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::AstNode;

pub struct ConversationLog {
    path: PathBuf,
}

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

    pub fn append_node(&self, node: &AstNode) -> 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(node)
            .context("serializing node for log")?;
        writeln!(file, "{}", line)
            .context("writing to conversation log")?;
        file.sync_all()
            .context("syncing conversation log")?;
        Ok(())
    }

    pub fn read_nodes(&self, max_bytes: u64) -> Result<Vec<AstNode>> {
        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))?;
            let mut discard = String::new();
            reader.read_line(&mut discard)?;
        }

        let mut nodes = Vec::new();
        for line in reader.lines() {
            let line = line.context("reading log tail")?;
            let line = line.trim();
            if line.is_empty() { continue; }
            if let Ok(node) = serde_json::from_str::<AstNode>(line) {
                nodes.push(node);
            }
        }
        Ok(nodes)
    }

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

    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(node) = serde_json::from_str::<AstNode>(&line) {
                if let Some(leaf) = node.leaf() {
                    if let Some(ts) = leaf.timestamp() {
                        return Some(ts);
                    }
                }
            }
        }
        None
    }
}