use std::pin::Pin;
use std::time::Duration;

use async_trait::async_trait;
use bytes::Bytes;
use futures_core::stream::Stream;
use futures_util::StreamExt;
use reqwest::Client;
use tracing::{debug, error, info};

use super::LlmProvider;
use crate::llm::error::LlmError;
use crate::llm::types::{
    ChatRequest, ChatResponse, OpenaiChatChunk, OpenaiChatResponse, StreamOptions,
};

pub struct OpenaiProvider {
    http_client: Client,
    base_url: String,
    api_key: String,
}

impl OpenaiProvider {
    pub fn new(base_url: String, api_key: String, _model: String) -> Self {
        let http_client = Client::builder()
            .timeout(Duration::from_secs(120))
            .build()
            .expect("创建 HTTP 客户端失败");

        Self {
            http_client,
            base_url,
            api_key,
        }
    }

    pub fn with_client(mut self, client: Client) -> Self {
        self.http_client = client;
        self
    }

    fn map_reqwest_error(e: reqwest::Error) -> LlmError {
        if e.is_timeout() {
            LlmError::Timeout {
                duration: Duration::from_secs(120),
            }
        } else if e.is_connect() {
            LlmError::Other(format!("连接失败: {}", e))
        } else {
            LlmError::Other(format!("请求失败: {}", e))
        }
    }
}

#[async_trait]
impl LlmProvider for OpenaiProvider {
    async fn chat(&self, request: ChatRequest) -> Result<ChatResponse, LlmError> {
        let url = format!("{}/chat/completions", self.base_url.trim_end_matches('/'));

        info!(model = %request.model, max_tokens = request.max_tokens, temperature = request.temperature, "发送 LLM 请求");

        let response = self
            .http_client
            .post(&url)
            .header("Authorization", format!("Bearer {}", self.api_key))
            .json(&request)
            .send()
            .await
            .map_err(|e| {
                error!(error = %e, "请求失败");
                Self::map_reqwest_error(e)
            })?;

        let status = response.status();
        let status_code: u16 = status.as_u16();

        if !status.is_success() {
            let retry_after = response
                .headers()
                .get("retry-after")
                .and_then(|v| v.to_str().ok())
                .and_then(|v| v.parse::<u64>().ok())
                .map(Duration::from_secs);
            let body_text = response.text().await.unwrap_or_default();

            error!(status = status_code, body = %body_text, "请求失败");

            return match status_code {
                401 => Err(LlmError::Authentication(body_text)),
                429 => Err(LlmError::RateLimit { retry_after }),
                _ if status_code >= 500 => Err(LlmError::Request {
                    status: status_code,
                    body: body_text,
                }),
                _ if status_code == 400 && body_text.contains("context_length_exceeded") => {
                    Err(LlmError::ContextLength {
                        actual: 0,
                        limit: 0,
                    })
                }
                _ => Err(LlmError::Request {
                    status: status_code,
                    body: body_text,
                }),
            };
        }

        let body_text = response.text().await.unwrap_or_default();
        debug!(body = %body_text, "收到响应体");

        let chat_response: OpenaiChatResponse = serde_json::from_str(&body_text).map_err(|e| {
            error!(error = %e, body = %body_text, "响应解析失败");
            LlmError::Other(format!("响应解析失败: {}", e))
        })?;

        debug!(response = ?chat_response, "收到 LLM 响应");

        Ok(ChatResponse::from(chat_response))
    }

    async fn chat_stream(
        &self,
        mut request: ChatRequest,
    ) -> Result<
        Pin<Box<dyn Stream<Item = Result<OpenaiChatChunk, LlmError>> + Send>>,
        LlmError,
    > {
        let url = format!("{}/chat/completions", self.base_url.trim_end_matches('/'));

        request.stream = Some(true);
        request.stream_options = Some(StreamOptions {
            include_usage: Some(true),
            include_obfuscation: None,
        });

        info!(model = %request.model, "发送 LLM 流式请求");

        let response = self
            .http_client
            .post(&url)
            .header("Authorization", format!("Bearer {}", self.api_key))
            .json(&request)
            .send()
            .await
            .map_err(|e| {
                error!(error = %e, "流式请求失败");
                Self::map_reqwest_error(e)
            })?;

        let status = response.status();
        let status_code: u16 = status.as_u16();

        if !status.is_success() {
            let body_text = response.text().await.unwrap_or_default();
            error!(status = status_code, body = %body_text, "流式请求失败");
            return Err(LlmError::Request {
                status: status_code,
                body: body_text,
            });
        }

        let byte_stream = response.bytes_stream().map(|r| {
            r.map_err(|e| LlmError::Other(format!("流式读取失败: {}", e)))
        });

        Ok(Box::pin(SseChunkStream::new(byte_stream)))
    }
}

struct SseChunkStream<S> {
    inner: S,
    buffer: String,
}

impl<S: Stream<Item = Result<Bytes, LlmError>> + Unpin> SseChunkStream<S> {
    fn new(stream: S) -> Self {
        Self {
            inner: stream,
            buffer: String::new(),
        }
    }
}

impl<S: Stream<Item = Result<Bytes, LlmError>> + Unpin> Stream for SseChunkStream<S> {
    type Item = Result<OpenaiChatChunk, LlmError>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> std::task::Poll<Option<Self::Item>> {
        loop {
            if let Some(pos) = self.buffer.find("\n") {
                let line = self.buffer.drain(..pos + 1).collect::<String>();
                let trimmed = line.trim();
                if trimmed.is_empty()
                    || trimmed == "data: [DONE]"
                    || trimmed == "[DONE]"
                    || trimmed == "data:"
                {
                    continue;
                }
                let data = if let Some(p) = trimmed.strip_prefix("data: ") {
                    p
                } else {
                    trimmed
                };
                match serde_json::from_str::<OpenaiChatChunk>(data) {
                    Ok(chunk) => return std::task::Poll::Ready(Some(Ok(chunk))),
                    Err(e) => {
                        return std::task::Poll::Ready(Some(Err(LlmError::Other(format!(
                            "Chunk 解析失败: {} | raw: {}",
                            e, data
                        )))));
                    }
                }
            }

            match Pin::new(&mut self.inner).poll_next(cx) {
                std::task::Poll::Ready(Some(Ok(bytes))) => {
                    if let Ok(s) = std::str::from_utf8(&bytes) {
                        self.buffer.push_str(s);
                    }
                }
                std::task::Poll::Ready(Some(Err(e))) => {
                    return std::task::Poll::Ready(Some(Err(e)));
                }
                std::task::Poll::Ready(None) => {
                    if self.buffer.is_empty() {
                        return std::task::Poll::Ready(None);
                    }
                    self.buffer.clear();
                    return std::task::Poll::Ready(None);
                }
                std::task::Poll::Pending => return std::task::Poll::Pending,
            }
        }
    }
}