package main

import (
	"flag"
	"fmt"
	pprofile "github.com/google/pprof/profile"
	"io"
	"log"
	"net/http"
	"os"
	"path"
	"slices"
	"strings"
	"sync"
	"time"
)

type stringList []string

func (i *stringList) String() string {
	return strings.Join(*i, ", ")
}

func (i *stringList) Set(value string) error {
	*i = append(*i, value)
	return nil
}

func main() {
	profileInterval := flag.Duration("profile-interval", time.Hour, "Profile every given duration")
	profileDuration := flag.Duration("profile-duration", time.Second*30, "Profile each time for this given duration")
	var endpoints stringList
	flag.Var(&endpoints, "endpoint", "Endpoint where a pprof HTTP API is exposed at, for example, http://127.0.0.1:6060. Can specify multiple")
	profileDirectory := flag.String("profile-directory", "/tmp", "Place where to dump generated merged profiles")
	profileName := flag.String("profile-name", "pgo-profile-latest.pprof", "Prefix to give latest generated file")

	flag.Parse()

	log.Printf("Profiling for %s every %s", *profileDuration, *profileInterval)

	var compactProfile *pprofile.Profile

	for range time.Tick(*profileInterval) {
		var wg sync.WaitGroup
		profiles := make([]*pprofile.Profile, len(endpoints))
		for i, endpoint := range endpoints {
			wg.Add(1)
			go func(i int, endpoint string) {
				defer wg.Done()
				log.Printf("attempting profile collection on %s", endpoint)
				if response, err := http.Get(fmt.Sprintf("%s/debug/pprof/profile?seconds=%d", endpoint, uint64(profileDuration.Seconds()))); err != nil {
					log.Printf("error collecting profile on %s: %s", endpoint, err)
					return
				} else {
					defer response.Body.Close()
					if response.StatusCode != http.StatusOK {
						if response.Header.Get("X-Go-Pprof") != "" && strings.Contains(response.Header.Get("Content-Type"), "text/plain") {
							// error is from pprof endpoint
							if body, err := io.ReadAll(response.Body); err == nil {
								log.Printf("error collecting profile on %s: got %d %s - %s", endpoint, response.StatusCode, response.Status, string(body))
								return
							}
						}
						log.Printf("error collecting profile on %s: expected status %d, got %d %s", endpoint, http.StatusOK, response.StatusCode, response.Status)
						return
					} else if profile, err := pprofile.Parse(response.Body); err != nil {
						log.Printf("error collecting profile on %s while reading: %s", endpoint, err)
						return
					} else {
						profiles[i] = profile
					}
				}
			}(i, endpoint)
		}
		wg.Wait()

		//remove any errored ones
		for i := len(profiles) - 1; i >= 0; i-- {
			if profiles[i] == nil {
				profiles = slices.Delete(profiles, i, i+1)
			}
		}
		if mergedProfile, err := pprofile.Merge(profiles); err != nil {
			log.Printf("could not merge profiles: %s", err)
		} else {
			if compactProfile != nil {
				if mergedWithPreviousProfile, err := pprofile.Merge([]*pprofile.Profile{mergedProfile, compactProfile}); err != nil {
					log.Printf("could not merge with previous profile: %s", err)
					//maybe redundant
					compactProfile = mergedProfile.Compact()
				} else {
					//maybe redundant
					compactProfile = mergedWithPreviousProfile.Compact()
				}
			} else {
				//maybe redundant
				compactProfile = mergedProfile.Compact()
			}

			func() {
				temporaryFile, err := os.CreateTemp("/tmp", "pgo-*")
				if err != nil {
					log.Printf("error opening temporary output profile: %s", err)
				} else {
					defer os.Remove(temporaryFile.Name())

					func() {
						defer temporaryFile.Sync()
						if err = compactProfile.Write(temporaryFile); err != nil {
							log.Printf("error writing temporary output profile: %s", err)
						}
					}()

					//copies to latest atomically
					log.Printf("writing profile at %d", time.Now().UTC().Unix())

					if err := func() error {
						if _, err = temporaryFile.Seek(0, io.SeekStart); err != nil {
							return err
						}
						w, err := os.Create(path.Join(*profileDirectory, *profileName+".tmp"))
						if err != nil {
							return err
						}
						defer w.Close()
						if _, err := io.Copy(w, temporaryFile); err != nil {
							return err
						}
						return nil
					}(); err != nil {
						log.Printf("error writing latest profile: %s", err)
					} else {
						_ = os.Rename(path.Join(*profileDirectory, *profileName+".tmp"), path.Join(*profileDirectory, *profileName))
					}
				}
			}()

		}
	}
}