package activator

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"

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

// InstallMarker is a box's own note that it finished a local install of
// one generation of a host. Nothing reads it to trust a local database:
// claim ruling R6 has every admitted writer purge and restore from the
// certified remote (region HA spec 1 H13, §5.5 withdrawn). It is kept for
// relocation's local install journal (§5.8), which plan 1b does not build.
type InstallMarker struct {
	Incarnation string `json:"incarnation"`
	Generation  string `json:"generation"`
	Stamp       int64  `json:"stamp"`
	DBMarker    string `json:"db_marker"`
	FilesSeq    int64  `json:"files_seq"`
}

func InstallMarkerPath(dataDir, host string) string {
	return filepath.Join(dataDir, ".installed", provision.InstanceID(host)+".json")
}

// WriteInstallMarker replaces the marker atomically and syncs both the
// file and its directory, so a marker that is read back was fully written.
func WriteInstallMarker(dataDir, host string, m InstallMarker) error {
	path := InstallMarkerPath(dataDir, host)
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return err
	}
	body, err := json.Marshal(m)
	if err != nil {
		return err
	}
	tmp, err := os.CreateTemp(dir, ".marker-*")
	if err != nil {
		return err
	}
	defer os.Remove(tmp.Name())
	if _, err := tmp.Write(body); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Sync(); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Close(); err != nil {
		return err
	}
	if err := os.Rename(tmp.Name(), path); err != nil {
		return err
	}
	d, err := os.Open(dir)
	if err != nil {
		return err
	}
	defer d.Close()
	return d.Sync()
}

// ReadInstallMarker returns the marker and whether there is one. A marker
// that exists but cannot be parsed is an error, never "absent": the caller
// restores either way, but it must not mistake damage for a clean slate.
func ReadInstallMarker(dataDir, host string) (InstallMarker, bool, error) {
	body, err := os.ReadFile(InstallMarkerPath(dataDir, host))
	if errors.Is(err, os.ErrNotExist) {
		return InstallMarker{}, false, nil
	}
	if err != nil {
		return InstallMarker{}, false, err
	}
	var m InstallMarker
	if err := json.Unmarshal(body, &m); err != nil {
		return InstallMarker{}, false, fmt.Errorf("activator: install marker for %s: %w", host, err)
	}
	return m, true, nil
}

func RemoveInstallMarker(dataDir, host string) error {
	err := os.Remove(InstallMarkerPath(dataDir, host))
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	return err
}