67 lines
1.8 KiB
JavaScript
67 lines
1.8 KiB
JavaScript
'use strict';
|
|
|
|
const format = require('./format');
|
|
|
|
/*
|
|
* function cascade(formats)
|
|
* Returns a function that invokes the `._format` function in-order
|
|
* for the specified set of `formats`. In this manner we say that Formats
|
|
* are "pipe-like", but not a pure pumpify implementation. Since there is no back
|
|
* pressure we can remove all of the "readable" plumbing in Node streams.
|
|
*/
|
|
function cascade(formats) {
|
|
if (!formats.every(isValidFormat)) {
|
|
return;
|
|
}
|
|
|
|
return info => {
|
|
let obj = info;
|
|
for (let i = 0; i < formats.length; i++) {
|
|
obj = formats[i].transform(obj, formats[i].options);
|
|
if (!obj) {
|
|
return false;
|
|
}
|
|
}
|
|
|
|
return obj;
|
|
};
|
|
}
|
|
|
|
/*
|
|
* function isValidFormat(format)
|
|
* If the format does not define a `transform` function throw an error
|
|
* with more detailed usage.
|
|
*/
|
|
function isValidFormat(fmt) {
|
|
if (typeof fmt.transform !== 'function') {
|
|
throw new Error([
|
|
'No transform function found on format. Did you create a format instance?',
|
|
'const myFormat = format(formatFn);',
|
|
'const instance = myFormat();'
|
|
].join('\n'));
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* function combine (info)
|
|
* Returns a new instance of the combine Format which combines the specified
|
|
* formats into a new format. This is similar to a pipe-chain in transform streams.
|
|
* We choose to combine the prototypes this way because there is no back pressure in
|
|
* an in-memory transform chain.
|
|
*/
|
|
module.exports = (...formats) => {
|
|
const combinedFormat = format(cascade(formats));
|
|
const instance = combinedFormat();
|
|
instance.Format = combinedFormat.Format;
|
|
return instance;
|
|
};
|
|
|
|
//
|
|
// Export the cascade method for use in cli and other
|
|
// combined formats that should not be assumed to be
|
|
// singletons.
|
|
//
|
|
module.exports.cascade = cascade;
|