local st = require "prosody.util.stanza";
local jid_bare = require "prosody.util.jid".bare;

local xmlns_privilege = "urn:xmpp:privilege:2";
local xmlns_forward = "urn:xmpp:forward:0";
local xmlns_carbons = "urn:xmpp:carbons:2";
local bare_sessions = prosody.bare_sessions;

local allowed_component_jid = module:get_option_string("privileged_entity_jid");

module:log("info", "mod_privileged_carbons loaded for host=%s privileged_entity_jid=%s", module.host or "?", allowed_component_jid or "");

local function iter_sessions(user_sessions)
	if not user_sessions or not user_sessions.sessions then
		return function() return nil end;
	end
	return pairs(user_sessions.sessions);
end

local function unwrap_forwarded_message(stanza)
	local privilege = stanza:get_child("privilege", xmlns_privilege);
	if not privilege then
		return nil;
	end
	local forwarded = privilege:get_child("forwarded", xmlns_forward);
	if not forwarded then
		return nil;
	end
	for _, tag in ipairs(forwarded.tags or {}) do
		if tag.name == "message" then
			return tag;
		end
	end
	return nil;
end

local function is_carbon_delivery(inner)
	if not inner then
		return false;
	end
	return inner:get_child("sent", xmlns_carbons) ~= nil
		or inner:get_child("received", xmlns_carbons) ~= nil;
end

local function build_sent_carbon(inner, user_bare)
	local function rebuild_stanza(node)
		if type(node) ~= "table" or not node.name then
			return node;
		end
		local attr = {};
		for k, v in pairs(node.attr or {}) do
			attr[k] = v;
		end
		local rebuilt = st.stanza(node.name, attr);
		for _, child in ipairs(node) do
			if type(child) == "table" and child.name then
				rebuilt:add_direct_child(rebuild_stanza(child));
			elseif type(child) == "string" then
				rebuilt:add_direct_child(child);
			end
		end
		return rebuilt;
	end
	local copy = rebuild_stanza(inner);
	local function normalize_client_ns(node)
		if not node then
			return;
		end
		if node.attr then
			if node.attr.xmlns == nil or node.attr.xmlns == "jabber:component:accept" then
				node.attr.xmlns = "jabber:client";
			end
		end
		if node.tags then
			for _, child in ipairs(node.tags) do
				normalize_client_ns(child);
			end
		end
	end
	normalize_client_ns(copy);
	return st.message({ from = user_bare, type = inner.attr.type or "chat", xmlns = "jabber:client" })
		:tag("sent", { xmlns = xmlns_carbons })
			:tag("forwarded", { xmlns = xmlns_forward })
				:add_child(copy):reset();
end

local function deliver_carbon_to_user_sessions(bare_jid, inner)
	local user_sessions = bare_sessions[bare_jid];
	if not user_sessions then
		module:log("debug", "Privileged carbon skipped for offline user %s", bare_jid);
		return true;
	end
	local carbon = build_sent_carbon(inner, bare_jid);
	local delivered = false;
	for _, session in iter_sessions(user_sessions) do
		if session.full_jid and session.send then
			local copy = st.clone(carbon);
			copy.attr.xmlns = "jabber:client";
			copy.attr.to = session.full_jid;
			session.rawsend(tostring(copy));
			delivered = true;
		end
	end
	module:log("info", "Privileged carbon delivered user=%s delivered=%s", bare_jid, tostring(delivered));
	return true;
end

local function handle_privileged_carbon(event)
	local origin, stanza = event.origin, event.stanza;
	if not origin or origin.type ~= "component" then
		return nil;
	end
	if allowed_component_jid and allowed_component_jid ~= "" and origin.host ~= allowed_component_jid then
		module:log("debug", "Ignoring privileged message from unexpected component %s", origin.host or "?");
		return nil;
	end

	local inner = unwrap_forwarded_message(stanza);
	if not inner then
		module:log("debug", "Ignoring privileged message without forwarded payload from %s", origin.host or "?");
		return nil;
	end

	local bare_from = jid_bare(inner.attr.from);
	if not bare_from or bare_from == "" then
		module:log("warn", "Rejected malformed privileged carbon from %s", origin.host or "?");
		return true;
	end
	if bare_from:match("@(.+)$") ~= module.host then
		module:log("debug", "Ignoring privileged carbon for remote host %s", bare_from);
		return nil;
	end

	return deliver_carbon_to_user_sessions(bare_from, inner);
end

module:hook("pre-message/host", handle_privileged_carbon, 10);
module:hook("message/host", handle_privileged_carbon, 10);