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use crate::evaluator::{Function, SyntaxError, EvaluationError, Context};
use std::collections::HashMap;
use crate::evaluator::functions::{SimpleFunction, FunctionWithContext};
use std::num::ParseFloatError;

const EMPTY_STRING: &str = "";

/// Provides a set of standard functions.
///
pub fn std_functions() -> HashMap<String, Box<dyn Function>> {
    let mut functions: HashMap<String, Box<dyn Function>> = HashMap::new();
    functions.insert("concat".to_string(), SimpleFunction::new(concat_function));
    functions.insert("+".to_string(), SimpleFunction::new(plus_function));
    functions.insert("-".to_string(), FunctionWithContext::new(minus_function));
    functions
}

/// Concatenates the parameters.
///
/// Eg.
/// ```text
/// concat 1 "hello" " " 3.14 "world!"
/// ```
/// Expected output:
/// ```text
/// 1hello 3.14world!
/// ```
pub fn concat_function(parameters: &[String]) -> String {
    let mut result = EMPTY_STRING.to_string();
    parameters.iter().for_each(|param| {
        result.push_str(param);
    });
    result
}

/// Adds (or concatenates) values.
/// If any of the parameters is not convertible to a number, then the rest will be concatenated.
///
/// Eg.
/// ```text
/// + 1 2 3.3
/// + 1 2 "hello" 3.3
/// ```
/// Expected output:
/// ```text
/// 6.3
/// 3hello3.3
/// ```
pub fn plus_function(parameters: &[String]) -> String {
    let mut result: String = EMPTY_STRING.to_string();
    let mut floating_result: Option<f64> = None;

    parameters.iter().for_each(|param| {
        if result.is_empty() {
            if let Result::Ok(value) = param.parse::<f64>() {
                floating_result = Some(floating_result.unwrap_or(0 as f64) + value);
            } else {
                if let Some(number) = floating_result
                    .map(|number| number.to_string()) {
                    result += &number
                }

                result.push_str(param);
            }
        } else {
            result.push_str(param);
        };
    });

    if result.is_empty() && floating_result.is_some() {
        floating_result.map(|number| number.to_string()).unwrap()
    } else {
        result
    }
}

/// Subtracts values.
/// If any of the parameters is not convertible to a number, then an error will be emitted with the invalid value.
///
/// Eg.
/// ```text
/// - 8.3 1 1.4
/// ```
/// Expected output:
/// ```text
/// 5.9
/// ```
pub fn minus_function(parameters: &[String], _context: &mut Context) -> Result<String, SyntaxError> {
    let mut index: usize = 0;
    let numbers: Result<Vec<f64>, ParseFloatError> = parameters.iter()
        .map(|number| {
            index += 1;
            number.parse::<f64>()
        })
        .collect();

    if let Result::Err(error) = numbers {
        Err(SyntaxError::new(EvaluationError::InvalidValues {
                description: Some(error.to_string()),
                values: vec![parameters[index - 1].clone()],
            })
        )
    } else {
        Ok(numbers.unwrap()
            .into_iter()
            .reduce(|a, b| a - b)
            .unwrap_or(0 as f64)
            .to_string()
        )
    }
}

#[cfg(test)]
mod tests {
    use crate::compile_template_from_file;
    use std::path::PathBuf;
    use std::collections::HashMap;
    use crate::functions::std_functions;
    use std::fs;

    #[test]
    fn should_compile_template() {
        let expected = fs::read_to_string(PathBuf::from("test-assets/stdlib-template-expected")).unwrap();
        let file = PathBuf::from("test-assets/stdlib-template");
        let functions = std_functions();
        let variables: HashMap<String, String> = HashMap::new();

        let result = compile_template_from_file(file, variables, functions);

        assert_eq!(result.ok(), Some(expected));
    }
}