use anyhow::{anyhow, Result};
use futures::{future::BoxFuture, stream::BoxStream, StreamExt};
use gpui::{AppContext, Global, Model, ModelContext, Task};
use language_model::{
    LanguageModel, LanguageModelProvider, LanguageModelProviderId, LanguageModelRegistry,
    LanguageModelRequest,
};
use smol::lock::{Semaphore, SemaphoreGuardArc};
use std::{pin::Pin, sync::Arc, task::Poll};
use ui::Context;

pub fn init(cx: &mut AppContext) {
    let completion_provider = cx.new_model(|cx| LanguageModelCompletionProvider::new(cx));
    cx.set_global(GlobalLanguageModelCompletionProvider(completion_provider));
}

struct GlobalLanguageModelCompletionProvider(Model<LanguageModelCompletionProvider>);

impl Global for GlobalLanguageModelCompletionProvider {}

pub struct LanguageModelCompletionProvider {
    active_provider: Option<Arc<dyn LanguageModelProvider>>,
    active_model: Option<Arc<dyn LanguageModel>>,
    request_limiter: Arc<Semaphore>,
}

const MAX_CONCURRENT_COMPLETION_REQUESTS: usize = 4;

pub struct LanguageModelCompletionResponse {
    pub inner: BoxStream<'static, Result<String>>,
    _lock: SemaphoreGuardArc,
}

impl futures::Stream for LanguageModelCompletionResponse {
    type Item = Result<String>;

    fn poll_next(
        mut self: Pin<&mut Self>,
        cx: &mut std::task::Context<'_>,
    ) -> Poll<Option<Self::Item>> {
        Pin::new(&mut self.inner).poll_next(cx)
    }
}

impl LanguageModelCompletionProvider {
    pub fn global(cx: &AppContext) -> Model<Self> {
        cx.global::<GlobalLanguageModelCompletionProvider>()
            .0
            .clone()
    }

    pub fn read_global(cx: &AppContext) -> &Self {
        cx.global::<GlobalLanguageModelCompletionProvider>()
            .0
            .read(cx)
    }

    #[cfg(any(test, feature = "test-support"))]
    pub fn test(cx: &mut AppContext) {
        let provider = cx.new_model(|cx| {
            let mut this = Self::new(cx);
            let available_model = LanguageModelRegistry::read_global(cx)
                .available_models(cx)
                .first()
                .unwrap()
                .clone();
            this.set_active_model(available_model, cx);
            this
        });
        cx.set_global(GlobalLanguageModelCompletionProvider(provider));
    }

    pub fn new(cx: &mut ModelContext<Self>) -> Self {
        cx.observe(&LanguageModelRegistry::global(cx), |_, _, cx| {
            cx.notify();
        })
        .detach();

        Self {
            active_provider: None,
            active_model: None,
            request_limiter: Arc::new(Semaphore::new(MAX_CONCURRENT_COMPLETION_REQUESTS)),
        }
    }

    pub fn active_provider(&self) -> Option<Arc<dyn LanguageModelProvider>> {
        self.active_provider.clone()
    }

    pub fn set_active_provider(
        &mut self,
        provider_id: LanguageModelProviderId,
        cx: &mut ModelContext<Self>,
    ) {
        self.active_provider = LanguageModelRegistry::read_global(cx).provider(&provider_id);
        self.active_model = None;
        cx.notify();
    }

    pub fn active_model(&self) -> Option<Arc<dyn LanguageModel>> {
        self.active_model.clone()
    }

    pub fn set_active_model(&mut self, model: Arc<dyn LanguageModel>, cx: &mut ModelContext<Self>) {
        if self.active_model.as_ref().map_or(false, |m| {
            m.id() == model.id() && m.provider_id() == model.provider_id()
        }) {
            return;
        }

        self.active_provider =
            LanguageModelRegistry::read_global(cx).provider(&model.provider_id());
        self.active_model = Some(model.clone());

        if let Some(provider) = self.active_provider.as_ref() {
            provider.load_model(model, cx);
        }

        cx.notify();
    }

    pub fn is_authenticated(&self, cx: &AppContext) -> bool {
        self.active_provider
            .as_ref()
            .map_or(false, |provider| provider.is_authenticated(cx))
    }

    pub fn authenticate(&self, cx: &AppContext) -> Task<Result<()>> {
        self.active_provider
            .as_ref()
            .map_or(Task::ready(Ok(())), |provider| provider.authenticate(cx))
    }

    pub fn reset_credentials(&self, cx: &AppContext) -> Task<Result<()>> {
        self.active_provider
            .as_ref()
            .map_or(Task::ready(Ok(())), |provider| {
                provider.reset_credentials(cx)
            })
    }

    pub fn count_tokens(
        &self,
        request: LanguageModelRequest,
        cx: &AppContext,
    ) -> Option<BoxFuture<'static, Result<usize>>> {
        if let Some(model) = self.active_model() {
            Some(model.count_tokens(request, cx))
        } else {
            None
        }
    }

    pub fn stream_completion(
        &self,
        request: LanguageModelRequest,
        cx: &AppContext,
    ) -> Task<Result<LanguageModelCompletionResponse>> {
        if let Some(language_model) = self.active_model() {
            let rate_limiter = self.request_limiter.clone();
            cx.spawn(|cx| async move {
                let lock = rate_limiter.acquire_arc().await;
                let response = language_model.stream_completion(request, &cx).await?;
                Ok(LanguageModelCompletionResponse {
                    inner: response,
                    _lock: lock,
                })
            })
        } else {
            Task::ready(Err(anyhow!("No active model set")))
        }
    }

    pub fn complete(&self, request: LanguageModelRequest, cx: &AppContext) -> Task<Result<String>> {
        let response = self.stream_completion(request, cx);
        cx.foreground_executor().spawn(async move {
            let mut chunks = response.await?;
            let mut completion = String::new();
            while let Some(chunk) = chunks.next().await {
                let chunk = chunk?;
                completion.push_str(&chunk);
            }
            Ok(completion)
        })
    }
}

#[cfg(test)]
mod tests {
    use futures::StreamExt;
    use gpui::AppContext;
    use settings::SettingsStore;
    use ui::Context;

    use crate::{
        LanguageModelCompletionProvider, LanguageModelRequest, MAX_CONCURRENT_COMPLETION_REQUESTS,
    };

    use language_model::LanguageModelRegistry;

    #[gpui::test]
    fn test_rate_limiting(cx: &mut AppContext) {
        SettingsStore::test(cx);
        let fake_provider = LanguageModelRegistry::test(cx);

        let model = LanguageModelRegistry::read_global(cx)
            .available_models(cx)
            .first()
            .cloned()
            .unwrap();

        let provider = cx.new_model(|cx| {
            let mut provider = LanguageModelCompletionProvider::new(cx);
            provider.set_active_model(model.clone(), cx);
            provider
        });

        let fake_model = fake_provider.test_model();

        // Enqueue some requests
        for i in 0..MAX_CONCURRENT_COMPLETION_REQUESTS * 2 {
            let response = provider.read(cx).stream_completion(
                LanguageModelRequest {
                    temperature: i as f32 / 10.0,
                    ..Default::default()
                },
                cx,
            );
            cx.background_executor()
                .spawn(async move {
                    let mut stream = response.await.unwrap();
                    while let Some(message) = stream.next().await {
                        message.unwrap();
                    }
                })
                .detach();
        }
        cx.background_executor().run_until_parked();
        assert_eq!(
            fake_model.completion_count(),
            MAX_CONCURRENT_COMPLETION_REQUESTS
        );

        // Get the first completion request that is in flight and mark it as completed.
        let completion = fake_model.pending_completions().into_iter().next().unwrap();
        fake_model.finish_completion(&completion);

        // Ensure that the number of in-flight completion requests is reduced.
        assert_eq!(
            fake_model.completion_count(),
            MAX_CONCURRENT_COMPLETION_REQUESTS - 1
        );

        cx.background_executor().run_until_parked();

        // Ensure that another completion request was allowed to acquire the lock.
        assert_eq!(
            fake_model.completion_count(),
            MAX_CONCURRENT_COMPLETION_REQUESTS
        );

        // Mark all completion requests as finished that are in flight.
        for request in fake_model.pending_completions() {
            fake_model.finish_completion(&request);
        }

        assert_eq!(fake_model.completion_count(), 0);

        // Wait until the background tasks acquire the lock again.
        cx.background_executor().run_until_parked();

        assert_eq!(
            fake_model.completion_count(),
            MAX_CONCURRENT_COMPLETION_REQUESTS - 1
        );

        // Finish all remaining completion requests.
        for request in fake_model.pending_completions() {
            fake_model.finish_completion(&request);
        }

        cx.background_executor().run_until_parked();

        assert_eq!(fake_model.completion_count(), 0);
    }
}