From b1c1256891ca6209f52cbb0bc64d0b1902c6469f Mon Sep 17 00:00:00 2001
From: Fabian Greffrath <fabian@greffrath.com>
Date: Mon, 27 Mar 2023 15:19:16 +0200
Subject: [PATCH] check if drag-n-dropped .lmp files could be demo lumps (#960)

and pass them to the -playdemo parameter if appropriate.
---
 src/d_main.c | 107 ++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 102 insertions(+), 5 deletions(-)

diff --git a/src/d_main.c b/src/d_main.c
index 2634d5e6..82f86231 100644
--- a/src/d_main.c
+++ b/src/d_main.c
@@ -1223,14 +1223,91 @@ enum
     FILETYPE_IWAD =    0x2,
     FILETYPE_PWAD =    0x4,
     FILETYPE_DEH =     0x8,
+    FILETYPE_DEMO =    0x10,
 };
 
+static boolean FileIsDemoLump(const char *filename)
+{
+    FILE *handle;
+    int count, ver;
+    byte buf[32], *p = buf;
+
+    handle = M_fopen(filename, "rb");
+
+    if (handle == NULL)
+    {
+        return false;
+    }
+
+    count = fread(buf, 1, sizeof(buf), handle);
+    fclose(handle);
+
+    if (count != sizeof(buf))
+    {
+        return false;
+    }
+
+    ver = *p++;
+
+    if (ver == 255) // skip UMAPINFO demo header
+    {
+        p += 26;
+        ver = *p++;
+    }
+
+    if (ver >= 0 && ver <= 4) // v1.0/v1.1/v1.2
+    {
+        p--;
+    }
+    else
+    {
+        switch (ver)
+        {
+            case 104: // v1.4
+            case 105: // v1.5
+            case 106: // v1.6/v1.666
+            case 107: // v1.7/v1.7a
+            case 108: // v1.8
+            case 109: // v1.9
+            case 111: // v1.91 hack
+                break;
+            case 200: // Boom
+            case 201:
+            case 202:
+            case 203: // MBF
+                p += 7; // skip signature and compatibility flag
+                break;
+            case 221: // MBF21
+                p += 6; // skip signature
+                break;
+            default:
+                return false;
+                break;
+        }
+    }
+
+    if (*p++ > 5) // skill
+    {
+        return false;
+    }
+    if (*p++ > 9) // episode
+    {
+        return false;
+    }
+    if (*p++ > 99) // map
+    {
+        return false;
+    }
+
+    return true;
+}
+
 static int GuessFileType(const char *name)
 {
     int ret = FILETYPE_UNKNOWN;
     const char *base;
     char *lower;
-    static boolean iwad_found = false;
+    static boolean iwad_found = false, demo_found = false;
 
     base = M_BaseName(name);
     lower = M_StringDuplicate(base);
@@ -1244,11 +1321,24 @@ static int GuessFileType(const char *name)
         iwad_found = true;
     }
     else if (M_StringEndsWith(lower, ".wad") ||
-             M_StringEndsWith(lower, ".lmp") ||
              M_StringEndsWith(lower, ".zip"))
     {
         ret = FILETYPE_PWAD;
     }
+    else if (M_StringEndsWith(lower, ".lmp"))
+    {
+        // only ever add one argument to the -playdemo parameter
+
+        if (demo_found == false && FileIsDemoLump(name))
+        {
+            ret = FILETYPE_DEMO;
+            demo_found = true;
+        }
+        else
+        {
+            ret = FILETYPE_PWAD;
+        }
+    }
     else if (M_StringEndsWith(lower, ".deh") ||
              M_StringEndsWith(lower, ".bex"))
     {
@@ -1287,10 +1377,11 @@ static void M_AddLooseFiles(void)
         return;
     }
 
-    // allocate space for up to three additional regular parameters
+    // allocate space for up to four additional regular parameters
+    // (-iwad, -merge, -deh, -playdemo)
 
-    arguments = malloc((myargc + 3) * sizeof(*arguments));
-    memset(arguments, 0, (myargc + 3) * sizeof(*arguments));
+    arguments = malloc((myargc + 4) * sizeof(*arguments));
+    memset(arguments, 0, (myargc + 4) * sizeof(*arguments));
 
     // check the command line and make sure it does not already
     // contain any regular parameters or response files
@@ -1340,6 +1431,12 @@ static void M_AddLooseFiles(void)
         arguments[myargc].type = FILETYPE_DEH - 1;
         myargc++;
     }
+    if (types & FILETYPE_DEMO)
+    {
+        arguments[myargc].str = M_StringDuplicate("-playdemo");
+        arguments[myargc].type = FILETYPE_DEMO - 1;
+        myargc++;
+    }
 
     newargv = malloc(myargc * sizeof(*newargv));