package main

import (
	"encoding/json"
	"fmt"
	"io"
	"os"
)

type journalIdentity struct {
	OperationID string `json:"operation_id"`
	State       string `json:"state"`
}

func readJournalOperation(path string) (journalIdentity, error) {
	file, err := os.Open(path)
	if err != nil {
		return journalIdentity{}, err
	}
	defer file.Close()
	var journal journalIdentity
	decoder := json.NewDecoder(io.LimitReader(file, 1024*1024))
	if err := decoder.Decode(&journal); err != nil {
		return journalIdentity{}, err
	}
	var trailing any
	if err := decoder.Decode(&trailing); err != io.EOF {
		return journalIdentity{}, fmt.Errorf("journal must contain exactly one JSON value")
	}
	if journal.OperationID == "" || journal.State == "" {
		return journalIdentity{}, fmt.Errorf("journal identity or state is empty")
	}
	return journal, nil
}