//! This is a port of the backtrace print.rs code which generates one-line backtraces. A lot of
//! simplifications were made for our specific use case.

use std::ffi::c_void;
use std::fmt::{Display, Formatter};
use std::{env, fmt};

use backtrace::{Backtrace, BacktraceFrame, BacktraceSymbol, BytesOrWideString, SymbolName};

/// Format a backtrace onto a single line.
/// Largely stolen from backtrace's Debug implementation.
pub fn fmt_backtrace(
    backtrace: &Backtrace,
    f: &mut Formatter,
    line_sep: &'static str,
    show_full_paths: bool,
) -> fmt::Result {
    // When printing paths we try to strip the cwd if it exists, otherwise
    // we just print the path as-is. Note that we also only do this for the
    // short format, because if it's full we presumably want to print
    // everything.
    let cwd = if !show_full_paths {
        env::current_dir().ok()
    } else {
        None
    };
    let mut print_path = move |fmt: &mut Formatter<'_>, path: BytesOrWideString<'_>| {
        let path = path.into_path_buf();
        if let Some(cwd) = &cwd {
            if let Ok(suffix) = path.strip_prefix(cwd) {
                return Display::fmt(&suffix.display(), fmt);
            }
        }
        Display::fmt(&path.display(), fmt)
    };

    let mut formatter = BacktraceFmt::new(f, line_sep, &mut print_path);
    for frame in backtrace.frames() {
        formatter.frame().backtrace_frame(frame)?;
    }
    Ok(())
}

/// A formatter for backtraces.
///
/// This type can be used to print a backtrace regardless of where the backtrace
/// itself comes from. If you have a `Backtrace` type then its `Debug`
/// implementation already uses this printing format.
struct BacktraceFmt<'a, 'b> {
    fmt: &'a mut fmt::Formatter<'b>,
    frame_index: usize,
    print_path:
        &'a mut (dyn FnMut(&mut fmt::Formatter<'_>, BytesOrWideString<'_>) -> fmt::Result + 'b),
    line_separator: &'static str,
}

impl<'a, 'b> BacktraceFmt<'a, 'b> {
    /// Create a new `BacktraceFmt` which will write output to the provided
    /// `fmt`.
    ///
    /// The `format` argument will control the style in which the backtrace is
    /// printed, and the `print_path` argument will be used to print the
    /// `BytesOrWideString` instances of filenames. This type itself doesn't do
    /// any printing of filenames, but this callback is required to do so.
    fn new(
        fmt: &'a mut fmt::Formatter<'b>,
        line_separator: &'static str,
        print_path: &'a mut (dyn FnMut(&mut fmt::Formatter<'_>, BytesOrWideString<'_>) -> fmt::Result
                     + 'b),
    ) -> Self {
        BacktraceFmt {
            fmt,
            frame_index: 0,
            line_separator,
            print_path,
        }
    }

    /// Adds a frame to the backtrace output.
    ///
    /// This commit returns an RAII instance of a `BacktraceFrameFmt` which can be used
    /// to actually print a frame, and on destruction it will increment the
    /// frame counter.
    fn frame(&mut self) -> BacktraceFrameFmt<'_, 'a, 'b> {
        BacktraceFrameFmt {
            fmt: self,
            symbol_index: 0,
        }
    }
}

/// A formatter for just one frame of a backtrace.
struct BacktraceFrameFmt<'fmt, 'a, 'b> {
    fmt: &'fmt mut BacktraceFmt<'a, 'b>,
    symbol_index: usize,
}

impl BacktraceFrameFmt<'_, '_, '_> {
    /// Prints a `BacktraceFrame` with this frame formatter.
    ///
    /// This will recursively print all `BacktraceSymbol` instances within the
    /// `BacktraceFrame`.
    ///
    /// # Required features
    ///
    /// This function requires the `std` feature of the `backtrace` crate to be
    /// enabled, and the `std` feature is enabled by default.
    fn backtrace_frame(&mut self, frame: &BacktraceFrame) -> fmt::Result {
        let symbols = frame.symbols();
        for symbol in symbols {
            self.backtrace_symbol(frame, symbol)?;
        }
        if symbols.is_empty() {
            self.print_raw(frame.ip(), None, None, None)?;
        }
        Ok(())
    }

    /// Prints a `BacktraceSymbol` within a `BacktraceFrame`.
    ///
    /// # Required features
    ///
    /// This function requires the `std` feature of the `backtrace` crate to be
    /// enabled, and the `std` feature is enabled by default.
    fn backtrace_symbol(
        &mut self,
        frame: &BacktraceFrame,
        symbol: &BacktraceSymbol,
    ) -> fmt::Result {
        self.print_raw_with_column(
            frame.ip(),
            symbol.name(),
            // TODO: this isn't great that we don't end up printing anything
            // with non-utf8 filenames. Thankfully almost everything is utf8 so
            // this shouldn't be too too bad.
            symbol
                .filename()
                .and_then(|p| Some(BytesOrWideString::Bytes(p.to_str()?.as_bytes()))),
            symbol.lineno(),
            symbol.colno(),
        )?;
        Ok(())
    }

    /// Adds a raw frame to the backtrace output.
    ///
    /// This method, unlike the previous, takes the raw arguments in case
    /// they're being source from different locations. Note that this may be
    /// called multiple times for one frame.
    fn print_raw(
        &mut self,
        frame_ip: *mut c_void,
        symbol_name: Option<SymbolName<'_>>,
        filename: Option<BytesOrWideString<'_>>,
        lineno: Option<u32>,
    ) -> fmt::Result {
        self.print_raw_with_column(frame_ip, symbol_name, filename, lineno, None)
    }

    /// Adds a raw frame to the backtrace output, including column information.
    ///
    /// This method, like the previous, takes the raw arguments in case
    /// they're being source from different locations. Note that this may be
    /// called multiple times for one frame.
    fn print_raw_with_column(
        &mut self,
        frame_ip: *mut c_void,
        symbol_name: Option<SymbolName<'_>>,
        filename: Option<BytesOrWideString<'_>>,
        lineno: Option<u32>,
        colno: Option<u32>,
    ) -> fmt::Result {
        self.print_raw_generic(frame_ip, symbol_name, filename, lineno, colno)?;
        self.symbol_index += 1;
        Ok(())
    }

    fn print_raw_generic(
        &mut self,
        frame_ip: *mut c_void,
        symbol_name: Option<SymbolName<'_>>,
        filename: Option<BytesOrWideString<'_>>,
        lineno: Option<u32>,
        colno: Option<u32>,
    ) -> fmt::Result {
        // No need to print "null" frames, it basically just means that the
        // system backtrace was a bit eager to trace back super far.
        if frame_ip.is_null() {
            return Ok(());
        }

        // Print the index of the frame as well as the optional instruction
        // pointer of the frame.
        write!(self.fmt.fmt, "({}) ", self.fmt.frame_index)?;
        write!(self.fmt.fmt, "{frame_ip:?} - ")?;

        // Next up write out the symbol name, using the alternate formatting for
        // more information if we're a full backtrace. Here we also handle
        // symbols which don't have a name,
        if let Some(name) = symbol_name {
            write!(self.fmt.fmt, "{name:#}")?;
        } else {
            write!(self.fmt.fmt, "<unknown>")?;
        }

        // And last up, print out the filename/line number if they're available.
        if let (Some(file), Some(line)) = (filename, lineno) {
            self.print_fileline(file, line, colno)?;
        }

        Ok(())
    }

    fn print_fileline(
        &mut self,
        file: BytesOrWideString<'_>,
        line: u32,
        colno: Option<u32>,
    ) -> fmt::Result {
        // Filename/line are printed on lines under the symbol name, so print
        // some appropriate whitespace to sort of right-align ourselves.
        write!(self.fmt.fmt, " @ ")?;

        // Delegate to our internal callback to print the filename and then
        // print out the line number.
        (self.fmt.print_path)(self.fmt.fmt, file)?;
        write!(self.fmt.fmt, ":{line}")?;

        // Add column number, if available.
        if let Some(colno) = colno {
            write!(self.fmt.fmt, ":{colno}")?;
        }

        write!(self.fmt.fmt, "{}", self.fmt.line_separator)?;
        Ok(())
    }
}

impl Drop for BacktraceFrameFmt<'_, '_, '_> {
    fn drop(&mut self) {
        self.fmt.frame_index += 1;
    }
}