if module:get_host() ~= "*" then
    module:log("error", "mix_pam should be used on the user host!");
end

local jid = require("util.jid");
local st = require("util.stanza");

-- Persistent storage
local mix_pam = module:open_store("mix_pam", "keyval");

-- Runtime data
local mix_hosts = {};

-- Namespaceing
local mix_pam_xmlns = "urn:xmpp:mix:pam:2";

module:add_feature(mix_pam_xmlns);
-- NOTE: To show that we archive messages
-- module:add_feature(mix_pam_xmlns.."#archive");

function add_mix_host(host)
    if mix_hosts[host] ~= nil then
        mix_hosts[host] = mix_hosts[host] + 1;
        module:log("debug", "Known MIX host has a new user");
    else
        module:log("debug", "Added %s as a new MIX host", host);
        mix_hosts[host] = 1;
    end
end

function remove_mix_host(host)
    if mix_hosts[host] ~= nil then 
        local count = mix_hosts[host];
        if count == 1 then
            mix_hosts[host] = nil;
            module:log("debug", "Removing %s as a mix host", host);
        else
            mix_hosts[host] = count - 1;
            module:log("debug", "Decrementing %s's user counter", host);
        end
    else
        module:log("debug", "Attempt to remove unknown MIX host");
    end
end

function is_mix_host(host)
    return mix_hosts[host] ~= nil;
end

function is_mix_message(stanza)
    return stanza:get_child("mix", "urn:xmpp:mix:core:1") ~= nil;
end

function module.load()
    mix_hosts = mix_pam:get("hosts");
    module:log("info", "Loaded known MIX hosts");
    
    if mix_hosts == nil then
        module:log("info", "No known MIX hosts loaded");
        mix_hosts = {};
        return;
    end
    for _, host in pairs(mix_hosts) do
        module:log("debug", "Known host: %s", host);
    end
end

local client_state_tracker = {}; -- [stanza ID] -> resource
function add_state(id, resource)
    client_state_tracker[id] = resource;
    module:log("debug", "Adding a resource %s for id %s", resource, id);
end
function has_state(id)
    return client_state_tracker[id] ~= nil;
end
function pop_state(id)
    module:log("debug", "Popping a resource for stanza id %s", id);

    if has_state(id) then
        local resource = client_state_tracker[id];
        client_state_tracker[id] = nil;
        return resource;
    end

    return nil;
end

module:hook("iq/self", function(event)
    local stanza = event.stanza;
    if #stanza.tags == 0 then return; end

    if stanza:get_child("client-join", mix_pam_xmlns) ~= nil then
        return handle_client_join(event);
    elseif stanza:get_child("client-leave", mix_pam_xmlns) ~= nil then
        return handle_client_leave(event);
    end
end);

function handle_client_join(event)
    -- Client requests to join
    module:log("debug", "client-join received");
    local stanza, origin = event.stanza, event.origin;
    local from, to = jid.bare(stanza.attr.from), jid.bare(stanza.attr.to);
    
    local client_join = stanza:get_child("client-join", mix_pam_xmlns);
    if client_join.attr.channel == nil then
        origin.send(st.error_reply(stanza, "cancel", "bad-request", "No channel specified"));
        return true;
    end
    local join = client_join:get_child("join", "urn:xmpp:mix:core:1");
    if join == nil then
        origin.send(st.error_reply(stanza, "cancel", "bad-request", "No join stanza"));
        return true;
    end

    -- Transform the client-join into a join
    local join_iq = st.iq({ type = "set", from = jid.bare(stanza.attr.from), to = client_join.attr.channel, id = stanza.attr.id, xmlns = "jabber:client" });
    join_iq:add_child(join);
    
    add_state(stanza.attr.id, jid.resource(stanza.attr.from));

    module:send(join_iq);
    return true;
end

function handle_client_leave(event)
    -- Client requests to leave
    module:log("debug", "client-leave received");
    local stanza, origin = event.stanza, event.origin;
    local from, to = jid.bare(stanza.attr.from), jid.bare(stanza.attr.to);
    
    local client_leave = stanza:get_child("client-leave", mix_pam_xmlns);
    if client_leave.attr.channel == nil then
        origin.send(st.error_reply(stanza, "cancel", "bad-request", "No channel specified"));
        return true;
    end
    local leave = client_leave:get_child("leave", "urn:xmpp:mix:core:1");
    if leave == nil then
        origin.send(st.error_reply(stanza, "cancel", "bad-request", "No leave stanza"));
        return true;
    end

    -- Transform the client-join into a join
    local leave_iq = st.iq({ type = "set", from = jid.bare(stanza.attr.from), to = client_leave.attr.channel, id = stanza.attr.id });
    leave_iq:add_child(leave);

    add_state(stanza.attr.id, jid.resource(stanza.attr.from));

    module:send(leave_iq);
    return true;
end

module:hook("iq/bare", function(event)
    -- We handle the MIX results here since IQ stanzas against bare JIDs
    -- don't make a lot of sense. We first have to translate them into
    -- full JIDs based on our stanza ID -> resource mapping
    if event.stanza:get_child("leave", "urn:xmpp:mix:core:1") ~= nil then
        return handle_mix_leave(event);
    elseif event.stanza:get_child("join", "urn:xmpp:mix:core:1") ~= nil then
        return handle_mix_join(event);
    elseif has_state(event.stanza.attr.id) then
        local tmp = st.clone(event.stanza);
        tmp.attr.to = tmp.attr.to.."/"..pop_state(tmp.attr.id);
        module:send(tmp);
        return true;
    end
end);

function handle_mix_join(event)
    -- The MIX server responded
    -- TODO: Do stuff to the user's roster
    module:log("debug", "Received MIX-JOIN result");
    add_mix_host(jid.host(event.stanza.attr.from));
    mix_pam:set("hosts", mix_hosts);
    
    local stanza = event.stanza;
    local channel_jid = stanza:get_child("join", "urn:xmpp:mix:core:1").attr.id.."#"..stanza.attr.from;
    local resource = pop_state(stanza.attr.id);
    if resource == nil then
        module:log("error", "Got a MIX join result for a not-requested id %s. Maybe the MIX server changed the stanza ID?", stanza.attr.id);
        return false;
    end

    local client_join = st.iq({ type = "result", id = stanza.attr.id, from = jid.bare(stanza.attr.to), to = stanza.attr.to.."/"..resource })
        :tag("client-join", { xmlns = mix_pam_xmlns, jid = channel_jid });
    client_join:add_child(stanza:get_child("join", "urn:xmpp:mix:core:1"));
    module:send(client_join); 
    return true;
end

function handle_mix_leave(event)
    -- The MIX server responded
    -- TODO: Do stuff to the user's roster
    module:log("debug", "Received MIX-LEAVE result");
    remove_mix_host(jid.host(event.stanza.attr.from));
    mix_pam:set("hosts", mix_hosts);
   
    local stanza = event.stanza;
    local resource = pop_state(stanza.attr.id);
    if resource == nil then
        module:log("error", "Got a MIX leave result for a not-requested id %s. Maybe the MIX server changed the stanza ID?", stanza.attr.id);
        return false;
    end

    local client_leave = st.iq({ type = "result", id = stanza.attr.id, from = jid.bare(stanza.attr.to), to = stanza.attr.to.."/"..resource })
        :tag("client-leave", { xmlns = mix_pam_xmlns });
    client_leave:add_child(stanza:get_child("leave", "urn:xmpp:mix:core:1"));
    module:send(client_leave); 
    return true;
end

local user_resources = {}; -- [bare jid] -> array of bound resources

module:hook("resource-bind", function(event)
    local jid, resource = jid.bare(event.session.full_jid), event.session.resource;
    if user_resources[jid] ~= nil then
        for _, r in pairs(user_resources) do
            if r == resource then return; end
        end

        table.insert(user_resources[jid], resource);
    else
        user_resources[jid] = { resource };
    end

    module:log("debug", "Caught resource %s of %s", resource, jid);
end);

module:hook("resource-unbind", function(event)
    local jid, resource = jid.bare(event.session.full_jid), event.session.resource;
    for i, r in pairs(user_resources[jid]) do
        if r == resource then
            table.remove(user_resources[jid], i);
            return;
        end
    end

    module:log("debug", "Unbind of not recorded resource %s (%s)", resource, jid);
end);

module:hook("message/bare", function(event)
    local stanza = event.stanza;
    local host = jid.host(stanza.attr.from);
    if not is_mix_host(host) then return; end
    if not is_mix_message(stanza) then return; end
  
    -- MIX-CORE says that if the message cannot be delivered, it should
    -- just be dropped
    if user_resources[stanza.attr.to] == nil then
        module:log("debug", "Skipping %s: No resource bound", stanza.attr.to);
        return true;
    end

    -- Per XEP we know that stanza.attr.to is the user's bare JID
    for _, resource in pairs(user_resources[stanza.attr.to]) do
        -- TODO: Only send to resources that advertise support for MIX (When MIX clients are available for testing)
        local msg = st.clone(stanza);
        msg.attr.to = stanza.attr.to.."/"..resource;
        module:send(msg);
        module:log("debug", "Sent message to %s", msg.attr.to);
    end
    return true;
end);