From c0ab87796673cfd48db3faa95ed06117b12a201c Mon Sep 17 00:00:00 2001
From: Peter Holmberg <peter.hlmbrg@gmail.com>
Date: Thu, 21 Mar 2019 13:45:50 +0100
Subject: [PATCH] adding function

---
 .../grafana-ui/src/utils/displayValue.test.ts |  6 +--
 packages/grafana-ui/src/utils/displayValue.ts | 44 ++++++++++++++++++-
 2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/packages/grafana-ui/src/utils/displayValue.test.ts b/packages/grafana-ui/src/utils/displayValue.test.ts
index bf0e7a89bba..8e7a4a421a2 100644
--- a/packages/grafana-ui/src/utils/displayValue.test.ts
+++ b/packages/grafana-ui/src/utils/displayValue.test.ts
@@ -1,5 +1,5 @@
 import { getDisplayProcessor, getColorFromThreshold, DisplayProcessor, DisplayValue } from './displayValue';
-import { MappingType, ValueMapping } from '../types/panel';
+import { MappingType, ValueMapping } from '../types';
 
 function assertSame(input: any, processors: DisplayProcessor[], match: DisplayValue) {
   processors.forEach(processor => {
@@ -128,7 +128,7 @@ describe('Format value', () => {
 
     const result = instance(value);
 
-    expect(result.text).toEqual('6.0');
+    expect(result.text).toEqual('6');
   });
 
   it('should return formatted value if there are no matching value mappings', () => {
@@ -141,7 +141,7 @@ describe('Format value', () => {
 
     const result = instance(value);
 
-    expect(result.text).toEqual('10.0');
+    expect(result.text).toEqual('10');
   });
 
   it('should return mapped value if there are matching value mappings', () => {
diff --git a/packages/grafana-ui/src/utils/displayValue.ts b/packages/grafana-ui/src/utils/displayValue.ts
index 75191f34434..04c78476595 100644
--- a/packages/grafana-ui/src/utils/displayValue.ts
+++ b/packages/grafana-ui/src/utils/displayValue.ts
@@ -15,7 +15,6 @@ export interface DisplayValue {
 export interface DisplayValueOptions {
   unit?: string;
   decimals?: DecimalCount;
-  scaledDecimals?: DecimalCount;
   dateFormat?: string; // If set try to convert numbers to date
 
   color?: string;
@@ -37,6 +36,7 @@ export type DisplayProcessor = (value: any) => DisplayValue;
 export function getDisplayProcessor(options?: DisplayValueOptions): DisplayProcessor {
   if (options && !_.isEmpty(options)) {
     const formatFunc = getValueFormat(options.unit || 'none');
+
     return (value: any) => {
       const { prefix, suffix, mappings, thresholds, theme } = options;
       let color = options.color;
@@ -47,12 +47,15 @@ export function getDisplayProcessor(options?: DisplayValueOptions): DisplayProce
       let shouldFormat = true;
       if (mappings && mappings.length > 0) {
         const mappedValue = getMappedValue(mappings, value);
+
         if (mappedValue) {
           text = mappedValue.text;
           const v = toNumber(text);
+
           if (!isNaN(v)) {
             numeric = v;
           }
+
           shouldFormat = false;
         }
       }
@@ -67,7 +70,8 @@ export function getDisplayProcessor(options?: DisplayValueOptions): DisplayProce
 
       if (!isNaN(numeric)) {
         if (shouldFormat && !_.isBoolean(value)) {
-          text = formatFunc(numeric, options.decimals, options.scaledDecimals, options.isUtc);
+          const decimalInfo = getDecimalsForValue(value);
+          text = formatFunc(numeric, decimalInfo.decimals, decimalInfo.scaledDecimals, options.isUtc);
         }
         if (thresholds && thresholds.length > 0) {
           color = getColorFromThreshold(numeric, thresholds, theme);
@@ -143,3 +147,39 @@ export function getColorFromThreshold(value: number, thresholds: Threshold[], th
   // Use the first threshold as the default color
   return getColorFromHexRgbOrName(thresholds[0].color, themeType);
 }
+
+export function getDecimalsForValue(value: number): { decimals: number; scaledDecimals: number } {
+  const delta = value / 2;
+  let dec = -Math.floor(Math.log(delta) / Math.LN10);
+
+  const magn = Math.pow(10, -dec);
+  const norm = delta / magn; // norm is between 1.0 and 10.0
+  let size;
+
+  if (norm < 1.5) {
+    size = 1;
+  } else if (norm < 3) {
+    size = 2;
+    // special case for 2.5, requires an extra decimal
+    if (norm > 2.25) {
+      size = 2.5;
+      ++dec;
+    }
+  } else if (norm < 7.5) {
+    size = 5;
+  } else {
+    size = 10;
+  }
+
+  size *= magn;
+
+  // reduce starting decimals if not needed
+  if (Math.floor(value) === value) {
+    dec = 0;
+  }
+
+  const decimals = Math.max(0, dec);
+  const scaledDecimals = decimals - Math.floor(Math.log(size) / Math.LN10) + 2;
+
+  return { decimals, scaledDecimals };
+}