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#![warn(clippy::pedantic)]

use super::{
    character_classes::DIGIT,
    context::Context,
    error::Error,
};

struct Shared {
    num_groups: usize,
    octet_buffer: String,
}

enum State {
    NotInOctet(Shared),
    ExpectDigitOrDot(Shared),
}

impl State {
    fn finalize(self) -> Result<(), Error> {
        match self {
            Self::NotInOctet(_) => Err(Error::TruncatedHost),
            Self::ExpectDigitOrDot(state) => {
                Self::finalize_expect_digit_or_dot(state)
            },
        }
    }

    fn finalize_expect_digit_or_dot(state: Shared) -> Result<(), Error> {
        let mut state = state;
        if !state.octet_buffer.is_empty() {
            state.num_groups += 1;
            if state.octet_buffer.parse::<u8>().is_err() {
                return Err(Error::InvalidDecimalOctet);
            }
        }
        match state.num_groups {
            4 => Ok(()),
            n if n < 4 => Err(Error::TooFewAddressParts),
            _ => Err(Error::TooManyAddressParts),
        }
    }

    fn new() -> Self {
        Self::NotInOctet(Shared {
            num_groups: 0,
            octet_buffer: String::new(),
        })
    }

    fn next(
        self,
        c: char,
    ) -> Result<Self, Error> {
        match self {
            Self::NotInOctet(state) => Self::next_not_in_octet(state, c),
            Self::ExpectDigitOrDot(state) => {
                Self::next_expect_digit_or_dot(state, c)
            },
        }
    }

    fn next_not_in_octet(
        state: Shared,
        c: char,
    ) -> Result<Self, Error> {
        let mut state = state;
        if DIGIT.contains(&c) {
            state.octet_buffer.push(c);
            Ok(Self::ExpectDigitOrDot(state))
        } else {
            Err(Error::IllegalCharacter(Context::Ipv4Address))
        }
    }

    fn next_expect_digit_or_dot(
        state: Shared,
        c: char,
    ) -> Result<Self, Error> {
        let mut state = state;
        if c == '.' {
            state.num_groups += 1;
            if state.num_groups > 4 {
                return Err(Error::TooManyAddressParts);
            }
            if state.octet_buffer.parse::<u8>().is_err() {
                return Err(Error::InvalidDecimalOctet);
            }
            state.octet_buffer.clear();
            Ok(Self::NotInOctet(state))
        } else if DIGIT.contains(&c) {
            state.octet_buffer.push(c);
            Ok(Self::ExpectDigitOrDot(state))
        } else {
            Err(Error::IllegalCharacter(Context::Ipv4Address))
        }
    }
}

pub fn validate_ipv4_address<T>(address: T) -> Result<(), Error>
where
    T: AsRef<str>,
{
    address.as_ref().chars().try_fold(State::new(), State::next)?.finalize()
}

#[cfg(test)]
mod tests {

    use super::*;

    #[test]
    fn good() {
        let test_vectors = [
            "0.0.0.0",
            "1.2.3.0",
            "1.2.3.4",
            "1.2.3.255",
            "1.2.255.4",
            "1.255.3.4",
            "255.2.3.4",
            "255.255.255.255",
        ];
        for test_vector in &test_vectors {
            assert!(validate_ipv4_address(*test_vector).is_ok());
        }
    }

    #[test]
    fn bad() {
        named_tuple!(
            struct TestVector {
                address_string: &'static str,
                expected_error: Error,
            }
        );
        let test_vectors: &[TestVector] = &[
            ("1.2.x.4", Error::IllegalCharacter(Context::Ipv4Address)).into(),
            ("1.2.3.4.8", Error::TooManyAddressParts).into(),
            ("1.2.3", Error::TooFewAddressParts).into(),
            ("1.2.3.", Error::TruncatedHost).into(),
            ("1.2.3.256", Error::InvalidDecimalOctet).into(),
            ("1.2.3.-4", Error::IllegalCharacter(Context::Ipv4Address)).into(),
            ("1.2.3. 4", Error::IllegalCharacter(Context::Ipv4Address)).into(),
            ("1.2.3.4 ", Error::IllegalCharacter(Context::Ipv4Address)).into(),
        ];
        for test_vector in test_vectors {
            let result = validate_ipv4_address(test_vector.address_string());
            assert!(result.is_err(), "{}", test_vector.address_string());
            assert_eq!(
                *test_vector.expected_error(),
                result.unwrap_err(),
                "{}",
                test_vector.address_string()
            );
        }
    }
}