feat: add dry run (#10)

* feat: add --dry-run flag

* feat: use pkg/diff to actually compare old and new changelog

Co-authored-by: Tran Hau <ngtranhau@gmail.com>

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/google/go-cmp v0.5.5 // indirect
 	github.com/haunt98/color v0.1.0
 	github.com/kevinburke/ssh_config v1.1.0 // indirect
+	github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/sebdah/goldie/v2 v2.5.3
 	github.com/sergi/go-diff v1.2.0 // indirect

go.sum

@@ -60,6 +60,8 @@ github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Ky
 github.com/mitchellh/go-homedir v1.1.0 h1:lukF9ziXFxDFPkA1vsr5zpc1XuPDn/wFntq5mG+4E0Y=
 github.com/mitchellh/go-homedir v1.1.0/go.mod h1:SfyaCUpYCn1Vlf4IUYiD9fPX4A5wJrkLzIz1N1q0pr0=
 github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e/go.mod h1:zD1mROLANZcx1PVRCS0qkT7pwLkGfwJo4zjcN/Tysno=
+github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e h1:aoZm08cpOy4WuID//EZDgcC4zIxODThtZNPirFr42+A=
+github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=

pkg/cli/action.go

@@ -27,6 +27,7 @@ type action struct {
 		output     string
 		filename   string
 		filetype   string
+		dryRun     bool
 	}
 }
 
@@ -49,6 +50,7 @@ func (a *action) getFlags(c *cli.Context) {
 	a.flags.output = a.getFlagValue(c, outputFlag, defaultOutput)
 	a.flags.filename = a.getFlagValue(c, filenameFlag, defaultFilename)
 	a.flags.filetype = a.getFlagValue(c, filetypeFlag, defaultFiletype)
+	a.flags.dryRun = c.Bool(dryRunFlag)
 
 	if a.flags.verbose {
 		a.log("flags %+v", a.flags)

pkg/cli/action_generate.go

@@ -10,6 +10,8 @@ import (
 	"github.com/haunt98/changeloguru/pkg/changelog"
 	"github.com/haunt98/changeloguru/pkg/convention"
 	"github.com/haunt98/changeloguru/pkg/git"
+	"github.com/haunt98/changeloguru/pkg/markdown"
+	"github.com/pkg/diff"
 	"github.com/urfave/cli/v2"
 	"golang.org/x/mod/semver"
 )
@@ -112,6 +114,16 @@ func (a *action) generateMarkdownChangelog(output, version string, commits []con
 	markdownGenerator := changelog.NewMarkdownGenerator(oldData, version, time.Now())
 	newData := markdownGenerator.Generate(commits, a.flags.scopes)
 
+	if a.flags.dryRun {
+		oldLines := strings.Split(oldData, string(markdown.NewlineToken))
+		newLines := strings.Split(newData, string(markdown.NewlineToken))
+		if err := diff.Slices("old", "new", oldLines, newLines, os.Stdout); err != nil {
+			return fmt.Errorf("failed to diff old and new data: %w", err)
+		}
+
+		return nil
+	}
+
 	if err := os.WriteFile(output, []byte(newData), 0o644); err != nil {
 		return fmt.Errorf("failed to write file %s: %w", output, err)
 	}

pkg/cli/app.go

@@ -14,6 +14,7 @@ const (
 	outputFlag     = "output"
 	filenameFlag   = "filename"
 	filetypeFlag   = "filetype"
+	dryRunFlag     = "dry-run"
 	verboseFlag    = "verbose"
 
 	// commands
@@ -82,6 +83,10 @@ func NewApp() *cli.App {
 						Usage:       "output `FILETYPE`",
 						DefaultText: defaultFiletype,
 					},
+					&cli.BoolFlag{
+						Name:  dryRunFlag,
+						Usage: "demo run without actually changing anything",
+					},
 				},
 				Action: a.RunGenerate,
 			},