riffdiff 2.22.2

use crate::commit_line::format_commit_line;
use crate::io::ErrorKind;
use std::io::{self, BufWriter, Write};
use std::process::exit;
use std::sync::mpsc::{sync_channel, Receiver, SyncSender};
use std::thread::{self, JoinHandle};

use crate::{constants::*, refiner};
use regex::Regex;
use threadpool::ThreadPool;

const HUNK_HEADER: &str = "\x1b[36m"; // Cyan

lazy_static! {
    static ref STATIC_HEADER_PREFIXES: Vec<(&'static str, &'static str)> = vec![
        ("diff ", FAINT),
        ("index ", FAINT),
        ("Binary files ", BOLD),
        ("copy from ", FAINT),
        ("copy to ", BOLD),
        ("rename from ", FAINT),
        ("rename to ", BOLD),
        ("similarity index ", FAINT),
        ("new file mode ", FAINT),
        ("deleted file mode ", FAINT),
        ("--- /dev/null", FAINT),
        ("+++ /dev/null", FAINT),
    ];
    static ref ANSI_COLOR_REGEX: Regex = Regex::new("\x1b\\[[0-9;]*[^0-9;]").unwrap();
}

#[must_use]
fn get_fixed_highlight(line: &str) -> Option<&str> {
    for static_header_prefix in STATIC_HEADER_PREFIXES.iter() {
        let prefix = static_header_prefix.0;
        if line.starts_with(prefix) {
            return Some(static_header_prefix.1);
        }
    }

    return None;
}

fn print<W: io::Write + Send>(stream: &mut BufWriter<W>, text: &str) {
    if let Err(error) = stream.write_all(text.as_bytes()) {
        if error.kind() == ErrorKind::BrokenPipe {
            // This is fine, somebody probably just quit their pager before it
            // was done reading our output.
            exit(0);
        }

        panic!("Error writing diff to pager: {:?}", error);
    }
}

/**
A StringFuture can perform diffing in a background thread.

Doing get() on a future that isn't done yet will block until the result is
available.
*/
struct StringFuture {
    // This field is only valid if we're done with the result_receiver (next
    // field)
    result: String,

    // If available, get() will await a result on this receiver, then populate
    // the result field and return it
    result_receiver: Option<Receiver<String>>,
}

impl StringFuture {
    /// Create an already-finished future
    pub fn from_string(result: String) -> StringFuture {
        return StringFuture {
            result,
            result_receiver: None,
        };
    }

    /// Call get() to get the result of this diff
    pub fn from_oldnew(
        old_text: String,
        new_text: String,
        thread_pool: &ThreadPool,
    ) -> StringFuture {
        // Create a String channel
        let (sender, receiver): (SyncSender<String>, Receiver<String>) = sync_channel(1);

        // Start diffing in a thread
        thread_pool.execute(move || {
            let mut result = String::new();
            for line in refiner::format(&old_text, &new_text) {
                result.push_str(&line);
                result.push('\n');
            }

            // Done, channel the result!
            sender.send(result).unwrap();
        });

        return StringFuture {
            result: "".to_string(),
            result_receiver: Some(receiver),
        };
    }

    #[allow(clippy::wrong_self_convention)]
    pub fn is_empty(&mut self) -> bool {
        return self.get().is_empty();
    }

    pub fn get(&mut self) -> &str {
        // If the result is still pending...
        if let Some(receiver) = &self.result_receiver {
            // ... wait for it
            self.result = receiver.recv().unwrap();
            self.result_receiver = None;
        }

        return &self.result;
    }
}

/**
The way this thing works from the outside is that you initialize it with an
output stream, you pass it one line of input at a time, and it writes
formatted lines to the output stream.

From the inside, it will collect blocks of either diff lines or not-diff-lines.

The not-diff-lines blocks will be enqueued for printing by the printing thread.

The diff lines blocks will also be enqueued for printing, but the actual diffing
will happen in background threads.
*/
pub struct LineCollector {
    old_text: String,
    new_text: String,
    plain_text: String,
    diff_seen: bool,
    consumer_thread: Option<JoinHandle<()>>,

    diffing_threads: ThreadPool,

    // FIXME: I'd rather have had a SyncSender of some trait here. That would
    // enable us to have two separate result implementations, one which just
    // returns a string and another that does a background computation first.
    // But I failed to figure out how when I tried, more Googling needed!
    queue_putter: SyncSender<StringFuture>,
}

impl Drop for LineCollector {
    fn drop(&mut self) {
        // Flush any outstanding lines. This can be done in any order, at most
        // one of them is going to do anything anyway.
        self.drain_oldnew();
        self.drain_plain();

        // Tell the consumer thread to drain and quit. Sending an empty string
        // like this is the secret handshake for requesting a shutdown.
        self.queue_putter
            .send(StringFuture::from_string("".to_string()))
            .unwrap();

        // Wait for the consumer thread to finish
        // https://stackoverflow.com/q/57670145/473672
        self.consumer_thread.take().map(JoinHandle::join);
    }
}

impl LineCollector {
    pub fn new<W: io::Write + Send + 'static>(output: W) -> LineCollector {
        // This is how many entries we can look ahead. An "entry" in this case
        // being either a plain text section or an oldnew section.
        //
        // Benchmark timings with different multipliers on an 8 logical cores
        // machine with a 6.6M lines / 208MB diff:
        //
        // 500x => 5.68s  <-- Not much better than 100x
        // 100x => 5.71s  <-- Somewhat better than 50x
        //  50x => 5.98s
        //  10x >= 7.41s  <-- Much worse than 50x
        let queue_size = num_cpus::get() * 100;

        // Allocate a queue where we can push our futures to the consumer thread
        let (queue_putter, queue_getter): (SyncSender<StringFuture>, Receiver<StringFuture>) =
            sync_channel(queue_size);

        // This thread takes futures and prints their results
        let thread_builder = thread::Builder::new().name("Output Printer Thread".to_string());
        let consumer = thread_builder
            .spawn(move || {
                let mut output = BufWriter::new(output);

                loop {
                    if let Ok(mut print_me) = queue_getter.recv() {
                        if print_me.is_empty() {
                            // Secret handshake received, done!
                            break;
                        }
                        print(&mut output, print_me.get());
                    }
                }
            })
            .unwrap();

        return LineCollector {
            old_text: String::from(""),
            new_text: String::from(""),
            plain_text: String::from(""),
            diff_seen: false,

            consumer_thread: Some(consumer),
            diffing_threads: ThreadPool::new(num_cpus::get()),
            queue_putter,
        };
    }

    fn drain_oldnew(&mut self) {
        if self.old_text.is_empty() && self.new_text.is_empty() {
            return;
        }

        self.queue_putter
            .send(StringFuture::from_oldnew(
                self.old_text.clone(),
                self.new_text.clone(),
                &self.diffing_threads,
            ))
            .unwrap();

        self.old_text.clear();
        self.new_text.clear();
    }

    fn drain_plain(&mut self) {
        if self.plain_text.is_empty() {
            return;
        }

        // Enqueue an already-resolved future
        self.queue_putter
            .send(StringFuture::from_string(String::from(&self.plain_text)))
            .unwrap();

        self.plain_text.clear();
    }

    fn consume_plain_line(&mut self, line: &str) {
        self.drain_oldnew();
        self.plain_text.push_str(line);
        self.plain_text.push('\n');
    }

    /// Like consume_plain_line(), but without outputting any trailing linefeed.
    fn consume_plain_linepart(&mut self, linepart: &str) {
        self.drain_oldnew();
        self.plain_text.push_str(linepart);
    }

    fn consume_old_line(&mut self, line: &str) {
        self.drain_plain();
        self.old_text.push_str(&line[1..]);
        self.old_text.push('\n');
    }

    fn consume_new_line(&mut self, line: &str) {
        self.drain_plain();
        self.new_text.push_str(&line[1..]);
        self.new_text.push('\n');
    }

    fn consume_no_eof_newline_marker(&mut self) {
        if !self.new_text.is_empty() {
            // New section comes after old, so if we get in here it's a new
            // section that doesn't end in a newline. Remove its trailing
            // newline.
            assert!(self.new_text.pop().unwrap() == '\n');
            return;
        }

        if !self.old_text.is_empty() {
            // Old text doesn't end in a newline, remove its trailing newline
            assert!(self.old_text.pop().unwrap() == '\n');
            return;
        }

        // It's a piece of unchanged text that doesn't end in a newline, just
        // consume the colorized marker as plain text
        self.consume_plain_line(&format!(
            "{}{}{}",
            NO_EOF_NEWLINE_COLOR, &NO_EOF_NEWLINE_MARKER, NORMAL
        ))
    }

    pub fn consume_plusminus_header(&mut self, line: &str) {
        self.consume_plain_linepart(BOLD);

        if let Some(last_tab_index) = line.rfind('\t') {
            self.consume_plain_linepart(&line[..last_tab_index]);

            // When I ran plain "diff" (no git involved), this trailing part
            // contained very precise file timestamps. I don't think those
            // provide much value, so let's faint them out.
            self.consume_plain_linepart(FAINT);
            self.consume_plain_linepart(&line[last_tab_index..]);
        } else {
            self.consume_plain_linepart(line);
        }

        self.consume_plain_line(NORMAL);
    }

    fn consume_hunk_header(&mut self, line: &str) {
        self.consume_plain_linepart(HUNK_HEADER);

        if let Some(second_atat_index) = line.find(" @@ ") {
            // Highlight the function name
            self.consume_plain_linepart(FAINT);
            self.consume_plain_linepart(&line[..(second_atat_index + 4)]);
            self.consume_plain_linepart(BOLD);
            self.consume_plain_linepart(&line[(second_atat_index + 4)..]);
        } else {
            self.consume_plain_linepart(line);
        }

        self.consume_plain_line(NORMAL);
    }

    fn without_ansi_escape_codes(input: &'_ str) -> std::borrow::Cow<'_, str> {
        return ANSI_COLOR_REGEX.replace_all(input, "");
    }

    pub fn consume_line(&mut self, line: String) {
        // Strip out incoming ANSI formatting. This enables us to highlight
        // already-colored input.
        let line = LineCollector::without_ansi_escape_codes(&line);

        if line.starts_with("diff") {
            self.diff_seen = true;
        }

        if let Some(fixed_highlight) = get_fixed_highlight(&line) {
            self.consume_plain_linepart(fixed_highlight);
            self.consume_plain_linepart(&line);
            self.consume_plain_line(NORMAL); // consume_plain_line() will add a linefeed to the output
            return;
        }

        if line.starts_with("commit") {
            self.consume_plain_line(&format_commit_line(&line, self.diff_seen));
            return;
        }

        if line.starts_with("--- ") || line.starts_with("+++ ") {
            self.consume_plusminus_header(&line);
            return;
        }

        if line.starts_with("@@ ") {
            self.consume_hunk_header(&line);
            return;
        }

        if line.is_empty() {
            self.consume_plain_line("");
            return;
        }

        if line.starts_with('-') {
            self.consume_old_line(&line);
            return;
        }

        if line.starts_with('+') {
            self.consume_new_line(&line);
            return;
        }

        if line == NO_EOF_NEWLINE_MARKER {
            self.consume_no_eof_newline_marker();
            return;
        }

        self.consume_plain_line(&line);
    }
}

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

    #[cfg(test)]
    use pretty_assertions::assert_eq;

    #[test]
    fn test_non_sgr() {
        assert_eq!(
            LineCollector::without_ansi_escape_codes("hel\x1b[0Klo"),
            "hello"
        );
    }

    #[test]
    fn test_sgr() {
        assert_eq!(
            LineCollector::without_ansi_escape_codes("hel\x1b[33mlo"),
            "hello"
        );
    }

    #[test]
    fn test_multi_sgr() {
        assert_eq!(
            LineCollector::without_ansi_escape_codes("hel\x1b[33;34mlo"),
            "hello"
        );
    }
}