WTF-897 Exchange Rate improvements

Allows the user to set the precision for their exchange rate values.

Config setting:
```
exchangerates:
  precision: 3
```

Default is `7`.

Also aligns converted values along the decimal place for improved
aesthetics.

Signed-off-by: Chris Cummer <chriscummer@me.com>

modules/exchangerates/settings.go

@@ -15,6 +15,8 @@ const (
 type Settings struct {
 	common *cfg.Common
 
+	precision int `help:"How many decimal places to display." optional:"true"`
+
 	rates map[string][]string `help:"Defines what currency rates we want to know about"`
 	order []string
 }
@@ -24,6 +26,8 @@ func NewSettingsFromYAML(name string, ymlConfig *config.Config, globalConfig *co
 	settings := Settings{
 		common: cfg.NewCommonSettingsFromModule(name, defaultTitle, defaultFocusable, ymlConfig, globalConfig),
 
+		precision: ymlConfig.UInt("precision", 7),
+
 		rates: map[string][]string{},
 		order: []string{},
 	}

modules/exchangerates/widget.go

@@ -1,11 +1,12 @@
-// Package exchangerates
 package exchangerates
 
 import (
 	"fmt"
+	"regexp"
 
 	"github.com/rivo/tview"
 	"github.com/wtfutil/wtf/view"
+	"github.com/wtfutil/wtf/wtf"
 )
 
 type Widget struct {
@@ -50,22 +51,36 @@ func (widget *Widget) Render() {
 /* -------------------- Unexported Functions -------------------- */
 
 func (widget *Widget) content() (string, string, bool) {
-	out := ""
-
 	if widget.err != nil {
-		out = widget.err.Error()
+		return widget.CommonSettings().Title, widget.err.Error(), false
-	} else {
+	}
-		for base, rates := range widget.settings.rates {
-			prefix := fmt.Sprintf("[%s]1 %s[white] = ", widget.settings.common.Colors.Subheading, base)
 
-			for idx, cur := range rates {
+	out := ""
+	idx := 0
+	for base, rates := range widget.settings.rates {
+		for _, cur := range rates {
 			rate := widget.rates[base][cur]
 
-				out += prefix
+			out += fmt.Sprintf(
-				out += fmt.Sprintf("[%s]%f %s[white]\n", widget.CommonSettings().RowColor(idx), rate, cur)
+				"[%s]1 %s = %s %s[white]\n",
-			}
+				widget.CommonSettings().RowColor(idx),
+				base,
+				widget.formatConversionRate(rate),
+				cur,
+			)
+
+			idx++
 		}
 	}
 
 	return widget.CommonSettings().Title, out, false
 }
+
+// formatConversionRate takes the raw conversion float and formats it to the precision the
+// user specifies in their config (or to the default value)
+func (widget *Widget) formatConversionRate(rate float64) string {
+	rate = wtf.TruncateFloat64(rate, widget.settings.precision)
+
+	r, _ := regexp.Compile(`\.?0*$`)
+	return r.ReplaceAllString(fmt.Sprintf("%10.7f", rate), "")
+}

wtf/numbers.go

@@ -0,0 +1,14 @@
+package wtf
+
+import "math"
+
+// Round rounds a float to an integer
+func Round(num float64) int {
+	return int(num + math.Copysign(0.5, num))
+}
+
+// TruncateFloat64 truncates the decimal places of a float64 to the specified precision
+func TruncateFloat64(num float64, precision int) float64 {
+	output := math.Pow(10, float64(precision))
+	return float64(Round(num*output)) / output
+}

wtf/numbers_test.go

@@ -0,0 +1,78 @@
+package wtf
+
+import (
+	"testing"
+
+	"gotest.tools/assert"
+)
+
+func Test_Round(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    float64
+		expected int
+	}{
+		{
+			name:     "negative",
+			input:    -3,
+			expected: -3,
+		},
+		{
+			name:     "integer",
+			input:    3,
+			expected: 3,
+		},
+		{
+			name:     "float down",
+			input:    3.123456,
+			expected: 3,
+		},
+		{
+			name:     "float up",
+			input:    3.998786,
+			expected: 4,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			actual := Round(tt.input)
+			assert.Equal(t, tt.expected, actual)
+		})
+	}
+}
+
+func Test_TruncateFloat(t *testing.T) {
+	tests := []struct {
+		name      string
+		input     float64
+		precision int
+		expected  float64
+	}{
+		{
+			name:      "negative precision",
+			input:     23.234567,
+			precision: -2,
+			expected:  0,
+		},
+		{
+			name:      "zero precision",
+			input:     23.234567,
+			precision: 0,
+			expected:  23,
+		},
+		{
+			name:      "positive precision",
+			input:     23.234567,
+			precision: 2,
+			expected:  23.23,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			actual := TruncateFloat64(tt.input, tt.precision)
+			assert.Equal(t, tt.expected, actual)
+		})
+	}
+}