refactor(vtt-thumbnail): [PKG-VTT-THUMB-04] type runtime data and resource boundaries

packages/artplayer-plugin-vtt-thumbnail/src/parseVtt.ts

@@ -0,0 +1,97 @@
+import type { Rectangle, Thumbnail } from './types'
+
+function invalid(line: number, message: string): never {
+  throw new TypeError(`Invalid VTT thumbnail at line ${line}: ${message}`)
+}
+
+function timestamp(value: string, line: number): number {
+  if (!/^\d{2,}(?::\d{2}){0,2}(?:\.\d{3})?$/.test(value))
+    invalid(line, 'invalid timestamp')
+  const [whole, fraction = '0'] = value.split('.')
+  const seconds = whole!.split(':').reduce((total, part) => total * 60 + Number(part), 0) + Number(fraction) / 1000
+  if (!Number.isSafeInteger(Math.floor(seconds)))
+    invalid(line, 'timestamp exceeds the supported numeric range')
+  return seconds
+}
+
+function rectangle(text: string, vttUrl: string, line: number): Rectangle & { url: string } {
+  const match = text.match(/^(.+)#([xywh]{4})=(.*)$/)
+  if (!match || new Set(match[2]!).size !== 4)
+    invalid(line, 'expected an image URL and four distinct xywh keys')
+  const values = match[3]!.split(',').map(value => value.trim())
+  if (values.length !== 4)
+    invalid(line, 'expected four rectangle coordinates')
+  const rect = {} as Rectangle
+  for (let index = 0; index < 4; index++) {
+    const key = match[2]![index] as keyof Rectangle
+    const value = values[index]!
+    if (!/^(?:\d+(?:\.\d+)?|\.\d+)$/.test(value) || !Number.isFinite(Number(value)))
+      invalid(line, 'rectangle coordinates must be finite non-negative decimals')
+    if ((key === 'w' || key === 'h') && Number(value) === 0)
+      invalid(line, 'rectangle width and height must be positive')
+    rect[key] = value
+  }
+  let url = match[1]!
+  if (!/^\/|(?:https?|ftp|file):\/\//i.test(url)) {
+    const segments = vttUrl.split('/')
+    segments.pop()
+    segments.push(url)
+    url = segments.join('/')
+  }
+  return { url, ...rect }
+}
+
+export function findThumbnail(thumbnails: readonly Thumbnail[], second: number): Thumbnail | undefined {
+  return thumbnails.find(item => second >= item.start && second <= item.end)
+}
+
+export default function parseVtt(text: unknown, vttUrl = ''): Thumbnail[] {
+  if (typeof text !== 'string')
+    invalid(1, 'expected text')
+  const lines = text.replace(/^\uFEFF/, '').split(/\r\n|\r|\n/)
+  let index = 0
+  function skipEmpty() {
+    while (index < lines.length && !lines[index]!.trim())
+      index++
+  }
+  skipEmpty()
+  if (index === lines.length)
+    return []
+  if (!/^WEBVTT(?:[\t ].*)?$/.test(lines[index]!.trim()) || lines[index]!.includes('-->'))
+    invalid(index + 1, 'expected WEBVTT header')
+  index++
+  const thumbnails: Thumbnail[] = []
+  while (index < lines.length) {
+    skipEmpty()
+    if (index === lines.length)
+      break
+    const first = lines[index]!.trim()
+    if (/^NOTE(?:[\t ]|$)/.test(first) || first === 'STYLE' || first === 'REGION') {
+      while (index < lines.length && lines[index]!.trim())
+        index++
+      continue
+    }
+    const identifierLine = index + 1
+    if (!first.includes('-->')) {
+      index++
+      if (index === lines.length || !lines[index]!.trim())
+        invalid(identifierLine, 'cue identifier must be followed by timing')
+    }
+    const timingLine = index + 1
+    const timing = lines[index]!.trim().match(/^([\d:.]+)[\t ]*-->[\t ]*([\d:.]+)(?:[\t ].*)?$/)
+    if (!timing)
+      invalid(timingLine, 'invalid cue timing')
+    const start = timestamp(timing[1]!, timingLine)
+    const end = timestamp(timing[2]!, timingLine)
+    if (end < start)
+      invalid(timingLine, 'cue end precedes its start')
+    index++
+    skipEmpty()
+    if (index === lines.length)
+      invalid(timingLine, 'missing sprite image')
+    const image = rectangle(lines[index]!.trim(), vttUrl, index + 1)
+    thumbnails.push({ start: Math.floor(start), end: Math.floor(end), ...image })
+    index++
+  }
+  return thumbnails
+}