//! Logging and progress line protocol (pure `std`).
//!
//! The GUI (Python or future native) consumes plain stdout lines as log text
//! and lines prefixed with `PROGRESS_PREFIX` as in-place "replace the last
//! line" progress. Keep this byte-compatible with
//! `pipeline_360_gui.py`'s expectations.

/// Prefix marking a progress (replace-last-line) message.
pub const PROGRESS_PREFIX: &str = "[progress] ";

/// A sink for emitted messages. `None` means raw stdout.
pub type Logger<'a> = Option<&'a dyn Fn(&str)>;

/// Emit a normal log line (message-only; the CLI/GUI decides whether to add a newline).
pub fn emit(message: &str, logger: Logger) {
    match logger {
        Some(f) => f(message),
        None => println!("{message}"),
    }
}

/// Emit a progress (replace-last-line) message with the `[progress] ` prefix.
pub fn emit_progress(message: &str, logger: Logger) {
    if let Some(f) = logger {
        f(&format!("{PROGRESS_PREFIX}{message}"));
    }
}

/// A stage header line, e.g. `==== STAGE 1/4: Extract Sharpest Frames ====`.
pub fn stage_header(index: usize, total: usize, title: &str, logger: Logger) {
    emit("", logger);
    emit(&format!("==== STAGE {index}/{total}: {title} ===="), logger);
}