NIP-25
======

Reactions
---------

`final` `optional`

A reaction is a `kind 7` event that is used to react to other events.

The generic reaction, represented by the `content` set to a `+` string, SHOULD
be interpreted as a "like" or "upvote".

A reaction with `content` set to `-` SHOULD be interpreted as a "dislike" or
"downvote". It SHOULD NOT be counted as a "like", and MAY be displayed as a
downvote or dislike on a post. A client MAY also choose to tally likes against
dislikes in a reddit-like system of upvotes and downvotes, or display them as
separate tallies.

The `content` MAY be an emoji, or [NIP-30](30.md) custom emoji in this case it MAY be interpreted as a "like" or "dislike",
or the client MAY display this emoji reaction on the post. If the `content` is an empty string then the client should
consider it a "+".

Tags
----

The reaction event SHOULD include `e` and `p` tags from the note the user is
reacting to. This allows users to be notified of reactions to posts they were
mentioned in. Including the `e` tags enables clients to pull all the reactions
associated with individual posts or all the posts in a thread.

The last `e` tag MUST be the `id` of the note that is being reacted to. 

The last `p` tag MUST be the `pubkey` of the event being reacted to.

The reaction event MAY include a `k` tag with the stringified kind number
of the reacted event as its value.

Example code

```swift
func make_like_event(pubkey: String, privkey: String, liked: NostrEvent) -> NostrEvent {
    var tags: [[String]] = liked.tags.filter { 
    	tag in tag.count >= 2 && (tag[0] == "e" || tag[0] == "p") 
    }
    tags.append(["e", liked.id])
    tags.append(["p", liked.pubkey])
    tags.append(["k", liked.kind])
    let ev = NostrEvent(content: "+", pubkey: pubkey, kind: 7, tags: tags)
    ev.calculate_id()
    ev.sign(privkey: privkey)
    return ev
}
```

Custom Emoji Reaction
---------------------

The client may specify a custom emoji ([NIP-30](30.md)) `:shortcode:` in the
reaction content. The client should refer to the emoji tag and render the
content as an emoji if shortcode is specified.

```json
{
  "kind": 7,
  "content": ":soapbox:",
  "tags": [
    ["emoji", "soapbox", "https://gleasonator.com/emoji/Gleasonator/soapbox.png"]
  ],
  "pubkey": "79c2cae114ea28a981e7559b4fe7854a473521a8d22a66bbab9fa248eb820ff6",
  "created_at": 1682790000
}
```

The content can be set only one `:shortcode:`. And emoji tag should be one.