// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// OpenEthereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

//! Deserializer of empty string values into optionals.

use serde::{
    de::{Error, IntoDeserializer, Visitor},
    Deserialize, Deserializer,
};
use std::{fmt, marker::PhantomData};

/// Deserializer of empty string values into optionals.
#[derive(Debug, PartialEq, Clone)]
pub enum MaybeEmpty<T> {
    /// Some.
    Some(T),
    /// None.
    None,
}

impl<'a, T> Deserialize<'a> for MaybeEmpty<T>
where
    T: Deserialize<'a>,
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'a>,
    {
        deserializer.deserialize_any(MaybeEmptyVisitor::new())
    }
}

struct MaybeEmptyVisitor<T> {
    _phantom: PhantomData<T>,
}

impl<T> MaybeEmptyVisitor<T> {
    fn new() -> Self {
        MaybeEmptyVisitor {
            _phantom: PhantomData,
        }
    }
}

impl<'a, T> Visitor<'a> for MaybeEmptyVisitor<T>
where
    T: Deserialize<'a>,
{
    type Value = MaybeEmpty<T>;

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        write!(formatter, "an empty string or string-encoded type")
    }

    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
    where
        E: Error,
    {
        self.visit_string(value.to_owned())
    }

    fn visit_string<E>(self, value: String) -> Result<Self::Value, E>
    where
        E: Error,
    {
        match value.is_empty() {
            true => Ok(MaybeEmpty::None),
            false => T::deserialize(value.into_deserializer()).map(MaybeEmpty::Some),
        }
    }
}

impl<T> Into<Option<T>> for MaybeEmpty<T> {
    fn into(self) -> Option<T> {
        match self {
            MaybeEmpty::Some(s) => Some(s),
            MaybeEmpty::None => None,
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::{hash::H256, maybe::MaybeEmpty};
    use ethereum_types;
    use serde_json;
    use std::str::FromStr;

    #[test]
    fn maybe_deserialization() {
        let s = r#"["", "5a39ed1020c04d4d84539975b893a4e7c53eab6c2965db8bc3468093a31bc5ae"]"#;
        let deserialized: Vec<MaybeEmpty<H256>> = serde_json::from_str(s).unwrap();
        assert_eq!(
            deserialized,
            vec![
                MaybeEmpty::None,
                MaybeEmpty::Some(H256(
                    ethereum_types::H256::from_str(
                        "5a39ed1020c04d4d84539975b893a4e7c53eab6c2965db8bc3468093a31bc5ae"
                    )
                    .unwrap()
                ))
            ]
        );
    }
}
