--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/rhg/src/blackbox.rs	Tue Feb 16 13:08:37 2021 +0100
@@ -0,0 +1,161 @@
+//! Logging for repository events, including commands run in the repository.
+
+use crate::CliInvocation;
+use format_bytes::format_bytes;
+use hg::errors::HgError;
+use hg::repo::Repo;
+use hg::utils::{files::get_bytes_from_os_str, shell_quote};
+
+const ONE_MEBIBYTE: u64 = 1 << 20;
+
+// TODO: somehow keep defaults in sync with `configitem` in `hgext/blackbox.py`
+const DEFAULT_MAX_SIZE: u64 = ONE_MEBIBYTE;
+const DEFAULT_MAX_FILES: u32 = 7;
+
+// Python does not support %.3f, only %f
+const DEFAULT_DATE_FORMAT: &str = "%Y/%m/%d %H:%M:%S%.3f";
+
+type DateTime = chrono::DateTime<chrono::Local>;
+
+pub struct ProcessStartTime {
+    /// For measuring duration
+    monotonic_clock: std::time::Instant,
+    /// For formatting with year, month, day, etc.
+    calendar_based: DateTime,
+}
+
+impl ProcessStartTime {
+    pub fn now() -> Self {
+        Self {
+            monotonic_clock: std::time::Instant::now(),
+            calendar_based: chrono::Local::now(),
+        }
+    }
+}
+
+pub struct Blackbox<'a> {
+    process_start_time: &'a ProcessStartTime,
+    /// Do nothing if this is `None`
+    configured: Option<ConfiguredBlackbox<'a>>,
+}
+
+struct ConfiguredBlackbox<'a> {
+    repo: &'a Repo,
+    max_size: u64,
+    max_files: u32,
+    date_format: &'a str,
+}
+
+impl<'a> Blackbox<'a> {
+    pub fn new(
+        invocation: &'a CliInvocation<'a>,
+        process_start_time: &'a ProcessStartTime,
+    ) -> Result<Self, HgError> {
+        let configured = if let Ok(repo) = invocation.repo {
+            let config = invocation.config();
+            if config.get(b"extensions", b"blackbox").is_none() {
+                // The extension is not enabled
+                None
+            } else {
+                Some(ConfiguredBlackbox {
+                    repo,
+                    max_size: config
+                        .get_byte_size(b"blackbox", b"maxsize")?
+                        .unwrap_or(DEFAULT_MAX_SIZE),
+                    max_files: config
+                        .get_u32(b"blackbox", b"maxfiles")?
+                        .unwrap_or(DEFAULT_MAX_FILES),
+                    date_format: config
+                        .get_str(b"blackbox", b"date-format")?
+                        .unwrap_or(DEFAULT_DATE_FORMAT),
+                })
+            }
+        } else {
+            // Without a local repository there’s no `.hg/blackbox.log` to
+            // write to.
+            None
+        };
+        Ok(Self {
+            process_start_time,
+            configured,
+        })
+    }
+
+    pub fn log_command_start(&self) {
+        if let Some(configured) = &self.configured {
+            let message = format_bytes!(b"(rust) {}", format_cli_args());
+            configured.log(&self.process_start_time.calendar_based, &message);
+        }
+    }
+
+    pub fn log_command_end(&self, exit_code: i32) {
+        if let Some(configured) = &self.configured {
+            let now = chrono::Local::now();
+            let duration = self
+                .process_start_time
+                .monotonic_clock
+                .elapsed()
+                .as_secs_f64();
+            let message = format_bytes!(
+                b"(rust) {} exited {} after {} seconds",
+                format_cli_args(),
+                exit_code,
+                format_bytes::Utf8(format_args!("{:.03}", duration))
+            );
+            configured.log(&now, &message);
+        }
+    }
+}
+
+impl ConfiguredBlackbox<'_> {
+    fn log(&self, date_time: &DateTime, message: &[u8]) {
+        let date = format_bytes::Utf8(date_time.format(self.date_format));
+        let user = users::get_current_username().map(get_bytes_from_os_str);
+        let user = user.as_deref().unwrap_or(b"???");
+        let rev = format_bytes::Utf8(match self.repo.dirstate_parents() {
+            Ok(parents) if parents.p2 == hg::revlog::node::NULL_NODE => {
+                format!("{:x}", parents.p1)
+            }
+            Ok(parents) => format!("{:x}+{:x}", parents.p1, parents.p2),
+            Err(_dirstate_corruption_error) => {
+                // TODO: log a non-fatal warning to stderr
+                "???".to_owned()
+            }
+        });
+        let pid = std::process::id();
+        let line = format_bytes!(
+            b"{} {} @{} ({})> {}\n",
+            date,
+            user,
+            rev,
+            pid,
+            message
+        );
+        let result =
+            hg::logging::LogFile::new(self.repo.hg_vfs(), "blackbox.log")
+                .max_size(Some(self.max_size))
+                .max_files(self.max_files)
+                .write(&line);
+        match result {
+            Ok(()) => {}
+            Err(_io_error) => {
+                // TODO: log a non-fatal warning to stderr
+            }
+        }
+    }
+}
+
+fn format_cli_args() -> Vec<u8> {
+    let mut args = std::env::args_os();
+    let _ = args.next(); // Skip the first (or zeroth) arg, the name of the `rhg` executable
+    let mut args = args.map(|arg| shell_quote(&get_bytes_from_os_str(arg)));
+    let mut formatted = Vec::new();
+    if let Some(arg) = args.next() {
+        formatted.extend(arg)
+    }
+    for arg in args {
+        formatted.push(b' ');
+        formatted.extend(arg)
+    }
+    formatted
+}