lw 0.4.1

//! "lw" log-watcher utility

//! LW docs

#![deny(
    missing_docs,
    unstable_features,
    unsafe_code,
    missing_debug_implementations,
    missing_copy_implementations,
    trivial_casts,
    trivial_numeric_casts,
    unused_import_braces,
    unused_qualifications
)]


#[macro_use]
extern crate log;

use kqueue_sys::*;
use kqueue::*;
use kqueue::Ident::*;
use std::io::prelude::*;
use std::io::{SeekFrom, BufReader};
use std::fs::File;
use std::fs::metadata;
use std::collections::HashMap;

use std::env;
use std::path::Path;
use walkdir::WalkDir;
use std::process::exit;
use std::fmt::Display;
use chrono::Local;
use colored::Colorize;
use log::LevelFilter;
use fern::Dispatch;


/// FileAndPosition alias type for HashMap of File path and file cursor position (in bytes)
type FileAndPosition = HashMap<String, u64>;

/// Defines stdout file
const STDOUT_DEV: &str = "/dev/stdout";

/// Minimum directory depth to watch
const MIN_DIR_DEPTH: usize = 1;

/// Maximum directory depth to watch
const MAX_DIR_DEPTH: usize = 3;


/// Utility to wrap fatal errors
fn fatal<S: Display>(fmt: S) -> ! {
    error!("FATAL ERROR: {}", fmt.to_string().red());
    exit(1)
}


/// Resursively filter out all unreadable/unaccessible/inproper and handle proper files
fn walkdir_recursive(mut kqueue_watcher: &mut Watcher, file_path: &Path) {
    WalkDir::new(&file_path)
        .follow_links(true)
        .min_depth(MIN_DIR_DEPTH)
        .max_depth(MAX_DIR_DEPTH)
        .into_iter()
        .filter_map(|element| element.ok())
        .for_each(|element| watch_file(&mut kqueue_watcher, element.path()));
}


fn main() {
    // Read value of DEBUG from env, if defined switch log level to Debug:
    let loglevel = match env::var("DEBUG") {
        Ok(_) => LevelFilter::Debug,
        Err(_) => LevelFilter::Info,
    };

    // Dispatch logger:
    Dispatch::new()
        .format(move |out, message, _record| {
            out.finish(format_args!(
                "{}: {}",
                Local::now().to_rfc3339().black(),
                message
            ))
        })
        .level(loglevel)
        .chain(
            File::open(STDOUT_DEV)
                .unwrap_or_else(|_|
                    fatal(format!("{}: STDOUT device {} is not available! Something is terribly wrong here!",
                             "FATAL ERROR".red(), STDOUT_DEV.yellow()))
                )
        )
        .apply()
        .unwrap_or_else(|err| {
            fatal(format!("{}: Couldn't initialize Log-Watcher. Details: {}",
                   "FATAL ERROR".red(), err.to_string().yellow()));
        });

    // mutable hashmap keeping position of all watched files:
    let mut watched_file_states = FileAndPosition::new();

    // mutable kqueue watcher:
    let mut kqueue_watcher
        = Watcher::new()
            .unwrap_or_else(|e| fatal(format!("Could not create kq watcher: {}", e)));

    // read paths given as arguments:
    let paths_to_watch: Vec<String>
        = env::args()
            .skip(1) // first arg is $0
            .collect();

    debug!("Watching paths: {}", paths_to_watch.join(", "));
    if paths_to_watch.is_empty() {
        fatal("No paths specified as arguments! You have to specify at least a single directory/file to watch!");
    }

    // initial watches for specified dirs/files:
    paths_to_watch
        .iter()
        .for_each(|a_path| {
            // Handle case when given a file as argument
            let file_path = Path::new(&a_path);
            watch_file(&mut kqueue_watcher, &file_path);
            walkdir_recursive(&mut kqueue_watcher, &file_path);
        });

    if kqueue_watcher
        .watch()
        .is_ok() {

        // handle events dynamically, including new files
        while let Some(an_event) = kqueue_watcher.iter().next() {
            match an_event.ident {
                Filename(_file_descriptor, abs_file_name) => {
                    let file_path = Path::new(&abs_file_name);
                    match metadata(file_path) {
                        Ok(metadata) => {
                            if metadata.is_dir() { // handle dirs
                                debug!("{}: {}", "+DirLoad".magenta(), abs_file_name.cyan());
                                walkdir_recursive(&mut kqueue_watcher, file_path);
                                kqueue_watcher
                                    .watch()
                                    .is_ok();
                            } else { // handle files
                                debug!("{}: {}", "+New".magenta(), abs_file_name.cyan());
                                watch_file(&mut kqueue_watcher, file_path);
                                kqueue_watcher
                                    .watch()
                                    .is_ok();
                                handle_file_event(&mut watched_file_states, &abs_file_name);
                            }
                        },

                        Err(error_cause) => {
                            // handle situation when logs are wiped out and unavailable to read anymore
                            error!("Metadata read failed for file: {}. Error cause: {}",
                                   &abs_file_name.cyan(), error_cause.to_string().red());
                            debug!("{}: {}", "-Watch".magenta(), abs_file_name.cyan());
                            kqueue_watcher
                                .remove_filename(file_path, EventFilter::EVFILT_VNODE)
                                .unwrap_or_else(|error_cause| error!("Could not remove watch on file: {:?}. Error cause: {}",
                                                                     abs_file_name.cyan(), error_cause.to_string().red()));
                            // try to build list if path exists
                            if file_path.exists() {
                                walkdir_recursive(&mut kqueue_watcher, file_path);
                                kqueue_watcher
                                    .watch()
                                    .is_ok();
                            } else {
                                fatal("Unable to find any dirs/files to watch!");
                            }
                        }
                    };
                },

                event =>
                    warn!("Unknown event: {:?}", event)
            }
        }
    }
}


/// kqueue flags, from: /usr/include/sys/event.h
/// NOTE_DELETE     0x00000001              /* vnode was removed */
/// NOTE_WRITE      0x00000002              /* data contents changed */
/// NOTE_EXTEND     0x00000004              /* size increased */
/// NOTE_ATTRIB     0x00000008              /* attributes changed */
/// NOTE_LINK       0x00000010              /* link count changed */
/// NOTE_RENAME     0x00000020              /* vnode was renamed */
/// NOTE_REVOKE     0x00000040              /* vnode access was revoked */
///
/// Add watch on specified file path
fn watch_file(kqueue_watcher: &mut Watcher, file: &Path) {
    debug!("{}: {}", "+Watch".magenta(), format!("{:?}", file).cyan());
    kqueue_watcher
        .add_filename(
            &file,
            EventFilter::EVFILT_VNODE,
            NOTE_WRITE | NOTE_LINK | NOTE_RENAME | NOTE_DELETE // | NOTE_EXTEND | NOTE_ATTRIB | NOTE_REVOKE
        )
        .unwrap_or_else(|error_cause| error!("Could not watch file {:?}. Error cause: {}",
                                             file, error_cause.to_string().red()));
}


/// Handle action triggered by an event
fn handle_file_event(states: &mut FileAndPosition, file_path: &str) {
    let file_entry_in_hashmap
        = states
            .iter()
            .find(|hashmap| *hashmap.0 == file_path);

    match file_entry_in_hashmap {
        Some((watched_file, file_position)) => {
            debug!("{}: {} {}", "+EventHandle".magenta(), watched_file.cyan(), format!("@{}", file_position).black());
            let file_size = match metadata(&watched_file) {
                Ok(file_metadata) => file_metadata.len(),
                Err(_) => 0,
            };
            if *file_position < file_size {
                seek_file_to_position_and_print(&watched_file, *file_position);
                states
                    .insert(file_path.to_string(), file_size);
            }
        },

        None => {
            states
                .insert(file_path.to_string(), 0);
        }
    }
}


/// Set file position in bytes and print new file contents
fn seek_file_to_position_and_print(file_to_watch: &str, file_position: u64) {
    match File::open(&file_to_watch) {
        Ok(some_file) => {
            let mut cursor = BufReader::new(some_file);
            cursor
                .seek(SeekFrom::Start(file_position))
                .unwrap_or_else(|_| 0);

            // TODO: show same file header once per file, not per event
            println!(); // just start new entry from \n
            info!("{}", file_to_watch.blue());
            let content: Vec<String>
                = cursor
                    .lines()
                    .filter_map(|line| line.ok())
                    .collect();
            println!("{}", content.join("\n"));
        },

        Err(error_cause) =>
            error!("Couldn't open file: {}. Error cause: {}",
                   file_to_watch.yellow(), error_cause.to_string().red()),
    }
}