use std::sync::Arc;

use crate::bus::ChatMessage;
use crate::memory::MemoryManager;
use crate::providers::{ChatCompletionRequest, LLMProvider, Message};

use crate::agent::AgentError;

/// Token estimation using ~4 chars/token heuristic with 1.2x safety margin.
pub fn estimate_tokens(messages: &[ChatMessage]) -> usize {
    let raw: usize = messages
        .iter()
        .map(|m| m.content.len().div_ceil(4) + 4)
        .sum();
    (raw as f64 * 1.2) as usize
}

/// Configuration for context compression.
#[derive(Debug, Clone)]
pub struct ContextCompressionConfig {
    /// Protect first N messages (system prompt, etc.)
    pub protect_first_n: usize,
    /// Protect last N messages (recent context)
    pub protect_last_n: usize,
    /// Maximum compression passes
    pub max_passes: u32,
    /// Maximum characters in summary
    pub summary_max_chars: usize,
    /// Characters to keep when trimming tool results
    pub tool_result_trim_chars: usize,
}

impl Default for ContextCompressionConfig {
    fn default() -> Self {
        Self {
            protect_first_n: 1,
            protect_last_n: 4,
            max_passes: 3,
            summary_max_chars: 4000,
            tool_result_trim_chars: 2000,
        }
    }
}

/// Context compressor that reduces message history when it exceeds token limits.
pub struct ContextCompressor {
    config: ContextCompressionConfig,
    context_window: usize,
    /// Threshold ratio to trigger compression (50% of context window)
    threshold_ratio: f64,
    /// Shared LLM provider for summarization
    provider: Arc<dyn LLMProvider>,
    /// Memory manager handle. Compressed context summaries are persisted
    /// as timeline memory entries.
    memory: Arc<MemoryManager>,
    /// Current session ID for timeline memory writes.
    session_id: Option<String>,
}

impl ContextCompressor {
    /// Create a new compressor with the given provider, context window size, and memory manager.
    pub fn new(
        provider: Arc<dyn LLMProvider>,
        context_window: usize,
        memory: Arc<MemoryManager>,
    ) -> Self {
        Self {
            config: ContextCompressionConfig::default(),
            context_window,
            threshold_ratio: 0.5,
            provider,
            memory,
            session_id: None,
        }
    }

    /// Create with custom configuration.
    pub fn with_config(
        provider: Arc<dyn LLMProvider>,
        context_window: usize,
        config: ContextCompressionConfig,
        memory: Arc<MemoryManager>,
    ) -> Self {
        Self {
            config,
            context_window,
            threshold_ratio: 0.5,
            provider,
            memory,
            session_id: None,
        }
    }

    /// Set the current session ID for timeline writes.
    pub fn set_session_id(&mut self, id: Option<String>) {
        self.session_id = id;
    }

    /// Get the compression threshold in tokens.
    fn threshold(&self) -> usize {
        (self.context_window as f64 * self.threshold_ratio) as usize
    }

    /// Fast-path: trim oversized tool results without LLM call.
    /// Returns the number of messages modified.
    fn fast_trim_tool_results(&self, messages: &mut [ChatMessage]) -> usize {
        let limit = self.config.tool_result_trim_chars;
        let mut modified = 0;

        for msg in messages.iter_mut() {
            if msg.role == "tool" && msg.content.len() > limit {
                let removed = msg.content.len() - limit;
                msg.content = format!(
                    "{}...\n\n[Output truncated - {} characters removed]",
                    &msg.content[..msg.content.ceil_char_boundary(limit)],
                    removed
                );
                modified += 1;
            }
        }

        modified
    }

    /// Main entry point - compresses history if over threshold.
    pub async fn compress_if_needed(
        &self,
        history: Vec<ChatMessage>,
    ) -> Result<Vec<ChatMessage>, AgentError> {
        // Check if compression is needed
        let tokens = estimate_tokens(&history);
        if tokens <= self.threshold() {
            return Ok(history);
        }

        #[cfg(debug_assertions)]
        tracing::debug!(
            tokens = tokens,
            threshold = self.threshold(),
            msg_count = history.len(),
            "Starting context compression"
        );

        // Fast trim pass first
        let trimmed = self.fast_trim_tool_results(&mut history.clone());
        if trimmed > 0 {
            let tokens_after = estimate_tokens(&history);
            #[cfg(debug_assertions)]
            tracing::debug!(
                trimmed_messages = trimmed,
                tokens_after = tokens_after,
                "Fast trim completed"
            );
            if tokens_after <= self.threshold() {
                return Ok(history);
            }
        }

        // LLM summarization pass
        let mut current_history = history;
        for pass in 0..self.config.max_passes {
            let tokens = estimate_tokens(&current_history);
            if tokens <= self.threshold() {
                break;
            }

            #[cfg(debug_assertions)]
            tracing::debug!(
                pass = pass + 1,
                tokens = tokens,
                "Compression pass"
            );

            match self.compress_once(&current_history).await {
                Ok(Some(compressed)) => {
                    current_history = compressed;
                }
                Ok(None) => {
                    // No more compressible content
                    break;
                }
                Err(e) => {
                    tracing::warn!(error = %e, "Compression pass failed, using current history");
                    break;
                }
            }
        }

        #[cfg(debug_assertions)]
        tracing::debug!(
            final_tokens = estimate_tokens(&current_history),
            final_msg_count = current_history.len(),
            "Context compression completed"
        );

        Ok(current_history)
    }

    /// Single compression pass - summarize middle messages between user turns.
    /// Returns Some(compressed) if compression happened, None if nothing to compress.
    async fn compress_once(
        &self,
        history: &[ChatMessage],
    ) -> Result<Option<Vec<ChatMessage>>, AgentError> {
        if history.len() <= self.config.protect_first_n + self.config.protect_last_n {
            return Ok(None);
        }

        // Find user message indices (excluding protected first messages)
        let user_indices: Vec<usize> = history
            .iter()
            .enumerate()
            .skip(self.config.protect_first_n)
            .filter(|(_, m)| m.role == "user")
            .map(|(i, _)| i)
            .collect();

        // Need at least one user message and content between users to compress
        if user_indices.len() < 2 {
            return Ok(None);
        }

        // Build segments: user -> (assistant turns) -> next user
        // We'll summarize the assistant turns between consecutive user messages
        let mut new_messages = history[..=user_indices[0]].to_vec();

        for i in 0..user_indices.len() - 1 {
            let user_idx = user_indices[i];
            let next_user_idx = user_indices[i + 1];

            new_messages.push(history[user_idx].clone());

            // Check if there's assistant content between these two user messages
            let between_start = user_idx + 1;
            let between_end = next_user_idx;

            if between_start < between_end {
                let between = &history[between_start..between_end];
                let summary = self.summarize_segment(between).await?;

                // Persist compressed summary as timeline memory entry
                let ts = chrono::Utc::now().format("%Y-%m-%d %H:%M").to_string();
                let timeline_content = format!("[{}] Compressed {} conversation segments:\n{}",
                    ts, between.len(), summary);
                let key = format!("ctx_compressed_{}", uuid::Uuid::new_v4());
                let mm = self.memory.clone();
                let sid = self.session_id.clone();
                tokio::spawn(async move {
                    if let Err(e) = mm.store(
                        &key,
                        &timeline_content,
                        crate::memory::MemoryCategory::Timeline,
                        sid.as_deref(),
                        Some(0.3),
                    ).await {
                        tracing::warn!(error = %e, "Failed to store compressed context as timeline");
                    }
                });

                // Add summary as a special user message
                new_messages.push(ChatMessage::user(format!(
                    "[Context Summary]\n\n{}",
                    summary
                )));
            }
        }

        // Add last user and everything after (protected)
        let last_user_idx = user_indices[user_indices.len() - 1];
        if last_user_idx < history.len() - 1 {
            // Add everything from last user onwards (protected)
            for i in last_user_idx..history.len() {
                new_messages.push(history[i].clone());
            }
        }

        // If nothing changed, return None
        if new_messages.len() == history.len() {
            return Ok(None);
        }

        Ok(Some(new_messages))
    }

    /// Summarize a segment of messages using LLM.
    async fn summarize_segment(
        &self,
        messages: &[ChatMessage],
    ) -> Result<String, AgentError> {
        if messages.is_empty() {
            return Ok(String::new());
        }

        // Build transcript for summarization
        let transcript = messages
            .iter()
            .map(|m| {
                let role = match m.role.as_str() {
                    "assistant" => "Assistant",
                    "tool" => "Tool",
                    _ => m.role.as_str(),
                };
                let name = m.tool_name
                    .as_ref()
                    .map(|n| format!(" ({})", n))
                    .unwrap_or_default();
                format!("{}: {}{}", role, m.content, name)
            })
            .collect::<Vec<_>>()
            .join("\n\n");

        // Truncate transcript if too long
        let transcript = if transcript.len() > self.config.summary_max_chars {
            format!(
                "{}...\n\n[Transcript truncated - {} characters removed]",
                &transcript[..transcript.ceil_char_boundary(self.config.summary_max_chars)],
                transcript.len() - self.config.summary_max_chars
            )
        } else {
            transcript
        };

        let prompt = format!(
            r#"You are a conversation compaction engine. Summarize the following conversation segment.

PRESERVE:
- All identifiers (UUIDs, hashes, file paths, URLs)
- Actions taken (tool calls, file operations, commands)
- Key information obtained (results, data, errors)
- Decisions and user preferences
- Current task status

OMIT:
- Verbose tool output (keep key results only)
- Repeated greetings or filler

Be concise, aim for {} characters or less.

---

{}

"#,
            self.config.summary_max_chars, transcript
        );

        let request = ChatCompletionRequest {
            messages: vec![Message::system("You are a helpful assistant."), Message::user(&prompt)],
            temperature: Some(0.3),
            max_tokens: Some(1000),
            tools: None,
        };

        match (*self.provider).chat(request).await {
            Ok(response) => Ok(response.content),
            Err(e) => {
                // Fallback: just truncate the transcript
                tracing::warn!(error = %e, "LLM summarization failed, using truncated transcript");
                Ok(transcript[..transcript.ceil_char_boundary(2000)].to_string())
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::providers::ChatCompletionResponse;
    use async_trait::async_trait;
    use std::sync::OnceLock;

    /// Mock provider for testing - panics if actually used for LLM calls
    struct MockProvider;

    #[async_trait]
    impl LLMProvider for MockProvider {
        async fn chat(
            &self,
            _request: ChatCompletionRequest,
        ) -> Result<ChatCompletionResponse, Box<dyn std::error::Error + Send + Sync>> {
            panic!("MockProvider.chat() called - not expected in test")
        }

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

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

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

    fn mock_provider() -> Arc<dyn LLMProvider> {
        Arc::new(MockProvider)
    }

    fn test_memory_manager() -> Arc<MemoryManager> {
        static MM: OnceLock<Arc<MemoryManager>> = OnceLock::new();
        MM.get_or_init(|| {
            let rt = tokio::runtime::Runtime::new().unwrap();
            rt.block_on(async {
                let tmp = std::env::temp_dir().join(format!("picobot_ctx_test_{}.db", std::process::id()));
                let storage = Arc::new(crate::storage::Storage::new(&tmp).await.unwrap());
                Arc::new(MemoryManager::new(storage, "test".into(), "test".into()))
            })
        }).clone()
    }

    #[test]
    fn test_estimate_tokens() {
        let messages = vec![
            ChatMessage::user("Hello"),
            ChatMessage::assistant("Hi there!"),
            ChatMessage::user("How are you?"),
        ];

        let tokens = estimate_tokens(&messages);
        // "Hello" (5) -> ceil(5/4)+4 = 2+4 = 6
        // "Hi there!" (8) -> ceil(8/4)+4 = 2+4 = 6
        // "How are you?" (11) -> ceil(11/4)+4 = 3+4 = 7
        // raw = 19, with 1.2x = ~23
        assert!(tokens > 18 && tokens < 30, "Expected ~23 tokens, got {}", tokens);
    }

    #[test]
    fn test_fast_trim() {
        let config = ContextCompressionConfig {
            tool_result_trim_chars: 50,
            ..Default::default()
        };
        let compressor = ContextCompressor::with_config(mock_provider(), 100_000, config, test_memory_manager());

        let mut messages = vec![
            ChatMessage::user("Hello"),
            ChatMessage::tool("call1", "bash", &"x".repeat(200)),
        ];

        let modified = compressor.fast_trim_tool_results(&mut messages);
        assert_eq!(modified, 1);
        assert!(messages[1].content.len() < 100);
    }

    #[test]
    fn test_threshold() {
        let compressor = ContextCompressor::new(mock_provider(), 128_000, test_memory_manager());
        assert_eq!(compressor.threshold(), 64_000);
    }
}