tmpl-source.go

package main

import (
	"bytes"
	"crypto/md5"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path"
	"strings"
	"text/template"

	"github.com/forj-oss/forjj-modules/trace"
)

// TmplSource represent a file source information as declared in templates.yaml
type TmplSource struct {
	Chmod os.FileMode

	// One of the following field must be set.
	Template  string // Define a template file.
	Source    string // Define a source file.
	Built     string // Define a built file.
	Generated string // Define a source file generated by a build task. The generated source file is then copied like Source.

	md5Generated []byte // if file exist, contains the md5sum of the source file before any change.

	Tag string // template string to use.
	If  string `yaml:"if"` // If `If` is empty, the file will be ignored. otherwise the file will copied/generated
	// as usual.
}

// Generate read a source file and interpret it with text/template.
// It reads the source file, generate the final file and state if file generated has been updated or not.
//
// It permits to use another template tag to avoid conflict with the code to generate.
// This Tag have to define a pair string. Ex: "(())" the string is split in 2, to define the begin and end tag. ie begin="((", end="))"
// "((" is invalid because begin == end == "("
// "[[]" is also invalid, because the tag size is not divided per 2 (size is 3)
//
// When a different tag is used, any existing {{}} in source file will be kept after the template generation.
func (ts *TmplSource) Generate(tmpl_data interface{}, template_dir, dest_path, dest_name string) (updated bool, _ error) {
	src := path.Join(template_dir, ts.Template)
	dest := path.Join(dest_path, dest_name)
	parent := path.Dir(dest)

	if parent != "." {
		if _, err := os.Stat(parent); err != nil {
			os.MkdirAll(parent, 0755)
			updated = true
		}
	}

	var data string
	if b, err := ioutil.ReadFile(src); err != nil {
		return false, fmt.Errorf("Load issue. %s", err)
	} else {
		data = string(b)
	}

	if ts.Tag != "" {
		if v := len(ts.Tag); v < 4 {
			return false, fmt.Errorf("%s: tag template string must have at least 2 cars for 'begin' and 'end' tag. '%s' is too small", ts.Template, ts.Tag)
		}
		if v := len(ts.Tag); v%2 != 0 {
			return false, fmt.Errorf("%s: tag template string must define begin and end different tag, each of same size. Got %d", ts.Template, v)
		}
		tagSize := len(ts.Tag) / 2
		tag1 := ts.Tag[0:tagSize]
		tag2 := ts.Tag[tagSize:]

		if tag1 == tag2 {
			return false, fmt.Errorf("%s: tag template string (%s) must define different string for begin/end tag. Got begin='%s' vs end='%s'",
				ts.Template, ts.Tag, tag1, tag2)
		}

		if tag1 == "{{" || tag1 == "}}" {
			return false, fmt.Errorf("%s: begin tag '%s' cannot be '{{' or '}}'", ts.Template, tag1)
		}
		if tag2 == "{{" || tag2 == "}}" {
			return false, fmt.Errorf("%s: end tag '%s' cannot be '{{' or '}}'", ts.Template, tag2)
		}

		gotrace.Trace("Tag: begin='%s', end='%s'", tag1, tag2)

		replacer := map[string]string{
			"}}": tag1 + "`}}`" + tag2,
			"{{": tag1 + "`{{`" + tag2,
			tag1: "{{",
			tag2: "}}",
		}
		for _, tagSel := range []string{"{{", "}}", tag1, tag2} {
			data = strings.Replace(data, tagSel, replacer[tagSel], -1)
		}
	}

	data = strings.Replace(data, "}}\\\n", "}}", -1)

	t, err := template.New(src).Funcs(template.FuncMap{
		"lookup": lookup,
	}).Parse(data)
	if err != nil {
		return false, fmt.Errorf("Template issue. %s", err)
	}

	orig_md5, _ := md5sum(dest)
	final_md5_file := md5.New()

	if out, err := os.Create(dest); err != nil {
		return false, fmt.Errorf("Unable to create %s. %s", dest, err)
	} else {
		multi_write_file := io.MultiWriter(out, final_md5_file)
		if err := t.Execute(multi_write_file, tmpl_data); err != nil {
			return false, fmt.Errorf("Unable to interpret %s. %s", dest, err)
		}
		out.Close()
	}
	final_md5 := final_md5_file.Sum(nil)
	if orig_md5 != nil {
		updated = updated || !bytes.Equal(orig_md5, final_md5)
	} else {
		updated = true
	}

	if u, err := set_rights(dest, ts.Chmod); err != nil {
		return false, fmt.Errorf("%s", err)
	} else {
		updated = updated || u
	}
	return
}

// Store generated source md5
func (ts *TmplSource) storeMD5(src string) {
	ts.md5Generated, _ = md5sum(src)
}