use anyhow::{anyhow, Result};
use clap::Command;
use std::io::Read;
use std::os::fd::FromRawFd;
use std::str::FromStr;

fn validate_diff_args(cmd: &mut Command, ids: &Vec<i64>, tags: &Vec<String>) {
    if !tags.is_empty() {
        cmd.error(
            clap::error::ErrorKind::InvalidValue,
            "Tags are not supported with --diff. Please provide exactly two IDs.",
        )
        .exit();
    }
    if ids.len() != 2 {
        cmd.error(
            clap::error::ErrorKind::InvalidValue,
            "You must supply exactly two IDs when using --diff.",
        )
        .exit();
    }
}

fn fetch_and_validate_items(
    conn: &mut rusqlite::Connection,
    ids: &Vec<i64>,
) -> Result<(crate::db::Item, crate::db::Item), anyhow::Error> {
    // Fetch items, ensuring they exist.
    let item_a = crate::db::get_item(conn, ids[0])?
        .ok_or_else(|| anyhow::anyhow!("Unable to find first item (ID: {}) in database", ids[0]))?;
    let item_b = crate::db::get_item(conn, ids[1])?
        .ok_or_else(|| anyhow::anyhow!("Unable to find second item (ID: {}) in database", ids[1]))?;

    log::debug!("MAIN: Found item A {:?}", item_a);
    log::debug!("MAIN: Found item B {:?}", item_b);

    let item_a_id = item_a.id.ok_or_else(|| anyhow!("Item A missing ID"))?;
    let item_b_id = item_b.id.ok_or_else(|| anyhow!("Item B missing ID"))?;
    
    // Validate that item IDs are positive to prevent path traversal issues
    if item_a_id <= 0 || item_b_id <= 0 {
        return Err(anyhow::anyhow!("Invalid item ID: {} or {}", item_a_id, item_b_id));
    }

    Ok((item_a, item_b))
}

fn get_item_tags(conn: &mut rusqlite::Connection, item: &crate::db::Item) -> Result<Vec<String>, anyhow::Error> {
    let tags: Vec<String> = crate::db::get_item_tags(conn, item)?
        .into_iter()
        .map(|x| x.name)
        .collect();
    Ok(tags)
}

fn setup_diff_paths_and_compression(
    data_path: &std::path::PathBuf,
    item_a: &crate::db::Item,
    item_b: &crate::db::Item,
) -> Result<(std::path::PathBuf, crate::compression_engine::CompressionType, std::path::PathBuf, crate::compression_engine::CompressionType), anyhow::Error> {
    let item_a_id = item_a.id.ok_or_else(|| anyhow::anyhow!("Item A missing ID"))?;
    let item_b_id = item_b.id.ok_or_else(|| anyhow::anyhow!("Item B missing ID"))?;

    let mut item_path_a = data_path.clone();
    item_path_a.push(item_a_id.to_string());
    let compression_type_a = crate::compression_engine::CompressionType::from_str(&item_a.compression)?;
    log::debug!("MAIN: Item A has compression type {:?}", compression_type_a);

    let mut item_path_b = data_path.clone();
    item_path_b.push(item_b_id.to_string());
    let compression_type_b = crate::compression_engine::CompressionType::from_str(&item_b.compression)?;
    log::debug!("MAIN: Item B has compression type {:?}", compression_type_b);

    Ok((item_path_a, compression_type_a, item_path_b, compression_type_b))
}

fn setup_diff_pipes() -> Result<((libc::c_int, libc::c_int), (libc::c_int, libc::c_int)), anyhow::Error> {
    use nix::unistd::pipe;
    use nix::Error as NixError;
    use std::os::fd::IntoRawFd;

    // Create pipes for diff's input
    let (fd_a_read, fd_a_write) = pipe()
        .map_err(|e: NixError| anyhow::anyhow!("Failed to create pipe A: {}", e))?;
    let (fd_b_read, fd_b_write) = pipe()
        .map_err(|e: NixError| anyhow::anyhow!("Failed to create pipe B: {}", e))?;

    Ok(((fd_a_read.into_raw_fd(), fd_a_write.into_raw_fd()), (fd_b_read.into_raw_fd(), fd_b_write.into_raw_fd())))
}


fn setup_fd_guards(fd_a_read: libc::c_int, fd_b_read: libc::c_int) -> (FdGuard, FdGuard) {
    // Wrap file descriptors in RAII guards
    let fd_a_read_guard = FdGuard::new(fd_a_read);
    let fd_b_read_guard = FdGuard::new(fd_b_read);
    (fd_a_read_guard, fd_b_read_guard)
}


fn spawn_diff_process(
    item_a_id: i64,
    item_a_tags: Vec<String>,
    item_b_id: i64,
    item_b_tags: Vec<String>,
    fd_a_read: libc::c_int,
    fd_b_read: libc::c_int,
) -> Result<std::process::Child, anyhow::Error> {
    log::debug!("MAIN: Creating child process for diff");
    let mut diff_command = std::process::Command::new("diff");
    diff_command
        .arg("-u")
        .arg("--label")
        .arg(format!(
            "Keep item A: {} {}",
            item_a_id,
            item_a_tags.join(" ")
        ))
        .arg(format!("/dev/fd/{}", fd_a_read))
        .arg("--label")
        .arg(format!(
            "Keep item B: {} {}",
            item_b_id,
            item_b_tags.join(" ")
        ))
        .arg(format!("/dev/fd/{}", fd_b_read))
        .stdin(std::process::Stdio::null())
        .stdout(std::process::Stdio::piped())
        .stderr(std::process::Stdio::piped());

    let child_process = diff_command
        .spawn()
        .map_err(|e| anyhow::anyhow!("Failed to execute diff command: {}", e))?;

    Ok(child_process)
}

// RAII guard for file descriptors to ensure they're closed
struct FdGuard {
    fd: libc::c_int,
}

impl FdGuard {
    fn new(fd: libc::c_int) -> Self {
        Self { fd }
    }
}

impl Drop for FdGuard {
    fn drop(&mut self) {
        let _ = nix::unistd::close(self.fd);
    }
}

// Create a function to write item data to a pipe
fn write_item_to_pipe(
    item_path: std::path::PathBuf,
    compression_type: crate::compression_engine::CompressionType,
    pipe_writer_raw: std::fs::File,
) -> Result<(), anyhow::Error> {
    use std::io::BufWriter;
    let mut buffered_pipe_writer = BufWriter::new(pipe_writer_raw);
    let engine =
        crate::compression_engine::get_compression_engine(compression_type).expect("Unable to get compression engine");
    log::debug!("THREAD: Sending item to diff");
    engine
        .copy(item_path, &mut buffered_pipe_writer)
        .map_err(|e| anyhow::anyhow!("Failed to copy/compress item: {}", e))?;
    log::debug!("THREAD: Done sending item to diff");
    Ok(())
}

// Function to spawn a writer thread for an item
fn spawn_writer_thread(
    item_path: std::path::PathBuf,
    compression_type: crate::compression_engine::CompressionType,
    fd_write: libc::c_int,
) -> std::thread::JoinHandle<Result<(), anyhow::Error>> {
    let pipe_writer_raw = unsafe { std::fs::File::from_raw_fd(fd_write) };
    std::thread::spawn(move || {
        write_item_to_pipe(item_path, compression_type, pipe_writer_raw)
    })
}

fn execute_diff_command(
    child_process: &mut std::process::Child,
) -> Result<(Vec<u8>, Vec<u8>), anyhow::Error> {
    let mut child_stdout_pipe = child_process
        .stdout
        .take()
        .expect("BUG: Failed to capture diff stdout pipe");
    let mut child_stderr_pipe = child_process
        .stderr
        .take()
        .expect("BUG: Failed to capture diff stderr pipe");

    log::debug!("MAIN: Creating threads for diff I/O");

    // Thread to read diff's standard output
    let stdout_reader_thread = std::thread::spawn(move || {
        let mut output_buffer = Vec::new();
        log::debug!("STDOUT_READER: Reading diff stdout");
        // child_stdout_pipe is a ChildStdout, which implements std::io::Read
        child_stdout_pipe
            .read_to_end(&mut output_buffer)
            .map_err(|e| anyhow::anyhow!("Failed to read diff stdout: {}", e))
            .map(|_| output_buffer) // Return the Vec<u8> on success
    });

    // Thread to read diff's standard error
    let stderr_reader_thread = std::thread::spawn(move || {
        let mut error_buffer = Vec::new();
        log::debug!("STDERR_READER: Reading diff stderr");
        child_stderr_pipe
            .read_to_end(&mut error_buffer)
            .map_err(|e| anyhow::anyhow!("Failed to read diff stderr: {}", e))
            .map(|_| error_buffer)
    });

    // Retrieve the captured output from the reader threads.
    let stdout_capture_result = stdout_reader_thread
        .join()
        .map_err(|panic_payload| {
            anyhow::anyhow!("Stdout reader thread panicked: {:?}", panic_payload)
        })?
        .map_err(|e| anyhow::anyhow!("Failed to read diff stdout: {}", e))?;

    let stderr_capture_result = stderr_reader_thread
        .join()
        .map_err(|panic_payload| {
            anyhow::anyhow!("Stderr reader thread panicked: {:?}", panic_payload)
        })?
        .map_err(|e| anyhow::anyhow!("Failed to read diff stderr: {}", e))?;

    Ok((stdout_capture_result, stderr_capture_result))
}

fn handle_diff_output(
    diff_status: std::process::ExitStatus,
    stdout_capture_result: Vec<u8>,
    stderr_capture_result: Vec<u8>,
) -> Result<(), anyhow::Error> {
    // Handle diff's exit status and output
    match diff_status.code() {
        Some(0) => {
            // Exit code 0: No differences
            log::debug!("MAIN: Diff successful, no differences found.");
            // Typically, diff -u doesn't print to stdout if no differences.
            // But if it did, it would be shown here.
            if !stdout_capture_result.is_empty() {
                println!("{}", String::from_utf8_lossy(&stdout_capture_result));
            }
        }
        Some(1) => {
            // Exit code 1: Differences found
            log::debug!("MAIN: Diff successful, differences found.");
            println!("{}", String::from_utf8_lossy(&stdout_capture_result));
        }
        Some(error_code) => {
            // Exit code > 1: Error in diff utility
            eprintln!("Diff command failed with exit code: {}", error_code);
            if !stdout_capture_result.is_empty() {
                eprintln!(
                    "Diff stdout before error:\n{}",
                    String::from_utf8_lossy(&stdout_capture_result)
                );
            }
            if !stderr_capture_result.is_empty() {
                eprintln!(
                    "Diff stderr:\n{}",
                    String::from_utf8_lossy(&stderr_capture_result)
                );
            }
            return Err(anyhow::anyhow!(
                "Diff command reported an error (exit code {})",
                error_code
            ));
        }
        None => {
            // Process terminated by a signal
            eprintln!("Diff command terminated by signal.");
            if !stderr_capture_result.is_empty() {
                eprintln!(
                    "Diff stderr before signal termination:\n{}",
                    String::from_utf8_lossy(&stderr_capture_result)
                );
            }
            return Err(anyhow::anyhow!("Diff command terminated by signal"));
        }
    }

    Ok(())
}

pub fn mode_diff(
    cmd: &mut Command,
    _settings: &crate::config::Settings,
    _config: &crate::config::Config,
    ids: &mut Vec<i64>,
    tags: &mut Vec<String>,
    conn: &mut rusqlite::Connection,
    data_path: std::path::PathBuf,
) -> Result<(), anyhow::Error> {
    validate_diff_args(cmd, ids, tags);
    let (item_a, item_b) = fetch_and_validate_items(conn, ids)?;

    let item_a_tags = get_item_tags(conn, &item_a)?;
    let item_b_tags = get_item_tags(conn, &item_b)?;

    let (item_path_a, compression_type_a, item_path_b, compression_type_b) = 
        setup_diff_paths_and_compression(&data_path, &item_a, &item_b)?;

    let ((fd_a_read, fd_a_write), (fd_b_read, fd_b_write)) = setup_diff_pipes()?;
    let (_fd_a_read_guard, _fd_b_read_guard) = setup_fd_guards(fd_a_read, fd_b_read);

    let item_a_id = item_a.id.ok_or_else(|| anyhow::anyhow!("Item A missing ID"))?;
    let item_b_id = item_b.id.ok_or_else(|| anyhow::anyhow!("Item B missing ID"))?;

    let mut child_process = spawn_diff_process(
        item_a_id,
        item_a_tags,
        item_b_id,
        item_b_tags,
        fd_a_read,
        fd_b_read,
    )?;

    // Close read ends in parent process - they're now guarded by FdGuard
    drop(_fd_a_read_guard);
    drop(_fd_b_read_guard);

    // Spawn writer threads for both items
    let writer_thread_a =
        spawn_writer_thread(item_path_a.clone(), compression_type_a.clone(), fd_a_write);

    let writer_thread_b =
        spawn_writer_thread(item_path_b.clone(), compression_type_b.clone(), fd_b_write);

    // Wait for writer threads to complete (meaning all input has been sent to diff)
    log::debug!("MAIN: Waiting on writer thread for item A");
    match writer_thread_a.join() {
        Ok(Ok(())) => {
            log::debug!("MAIN: Writer thread for item A completed successfully.");
        }
        Ok(Err(e)) => {
            return Err(anyhow::anyhow!("Writer thread for item A failed: {}", e));
        }
        Err(panic_payload) => {
            return Err(anyhow::anyhow!(
                "Writer thread for item A (ID: {}) panicked: {:?}",
                ids[0],
                panic_payload
            ));
        }
    }

    log::debug!("MAIN: Waiting on writer thread for item B");
    match writer_thread_b.join() {
        Ok(Ok(())) => {
            log::debug!("MAIN: Writer thread for item B completed successfully.");
        }
        Ok(Err(e)) => {
            return Err(anyhow::anyhow!("Writer thread for item B failed: {}", e));
        }
        Err(panic_payload) => {
            return Err(anyhow::anyhow!(
                "Writer thread for item B (ID: {}) panicked: {:?}",
                ids[1],
                panic_payload
            ));
        }
    }
    
    log::debug!("MAIN: Done waiting on input-writer threads.");

    // Now that all input has been sent and input pipes will be closed by threads exiting,
    // wait for the diff child process to terminate.
    log::debug!("MAIN: Waiting for diff child process to finish...");
    let diff_status = child_process
        .wait()
        .map_err(|e| anyhow::anyhow!("Failed to wait on diff command: {}", e))?;
    log::debug!(
        "MAIN: Diff child process finished with status: {}",
        diff_status
    );

    let (stdout_capture_result, stderr_capture_result) = execute_diff_command(&mut child_process)?;
    handle_diff_output(diff_status, stdout_capture_result, stderr_capture_result)?;

    Ok(())
}