replace dockerMustExist with pandocMustExist dependency on build and serve commands

internal/cli/app.go

@@ -7,7 +7,10 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"regexp"
+	"strconv"
 	"strings"
 	"time"
 
@@ -96,6 +99,54 @@ func ticketingMustBeConfigured(c *cli.Context) error {
 	return nil
 }
 
+func pandocMustExist(c *cli.Context) error {
+	pandocErr := fmt.Errorf("Please install either Docker or the pandoc package and re-run `%s`", c.Command.Name)
+
+	err := pandocBinaryMustExist(c)
+	fmt.Println(err)
+	if err != nil {
+		err = dockerMustExist(c)
+		if err != nil {
+			return pandocErr
+		}
+	}
+	return nil
+}
+
+func pandocBinaryMustExist(c *cli.Context) error {
+	cmd := exec.Command("pandoc", "-v")
+	outputRaw, err := cmd.Output()
+	if err != nil {
+		return errors.Wrap(err, "error calling pandoc")
+	}
+
+	output := strings.TrimSpace((string(outputRaw)))
+	versionErr := errors.New("cannot determine pandoc version")
+	if !strings.HasPrefix(output, "pandoc") {
+		return versionErr
+	}
+
+	re := regexp.MustCompile(`pandoc (\d+)\.(\d+)`)
+	result := re.FindStringSubmatch(output)
+	if len(result) != 3 {
+		return versionErr
+	}
+
+	major, err := strconv.Atoi(result[1])
+	if err != nil {
+		return versionErr
+	}
+	minor, err := strconv.Atoi(result[2])
+	if err != nil {
+		return versionErr
+	}
+
+	if major < 2 || minor < 1 {
+		return errors.New("pandoc 2.1 or greater required")
+	}
+	return nil
+}
+
 func dockerMustExist(c *cli.Context) error {
 	dockerErr := fmt.Errorf("Docker must be available in order to run `%s`", c.Command.Name)
 

internal/cli/build.go

@@ -11,7 +11,7 @@ var buildCommand = cli.Command{
 	ShortName: "b",
 	Usage:     "generate a static website summarizing the compliance program",
 	Action:    buildAction,
-	Before:    beforeAll(dockerMustExist, cleanContainers),
+	Before:    beforeAll(pandocMustExist, cleanContainers),
 }
 
 func buildAction(c *cli.Context) error {

internal/cli/serve.go

@@ -10,7 +10,7 @@ var serveCommand = cli.Command{
 	Name:   "serve",
 	Usage:  "live updating version of the build command",
 	Action: serveAction,
-	Before: beforeAll(dockerMustExist, cleanContainers),
+	Before: beforeAll(pandocMustExist, cleanContainers),
 }
 
 func serveAction(c *cli.Context) error {