//! Provider traits and registries.

use crate::{types::*, Error, Result};
use anyhow::anyhow;
use futures::{Stream, StreamExt};
use std::any::Any;
use std::future::Future;
use std::pin::Pin;
use std::sync::Arc;

/// A stream of chat responses
pub type ChatStream = Pin<Box<dyn Stream<Item = Result<ChatResponse>> + Send>>;

/// Trait for LLM providers (Ollama, OpenAI, Anthropic, etc.) with zero-cost static dispatch.
pub trait LLMProvider: Send + Sync + 'static + Any + Sized {
    type Stream: Stream<Item = Result<ChatResponse>> + Send + 'static;

    type ListModelsFuture<'a>: Future<Output = Result<Vec<ModelInfo>>> + Send
    where
        Self: 'a;

    type ChatFuture<'a>: Future<Output = Result<ChatResponse>> + Send
    where
        Self: 'a;

    type ChatStreamFuture<'a>: Future<Output = Result<Self::Stream>> + Send
    where
        Self: 'a;

    type HealthCheckFuture<'a>: Future<Output = Result<()>> + Send
    where
        Self: 'a;

    fn name(&self) -> &str;

    fn list_models(&self) -> Self::ListModelsFuture<'_>;
    fn chat(&self, request: ChatRequest) -> Self::ChatFuture<'_>;
    fn chat_stream(&self, request: ChatRequest) -> Self::ChatStreamFuture<'_>;
    fn health_check(&self) -> Self::HealthCheckFuture<'_>;

    fn config_schema(&self) -> serde_json::Value {
        serde_json::json!({})
    }

    fn as_any(&self) -> &(dyn Any + Send + Sync) {
        self
    }
}

/// Helper that implements [`LLMProvider::chat`] in terms of [`LLMProvider::chat_stream`].
pub async fn chat_via_stream<'a, P>(provider: &'a P, request: ChatRequest) -> Result<ChatResponse>
where
    P: LLMProvider + 'a,
{
    let stream = provider.chat_stream(request).await?;
    let mut boxed: ChatStream = Box::pin(stream);
    match boxed.next().await {
        Some(Ok(response)) => Ok(response),
        Some(Err(err)) => Err(err),
        None => Err(Error::Provider(anyhow!(
            "Empty chat stream from provider {}",
            provider.name()
        ))),
    }
}

/// Object-safe wrapper trait for runtime-configurable provider usage.
#[async_trait::async_trait]
pub trait Provider: Send + Sync {
    /// Get the name of this provider.
    fn name(&self) -> &str;

    /// List available models from this provider.
    async fn list_models(&self) -> Result<Vec<ModelInfo>>;

    /// Send a chat completion request.
    async fn chat(&self, request: ChatRequest) -> Result<ChatResponse>;

    /// Send a streaming chat completion request.
    async fn chat_stream(&self, request: ChatRequest) -> Result<ChatStream>;

    /// Check if the provider is available/healthy.
    async fn health_check(&self) -> Result<()>;

    /// Get provider-specific configuration schema.
    fn config_schema(&self) -> serde_json::Value {
        serde_json::json!({})
    }

    fn as_any(&self) -> &(dyn Any + Send + Sync);
}

#[async_trait::async_trait]
impl<T> Provider for T
where
    T: LLMProvider,
{
    fn name(&self) -> &str {
        LLMProvider::name(self)
    }

    async fn list_models(&self) -> Result<Vec<ModelInfo>> {
        LLMProvider::list_models(self).await
    }

    async fn chat(&self, request: ChatRequest) -> Result<ChatResponse> {
        LLMProvider::chat(self, request).await
    }

    async fn chat_stream(&self, request: ChatRequest) -> Result<ChatStream> {
        let stream = LLMProvider::chat_stream(self, request).await?;
        Ok(Box::pin(stream))
    }

    async fn health_check(&self) -> Result<()> {
        LLMProvider::health_check(self).await
    }

    fn config_schema(&self) -> serde_json::Value {
        LLMProvider::config_schema(self)
    }

    fn as_any(&self) -> &(dyn Any + Send + Sync) {
        LLMProvider::as_any(self)
    }
}

/// Configuration for a provider
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct ProviderConfig {
    /// Provider type identifier
    pub provider_type: String,
    /// Base URL for API calls
    pub base_url: Option<String>,
    /// API key or token
    pub api_key: Option<String>,
    /// Additional provider-specific configuration
    #[serde(flatten)]
    pub extra: std::collections::HashMap<String, serde_json::Value>,
}

/// A registry of providers
pub struct ProviderRegistry {
    providers: std::collections::HashMap<String, Arc<dyn Provider>>,
}

impl ProviderRegistry {
    /// Create a new provider registry
    pub fn new() -> Self {
        Self {
            providers: std::collections::HashMap::new(),
        }
    }

    /// Register a provider using static dispatch.
    pub fn register<P: LLMProvider + 'static>(&mut self, provider: P) {
        self.register_arc(Arc::new(provider));
    }

    /// Register an already wrapped provider
    pub fn register_arc(&mut self, provider: Arc<dyn Provider>) {
        let name = provider.name().to_string();
        self.providers.insert(name, provider);
    }

    /// Get a provider by name
    pub fn get(&self, name: &str) -> Option<Arc<dyn Provider>> {
        self.providers.get(name).cloned()
    }

    /// List all registered provider names
    pub fn list_providers(&self) -> Vec<String> {
        self.providers.keys().cloned().collect()
    }

    /// Get all models from all providers
    pub async fn list_all_models(&self) -> Result<Vec<ModelInfo>> {
        let mut all_models = Vec::new();

        for provider in self.providers.values() {
            match provider.list_models().await {
                Ok(mut models) => all_models.append(&mut models),
                Err(_) => {
                    // Continue with other providers
                }
            }
        }

        Ok(all_models)
    }
}

impl Default for ProviderRegistry {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
pub mod test_utils {
    use super::*;
    use crate::types::{ChatRequest, ChatResponse, Message, ModelInfo, Role};
    use futures::stream;
    use std::future::{ready, Ready};

    /// Mock provider for testing
    #[derive(Default)]
    pub struct MockProvider;

    impl LLMProvider for MockProvider {
        type Stream = stream::Iter<std::vec::IntoIter<Result<ChatResponse>>>;
        type ListModelsFuture<'a> = Ready<Result<Vec<ModelInfo>>>;
        type ChatFuture<'a> = Ready<Result<ChatResponse>>;
        type ChatStreamFuture<'a> = Ready<Result<Self::Stream>>;
        type HealthCheckFuture<'a> = Ready<Result<()>>;

        fn name(&self) -> &str {
            "mock"
        }

        fn list_models(&self) -> Self::ListModelsFuture<'_> {
            ready(Ok(vec![ModelInfo {
                id: "mock-model".to_string(),
                provider: "mock".to_string(),
                name: "mock-model".to_string(),
                description: None,
                context_window: None,
                capabilities: vec![],
                supports_tools: false,
            }]))
        }

        fn chat(&self, request: ChatRequest) -> Self::ChatFuture<'_> {
            ready(Ok(self.build_response(&request)))
        }

        fn chat_stream(&self, request: ChatRequest) -> Self::ChatStreamFuture<'_> {
            let response = self.build_response(&request);
            ready(Ok(stream::iter(vec![Ok(response)])))
        }

        fn health_check(&self) -> Self::HealthCheckFuture<'_> {
            ready(Ok(()))
        }
    }

    impl MockProvider {
        fn build_response(&self, request: &ChatRequest) -> ChatResponse {
            let content = format!(
                "Mock response to: {}",
                request
                    .messages
                    .last()
                    .map(|m| m.content.clone())
                    .unwrap_or_default()
            );

            ChatResponse {
                message: Message::new(Role::Assistant, content),
                usage: None,
                is_streaming: false,
                is_final: true,
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::test_utils::MockProvider;
    use super::*;
    use crate::types::{ChatParameters, ChatRequest, ChatResponse, Message, ModelInfo, Role};
    use futures::stream;
    use std::future::{ready, Ready};
    use std::sync::Arc;

    struct StreamingProvider;

    impl LLMProvider for StreamingProvider {
        type Stream = stream::Iter<std::vec::IntoIter<Result<ChatResponse>>>;
        type ListModelsFuture<'a> = Ready<Result<Vec<ModelInfo>>>;
        type ChatFuture<'a> = Ready<Result<ChatResponse>>;
        type ChatStreamFuture<'a> = Ready<Result<Self::Stream>>;
        type HealthCheckFuture<'a> = Ready<Result<()>>;

        fn name(&self) -> &str {
            "streaming"
        }

        fn list_models(&self) -> Self::ListModelsFuture<'_> {
            ready(Ok(vec![ModelInfo {
                id: "stream-model".to_string(),
                provider: "streaming".to_string(),
                name: "stream-model".to_string(),
                description: None,
                context_window: None,
                capabilities: vec!["chat".to_string()],
                supports_tools: false,
            }]))
        }

        fn chat(&self, request: ChatRequest) -> Self::ChatFuture<'_> {
            ready(Ok(self.response(&request)))
        }

        fn chat_stream(&self, request: ChatRequest) -> Self::ChatStreamFuture<'_> {
            let response = self.response(&request);
            ready(Ok(stream::iter(vec![Ok(response)])))
        }

        fn health_check(&self) -> Self::HealthCheckFuture<'_> {
            ready(Ok(()))
        }
    }

    impl StreamingProvider {
        fn response(&self, request: &ChatRequest) -> ChatResponse {
            let reply = format!(
                "echo:{}",
                request
                    .messages
                    .last()
                    .map(|m| m.content.clone())
                    .unwrap_or_default()
            );
            ChatResponse {
                message: Message::new(Role::Assistant, reply),
                usage: None,
                is_streaming: true,
                is_final: true,
            }
        }
    }

    #[tokio::test]
    async fn default_chat_reads_from_stream() {
        let provider = StreamingProvider;
        let request = ChatRequest {
            model: "stream-model".to_string(),
            messages: vec![Message::new(Role::User, "ping".to_string())],
            parameters: ChatParameters::default(),
            tools: None,
        };

        let response = LLMProvider::chat(&provider, request)
            .await
            .expect("chat succeeded");
        assert_eq!(response.message.content, "echo:ping");
        assert!(response.is_final);
    }

    #[tokio::test]
    async fn registry_registers_static_provider() {
        let mut registry = ProviderRegistry::new();
        registry.register(StreamingProvider);

        let provider = registry.get("streaming").expect("provider registered");
        let models = provider.list_models().await.expect("models listed");
        assert_eq!(models[0].id, "stream-model");
    }

    #[tokio::test]
    async fn registry_accepts_dynamic_provider() {
        let mut registry = ProviderRegistry::new();
        let provider: Arc<dyn Provider> = Arc::new(MockProvider::default());
        registry.register_arc(provider.clone());

        let fetched = registry.get("mock").expect("mock provider present");
        let request = ChatRequest {
            model: "mock-model".to_string(),
            messages: vec![Message::new(Role::User, "hi".to_string())],
            parameters: ChatParameters::default(),
            tools: None,
        };
        let response = Provider::chat(fetched.as_ref(), request)
            .await
            .expect("chat succeeded");
        assert_eq!(response.message.content, "Mock response to: hi");
    }
}