// Copyright (c) Huawei Technologies Co., Ltd. 2022-2022. All rights reserved.

// runtime
package runtime

import (
	"fmt"
	"net/http"
	"runtime"
	"sync"
	"time"
)

const (
	runtimeCallTimes = 3
)

var (
	// ReallyCrash controls the behavior of HandleCrash and defaults to
	// true. It's exposed so components can optionally set to false
	// to restore prior behavior. This flag is mostly used for tests to validate
	// crash conditions.
	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.
//
// E.g., you can provide one or more additional handlers for something like shutting down go routines gracefully.
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 (except in the special case of http.ErrAbortHandler).
func logPanic(r interface{}) {
	if r == http.ErrAbortHandler {
		// honor the http.ErrAbortHandler sentinel panic value:
		//   ErrAbortHandler is a sentinel panic value to abort a handler.
		//   While any panic from ServeHTTP aborts the response to the client,
		//   panicking with ErrAbortHandler also suppresses logging of a stack trace to the server's error log.
		return
	}

	// Same as stdlib http server code. Manually allocate stack trace buffer size
	// to prevent excessively large logs
	const size = 64 << 10
	stacktrace := make([]byte, size)
	stacktrace = stacktrace[:runtime.Stack(stacktrace, false)]
	if _, ok := r.(string); ok {
		fmt.Printf("Observed a panic: %s\n%s", r, stacktrace)
	} else {
		fmt.Printf("Observed a panic: %#v (%v)\n%s", r, r, stacktrace)
	}
}

// ErrorHandlers is a list of functions which will be invoked when a nonreturnable
// 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) {
	fmt.Printf("error: %v", err)
}

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 {
		// If the time moves backwards for any reason, do nothing
		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(runtimeCallTimes, 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 {
		// Same as stdlib http server code. Manually allocate stack trace buffer size
		// to prevent excessively large logs
		const size = 64 << 10
		stacktrace := make([]byte, size)
		stacktrace = stacktrace[:runtime.Stack(stacktrace, false)]

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