// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! As always, windows has something very different than unix, we mainly want
//! to avoid having to depend too much on libunwind for windows.
//!
//! If you google around, you'll find a fair bit of references to built-in
//! functions to get backtraces on windows. It turns out that most of these are
//! in an external library called dbghelp. I was unable to find this library
//! via `-ldbghelp`, but it is apparently normal to do the `dlopen` equivalent
//! of it.
//!
//! You'll also find that there's a function called CaptureStackBackTrace
//! mentioned frequently (which is also easy to use), but sadly I didn't have a
//! copy of that function in my mingw install (maybe it was broken?). Instead,
//! this takes the route of using StackWalk64 in order to walk the stack.

#![allow(deprecated)] // dynamic_lib

use io::prelude::*;

use io;
use libc::c_void;
use mem;
use ptr;
use sync::StaticMutex;
use sys::c;
use sys::dynamic_lib::DynamicLibrary;

macro_rules! sym {
    ($lib:expr, $e:expr, $t:ident) => (
        match $lib.symbol($e) {
            Ok(f) => $crate::mem::transmute::<usize, $t>(f),
            Err(..) => return Ok(())
        }
    )
}

#[cfg(target_env = "msvc")]
#[path = "printing/msvc.rs"]
mod printing;

#[cfg(target_env = "gnu")]
#[path = "printing/gnu.rs"]
mod printing;

type SymInitializeFn =
    unsafe extern "system" fn(c::HANDLE, *mut c_void,
                              c::BOOL) -> c::BOOL;
type SymCleanupFn =
    unsafe extern "system" fn(c::HANDLE) -> c::BOOL;

type StackWalk64Fn =
    unsafe extern "system" fn(c::DWORD, c::HANDLE, c::HANDLE,
                              *mut c::STACKFRAME64, *mut c::CONTEXT,
                              *mut c_void, *mut c_void,
                              *mut c_void, *mut c_void) -> c::BOOL;

#[cfg(target_arch = "x86")]
pub fn init_frame(frame: &mut c::STACKFRAME64,
                  ctx: &c::CONTEXT) -> c::DWORD {
    frame.AddrPC.Offset = ctx.Eip as u64;
    frame.AddrPC.Mode = c::ADDRESS_MODE::AddrModeFlat;
    frame.AddrStack.Offset = ctx.Esp as u64;
    frame.AddrStack.Mode = c::ADDRESS_MODE::AddrModeFlat;
    frame.AddrFrame.Offset = ctx.Ebp as u64;
    frame.AddrFrame.Mode = c::ADDRESS_MODE::AddrModeFlat;
    c::IMAGE_FILE_MACHINE_I386
}

#[cfg(target_arch = "x86_64")]
pub fn init_frame(frame: &mut c::STACKFRAME64,
                  ctx: &c::CONTEXT) -> c::DWORD {
    frame.AddrPC.Offset = ctx.Rip as u64;
    frame.AddrPC.Mode = c::ADDRESS_MODE::AddrModeFlat;
    frame.AddrStack.Offset = ctx.Rsp as u64;
    frame.AddrStack.Mode = c::ADDRESS_MODE::AddrModeFlat;
    frame.AddrFrame.Offset = ctx.Rbp as u64;
    frame.AddrFrame.Mode = c::ADDRESS_MODE::AddrModeFlat;
    c::IMAGE_FILE_MACHINE_AMD64
}

struct Cleanup {
    handle: c::HANDLE,
    SymCleanup: SymCleanupFn,
}

impl Drop for Cleanup {
    fn drop(&mut self) {
        unsafe { (self.SymCleanup)(self.handle); }
    }
}

pub fn write(w: &mut Write) -> io::Result<()> {
    // According to windows documentation, all dbghelp functions are
    // single-threaded.
    static LOCK: StaticMutex = StaticMutex::new();
    let _g = LOCK.lock();

    let dbghelp = match DynamicLibrary::open("dbghelp.dll") {
        Ok(lib) => lib,
        Err(..) => return Ok(()),
    };
    unsafe {
        // Fetch the symbols necessary from dbghelp.dll
        let SymInitialize = sym!(dbghelp, "SymInitialize", SymInitializeFn);
        let SymCleanup = sym!(dbghelp, "SymCleanup", SymCleanupFn);
        let StackWalk64 = sym!(dbghelp, "StackWalk64", StackWalk64Fn);

        // Allocate necessary structures for doing the stack walk
        let process = c::GetCurrentProcess();
        let thread = c::GetCurrentThread();
        let mut context: c::CONTEXT = mem::zeroed();
        c::RtlCaptureContext(&mut context);
        let mut frame: c::STACKFRAME64 = mem::zeroed();
        let image = init_frame(&mut frame, &context);

        // Initialize this process's symbols
        let ret = SymInitialize(process, ptr::null_mut(), c::TRUE);
        if ret != c::TRUE { return Ok(()) }
        let _c = Cleanup { handle: process, SymCleanup: SymCleanup };

        // And now that we're done with all the setup, do the stack walking!
        // Start from -1 to avoid printing this stack frame, which will
        // always be exactly the same.
        let mut i = -1;
        try!(write!(w, "stack backtrace:\n"));
        while StackWalk64(image, process, thread, &mut frame, &mut context,
                          ptr::null_mut(),
                          ptr::null_mut(),
                          ptr::null_mut(),
                          ptr::null_mut()) == c::TRUE {
            let addr = frame.AddrPC.Offset;
            if addr == frame.AddrReturn.Offset || addr == 0 ||
               frame.AddrReturn.Offset == 0 { break }

            i += 1;

            if i >= 0 {
                try!(printing::print(w, i, addr - 1, process, &dbghelp));
            }
        }

        Ok(())
    }
}