/
stegosaurus.go
246 lines (209 loc) · 5.79 KB
/
stegosaurus.go
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package main
import (
"flag"
"fmt"
"html/template"
"io"
"io/ioutil"
"log"
"os"
"path/filepath"
"regexp"
"strings"
"gopkg.in/yaml.v2"
)
const contextFilename = "context.yml"
var sourceDir = flag.String("source", "templates", "The directory to walk for source templates and files.")
var outputDir = flag.String("destination", "output", "The directory for all output. It will be created if it doesn't exist.")
func main() {
flag.Parse()
context := loadContext()
t := template.New("<root>")
err := loadBaseTemplates(t)
if err != nil {
log.Fatalf("Error loading templates: %v", err)
}
err = evalTemplates(t, context)
if err != nil {
log.Fatalf("Error evaluating templates: %v", err)
}
}
// loadTemplates walks sourceDir and loads all base templates into t. These
// are files that have a '.tmpl' extensions and a leading underscore. The
// template name is the filename with those stripped.
func loadBaseTemplates(t *template.Template) error {
return filepath.Walk(*sourceDir, func(path string, info os.FileInfo, err error) error {
if err != nil {
return err
}
if info.IsDir() {
return nil
}
basename := filepath.Base(path)
// Only handle files that start with _
if !strings.HasPrefix(basename, "_") {
return nil
}
// Only handle files with ".tmpl" extension
ext := filepath.Ext(basename)
if ext != ".tmpl" {
return nil
}
fmt.Printf("Loading template file: %v\n", path)
// Strip off "_" and ".tmpl"
name := strings.TrimPrefix(strings.TrimSuffix(basename, filepath.Ext(basename)), "_")
data, err := ioutil.ReadFile(path)
_, err = t.New(name).Parse(string(data))
if err != nil {
return err
}
return nil
})
}
// evalTemplates walks sourceDir and either copies files or evaluates
// templates. The results are put into outputDir Anything that has a '.tmpl'
// extension but no leading underscore is evaluated. Any non-template file is
// just copied.
//
// Template files are preprocessed first to extract an optional leading YAML
// document. This is merged into the template evaluation context.
func evalTemplates(t *template.Template, context interface{}) error {
return filepath.Walk(*sourceDir, func(path string, info os.FileInfo, err error) error {
if err != nil {
return err
}
if info.IsDir() {
return nil
}
basename := filepath.Base(path)
// Skip if the file begins with "_"
if strings.HasPrefix(basename, "_") {
return nil
}
// Find where we are going to put this output
rel, err := filepath.Rel(*sourceDir, path)
if err != nil {
return err
}
output := filepath.Join(*outputDir, rel)
ext := filepath.Ext(basename)
if ext == ".tmpl" {
output = strings.TrimSuffix(output, ".tmpl")
fmt.Printf("Rendering %v to %v\n", path, output)
return evalTemplate(path, output, t, context)
} else {
fmt.Printf("Copying %v to %v\n", path, output)
return copyFile(path, output)
}
return nil
})
}
// evalTemplate evaluates a single template (path) and saves it to output.
func evalTemplate(path string, output string, t *template.Template, context interface{}) error {
newT, err := t.Clone()
if err != nil {
return err
}
tData, err := ioutil.ReadFile(path)
if err != nil {
return err
}
// Pull out front matter
tData, context, err = processFrontmatter(tData, context)
if err != nil {
return err
}
_, err = newT.Parse(string(tData))
if err != nil {
return err
}
err = os.MkdirAll(filepath.Dir(output), os.ModePerm)
if err != nil {
return err
}
of, err := os.Create(output)
if err != nil {
return err
}
defer of.Close()
// Ideally we wouldn't have to name the template here, but
// https://github.com/golang/go/issues/12996
return newT.ExecuteTemplate(of, "<root>", context)
}
// processFrontmatter strips a leading YAML document from data and updates
// context with its contents. The remaining doc, and cloned and updated
// context are returned.
func processFrontmatter(data []byte, context interface{}) ([]byte, interface{}, error) {
r := regexp.MustCompile(`(?m)^---\s*$`)
fmStart := r.FindIndex(data)
if fmStart == nil || fmStart[0] != 0 {
return data, context, nil
}
retData := data[fmStart[1]+1:]
fmEnd := r.FindIndex(retData)
if fmEnd == nil {
return nil, nil, fmt.Errorf("Cannot find end of front matter.")
}
fmData := retData[0:fmEnd[0]]
retData = retData[fmEnd[1]:]
retContext := dumbClone(context)
err := yaml.Unmarshal(fmData, &retContext)
if err != nil {
return nil, nil, err
}
return retData, retContext, nil
}
// dumbClone does a simple clone by serializing to yaml and reparsing. This
// only works when the top level thing is a map.
func dumbClone(in interface{}) map[interface{}]interface{} {
s, err := yaml.Marshal(in)
if err != nil {
panic(err)
}
out := make(map[interface{}]interface{})
err = yaml.Unmarshal(s, &out)
return out
}
// copyFile copies a file from path to output. It makes no attempt to handle
// permissions, links or non-normal files.
func copyFile(path, output string) error {
s, err := os.Open(path)
if err != nil {
return nil
}
defer s.Close()
err = os.MkdirAll(filepath.Dir(output), os.ModePerm)
if err != nil {
return err
}
d, err := os.Create(output)
if err != nil {
return err
}
defer d.Close()
_, err = io.Copy(d, s)
if err != nil {
return err
}
return nil
}
// loadContext parses contextFilename into a new map and returns it.
func loadContext() map[interface{}]interface{} {
ret := make(map[interface{}]interface{})
f, err := os.Open(contextFilename)
if err != nil {
if os.IsNotExist(err) {
return ret
}
log.Fatalf("Could not open %s: %v", contextFilename, err)
}
data, err := ioutil.ReadAll(f)
if err != nil {
log.Fatalf("Could not read %s: %v", contextFilename, err)
}
err = yaml.Unmarshal(data, &ret)
if err != nil {
log.Fatalf("Could not unmarshal %s: %v", contextFilename, err)
}
return ret
}