// observe.rs — Shared observation socket + logfile
//
// Two mechanisms:
//   1. Logfile (~/.consciousness/agent-sessions/observe.log) — append-only
//      plain text of the conversation. `poc-agent read` prints new
//      content since last read using a byte-offset cursor file.
//   2. Unix socket — for live streaming (`poc-agent read -f`) and
//      sending input (`poc-agent write <msg>`).
//
// The logfile is the history. The socket is the live wire.

use anyhow::{Context, Result};
use std::fs::{File, OpenOptions};
use std::io::{BufRead, BufReader, Seek, SeekFrom, Write};
use std::path::{Path, PathBuf};
use crate::agent::context::ConversationEntry;

pub struct ConversationLog {
    path: PathBuf,
}

impl ConversationLog {
    pub fn new(path: PathBuf) -> Result<Self> {
        // Ensure parent directory exists
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent)
                .with_context(|| format!("creating log dir {}", parent.display()))?;
        }
        Ok(Self { path })
    }

    /// Append a conversation entry to the log.
    pub fn append(&self, entry: &ConversationEntry) -> Result<()> {
        let mut file = OpenOptions::new()
            .create(true)
            .append(true)
            .open(&self.path)
            .with_context(|| format!("opening log {}", self.path.display()))?;

        let line = serde_json::to_string(entry)
            .context("serializing entry for log")?;
        writeln!(file, "{}", line)
            .context("writing to conversation log")?;
        file.sync_all()
            .context("syncing conversation log")?;
        Ok(())
    }

    /// Read the tail of the log (last `max_bytes` bytes).
    /// Seeks to `file_len - max_bytes`, skips the first partial line,
    /// then parses forward. For logs smaller than `max_bytes`, reads everything.
    pub fn read_tail(&self, max_bytes: u64) -> Result<Vec<ConversationEntry>> {
        if !self.path.exists() {
            return Ok(Vec::new());
        }
        let file = File::open(&self.path)
            .with_context(|| format!("opening log {}", self.path.display()))?;
        let file_len = file.metadata()?.len();
        let mut reader = BufReader::new(file);

        if file_len > max_bytes {
            reader.seek(SeekFrom::Start(file_len - max_bytes))?;
            // Skip partial first line
            let mut discard = String::new();
            reader.read_line(&mut discard)?;
        }

        let mut entries = Vec::new();
        for line in reader.lines() {
            let line = line.context("reading log tail")?;
            let line = line.trim();
            if line.is_empty() {
                continue;
            }
            // Try ConversationEntry first (new format), fall back to bare Message (old logs)
            if let Ok(entry) = serde_json::from_str::<ConversationEntry>(line) {
                entries.push(entry);
            }
        }
        Ok(entries)
    }

    pub fn path(&self) -> &Path {
        &self.path
    }

    /// Get the timestamp of the oldest message in the log.
    pub fn oldest_timestamp(&self) -> Option<chrono::DateTime<chrono::Utc>> {
        let file = File::open(&self.path).ok()?;
        let reader = BufReader::new(file);
        for line in reader.lines().flatten() {
            let line = line.trim().to_string();
            if line.is_empty() { continue; }
            if let Ok(entry) = serde_json::from_str::<ConversationEntry>(&line) {
                if let Some(ts) = &entry.message().timestamp {
                    if let Ok(dt) = chrono::DateTime::parse_from_rfc3339(ts) {
                        return Some(dt.to_utc());
                    }
                    // Try other formats
                    if let Ok(dt) = chrono::NaiveDateTime::parse_from_str(ts, "%Y-%m-%dT%H:%M:%S") {
                        return Some(dt.and_utc());
                    }
                }
            }
        }
        None
    }
}