From 478d1466d9cfc3792dc5a314e5fcf05dc1cbdf5d Mon Sep 17 00:00:00 2001
From: Sascha Andres <sascha.andres@outlook.com>
Date: Tue, 7 Mar 2017 20:07:03 +0100
Subject: [PATCH] First implementation of dynamic variables

---
 variable_handling.go | 59 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 56 insertions(+), 3 deletions(-)

diff --git a/variable_handling.go b/variable_handling.go
index f6a14060..910092a1 100644
--- a/variable_handling.go
+++ b/variable_handling.go
@@ -5,10 +5,14 @@ import (
 	"encoding/json"
 	"io/ioutil"
 	"os"
+	"os/exec"
+	"regexp"
 	"runtime"
 	"strings"
 	"text/template"
 
+	"fmt"
+
 	"github.com/BurntSushi/toml"
 	"gopkg.in/yaml.v2"
 )
@@ -16,22 +20,71 @@ import (
 var (
 	// TaskvarsFilePath file containing additional variables
 	TaskvarsFilePath = "Taskvars"
+	// DynamicVariablePattern is a pattern to test if a variable should get filled from running the content. It must contain a command group
+	DynamicVariablePattern = "^@(?P<command>.*)" // alternative proposal: ^$((?P<command>.*))$
+	// ErrCommandGroupNotFound returned when the command group is not present
+	ErrCommandGroupNotFound = fmt.Errorf("%s does not contain the command group", DynamicVariablePattern)
 )
 
+func handleDynamicVariableContent(value string) (string, error) {
+	if value == "" {
+		return value, nil
+	}
+	re := regexp.MustCompile(DynamicVariablePattern)
+	if !re.MatchString(value) {
+		return value, nil
+	}
+	subExpressionIndex := 0
+	for index, value := range re.SubexpNames() {
+		if value == "command" {
+			subExpressionIndex = index
+			break
+		}
+	}
+	if subExpressionIndex == 0 {
+		return "", ErrCommandGroupNotFound
+	}
+	var cmd *exec.Cmd
+	if ShExists {
+		cmd = exec.Command(ShPath, "-c", re.FindStringSubmatch(value)[subExpressionIndex])
+	} else {
+		cmd = exec.Command("cmd", "/C", re.FindStringSubmatch(value)[subExpressionIndex])
+	}
+	cmd.Stdin = os.Stdin
+	cmd.Stderr = os.Stderr
+	bytes, err := cmd.Output()
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(string(bytes)), nil
+}
+
 func (t Task) handleVariables() (map[string]string, error) {
 	localVariables := make(map[string]string)
 	for key, value := range t.Vars {
-		localVariables[key] = value
+		val, err := handleDynamicVariableContent(value)
+		if err != nil {
+			return nil, err
+		}
+		localVariables[key] = val
 	}
 	if fileVariables, err := readTaskvarsFile(); err == nil {
 		for key, value := range fileVariables {
-			localVariables[key] = value
+			val, err := handleDynamicVariableContent(value)
+			if err != nil {
+				return nil, err
+			}
+			localVariables[key] = val
 		}
 	} else {
 		return nil, err
 	}
 	for key, value := range getEnvironmentVariables() {
-		localVariables[key] = value
+		val, err := handleDynamicVariableContent(value)
+		if err != nil {
+			return nil, err
+		}
+		localVariables[key] = val
 	}
 	return localVariables, nil
 }