#![allow(clippy::needless_doctest_main, clippy::must_use_candidate)]
//! `alog` is a simple log file anonymizer.
//!
//! ## About
//!
//! In fact by default `alog` just replaces the first *word* on every line of any input stream
//! with a customizable string.
//!
//! With version 0.6 you can (at a substantial cost of CPU cycles) replace the `$remote_user`
//! with `"-"` ([`Config::authuser`] set to `true`) as well. Defaults to `false`.
//!
//! With [`Config::trim`] set to `false` the first *word* can be the (zero width)
//! anchor ^ or a single `b' '` (Space) separated by a `b' '` from the remainder of the line.
//! This was the default behaviour prior to version 0.6.
//!
//! So "log file anonymizer" might be a bit of an overstatement, but `alog` can be used to (very
//! efficiently) replace the `$remote_addr` part in many access log formats, e.g. Nginx' default
//! combined log format:
//!
//! ```text
//! log_format combined '$remote_addr - $remote_user [$time_local] '
//!                     '"$request" $status $body_bytes_sent '
//!                     '"$http_referer" "$http_user_agent"';
//! ```
//!
//! By default any parseable `$remote_addr` is replaced by it's *localhost* representation,
//!
//! * any valid IPv4 address is replaced by *127.0.0.1*,
//! * any valid IPv6 address is replaced by *::1* and
//! * any String (what might be a domain name) with *localhost*.
//!
//! Lines without a 'first word' will remain unchanged (but can be skipped with [`Config::skip`]
//! set to `true`).
//!
//! Starting with version 0.6 all Space and Tabulator (`b'\t'`) characters will be removed from
//! the beginning of each line before replacing any `$remote_addr` by default. To switch back to
//! the previous behaviour just set [`Config::trim`] to `false`.
//!
//! ### Personal data in server logs
//!
//! The default configuration of popular web servers including Apache Web Server and Nginx collect
//! and store at least two of the following three types of logs:
//!
//! 1. access logs
//! 2. error logs (including processing-language logs like PHP)
//! 3. security audit logs
//!
//! All of these logs contain personal information by default. IP addresses are specifically
//! defined as personal data by the [GDPR].  The logs can also contain usernames if your web
//! service uses them as part of their URL structure, and even the referral information that’s
//! logged by default **can** contain personal information (or other sensitive data).
//!
//! So keep in mind, just removing the IP / `$remote_addr` or `$remote_user` part might not be
//! enough to fully anonymize any given log file.
//!
//! [GDPR]: https://gdpr.eu/article-4-definitions/

use std::cmp::Ordering;
use std::fs::File;
use std::fs::OpenOptions;
use std::io::{self, BufRead, BufReader, BufWriter, Write};
use std::net;
use std::path::Path;
use std::process;

use regex::bytes::Regex;

#[macro_use(lazy_static)]
extern crate lazy_static;

lazy_static! {
    // $remote_user *can* contain whitespaces, so we search for the 'next'
    // field (`$time_local`) instead
    static ref RE: Regex = Regex::new(" \\[[0-9]{1,2}/").unwrap();
}

/// INPUT / OUTPUT config
#[derive(Debug)]
pub struct IOConfig<'a> {
    /// List of input paths / files, e.g. Some(vec![Path::new("/tmp/test1.log"), Path::new("/tmp/test2.log")])
    /// If set to `None` the reader will read from Stdin.
    input: Option<Vec<&'a Path>>,
    /// Single output path / file
    /// If set to `None` the writer will write to Stdout.
    output: Option<&'a Path>,
}

/// Collection of replacement strings / config flags
#[allow(clippy::struct_excessive_bools)]
#[derive(Debug)]
pub struct Config<'a> {
    /// IPv4-parseable `$remote_addr` replacement string
    pub ipv4: &'a str,
    /// IPv6-parseable `$remote_addr` replacement string
    pub ipv6: &'a str,
    /// `$remote_addr` replacement string
    pub host: &'a str,
    /// Skip lines w/o a `$remote_addr` part / first word
    pub skip: bool,
    /// Try to clear the authuser field
    pub authuser: bool,
    /// Trim spaces from the start of every line
    pub trim: bool,
    /// Don't clear authuser fields starting with "- ["
    /// We assume these fields are already cleared.
    pub optimize: bool,
    /// Flush output after each line
    pub flush: bool,
}

/// defaults to `None` for both input and output
impl<'a> Default for IOConfig<'a> {
    fn default() -> Self {
        IOConfig {
            input: None,
            output: None,
        }
    }
}

/// `$remote_addr` replacements default to an equivalent of *localhost*
impl<'a> Default for Config<'a> {
    fn default() -> Self {
        Config {
            ipv4: "127.0.0.1",
            ipv6: "::1",
            host: "localhost",
            skip: false,
            authuser: false,
            trim: true,
            optimize: true,
            flush: false,
        }
    }
}

impl<'a> Config<'a> {
    pub fn new() -> Self {
        Self::default()
    }

    /// Get IPv4 replacement value
    pub fn get_ipv4_value(&self) -> &'a str {
        &self.ipv4
    }

    /// Get IPv6 replacement value
    pub fn get_ipv6_value(&self) -> &'a str {
        &self.ipv6
    }

    /// Get string replacement value
    pub fn get_host_value(&self) -> &'a str {
        &self.host
    }

    /// Get `skip` value
    pub fn get_skip(&self) -> bool {
        self.skip
    }

    /// Get `authuser` value
    pub fn get_authuser(&self) -> bool {
        self.authuser
    }

    /// Get `trim` value
    pub fn get_trim(&self) -> bool {
        self.trim
    }

    /// Get `optimize` value
    pub fn get_optimize(&self) -> bool {
        self.optimize
    }

    /// Get `flush` value
    pub fn get_flush(&self) -> bool {
        self.flush
    }

    /// Set IPv4 replacement `String`
    pub fn set_ipv4_value(&mut self, ipv4: &'a str) {
        self.ipv4 = ipv4;
    }

    /// Set IPv6 replacement `String`
    pub fn set_ipv6_value(&mut self, ipv6: &'a str) {
        self.ipv6 = ipv6;
    }

    /// Set `hostname` replacement `String`
    pub fn set_host_value(&mut self, host: &'a str) {
        self.host = host;
    }

    /// Set `flush` field
    pub fn set_flush(&mut self, b: bool) {
        self.flush = b;
    }

    /// Set `authuser` field
    pub fn set_authuser(&mut self, b: bool) {
        self.authuser = b;
    }

    /// Set `trim` field
    pub fn set_trim(&mut self, b: bool) {
        self.trim = b;
    }

    /// Set `optimize` field
    pub fn set_optimize(&mut self, b: bool) {
        self.optimize = b;
    }

    /// Set `skip` field
    pub fn set_skip(&mut self, b: bool) {
        self.skip = b;
    }
}

impl<'a> IOConfig<'a> {
    pub fn new() -> Self {
        Self::default()
    }

    /// Get input / reader names, if any (defaults to `None`)
    pub fn get_input(&self) -> Option<&Vec<&'a Path>> {
        self.input.as_ref()
    }

    /// Get output / writer name (defaults to `None`)
    pub fn get_output(&self) -> Option<&'a Path> {
        self.output
    }

    /// Add input `Path`
    pub fn push_input<P: AsRef<Path> + ?Sized>(&mut self, i: &'a P) {
        if let Some(input) = &mut self.input {
            input.push(i.as_ref());
        } else {
            self.input = Some(vec![]);
            self.push_input(i);
        }
    }

    /// Set output `Path`
    pub fn set_output(&mut self, o: &'a Path) {
        self.output = Some(o);
    }
}

/// Reads lines from `reader`, if there is a '*first word*' (any String separated from the
/// remainder of the line by a b' ' (Space) byte) this word will be replaced
///
/// Any word, that can be parsed as
/// * [`std::net::Ipv4Addr`] will be replaced with [`alog::Config::ipv4`],
/// * [`std::net::Ipv6Addr`] will be replaced with [`alog::Config::ipv6`],
/// * any other *word* will be replaced with [`alog::Config::host`].
///
/// Any line without a 'first word' will be written as is if [`alog::Config::get_skip()`] returns
/// `false` (default), or will be skipped otherwise.
///
/// ## Errors
///
/// This function will return an I/O error if the underlying reader or writer returns an error.
///
/// [`alog::Config::get_ipv4_value()`]: ./struct.Config.html#method.get_ipv4_value
/// [`alog::Config::get_ipv6_value()`]: ./struct.Config.html#method.get_ipv6_value
/// [`alog::Config::get_host_value()`]: ./struct.Config.html#method.get_host_value
fn replace_remote_address<R: BufRead, W: Write>(
    config: &Config,
    mut reader: R,
    mut writer: W,
) -> Result<(), std::io::Error> {
    let mut buf = vec![];

    'lines: loop {
        buf.clear();
        let bytes_read = reader.read_until(b'\n', &mut buf)?;
        if bytes_read == 0 {
            break;
        } else {
            #[allow(clippy::match_wildcard_for_single_variants)]
            if config.get_trim() {
                let s = match buf.iter().position(|&x| x != b' ' && x != b'\t') {
                    Some(s) => s,
                    _ => 0,
                };
                buf.drain(..s);
            }
            for (i, byte) in buf[..].iter().enumerate() {
                if *byte == b' ' {
                    if String::from_utf8_lossy(&buf[..i])
                        .parse::<net::Ipv4Addr>()
                        .is_ok()
                    {
                        write!(&mut writer, "{}", config.get_ipv4_value())?;
                    } else if String::from_utf8_lossy(&buf[..i])
                        .parse::<net::Ipv6Addr>()
                        .is_ok()
                    {
                        write!(&mut writer, "{}", config.get_ipv6_value())?;
                    } else {
                        write!(&mut writer, "{}", config.get_host_value())?;
                    }
                    if config.get_authuser() {
                        // trying to avoid the regex' overhead
                        match &buf[i + 3..i + 6].iter().cmp(b"- [") {
                            Ordering::Equal if config.get_optimize() => {
                                writer.write_all(&buf[i..])?
                            }
                            _ => {
                                if let Some(time_field) = RE.find_at(&buf, i) {
                                    write!(&mut writer, " - -")?;
                                    writer.write_all(&buf[time_field.start()..])?;
                                } else {
                                    writer.write_all(&buf[i..])?;
                                }
                            }
                        }
                    } else {
                        writer.write_all(&buf[i..])?;
                    }
                    if config.get_flush() {
                        writer.flush()?;
                    }
                    continue 'lines;
                }
            }
            if !config.get_skip() {
                writer.write_all(&buf)?;
                if config.get_flush() {
                    writer.flush()?;
                }
            }
        };
    }
    writer.flush()?;
    Ok(())
}

/// Creates a reader (defaults to [`std::io::Stdin`]) and writer (defaults to [`std::io::Stdout`])
/// from [`alog::IOConfig`] and uses both along with [`alog::Config`] to actually replace
/// any first *word* in `reader` with strings stored in [`alog::Config`].
///
/// ## Errors
///
/// Exits when the output already exists or the new reader / writer retruns an error.
///
/// ## Example
///
/// ```[no_run]
/// extern crate alog;
///
/// fn main() {
///     alog::run(
///         &alog::Config {
///             host: "XXX",
///             ..Default::default()
///         },
///         &alog::IOConfig::default()
///     );
/// }
/// ```
///
/// [`alog::Config`]: ./struct.Config.html
/// [`alog::IOConfig`]: ./struct.IOConfig.html
/// [`alog::IOConfig::get_output()`]: ./struct.IOConfig.html#method.get_output
/// [`std::io::Stdin`]: https://doc.rust-lang.org/std/io/struct.Stdin.html
/// [`std::io::Stdout`]: https://doc.rust-lang.org/std/io/struct.Stdout.html
/// [`std::net::Ipv4Addr`]: https://doc.rust-lang.org/std/net/struct.Ipv4Addr.html
/// [`std::net::Ipv6Addr`]: https://doc.rust-lang.org/std/net/struct.Ipv6Addr.html
pub fn run(config: &Config, ioconfig: &IOConfig) {
    // Set writer
    let stdout = io::stdout();
    let mut writer: Box<dyn Write> = match ioconfig.get_output() {
        Some(output) => {
            let f = OpenOptions::new()
                .write(true)
                .create_new(true)
                .open(Path::new(output));
            let f = match f {
                Ok(file) => file,
                Err(e) => {
                    eprintln!("Error writing to file {}: {}.", output.display(), e);
                    std::process::exit(1);
                }
            };
            Box::new(BufWriter::new(f)) as _
        }
        None => Box::new(BufWriter::new(stdout.lock())),
    };

    // Set reader
    if let Some(input) = ioconfig.get_input() {
        for arg in input {
            let f = File::open(Path::new(arg));
            let f = match f {
                Ok(file) => file,
                Err(e) => {
                    eprintln!("Error reading file '{}': {}.", arg.display(), e);
                    if let Some(output) = ioconfig.get_output() {
                        std::fs::remove_file(Path::new(output)).unwrap();
                    }
                    process::exit(1);
                }
            };
            let reader: Box<dyn BufRead> = Box::new(BufReader::new(f));
            if let Err(e) = replace_remote_address(config, reader, &mut writer) {
                eprintln!("Error: {}", e);
                if let Some(output) = ioconfig.get_output() {
                    std::fs::remove_file(Path::new(output)).unwrap();
                }
                process::exit(1);
            }
        }
    } else {
        let stdin = io::stdin();
        let reader: Box<dyn BufRead> = Box::new(stdin.lock());
        if let Err(e) = replace_remote_address(config, reader, &mut writer) {
            eprintln!("Error: {}", e);
            if let Some(output) = ioconfig.get_output() {
                std::fs::remove_file(Path::new(output)).unwrap();
            }
            process::exit(1);
        }
    }
}

/// Like [`alog::run`] but will let you pass your own `reader` and `writer`. Replacement strings
/// and config flags will still be read from [`alog::Config`].
///
/// ## Errors
///
/// Exits when the new reader or writer retruns an error.
///
/// ## Example
///
/// ```
/// use std::io::Cursor;
///
/// let line = Cursor::new(b"8.8.8.8 XxX");
/// let mut buffer = vec![];
///
/// alog::run_raw(&alog::Config::default(), line, &mut buffer);
/// assert_eq!(buffer, b"127.0.0.1 XxX");
/// ```
///
/// To read from Stdin and write to Stdout:
///
/// ```no_run
/// use std::io::{self, BufReader, BufWriter};
///
/// // Consider wrapping io::stdout in BufWriter
/// let stdin = io::stdin();
/// let stdout = io::stdout();
/// alog::run_raw(&alog::Config::default(), stdin.lock(), stdout.lock());
/// ```
///
/// [`alog::run`]: ./fn.run.html
/// [`alog::Config`]: ./struct.Config.html
pub fn run_raw<R: BufRead, W: Write>(config: &Config, reader: R, mut writer: W) {
    if let Err(e) = replace_remote_address(config, reader, &mut writer) {
        eprintln!("Error: {}", e);
        process::exit(1);
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn run_raw_function() {
        use std::io::Cursor;
        let line = Cursor::new(b"8.8.8.8 XxX");
        let mut buffer = vec![];

        run_raw(&Config::default(), line, &mut buffer);
        assert_eq!(buffer, b"127.0.0.1 XxX");
    }

    #[test]
    fn replace_ipv4() {
        use std::io::Cursor;
        let mut buffer = Cursor::new(vec![]);
        let log = Box::new("8.8.8.8 - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes());
        let local_log = "127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes();

        replace_remote_address(&Config::default(), log, &mut buffer).unwrap();
        assert_eq!(&buffer.into_inner(), &local_log);
    }

    #[test]
    fn replace_ipv6() {
        use std::io::Cursor;
        let mut buffer = Cursor::new(vec![]);
        let log = Box::new("2a00:1450:4001:81b::2004 - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes());
        let local_log = "::1 - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes();

        replace_remote_address(&Config::default(), log, &mut buffer).unwrap();
        assert_eq!(&buffer.into_inner(), &local_log);
    }

    #[test]
    fn replace_host() {
        use std::io::Cursor;
        let mut buffer = Cursor::new(vec![]);
        let log = Box::new("google.com - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes());
        let local_log = "localhost - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes();

        replace_remote_address(&Config::default(), log, &mut buffer).unwrap();
        assert_eq!(&buffer.into_inner(), &local_log);
    }

    #[test]
    fn clear_authuser() {
        use std::io::Cursor;
        let mut buffer = Cursor::new(vec![]);
        let log = Box::new("8.8.8.8 - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes());
        let local_log = "127.0.0.1 - - [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes();

        let mut conf = Config::default();
        conf.set_authuser(true);

        replace_remote_address(&conf, log, &mut buffer).unwrap();
        assert_eq!(&buffer.into_inner(), &local_log);
    }

    #[test]
    fn replace_custom_ipv4() {
        use std::io::Cursor;
        let mut buffer = Cursor::new(vec![]);
        let log = Box::new("8.8.8.8 - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes());
        let local_log = "custom_ipv4 - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes();

        let mut conf = Config::default();
        conf.set_ipv4_value("custom_ipv4");

        replace_remote_address(&conf, log, &mut buffer).unwrap();
        assert_eq!(&buffer.into_inner(), &local_log);
    }

    #[test]
    fn replace_custom_ipv6() {
        use std::io::Cursor;
        let mut buffer = Cursor::new(vec![]);
        let log = Box::new("2a00:1450:4001:81b::2004 - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes());
        let local_log = "custom_ipv6 - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes();

        let mut conf = Config::default();
        conf.set_ipv6_value("custom_ipv6");

        replace_remote_address(&conf, log, &mut buffer).unwrap();
        assert_eq!(&buffer.into_inner(), &local_log);
    }

    #[test]
    fn replace_custom_host() {
        use std::io::Cursor;
        let mut buffer = Cursor::new(vec![]);
        let log = Box::new("google.com - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes());
        let local_log = "custom_host - frank [10/Oct/2000:13:55:36 -0700] \"GET /apache_pb.gif HTTP/1.0\" 200 2326 \"http://www.example.com/start.html\" \"Mozilla/4.08 [en] (Win98; I ;Nav)\"".as_bytes();

        let mut conf = Config::default();
        conf.set_host_value("custom_host");

        replace_remote_address(&conf, log, &mut buffer).unwrap();
        assert_eq!(&buffer.into_inner(), &local_log);
    }
}