package main

import (
	"context"
	"crypto/tls"
	"crypto/x509"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"os"
	"os/signal"
	"strings"
	"syscall"
	"time"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/dynamic"
	coordinationv1 "k8s.io/client-go/kubernetes/typed/coordination/v1"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/leaderelection"
	"k8s.io/client-go/tools/leaderelection/resourcelock"
)

func main() {
	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer stop()
	if err := run(ctx, os.Args[1:]); err != nil && !errors.Is(err, context.Canceled) {
		slog.Error("project delivery", "error", err)
		os.Exit(1)
	}
}

func run(ctx context.Context, arguments []string) error {
	if len(arguments) != 1 {
		return errors.New("expected one command: run")
	}
	switch arguments[0] {
	case "run":
		return runController(ctx)
	default:
		return fmt.Errorf("unknown command %q", arguments[0])
	}
}

func runController(ctx context.Context) error {
	clientConfig, err := rest.InClusterConfig()
	if err != nil {
		return fmt.Errorf("load Kubernetes configuration: %w", err)
	}
	client, err := dynamic.NewForConfig(clientConfig)
	if err != nil {
		return fmt.Errorf("create Kubernetes client: %w", err)
	}
	forgejoHTTP, err := httpClient(os.Getenv("FORGEJO_CA_PATH"), 30*time.Second)
	if err != nil {
		return err
	}
	publicToken, err := secretFile(os.Getenv("FORGEJO_PUBLIC_TOKEN_PATH"))
	if err != nil {
		return err
	}
	privateToken, err := secretFile(os.Getenv("FORGEJO_PRIVATE_TOKEN_PATH"))
	if err != nil {
		return err
	}
	publicRefs, err := newForgejoClient(
		valueOrDefault("FORGEJO_PUBLIC_URL", "http://forge-git-http.forgejo-public.svc.cluster.local:3000"),
		forgejoHTTP,
		publicToken,
	)
	if err != nil {
		return err
	}
	privateRefs, err := newForgejoClient(
		valueOrDefault("FORGEJO_PRIVATE_URL", "http://forgejo-http.forgejo.svc.cluster.local:3000"),
		forgejoHTTP,
		privateToken,
	)
	if err != nil {
		return err
	}
	refs, err := newForgejoRouter(
		forgejoRoute{authority: valueOrDefault("FORGEJO_PUBLIC_AUTHORITY", "git.quorate.dev"), source: publicRefs},
		forgejoRoute{authority: valueOrDefault("FORGEJO_PRIVATE_AUTHORITY", "forge.quorate.internal"), source: privateRefs},
	)
	if err != nil {
		return err
	}
	config, err := loadControllerConfig()
	if err != nil {
		return err
	}
	instance := controller{client: client, source: refs, now: time.Now, config: config}
	coordination, err := coordinationv1.NewForConfig(clientConfig)
	if err != nil {
		return err
	}
	identity, err := os.Hostname()
	if err != nil {
		return err
	}
	namespace := os.Getenv("POD_NAMESPACE")
	if namespace == "" {
		return errors.New("POD_NAMESPACE is required")
	}
	return instance.lead(ctx, &resourcelock.LeaseLock{
		LeaseMeta:  metav1.ObjectMeta{Name: "project-delivery", Namespace: namespace},
		Client:     coordination,
		LockConfig: resourcelock.ResourceLockConfig{Identity: identity},
	})
}

func secretFile(path string) (string, error) {
	if path == "" {
		return "", nil
	}
	value, err := os.ReadFile(path)
	if err != nil {
		return "", fmt.Errorf("read secret file: %w", err)
	}
	secret := strings.TrimSpace(string(value))
	if secret == "" {
		return "", errors.New("secret file is empty")
	}
	return secret, nil
}

func loadControllerConfig() (controllerConfig, error) {
	pollInterval, err := durationFromEnvironment("POLL_INTERVAL", 20*time.Second)
	if err != nil {
		return controllerConfig{}, err
	}
	bucketInterval, err := durationFromEnvironment("OBSERVATION_BUCKET_INTERVAL", time.Minute)
	if err != nil {
		return controllerConfig{}, err
	}
	requestTimeout, err := durationFromEnvironment("REQUEST_TIMEOUT", 15*time.Second)
	if err != nil {
		return controllerConfig{}, err
	}
	return controllerConfig{
		pollInterval:   pollInterval,
		bucketInterval: bucketInterval,
		requestTimeout: requestTimeout,
		templateQuiet:  bucketInterval,
	}, nil
}

func durationFromEnvironment(name string, fallback time.Duration) (time.Duration, error) {
	value := os.Getenv(name)
	if value == "" {
		return fallback, nil
	}
	duration, err := time.ParseDuration(value)
	if err != nil || duration <= 0 {
		return 0, fmt.Errorf("%s must be a positive duration", name)
	}
	return duration, nil
}

func valueOrDefault(name, fallback string) string {
	if value := os.Getenv(name); value != "" {
		return value
	}
	return fallback
}

func httpClient(caPath string, timeout time.Duration) (*http.Client, error) {
	transport := http.DefaultTransport.(*http.Transport).Clone()
	if caPath != "" {
		pem, err := os.ReadFile(caPath)
		if err != nil {
			return nil, fmt.Errorf("read HTTP CA: %w", err)
		}
		roots, err := x509.SystemCertPool()
		if err != nil {
			return nil, fmt.Errorf("load system roots: %w", err)
		}
		if !roots.AppendCertsFromPEM(pem) {
			return nil, errors.New("HTTP CA contains no certificate")
		}
		transport.TLSClientConfig = &tls.Config{RootCAs: roots}
	}
	return &http.Client{Transport: transport, Timeout: timeout}, nil
}

func (c *controller) lead(ctx context.Context, lock resourcelock.Interface) error {
	electionCtx, cancel := context.WithCancel(ctx)
	defer cancel()
	controllerErr := make(chan error, 1)
	elector, err := leaderelection.NewLeaderElector(leaderelection.LeaderElectionConfig{
		Lock:          lock,
		LeaseDuration: 30 * time.Second,
		RenewDeadline: 20 * time.Second,
		RetryPeriod:   5 * time.Second,
		Name:          "project-delivery",
		Callbacks: leaderelection.LeaderCallbacks{
			OnStartedLeading: func(leaderCtx context.Context) {
				controllerErr <- c.run(leaderCtx)
				cancel()
			},
			OnStoppedLeading: func() {
				if ctx.Err() == nil {
					select {
					case controllerErr <- errors.New("leadership lost"):
					default:
					}
				}
			},
		},
	})
	if err != nil {
		return err
	}
	elector.Run(electionCtx)
	select {
	case err := <-controllerErr:
		return err
	default:
		return ctx.Err()
	}
}