use nu_engine::eval_expression;
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EvaluationContext};
use nu_protocol::{PipelineData, Signature, SyntaxShape, Value};

#[derive(Clone)]
pub struct Let;

impl Command for Let {
    fn name(&self) -> &str {
        "let"
    }

    fn usage(&self) -> &str {
        "Create a variable and give it a value."
    }

    fn signature(&self) -> nu_protocol::Signature {
        Signature::build("let")
            .required("var_name", SyntaxShape::VarWithOptType, "variable name")
            .required(
                "initial_value",
                SyntaxShape::Keyword(b"=".to_vec(), Box::new(SyntaxShape::Expression)),
                "equals sign followed by value",
            )
    }

    fn run(
        &self,
        context: &EvaluationContext,
        call: &Call,
        _input: PipelineData,
    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
        let var_id = call.positional[0]
            .as_var()
            .expect("internal error: missing variable");

        let keyword_expr = call.positional[1]
            .as_keyword()
            .expect("internal error: missing keyword");

        let rhs = eval_expression(context, keyword_expr)?;

        //println!("Adding: {:?} to {}", rhs, var_id);

        context.add_var(var_id, rhs);
        Ok(PipelineData::new())
    }
}