use std::cell::RefCell;
use std::sync::mpsc::{Receiver, Sender};
use std::sync::Arc;
use std::sync::{Mutex, RwLock};
use std::time::Duration;

use crossbeam::queue::ArrayQueue;
use log::{Level, LevelFilter, Log, Metadata, Record, SetLoggerError};
use logger as c_log;
use once_cell::sync::{Lazy, OnceCell};
use shadow_shim_helper_rs::emulated_time::EmulatedTime;
use shadow_shim_helper_rs::util::time::TimeParts;

use crate::core::worker::Worker;
use crate::host::host::HostInfo;

/// Trigger an asynchronous flush when this many lines are queued.
const ASYNC_FLUSH_QD_LINES_THRESHOLD: usize = 100_000;

/// Performs a *synchronous* flush when this many lines are queued.  i.e. if
/// after reaching the `ASYNC_FLUSH_QD_LINES_THRESHOLD`, log lines are still
/// coming in faster than they can actually be flushed, when we reach this limit
/// we'll pause and let it finish flushing rather than letting the queue
/// continue growing.
const SYNC_FLUSH_QD_LINES_THRESHOLD: usize = 10 * ASYNC_FLUSH_QD_LINES_THRESHOLD;

/// Logging thread flushes at least this often.
const MIN_FLUSH_FREQUENCY: Duration = Duration::from_secs(10);

static SHADOW_LOGGER: Lazy<ShadowLogger> = Lazy::new(ShadowLogger::new);

/// Initialize the Shadow logger.
pub fn init(
    max_log_level: LevelFilter,
    report_errors_to_stderr: bool,
) -> Result<(), SetLoggerError> {
    SHADOW_LOGGER.set_max_level(max_log_level);
    SHADOW_LOGGER.set_report_errors_to_stderr(report_errors_to_stderr);

    log::set_logger(&*SHADOW_LOGGER)?;

    // Shadow's logger has its own logic for deciding the max level (see `ShadowLogger::enabled`),
    // so the log crate should give us all log messages and we can decide whether to show it or not.
    log::set_max_level(log::LevelFilter::Trace);

    // Start the thread that will receive log records and flush them to output.
    std::thread::Builder::new()
        .name("shadow-logger".to_string())
        .spawn(move || SHADOW_LOGGER.logger_thread_fn())
        .unwrap();

    // Arrange to flush the logger on panic.
    let default_panic_handler = std::panic::take_hook();
    std::panic::set_hook(Box::new(move |panic_info| {
        // Attempt to flush the logger. We want to avoid a recursive panic, so
        // we flush the queue on the current thread instead of trying to send
        // a command to the logger thread (because our thread-local sender
        // may have already been destructed, and because the logger thread
        // itself may be in a bad state), and ignore errors.
        SHADOW_LOGGER.flush_records(None).ok();
        default_panic_handler(panic_info);
    }));

    Ok(())
}

/// A logger specialized for Shadow.
///
/// It attaches simulation context to log entries (e.g. sim time, running
/// process, etc.). It's also designed for high performance to accomodate heavy
/// logging from multiple threads.
pub struct ShadowLogger {
    // Channel used to send commands to the logger's thread.
    //
    // The Sender half of a channel isn't Sync, so we must protect it with a
    // Mutex to make ShadowLogger be Sync. This is only accessed once per
    // thread, though, to clone into the thread-local SENDER.
    command_sender: Mutex<Sender<LoggerCommand>>,

    // Like the sender, needs a Mutex for ShadowLogger to be Sync.
    // The Mutex is only locked once though by the logger thread, which keeps
    // it locked for as long as it's running.
    command_receiver: Mutex<Receiver<LoggerCommand>>,

    // A lock-free queue for individual log records. We don't put the records
    // themselves in the `command_sender`, because `Sender` doesn't support
    // getting the queue length. Conversely we don't put commands in this queue
    // because it doesn't support blocking operations.
    //
    // The size is roughly SYNC_FLUSH_QD_LINES_THRESHOLD *
    // size_of<ShadowLogRecord>; we might want to consider SegQueue (which grows
    // and shrinks dynamically) instead if we ever make SYNC_FLUSH_QD_LINES_THRESHOLD very
    // large.
    records: ArrayQueue<ShadowLogRecord>,

    // When false, sends a (still-asynchronous) flush command to the logger
    // thread every time a record is pushed into `records`.
    buffering_enabled: RwLock<bool>,

    // The maximum log level, unless overridden by a host-specific log level.
    max_log_level: OnceCell<LevelFilter>,

    // Whether to report errors to stderr in addition to logging to stdout.
    report_errors_to_stderr: OnceCell<bool>,
}

thread_local!(static SENDER: RefCell<Option<Sender<LoggerCommand>>> = const{ RefCell::new(None)});
thread_local!(static THREAD_NAME: String = get_thread_name());
thread_local!(static THREAD_ID: nix::unistd::Pid = nix::unistd::gettid());

fn get_thread_name() -> String {
    let mut thread_name = Vec::<i8>::with_capacity(16);
    let res = unsafe {
        thread_name.set_len(thread_name.capacity());
        // ~infallible when host_name is at least 16 bytes.
        libc::pthread_getname_np(
            libc::pthread_self(),
            thread_name.as_mut_ptr(),
            thread_name.len(),
        )
    };
    // The most likely cause of failure is a bug in the caller.
    debug_assert_eq!(
        res,
        0,
        "pthread_getname_np: {}",
        nix::errno::Errno::from_raw(res),
    );
    if res == 0 {
        // SAFETY: We just initialized the input buffer `thread_name`, and
        // `thread_name_cstr` won't outlive it.
        let thread_name_cstr = unsafe { std::ffi::CStr::from_ptr(thread_name.as_ptr()) };
        return thread_name_cstr.to_owned().to_string_lossy().to_string();
    }

    // Another potential reason for failure is if it couldn't open
    // /proc/self/task/[tid]/comm. We're probably in a bad state anyway if that
    // happens, but try to recover anyway.

    // Empty string
    String::new()
}

impl ShadowLogger {
    fn new() -> ShadowLogger {
        let (sender, receiver) = std::sync::mpsc::channel();

        ShadowLogger {
            records: ArrayQueue::new(SYNC_FLUSH_QD_LINES_THRESHOLD),
            command_sender: Mutex::new(sender),
            command_receiver: Mutex::new(receiver),
            buffering_enabled: RwLock::new(false),
            max_log_level: OnceCell::new(),
            report_errors_to_stderr: OnceCell::new(),
        }
    }

    // Function executed by the logger's helper thread, onto which we offload as
    // much work as we can.
    fn logger_thread_fn(&self) {
        let command_receiver = self.command_receiver.lock().unwrap();

        loop {
            use std::sync::mpsc::RecvTimeoutError;
            match command_receiver.recv_timeout(MIN_FLUSH_FREQUENCY) {
                Ok(LoggerCommand::Flush(done_sender)) => self.flush_records(done_sender).unwrap(),
                Err(RecvTimeoutError::Timeout) => {
                    // Flush
                    self.flush_records(None).unwrap();
                }
                Err(e) => panic!("Unexpected error {}", e),
            }
        }
    }

    // Function called by the logger's helper thread to flush the contents of
    // self.records. If `done_sender` is provided, it's notified after the flush
    // has completed.
    fn flush_records(&self, done_sender: Option<Sender<()>>) -> std::io::Result<()> {
        use std::io::Write;

        // Only flush records that are already in the queue, not ones that
        // arrive while we're flushing. Otherwise callers who perform a
        // synchronous flush (whether this flush operation or another one that
        // arrives while we're flushing) will be left waiting longer than
        // necessary. Also keeps us from holding the stdout lock indefinitely.
        let mut toflush = self.records.len();

        let stdout_unlocked = std::io::stdout();
        let stdout_locked = stdout_unlocked.lock();
        let mut stdout = std::io::BufWriter::new(stdout_locked);

        while toflush > 0 {
            let record = match self.records.pop() {
                Some(r) => r,
                None => {
                    // This can happen if another thread panics while the
                    // logging thread is flushing. In that case both threads
                    // will be consuming from the queue.
                    break;
                }
            };
            toflush -= 1;

            write!(stdout, "{record}")?;

            if record.level <= Level::Error && *self.report_errors_to_stderr.get().unwrap() {
                // *also* summarize on stderr.

                // First flush stdout to avoid confusing interleaving if stdout and stderr are merged.
                stdout.flush()?;

                // Summarize on stderr. We use a `BufWriter` to try to help
                // ensure we ultimately make a single `write` syscall, though
                // the flushes above and below *should* already prevent any
                // interleaving with stdout.
                let stderr_unlocked = std::io::stderr();
                let stderr_locked = stderr_unlocked.lock();
                let mut stderr = std::io::BufWriter::new(stderr_locked);
                writeln!(stderr, "Error: {}", record.message)?;

                // Explicitly flush before dropping to detect errors.
                stderr.flush()?;
                drop(stderr);
            }
        }

        // Explicitly flush before dropping to detect errors.
        stdout.flush()?;
        drop(stdout);

        if let Some(done_sender) = done_sender {
            // We can't log from this thread without risking deadlock, so in the
            // unlikely case that the calling thread has gone away, just print
            // directly.
            done_sender.send(()).unwrap_or_else(|e| {
                println!(
                    "WARNING: Logger couldn't notify
                calling thread: {:?}",
                    e
                )
            });
        }
        Ok(())
    }

    /// When disabled, the logger thread is notified to write each record as
    /// soon as it's created.  The calling thread still isn't blocked on the
    /// record actually being written, though.
    pub fn set_buffering_enabled(&self, buffering_enabled: bool) {
        let mut writer = self.buffering_enabled.write().unwrap();
        *writer = buffering_enabled;
    }

    /// If the maximum log level has not yet been set, returns `LevelFilter::Trace`.
    pub fn max_level(&self) -> LevelFilter {
        self.max_log_level
            .get()
            .copied()
            .unwrap_or(LevelFilter::Trace)
    }

    /// Set the default maximum log level, but this can be overridden per-host. Is only intended to
    /// be called from `init()`. Will panic if called more than once.
    fn set_max_level(&self, level: LevelFilter) {
        self.max_log_level.set(level).unwrap()
    }

    /// Set whether to report errors to stderr in addition to logging on stdout.
    ///
    /// Is only intended to be called from `init()`. Will panic if called more
    /// than once.
    fn set_report_errors_to_stderr(&self, val: bool) {
        self.report_errors_to_stderr.set(val).unwrap()
    }

    // Send a flush command to the logger thread.
    fn flush_impl(&self, notify_done: Option<Sender<()>>) {
        self.send_command(LoggerCommand::Flush(notify_done))
    }

    // Send a flush command to the logger thread and block until it's completed.
    fn flush_sync(&self) {
        let (done_sender, done_receiver) = std::sync::mpsc::channel();
        self.flush_impl(Some(done_sender));
        done_receiver.recv().unwrap();
    }

    // Send a flush command to the logger thread.
    fn flush_async(&self) {
        self.flush_impl(None);
    }

    // Send a command to the logger thread.
    fn send_command(&self, cmd: LoggerCommand) {
        SENDER
            .try_with(|thread_sender| {
                if thread_sender.borrow().is_none() {
                    let lock = self.command_sender.lock().unwrap();
                    *thread_sender.borrow_mut() = Some(lock.clone());
                }
                thread_sender
                    .borrow()
                    .as_ref()
                    .unwrap()
                    .send(cmd)
                    .unwrap_or_else(|e| {
                        println!("WARNING: Couldn't send command to logger thread: {:?}", e);
                    });
            })
            .unwrap_or_else(|e| {
                println!(
                    "WARNING: Couldn't get sender channel to logger thread: {:?}",
                    e
                );
            });
    }
}

impl Log for ShadowLogger {
    fn enabled(&self, metadata: &Metadata) -> bool {
        let filter = match Worker::with_active_host(|host| host.info().log_level) {
            Some(Some(level)) => level,
            _ => self.max_level(),
        };
        metadata.level() <= filter
    }

    fn log(&self, record: &Record) {
        if !self.enabled(record.metadata()) {
            return;
        }

        let message = std::fmt::format(*record.args());

        let host_info = Worker::with_active_host(|host| host.info().clone());

        let mut shadowrecord = ShadowLogRecord {
            level: record.level(),
            file: record.file_static(),
            module_path: record.module_path_static(),
            line: record.line(),
            message,
            wall_time: Duration::from_micros(unsafe {
                u64::try_from(c_log::logger_elapsed_micros()).unwrap()
            }),

            emu_time: Worker::current_time(),
            thread_name: THREAD_NAME
                .try_with(|name| (*name).clone())
                .unwrap_or_else(|_| get_thread_name()),
            thread_id: THREAD_ID
                .try_with(|id| *id)
                .unwrap_or_else(|_| nix::unistd::gettid()),
            host_info,
        };

        loop {
            match self.records.push(shadowrecord) {
                Ok(()) => break,
                Err(r) => {
                    // Queue is full. Flush it and try again.
                    shadowrecord = r;
                    self.flush_sync();
                }
            }
        }

        if record.level() == Level::Error {
            // Unlike in Shadow's C code, we don't abort the program on Error
            // logs. In Rust the same purpose is filled with `panic` and
            // `unwrap`. C callers will still exit or abort via the lib/logger wrapper.
            //
            // Flush *synchronously*, since we're likely about to crash one way or another.
            self.flush_sync();
        } else if self.records.len() > ASYNC_FLUSH_QD_LINES_THRESHOLD
            || !*self.buffering_enabled.read().unwrap()
        {
            self.flush_async();
        }
    }

    fn flush(&self) {
        self.flush_sync();
    }
}

struct ShadowLogRecord {
    level: Level,
    file: Option<&'static str>,
    module_path: Option<&'static str>,
    line: Option<u32>,
    message: String,
    wall_time: Duration,

    emu_time: Option<EmulatedTime>,
    thread_name: String,
    thread_id: nix::unistd::Pid,
    host_info: Option<Arc<HostInfo>>,
}

impl std::fmt::Display for ShadowLogRecord {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        {
            let parts = TimeParts::from_nanos(self.wall_time.as_nanos());
            write!(
                f,
                "{:02}:{:02}:{:02}.{:06}",
                parts.hours,
                parts.mins,
                parts.secs,
                parts.nanos / 1000
            )?;
        }
        write!(f, " [{}:{}]", self.thread_id, self.thread_name)?;
        if let Some(emu_time) = self.emu_time {
            let sim_time = emu_time.duration_since(&EmulatedTime::SIMULATION_START);
            let parts = TimeParts::from_nanos(sim_time.as_nanos());
            write!(
                f,
                " {:02}:{:02}:{:02}.{:09}",
                parts.hours, parts.mins, parts.secs, parts.nanos
            )?;
        } else {
            write!(f, " n/a")?;
        }
        write!(f, " [{level}]", level = self.level)?;
        if let Some(host) = &self.host_info {
            write!(
                f,
                " [{hostname}:{ip}]",
                hostname = host.name,
                ip = host.default_ip,
            )?;
        } else {
            write!(f, " [n/a]",)?;
        }
        write!(
            f,
            " [{file}:",
            file = self
                .file
                .map(|f| if let Some(sep_pos) = f.rfind('/') {
                    &f[(sep_pos + 1)..]
                } else {
                    f
                })
                .unwrap_or("n/a"),
        )?;
        if let Some(line) = self.line {
            write!(f, "{line}", line = line)?;
        } else {
            write!(f, "n/a")?;
        }
        writeln!(
            f,
            "] [{module}] {msg}",
            module = self.module_path.unwrap_or("n/a"),
            msg = self.message
        )?;
        Ok(())
    }
}

enum LoggerCommand {
    // Flush; takes an optional one-shot channel to notify that the flush has completed.
    Flush(Option<Sender<()>>),
}

pub fn set_buffering_enabled(buffering_enabled: bool) {
    SHADOW_LOGGER.set_buffering_enabled(buffering_enabled);
}

mod export {
    use super::*;

    /// When disabled, the logger thread is notified to write each record as
    /// soon as it's created.  The calling thread still isn't blocked on the
    /// record actually being written, though.
    #[no_mangle]
    pub unsafe extern "C-unwind" fn shadow_logger_setEnableBuffering(buffering_enabled: i32) {
        set_buffering_enabled(buffering_enabled != 0)
    }
}