package main

import (
	"io/ioutil"
	"math"
	"os"
	"os/exec"
	"path/filepath"
	"testing"
	"time"
)

const prog = `
package main

import (
        "fmt"
        "html"
        "log"
        "net/http"
)

func main() {
        http.HandleFunc("/bar", func(w http.ResponseWriter, r *http.Request) {
                fmt.Fprintf(w, "Hello, %q", html.EscapeString(r.URL.Path))
        })

        go http.ListenAndServe(":8080", nil)

        // Exit immediately so we can easily measure startup.
        log.Printf("Exiting...")
}`

func TestBuildModeSpeedComparisons(t *testing.T) {
	tmpDir, err := ioutil.TempDir("", "issue36028")
	if err != nil {
		t.Fatalf("Failed to create tmp directory: %v", err)
	}
	defer os.RemoveAll(tmpDir)

	mainGoFile := filepath.Join(tmpDir, "http.go")
	if err := ioutil.WriteFile(mainGoFile, []byte(prog), 0600); err != nil {
		t.Fatalf("Failed to write file: %v", err)
	}

	staticFile := filepath.Join(tmpDir, "http.static")
	pieFile := filepath.Join(tmpDir, "http.ext.pie")
	pieLinkFile := filepath.Join(tmpDir, "http.int.pie")
	var noEnv []string
	_, output, err := execIt(noEnv, "go", "build", "-o", staticFile, mainGoFile)
	if err != nil {
		t.Fatalf("Failed to build object file: %v\n%s", err, output)
	}
	_, output, err = execIt(noEnv, "go", "build", "-buildmode=pie", "-o", pieFile, mainGoFile)
	if err != nil {
		t.Fatalf("Failed to build PIE file: %v\n%s", err, output)
	}
	cgoEnabled0 := append(os.Environ(), "CGO_ENABLED=0")
	// TODO: Get @prattmic to properly add the slow build flags here.
	_, output, err = execIt(cgoEnabled0, "go", "build", "-ldflags=-linkmode=internal", "-o", pieLinkFile, mainGoFile)
	if err != nil {
		t.Fatalf("Failed to build PIE -linkmode file: %v\n%s", err, output)
	}

	durStatic, _, _ := execIt(noEnv, staticFile)
	durPIE, _, _ := execIt(noEnv, pieFile)
	durPIELink, _, _ := execIt(noEnv, pieLinkFile)

	values := []struct {
		name  string
		value time.Duration
	}{
		{"durStatic", durStatic},
		{"durPIE", durPIE},
		{"durPIELink", durPIELink},
	}
	sum := 0.0
	for _, value := range values {
		sum += float64(value.value)
	}
	mean := sum / float64(len(values))
	sumOfSquares := 0.0
	for _, value := range values {
		sumOfSquares += math.Pow(float64(value.value)-mean, 2.0)
	}
	variance := sumOfSquares / float64(len(values))
	σ := math.Pow(variance, 0.5)

        // Heuristic: outlier detection by 3 sigma-rule.
	t.Logf("σ stdDev: %s", time.Duration(σ))
	meanMinus2σ := time.Duration(mean - 2*σ)
	meanPlus2σ := time.Duration(mean + 2*σ)
	for _, value := range values {
		if value.value > meanPlus2σ {
			t.Errorf("Anomaly: %q: %s > (μ + 2σ = %s)", value.name, value.value, meanPlus2σ)
		} else if value.value  < meanMinus2σ {
			t.Errorf("Anomaly: %q: %s < (μ - 2σ = %s)", value.name, value.value, meanMinus2σ)
		}
	}
}

func execIt(env []string, prog string, args ...string) (dur time.Duration, output []byte, err error) {
	startTime := time.Now()
	defer func() {
		dur = time.Now().Sub(startTime)
	}()
	cmd := exec.Command(prog, args...)
	cmd.Env = env
	output, err = cmd.CombinedOutput()
	return
}