1 files changed, 66 insertions, 0 deletions
diff --git a/src/guff/template.cr b/src/guff/template.cr
new file mode 100644
index 0000000..01a4c86
--- /dev/null
+++ b/src/guff/template.cr
@@ -0,0 +1,66 @@
+module Guff
+  class Template
+    getter :string
+
+    def initialize(@string : String)
+      @tokens = scan(@string)
+      @has_keys = @tokens.select { |t| t.type == :key }.size > 0
+    end
+
+    def run(args = nil : Hash(String, String)?) : String
+      if @has_keys
+        # check template args
+        if args || args.size == 0
+          raise "missing template args: %s" % [@tokens.select { |t| 
+            t.type == :key
+          }.join(", ")]
+        end
+
+        # build result
+        String.builder do |r|
+          @tokens.each do |t|
+            r << t.get(args)
+          end
+        end
+      else
+        # no keys, return literal string
+        @string
+      end
+    end
+
+    SCAN_RE = %r{
+      # match key
+      (?:%\{(?<key>[^\}]+)\})
+
+      |
+
+      # match literal value
+      (?<val>[^%]+)
+
+      |
+
+      # match literal percent
+      (?<pct>%)
+    }mx
+
+    private def scan(s : String)
+      r = [] of TemplateToken
+
+      s.scan(SCAN_RE) do |md|
+        if md["key"]?
+          r << TemplateToken.new(:key, md["key"].strip)
+        elsif md["val"]?
+          r << TemplateToken.new(:val, md["val"])
+        elsif md["pct"]?
+          r << TemplateToken.new(:val, "%")
+        else
+          # never reached
+          raise "unknown match: #{md}"
+        end
+      end
+
+      # return result
+      r
+    end
+  end
+end