test: cover EXIF image orientation

example/__tests__/fixtures/exif-orientation.ts

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+import type { EncodedImageData } from 'react-native-nitro-image'
+
+export type ExifOrientation = 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8
+export type FixtureColor = 'red' | 'green' | 'blue' | 'yellow'
+
+export interface ExifOrientationCase {
+  orientation: ExifOrientation
+  name: string
+  width: number
+  height: number
+  corners: readonly [FixtureColor, FixtureColor, FixtureColor, FixtureColor]
+}
+
+export const STORED_WIDTH = 120
+export const STORED_HEIGHT = 80
+
+/**
+ * The JPEG's stored pixels are four solid quadrants:
+ *
+ * red   | green
+ * blue  | yellow
+ *
+ * `corners` describes the logical top-left, top-right, bottom-left, and
+ * bottom-right colors after applying each EXIF orientation.
+ */
+export const EXIF_ORIENTATION_CASES: readonly ExifOrientationCase[] = [
+  {
+    orientation: 1,
+    name: 'up',
+    width: 120,
+    height: 80,
+    corners: ['red', 'green', 'blue', 'yellow'],
+  },
+  {
+    orientation: 2,
+    name: 'up mirrored',
+    width: 120,
+    height: 80,
+    corners: ['green', 'red', 'yellow', 'blue'],
+  },
+  {
+    orientation: 3,
+    name: 'down',
+    width: 120,
+    height: 80,
+    corners: ['yellow', 'blue', 'green', 'red'],
+  },
+  {
+    orientation: 4,
+    name: 'down mirrored',
+    width: 120,
+    height: 80,
+    corners: ['blue', 'yellow', 'red', 'green'],
+  },
+  {
+    orientation: 5,
+    name: 'left mirrored',
+    width: 80,
+    height: 120,
+    corners: ['red', 'blue', 'green', 'yellow'],
+  },
+  {
+    orientation: 6,
+    name: 'right',
+    width: 80,
+    height: 120,
+    corners: ['blue', 'red', 'yellow', 'green'],
+  },
+  {
+    orientation: 7,
+    name: 'right mirrored',
+    width: 80,
+    height: 120,
+    corners: ['yellow', 'green', 'blue', 'red'],
+  },
+  {
+    orientation: 8,
+    name: 'left',
+    width: 80,
+    height: 120,
+    corners: ['green', 'yellow', 'red', 'blue'],
+  },
+]
+
+// A 120x80 JPEG with an EXIF orientation entry and the quadrant pattern above.
+// Keeping it inline gives every Harness runner the exact same encoded bytes.
+const JPEG_BASE64 = [
+  '/9j/4AAQSkZJRgABAQAASABIAAD/4QBYRXhpZgAATU0AKgAAAAgAAgESAAMAAAABAAEAAIdpAAQAAAABAAAAJgAA',
+  'AAAAA6ABAAMAAAABAAEAAKACAAQAAAABAAAAeKADAAQAAAABAAAAUAAAAAD/7QA4UGhvdG9zaG9wIDMuMAA4QklN',
+  'BAQAAAAAAAA4QklNBCUAAAAAABDUHYzZjwCyBOmACZjs+EJ+/8AAEQgAUAB4AwEiAAIRAQMRAf/EAB8AAAEFAQEB',
+  'AQEBAAAAAAAAAAABAgMEBQYHCAkKC//EALUQAAIBAwMCBAMFBQQEAAABfQECAwAEEQUSITFBBhNRYQcicRQygZGh',
+  'CCNCscEVUtHwJDNicoIJChYXGBkaJSYnKCkqNDU2Nzg5OkNERUZHSElKU1RVVldYWVpjZGVmZ2hpanN0dXZ3eHl6',
+  'g4SFhoeIiYqSk5SVlpeYmZqio6Slpqeoqaqys7S1tre4ubrCw8TFxsfIycrS09TV1tfY2drh4uPk5ebn6Onq8fLz',
+  '9PX29/j5+v/EAB8BAAMBAQEBAQEBAQEAAAAAAAABAgMEBQYHCAkKC//EALURAAIBAgQEAwQHBQQEAAECdwABAgMR',
+  'BAUhMQYSQVEHYXETIjKBCBRCkaGxwQkjM1LwFWJy0QoWJDThJfEXGBkaJicoKSo1Njc4OTpDREVGR0hJSlNUVVZX',
+  'WFlaY2RlZmdoaWpzdHV2d3h5eoKDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT',
+  '1NXW19jZ2uLj5OXm5+jp6vLz9PX29/j5+v/bAEMAAQEBAQEBAgEBAgICAgICAwICAgIDBAMDAwMDBAUEBAQEBAQF',
+  'BQUFBQUFBQYGBgYGBgcHBwcHCAgICAgICAgICP/bAEMBAQEBAgICAwICAwgFBQUICAgICAgICAgICAgICAgICAgI',
+  'CAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICP/dAAQACP/aAAwDAQACEQMRAD8A/Oeiiiv85z/tICiiigAo',
+  'oooAK+xP2Tf+Y/8A9uP/ALXr47r7E/ZN/wCY/wD9uP8A7Xr4fxI/5EuI/wC3f/S4n+Rv7dr/AJRU43/7kf8A1ZYM',
+  '+xKKKK/lc/8AOpCiiigAooooAKKKKAP/0Pznooor/Oc/7SAooooAKKKKACvsT9k3/mP/APbj/wC16+O6+xP2Tf8A',
+  'mP8A/bj/AO16+H8SP+RLiP8At3/0uJ/kb+3a/wCUVON/+5H/ANWWDPsSiiiv5XP/ADqQooooAKKKKACiiigD/9H8',
+  '56K/Meiv9GP+KAf/AFXf/lh/9+n+sH/Fbv8A6ov/AMvf/vQ/TiivzHoo/wCKAf8A1Xf/AJYf/fof8Vu/+qL/APL3',
+  '/wC9D9OKK/Meij/igH/1Xf8A5Yf/AH6H/Fbv/qi//L3/AO9D9OK+xP2Tf+Y//wBuP/tevwDr+lj/AIN3/wDmr/8A',
+  '3Kn/ALlq/hj9pR+yi/4g14KcR+JP+tP176j9W/c/VfY8/tsXQw/8T6zV5eX2vP8Aw5X5eXS91/OH0t/p2/8AEwnh',
+  '7mvhB/Yf9mf2l7L/AGj2/wBY9n9Xr0sV/B9jQ5+f2HJ/Fjy83N73Lyv2iiv3wor/AJSv+I/f9QH/AJU/+0P8Uv8A',
+  'ikH/ANVZ/wCWn/30fgfRX74UUf8AEfv+oD/yp/8AaB/xSD/6qz/y0/8Avo/A+iv3woo/4j9/1Af+VP8A7QP+KQf/',
+  'AFVn/lp/99H4H0V++FFH/Efv+oD/AMqf/aB/xSD/AOqs/wDLT/76P//S/mvooor/ALSD+dwooooAKKKKACv6WP8A',
+  'g3f/AOav/wDcqf8AuWr+aev6WP8Ag3f/AOav/wDcqf8AuWr/ABp/0gj/AJRE49/7kP8A1Z4I/VPBP/kp8F/2/wD+',
+  'm5n9LFFFFf8Amen9+BRRRQAUUUUAFFFFAH//0/5r6KKK/wC0g/ncKKKKACiiigAr+lj/AIN3/wDmr/8A3Kn/ALlq',
+  '/mnr+lj/AIN3/wDmr/8A3Kn/ALlq/wAaf9II/wCUROPf+5D/ANWeCP1TwT/5KfBf9v8A/puZ/SxRRRX/AJnp/fgU',
+  'UUUAFFFFABRRRQB//9k=',
+].join('')
+
+const BASE64_ALPHABET =
+  'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
+const ORIENTATION_ENTRY_PREFIX = [0x01, 0x12, 0x00, 0x03, 0, 0, 0, 1]
+
+function decodeBase64(value: string): Uint8Array {
+  const bytes: number[] = []
+  let accumulator = 0
+  let bitCount = 0
+
+  for (const character of value) {
+    if (character === '=') break
+
+    const decoded = BASE64_ALPHABET.indexOf(character)
+    if (decoded < 0) {
+      throw new Error(`Invalid Base64 character: ${character}`)
+    }
+
+    accumulator = (accumulator << 6) | decoded
+    bitCount += 6
+
+    if (bitCount >= 8) {
+      bitCount -= 8
+      bytes.push((accumulator >> bitCount) & 0xff)
+      accumulator &= (1 << bitCount) - 1
+    }
+  }
+
+  return Uint8Array.from(bytes)
+}
+
+function findSequence(bytes: Uint8Array, sequence: readonly number[]): number {
+  const finalStart = bytes.length - sequence.length
+  for (let start = 0; start <= finalStart; start++) {
+    let matches = true
+    for (let offset = 0; offset < sequence.length; offset++) {
+      if (bytes[start + offset] !== sequence[offset]) {
+        matches = false
+        break
+      }
+    }
+    if (matches) return start
+  }
+  return -1
+}
+
+export function makeExifOrientationJpeg(
+  orientation: ExifOrientation,
+): EncodedImageData {
+  const bytes = decodeBase64(JPEG_BASE64)
+  const entryOffset = findSequence(bytes, ORIENTATION_ENTRY_PREFIX)
+  if (entryOffset < 0) {
+    throw new Error('EXIF orientation entry is missing from the JPEG fixture')
+  }
+
+  // The fixture's TIFF data is big-endian. A SHORT value is stored in the first
+  // two bytes of the four-byte value field immediately following the entry.
+  bytes[entryOffset + 8] = 0
+  bytes[entryOffset + 9] = orientation
+
+  const buffer = new ArrayBuffer(bytes.byteLength)
+  new Uint8Array(buffer).set(bytes)
+
+  return {
+    buffer,
+    width: STORED_WIDTH,
+    height: STORED_HEIGHT,
+    imageFormat: 'jpg',
+  }
+}