package state

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"time"
)

const (
	IntentNormal            = "normal"
	IntentStartupInProgress = "startup_in_progress"
	IntentShuttingDown      = "shutting_down"
	IntentShutdownComplete  = "shutdown_complete"
)

type Intent struct {
	State     string    `json:"state"`
	Reason    string    `json:"reason,omitempty"`
	Source    string    `json:"source,omitempty"`
	UpdatedAt time.Time `json:"updated_at"`
}

func ReadIntent(path string) (Intent, error) {
	b, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return Intent{}, nil
		}
		return Intent{}, err
	}
	if len(b) == 0 {
		return Intent{}, nil
	}
	var in Intent
	if err := json.Unmarshal(b, &in); err != nil {
		return Intent{}, err
	}
	return in, nil
}

func WriteIntent(path string, in Intent) error {
	if in.UpdatedAt.IsZero() {
		in.UpdatedAt = time.Now().UTC()
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o750); err != nil {
		return err
	}
	b, err := json.MarshalIndent(in, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(path, b, 0o640)
}

func MustWriteIntent(path string, state string, reason string, source string) error {
	switch state {
	case IntentNormal, IntentStartupInProgress, IntentShuttingDown, IntentShutdownComplete:
	default:
		return fmt.Errorf("invalid intent state: %s", state)
	}
	return WriteIntent(path, Intent{
		State:     state,
		Reason:    reason,
		Source:    source,
		UpdatedAt: time.Now().UTC(),
	})
}