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//! Json U256 serde helpers.

use alloy_primitives::U256;
use serde::{de::Error, Deserialize, Deserializer};
use serde_json::Value;

/// Supports parsing the TTD as an `Option<u64>`, or `Option<f64>` specifically for the mainnet TTD
/// (5.875e22).
pub fn deserialize_json_ttd_opt<'de, D>(deserializer: D) -> Result<Option<U256>, D::Error>
where
    D: Deserializer<'de>,
{
    Option::<Value>::deserialize(deserializer)?.map(ttd_from_value::<D>).transpose()
}

/// Converts the given [serde_json::Value] into a `U256` value for TTD deserialization.
fn ttd_from_value<'de, D>(val: Value) -> Result<U256, D::Error>
where
    D: Deserializer<'de>,
{
    let val = match val {
        Value::Number(num) => num,
        Value::String(raw) => return raw.parse().map_err(D::Error::custom),
        _ => return Err(Error::custom("TTD must be a number or string")),
    };

    let num = if let Some(val) = val.as_u64() {
        U256::from(val)
    } else if let Some(value) = val.as_f64() {
        // The ethereum mainnet TTD is 58750000000000000000000, and geth serializes this
        // without quotes, because that is how golang `big.Int`s marshal in JSON. Numbers
        // are arbitrary precision in JSON, so this is valid JSON. This number is also
        // greater than a `u64`.
        //
        // Unfortunately, serde_json only supports parsing up to `u64`, resorting to `f64`
        // once `u64` overflows:
        // <https://github.com/serde-rs/json/blob/4bc1eaa03a6160593575bc9bc60c94dba4cab1e3/src/de.rs#L1411-L1415>
        // <https://github.com/serde-rs/json/blob/4bc1eaa03a6160593575bc9bc60c94dba4cab1e3/src/de.rs#L479-L484>
        // <https://github.com/serde-rs/json/blob/4bc1eaa03a6160593575bc9bc60c94dba4cab1e3/src/de.rs#L102-L108>
        //
        // serde_json does have an arbitrary precision feature, but this breaks untagged
        // enums in serde:
        // <https://github.com/serde-rs/serde/issues/2230>
        // <https://github.com/serde-rs/serde/issues/1183>
        //
        // To solve this, we use the captured float and return the TTD as a U256 if it's equal.
        if value == 5.875e22 {
            U256::from(58750000000000000000000u128)
        } else {
            // We could try to convert to a u128 here but there would probably be loss of
            // precision, so we just return an error.
            return Err(Error::custom("Deserializing a large non-mainnet TTD is not supported"));
        }
    } else {
        // must be i64 - negative numbers are not supported
        return Err(Error::custom("Negative TTD values are invalid and will not be deserialized"));
    };

    Ok(num)
}

#[cfg(test)]
mod tests {
    #[cfg(not(feature = "std"))]
    use alloc::{vec, vec::Vec};
    use alloy_primitives::U256;
    use serde::{Deserialize, Serialize};
    use serde_json::json;

    #[test]
    fn jsonu256_deserialize() {
        let deserialized: Vec<U256> =
            serde_json::from_str(r#"["","0", "0x","10",10,"0x10"]"#).unwrap();
        assert_eq!(
            deserialized,
            vec![
                U256::ZERO,
                U256::ZERO,
                U256::ZERO,
                U256::from(10),
                U256::from(10),
                U256::from(16),
            ]
        );
    }

    #[test]
    fn jsonu256_serialize() {
        let data = U256::from(16);
        let serialized = serde_json::to_string(&data).unwrap();

        assert_eq!(serialized, r#""0x10""#);
    }

    #[test]
    fn deserialize_ttd() {
        #[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
        struct Ttd(#[serde(deserialize_with = "super::deserialize_json_ttd_opt")] Option<U256>);

        let deserialized: Vec<Ttd> = serde_json::from_str(
            r#"["",0,"0","0x0","58750000000000000000000",58750000000000000000000]"#,
        )
        .unwrap();
        assert_eq!(
            deserialized,
            vec![
                Ttd(Some(U256::ZERO)),
                Ttd(Some(U256::ZERO)),
                Ttd(Some(U256::ZERO)),
                Ttd(Some(U256::ZERO)),
                Ttd(Some(U256::from(58750000000000000000000u128))),
                Ttd(Some(U256::from(58750000000000000000000u128))),
            ]
        );
    }

    #[test]
    fn deserialize_ttd_none() {
        #[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
        struct Ttd(#[serde(deserialize_with = "super::deserialize_json_ttd_opt")] Option<U256>);

        // Deserialize null as None
        let deserialized: Ttd = serde_json::from_value(json!(null)).unwrap();
        assert_eq!(deserialized, Ttd(None));
    }

    #[test]
    fn deserialize_ttd_invalid_string() {
        #[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
        struct Ttd(#[serde(deserialize_with = "super::deserialize_json_ttd_opt")] Option<U256>);

        // Invalid string that cannot be parsed into U256
        let result: Result<Ttd, _> = serde_json::from_value(json!("invalid_string"));
        assert!(result.is_err());
    }

    #[test]
    fn deserialize_ttd_large_non_mainnet() {
        #[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
        struct Ttd(#[serde(deserialize_with = "super::deserialize_json_ttd_opt")] Option<U256>);

        // Test for a large number not equal to 5.875e22, which should result in an error
        let result: Result<Ttd, _> = serde_json::from_value(json!(6.0e22));
        assert!(result.is_err());
    }

    #[test]
    fn deserialize_ttd_negative_number() {
        #[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
        struct Ttd(#[serde(deserialize_with = "super::deserialize_json_ttd_opt")] Option<U256>);

        // Test for a negative number which should not be allowed
        let result: Result<Ttd, _> = serde_json::from_value(json!(-1));
        assert!(result.is_err());
    }

    #[test]
    fn deserialize_ttd_as_string() {
        #[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
        struct Ttd(#[serde(deserialize_with = "super::deserialize_json_ttd_opt")] Option<U256>);

        // Test for valid TTD as a string
        let deserialized: Ttd = serde_json::from_value(json!("0x12345")).unwrap();
        assert_eq!(deserialized, Ttd(Some(U256::from(0x12345))));
    }
}