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use nu_engine::CallExt;
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{
Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData, ShellError,
Signature, Span, SyntaxShape, Type, Value,
};
#[derive(Clone)]
pub struct First;
impl Command for First {
fn name(&self) -> &str {
"first"
}
fn signature(&self) -> Signature {
Signature::build("first")
.optional(
"rows",
SyntaxShape::Int,
"starting from the front, the number of rows to return",
)
.category(Category::Filters)
}
fn usage(&self) -> &str {
"Show only the first number of rows."
}
fn run(
&self,
engine_state: &EngineState,
stack: &mut Stack,
call: &Call,
input: PipelineData,
) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
first_helper(engine_state, stack, call, input)
}
fn examples(&self) -> Vec<Example> {
vec![
Example {
description: "Return the first item of a list/table",
example: "[1 2 3] | first",
result: Some(Value::test_int(1)),
},
Example {
description: "Return the first 2 items of a list/table",
example: "[1 2 3] | first 2",
result: Some(Value::List {
vals: vec![Value::test_int(1), Value::test_int(2)],
span: Span::test_data(),
}),
},
]
}
}
fn first_helper(
engine_state: &EngineState,
stack: &mut Stack,
call: &Call,
input: PipelineData,
) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
let head = call.head;
let rows: Option<i64> = call.opt(engine_state, stack, 0)?;
let mut rows_desired: usize = match rows {
Some(x) => x as usize,
None => 1,
};
let ctrlc = engine_state.ctrlc.clone();
let metadata = input.metadata();
let mut input_peek = input.into_iter().peekable();
if input_peek.peek().is_some() {
match input_peek
.peek()
.ok_or_else(|| {
ShellError::GenericError(
"Error in first".into(),
"unable to pick on next value".into(),
Some(call.head),
None,
Vec::new(),
)
})?
.get_type()
{
Type::Binary => {
match &mut input_peek.next() {
Some(v) => match &v {
Value::Binary { val, .. } => {
let bytes = val;
if bytes.len() >= rows_desired {
// We only want to see a certain amount of the binary
// so let's grab those parts
let output_bytes = bytes[0..rows_desired].to_vec();
Ok(Value::Binary {
val: output_bytes,
span: head,
}
.into_pipeline_data())
} else {
// if we want more rows that the current chunk size (8192)
// we must gradually get bigger chunks while testing
// if it's within the requested rows_desired size
let mut bigger: Vec<u8> = vec![];
bigger.extend(bytes);
while bigger.len() < rows_desired {
match input_peek.next() {
Some(Value::Binary { val, .. }) => bigger.extend(val),
_ => {
// We're at the end of our data so let's break out of this loop
// and set the rows_desired to the size of our data
rows_desired = bigger.len();
break;
}
}
}
let output_bytes = bigger[0..rows_desired].to_vec();
Ok(Value::Binary {
val: output_bytes,
span: head,
}
.into_pipeline_data())
}
}
_ => todo!(),
},
None => Ok(input_peek
.into_iter()
.take(rows_desired)
.into_pipeline_data(ctrlc)
.set_metadata(metadata)),
}
}
_ => {
if rows_desired == 1 {
match input_peek.next() {
Some(val) => Ok(val.into_pipeline_data()),
None => Err(ShellError::AccessBeyondEndOfStream(head)),
}
} else {
Ok(input_peek
.into_iter()
.take(rows_desired)
.into_pipeline_data(ctrlc)
.set_metadata(metadata))
}
}
}
} else {
Err(ShellError::UnsupportedInput(
String::from("Cannot perform into string on empty input"),
head,
))
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_examples() {
use crate::test_examples;
test_examples(First {})
}
}