module S1AP_Server {

/* S1AP Server, runs on top of S1AP_CodecPort, accepting the S1AP
 * connections and forwarding S1AP PDUs to/from the ConnHdlr components.
 * A ConnHdlr component may subscribe for one or more S1AP connections
 * using the Global_ENB_ID value, which is sent in S1AP SetupReq.
 *
 * (C) 2024 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
 * Author: Vadim Yanitskiy <vyanitskiy@sysmocom.de>
 *
 * All rights reserved.
 *
 * Released under the terms of GNU General Public License, Version 2 or
 * (at your option) any later version.
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

import from General_Types all;
import from Osmocom_Types all;
import from IPL4asp_Types all;

import from S1AP_CodecPort all;
import from S1AP_CodecPort_CtrlFunct all;
import from S1AP_Types all;
import from S1AP_Constants all;
import from S1AP_PDU_Contents all;
import from S1AP_PDU_Descriptions all;
import from S1AP_IEs all;
import from S1AP_Templates all;

type enumerated S1APSRV_Event {
	S1APSRV_EVENT_CONN_UP,
	S1APSRV_EVENT_CONN_DOWN
};

type port S1APSRV_CONN_PT message {
	inout S1AP_PDU, S1APSRV_Event;
} with { extension "internal" };

type component S1APSRV_ConnHdlr {
	port S1APSRV_CONN_PT S1AP_CONN;
	port S1APSRV_PROC_PT S1AP_PROC;
};

type record S1APSRV_ConnParams {
	HostName local_ip,
	PortNumber local_port
};

type component S1AP_Server_CT {
	/* port facing to the SUT */
	port S1AP_CODEC_PT S1AP;
	/* all S1APSRV_ConnHdlr S1AP ports connect here */
	port S1APSRV_CONN_PT S1AP_CLIENT;
	/* procedure based port to register for incoming connections */
	port S1APSRV_PROC_PT S1AP_PROC;

	/* active eNB connections */
	var ConnList g_conn_list;
	/* registered ConnHdlr */
	var ConnHdlrList g_conn_hdlr_list;

	var S1APSRV_ConnParams g_cpars;
	var ConnectionId g_s1ap_conn_id := -1;
};


/* represents a single eNB connection */
private type record ConnData {
	ConnectionId conn_id,
	Global_ENB_ID genb_id /* can be unbound */
};
private type record of ConnData ConnList;

/* represents a single ConnHdlr item */
private type record ConnHdlrData {
	S1APSRV_ConnHdlr vc_conn,
	Global_ENB_ID genb_id,
	ConnectionId conn_id /* can be -1 */
};
private type record of ConnHdlrData ConnHdlrList;

private template (present) S1AP_RecvFrom
tr_S1AP_RecvFrom_R(template (present) S1AP_PDU msg := ?,
		   template (present) ConnectionId conn_id := ?) := {
	connId := conn_id,
	remName := ?,
	remPort := ?,
	locName := ?,
	locPort := ?,
	msg := msg
};

const SctpTuple c_SctpTuple_S1AP := {
	sinfo_stream := omit,
	sinfo_ppid := 18, /* S1AP */
	remSocks := omit,
	assocId := omit
};

/***********************************************************************************
 * Connection management API
 **********************************************************************************/

/* find a connection [index] by a connection ID */
private function f_conn_find_by_conn_id(ConnectionId conn_id)
runs on S1AP_Server_CT return integer {
	for (var integer i := 0; i < lengthof(g_conn_list); i := i + 1) {
		if (g_conn_list[i].conn_id == conn_id) {
			return i;
		}
	}

	return -1;
}

/* find a connection [index] by a global eNB ID */
private function f_conn_find_by_genb_id(Global_ENB_ID genb_id)
runs on S1AP_Server_CT return integer {
	for (var integer i := 0; i < lengthof(g_conn_list); i := i + 1) {
		if (isbound(g_conn_list[i].genb_id) and
		    g_conn_list[i].genb_id == genb_id) {
			return i;
		}
	}

	return -1;
}

/* add a new connection, return its index */
private function f_conn_add(ConnectionId conn_id)
runs on S1AP_Server_CT return integer {
	var ConnData conn := { conn_id, - };
	var integer idx;

	if (f_conn_find_by_conn_id(conn_id) != -1) {
		setverdict(fail, "Connection (id=", conn_id, ") is already added");
		mtc.stop;
	}

	idx := lengthof(g_conn_list);
	g_conn_list := g_conn_list & { conn };
	log("Connection (id=", conn_id, ") is registered");

	return idx;
}

/* del an existing connection */
private function f_conn_del(ConnectionId conn_id)
runs on S1AP_Server_CT {
	var ConnList conn_list := { };

	for (var integer i := 0; i < lengthof(g_conn_list); i := i + 1) {
		if (g_conn_list[i].conn_id == conn_id) {
			if (isbound(g_conn_list[i].genb_id)) {
				f_ConnHdlr_update(g_conn_list[i].genb_id, -1);
			}
		} else {
			conn_list := conn_list & { g_conn_list[i] };
		}
	}

	if (lengthof(conn_list) == lengthof(g_conn_list)) {
		setverdict(fail, "Connection (id=", conn_id, ") is not known");
		mtc.stop;
	}

	g_conn_list := conn_list;
	log("Connection (id=", conn_id, ") is deleted");
}

/* add a new connection, return its index */
private function f_conn_set_genb_id(ConnectionId conn_id, Global_ENB_ID genb_id)
runs on S1AP_Server_CT {
	var integer idx;

	if (f_conn_find_by_genb_id(genb_id) != -1) {
		setverdict(fail, "Duplicate Global eNB ID ", genb_id);
		mtc.stop;
	}

	idx := f_conn_find_by_conn_id(conn_id);
	if (idx == -1) {
		setverdict(fail, "Connection (id=", conn_id, ") is not known");
		mtc.stop;
	}

	g_conn_list[idx].genb_id := genb_id;

	f_ConnHdlr_update(genb_id, conn_id);
}

private function f_conn_close(ConnectionId conn_id)
runs on S1AP_Server_CT {
	log("Closing an eNB connection (id=", conn_id, ")");
	S1AP_CodecPort_CtrlFunct.f_IPL4_close(S1AP, conn_id,
					      { sctp := c_SctpTuple_S1AP });
	f_conn_del(conn_id);
}

private function f_conn_close_by_genb_id(Global_ENB_ID genb_id)
runs on S1AP_Server_CT {
	var integer idx;

	idx := f_conn_find_by_genb_id(genb_id);
	if (idx == -1) {
		setverdict(fail, "There is no connection for Global eNB ID ", genb_id);
		mtc.stop;
	}

	f_conn_close(g_conn_list[idx].conn_id);
}

/***********************************************************************************
 * ConnHdlr management API
 **********************************************************************************/

/* find a ConnHdlr [index] by a connection ID */
private function f_ConnHdlr_find_by_conn_id(ConnectionId conn_id)
runs on S1AP_Server_CT return integer {
	for (var integer i := 0; i < lengthof(g_conn_hdlr_list); i := i + 1) {
		if (g_conn_hdlr_list[i].conn_id == conn_id) {
			return i;
		}
	}

	return -1;
}

/* find a ConnHdlr [index] by a global eNB ID */
private function f_ConnHdlr_find_by_genb_id(Global_ENB_ID genb_id)
runs on S1AP_Server_CT return integer {
	for (var integer i := 0; i < lengthof(g_conn_hdlr_list); i := i + 1) {
		if (g_conn_hdlr_list[i].genb_id == genb_id) {
			return i;
		}
	}

	return -1;
}

/* find a ConnHdlr [index] by a component reference */
private function f_ConnHdlr_find_by_vc_conn(S1APSRV_ConnHdlr vc_conn)
runs on S1AP_Server_CT return integer {
	for (var integer i := 0; i < lengthof(g_conn_hdlr_list); i := i + 1) {
		if (g_conn_hdlr_list[i].vc_conn == vc_conn) {
			return i;
		}
	}

	return -1;
}

private function f_ConnHdlr_add(S1APSRV_ConnHdlr vc_conn, Global_ENB_ID genb_id)
runs on S1AP_Server_CT {
	var ConnectionId conn_id := -1;
	var integer idx;

	if (f_ConnHdlr_find_by_genb_id(genb_id) != -1) {
		setverdict(fail, "Global eNB ID ", genb_id, " is already registered");
		mtc.stop;
	}

	idx := f_conn_find_by_genb_id(genb_id);
	if (idx != -1) {
		conn_id := g_conn_list[idx].conn_id;
	}

	g_conn_hdlr_list := g_conn_hdlr_list & { {vc_conn, genb_id, conn_id} };
	log("Global eNB ID ", genb_id, " has been registered");
}

private function f_ConnHdlr_del(integer idx)
runs on S1AP_Server_CT {
	var ConnHdlrList conn_hdlr_list := { };

	for (var integer i := 0; i < lengthof(g_conn_hdlr_list); i := i + 1) {
		if (i != idx) {
			conn_hdlr_list := conn_hdlr_list & { g_conn_hdlr_list[i] };
		}
	}

	g_conn_hdlr_list := conn_hdlr_list;
}

private function f_ConnHdlr_del_by_genb_id(Global_ENB_ID genb_id)
runs on S1AP_Server_CT {
	var integer idx;

	idx := f_ConnHdlr_find_by_genb_id(genb_id);
	if (idx == -1) {
		setverdict(fail, "Global eNB ID ", genb_id, " is not registered");
		mtc.stop;
	}

	f_ConnHdlr_del(idx);
	log("Global eNB ID ", genb_id, " has been unregistered");
}

private function f_ConnHdlr_update(Global_ENB_ID genb_id, ConnectionId conn_id)
runs on S1AP_Server_CT {
	for (var integer i := 0; i < lengthof(g_conn_hdlr_list); i := i + 1) {
		if (g_conn_hdlr_list[i].genb_id == genb_id) {
			g_conn_hdlr_list[i].conn_id := conn_id;
			/* notify the ConnHdlr about connection state */
			var S1APSRV_Event ev;
			if (conn_id == -1) {
				ev := S1APSRV_EVENT_CONN_DOWN;
			} else {
				ev := S1APSRV_EVENT_CONN_UP;
			}
			S1AP_CLIENT.send(ev) to g_conn_hdlr_list[i].vc_conn;
		}
	}
}

signature S1APSRV_register(in S1APSRV_ConnHdlr vc_conn, in Global_ENB_ID genb_id);
signature S1APSRV_unregister(in S1APSRV_ConnHdlr vc_conn, in Global_ENB_ID genb_id);
signature S1APSRV_close_conn(in S1APSRV_ConnHdlr vc_conn, in Global_ENB_ID genb_id);

type port S1APSRV_PROC_PT procedure {
	inout S1APSRV_register;
	inout S1APSRV_unregister;
	inout S1APSRV_close_conn;
} with { extension "internal" };

function f_ConnHdlr_register(Global_ENB_ID genb_id)
runs on S1APSRV_ConnHdlr {
	S1AP_PROC.call(S1APSRV_register:{self, genb_id}) {
		[] S1AP_PROC.getreply(S1APSRV_register:{?, ?}) { };
	}
}

function f_ConnHdlr_unregister(Global_ENB_ID genb_id)
runs on S1APSRV_ConnHdlr {
	S1AP_PROC.call(S1APSRV_unregister:{self, genb_id}) {
		[] S1AP_PROC.getreply(S1APSRV_unregister:{?, ?}) { };
	}
}

function f_ConnHdlr_close_conn(Global_ENB_ID genb_id)
runs on S1APSRV_ConnHdlr {
	S1AP_PROC.call(S1APSRV_close_conn:{self, genb_id}) {
		[] S1AP_PROC.getreply(S1APSRV_close_conn:{?, ?}) { };
	}
}

function main(S1APSRV_ConnParams cpars) runs on S1AP_Server_CT {
	var Result res;

	g_cpars := cpars;
	g_conn_list := { };
	g_conn_hdlr_list := { };

	map(self:S1AP, system:S1AP_CODEC_PT);
	res := S1AP_CodecPort_CtrlFunct.f_IPL4_listen(S1AP,
						      cpars.local_ip, cpars.local_port,
						      { sctp := c_SctpTuple_S1AP });
	if (not ispresent(res.connId)) {
		setverdict(fail, "Could not create an S1AP socket, check your configuration");
		mtc.stop;
	}
	g_s1ap_conn_id := res.connId;

	log("SCTP server listening on ", cpars.local_ip, ":", cpars.local_port);

	while (true) {
		var S1APSRV_ConnHdlr vc_conn;
		var S1AP_RecvFrom mrf;
		var S1AP_PDU msg;

		var Global_ENB_ID genb_id;
		var PortEvent pev;

		alt {
		/* S1AP PDU from a peer (eNB) */
		[] S1AP.receive(tr_S1AP_RecvFrom_R) -> value mrf {
			if (match(mrf.msg, tr_S1AP_SetupReq)) {
				genb_id := mrf.msg.initiatingMessage.value_.S1SetupRequest.protocolIEs[0].value_.Global_ENB_ID;
				f_conn_set_genb_id(mrf.connId, genb_id);
			}
			var integer idx := f_ConnHdlr_find_by_conn_id(mrf.connId);
			if (idx != -1) {
				S1AP_CLIENT.send(mrf.msg) to g_conn_hdlr_list[idx].vc_conn;
			} /* else: no ConnHdlr, drop PDU */
			}
		/* S1AP PDU from a ConnHdlr: pass on transparently */
		[] S1AP_CLIENT.receive(S1AP_PDU:?) -> value msg sender vc_conn {
			var integer idx := f_ConnHdlr_find_by_vc_conn(vc_conn);
			if (idx == -1) {
				setverdict(fail, "Component ", vc_conn, " is not registered");
				mtc.stop;
			}
			if (g_conn_hdlr_list[idx].conn_id == -1) {
				setverdict(fail, "S1AP connection is not up");
				mtc.stop;
			}
			S1AP.send(t_S1AP_Send(g_conn_hdlr_list[idx].conn_id, msg));
			}

		/* connection opened/closed events */
		[] S1AP.receive(PortEvent:{connOpened := ?}) -> value pev {
			log("eNB connection (id=", pev.connOpened.connId, ", ",
			    pev.connOpened.remName, ":", pev.connOpened.remPort, ") ",
			    "established");
			f_conn_add(pev.connOpened.connId);
			}
		[] S1AP.receive(PortEvent:{connClosed := ?}) -> value pev {
			log("eNB connection (id=", pev.connClosed.connId, ", ",
			    pev.connClosed.remName, ":", pev.connClosed.remPort, ") ",
			    "closed");
			f_conn_del(pev.connClosed.connId);
			}

		/* SCTP events we don't care about */
		[] S1AP.receive(PortEvent:{sctpEvent := ?}) { }

		/* ConnHdlr registration/unregistration */
		[] S1AP_PROC.getcall(S1APSRV_register:{?, ?}) -> param(vc_conn, genb_id) {
			f_ConnHdlr_add(vc_conn, genb_id);
			S1AP_PROC.reply(S1APSRV_register:{vc_conn, genb_id}) to vc_conn;
			}
		[] S1AP_PROC.getcall(S1APSRV_unregister:{?, ?}) -> param(vc_conn, genb_id) {
			f_ConnHdlr_del_by_genb_id(genb_id);
			S1AP_PROC.reply(S1APSRV_unregister:{vc_conn, genb_id}) to vc_conn;
			}
		[] S1AP_PROC.getcall(S1APSRV_close_conn:{?, ?}) -> param(vc_conn, genb_id) {
			f_conn_close_by_genb_id(genb_id);
			S1AP_PROC.reply(S1APSRV_close_conn:{vc_conn, genb_id}) to vc_conn;
			}
		}
	}
}

}