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use std::fmt;

use serde::Serialize;

/// A custom attribute on a container, variant, or field.
///
/// Applied by using the `#[configurable(metadata(...))]` helper. Two forms are supported:
///
/// - as a flag (`#[configurable(metadata(some_flag))]`)
/// - as a key/value pair (`#[configurable(metadata(status = "beta"))]`)
///
/// Custom attributes are added to the relevant schema definition as a custom field, `_metadata`, and stored as an
/// object. For key/value pairs, they are added as-is to the object. For flags, the flag name is the property name, and
/// the value will always be `true`.
#[derive(Clone, Debug)]
pub enum CustomAttribute {
    /// A standalone flag.
    ///
    /// Common for marking items as supporting a particular feature i.e. marking fields that can use the event template syntax.
    Flag(String),

    /// A key/value pair.
    ///
    /// Used for most metadata, where a given key could have many different possible values i.e. the status of a
    /// component (alpha, beta, stable, deprecated, etc).
    KeyValue {
        key: String,
        value: serde_json::Value,
    },
}

impl CustomAttribute {
    pub fn flag<N>(name: N) -> Self
    where
        N: fmt::Display,
    {
        Self::Flag(name.to_string())
    }

    pub fn kv<K, V>(key: K, value: V) -> Self
    where
        K: fmt::Display,
        V: Serialize,
    {
        Self::KeyValue {
            key: key.to_string(),
            value: serde_json::to_value(value).expect("should not fail to serialize value to JSON"),
        }
    }

    pub const fn is_flag(&self) -> bool {
        matches!(self, Self::Flag(_))
    }

    pub const fn is_kv(&self) -> bool {
        matches!(self, Self::KeyValue { .. })
    }
}