pipa-lang 1.0.0-alpha.1

A tiny template language
Documentation 
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// SPDX-FileCopyrightText: Copyright 2026 olav@occy.org
// SPDX-License-Identifier: MPL-2.0

use crate::lang::adapter::Adapter;
use crate::lang::args::eval_args;
use crate::lang::arity::Arity;
use crate::lang::arity::assert_func_arity;
use crate::lang::error::Error;
use crate::lang::error::ErrorKind;
use crate::lang::machine::Machine;
use crate::lang::node::Node;
use crate::value::Value;
use crate::value::number::Number;

pub(crate) fn truncate_start(
    adapter: &impl Adapter,
    machine: &mut Machine<'_>,
    stdin: Option<&Value>,
    node: Node,
) -> Result<Value, Error> {
    assert_func_arity(adapter, machine, stdin, &node, &Arity::min(2))?;

    let mut values = eval_args(adapter, machine, stdin, node)?;
    let mut value = values.pop().flatten().unwrap_or_default().join();
    let length = values.pop().flatten().unwrap_or_default();

    let Some(length) = length.as_number() else {
        return Err(Error {
            kind: ErrorKind::Func,
            source: adapter.template_source().map(String::from),
            span: machine.span,
            message: "truncate-start: bad length".into(),
        });
    };

    if Number::from(value.len()) <= length {
        return Ok(Value::from(value));
    }

    let trail = values.pop().flatten().unwrap_or_else(|| Value::from("..."));
    value.reverse();
    value.truncate(length.try_into().unwrap_or_default());
    value.reverse();
    Ok(Value::from([trail.join(), value].concat()))
}