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