fix: more efficiently handle back to back styles

src/bbansi.nim

@@ -13,6 +13,8 @@ type
     plain: string
     spans: seq[BbSpan]
 
+proc len(span: BbSpan): int = span.slice[1] - span.slice[0]
+
 proc `&`*(x: BbString, y: string): BbString =
   result = x
   result.raw &= y
@@ -36,9 +38,11 @@ proc `$`*(bbs: BbString): string =
   if noColor: return bbs.plain
 
   for span in bbs.spans:
+    if span.len == 0:
+      continue
     var codes = ""
     if span.styles.len > 0:
-      codes = collect(for style in span.styles: style.toAnsiCode).join("")
+      codes = span.styles.join(" ").toAnsiCode
 
     result.add codes
     result.add bbs.plain[span.slice[0]..span.slice[1]]
@@ -47,6 +51,7 @@ proc `$`*(bbs: BbString): string =
       result.add bbReset
 
 proc endSpan(bbs: var BbString) =
+  if bbs.plain.len != 0:
     bbs.spans[^1].slice[1] = bbs.plain.len-1
 
 proc newSpan(bbs: var BbString, pattern: string) =

tests/tbasic.nim

@@ -21,7 +21,7 @@ suite "basic":
 
   test "closing":
     bbCheck "[bold]Bold[red] Bold Red[/red] Bold Only",
-      "\e[1mBold\e[0m\e[1m\e[31m Bold Red\e[0m\e[1m Bold Only\e[0m" 
+      "\e[1mBold\e[0m\e[1;31m Bold Red\e[0m\e[1m Bold Only\e[0m"
 
   test "abbreviated":
     bbCheck "[b]Bold[/] Not Bold", "\e[1mBold\e[0m Not Bold"

tests/tcli.nim

@@ -19,5 +19,5 @@ suite "cli":
     check execCmdEx(cmd).exitCode == 0
   test "simple":
     check "\e[31mRed\e[0m" == cliRun "[red]Red[/]"
-    check "\e[1m\e[0m\e[1m\e[31mRed\e[0m\e[1m Not Red but Bold\e[0m" ==
+    check "\e[1;31mRed\e[0m\e[1m Not Red but Bold\e[0m" ==
         cliRun "'[red]Red[/] Not Red but Bold' " & "--style:bold"