/* @flow */
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const range = 2
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export function generateCodeFrame (
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source: string,
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start: number = 0,
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end: number = source.length
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): string {
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const lines = source.split(/\r?\n/)
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let count = 0
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const res = []
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for (let i = 0; i < lines.length; i++) {
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count += lines[i].length + 1
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if (count >= start) {
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for (let j = i - range; j <= i + range || end > count; j++) {
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if (j < 0 || j >= lines.length) continue
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res.push(`${j + 1}${repeat(` `, 3 - String(j + 1).length)}| ${lines[j]}`)
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const lineLength = lines[j].length
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if (j === i) {
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// push underline
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const pad = start - (count - lineLength) + 1
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const length = end > count ? lineLength - pad : end - start
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res.push(` | ` + repeat(` `, pad) + repeat(`^`, length))
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} else if (j > i) {
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if (end > count) {
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const length = Math.min(end - count, lineLength)
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res.push(` | ` + repeat(`^`, length))
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}
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count += lineLength + 1
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}
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}
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break
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}
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}
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return res.join('\n')
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}
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function repeat (str, n) {
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let result = ''
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if (n > 0) {
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while (true) { // eslint-disable-line
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if (n & 1) result += str
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n >>>= 1
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if (n <= 0) break
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str += str
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}
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}
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return result
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}
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