use nu_engine::eval_expression_with_input;
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape};

#[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",
            )
            .category(Category::Core)
    }

    fn extra_usage(&self) -> &str {
        r#"This command is a parser keyword. For details, check
https://www.nushell.sh/book/thinking_in_nushell.html#parsing-and-evaluation-are-different-stages"#
    }

    fn is_parser_keyword(&self) -> bool {
        true
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
        let var_id = call
            .positional_nth(0)
            .expect("checked through parser")
            .as_var()
            .expect("internal error: missing variable");

        let keyword_expr = call
            .positional_nth(1)
            .expect("checked through parser")
            .as_keyword()
            .expect("internal error: missing keyword");

        let rhs = eval_expression_with_input(
            engine_state,
            stack,
            keyword_expr,
            input,
            call.redirect_stdout,
            call.redirect_stderr,
        )?;

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

        stack.add_var(var_id, rhs.into_value(call.head));
        Ok(PipelineData::new(call.head))
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Set a variable to a value",
                example: "let x = 10",
                result: None,
            },
            Example {
                description: "Set a variable to the result of an expression",
                example: "let x = 10 + 100",
                result: None,
            },
            Example {
                description: "Set a variable based on the condition",
                example: "let x = if false { -1 } else { 1 }",
                result: None,
            },
        ]
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_examples() {
        use crate::test_examples;

        test_examples(Let {})
    }
}
