4 files changed, 137 insertions, 0 deletions
diff --git a/internal/mapr/funcs/function.go b/internal/mapr/funcs/function.go
new file mode 100644
index 0000000..52aaa98
--- /dev/null
+++ b/internal/mapr/funcs/function.go
@@ -0,0 +1,66 @@
+package funcs
+
+import (
+	"fmt"
+	"strings"
+)
+
+// CallbackFunc is a function which can be executed by the mapreduce engine
+type CallbackFunc func(text string) string
+
+// Function embeddes the function name to the callback function
+type Function struct {
+	// Name of the callback function
+	Name string
+	call CallbackFunc
+}
+
+// FunctionStack is a list of functions stacked each other
+type FunctionStack []Function
+
+// NewFunctionStack parses the input string, e.g. foo(bar("arg")) and returns a corresponding function stack.
+func NewFunctionStack(in string) (FunctionStack, string, error) {
+	var fs FunctionStack
+
+	getCallback := func(name string) (CallbackFunc, error) {
+		var cb CallbackFunc
+
+		switch name {
+		case "md5sum":
+			return Md5Sum, nil
+		case "maskdigits":
+			return MaskDigits, nil
+		default:
+			return cb, fmt.Errorf("unknown function '%s'", name)
+		}
+	}
+
+	aux := in
+	for strings.HasSuffix(aux, ")") {
+		index := strings.Index(aux, "(")
+		if index <= 0 {
+			return fs, "", fmt.Errorf("unable to parse function '%s' at '%s'", in, aux)
+		}
+		name := aux[0:index]
+
+		call, err := getCallback(name)
+		if err != nil {
+			return fs, "", err
+		}
+		fs = append(fs, Function{name, call})
+		aux = aux[index+1 : len(aux)-1]
+	}
+
+	return fs, aux, nil
+}
+
+// Call the function stack.
+func (fs FunctionStack) Call(str string) string {
+	for i := len(fs) - 1; i >= 0; i-- {
+		//logger.Debug("Call", fs[i].Name, str)
+		str = fs[i].call(str)
+		//logger.Debug("Call.result", fs[i].Name, str)
+	}
+
+	return str
+}
diff --git a/internal/mapr/funcs/function_test.go b/internal/mapr/funcs/function_test.go
new file mode 100644
index 0000000..415683c
--- /dev/null
+++ b/internal/mapr/funcs/function_test.go
@@ -0,0 +1,45 @@
+package funcs
+
+import "testing"
+
+func TestFunction(t *testing.T) {
+	input := "md5sum($line)"
+	fs, arg, err := NewFunctionStack(input)
+	if err != nil {
+		t.Errorf("error parsing function input '%s': %s (%v)\n", input, err.Error(), fs)
+	}
+	if arg != "$line" {
+		t.Errorf("error parsing function input '%s': expected argument '$line' but got '%s' (%v)\n", input, arg, fs)
+	}
+	t.Log(input, fs, arg)
+
+	result := fs.Call(input)
+	if result != "b38699013d79e50d9d122433753959c1" {
+		t.Errorf("error executing function stack '%s': expected result 'b38699013d79e50d9d122433753959c1' but got '%s' (%v)\n", input, result, fs)
+	}
+
+	input = "maskdigits(md5sum(maskdigits($line)))"
+	fs, arg, err = NewFunctionStack(input)
+	if err != nil {
+		t.Errorf("error parsing function input '%s': %s (%v)\n", input, err.Error(), fs)
+	}
+	if arg != "$line" {
+		t.Errorf("error parsing function input '%s': expected argument '$line' but got '%s' (%v)\n", input, arg, fs)
+	}
+	t.Log(input, fs, arg)
+
+	result = fs.Call(input)
+	if result != ".fac.bbe..bb.........d...a.c..b." {
+		t.Errorf("error executing function stack '%s': expected result '.fac.bbe..bb.........d...a.c..b.' but got '%s' (%v)\n", input, result, fs)
+	}
+
+	input = "md5sum$line)"
+	if fs, _, err := NewFunctionStack(input); err == nil {
+		t.Errorf("Expected error parsing function input '%s' (%v) but got no error\n", input, fs)
+	}
+
+	input = "md5sum(makedigits$line))"
+	if fs, _, err := NewFunctionStack(input); err == nil {
+		t.Errorf("Expected error parsing function input '%s' (%v) but got no error\n", input, fs)
+	}
+}
diff --git a/internal/mapr/funcs/maskdigits.go b/internal/mapr/funcs/maskdigits.go
new file mode 100644
index 0000000..d51f3d8
--- /dev/null
+++ b/internal/mapr/funcs/maskdigits.go
@@ -0,0 +1,14 @@
+package funcs
+
+// MaskDigits masks all digits (replaces them with .)
+func MaskDigits(input string) string {
+	s := []byte(input)
+
+	for i, b := range s {
+		if '0' <= b && b <= '9' {
+			s[i] = '.'
+		}
+	}
+
+	return string(s)
+}
diff --git a/internal/mapr/funcs/md5sum.go b/internal/mapr/funcs/md5sum.go
new file mode 100644
index 0000000..e3cc7e6
--- /dev/null
+++ b/internal/mapr/funcs/md5sum.go
@@ -0,0 +1,12 @@
+package funcs
+
+import (
+	"crypto/md5"
+	"encoding/hex"
+)
+
+// Md5Sum returns the hex encoded MD5 checksum of a given input string.
+func Md5Sum(text string) string {
+	hash := md5.Sum([]byte(text))
+	return hex.EncodeToString(hash[:])
+}