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use std::collections::HashMap;

use serde_json::value::{from_value, to_value, Value};

use errors::Result;

/// The global function type definition
pub type GlobalFn = Box<Fn(HashMap<String, Value>) -> Result<Value> + Sync + Send>;

pub fn make_range_fn() -> GlobalFn {
    Box::new(move |args| -> Result<Value> {
        let start = match args.get("start") {
            Some(val) => match from_value::<usize>(val.clone()) {
                Ok(v) => v,
                Err(_) => bail!(
                    "Global function `range` received start={} but `start` can only be a number"
                ),
            },
            None => 0,
        };
        let step_by = match args.get("step_by") {
            Some(val) => match from_value::<usize>(val.clone()) {
                Ok(v) => v,
                Err(_) => bail!(
                    "Global function `range` received step_by={} but `step` can only be a number"
                ),
            },
            None => 1,
        };
        let end = match args.get("end") {
            Some(val) => match from_value::<usize>(val.clone()) {
                Ok(v) => v,
                Err(_) => {
                    bail!("Global function `range` received end={} but `end` can only be a number")
                }
            },
            None => bail!("Global function `range` was called without a `end` argument"),
        };

        if start > end {
            bail!("Global function `range` was called without a `start` argument greater than the `end` one");
        }

        let mut i = start;
        let mut res = vec![];
        while i < end {
            res.push(i);
            i += step_by;
        }
        Ok(to_value(res).unwrap())
    })
}

#[cfg(test)]
mod tests {
    use std::collections::HashMap;

    use serde_json::value::to_value;

    use super::make_range_fn;

    #[test]
    fn test_range_default() {
        let mut args = HashMap::new();
        args.insert("end".to_string(), to_value(5).unwrap());

        let res = make_range_fn()(args).unwrap();
        assert_eq!(res, to_value(vec![0, 1, 2, 3, 4]).unwrap());
    }

    #[test]
    fn test_range_start() {
        let mut args = HashMap::new();
        args.insert("end".to_string(), to_value(5).unwrap());
        args.insert("start".to_string(), to_value(1).unwrap());

        let res = make_range_fn()(args).unwrap();
        assert_eq!(res, to_value(vec![1, 2, 3, 4]).unwrap());
    }

    #[test]
    fn test_range_start_greater_than_end() {
        let mut args = HashMap::new();
        args.insert("end".to_string(), to_value(5).unwrap());
        args.insert("start".to_string(), to_value(6).unwrap());

        assert!(make_range_fn()(args).is_err());
    }

    #[test]
    fn test_range_step_by() {
        let mut args = HashMap::new();
        args.insert("end".to_string(), to_value(10).unwrap());
        args.insert("step_by".to_string(), to_value(2).unwrap());

        let res = make_range_fn()(args).unwrap();
        assert_eq!(res, to_value(vec![0, 2, 4, 6, 8]).unwrap());
    }
}