package caddyfile

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"

	"github.com/psviderski/uncloud/internal/fs"
	"github.com/psviderski/uncloud/internal/machine/store"
	"github.com/psviderski/uncloud/pkg/api"
)

const (
	CaddyGroup = "uncloud"
	VerifyPath = "/.uncloud-verify"
)

// Controller monitors container changes in the cluster store and generates a configuration file for Caddy reverse
// proxy. The generated Caddyfile allows Caddy to route external traffic to service containers across the internal
// network.
type Controller struct {
	store          *store.Store
	path           string
	verifyResponse string
}

func NewController(store *store.Store, path string, verifyResponse string) (*Controller, error) {
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0750); err != nil {
		return nil, fmt.Errorf("create parent directory for Caddy configuration '%s': %w", dir, err)
	}
	if err := fs.Chown(dir, "", CaddyGroup); err != nil {
		return nil, fmt.Errorf("change owner of parent directory for Caddy configuration '%s': %w", dir, err)
	}

	return &Controller{
		store:          store,
		path:           path,
		verifyResponse: verifyResponse,
	}, nil
}

func (c *Controller) Run(ctx context.Context) error {
	containerRecords, changes, err := c.store.SubscribeContainers(ctx)
	if err != nil {
		return fmt.Errorf("subscribe to container changes: %w", err)
	}
	slog.Info("Subscribed to container changes in the cluster to generate Caddy configuration.")

	containers, err := c.filterAvailableContainers(containerRecords)
	if err != nil {
		return fmt.Errorf("filter available containers: %w", err)
	}
	if err = c.generateConfig(containers); err != nil {
		return fmt.Errorf("generate Caddy configuration: %w", err)
	}

	for {
		select {
		case _, ok := <-changes:
			if !ok {
				return fmt.Errorf("containers subscription failed")
			}
			slog.Debug("Cluster containers changed, updating Caddy configuration.")

			containerRecords, err = c.store.ListContainers(ctx, store.ListOptions{})
			if err != nil {
				slog.Error("Failed to list containers.", "err", err)
				continue
			}
			containers, err = c.filterAvailableContainers(containerRecords)
			if err != nil {
				slog.Error("Failed to filter available containers.", "err", err)
				continue
			}
			if err = c.generateConfig(containers); err != nil {
				slog.Error("Failed to generate Caddy configuration.", "err", err)
			}

			slog.Debug("Updated Caddy configuration.", "path", c.path)
		case <-ctx.Done():
			return nil
		}
	}
}

// filterAvailableContainers filters out containers from this machine that are likely unavailable. The availability
// is determined by the cluster membership state of the machine that the container is running on.
// TODO: implement machine membership check using Corrossion Admin client.
func (c *Controller) filterAvailableContainers(
	containerRecords []store.ContainerRecord,
) ([]api.ServiceContainer, error) {
	containers := make([]api.ServiceContainer, len(containerRecords))
	for i, cr := range containerRecords {
		containers[i] = api.ServiceContainer{
			Container: cr.Container,
			// TODO: restore ServiceSpec from the container record once it's saved in the store.
		}
	}
	return containers, nil
}

func (c *Controller) generateConfig(containers []api.ServiceContainer) error {
	config, err := GenerateConfig(containers, c.verifyResponse)
	if err != nil {
		return err
	}

	configBytes, err := json.MarshalIndent(config, "", "    ")
	if err != nil {
		return fmt.Errorf("marshal Caddy configuration: %w", err)
	}

	if err = os.WriteFile(c.path, configBytes, 0640); err != nil {
		return fmt.Errorf("write Caddy configuration to file '%s': %w", c.path, err)
	}
	if err = fs.Chown(c.path, "", CaddyGroup); err != nil {
		return fmt.Errorf("change owner of Caddy configuration file '%s': %w", c.path, err)
	}

	return nil
}