Sort page alphanumerically

See https://ux.stackexchange.com/questions/95431/how-should-sorting-work-when-numeric-is-mixed-with-alpha-numeric

src/library.cr

@@ -2,6 +2,7 @@ require "zip"
 require "mime"
 require "json"
 require "uri"
+require "./util"
 
 struct Image
 	property data : Bytes
@@ -44,7 +45,7 @@ class Entry
 					["image/jpeg", "image/png"].includes? \
 					MIME.from_filename? e.filename
 				}
-				.sort { |a, b| a.filename <=> b.filename }
+				.sort { |a, b| compare_alphanumerically(split_by_alphanumeric(a.filename), split_by_alphanumeric(b.filename)) }
 				.[page_num - 1]
 			page.open do |io|
 				slice = Bytes.new page.uncompressed_size

src/util.cr

@@ -32,3 +32,50 @@ def request_path_startswith(env, ary)
 	end
 	return false
 end
+
+def is_numeric(str)
+	/^\d+/.match(str) != nil
+end
+
+def split_by_alphanumeric(str)
+	is_number = false
+	arr = [] of String
+	arr.push(
+		str.split("").reduce("") do |memo, c|
+			if (is_number)
+				if is_numeric(c)
+					memo + c
+				else
+					arr.push(memo) if memo != ""
+					is_number = false
+					c
+				end
+		      else
+				if is_numeric(c) # number
+					arr.push(memo) if memo != ""
+					is_number = true
+					c
+				else
+					memo + c
+				end
+			end
+		end
+	)
+	arr
+end
+
+def compare_alphanumerically(c, d)
+	is_c_bigger = c.size <=> d.size
+	begin
+		c.zip(d) do |a, b|
+			if is_numeric(a) && is_numeric(b)
+				compare = a.to_i <=> b.to_i
+				return compare if compare != 0
+			else
+				compare = a <=> b
+				return compare if compare != 0
+			end
+		end
+		is_c_bigger
+	end
+end