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//! Types for representing an [`Amount`]

use nom::{
    branch::alt,
    character::complete::{one_of, satisfy, space1},
    combinator::{map, not, opt, peek, recognize},
    multi::many_till,
    sequence::{pair, separated_pair},
    IResult,
};

#[cfg(all(test, feature = "unstable"))]
use crate::pest_parser::Pair;

pub use self::expression::{ConversionError, Expression, Value};

pub(crate) mod expression;

/// A beancount amount
///
/// The amount is the combination of an [`Expression`] and the currency.
#[derive(Debug, Clone, PartialEq)]
pub struct Amount<'a> {
    pub(crate) expression: Expression,
    pub(crate) currency: &'a str,
}

impl<'a> Amount<'a> {
    #[cfg(any(test))]
    pub(crate) fn new(value: impl Into<rust_decimal::Decimal>, currency: &'a str) -> Self {
        Self {
            expression: Expression::value(value),
            currency,
        }
    }

    /// Returns the [`Expression`] which may be inspected or evaluated
    #[must_use]
    pub fn expression(&self) -> &Expression {
        &self.expression
    }

    /// Evaluate the expression and returns the value
    #[must_use]
    pub fn value(&self) -> Value {
        self.expression.evaluate()
    }

    /// Returns the currency
    #[must_use]
    pub fn currency(&self) -> &'a str {
        self.currency
    }

    #[cfg(all(test, feature = "unstable"))]
    pub(crate) fn from_pair(pair: Pair<'_>) -> Amount<'_> {
        let mut inner = pair.into_inner();
        let expression = Expression::from_pair(inner.next().expect("no value in amount"));
        let currency = inner.next().expect("no currency in amount").as_str();
        Amount {
            expression,
            currency,
        }
    }
}

pub(crate) fn amount(input: &str) -> IResult<&str, Amount<'_>> {
    map(
        separated_pair(expression::parse, space1, currency),
        |(expression, currency)| Amount {
            expression,
            currency,
        },
    )(input)
}

fn current_first_char(input: &str) -> IResult<&str, char> {
    satisfy(|c: char| c.is_ascii_uppercase() && c.is_ascii_alphabetic())(input)
}

fn current_middle_char(input: &str) -> IResult<&str, char> {
    alt((
        satisfy(|c: char| c.is_ascii_uppercase() && c.is_ascii_alphabetic()),
        satisfy(char::is_numeric),
        one_of("'._-"),
    ))(input)
}

fn current_last_char(input: &str) -> IResult<&str, char> {
    alt((
        satisfy(|c: char| c.is_ascii_uppercase() && c.is_ascii_alphabetic()),
        satisfy(char::is_numeric),
    ))(input)
}

pub(crate) fn currency(input: &str) -> IResult<&str, &str> {
    recognize(pair(
        current_first_char,
        opt(pair(
            many_till(
                current_middle_char,
                peek(pair(current_last_char, not(current_middle_char))),
            ),
            current_last_char,
        )),
    ))(input)
}

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

    use nom::combinator::all_consuming;

    #[test]
    fn parse_amount() {
        assert_eq!(
            amount("10 CHF"),
            Ok((
                "",
                Amount {
                    expression: Expression::value(10),
                    currency: "CHF"
                }
            ))
        );
    }

    #[test]
    fn invalid_amount() {
        assert!(amount("10 chf").is_err());
    }

    #[rstest]
    fn valid_currency(#[values("CHF", "X-A", "X_A", "X'A", "A", "AB", "A2", "R2D2")] input: &str) {
        assert_eq!(all_consuming(currency)(input), Ok(("", input)));
    }

    #[rstest]
    fn invalid_currency(#[values("CHF-", "X-a", "1A", "aA")] input: &str) {
        let p = all_consuming(currency)(input);
        assert!(p.is_err(), "Result was actually: {p:#?}");
    }
}