Added support for SMMA. (#247)

# Describe Request

Added support for Smoothed Moving Average (SMMA).

Fixed #246 

# Change Type

New Indicator.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Introduced the Smoothed Moving Average (SMMA) indicator to enhance
trend analysis capabilities.
	- Added documentation for the SMMA indicator in the README file.

- **Tests**
- Implemented a new test suite to validate the functionality of the SMMA
computation.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

README.md

@@ -48,6 +48,7 @@ The following list of indicators are currently supported by this package:
 -	[Rolling Moving Average (RMA)](trend/README.md#type-rma)
 -	[Simple Moving Average (SMA)](trend/README.md#type-sma)
 -	[Since Change](helper/README.md#func-since)
+-   [Smoothed Moving Average (SMMA)](trend/README.md#type-smma)
 -	[Triple Exponential Moving Average (TEMA)](trend/README.md#type-tema)
 -	[Triangular Moving Average (TRIMA)](trend/README.md#type-trima)
 -	[Triple Exponential Average (TRIX)](trend/README.md#type-trix)

trend/README.md

@@ -115,6 +115,12 @@ The information provided on this project is strictly for informational purposes
   - [func \(s \*Sma\[T\]\) Compute\(c \<\-chan T\) \<\-chan T](<#Sma[T].Compute>)
   - [func \(s \*Sma\[T\]\) IdlePeriod\(\) int](<#Sma[T].IdlePeriod>)
   - [func \(s \*Sma\[T\]\) String\(\) string](<#Sma[T].String>)
+- [type Smma](<#Smma>)
+  - [func NewSmma\[T helper.Number\]\(\) \*Smma\[T\]](<#NewSmma>)
+  - [func NewSmmaWithPeriod\[T helper.Number\]\(period int\) \*Smma\[T\]](<#NewSmmaWithPeriod>)
+  - [func \(s \*Smma\[T\]\) Compute\(c \<\-chan T\) \<\-chan T](<#Smma[T].Compute>)
+  - [func \(s \*Smma\[T\]\) IdlePeriod\(\) int](<#Smma[T].IdlePeriod>)
+  - [func \(s \*Smma\[T\]\) String\(\) string](<#Smma[T].String>)
 - [type Tema](<#Tema>)
   - [func NewTema\[T helper.Number\]\(\) \*Tema\[T\]](<#NewTema>)
   - [func \(t \*Tema\[T\]\) Compute\(c \<\-chan T\) \<\-chan T](<#Tema[T].Compute>)
@@ -300,6 +306,15 @@ const (
 )
 ```
 
+<a name="DefaultSmmaPeriod"></a>
+
+```go
+const (
+    // DefaultSmmaPeriod is the default SMMA period of 7.
+    DefaultSmmaPeriod = 7
+)
+```
+
 <a name="DefaultTrimaPeriod"></a>
 
 ```go
@@ -1424,6 +1439,77 @@ func (s *Sma[T]) String() string
 
 String is the string representation of the SMA.
 
+<a name="Smma"></a>
+## type [Smma](<https://github.com/cinar/indicator/blob/master/trend/smma.go#L29-L32>)
+
+Smma represents the parameters for calculating the Smoothed Moving Average \(SMMA\).
+
+```
+SMMA[0] = SMA(N)
+SMMA[i] = ((SMMA[i-1] * (N - 1)) + Close[i]) / N
+```
+
+Example:
+
+```
+smma := trend.NewSmma[float64]()
+smma.Period = 10
+
+result := smma.Compute(c)
+```
+
+```go
+type Smma[T helper.Number] struct {
+    // Time period.
+    Period int
+}
+```
+
+<a name="NewSmma"></a>
+### func [NewSmma](<https://github.com/cinar/indicator/blob/master/trend/smma.go#L35>)
+
+```go
+func NewSmma[T helper.Number]() *Smma[T]
+```
+
+NewSmma function initializes a new SMMA instance with the default parameters.
+
+<a name="NewSmmaWithPeriod"></a>
+### func [NewSmmaWithPeriod](<https://github.com/cinar/indicator/blob/master/trend/smma.go#L42>)
+
+```go
+func NewSmmaWithPeriod[T helper.Number](period int) *Smma[T]
+```
+
+NewSmmaWithPeriod function initializes a new SMMA instance with the given period.
+
+<a name="Smma[T].Compute"></a>
+### func \(\*Smma\[T\]\) [Compute](<https://github.com/cinar/indicator/blob/master/trend/smma.go#L50>)
+
+```go
+func (s *Smma[T]) Compute(c <-chan T) <-chan T
+```
+
+Compute function takes a channel of numbers and computes the SMMA over the specified period.
+
+<a name="Smma[T].IdlePeriod"></a>
+### func \(\*Smma\[T\]\) [IdlePeriod](<https://github.com/cinar/indicator/blob/master/trend/smma.go#L72>)
+
+```go
+func (s *Smma[T]) IdlePeriod() int
+```
+
+IdlePeriod is the initial period that SMMA yield any results.
+
+<a name="Smma[T].String"></a>
+### func \(\*Smma\[T\]\) [String](<https://github.com/cinar/indicator/blob/master/trend/smma.go#L77>)
+
+```go
+func (s *Smma[T]) String() string
+```
+
+String is the string representation of the SMMA.
+
 <a name="Tema"></a>
 ## type [Tema](<https://github.com/cinar/indicator/blob/master/trend/tema.go#L18-L22>)
 

trend/smma.go

@@ -0,0 +1,76 @@
+// Copyright (c) 2021-2024 Onur Cinar.
+// The source code is provided under GNU AGPLv3 License.
+// https://github.com/cinar/indicator
+
+package trend
+
+import (
+	"fmt"
+
+	"github.com/cinar/indicator/v2/helper"
+)
+
+const (
+	// DefaultSmmaPeriod is the default SMMA period of 7.
+	DefaultSmmaPeriod = 7
+)
+
+// Smma represents the parameters for calculating the Smoothed Moving Average (SMMA).
+//
+//	SMMA[0] = SMA(N)
+//	SMMA[i] = ((SMMA[i-1] * (N - 1)) + Close[i]) / N
+//
+// Example:
+//
+//	smma := trend.NewSmma[float64]()
+//	smma.Period = 10
+//
+//	result := smma.Compute(c)
+type Smma[T helper.Number] struct {
+	// Time period.
+	Period int
+}
+
+// NewSmma function initializes a new SMMA instance with the default parameters.
+func NewSmma[T helper.Number]() *Smma[T] {
+	return NewSmmaWithPeriod[T](DefaultSmmaPeriod)
+}
+
+// NewSmmaWithPeriod function initializes a new SMMA instance with the given period.
+func NewSmmaWithPeriod[T helper.Number](period int) *Smma[T] {
+	return &Smma[T]{
+		Period: period,
+	}
+}
+
+// Compute function takes a channel of numbers and computes the SMMA over the specified period.
+func (s *Smma[T]) Compute(c <-chan T) <-chan T {
+	result := make(chan T, cap(c))
+
+	go func() {
+		defer close(result)
+
+		// Initial SMMA value is the SMA.
+		sma := NewSmaWithPeriod[T](s.Period)
+
+		before := <-sma.Compute(helper.Head(c, s.Period))
+		result <- before
+
+		for n := range c {
+			before = ((before * (T(s.Period) - 1)) + n) / T(s.Period)
+			result <- before
+		}
+	}()
+
+	return result
+}
+
+// IdlePeriod is the initial period that SMMA yield any results.
+func (s *Smma[T]) IdlePeriod() int {
+	return s.Period - 1
+}
+
+// String is the string representation of the SMMA.
+func (s *Smma[T]) String() string {
+	return fmt.Sprintf("SMMA(%d)", s.Period)
+}

trend/smma_test.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2021-2024 Onur Cinar.
+// The source code is provided under GNU AGPLv3 License.
+// https://github.com/cinar/indicator
+
+package trend_test
+
+import (
+	"testing"
+
+	"github.com/cinar/indicator/v2/helper"
+	"github.com/cinar/indicator/v2/trend"
+)
+
+func TestSmma(t *testing.T) {
+	type Data struct {
+		Close float64
+		Smma  float64
+	}
+
+	input, err := helper.ReadFromCsvFile[Data]("testdata/smma.csv", true)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	inputs := helper.Duplicate(input, 2)
+	closing := helper.Map(inputs[0], func(d *Data) float64 { return d.Close })
+	expected := helper.Map(inputs[1], func(d *Data) float64 { return d.Smma })
+
+	smma := trend.NewSmma[float64]()
+
+	actual := smma.Compute(closing)
+	actual = helper.RoundDigits(actual, 2)
+
+	expected = helper.Skip(expected, smma.IdlePeriod())
+
+	err = helper.CheckEquals(actual, expected)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestSmmaString(t *testing.T) {
+	expected := "SMMA(10)"
+	actual := trend.NewSmmaWithPeriod[float64](10).String()
+
+	if actual != expected {
+		t.Fatalf("actual %v expected %v", actual, expected)
+	}
+}