use crate::agents::AgentEvent;
use chrono::Utc;
use serde::{Deserialize, Serialize};
use std::fs::{self, File, OpenOptions};
use std::io::{BufRead, BufReader, Write};
use std::path::{Path, PathBuf};


/// A single line in the agent log file (JSONL format).
#[derive(Debug, Serialize, Deserialize)]
pub struct LogEntry {
    pub timestamp: String,
    #[serde(flatten)]
    pub event: serde_json::Value,
}

/// Writes agent events to a persistent log file (JSONL format).
///
/// Each agent session gets its own log file at:
///   `.story_kit/logs/{story_id}/{agent_name}-{session_id}.log`
pub struct AgentLogWriter {
    file: File,
}

impl AgentLogWriter {
    /// Create a new log writer, creating the directory structure as needed.
    ///
    /// The log file is opened in append mode so that a restart mid-session
    /// won't overwrite earlier output.
    pub fn new(
        project_root: &Path,
        story_id: &str,
        agent_name: &str,
        session_id: &str,
    ) -> Result<Self, String> {
        let dir = log_dir(project_root, story_id);
        fs::create_dir_all(&dir)
            .map_err(|e| format!("Failed to create log directory {}: {e}", dir.display()))?;

        let path = dir.join(format!("{agent_name}-{session_id}.log"));
        let file = OpenOptions::new()
            .create(true)
            .append(true)
            .open(&path)
            .map_err(|e| format!("Failed to open log file {}: {e}", path.display()))?;

        Ok(Self { file })
    }

    /// Write an agent event as a JSONL line with an ISO 8601 timestamp.
    pub fn write_event(&mut self, event: &AgentEvent) -> Result<(), String> {
        let event_value =
            serde_json::to_value(event).map_err(|e| format!("Failed to serialize event: {e}"))?;

        let entry = LogEntry {
            timestamp: Utc::now().to_rfc3339(),
            event: event_value,
        };

        let mut line =
            serde_json::to_string(&entry).map_err(|e| format!("Failed to serialize entry: {e}"))?;
        line.push('\n');

        self.file
            .write_all(line.as_bytes())
            .map_err(|e| format!("Failed to write log entry: {e}"))?;

        Ok(())
    }
}

/// Return the log directory for a story.
fn log_dir(project_root: &Path, story_id: &str) -> PathBuf {
    project_root
        .join(".story_kit")
        .join("logs")
        .join(story_id)
}

/// Return the path to a specific log file.
pub fn log_file_path(
    project_root: &Path,
    story_id: &str,
    agent_name: &str,
    session_id: &str,
) -> PathBuf {
    log_dir(project_root, story_id).join(format!("{agent_name}-{session_id}.log"))
}

/// Read all log entries from a log file.
pub fn read_log(path: &Path) -> Result<Vec<LogEntry>, String> {
    let file =
        File::open(path).map_err(|e| format!("Failed to open log file {}: {e}", path.display()))?;
    let reader = BufReader::new(file);
    let mut entries = Vec::new();

    for line in reader.lines() {
        let line = line.map_err(|e| format!("Failed to read log line: {e}"))?;
        let trimmed = line.trim();
        if trimmed.is_empty() {
            continue;
        }
        let entry: LogEntry = serde_json::from_str(trimmed)
            .map_err(|e| format!("Failed to parse log entry: {e}"))?;
        entries.push(entry);
    }

    Ok(entries)
}

/// Find the most recent log file for a given story+agent combination.
///
/// Scans `.story_kit/logs/{story_id}/` for files matching `{agent_name}-*.log`
/// and returns the one with the most recent modification time.
pub fn find_latest_log(
    project_root: &Path,
    story_id: &str,
    agent_name: &str,
) -> Option<PathBuf> {
    let dir = log_dir(project_root, story_id);
    if !dir.is_dir() {
        return None;
    }

    let prefix = format!("{agent_name}-");
    let mut best: Option<(PathBuf, std::time::SystemTime)> = None;

    let entries = fs::read_dir(&dir).ok()?;
    for entry in entries.flatten() {
        let path = entry.path();
        let name = match path.file_name().and_then(|n| n.to_str()) {
            Some(n) => n.to_string(),
            None => continue,
        };
        if !name.starts_with(&prefix) || !name.ends_with(".log") {
            continue;
        }
        let modified = match entry.metadata().and_then(|m| m.modified()) {
            Ok(t) => t,
            Err(_) => continue,
        };
        if best.as_ref().is_none_or(|(_, t)| modified > *t) {
            best = Some((path, modified));
        }
    }

    best.map(|(p, _)| p)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::agents::AgentEvent;
    use tempfile::tempdir;

    #[test]
    fn test_log_writer_creates_directory_and_file() {
        let tmp = tempdir().unwrap();
        let root = tmp.path();

        let _writer =
            AgentLogWriter::new(root, "42_story_foo", "coder-1", "sess-abc123").unwrap();

        let expected_path = root
            .join(".story_kit")
            .join("logs")
            .join("42_story_foo")
            .join("coder-1-sess-abc123.log");
        assert!(expected_path.exists(), "Log file should exist");
    }

    #[test]
    fn test_log_writer_writes_jsonl_with_timestamps() {
        let tmp = tempdir().unwrap();
        let root = tmp.path();

        let mut writer =
            AgentLogWriter::new(root, "42_story_foo", "coder-1", "sess-001").unwrap();

        let event = AgentEvent::Status {
            story_id: "42_story_foo".to_string(),
            agent_name: "coder-1".to_string(),
            status: "running".to_string(),
        };
        writer.write_event(&event).unwrap();

        let event2 = AgentEvent::Output {
            story_id: "42_story_foo".to_string(),
            agent_name: "coder-1".to_string(),
            text: "Hello world".to_string(),
        };
        writer.write_event(&event2).unwrap();

        // Read the file and verify
        let path = log_file_path(root, "42_story_foo", "coder-1", "sess-001");
        let content = fs::read_to_string(&path).unwrap();
        let lines: Vec<&str> = content.lines().collect();
        assert_eq!(lines.len(), 2, "Should have 2 log lines");

        // Parse each line as valid JSON with a timestamp
        for line in &lines {
            let entry: LogEntry = serde_json::from_str(line).unwrap();
            assert!(!entry.timestamp.is_empty(), "Timestamp should be present");
            // Verify it's a valid ISO 8601 timestamp
            chrono::DateTime::parse_from_rfc3339(&entry.timestamp)
                .expect("Timestamp should be valid RFC3339");
        }

        // Verify the first entry is a status event
        let entry1: LogEntry = serde_json::from_str(lines[0]).unwrap();
        assert_eq!(entry1.event["type"], "status");
        assert_eq!(entry1.event["status"], "running");

        // Verify the second entry is an output event
        let entry2: LogEntry = serde_json::from_str(lines[1]).unwrap();
        assert_eq!(entry2.event["type"], "output");
        assert_eq!(entry2.event["text"], "Hello world");
    }

    #[test]
    fn test_read_log_parses_written_events() {
        let tmp = tempdir().unwrap();
        let root = tmp.path();

        let mut writer =
            AgentLogWriter::new(root, "42_story_foo", "coder-1", "sess-002").unwrap();

        let events = vec![
            AgentEvent::Status {
                story_id: "42_story_foo".to_string(),
                agent_name: "coder-1".to_string(),
                status: "running".to_string(),
            },
            AgentEvent::Output {
                story_id: "42_story_foo".to_string(),
                agent_name: "coder-1".to_string(),
                text: "Processing...".to_string(),
            },
            AgentEvent::AgentJson {
                story_id: "42_story_foo".to_string(),
                agent_name: "coder-1".to_string(),
                data: serde_json::json!({"type": "tool_use", "name": "read_file"}),
            },
            AgentEvent::Done {
                story_id: "42_story_foo".to_string(),
                agent_name: "coder-1".to_string(),
                session_id: Some("sess-002".to_string()),
            },
        ];

        for event in &events {
            writer.write_event(event).unwrap();
        }

        let path = log_file_path(root, "42_story_foo", "coder-1", "sess-002");
        let entries = read_log(&path).unwrap();
        assert_eq!(entries.len(), 4, "Should read back all 4 events");

        // Verify event types round-trip correctly
        assert_eq!(entries[0].event["type"], "status");
        assert_eq!(entries[1].event["type"], "output");
        assert_eq!(entries[2].event["type"], "agent_json");
        assert_eq!(entries[3].event["type"], "done");
    }

    #[test]
    fn test_separate_sessions_produce_separate_files() {
        let tmp = tempdir().unwrap();
        let root = tmp.path();

        let mut writer1 =
            AgentLogWriter::new(root, "42_story_foo", "coder-1", "sess-aaa").unwrap();
        let mut writer2 =
            AgentLogWriter::new(root, "42_story_foo", "coder-1", "sess-bbb").unwrap();

        writer1
            .write_event(&AgentEvent::Output {
                story_id: "42_story_foo".to_string(),
                agent_name: "coder-1".to_string(),
                text: "from session aaa".to_string(),
            })
            .unwrap();

        writer2
            .write_event(&AgentEvent::Output {
                story_id: "42_story_foo".to_string(),
                agent_name: "coder-1".to_string(),
                text: "from session bbb".to_string(),
            })
            .unwrap();

        let path1 = log_file_path(root, "42_story_foo", "coder-1", "sess-aaa");
        let path2 = log_file_path(root, "42_story_foo", "coder-1", "sess-bbb");

        assert_ne!(path1, path2, "Different sessions should use different files");

        let entries1 = read_log(&path1).unwrap();
        let entries2 = read_log(&path2).unwrap();

        assert_eq!(entries1.len(), 1);
        assert_eq!(entries2.len(), 1);
        assert_eq!(entries1[0].event["text"], "from session aaa");
        assert_eq!(entries2[0].event["text"], "from session bbb");
    }

    #[test]
    fn test_find_latest_log_returns_most_recent() {
        let tmp = tempdir().unwrap();
        let root = tmp.path();

        // Create two log files with a small delay
        let mut writer1 =
            AgentLogWriter::new(root, "42_story_foo", "coder-1", "sess-old").unwrap();
        writer1
            .write_event(&AgentEvent::Output {
                story_id: "42_story_foo".to_string(),
                agent_name: "coder-1".to_string(),
                text: "old".to_string(),
            })
            .unwrap();
        drop(writer1);

        // Touch the second file to ensure it's newer
        std::thread::sleep(std::time::Duration::from_millis(50));

        let mut writer2 =
            AgentLogWriter::new(root, "42_story_foo", "coder-1", "sess-new").unwrap();
        writer2
            .write_event(&AgentEvent::Output {
                story_id: "42_story_foo".to_string(),
                agent_name: "coder-1".to_string(),
                text: "new".to_string(),
            })
            .unwrap();
        drop(writer2);

        let latest = find_latest_log(root, "42_story_foo", "coder-1").unwrap();
        assert!(
            latest.to_string_lossy().contains("sess-new"),
            "Should find the newest log file, got: {}",
            latest.display()
        );
    }

    #[test]
    fn test_find_latest_log_returns_none_for_missing_dir() {
        let tmp = tempdir().unwrap();
        let result = find_latest_log(tmp.path(), "nonexistent", "coder-1");
        assert!(result.is_none());
    }

    #[test]
    fn test_log_files_persist_on_disk() {
        let tmp = tempdir().unwrap();
        let root = tmp.path();

        let path = {
            let mut writer =
                AgentLogWriter::new(root, "42_story_foo", "coder-1", "sess-persist").unwrap();
            writer
                .write_event(&AgentEvent::Status {
                    story_id: "42_story_foo".to_string(),
                    agent_name: "coder-1".to_string(),
                    status: "running".to_string(),
                })
                .unwrap();
            log_file_path(root, "42_story_foo", "coder-1", "sess-persist")
            // writer is dropped here
        };

        // File should still exist and be readable
        assert!(path.exists(), "Log file should persist after writer is dropped");
        let entries = read_log(&path).unwrap();
        assert_eq!(entries.len(), 1);
        assert_eq!(entries[0].event["type"], "status");
    }
}