module:depends("muc");

local jid_resource = require "util.jid".resource;

local prefixes = module:get_option("muc_inject_mentions_prefixes", nil)

local suffixes = module:get_option("muc_inject_mentions_suffixes", nil)

local enabled_rooms = module:get_option("muc_inject_mentions_enabled_rooms", nil)

local disabled_rooms = module:get_option("muc_inject_mentions_disabled_rooms", nil)

local reference_xmlns = "urn:xmpp:reference:0"

local function is_room_eligible(jid)

    if not enabled_rooms and not disabled_rooms then

        return true;

    end

    if enabled_rooms and not disabled_rooms then

        for _, _jid in ipairs(enabled_rooms) do

            if _jid == jid then

                return true

            end

        end

        return false

    end

    if disabled_rooms and not enabled_rooms then

        for _, _jid in ipairs(disabled_rooms) do

            if _jid == jid then

                return false

            end

        end

        return true

    end

    return true

end

local function has_nick_prefix(body, first)

    -- There is no prefix

    -- but mention could still be valid

    if first == 1 then return true end

    -- There are no configured prefixes

    if not prefixes or #prefixes < 1 then return false end

    -- Preffix must have a space before it,

    -- be the first character of the body

    -- or be the first character after a new line

    if body:sub(first - 2, first - 2) ~= "" and

        body:sub(first - 2, first - 2) ~= " " and

        body:sub(first - 2, first - 2) ~= "\n"

    then

        return false

    end

    local preffix = body:sub(first - 1, first - 1)

    for _, _preffix in ipairs(prefixes) do

        if preffix == _preffix then

            return true

        end

    end

    return false

end

local function has_nick_suffix(body, last)

    -- There is no suffix

    -- but mention could still be valid

    if last == #body then return true end

    -- There are no configured suffixes

    if not suffixes or #suffixes < 1 then return false end

    -- Suffix must have a space after it,

    -- be the last character of the body

    -- or be the last character before a new line

    if body:sub(last + 2, last + 2) ~= "" and

        body:sub(last + 2, last + 2) ~= " " and

        body:sub(last + 2, last + 2) ~= "\n"

    then

        return false

    end

    local suffix = body:sub(last+1, last+1)

    for _, _suffix in ipairs(suffixes) do

        if suffix == _suffix then

            return true

        end

    end

    return false

end

local function search_mentions(room, stanza)

    local body = stanza:get_child("body"):get_text();

    local mentions = {}

    for _, occupant in pairs(room._occupants) do

        local nick = jid_resource(occupant.nick);

        -- Check for multiple mentions to the same nickname in a message

        -- Hey @nick remember to... Ah, also @nick please let me know if...

        local matches = {}

        local _first

        local _last = 0

        while true do

            -- Use plain search as nick could contain

            -- characters used in Lua patterns

            _first, _last = body:find(nick, _last + 1, true)

            if _first == nil then break end

            table.insert(matches, {first=_first, last=_last})

        end

        -- Filter out intentional mentions from unintentional ones

        for _, match in ipairs(matches) do

            local bare_jid = occupant.bare_jid

            local first, last = match.first, match.last

            -- Body only contains nickname

            if first == 1 and last == #body then

                table.insert(mentions, {bare_jid=bare_jid, first=first, last=last})

            -- Nickname between spaces

            elseif body:sub(first - 1, first - 1) == " " and

                body:sub(last + 1, last + 1) == " "

            then

                table.insert(mentions, {bare_jid=bare_jid, first=first, last=last})

            else

                -- Check if occupant is mentioned using affixes

                local has_preffix = has_nick_prefix(body, first)

                local has_suffix = has_nick_suffix(body, last)

                -- @nickname: ...

                if has_preffix and has_suffix then

                    table.insert(mentions, {bare_jid=bare_jid, first=first, last=last})

                -- @nickname ...

                elseif has_preffix and not has_suffix then

                    if body:sub(last + 1, last + 1) == " " or

                        body:sub(last + 1, last + 1) == "\n"

                    then

                        table.insert(mentions, {bare_jid=bare_jid, first=first, last=last})

                    end

                -- nickname: ...

                elseif not has_preffix and has_suffix then

                        table.insert(mentions, {bare_jid=bare_jid, first=first, last=last})

                    end

                end

            end

        end

    end

    return mentions

end

local function muc_inject_mentions(event)

    local room, stanza = event.room, event.stanza;

    -- Inject mentions only if the room is configured for them

    if not is_room_eligible(room.jid) then return; end

    -- Only act on messages that do not include references.

    -- If references are found, it is assumed the client has mentions support

    if stanza:get_child("reference", reference_xmlns) then return; end

    local mentions = search_mentions(room, stanza)

    for _, mention in ipairs(mentions) do

        -- https://xmpp.org/extensions/xep-0372.html#usecase_mention

        stanza:tag(

            "reference", {

                xmlns=reference_xmlns,

                begin=tostring(mention.first - 1), -- count starts at 0

                ["end"]=tostring(mention.last - 1),

                type="mention",

                uri="xmpp:" .. mention.bare_jid,

            }

        ):up()

    end

end

module:hook("muc-occupant-groupchat", muc_inject_mentions)