[feature] Allow users to set default interaction policies per status visibility (#3108)

* [feature] Allow users to set default interaction policies

* use vars for default policies

* avoid some code repetition

* unfuck form binding

* avoid bonkers loop

* beep boop

* put policyValsToAPIPolicyVals in separate function

* don't bother with slices.Grow

* oops

internal/typeutils/frontendtointernal.go

@@ -18,6 +18,10 @@
 package typeutils
 
 import (
+	"fmt"
+	"net/url"
+	"slices"
+
 	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 )
@@ -57,3 +61,171 @@ func APIFilterActionToFilterAction(m apimodel.FilterAction) gtsmodel.FilterActio
 	}
 	return gtsmodel.FilterActionNone
 }
+
+func APIPolicyValueToPolicyValue(u apimodel.PolicyValue) (gtsmodel.PolicyValue, error) {
+	switch u {
+	case apimodel.PolicyValuePublic:
+		return gtsmodel.PolicyValuePublic, nil
+
+	case apimodel.PolicyValueFollowers:
+		return gtsmodel.PolicyValueFollowers, nil
+
+	case apimodel.PolicyValueFollowing:
+		return gtsmodel.PolicyValueFollowing, nil
+
+	case apimodel.PolicyValueMutuals:
+		return gtsmodel.PolicyValueMutuals, nil
+
+	case apimodel.PolicyValueMentioned:
+		return gtsmodel.PolicyValueMentioned, nil
+
+	case apimodel.PolicyValueAuthor:
+		return gtsmodel.PolicyValueAuthor, nil
+
+	case apimodel.PolicyValueMe:
+		err := fmt.Errorf("policyURI %s has no corresponding internal model", apimodel.PolicyValueMe)
+		return "", err
+
+	default:
+		// Parse URI to ensure it's a
+		// url with a valid protocol.
+		url, err := url.Parse(string(u))
+		if err != nil {
+			err := fmt.Errorf("could not parse non-predefined policy value as uri: %w", err)
+			return "", err
+		}
+
+		if url.Host != "http" && url.Host != "https" {
+			err := fmt.Errorf("non-predefined policy values must have protocol 'http' or 'https' (%s)", u)
+			return "", err
+		}
+
+		return gtsmodel.PolicyValue(u), nil
+	}
+}
+
+func APIInteractionPolicyToInteractionPolicy(
+	p *apimodel.InteractionPolicy,
+	v apimodel.Visibility,
+) (*gtsmodel.InteractionPolicy, error) {
+	visibility := APIVisToVis(v)
+
+	convertURIs := func(apiURIs []apimodel.PolicyValue) (gtsmodel.PolicyValues, error) {
+		policyURIs := gtsmodel.PolicyValues{}
+		for _, apiURI := range apiURIs {
+			uri, err := APIPolicyValueToPolicyValue(apiURI)
+			if err != nil {
+				return nil, err
+			}
+
+			if !uri.FeasibleForVisibility(visibility) {
+				err := fmt.Errorf("policyURI %s is not feasible for visibility %s", apiURI, v)
+				return nil, err
+			}
+
+			policyURIs = append(policyURIs, uri)
+		}
+		return policyURIs, nil
+	}
+
+	canLikeAlways, err := convertURIs(p.CanFavourite.Always)
+	if err != nil {
+		err := fmt.Errorf("error converting %s.can_favourite.always: %w", v, err)
+		return nil, err
+	}
+
+	canLikeWithApproval, err := convertURIs(p.CanFavourite.WithApproval)
+	if err != nil {
+		err := fmt.Errorf("error converting %s.can_favourite.with_approval: %w", v, err)
+		return nil, err
+	}
+
+	canReplyAlways, err := convertURIs(p.CanReply.Always)
+	if err != nil {
+		err := fmt.Errorf("error converting %s.can_reply.always: %w", v, err)
+		return nil, err
+	}
+
+	canReplyWithApproval, err := convertURIs(p.CanReply.WithApproval)
+	if err != nil {
+		err := fmt.Errorf("error converting %s.can_reply.with_approval: %w", v, err)
+		return nil, err
+	}
+
+	canAnnounceAlways, err := convertURIs(p.CanReblog.Always)
+	if err != nil {
+		err := fmt.Errorf("error converting %s.can_reblog.always: %w", v, err)
+		return nil, err
+	}
+
+	canAnnounceWithApproval, err := convertURIs(p.CanReblog.WithApproval)
+	if err != nil {
+		err := fmt.Errorf("error converting %s.can_reblog.with_approval: %w", v, err)
+		return nil, err
+	}
+
+	// Normalize URIs.
+	//
+	// 1. Ensure canLikeAlways, canReplyAlways,
+	//    and canAnnounceAlways include self
+	//    (either explicitly or within public).
+
+	// ensureIncludesSelf adds the "author" PolicyValue
+	// to given slice of PolicyValues, if not already
+	// explicitly or implicitly included.
+	ensureIncludesSelf := func(vals gtsmodel.PolicyValues) gtsmodel.PolicyValues {
+		includesSelf := slices.ContainsFunc(
+			vals,
+			func(uri gtsmodel.PolicyValue) bool {
+				return uri == gtsmodel.PolicyValuePublic ||
+					uri == gtsmodel.PolicyValueAuthor
+			},
+		)
+
+		if includesSelf {
+			// This slice of policy values
+			// already includes self explicitly
+			// or implicitly, nothing to change.
+			return vals
+		}
+
+		// Need to add self/author to
+		// this slice of policy values.
+		vals = append(vals, gtsmodel.PolicyValueAuthor)
+		return vals
+	}
+
+	canLikeAlways = ensureIncludesSelf(canLikeAlways)
+	canReplyAlways = ensureIncludesSelf(canReplyAlways)
+	canAnnounceAlways = ensureIncludesSelf(canAnnounceAlways)
+
+	// 2. Ensure canReplyAlways includes mentioned
+	//    accounts (either explicitly or within public).
+	if !slices.ContainsFunc(
+		canReplyAlways,
+		func(uri gtsmodel.PolicyValue) bool {
+			return uri == gtsmodel.PolicyValuePublic ||
+				uri == gtsmodel.PolicyValueMentioned
+		},
+	) {
+		canReplyAlways = append(
+			canReplyAlways,
+			gtsmodel.PolicyValueMentioned,
+		)
+	}
+
+	return &gtsmodel.InteractionPolicy{
+		CanLike: gtsmodel.PolicyRules{
+			Always:       canLikeAlways,
+			WithApproval: canLikeWithApproval,
+		},
+		CanReply: gtsmodel.PolicyRules{
+			Always:       canReplyAlways,
+			WithApproval: canReplyWithApproval,
+		},
+		CanAnnounce: gtsmodel.PolicyRules{
+			Always:       canAnnounceAlways,
+			WithApproval: canAnnounceWithApproval,
+		},
+	}, nil
+}