/*
 * Copyright (c) 2020 Baidu, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package runtime

import (
	"fmt"
	"runtime"
	"sync"
	"time"

	"github.com/baidu/easyfaas/pkg/util/logs"
)

var (
	// ReallyCrash controls the behavior of HandleCrash and now defaults
	// true. It's still exposed so components can optionally set to false
	// to restore prior behavior.
	ReallyCrash = true
)

// PanicHandlers is a list of functions which will be invoked when a panic happens.
var PanicHandlers = []func(interface{}){logPanic}

// HandleCrash simply catches a crash and logs an error. Meant to be called via
// defer.  Additional context-specific handlers can be provided, and will be
// called in case of panic.  HandleCrash actually crashes, after calling the
// handlers and logging the panic message.
//
// TODO: remove this function. We are switching to a world where it's safe for
// apiserver to panic, since it will be restarted by kubelet. At the beginning
// of the Kubernetes project, nothing was going to restart apiserver and so
// catching panics was important. But it's actually much simpler for montoring
// software if we just exit when an unexpected panic happens.
func HandleCrash(additionalHandlers ...func(interface{})) {
	if r := recover(); r != nil {
		for _, fn := range PanicHandlers {
			fn(r)
		}
		for _, fn := range additionalHandlers {
			fn(r)
		}
		if ReallyCrash {
			// Actually proceed to panic.
			panic(r)
		}
	}
}

// logPanic logs the caller tree when a panic occurs.
func logPanic(r interface{}) {
	callers := getCallers(r)
	logs.Errorf("Observed a panic: %#v (%v)\n%v", r, r, callers)
}

func getCallers(r interface{}) string {
	callers := ""
	for i := 0; true; i++ {
		_, file, line, ok := runtime.Caller(i)
		if !ok {
			break
		}
		callers = callers + fmt.Sprintf("%v:%v\n", file, line)
	}

	return callers
}

// ErrorHandlers is a list of functions which will be invoked when an unreturnable
// error occurs.
// TODO(lavalamp): for testability, this and the below HandleError function
// should be packaged up into a testable and reusable object.
var ErrorHandlers = []func(error){
	logError,
	(&rudimentaryErrorBackoff{
		lastErrorTime: time.Now(),
		// 1ms was the number folks were able to stomach as a global rate limit.
		// If you need to log errors more than 1000 times a second you
		// should probably consider fixing your code instead. :)
		minPeriod: time.Millisecond,
	}).OnError,
}

// HandlerError is a method to invoke when a non-user facing piece of code cannot
// return an error and needs to indicate it has been ignored. Invoking this method
// is preferable to logging the error - the default behavior is to log but the
// errors may be sent to a remote server for analysis.
func HandleError(err error) {
	// this is sometimes called with a nil error.  We probably shouldn't fail and should do nothing instead
	if err == nil {
		return
	}

	for _, fn := range ErrorHandlers {
		fn(err)
	}
}

// logError prints an error with the call stack of the location it was reported
func logError(err error) {
	// logs.ErrorDepth(2, err)
	logs.Error(err.Error())
}

type rudimentaryErrorBackoff struct {
	minPeriod time.Duration // immutable
	// TODO(lavalamp): use the clock for testability. Need to move that
	// package for that to be accessible here.
	lastErrorTimeLock sync.Mutex
	lastErrorTime     time.Time
}

// OnError will block if it is called more often than the embedded period time.
// This will prevent overly tight hot error loops.
func (r *rudimentaryErrorBackoff) OnError(error) {
	r.lastErrorTimeLock.Lock()
	defer r.lastErrorTimeLock.Unlock()
	d := time.Since(r.lastErrorTime)
	if d < r.minPeriod {
		time.Sleep(r.minPeriod - d)
	}
	r.lastErrorTime = time.Now()
}

// GetCaller returns the caller of the function that calls it.
func GetCaller() string {
	var pc [1]uintptr
	runtime.Callers(3, pc[:])
	f := runtime.FuncForPC(pc[0])
	if f == nil {
		return fmt.Sprintf("Unable to find caller")
	}
	return f.Name()
}

// RecoverFromPanic replaces the specified error with an error containing the
// original error, and  the call tree when a panic occurs. This enables error
// handlers to handle errors and panics the same way.
func RecoverFromPanic(err *error) {
	if r := recover(); r != nil {
		callers := getCallers(r)

		*err = fmt.Errorf(
			"recovered from panic %q. (err=%v) Call stack:\n%v",
			r,
			*err,
			callers)
	}
}
