package haproxy

import (
	"bytes"
	"context"
	"crypto/sha256"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"os/exec"
	"sync"
	"text/template"
)

type ServiceManager interface {
	Reload(context.Context) error
}

type HAProxyManager struct {
	sync.Mutex

	configFile     string
	serviceManager ServiceManager
	template       *template.Template
	hash           []byte
}

func NewHAProxyManager(configFile string) (*HAProxyManager, error) {
	t, err := template.New("haproxy").Parse(haproxyConfigTemplate)
	if err != nil {
		return nil, err
	}
	return &HAProxyManager{
		configFile:     configFile,
		serviceManager: NewSystemdManager("haproxy"),
		template:       t,
	}, nil
}

func (ha *HAProxyManager) checkConfig(ctx context.Context, lbs Config) (hash []byte, err error) {
	tmp, err := ioutil.TempFile(os.TempDir(), "haproxy_")
	if err != nil {
		return
	}
	defer tmp.Close()
	defer os.Remove(tmp.Name())
	h := sha256.New()
	w := io.MultiWriter(tmp, h)
	err = ha.template.Execute(w, lbs)
	if err != nil {
		return
	}
	hash = h.Sum(nil)
	out, err := exec.CommandContext(ctx, "haproxy", "-c", "-f", tmp.Name()).CombinedOutput()
	if err != nil {
		err = fmt.Errorf("%s:%w", string(out), err)
	}
	return hash, err
}

func (ha *HAProxyManager) UpdateConfig(ctx context.Context, lbs Config) error {
	ha.Lock()
	defer ha.Unlock()
	hash, err := ha.checkConfig(ctx, lbs)
	if err != nil {
		return err
	}
	if bytes.Equal(ha.hash, hash) {
		return nil
	}
	file, err := os.OpenFile(ha.configFile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
	if err != nil {
		return err
	}
	err = ha.template.Execute(file, lbs)
	if err != nil {
		file.Close()
		return err
	}
	file.Close()
	ha.hash = hash
	return ha.serviceManager.Reload(ctx)
}