gulp-replace if content of files match regex - gulp

Question

I have a folder of HTML files that contain a comment at the top with metadata. I would like to run one gulp-replace operation if the metadata matches one regex, and another gulp-replace operation if it doesn't match, then continue on with the rest of the tasks pipeline. If tried various iterations using gulp-if but it always results in "TypeError: undefined is not a function" errors
import gulp from 'gulp';
import plugins from 'gulp-load-plugins';
const $ = plugins();
function preprocess() {
var template_data = new RegExp('<!-- template_language:(\\w+)? -->\n', 'i');
var handlebars = new RegExp('<!-- template_language:handlebars -->', 'i');
var primaryColor = new RegExp('#dc002d', 'gi');
var mailchimpColorTag = '*|PRIMARY_COLOR|*';
var handlebarsColorTag = '{{PRIMARY_COLOR}}';
var replaceCondition = function (file) {
return file.contents.toString().match(handlebars);
}
return gulp.src('dist/**/*.html')
.pipe($.if(
replaceCondition,
$.replace(primaryColor, handlebarsColorTag),
$.replace(primaryColor, mailchimpColorTag)
))
.pipe($.replace, template_data, '')
.pipe(gulp.dest('dist'));
}
What's the most efficient way to go about this?

Answer 1

gulp-filter was the answer. Whereas gulp-if can be used to decide whether a particular operation should be applied to the whole stream, gulp-filter can be used to decide which files in a stream an operation should be applied to.
import gulp from 'gulp';
import plugins from 'gulp-load-plugins';
const $ = plugins();
function preprocess() {
var template_language = new RegExp('<!-- template_language:(\\w+)? -->\n', 'i');
var handlebars = 'handlebars';
var primaryColor = new RegExp('#dc002d', 'gi');
var handlebarsColorTag = '{{PRIMARY_COLOR}}';
var handlebarsCondition = function (file) {
var match = file.contents.toString().match(template_language);
return (match && match[1] == handlebars);
}
var handlebarsFilter = $.filter(handlebarsCondition, {restore: true});
var mailchimpColorTag = '*|PRIMARY_COLOR|*';
var mailchimpCondition = function (file) {
return !handlebarsCondition(file);
}
var mailchimpFilter = $.filter(mailchimpCondition, {restore: true});
return gulp.src('dist/**/*.html')
.pipe(handlebarsFilter)
.pipe($.replace(primaryColor, handlebarsColorTag))
.pipe($.debug({title: 'Applying ' + handlebarsColorTag}))
.pipe(handlebarsFilter.restore)
.pipe(mailchimpFilter)
.pipe($.replace(primaryColor, mailchimpColorTag))
.pipe($.debug({title: 'Applying ' + mailchimpColorTag}))
.pipe(mailchimpFilter.restore)
.pipe($.replace(template_language, ''))
.pipe(gulp.dest('dist'));
}