use crate::types::{Conversation, Message};
use crate::Result;
use serde_json::{Number, Value};
use std::collections::{HashMap, VecDeque};
use std::time::{Duration, Instant};
use uuid::Uuid;

const STREAMING_FLAG: &str = "streaming";
const LAST_CHUNK_TS: &str = "last_chunk_ts";
const PLACEHOLDER_FLAG: &str = "placeholder";

/// Manage active and historical conversations, including streaming updates.
pub struct ConversationManager {
    active: Conversation,
    history: VecDeque<Conversation>,
    message_index: HashMap<Uuid, usize>,
    streaming: HashMap<Uuid, StreamingMetadata>,
    max_history: usize,
}

#[derive(Debug, Clone)]
pub struct StreamingMetadata {
    started: Instant,
    last_update: Instant,
}

impl ConversationManager {
    /// Create a new conversation manager with a default model
    pub fn new(model: impl Into<String>) -> Self {
        Self::with_history_capacity(model, 32)
    }

    /// Create with explicit history capacity
    pub fn with_history_capacity(model: impl Into<String>, max_history: usize) -> Self {
        let conversation = Conversation::new(model.into());
        Self {
            active: conversation,
            history: VecDeque::new(),
            message_index: HashMap::new(),
            streaming: HashMap::new(),
            max_history: max_history.max(1),
        }
    }

    /// Access the active conversation
    pub fn active(&self) -> &Conversation {
        &self.active
    }

    /// Mutable access to the active conversation (auto refreshing indexes afterwards)
    fn active_mut(&mut self) -> &mut Conversation {
        &mut self.active
    }

    /// Replace the active conversation with a provided one, archiving the existing conversation if it contains data
    pub fn load(&mut self, conversation: Conversation) {
        if !self.active.messages.is_empty() {
            self.archive_active();
        }

        self.message_index.clear();
        for (idx, message) in conversation.messages.iter().enumerate() {
            self.message_index.insert(message.id, idx);
        }

        self.stream_reset();
        self.active = conversation;
    }

    /// Start a brand new conversation, archiving the previous one
    pub fn start_new(&mut self, model: Option<String>, name: Option<String>) {
        self.archive_active();
        let model = model.unwrap_or_else(|| self.active.model.clone());
        self.active = Conversation::new(model);
        self.active.name = name;
        self.message_index.clear();
        self.stream_reset();
    }

    /// Archive the active conversation into history
    pub fn archive_active(&mut self) {
        if self.active.messages.is_empty() {
            return;
        }

        let mut archived = self.active.clone();
        archived.updated_at = std::time::SystemTime::now();
        self.history.push_front(archived);

        while self.history.len() > self.max_history {
            self.history.pop_back();
        }
    }

    /// Get immutable history
    pub fn history(&self) -> impl Iterator<Item = &Conversation> {
        self.history.iter()
    }

    /// Add a user message and return its identifier
    pub fn push_user_message(&mut self, content: impl Into<String>) -> Uuid {
        let message = Message::user(content.into());
        self.register_message(message)
    }

    /// Add a system message and return its identifier
    pub fn push_system_message(&mut self, content: impl Into<String>) -> Uuid {
        let message = Message::system(content.into());
        self.register_message(message)
    }

    /// Add an assistant message (non-streaming) and return its identifier
    pub fn push_assistant_message(&mut self, content: impl Into<String>) -> Uuid {
        let message = Message::assistant(content.into());
        self.register_message(message)
    }

    /// Push an arbitrary message into the active conversation
    pub fn push_message(&mut self, message: Message) -> Uuid {
        self.register_message(message)
    }

    /// Start tracking a streaming assistant response, returning the message id to update
    pub fn start_streaming_response(&mut self) -> Uuid {
        let mut message = Message::assistant(String::new());
        message
            .metadata
            .insert(STREAMING_FLAG.to_string(), Value::Bool(true));
        let id = message.id;
        self.register_message(message);
        self.streaming.insert(
            id,
            StreamingMetadata {
                started: Instant::now(),
                last_update: Instant::now(),
            },
        );
        id
    }

    /// Append streaming content to an assistant message
    pub fn append_stream_chunk(
        &mut self,
        message_id: Uuid,
        chunk: &str,
        is_final: bool,
    ) -> Result<()> {
        let index = self
            .message_index
            .get(&message_id)
            .copied()
            .ok_or_else(|| crate::Error::Unknown(format!("Unknown message id: {message_id}")))?;

        let conversation = self.active_mut();
        if let Some(message) = conversation.messages.get_mut(index) {
            let was_placeholder = message
                .metadata
                .remove(PLACEHOLDER_FLAG)
                .and_then(|v| v.as_bool())
                .unwrap_or(false);

            if was_placeholder {
                message.content.clear();
            }

            if !chunk.is_empty() {
                message.content.push_str(chunk);
            }
            message.timestamp = std::time::SystemTime::now();
            let millis = std::time::SystemTime::now()
                .duration_since(std::time::UNIX_EPOCH)
                .unwrap_or_default()
                .as_millis() as u64;
            message.metadata.insert(
                LAST_CHUNK_TS.to_string(),
                Value::Number(Number::from(millis)),
            );

            if is_final {
                message
                    .metadata
                    .insert(STREAMING_FLAG.to_string(), Value::Bool(false));
                self.streaming.remove(&message_id);
            } else if let Some(info) = self.streaming.get_mut(&message_id) {
                info.last_update = Instant::now();
            }
        }

        Ok(())
    }

    /// Set placeholder text for a streaming message
    pub fn set_stream_placeholder(
        &mut self,
        message_id: Uuid,
        text: impl Into<String>,
    ) -> Result<()> {
        let index = self
            .message_index
            .get(&message_id)
            .copied()
            .ok_or_else(|| crate::Error::Unknown(format!("Unknown message id: {message_id}")))?;

        if let Some(message) = self.active_mut().messages.get_mut(index) {
            message.content = text.into();
            message.timestamp = std::time::SystemTime::now();
            message
                .metadata
                .insert(PLACEHOLDER_FLAG.to_string(), Value::Bool(true));
        }

        Ok(())
    }

    /// Update the active model (used when user changes model mid session)
    pub fn set_model(&mut self, model: impl Into<String>) {
        self.active.model = model.into();
        self.active.updated_at = std::time::SystemTime::now();
    }

    /// Provide read access to the cached streaming metadata
    pub fn streaming_metadata(&self, message_id: &Uuid) -> Option<StreamingMetadata> {
        self.streaming.get(message_id).cloned()
    }

    /// Remove inactive streaming messages that have stalled beyond the provided timeout
    pub fn expire_stalled_streams(&mut self, idle_timeout: Duration) -> Vec<Uuid> {
        let cutoff = Instant::now() - idle_timeout;
        let mut expired = Vec::new();

        self.streaming.retain(|id, meta| {
            if meta.last_update < cutoff {
                expired.push(*id);
                false
            } else {
                true
            }
        });

        expired
    }

    /// Clear all state
    pub fn clear(&mut self) {
        self.active.clear();
        self.history.clear();
        self.message_index.clear();
        self.streaming.clear();
    }

    fn register_message(&mut self, message: Message) -> Uuid {
        let id = message.id;
        let idx;
        {
            let conversation = self.active_mut();
            idx = conversation.messages.len();
            conversation.messages.push(message);
            conversation.updated_at = std::time::SystemTime::now();
        }
        self.message_index.insert(id, idx);
        id
    }

    fn stream_reset(&mut self) {
        self.streaming.clear();
    }
}

impl StreamingMetadata {
    /// Duration since the stream started
    pub fn elapsed(&self) -> Duration {
        self.started.elapsed()
    }

    /// Duration since the last chunk was received
    pub fn idle_duration(&self) -> Duration {
        self.last_update.elapsed()
    }

    /// Timestamp when streaming started
    pub fn started_at(&self) -> Instant {
        self.started
    }

    /// Timestamp of most recent update
    pub fn last_update_at(&self) -> Instant {
        self.last_update
    }
}