// src/corporate/atomic_writer.rs
//
// Atomic JSONL writer that prevents partial/corrupted results from being written

use anyhow::Result;
use serde::Serialize;
use std::collections::HashMap;
use std::path::PathBuf;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use tokio::fs::{File, OpenOptions};
use tokio::io::AsyncWriteExt;
use tokio::sync::mpsc;

/// Command to write or validate data
#[derive(Debug)]
pub enum WriteCommand<T> {
    /// Stage a result for writing (held in memory until committed)
    Stage { id: String, data: T },
    
    /// Commit staged result to disk (atomic write)
    Commit { id: String },
    
    /// Rollback staged result (discard without writing)
    Rollback { id: String },
    
    /// Commit all pending staged results and flush
    CommitAll,
    
    /// Shutdown writer gracefully (only commits valid staged results)
    Shutdown,
}

/// Result of a write operation
#[derive(Debug)]
pub struct WriteResult {
    pub id: String,
    pub success: bool,
    pub error: Option<String>,
}

/// Atomic writer that prevents partial results from being written
pub struct AtomicJsonlWriter<T> {
    file: File,
    staged: HashMap<String, T>,
    committed_count: usize,
    rollback_count: usize,
}

impl<T: Serialize + Clone> AtomicJsonlWriter<T> {
    pub async fn new(path: PathBuf) -> Result<Self> {
        // Ensure parent directory exists
        if let Some(parent) = path.parent() {
            tokio::fs::create_dir_all(parent).await?;
        }
        
        let file = OpenOptions::new()
            .create(true)
            .append(true)
            .open(&path)
            .await?;
        
        crate::util::logger::log_info(&format!(
            "Atomic writer initialized: {:?}",
            path
        )).await;
        
        Ok(Self {
            file,
            staged: HashMap::new(),
            committed_count: 0,
            rollback_count: 0,
        })
    }
    
    /// Stage data for writing (held in memory, not yet written)
    pub async fn stage(&mut self, id: String, data: T) {
        crate::util::logger::log_info(&format!(
            "Staging result for: {} (total staged: {})",
            id,
            self.staged.len() + 1
        )).await;
        
        self.staged.insert(id, data);
    }
    
    /// Commit a staged result to disk (atomic write)
    pub async fn commit(&mut self, id: &str) -> Result<()> {
        if let Some(data) = self.staged.remove(id) {
            // Serialize to JSON
            let json_line = serde_json::to_string(&data)?;
            
            // Write atomically (single syscall)
            self.file.write_all(json_line.as_bytes()).await?;
            self.file.write_all(b"\n").await?;
            self.file.flush().await?;
            
            self.committed_count += 1;
            
            crate::util::logger::log_info(&format!(
                "✓ Committed result for: {} (total committed: {})",
                id, self.committed_count
            )).await;
            
            Ok(())
        } else {
            Err(anyhow::anyhow!("No staged result found for id: {}", id))
        }
    }
    
    /// Rollback a staged result (discard without writing)
    pub async fn rollback(&mut self, id: &str) {
        if self.staged.remove(id).is_some() {
            self.rollback_count += 1;
            
            crate::util::logger::log_warn(&format!(
                "⚠ Rolled back result for: {} (total rollbacks: {})",
                id, self.rollback_count
            )).await;
        }
    }
    
    /// Commit all staged results
    pub async fn commit_all(&mut self) -> Result<usize> {
        let ids: Vec<String> = self.staged.keys().cloned().collect();
        let mut committed = 0;
        
        for id in ids {
            if let Ok(()) = self.commit(&id).await {
                committed += 1;
            }
        }
        
        Ok(committed)
    }
    
    /// Rollback all staged results (discard everything)
    pub async fn rollback_all(&mut self) -> usize {
        let count = self.staged.len();
        self.staged.clear();
        self.rollback_count += count;
        
        crate::util::logger::log_warn(&format!(
            "⚠ Rolled back all {} staged results",
            count
        )).await;
        
        count
    }
    
    /// Get statistics
    pub fn stats(&self) -> WriterStats {
        WriterStats {
            staged_count: self.staged.len(),
            committed_count: self.committed_count,
            rollback_count: self.rollback_count,
        }
    }
}

#[derive(Debug, Clone)]
pub struct WriterStats {
    pub staged_count: usize,
    pub committed_count: usize,
    pub rollback_count: usize,
}

/// Managed writer service that runs in its own task
pub struct AtomicWriterService<T> {
    rx: mpsc::UnboundedReceiver<WriteCommand<T>>,
    writer: AtomicJsonlWriter<T>,
    shutdown_flag: Arc<AtomicBool>,
}

impl<T: Serialize + Clone> AtomicWriterService<T> {
    pub async fn new(
        path: PathBuf,
        rx: mpsc::UnboundedReceiver<WriteCommand<T>>,
        shutdown_flag: Arc<AtomicBool>,
    ) -> Result<Self> {
        let writer = AtomicJsonlWriter::new(path).await?;
        
        Ok(Self {
            rx,
            writer,
            shutdown_flag,
        })
    }
    
    /// Main service loop
    pub async fn run(mut self) {
        crate::util::logger::log_info("Atomic writer service started").await;
        
        while let Some(cmd) = self.rx.recv().await {
            // Check for shutdown flag
            if self.shutdown_flag.load(Ordering::SeqCst) {
                crate::util::logger::log_warn(
                    "Shutdown detected - processing only Commit/Rollback commands"
                ).await;
                
                // Only process commit/rollback commands during shutdown
                match cmd {
                    WriteCommand::Commit { id } => {
                        if let Err(e) = self.writer.commit(&id).await {
                            crate::util::logger::log_error(&format!(
                                "Failed to commit {}: {}",
                                id, e
                            )).await;
                        }
                    }
                    WriteCommand::Rollback { id } => {
                        self.writer.rollback(&id).await;
                    }
                    WriteCommand::CommitAll => {
                        match self.writer.commit_all().await {
                            Ok(count) => {
                                crate::util::logger::log_info(&format!(
                                    "Committed {} results during shutdown",
                                    count
                                )).await;
                            }
                            Err(e) => {
                                crate::util::logger::log_error(&format!(
                                    "Failed to commit all: {}",
                                    e
                                )).await;
                            }
                        }
                    }
                    WriteCommand::Shutdown => break,
                    _ => {
                        // Ignore Stage commands during shutdown
                        crate::util::logger::log_warn(
                            "Ignoring new Stage command during shutdown"
                        ).await;
                    }
                }
                continue;
            }
            
            // Normal operation
            match cmd {
                WriteCommand::Stage { id, data } => {
                    self.writer.stage(id, data).await;
                }
                WriteCommand::Commit { id } => {
                    if let Err(e) = self.writer.commit(&id).await {
                        crate::util::logger::log_error(&format!(
                            "Failed to commit {}: {}",
                            id, e
                        )).await;
                    }
                }
                WriteCommand::Rollback { id } => {
                    self.writer.rollback(&id).await;
                }
                WriteCommand::CommitAll => {
                    match self.writer.commit_all().await {
                        Ok(count) => {
                            crate::util::logger::log_info(&format!(
                                "Committed all {} staged results",
                                count
                            )).await;
                        }
                        Err(e) => {
                            crate::util::logger::log_error(&format!(
                                "Failed to commit all: {}",
                                e
                            )).await;
                        }
                    }
                }
                WriteCommand::Shutdown => break,
            }
        }
        
        // Final shutdown - rollback any remaining staged items
        let stats = self.writer.stats();
        if stats.staged_count > 0 {
            crate::util::logger::log_warn(&format!(
                "⚠ Shutdown with {} uncommitted results - rolling back",
                stats.staged_count
            )).await;
            
            self.writer.rollback_all().await;
        }
        
        crate::util::logger::log_info(&format!(
            "Atomic writer service stopped. Final stats: {} committed, {} rolled back",
            stats.committed_count,
            stats.rollback_count
        )).await;
    }
}

/// Handle for sending write commands
#[derive(Clone)]
pub struct AtomicWriterHandle<T> {
    tx: mpsc::UnboundedSender<WriteCommand<T>>,
}

impl<T> AtomicWriterHandle<T> {
    pub fn new(tx: mpsc::UnboundedSender<WriteCommand<T>>) -> Self {
        Self { tx }
    }
    
    /// Stage data for writing (does not write immediately)
    pub fn stage(&self, id: String, data: T) {
        let _ = self.tx.send(WriteCommand::Stage { id, data });
    }
    
    /// Commit staged data to disk
    pub fn commit(&self, id: String) {
        let _ = self.tx.send(WriteCommand::Commit { id });
    }
    
    /// Rollback staged data (discard)
    pub fn rollback(&self, id: String) {
        let _ = self.tx.send(WriteCommand::Rollback { id });
    }
    
    /// Commit all staged data
    pub fn commit_all(&self) {
        let _ = self.tx.send(WriteCommand::CommitAll);
    }
    
    /// Shutdown writer gracefully
    pub fn shutdown(&self) {
        let _ = self.tx.send(WriteCommand::Shutdown);
    }
}

/// Create atomic writer service
pub async fn create_atomic_writer<T: Serialize + Clone + Send + 'static>(
    path: PathBuf,
    shutdown_flag: Arc<AtomicBool>,
) -> Result<(AtomicWriterHandle<T>, tokio::task::JoinHandle<()>)> {
    let (tx, rx) = mpsc::unbounded_channel();
    
    let service = AtomicWriterService::new(path, rx, shutdown_flag).await?;
    let handle = tokio::spawn(async move {
        service.run().await;
    });
    
    Ok((AtomicWriterHandle::new(tx), handle))
}