package ap

import (
	"encoding/json"
	"fmt"
	"net/url"

	"github.com/piprate/json-gold/ld"
)

type ApThing map[string]any

type RemoteDocumentLoader struct{}

// Try and parse a remote ActivityPub object into a more usable form
// Result is a map[string]any where the keys defined in /ap/constants.go should be usable,
// depending on the type of object
// The general approach for fetching an object will be to fetch the main object
// and only store the ID for sub-objects to fetch them later
func ParseFromUrl(u *url.URL) (ApThing, error) {
	opts := ld.NewJsonLdOptions("")
	processor := ld.NewJsonLdProcessor()
	// TODO: Add custom document parser (copy default implementation) that includes verification

	// Explanation:
	// Expansion removes the context from a document (json-ld activitypub data)
	// and turns every field into something along the lines of
	// "https://example.com/ns#ObjectType": <Insert data for that object here>
	// This makes it easier to deal with things as they now have a very consistent naming scheme
	// See /ap/constants.go for those

	parsed, err := processor.Expand(u.String(), opts)
	if err != nil {
		return nil, fmt.Errorf("failed to process remote document: %w", err)
	}
	if len(parsed) == 0 {
		return nil, fmt.Errorf("document has a length of 0")
	}
	typed, ok := parsed[0].(ApThing)
	if !ok {
		return nil, fmt.Errorf("couldn't cast data to ApThing")
	}
	return typed, nil
}

// Compact an AP object down into a compressed json-ld form
// That compacted form should be accepted by all AP servers
// It also handles context for any fields
// Content should only use keys defined in /ap/constants.go though
// Other things might get lost in translation
func Compact(content map[string]any) ([]byte, error) {
	opts := ld.NewJsonLdOptions("")
	processor := ld.NewJsonLdProcessor()
	res, err := processor.Compact(content, allContext, opts)
	if err != nil {
		return nil, fmt.Errorf("failed to compact data: %w", err)
	}
	return json.Marshal(res)
}