// Copyright 2019 The Tari Project
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use async_trait::async_trait;

use crate::context::ServiceInitializerContext;

pub type ServiceInitializationError = anyhow::Error;

type Output = Result<(), ServiceInitializationError>;

/// Implementors of this trait will initialize a service
/// The `StackBuilder` builds impls of this trait.
#[async_trait]
pub trait ServiceInitializer {
    /// Async initialization code for a service
    async fn initialize(&mut self, context: ServiceInitializerContext) -> Output;
}

/// Implementation of ServiceInitializer for any function matching the signature of `ServiceInitializer::initialize`
/// This allows the following "short-hand" syntax to be used:
///
/// ```edition2018
/// # use tari_service_framework::ServiceInitializerContext;
/// # use tokio::runtime;
/// let my_initializer = |context: ServiceInitializerContext| {
///     // initialization code
///     futures::future::ready(Result::<_, ()>::Ok(()))
/// };
/// ```
#[async_trait]
impl<TFunc> ServiceInitializer for TFunc
where TFunc: FnMut(ServiceInitializerContext) -> Output + Send
{
    async fn initialize(&mut self, context: ServiceInitializerContext) -> Output {
        (self)(context)
    }
}

/// An implementation of `ServiceInitializer` that wraps an `impl FnOnce`
pub struct InitializerFn<TFunc>(Option<TFunc>);

impl<TFunc> InitializerFn<TFunc> {
    pub fn new(f: TFunc) -> Self {
        Self(Some(f))
    }
}

#[async_trait]
impl<TFunc> ServiceInitializer for InitializerFn<TFunc>
where TFunc: FnOnce(ServiceInitializerContext) -> Output + Send
{
    async fn initialize(&mut self, context: ServiceInitializerContext) -> Output {
        let f = self.0.take().expect("initializer called more than once");
        (f)(context)
    }
}
