//! JSONL-based session persistence for channel conversations.
//!
//! Each session (keyed by `channel_sender` or `channel_thread_sender`) is stored
//! as an append-only JSONL file in `{workspace}/sessions/`. Messages are appended
//! one-per-line as JSON, never modifying old lines. On daemon restart, sessions
//! are loaded from disk to restore conversation context.

use crate::channels::session_backend::SessionBackend;
use crate::providers::traits::ChatMessage;
use std::io::{BufRead, Write};
use std::path::{Path, PathBuf};

/// Append-only JSONL session store for channel conversations.
pub struct SessionStore {
    sessions_dir: PathBuf,
}

impl SessionStore {
    /// Create a new session store, ensuring the sessions directory exists.
    pub fn new(workspace_dir: &Path) -> std::io::Result<Self> {
        let sessions_dir = workspace_dir.join("sessions");
        std::fs::create_dir_all(&sessions_dir)?;
        Ok(Self { sessions_dir })
    }

    /// Compute the file path for a session key, sanitizing for filesystem safety.
    fn session_path(&self, session_key: &str) -> PathBuf {
        let safe_key: String = session_key
            .chars()
            .map(|c| {
                if c.is_alphanumeric() || c == '_' || c == '-' {
                    c
                } else {
                    '_'
                }
            })
            .collect();
        self.sessions_dir.join(format!("{safe_key}.jsonl"))
    }

    /// Load all messages for a session from its JSONL file.
    /// Returns an empty vec if the file does not exist or is unreadable.
    pub fn load(&self, session_key: &str) -> Vec<ChatMessage> {
        let path = self.session_path(session_key);
        let file = match std::fs::File::open(&path) {
            Ok(f) => f,
            Err(_) => return Vec::new(),
        };

        let reader = std::io::BufReader::new(file);
        let mut messages = Vec::new();

        for line in reader.lines() {
            let Ok(line) = line else { continue };
            let trimmed = line.trim();
            if trimmed.is_empty() {
                continue;
            }
            if let Ok(msg) = serde_json::from_str::<ChatMessage>(trimmed) {
                messages.push(msg);
            }
        }

        messages
    }

    /// Append a single message to the session JSONL file.
    pub fn append(&self, session_key: &str, message: &ChatMessage) -> std::io::Result<()> {
        let path = self.session_path(session_key);
        let mut file = std::fs::OpenOptions::new()
            .create(true)
            .append(true)
            .open(&path)?;

        let json = serde_json::to_string(message)
            .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e))?;

        writeln!(file, "{json}")?;
        Ok(())
    }

    /// Remove the last message from a session's JSONL file.
    ///
    /// Rewrite approach: load all messages, drop the last, rewrite. This is
    /// O(n) but rollbacks are rare.
    pub fn remove_last(&self, session_key: &str) -> std::io::Result<bool> {
        let mut messages = self.load(session_key);
        if messages.is_empty() {
            return Ok(false);
        }
        messages.pop();
        self.rewrite(session_key, &messages)?;
        Ok(true)
    }

    /// Compact a session file by rewriting only valid messages (removes corrupt lines).
    pub fn compact(&self, session_key: &str) -> std::io::Result<()> {
        let messages = self.load(session_key);
        self.rewrite(session_key, &messages)
    }

    fn rewrite(&self, session_key: &str, messages: &[ChatMessage]) -> std::io::Result<()> {
        let path = self.session_path(session_key);
        let mut file = std::fs::File::create(&path)?;
        for msg in messages {
            let json = serde_json::to_string(msg)
                .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e))?;
            writeln!(file, "{json}")?;
        }
        Ok(())
    }

    /// List all session keys that have files on disk.
    pub fn list_sessions(&self) -> Vec<String> {
        let entries = match std::fs::read_dir(&self.sessions_dir) {
            Ok(e) => e,
            Err(_) => return Vec::new(),
        };

        entries
            .filter_map(|entry| {
                let entry = entry.ok()?;
                let name = entry.file_name().into_string().ok()?;
                name.strip_suffix(".jsonl").map(String::from)
            })
            .collect()
    }
}

impl SessionBackend for SessionStore {
    fn load(&self, session_key: &str) -> Vec<ChatMessage> {
        self.load(session_key)
    }

    fn append(&self, session_key: &str, message: &ChatMessage) -> std::io::Result<()> {
        self.append(session_key, message)
    }

    fn remove_last(&self, session_key: &str) -> std::io::Result<bool> {
        self.remove_last(session_key)
    }

    fn list_sessions(&self) -> Vec<String> {
        self.list_sessions()
    }

    fn compact(&self, session_key: &str) -> std::io::Result<()> {
        self.compact(session_key)
    }
}

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

    #[test]
    fn round_trip_append_and_load() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();

        store
            .append("telegram_user123", &ChatMessage::user("hello"))
            .unwrap();
        store
            .append("telegram_user123", &ChatMessage::assistant("hi there"))
            .unwrap();

        let messages = store.load("telegram_user123");
        assert_eq!(messages.len(), 2);
        assert_eq!(messages[0].role, "user");
        assert_eq!(messages[0].content, "hello");
        assert_eq!(messages[1].role, "assistant");
        assert_eq!(messages[1].content, "hi there");
    }

    #[test]
    fn load_nonexistent_session_returns_empty() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();

        let messages = store.load("nonexistent");
        assert!(messages.is_empty());
    }

    #[test]
    fn key_sanitization() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();

        // Keys with special chars should be sanitized
        store
            .append("slack/thread:123/user", &ChatMessage::user("test"))
            .unwrap();

        let messages = store.load("slack/thread:123/user");
        assert_eq!(messages.len(), 1);
    }

    #[test]
    fn list_sessions_returns_keys() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();

        store
            .append("telegram_alice", &ChatMessage::user("hi"))
            .unwrap();
        store
            .append("discord_bob", &ChatMessage::user("hey"))
            .unwrap();

        let mut sessions = store.list_sessions();
        sessions.sort();
        assert_eq!(sessions.len(), 2);
        assert!(sessions.contains(&"discord_bob".to_string()));
        assert!(sessions.contains(&"telegram_alice".to_string()));
    }

    #[test]
    fn append_is_truly_append_only() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();
        let key = "test_session";

        store.append(key, &ChatMessage::user("msg1")).unwrap();
        store.append(key, &ChatMessage::user("msg2")).unwrap();

        // Read raw file to verify append-only format
        let path = store.session_path(key);
        let content = std::fs::read_to_string(&path).unwrap();
        let lines: Vec<&str> = content.trim().lines().collect();
        assert_eq!(lines.len(), 2);
    }

    #[test]
    fn remove_last_drops_final_message() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();

        store
            .append("rm_test", &ChatMessage::user("first"))
            .unwrap();
        store
            .append("rm_test", &ChatMessage::user("second"))
            .unwrap();

        assert!(store.remove_last("rm_test").unwrap());
        let messages = store.load("rm_test");
        assert_eq!(messages.len(), 1);
        assert_eq!(messages[0].content, "first");
    }

    #[test]
    fn remove_last_empty_returns_false() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();
        assert!(!store.remove_last("nonexistent").unwrap());
    }

    #[test]
    fn compact_removes_corrupt_lines() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();
        let key = "compact_test";

        let path = store.session_path(key);
        std::fs::create_dir_all(path.parent().unwrap()).unwrap();
        let mut file = std::fs::File::create(&path).unwrap();
        writeln!(file, r#"{{"role":"user","content":"ok"}}"#).unwrap();
        writeln!(file, "corrupt line").unwrap();
        writeln!(file, r#"{{"role":"assistant","content":"hi"}}"#).unwrap();

        store.compact(key).unwrap();

        let raw = std::fs::read_to_string(&path).unwrap();
        assert_eq!(raw.trim().lines().count(), 2);
    }

    #[test]
    fn session_backend_trait_works_via_dyn() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();
        let backend: &dyn SessionBackend = &store;

        backend
            .append("trait_test", &ChatMessage::user("hello"))
            .unwrap();
        let msgs = backend.load("trait_test");
        assert_eq!(msgs.len(), 1);
    }

    #[test]
    fn handles_corrupt_lines_gracefully() {
        let tmp = TempDir::new().unwrap();
        let store = SessionStore::new(tmp.path()).unwrap();
        let key = "corrupt_test";

        // Write valid message + corrupt line + valid message
        let path = store.session_path(key);
        std::fs::create_dir_all(path.parent().unwrap()).unwrap();
        let mut file = std::fs::File::create(&path).unwrap();
        writeln!(file, r#"{{"role":"user","content":"hello"}}"#).unwrap();
        writeln!(file, "this is not valid json").unwrap();
        writeln!(file, r#"{{"role":"assistant","content":"world"}}"#).unwrap();

        let messages = store.load(key);
        assert_eq!(messages.len(), 2);
        assert_eq!(messages[0].content, "hello");
        assert_eq!(messages[1].content, "world");
    }
}
