package instancectl

import (
	"context"
	"errors"
	"fmt"
	"os"
	"path/filepath"

	"github.com/carlosframework/platform/internal/safefile"
)

// clearLegacyClaimLaunch removes a claim launch snapshot before the legacy
// controller may reuse the main run unit. Artifact-free hosts keep the old
// path: they do not acquire a systemd query or cgroup read.
func (s *Server) clearLegacyClaimLaunch(ctx context.Context, host string) error {
	if s.DropInDir == "" || s.ExeRoot == "" || s.DataRoot == "" || s.CgroupRoot == "" {
		return nil
	}
	u := ClaimUnits{
		Systemctl:  s.Systemctl,
		CgroupRoot: s.CgroupRoot,
		ExeRoot:    s.ExeRoot,
		UnitRoot:   s.DropInDir,
		DataRoot:   s.DataRoot,
	}
	source, dropin, err := u.launchPaths(host)
	if err != nil {
		return err
	}
	found := false
	dropinPath := filepath.Join(dropin, "60-claim-launch.conf")
	var dropinBody []byte
	for _, path := range []string{
		filepath.Join(source, "launch.json"),
		filepath.Join(source, "permit.json"),
		filepath.Join(source, "exec.sock"),
		dropinPath,
	} {
		if _, err := os.Lstat(path); err == nil {
			found = true
			if path == dropinPath {
				dropinBody, err = safefile.ReadFile(path)
				if err != nil {
					return fmt.Errorf("read claim launch %s: %w", path, err)
				}
			}
		} else if !errors.Is(err, os.ErrNotExist) {
			return fmt.Errorf("inspect claim launch %s: %w", path, err)
		}
	}
	if !found {
		return nil
	}
	// Gone proves both facts required before clearLaunch mutates either
	// artifact: systemd says the unit is idle and its cgroup is empty.
	if err := u.Gone(ctx, host, ""); err != nil {
		// clearLaunch removes the drop-in before daemon-reload. Restore it
		// when that reload fails, so a later attempt cannot mistake a cached
		// systemd binding for an artifact-free host and start through it.
		if dropinBody != nil {
			if _, statErr := os.Lstat(dropinPath); errors.Is(statErr, os.ErrNotExist) {
				restoreErr := safefile.WriteFile(dropinPath, dropinBody, 0644)
				if restoreErr != nil {
					err = errors.Join(err, fmt.Errorf("restore claim launch drop-in: %w", restoreErr))
				}
			}
		}
		return fmt.Errorf("clear claim launch for %s: %w", host, err)
	}
	return nil
}