78 lines
2.7 KiB
TypeScript
78 lines
2.7 KiB
TypeScript
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import { StringLike } from './StringLike';
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function isalpha(char: number) {
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return RegExp(/^\p{L}/, 'u').test(String.fromCharCode(char));
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}
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/// A simple function for formatting strings in a more expressive manner.
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/// While JavaScript *does* have string interpolation, it's not a total replacement
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/// for just formatting strings, and a method like this is better for data independent formatting.
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///
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/// ## Example usage
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///
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/// ```typescript
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/// let hello = Format("Hello, {0}!", "World");
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/// ```
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export function Format(pattern: string, ...args: Array<StringLike>) {
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let argumentsAsStrings: Array<string> = [...args].map((el) => {
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// This catches cases where the thing already is a string
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if (typeof el == 'string') return el as string;
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return el.toString();
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});
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let pat = pattern;
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// Handle pattern ("{0} {1} {2} {3} {4} {5}") syntax if found
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for (let i = 0; i < pat.length; ++i) {
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if (pat[i] == '{') {
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let replacementStart = i;
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let foundSpecifierEnd = false;
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// Make sure the specifier is not cut off (the last character of the string)
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if (i + 3 > pat.length) {
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throw new Error(`Error in format pattern "${pat}": Cutoff/invalid format specifier`);
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}
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// Try and find the specifier end ('}').
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// Whitespace and a '{' are considered errors.
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for (let j = i + 1; j < pat.length; ++j) {
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switch (pat[j]) {
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case '}':
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foundSpecifierEnd = true;
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i = j;
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break;
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case '{':
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throw new Error(`Error in format pattern "${pat}": Cannot start a format specifier in an existing replacement`);
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case ' ':
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throw new Error(`Error in format pattern "${pat}": Whitespace inside format specifier`);
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case '-':
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throw new Error(`Error in format pattern "${pat}": Malformed format specifier`);
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default:
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if (isalpha(pat.charCodeAt(j))) throw new Error(`Error in format pattern "${pat}": Malformed format specifier`);
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break;
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}
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if (foundSpecifierEnd) break;
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}
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if (!foundSpecifierEnd) throw new Error(`Error in format pattern "${pat}": No terminating "}" character found`);
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// Get the beginning and trailer
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let beginning = pat.substring(0, replacementStart);
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let trailer = pat.substring(replacementStart + 3);
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let argumentIndex = parseInt(pat.substring(replacementStart + 1, i));
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if (Number.isNaN(argumentIndex) || argumentIndex > argumentsAsStrings.length) throw new Error(`Error in format pattern "${pat}": Argument index out of bounds`);
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// This is seriously the only decent way to do this in javascript
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// thanks brendan eich (replace this thanking with more choice words in your head)
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pat = beginning + argumentsAsStrings[argumentIndex] + trailer;
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}
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}
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return pat;
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}
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