package main

// Run with:
//
// On master this allocates 30+GB of memory and never finishes.
//
// go build -o reproducer reproducer.go && time ./reproducer
// Now passing 1262568 bytes to ParseSchema() to demonstrate the benefit of the json marshaling change
// Alloc = 4160 MiB	TotalAlloc = 5630 MiB	Sys = 5578 MiB	NumGC = 18
// Alloc = 8312 MiB	TotalAlloc = 11174 MiB	Sys = 11120 MiB	NumGC = 19
// Alloc = 19392 MiB	TotalAlloc = 22254 MiB	Sys = 22203 MiB	NumGC = 19
// Alloc = 16616 MiB	TotalAlloc = 22254 MiB	Sys = 22203 MiB	NumGC = 20
// Alloc = 16616 MiB	TotalAlloc = 22254 MiB	Sys = 22203 MiB	NumGC = 20
// Alloc = 16616 MiB	TotalAlloc = 22254 MiB	Sys = 22203 MiB	NumGC = 20
// Alloc = 33223 MiB	TotalAlloc = 44405 MiB	Sys = 44371 MiB	NumGC = 21
// Alloc = 33223 MiB	TotalAlloc = 44405 MiB	Sys = 44371 MiB	NumGC = 21
// Alloc = 33223 MiB	TotalAlloc = 44405 MiB	Sys = 44371 MiB	NumGC = 21
// Alloc = 33223 MiB	TotalAlloc = 44405 MiB	Sys = 44371 MiB	NumGC = 21
// Alloc = 33223 MiB	TotalAlloc = 44405 MiB	Sys = 44371 MiB	NumGC = 21
//
// With the position JSON annotation change this finishes in well under a second.
//
// go build -o reproducer reproducer.go && time ./reproducer
// Now passing 1262568 bytes to ParseSchema() to demonstrate the benefit of the json marshaling change
// Got 3705551 bytes of JSON
//
// real	0m0.380s
// user	0m0.075s
// sys	0m0.020s

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"runtime"
	"time"

	"github.com/vektah/gqlparser/v2/ast"
	"github.com/vektah/gqlparser/v2/parser"
)

// Complex GQL schema to test with
const gqlSchema = `https://docs.github.com/public/fpt/schema.docs.graphql`

// Seconds between memory dump information
const memDumpSeconds = 3

func main() {
	b, err := downloadSchema(gqlSchema)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error downloading: %s\n", err)
	}

	// Dump the memory usage every few seconds
	ticker := time.NewTicker(memDumpSeconds * time.Second)
	done := make(chan bool)
	go func() {
		for {
			select {
			case <-ticker.C:
				PrintMemUsage()
			case <-done:
				ticker.Stop()
				return
			}
		}
	}()

	// This should allocate a bunch of memory and not return
	fmt.Fprintf(os.Stderr, "Now passing %d bytes to ParseSchema() to demonstrate the benefit of the json marshaling change\n", len(b))

	// Parse schema
	doc, err := parser.ParseSchema(&ast.Source{Input: string(b), Name: "github.graphql"})
	if err != nil {
		panic(err)
	}

	// Marshal to JSON
	s, err := json.Marshal(doc)
	if err != nil {
		panic(err)
	}
	fmt.Fprintf(os.Stderr, "Got %d bytes of JSON\n", len(s))

	// Stop printing memory usage
	done <- true
}

func downloadSchema(url string) ([]byte, error) {
	response, err := http.Get(url)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error while downloading %s - %s\n", url, err)
		return []byte{}, err
	}
	defer response.Body.Close()
	return io.ReadAll(response.Body)
}

// From: https://gist.github.com/j33ty/79e8b736141be19687f565ea4c6f4226
// PrintMemUsage outputs the current, total and OS memory being used. As well as the number
// of garage collection cycles completed.
func PrintMemUsage() {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	// For info on each, see: https://golang.org/pkg/runtime/#MemStats
	fmt.Printf("Alloc = %v MiB", bToMb(m.Alloc))
	fmt.Printf("\tTotalAlloc = %v MiB", bToMb(m.TotalAlloc))
	fmt.Printf("\tSys = %v MiB", bToMb(m.Sys))
	fmt.Printf("\tNumGC = %v\n", m.NumGC)
}

func bToMb(b uint64) uint64 {
	return b / 1024 / 1024
}