GitSigns: Implement "One Fat Diff" option

Depending on the original file it was possible for the diff to fail.
This happened specifically when a chunk's anchor line was over 80
characters long. In this case git's unified diff output shortens the
chunk's anchor line.

Since the script was searching for a subtitle line identical to the
chunk's anchor line, this would fail.

This introduces an option to bypass looking for the anchor line by
having the diff just be one huge chunk instead of invididual chunks per
change (±2 lines).

Note we're intentionally not saving the one_fat_diff variable because
it's supposed to be an intentional choice, not a default when it was
used once.

Author: mihawk90

macros/arch.GitSigns.moon

@@ -1,6 +1,6 @@
 export script_name = "Git Signs"
 export script_description = "Displays git diffs in Aegisub"
-export script_version = "0.2.4"
+export script_version = "0.3.0"
 export script_namespace = "arch.GitSigns"
 export script_author = "arch1t3cht"
 
@@ -45,13 +45,16 @@ check_has_git = () ->
     return has_git
 
 
-get_git_diff = (ref) ->
+get_git_diff = (ref, subs, one_fat_diff) ->
     dir = aegisub.decode_path("?script")
     if dir == "?script"
         aegisub.log("File isn't saved! Aborting.")
         aegisub.cancel()
 
-    handle = io.popen("#{get_git()} -C \"#{dir}\" diff --raw -p \"#{ref}\" \"#{aegisub.file_name()}\"")
+    local git_u_arg
+    if one_fat_diff == true
+        git_u_arg = "--unified=#{#subs}"
+    handle = io.popen("#{get_git()} -C \"#{dir}\" diff --raw #{git_u_arg} -p \"#{ref}\" \"#{aegisub.file_name()}\"")
     return handle\read("*a")
 
 
@@ -138,7 +141,7 @@ show_diff_lines = (subs, diff, show_before) ->
                         break
 
                 if offset == nil
-                    aegisub.log("Diff didn't match the subtitles! Make sure to save your file.\n")
+                    aegisub.log("Diff didn't match the subtitles! Make sure to save your file.\nYou can try again with the \"One Fat Diff\" option enabled.\n")
                     aegisub.cancel()
 
             break unless offset == nil
@@ -199,8 +202,14 @@ show_diff_diag = (subs, sel) ->
         label: "Show before and after",
         hint: "Add commented lines marked [Git -] showing how the line looked before the change.",
         name: "show_before",
-        value: config.c.show_before
-        x: 2, y: 1, width: 2, height: 2,
+        value: config.c.show_before,
+        x: 2, y: 1, width: 2, height: 1,
+    },{
+        class: "checkbox",
+        label: "One Fat Diff (potentially very slow!)",
+        hint: "Have git output one fat diff from beginning to end of the file with no chunks. Use only when diff fails without this.",
+        name: "one_fat_diff",
+        x: 2, y: 2, width: 2, height: 1,
     }})
 
     return if not btn
@@ -209,7 +218,7 @@ show_diff_diag = (subs, sel) ->
     config\write()
 
     ref = "#{result.ref}~#{result.before}"
-    diff = get_git_diff(ref)
+    diff = get_git_diff(ref, subs, result.one_fat_diff)
 
     current_diff = diff
     show_diff_lines(subs, diff, result.show_before)