From 8ce94eca5bfdc2c2526ca09cc176da05c99a06aa Mon Sep 17 00:00:00 2001
From: Jeff Williams <kanobe@gmail.com>
Date: Thu, 8 Jun 2023 09:49:05 -0400
Subject: [PATCH] Tolerate leading zeros in numeric color parameters

---
 ansi.go      | 18 ++++++++++++++----
 ansi_test.go | 22 ++++++++++++++++++++++
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/ansi.go b/ansi.go
index ddfdb94..7a2ae7a 100644
--- a/ansi.go
+++ b/ansi.go
@@ -2,9 +2,10 @@ package ansi
 
 import (
 	"fmt"
-	"github.com/rivo/uniseg"
 	"strconv"
 	"strings"
+
+	"github.com/rivo/uniseg"
 )
 
 // TextStyle is a type representing the
@@ -321,6 +322,7 @@ func Parse(input string, options ...ParseOption) ([]*StyledText, error) {
 				skip--
 				continue
 			}
+			param = stripLeadingZeros(param)
 			switch param {
 			case "0", "":
 				colourMap = ColourMap["Regular"]
@@ -369,9 +371,10 @@ func Parse(input string, options ...ParseOption) ([]*StyledText, error) {
 					return nil, invalid
 				}
 				// 256 colours
-				if params[index+1] == "5" {
+				param1 := stripLeadingZeros(params[index+1])
+				if param1 == "5" {
 					skip = 2
-					colIndexText := params[index+2]
+					colIndexText := stripLeadingZeros(params[index+2])
 					colIndex, err := strconv.Atoi(colIndexText)
 					if err != nil {
 						return nil, invalid256ColSequence
@@ -391,7 +394,7 @@ func Parse(input string, options ...ParseOption) ([]*StyledText, error) {
 				if len(params)-index < 5 {
 					return nil, invalidTrueColorSequence
 				}
-				if params[index+1] != "2" {
+				if param1 != "2" {
 					return nil, invalidTrueColorSequence
 				}
 				var r, g, b uint8
@@ -465,6 +468,13 @@ func Parse(input string, options ...ParseOption) ([]*StyledText, error) {
 	}
 }
 
+func stripLeadingZeros(s string) string {
+	if len(s) < 2 {
+		return s
+	}
+	return strings.TrimLeft(s, "0")
+}
+
 // HasEscapeCodes tests that input has escape codes.
 func HasEscapeCodes(input string) bool {
 	return strings.IndexAny(input, "\033[") != -1
diff --git a/ansi_test.go b/ansi_test.go
index 113a0cf..cd90267 100644
--- a/ansi_test.go
+++ b/ansi_test.go
@@ -687,3 +687,25 @@ func TestLength(t *testing.T) {
 		})
 	}
 }
+
+func TestStripLeadingZeros(t *testing.T) {
+	is2 := is.New(t)
+	tests := []struct {
+		name    string
+		input   string
+		want    string
+	}{
+		{"Blank", "", ""},
+		{"One rune not 0", "4", "4"},
+		{"Only 0", "0", "0"},
+		{"Multi-digit non-0", "35", "35"},
+		{"Two-digit leading 0", "05", "5"},
+		{"Three-digit leading 0", "045", "45"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := stripLeadingZeros(tt.input)
+			is2.Equal(got, tt.want)
+		})
+	}
+}