servitor/shared/extractor.go

package shared

import (
	"errors"
	"net/url"
	"time"
)

// TODO throughout this file: attach the problematic object to the error

type JSON = map[string]any

func Get[T any](o JSON, key string) (T, error) {
	var zero T
	if value, ok := o[key]; !ok {
		return zero, errors.New("Object does not contain key " + key)
	} else if value, ok := value.(T); !ok {
		return zero, errors.New("Key " + key + " is not of the desired type")
	} else {
		return value, nil
	}
}

// some fields have "natural language values" meaning that I should check
// `contentMap[language]`, followed by `content`, followed by `contentMap["und"]`
// to find the content of the post
// https://www.w3.org/TR/activitystreams-core/#naturalLanguageValues
func GetNatural(o JSON, key string, language string) (string, error) {
	values, valuesErr := Get[JSON](o, key+"Map")

	if valuesErr == nil {
		if value, err := Get[string](values, language); err == nil {
			return value, nil
		}
	}

	if value, err := Get[string](o, key); err == nil {
		return value, nil
	}

	if valuesErr == nil {
		if value, err := Get[string](values, "und"); err == nil {
			return value, nil
		}
	}

	return "", errors.New("Natural language key " + key + " is not correctly present in object")
}

// there may be a nice way to extract this logic out but for now it doesn't matter
func GetTime(o JSON, key string) (time.Time, error) {
	if value, err := Get[string](o, key); err != nil {
		return time.Time{}, err
	} else {
		return time.Parse(time.RFC3339, value)
	}
}
func GetURL(o JSON, key string) (*url.URL, error) {
	if value, err := Get[string](o, key); err != nil {
		return nil, err
	} else {
		return url.Parse(value)
	}
}