use super::thinking::ThinkingStateManager;
use super::{LlmProvider, create_http_client};
use anyhow::{Context, Result, bail};
use async_trait::async_trait;
use serde::{Deserialize, Serialize};
use std::sync::Arc;
use std::time::Duration;

/// DeepSeek API client
pub struct DeepSeekClient {
    base_url: String,
    api_key: String,
    model: String,
    client: reqwest::Client,
    thinking_enabled: bool,
    reasoning_effort: Option<String>,
    max_tokens: u32,
    temperature: f32,
    thinking_state: Option<Arc<ThinkingStateManager>>,
}

#[derive(Debug, Serialize)]
struct ChatCompletionRequest {
    model: String,
    messages: Vec<Message>,
    #[serde(skip_serializing_if = "Option::is_none")]
    max_tokens: Option<u32>,
    #[serde(skip_serializing_if = "Option::is_none")]
    temperature: Option<f32>,
    #[serde(skip_serializing_if = "Option::is_none")]
    top_p: Option<f32>,
    #[serde(skip_serializing_if = "Option::is_none")]
    presence_penalty: Option<f32>,
    #[serde(skip_serializing_if = "Option::is_none")]
    frequency_penalty: Option<f32>,
    stream: bool,
    #[serde(skip_serializing_if = "Option::is_none")]
    thinking: Option<ThinkingConfig>,
    #[serde(skip_serializing_if = "Option::is_none")]
    reasoning_effort: Option<String>,
}

#[derive(Debug, Serialize)]
struct ThinkingConfig {
    #[serde(rename = "type")]
    thinking_type: String,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
struct Message {
    role: String,
    content: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    reasoning_content: Option<String>,
}

#[derive(Debug, Deserialize)]
struct ChatCompletionResponse {
    choices: Vec<Choice>,
}

#[derive(Debug, Deserialize)]
struct Choice {
    message: Message,
    #[serde(default)]
    reasoning_content: Option<String>,
}

// --- Streaming response structures ---

#[derive(Debug, Deserialize)]
struct StreamChunk {
    choices: Vec<StreamChoice>,
}

#[derive(Debug, Deserialize)]
struct StreamChoice {
    delta: StreamDelta,
    #[serde(default)]
    finish_reason: Option<String>,
    index: Option<u32>,
}

#[derive(Debug, Deserialize, Default)]
struct StreamDelta {
    #[serde(default)]
    content: Option<String>,
    #[serde(default)]
    reasoning_content: Option<String>,
}

#[derive(Debug, Deserialize)]
struct ErrorResponse {
    error: ApiError,
}

#[derive(Debug, Deserialize)]
struct ApiError {
    message: String,
    #[serde(rename = "type")]
    error_type: String,
}

impl DeepSeekClient {
    pub fn new(api_key: &str, model: &str) -> Result<Self> {
        let client = create_http_client(Duration::from_secs(300))?;

        Ok(Self {
            base_url: "https://api.deepseek.com".to_string(),
            api_key: api_key.to_string(),
            model: model.to_string(),
            client,
            thinking_enabled: false,
            reasoning_effort: None,
            max_tokens: 500,
            temperature: 0.7,
            thinking_state: None,
        })
    }

    pub fn with_base_url(api_key: &str, model: &str, base_url: &str) -> Result<Self> {
        let client = create_http_client(Duration::from_secs(300))?;

        Ok(Self {
            base_url: base_url.trim_end_matches('/').to_string(),
            api_key: api_key.to_string(),
            model: model.to_string(),
            client,
            thinking_enabled: false,
            reasoning_effort: None,
            max_tokens: 500,
            temperature: 0.7,
            thinking_state: None,
        })
    }

    pub fn with_timeout(mut self, timeout: Duration) -> Result<Self> {
        self.client = create_http_client(timeout)?;
        Ok(self)
    }

    pub fn with_thinking(mut self, enabled: bool) -> Self {
        self.thinking_enabled = enabled;
        self
    }

    pub fn with_reasoning_effort(mut self, effort: Option<String>) -> Self {
        self.reasoning_effort = effort;
        self
    }

    pub fn with_max_tokens(mut self, max_tokens: u32) -> Self {
        self.max_tokens = max_tokens;
        self
    }

    pub fn with_temperature(mut self, temperature: f32) -> Self {
        self.temperature = temperature;
        self
    }

    pub fn with_thinking_state(mut self, state: Arc<ThinkingStateManager>) -> Self {
        self.thinking_state = Some(state);
        self
    }

    pub async fn list_models(&self) -> Result<Vec<String>> {
        let url = format!("{}/models", self.base_url);

        let response = self
            .client
            .get(&url)
            .header("Authorization", format!("Bearer {}", self.api_key))
            .send()
            .await
            .context("Failed to list DeepSeek models")?;

        if !response.status().is_success() {
            let status = response.status();
            let text = response.text().await.unwrap_or_default();
            bail!("DeepSeek API error: {} - {}", status, text);
        }

        #[derive(Deserialize)]
        struct ModelsResponse {
            data: Vec<ModelId>,
        }

        #[derive(Deserialize)]
        struct ModelId {
            id: String,
        }

        let result: ModelsResponse = response
            .json()
            .await
            .context("Failed to parse DeepSeek response")?;

        Ok(result.data.into_iter().map(|m| m.id).collect())
    }

    pub async fn validate_key(&self) -> Result<bool> {
        match self.list_models().await {
            Ok(_) => Ok(true),
            Err(e) => {
                let err_str = e.to_string();
                if err_str.contains("401") || err_str.contains("Unauthorized") {
                    Ok(false)
                } else {
                    Err(e)
                }
            }
        }
    }
}

#[async_trait]
impl LlmProvider for DeepSeekClient {
    async fn generate(&self, prompt: &str) -> Result<String> {
        let messages = vec![Message {
            role: "user".to_string(),
            content: prompt.to_string(),
            reasoning_content: None,
        }];

        self.chat_completion_with_retry(messages).await
    }

    async fn generate_with_system(&self, system: &str, user: &str) -> Result<String> {
        let mut messages = vec![];

        if !system.is_empty() {
            messages.push(Message {
                role: "system".to_string(),
                content: system.to_string(),
                reasoning_content: None,
            });
        }

        messages.push(Message {
            role: "user".to_string(),
            content: user.to_string(),
            reasoning_content: None,
        });

        self.chat_completion_with_retry(messages).await
    }

    async fn is_available(&self) -> bool {
        self.validate_key().await.unwrap_or(false)
    }

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

impl DeepSeekClient {
    async fn chat_completion_with_retry(&self, messages: Vec<Message>) -> Result<String> {
        let mut last_error = None;

        for attempt in 1..=3 {
            match self.chat_completion(messages.clone()).await {
                Ok(result) => return Ok(result),
                Err(e) => {
                    let err_msg = e.to_string();
                    // 网络临时错误才重试
                    let is_retryable = err_msg.contains("timeout")
                        || err_msg.contains("connection")
                        || err_msg.contains("temporary")
                        || err_msg.contains("5")
                            && (err_msg.contains("500")
                                || err_msg.contains("502")
                                || err_msg.contains("503")
                                || err_msg.contains("504"));

                    if !is_retryable || attempt == 3 {
                        last_error = Some(e);
                        break;
                    }

                    // 指数退避
                    tokio::time::sleep(Duration::from_millis(500 * 2u64.pow(attempt - 1))).await;
                }
            }
        }

        Err(last_error.unwrap_or_else(|| anyhow::anyhow!("Request failed after retries")))
    }

    async fn chat_completion(&self, messages: Vec<Message>) -> Result<String> {
        let url = format!("{}/chat/completions", self.base_url);

        let thinking = if self.thinking_enabled {
            Some(ThinkingConfig {
                thinking_type: "enabled".to_string(),
            })
        } else {
            None
        };

        // 思考模式下，temperature/top_p 等参数不应传递
        // 非思考模式下可以正常传递
        let (temperature, max_tokens, top_p, presence_penalty, frequency_penalty) =
            if self.thinking_enabled {
                (None, Some(self.max_tokens), None, None, None)
            } else {
                (
                    Some(self.temperature),
                    Some(self.max_tokens),
                    None,
                    None,
                    None,
                )
            };

        let reasoning_effort = if self.thinking_enabled {
            self.reasoning_effort.clone()
        } else {
            None
        };

        let request = ChatCompletionRequest {
            model: self.model.clone(),
            messages: messages.clone(),
            max_tokens,
            temperature,
            top_p,
            presence_penalty,
            frequency_penalty,
            stream: self.thinking_enabled,
            thinking,
            reasoning_effort,
        };

        if self.thinking_enabled {
            self.streaming_chat_completion(&url, &request).await
        } else {
            self.non_streaming_chat_completion(&url, &request).await
        }
    }

    /// 非流式请求（非思考模式）
    async fn non_streaming_chat_completion(
        &self,
        url: &str,
        request: &ChatCompletionRequest,
    ) -> Result<String> {
        let response = self
            .client
            .post(url)
            .header("Authorization", format!("Bearer {}", self.api_key))
            .header("Content-Type", "application/json")
            .json(request)
            .send()
            .await
            .context("Failed to send request to DeepSeek")?;

        let status = response.status();

        if !status.is_success() {
            let text = response.text().await.unwrap_or_default();

            if let Ok(error) = serde_json::from_str::<ErrorResponse>(&text) {
                bail!(
                    "DeepSeek API error: {} ({})",
                    error.error.message,
                    error.error.error_type
                );
            }

            bail!("DeepSeek API error: {} - {}", status, text);
        }

        let result: ChatCompletionResponse = response
            .json()
            .await
            .context("Failed to parse DeepSeek response")?;

        result
            .choices
            .into_iter()
            .next()
            .map(|c| c.message.content.trim().to_string())
            .filter(|s| !s.is_empty())
            .ok_or_else(|| anyhow::anyhow!("No response from DeepSeek"))
    }

    /// 流式请求（思考模式），处理 reasoning_content 和 content
    async fn streaming_chat_completion(
        &self,
        url: &str,
        request: &ChatCompletionRequest,
    ) -> Result<String> {
        let response = self
            .client
            .post(url)
            .header("Authorization", format!("Bearer {}", self.api_key))
            .header("Content-Type", "application/json")
            .header("Accept", "text/event-stream")
            .json(request)
            .send()
            .await
            .context("Failed to send streaming request to DeepSeek")?;

        let status = response.status();

        if !status.is_success() {
            let text = response.text().await.unwrap_or_default();

            if let Ok(error) = serde_json::from_str::<ErrorResponse>(&text) {
                bail!(
                    "DeepSeek API error: {} ({})",
                    error.error.message,
                    error.error.error_type
                );
            }

            bail!("DeepSeek API error: {} - {}", status, text);
        }

        let mut content_buffer = String::new();
        let mut has_reasoning = false;
        let mut has_content = false;
        let mut stream_ended = false;

        let thinking_state = self.thinking_state.as_ref();

        let mut byte_stream = response.bytes_stream();
        let mut line_buffer = String::new();

        use futures_util::StreamExt;

        while let Some(chunk) = byte_stream.next().await {
            let chunk = chunk.context("Failed to read streaming response chunk")?;
            let chunk_str =
                String::from_utf8(chunk.to_vec()).context("Invalid UTF-8 in stream chunk")?;

            line_buffer.push_str(&chunk_str);

            // 处理完整行
            while let Some(line_end) = line_buffer.find('\n') {
                let line = line_buffer[..line_end].trim().to_string();
                line_buffer = line_buffer[line_end + 1..].to_string();

                if line.is_empty() {
                    continue;
                }

                // SSE 格式：data: {...} 或 data: [DONE]
                if line == "data: [DONE]" {
                    stream_ended = true;
                    break;
                }

                if let Some(json_str) = line.strip_prefix("data: ") {
                    match serde_json::from_str::<StreamChunk>(json_str) {
                        Ok(chunk) => {
                            for choice in &chunk.choices {
                                // 处理 reasoning_content
                                if let Some(ref reasoning) = choice.delta.reasoning_content
                                    && !reasoning.is_empty()
                                {
                                    if !has_reasoning {
                                        has_reasoning = true;
                                        if let Some(state) = thinking_state {
                                            state.start_thinking();
                                        }
                                    }
                                    // reasoning_content 不对外输出，仅用于内部状态判断
                                    continue;
                                }

                                // 处理 content
                                if let Some(ref content) = choice.delta.content
                                    && !content.is_empty()
                                {
                                    // reasoning 结束，content 开始出现时移除 thinking 标识
                                    if has_reasoning
                                        && !has_content
                                        && let Some(state) = thinking_state
                                    {
                                        state.end_thinking();
                                    }
                                    has_content = true;
                                    content_buffer.push_str(content);
                                }

                                // 检查 finish_reason
                                if let Some(ref reason) = choice.finish_reason
                                    && reason == "stop"
                                {
                                    stream_ended = true;
                                }
                            }
                        }
                        Err(_) => {
                            // 忽略无法解析的行（可能是心跳或注释）
                        }
                    }
                }
            }

            if stream_ended {
                break;
            }
        }

        // 确保思考状态已结束
        if let Some(state) = thinking_state {
            state.end_thinking();
        }

        let result = content_buffer.trim().to_string();

        if result.is_empty() {
            if has_reasoning && !has_content {
                bail!(
                    "DeepSeek returned reasoning content but no final answer. \
                     The model may have entered an incomplete thinking state. \
                     Please try again or disable thinking mode."
                );
            }
            bail!(
                "No response from DeepSeek. \
                 If thinking mode is enabled, try disabling it or ensure the model supports it."
            );
        }

        Ok(result)
    }
}

/// 可用 DeepSeek 模型列表
/// deepseek-chat / deepseek-reasoner 将于 2026-07-24 停用，推荐使用 V4 系列
pub const DEEPSEEK_MODELS: &[&str] = &[
    "deepseek-v4-flash",
    "deepseek-v4-pro",
    // 兼容旧版模型 ID（将于 2026-07-24 停用）
    "deepseek-chat",
    "deepseek-reasoner",
];

pub fn is_valid_model(model: &str) -> bool {
    DEEPSEEK_MODELS.contains(&model)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_model_validation_v4() {
        assert!(is_valid_model("deepseek-v4-flash"));
        assert!(is_valid_model("deepseek-v4-pro"));
        assert!(is_valid_model("deepseek-chat"));
        assert!(is_valid_model("deepseek-reasoner"));
        assert!(!is_valid_model("invalid-model"));
        assert!(!is_valid_model("deepseek-v3"));
    }

    #[test]
    fn test_client_builder_defaults() {
        let client = DeepSeekClient::new("test-key", "deepseek-v4-flash").unwrap();
        assert!(!client.thinking_enabled);
        assert_eq!(client.max_tokens, 500);
        assert_eq!(client.temperature, 0.7);
        assert!(client.reasoning_effort.is_none());
        assert!(client.thinking_state.is_none());
    }

    #[test]
    fn test_client_builder_with_thinking() {
        let client = DeepSeekClient::new("test-key", "deepseek-v4-flash")
            .unwrap()
            .with_thinking(true)
            .with_reasoning_effort(Some("high".to_string()))
            .with_max_tokens(1000)
            .with_temperature(0.5);

        assert!(client.thinking_enabled);
        assert_eq!(client.reasoning_effort, Some("high".to_string()));
        assert_eq!(client.max_tokens, 1000);
        assert_eq!(client.temperature, 0.5);
    }

    #[test]
    fn test_thinking_config_serialization() {
        let config = ThinkingConfig {
            thinking_type: "enabled".to_string(),
        };
        let json = serde_json::to_string(&config).unwrap();
        assert_eq!(json, r#"{"type":"enabled"}"#);
    }

    #[test]
    fn test_message_serialization_without_reasoning() {
        let msg = Message {
            role: "user".to_string(),
            content: "Hello".to_string(),
            reasoning_content: None,
        };
        let json = serde_json::to_string(&msg).unwrap();
        assert!(!json.contains("reasoning_content"));
    }

    #[test]
    fn test_stream_delta_parsing() {
        let json = r#"{"content":"Hello","reasoning_content":null}"#;
        let delta: StreamDelta = serde_json::from_str(json).unwrap();
        assert_eq!(delta.content, Some("Hello".to_string()));
        assert!(delta.reasoning_content.is_none());
    }

    #[test]
    fn test_stream_delta_reasoning_only() {
        let json = r#"{"content":null,"reasoning_content":"Let me think..."}"#;
        let delta: StreamDelta = serde_json::from_str(json).unwrap();
        assert!(delta.content.is_none());
        assert_eq!(delta.reasoning_content, Some("Let me think...".to_string()));
    }
}