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68 lines
2.2 KiB
68 lines
2.2 KiB
3 years ago
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// Limited implementation of python % string operator, supports only %s and %r for now
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// (other formats are not used here, but may appear in custom templates)
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'use strict'
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const { inspect } = require('util')
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module.exports = function sub(pattern, ...values) {
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let regex = /%(?:(%)|(-)?(\*)?(?:\((\w+)\))?([A-Za-z]))/g
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let result = pattern.replace(regex, function (_, is_literal, is_left_align, is_padded, name, format) {
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if (is_literal) return '%'
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let padded_count = 0
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if (is_padded) {
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if (values.length === 0) throw new TypeError('not enough arguments for format string')
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padded_count = values.shift()
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if (!Number.isInteger(padded_count)) throw new TypeError('* wants int')
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}
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let str
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if (name !== undefined) {
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let dict = values[0]
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if (typeof dict !== 'object' || dict === null) throw new TypeError('format requires a mapping')
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if (!(name in dict)) throw new TypeError(`no such key: '${name}'`)
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str = dict[name]
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} else {
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if (values.length === 0) throw new TypeError('not enough arguments for format string')
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str = values.shift()
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}
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switch (format) {
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case 's':
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str = String(str)
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break
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case 'r':
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str = inspect(str)
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break
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case 'd':
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case 'i':
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if (typeof str !== 'number') {
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throw new TypeError(`%${format} format: a number is required, not ${typeof str}`)
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}
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str = String(str.toFixed(0))
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break
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default:
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throw new TypeError(`unsupported format character '${format}'`)
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}
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if (padded_count > 0) {
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return is_left_align ? str.padEnd(padded_count) : str.padStart(padded_count)
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} else {
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return str
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}
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})
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if (values.length) {
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if (values.length === 1 && typeof values[0] === 'object' && values[0] !== null) {
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// mapping
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} else {
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throw new TypeError('not all arguments converted during string formatting')
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}
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}
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return result
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}
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