/*

SPDX-Copyright: Copyright (c) Brad Rydzewski, project contributors, Capital One Services, LLC
SPDX-License-Identifier: Apache-2.0
Copyright 2017 Brad Rydzewski, project contributors, Capital One Services, LLC

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 middleware

import (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net/http/httputil"
	"runtime"

	"github.com/Sirupsen/logrus"
	"github.com/gin-gonic/gin"
)

var (
	dunno     = []byte("???")
	centerDot = []byte("·")
	dot       = []byte(".")
	slash     = []byte("/")
	reset     = string([]byte{27, 91, 48, 109})
)

// Recovery returns a middleware that recovers from any panics and writes a 500 if there was one.
func Recovery(sunlight bool) gin.HandlerFunc {
	return RecoveryWithWriter(gin.DefaultErrorWriter, sunlight)
}

func RecoveryWithWriter(out io.Writer, sunlight bool) gin.HandlerFunc {
	logger := log.New(out, "\n\n\x1b[31m", log.LstdFlags)
	return func(c *gin.Context) {
		defer func() {
			if err := recover(); err != nil {
				stack := stack(3)
				logrus.Error("Recovering from panic. Preserving stack trace.")
				httprequest, _ := httputil.DumpRequest(c.Request, false)
				logger.Printf("[Recovery] panic recovered:\n%s\n%s\n%s%s", string(httprequest), err, stack, reset)
				if sunlight {
					c.String(500, "[Recovery] panic recovered: %s\n%s",
						err,
						stack)
				} else {
					c.String(500, "Internal server error")
				}
			}
		}()
		c.Next()
	}
}

// stack returns a nicely formated stack frame, skipping skip frames
func stack(skip int) []byte {
	buf := new(bytes.Buffer) // the returned data
	// As we loop, we open files and read them. These variables record the currently
	// loaded file.
	var lines [][]byte
	var lastFile string
	for i := skip; ; i++ { // Skip the expected number of frames
		pc, file, line, ok := runtime.Caller(i)
		if !ok {
			break
		}
		// Print this much at least.  If we can't find the source, it won't show.
		fmt.Fprintf(buf, "%s:%d (0x%x)\n", file, line, pc)
		if file != lastFile {
			data, err := ioutil.ReadFile(file)
			if err != nil {
				continue
			}
			lines = bytes.Split(data, []byte{'\n'})
			lastFile = file
		}
		fmt.Fprintf(buf, "\t%s: %s\n", function(pc), source(lines, line))
	}
	return buf.Bytes()
}

// source returns a space-trimmed slice of the n'th line.
func source(lines [][]byte, n int) []byte {
	n-- // in stack trace, lines are 1-indexed but our array is 0-indexed
	if n < 0 || n >= len(lines) {
		return dunno
	}
	return bytes.TrimSpace(lines[n])
}

// function returns, if possible, the name of the function containing the PC.
func function(pc uintptr) []byte {
	fn := runtime.FuncForPC(pc)
	if fn == nil {
		return dunno
	}
	name := []byte(fn.Name())
	// The name includes the path name to the package, which is unnecessary
	// since the file name is already included.  Plus, it has center dots.
	// That is, we see
	//	runtime/debug.*T·ptrmethod
	// and want
	//	*T.ptrmethod
	// Also the package path might contains dot (e.g. code.google.com/...),
	// so first eliminate the path prefix
	if lastslash := bytes.LastIndex(name, slash); lastslash >= 0 {
		name = name[lastslash+1:]
	}
	if period := bytes.Index(name, dot); period >= 0 {
		name = name[period+1:]
	}
	name = bytes.Replace(name, centerDot, dot, -1)
	return name
}
