SyntaxShape::Int,
            "starting from the back, the number of rows to return",
        )
    }

    fn usage(&self) -> &str {
        "Show only the last number of rows."
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        let rows: Option<i64> = call.opt(engine_state, stack, 0)?;

        let vlength = length(input)?;
        dbg!(vlength);

        let end_rows_desired = if let Some(quantity) = rows {
            quantity
        } else {
            1
        };

        let beginning_rows_to_skip = if end_rows_desired < vlength {
            vlength - end_rows_desired
        } else {
            0
        };

        dbg!(beginning_rows_to_skip);

        //  let iter = v.into_iter().skip(beginning_rows_to_skip);

        //dbg!(input.clone());
        /*
                match input {
                    PipelineData::Stream(stream) => Ok(stream.into_pipeline_data()),
                    PipelineData::Value(Value::List { vals, .. }) => {
                        Ok(vals.into_iter().into_pipeline_data())
                    }
                    _ => {
                        dbg!("Fall to the bottom");
                        Ok(PipelineData::Value(Value::Nothing { span: call.head }))
                    }
                }
        */
        Ok(PipelineData::Value(Value::Nothing { span: call.head }))
    }
}

fn length(input: PipelineData) -> Result<i64, nu_protocol::ShellError> {
    match input {
        PipelineData::Value(Value::Nothing { .. }) => Ok(1),
        _ => Ok(input.into_iter().count() as i64),
    }
}