From c914ac99b4e39110bca1203b4d12e9078d406656 Mon Sep 17 00:00:00 2001
From: Nev3r <apophycens@gmail.com>
Date: Wed, 29 Jul 2020 17:26:43 +0200
Subject: [PATCH] Bring back P_FindSpecialLineFromTag() for backwards
 compatibility reasons; emulate the old taglist behavior for this function.

---
 src/lua_baselib.c | 13 +++++++++++++
 src/taglist.c     | 42 ++++++++++++++++++++++++++++++++++++++++++
 src/taglist.h     |  3 ++-
 3 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/src/lua_baselib.c b/src/lua_baselib.c
index a8a45ba20..5d1db5641 100644
--- a/src/lua_baselib.c
+++ b/src/lua_baselib.c
@@ -32,6 +32,7 @@
 #include "lua_script.h"
 #include "lua_libs.h"
 #include "lua_hud.h" // hud_running errors
+#include "taglist.h" // P_FindSpecialLineFromTag
 
 #define NOHUD if (hud_running)\
 return luaL_error(L, "HUD rendering code should not call this function!");
@@ -2094,6 +2095,17 @@ static int lib_pFindHighestCeilingSurrounding(lua_State *L)
 	return 1;
 }
 
+static int lib_pFindSpecialLineFromTag(lua_State *L)
+{
+	INT16 special = (INT16)luaL_checkinteger(L, 1);
+	INT16 line = (INT16)luaL_checkinteger(L, 2);
+	INT32 start = (INT32)luaL_optinteger(L, 3, -1);
+	NOHUD
+	INLEVEL
+	lua_pushinteger(L, P_FindSpecialLineFromTag(special, line, start));
+	return 1;
+}
+
 static int lib_pSwitchWeather(lua_State *L)
 {
 	INT32 weathernum = (INT32)luaL_checkinteger(L, 1);
@@ -3581,6 +3593,7 @@ static luaL_Reg lib[] = {
 	{"P_FindNextLowestFloor",lib_pFindNextLowestFloor},
 	{"P_FindLowestCeilingSurrounding",lib_pFindLowestCeilingSurrounding},
 	{"P_FindHighestCeilingSurrounding",lib_pFindHighestCeilingSurrounding},
+	{"P_FindSpecialLineFromTag",lib_pFindSpecialLineFromTag},
 	{"P_SwitchWeather",lib_pSwitchWeather},
 	{"P_LinedefExecute",lib_pLinedefExecute},
 	{"P_SpawnLightningFlash",lib_pSpawnLightningFlash},
diff --git a/src/taglist.c b/src/taglist.c
index 2c1ac85d7..7fd2601c7 100644
--- a/src/taglist.c
+++ b/src/taglist.c
@@ -284,6 +284,48 @@ INT32 Tag_FindLineSpecial(const INT16 special, const mtag_t tag)
 	return -1;
 }
 
+/// Backwards compatibility iteration function for Lua scripts.
+INT32 P_FindSpecialLineFromTag(INT16 special, INT16 tag, INT32 start)
+{
+	if (tag == -1)
+	{
+		start++;
+
+		if (start >= (INT32)numlines)
+			return -1;
+
+		while (start < (INT32)numlines && lines[start].special != special)
+			start++;
+
+		return start;
+	}
+	else
+	{
+		size_t p = 0;
+		INT32 id;
+
+		// For backwards compatibility's sake, simulate the old linked taglist behavior:
+		// Iterate through the taglist and find the "start" line's position in the list,
+		// And start checking with the next one (if it exists).
+		if (start != -1)
+		{
+			for (; (id = Tag_Iterate_Lines(tag, p)) >= 0; p++)
+				if (id == start)
+				{
+					p++;
+					break;
+				}
+		}
+
+		for (; (id = Tag_Iterate_Lines(tag, p)) >= 0; p++)
+			if (lines[id].special == special)
+				return id;
+
+		return -1;
+	}
+}
+
+
 // Ingame list manipulation.
 
 void Tag_SectorFSet (const size_t id, const mtag_t tag)
diff --git a/src/taglist.h b/src/taglist.h
index d1acff6cb..7c3b4ad52 100644
--- a/src/taglist.h
+++ b/src/taglist.h
@@ -44,7 +44,8 @@ INT32 Tag_Iterate_Sectors (const mtag_t tag, const size_t p);
 INT32 Tag_Iterate_Lines (const mtag_t tag, const size_t p);
 INT32 Tag_Iterate_Things (const mtag_t tag, const size_t p);
 
-INT32 Tag_FindLineSpecial(const INT16 special, const INT16 tag);
+INT32 Tag_FindLineSpecial(const INT16 special, const mtag_t tag);
+INT32 P_FindSpecialLineFromTag(INT16 special, INT16 tag, INT32 start);
 
 #define TAG_ITER_C size_t kkkk;
 #define TAG_ITER(fn, tag, id) for(kkkk = 0; (id = fn(tag, kkkk)) >= 0; kkkk++)