use nu_engine::{eval_block_with_early_return, CallExt};

use nu_protocol::ast::Call;
use nu_protocol::engine::{Closure, Command, EngineState, Stack};
use nu_protocol::{
    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, SyntaxShape, Type,
    Value,
};

#[derive(Clone)]
pub struct Reduce;

impl Command for Reduce {
    fn name(&self) -> &str {
        "reduce"
    }

    fn signature(&self) -> Signature {
        Signature::build("reduce")
            .input_output_types(vec![
                (Type::List(Box::new(Type::Any)), Type::Any),
                (Type::Table(vec![]), Type::Any),
                (Type::Range, Type::Any),
            ])
            .named(
                "fold",
                SyntaxShape::Any,
                "reduce with initial value",
                Some('f'),
            )
            .required(
                "closure",
                SyntaxShape::Closure(Some(vec![
                    SyntaxShape::Any,
                    SyntaxShape::Any,
                    SyntaxShape::Int,
                ])),
                "Reducing function.",
            )
            .allow_variants_without_examples(true)
            .category(Category::Filters)
    }

    fn usage(&self) -> &str {
        "Aggregate a list to a single value using an accumulator closure."
    }

    fn search_terms(&self) -> Vec<&str> {
        vec!["map", "fold", "foldl"]
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                example: "[ 1 2 3 4 ] | reduce {|it, acc| $it + $acc }",
                description: "Sum values of a list (same as 'math sum')",
                result: Some(Value::test_int(10)),
            },
            Example {
                example:
                    "[ 8 7 6 ] | enumerate | reduce --fold 0 {|it, acc| $acc + $it.item + $it.index }",
                description: "Sum values of a list, plus their indexes",
                result: Some(Value::test_int(24)),
            },
            Example {
                example: "[ 1 2 3 4 ] | reduce --fold 10 {|it, acc| $acc + $it }",
                description: "Sum values with a starting value (fold)",
                result: Some(Value::test_int(20)),
            },
            Example {
                example: r#"[ i o t ] | reduce --fold "Arthur, King of the Britons" {|it, acc| $acc | str replace --all $it "X" }"#,
                description: "Replace selected characters in a string with 'X'",
                result: Some(Value::test_string("ArXhur, KXng Xf Xhe BrXXXns")),
            },
            Example {
                example: r#"['foo.gz', 'bar.gz', 'baz.gz'] | enumerate | reduce --fold '' {|str all| $"($all)(if $str.index != 0 {'; '})($str.index + 1)-($str.item)" }"#,
                description:
                    "Add ascending numbers to each of the filenames, and join with semicolons.",
                result: Some(Value::test_string("1-foo.gz; 2-bar.gz; 3-baz.gz")),
            },
            Example {
                example: r#"let s = "Str"; 0..2 | reduce --fold '' {|it, acc| $acc + $s}"#,
                description:
                    "Concatenate a string with itself, using a range to determine the number of times.",
                result: Some(Value::test_string("StrStrStr")),
            },
        ]
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        let span = call.head;

        let fold: Option<Value> = call.get_flag(engine_state, stack, "fold")?;
        let capture_block: Closure = call.req(engine_state, stack, 0)?;
        let mut stack = stack.captures_to_stack(capture_block.captures);
        let block = engine_state.get_block(capture_block.block_id);
        let ctrlc = engine_state.ctrlc.clone();

        let orig_env_vars = stack.env_vars.clone();
        let orig_env_hidden = stack.env_hidden.clone();

        let redirect_stdout = call.redirect_stdout;
        let redirect_stderr = call.redirect_stderr;

        // To enumerate over the input (for the index argument),
        // it must be converted into an iterator using into_iter().
        let mut input_iter = input.into_iter();

        let start_val = if let Some(val) = fold {
            val
        } else if let Some(val) = input_iter.next() {
            val
        } else {
            return Err(ShellError::GenericError {
                error: "Expected input".into(),
                msg: "needs input".into(),
                span: Some(span),
                help: None,
                inner: vec![],
            });
        };

        let mut acc = start_val;

        let mut input_iter = input_iter.peekable();

        while let Some(x) = input_iter.next() {
            // with_env() is used here to ensure that each iteration uses
            // a different set of environment variables.
            // Hence, a 'cd' in the first loop won't affect the next loop.
            stack.with_env(&orig_env_vars, &orig_env_hidden);

            // Element argument
            if let Some(var) = block.signature.get_positional(0) {
                if let Some(var_id) = &var.var_id {
                    stack.add_var(*var_id, x);
                }
            }

            // Accumulator argument
            if let Some(var) = block.signature.get_positional(1) {
                if let Some(var_id) = &var.var_id {
                    stack.add_var(*var_id, acc);
                }
            }

            acc = eval_block_with_early_return(
                engine_state,
                &mut stack,
                block,
                PipelineData::empty(),
                // redirect stdout until its the last input value
                redirect_stdout || input_iter.peek().is_some(),
                redirect_stderr,
            )?
            .into_value(span);

            if nu_utils::ctrl_c::was_pressed(&ctrlc) {
                break;
            }
        }

        Ok(acc.with_span(span).into_pipeline_data())
    }
}

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

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

        test_examples(Reduce {})
    }
}