// SPDX-FileCopyrightText: 2025 Łukasz Niemier <#@hauleth.dev>
//
// SPDX-License-Identifier: EUPL-1.2

use std::fmt;
use std::str::FromStr;

use serde::{Deserialize, Deserializer, de};

pub fn string_or_struct<'de, T, D>(deserializer: D) -> Result<T, D::Error>
where
    T: Deserialize<'de> + FromStr,
    D: Deserializer<'de>,
    <T as FromStr>::Err: fmt::Display,
{
    // This is a Visitor that forwards string types to T's `FromStr` impl and
    // forwards map types to T's `Deserialize` impl. The `PhantomData` is to
    // keep the compiler from complaining about T being an unused generic type
    // parameter. We need T in order to know the Value type for the Visitor
    // impl.
    struct StringOrStruct<T>(std::marker::PhantomData<fn() -> T>);

    impl<'de, T> de::Visitor<'de> for StringOrStruct<T>
    where
        T: Deserialize<'de> + FromStr,
        <T as FromStr>::Err: fmt::Display,
    {
        type Value = T;

        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("string or map")
        }

        fn visit_str<E>(self, value: &str) -> Result<T, E>
        where
            E: de::Error,
        {
            FromStr::from_str(value).map_err(de::Error::custom)
        }

        fn visit_map<M>(self, map: M) -> Result<T, M::Error>
        where
            M: de::MapAccess<'de>,
        {
            // `MapAccessDeserializer` is a wrapper that turns a `MapAccess`
            // into a `Deserializer`, allowing it to be used as the input to T's
            // `Deserialize` implementation. T then deserializes itself using
            // the entries from the map visitor.
            Deserialize::deserialize(de::value::MapAccessDeserializer::new(map))
        }
    }

    deserializer.deserialize_any(StringOrStruct(Default::default()))
}

pub fn from_str<'de, T, D>(deserializer: D) -> Result<T, D::Error>
where
    T: FromStr,
    D: Deserializer<'de>,
    <T as FromStr>::Err: fmt::Display,
{
    struct DeFromStr<T>(std::marker::PhantomData<T>);

    impl<T> de::Visitor<'_> for DeFromStr<T>
    where
        T: FromStr,
        <T as FromStr>::Err: fmt::Display,
    {
        type Value = T;

        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("string or map")
        }

        fn visit_str<E>(self, value: &str) -> Result<T, E>
        where
            E: de::Error,
        {
            FromStr::from_str(value).map_err(de::Error::custom)
        }
    }

    deserializer.deserialize_any(DeFromStr(Default::default()))
}