From ae3770ae304f4c9d5ee1220e8844e5bc701928ab Mon Sep 17 00:00:00 2001
From: Sam Becker <sam@sambecker.com>
Date: Fri, 12 Apr 2024 12:20:24 -0500
Subject: [PATCH] Refine fraction formatting behavior

---
 __tests__/exif.test.ts | 12 ++++++++++++
 src/utility/number.ts  | 44 ++++++++++++++++++++++++++++++++----------
 2 files changed, 46 insertions(+), 10 deletions(-)

diff --git a/__tests__/exif.test.ts b/__tests__/exif.test.ts
index b3a20c72..ea770f9b 100644
--- a/__tests__/exif.test.ts
+++ b/__tests__/exif.test.ts
@@ -12,23 +12,35 @@ describe('EXIF', () => {
       expect(formatExposureTime(1.5)).toBe('1.5s');
     });
     it('exposure compensation', () => {
+      expect(formatExposureCompensation(1)).toBe('+1ev');
       expect(formatExposureCompensation(-1)).toBe('-1ev');
       expect(formatExposureCompensation(0)).toBe(undefined);
       expect(formatExposureCompensation(0.25)).toBe('+1/4ev');
       expect(formatExposureCompensation(0.33)).toBe('+1/3ev');
       expect(formatExposureCompensation(0.333)).toBe('+1/3ev');
+      expect(formatExposureCompensation(-0.25)).toBe('-1/4ev');
+      expect(formatExposureCompensation(-0.33)).toBe('-1/3ev');
+      expect(formatExposureCompensation(-0.333)).toBe('-1/3ev');
       expect(formatExposureCompensation(0.5)).toBe('+1/2ev');
+      expect(formatExposureCompensation(0.4998458896569944)).toBe('+1/2ev');
       expect(formatExposureCompensation(0.66)).toBe('+2/3ev');
       expect(formatExposureCompensation(0.67)).toBe('+2/3ev');
       expect(formatExposureCompensation(0.015625)).toBe('+1/64ev');
       expect(formatExposureCompensation(-0.015625)).toBe('-1/64ev');
       expect(formatExposureCompensation(1)).toBe('+1ev');
+      expect(formatExposureCompensation(1.1)).toBe('+1 1/10ev');
+      expect(formatExposureCompensation(-1.1)).toBe('-1 1/10ev');
+      expect(formatExposureCompensation(1.7)).toBe('+1 7/10ev');
+      expect(formatExposureCompensation(-1.7)).toBe('-1 7/10ev');
       expect(formatExposureCompensation(-1.33)).toBe('-1 1/3ev');
       expect(formatExposureCompensation(1.33)).toBe('+1 1/3ev');
       expect(formatExposureCompensation(1.333)).toBe('+1 1/3ev');
       expect(formatExposureCompensation(1.3333)).toBe('+1 1/3ev');
       expect(formatExposureCompensation(1.5)).toBe('+1 1/2ev');
+      expect(formatExposureCompensation(2.5)).toBe('+2 1/2ev');
+      expect(formatExposureCompensation(-2.5)).toBe('-2 1/2ev');
       expect(formatExposureCompensation(1.9960938)).toBe('+2ev');
+      expect(formatExposureCompensation(-1.9960938)).toBe('-2ev');
       // Ignore long fractions
       expect(formatExposureCompensation(-0.119)).toBe('-0.12ev');
       expect(formatExposureCompensation(-0.112340989)).toBe('-0.11ev');
diff --git a/src/utility/number.ts b/src/utility/number.ts
index 701e9f15..47fff79b 100644
--- a/src/utility/number.ts
+++ b/src/utility/number.ts
@@ -14,10 +14,13 @@ const gcd = (a: number, b: number): number => {
   }
 };
 
-const formatDecimalToFraction = (decimal: number) => {
-  if (Math.abs(decimal - 0.33) < 0.011) {
+const formatDecimalToFraction = (_decimal: number) => {
+  // Prevent imprecision which causes numbers such as,
+  // 0.1 to equal 0.10000000000000009
+  const decimal = parseFloat(_decimal.toPrecision(8));
+  if (Math.abs(Math.abs(decimal) - 0.33) < 0.011) {
     return '1/3';
-  } else if (Math.abs(decimal - 0.66) <= 0.011) {
+  } else if (Math.abs(Math.abs(decimal) - 0.66) <= 0.011) {
     return '2/3';
   } else {
     const length = decimal.toString().length - 2;
@@ -34,22 +37,43 @@ const formatDecimalToFraction = (decimal: number) => {
   }
 };
 
+const STICKY_THRESHOLD = 0.011;
+const STICKY_DECIMALS = [0.25, 0.33, 0.5, 0.66, 0.75];
+const MAX_FRACTION_LENGTH = 4; // 1/64 not 1/100
+
 export const formatNumberToFraction = (number: number) => {
-  const decimal = (1 - number % 1) > 0.01
+  const sign = number >= 0 ? '+' : '-';
+
+  let decimal = (1 - Math.abs(number % 1)) > STICKY_THRESHOLD
     ? number % 1
     : 0;
-  const integer = Math.round(Math.abs(number - decimal));
+  if (decimal !== 0) {
+    for (const stickyDecimal of STICKY_DECIMALS) {
+      if (Math.abs(Math.abs(decimal) - stickyDecimal) < STICKY_THRESHOLD) {
+        decimal = decimal < 0 ? -stickyDecimal : stickyDecimal;
+        break;
+      }
+    }
+  }
+
+  let integer = Math.round(Math.abs(number - decimal));
+  if (Math.abs(decimal) === 1) {
+    decimal = 0;
+    integer += 1;
+  }
+
   const fraction = decimal !== 0
     ? formatDecimalToFraction(Math.abs(decimal))
     : '';
-  const sign = number >= 0 ? '+' : '-';
-  // Ensure fractions are not too long
-  if (!fraction || fraction.length <= 4) {
-    const whole = integer > 0
+
+  // Ensure fractions aren't too long
+  if (!fraction || fraction.length <= MAX_FRACTION_LENGTH) {
+    const integerString = integer > 0
       ? fraction ? `${integer} ` : integer
       : fraction ? '' : '0';
-    return `${sign}${whole}${fraction}`;
+    return `${sign}${integerString}${fraction}`;
   } else {
+    // console.log({ fraction });
     const decimalFormatted = decimal.toPrecision(2).replace(/^-*0+/, '');
     return `${sign}${integer}${decimalFormatted}`;
   }