use std::collections::VecDeque;
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 Last;
impl Command for Last {
fn name(&self) -> &str {
"last"
}
fn signature(&self) -> Signature {
Signature::build("last")
.input_output_types(vec![
(
Type::List(Box::new(Type::Any)),
Type::Any,
),
(Type::Binary, Type::Binary),
(Type::Range, Type::Any),
])
.optional(
"rows",
SyntaxShape::Int,
"Starting from the back, the number of rows to return.",
)
.category(Category::Filters)
}
fn usage(&self) -> &str {
"Return only the last several rows of the input. Counterpart of `first`. Opposite of `drop`."
}
fn examples(&self) -> Vec<Example> {
vec![
Example {
example: "[1,2,3] | last 2",
description: "Return the last 2 items of a list/table",
result: Some(Value::list(
vec![Value::test_int(2), Value::test_int(3)],
Span::test_data(),
)),
},
Example {
example: "[1,2,3] | last",
description: "Return the last item of a list/table",
result: Some(Value::test_int(3)),
},
Example {
example: "0x[01 23 45] | last 2",
description: "Return the last 2 bytes of a binary value",
result: Some(Value::binary(vec![0x23, 0x45], Span::test_data())),
},
Example {
example: "1..3 | last",
description: "Return the last item of a range",
result: Some(Value::test_int(3)),
},
]
}
fn run(
&self,
engine_state: &EngineState,
stack: &mut Stack,
call: &Call,
input: PipelineData,
) -> Result<PipelineData, ShellError> {
let head = call.head;
let rows: Option<i64> = call.opt(engine_state, stack, 0)?;
let return_single_element = rows.is_none();
let rows_desired: usize = match rows {
Some(i) if i < 0 => return Err(ShellError::NeedsPositiveValue { span: head }),
Some(x) => x as usize,
None => 1,
};
let ctrlc = engine_state.ctrlc.clone();
let metadata = input.metadata();
if rows_desired == 0 {
return Ok(Vec::<Value>::new().into_pipeline_data_with_metadata(metadata, ctrlc));
}
match input {
PipelineData::ListStream(_, _) | PipelineData::Value(Value::Range { .. }, _) => {
let iterator = input.into_iter_strict(head)?;
let mut buf = VecDeque::<_>::new();
for row in iterator {
if buf.len() == rows_desired {
buf.pop_front();
}
buf.push_back(row);
}
if return_single_element {
if let Some(last) = buf.pop_back() {
Ok(last.into_pipeline_data_with_metadata(metadata))
} else {
Ok(PipelineData::empty().set_metadata(metadata))
}
} else {
Ok(buf.into_pipeline_data_with_metadata(metadata, ctrlc))
}
}
PipelineData::Value(val, _) => {
let val_span = val.span();
match val {
Value::List { vals, .. } => {
if return_single_element {
if let Some(v) = vals.last() {
Ok(v.clone().into_pipeline_data())
} else {
Err(ShellError::AccessEmptyContent { span: head })
}
} else {
Ok(vals
.into_iter()
.rev()
.take(rows_desired)
.rev()
.into_pipeline_data_with_metadata(metadata, ctrlc))
}
}
Value::Binary { val, .. } => {
if return_single_element {
if let Some(b) = val.last() {
Ok(PipelineData::Value(
Value::int(*b as i64, val_span),
metadata,
))
} else {
Err(ShellError::AccessEmptyContent { span: head })
}
} else {
let slice: Vec<u8> =
val.into_iter().rev().take(rows_desired).rev().collect();
Ok(PipelineData::Value(
Value::binary(slice, val_span),
metadata,
))
}
}
Value::Error { error, .. } => Err(*error),
other => Err(ShellError::OnlySupportsThisInputType {
exp_input_type: "list, binary or range".into(),
wrong_type: other.get_type().to_string(),
dst_span: head,
src_span: other.span(),
}),
}
}
PipelineData::ExternalStream { span, .. } => {
Err(ShellError::OnlySupportsThisInputType {
exp_input_type: "list, binary or range".into(),
wrong_type: "raw data".into(),
dst_span: head,
src_span: span,
})
}
PipelineData::Empty => Err(ShellError::OnlySupportsThisInputType {
exp_input_type: "list, binary or range".into(),
wrong_type: "null".into(),
dst_span: call.head,
src_span: call.head,
}),
}
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_examples() {
use crate::test_examples;
test_examples(Last {})
}
}