// Package app defines the generic [App] interface.
package app

import (
	"context"
	"log"
	"syscall"
	"time"

	"hakurei.app/hst"
	"hakurei.app/internal/app/state"
	"hakurei.app/internal/sys"
)

type App interface {
	// ID returns a copy of [ID] held by App.
	ID() state.ID

	// Seal determines the outcome of config as a [SealedApp].
	// The value of config might be overwritten and must not be used again.
	Seal(config *hst.Config) (SealedApp, error)

	String() string
}

type SealedApp interface {
	// Run commits sealed system setup and starts the app process.
	Run(rs *RunState) error
}

// RunState stores the outcome of a call to [SealedApp.Run].
type RunState struct {
	// Time is the exact point in time where the process was created.
	// Location must be set to UTC.
	//
	// Time is nil if no process was ever created.
	Time *time.Time
	// RevertErr is stored by the deferred revert call.
	RevertErr error
	// WaitErr is the generic error value created by the standard library.
	WaitErr error

	syscall.WaitStatus
}

// SetStart stores the current time in [RunState] once.
func (rs *RunState) SetStart() {
	if rs.Time != nil {
		panic("attempted to store time twice")
	}
	now := time.Now().UTC()
	rs.Time = &now
}

func MustNew(ctx context.Context, os sys.State) App {
	a, err := New(ctx, os)
	if err != nil {
		log.Fatalf("cannot create app: %v", err)
	}
	return a
}