Add the reverseRangeFunc & rangeFunc methods on ArrayUtils cont…

…ract to support decreasing ranges (#17)

* Add the reverseRangeFunc and reverseRange methods on ArrayUtils contract to support decreasing ranges

* Add Cadence tests for ArrayUtils smart contract

* Replace the reverseRange function with reverse

The reverse function accepts an array as an argument, and returns
its reversed version.

cadence/contracts/ArrayUtils.cdc

@@ -2,22 +2,32 @@
 
 pub contract ArrayUtils {
 
-    pub fun rangeFunc(_ start: Int, _ end: Int, _ f : ((Int):Void) ) {
+    pub fun rangeFunc(_ start: Int, _ end: Int, _ f: ((Int): Void)) {
         var current = start
-        while current < end{
+        while current < end {
             f(current)
             current = current + 1
         }
     }
 
-    pub fun range(_ start: Int, _ end: Int): [Int]{
-        var res:[Int] = []
-        self.rangeFunc(start, end, fun (i:Int){
+    pub fun range(_ start: Int, _ end: Int): [Int] {
+        var res: [Int] = []
+        self.rangeFunc(start, end, fun (i: Int) {
             res.append(i)
         })
         return res
     }
 
+    pub fun reverse(_ array: [Int]): [Int] {
+        var res: [Int] = []
+        var i: Int = array.length - 1
+        while i >= 0 {
+            res.append(array[i])
+            i = i - 1
+        }
+        return res
+    }
+
     pub fun transform(_ array: &[AnyStruct], _ f : ((AnyStruct): AnyStruct)){
         for i in self.range(0, array.length){
             array[i] = f(array[i])

test/ArrayUtils_test.cdc

@@ -0,0 +1,135 @@
+import Test
+import ArrayUtils from "../cadence/contracts/ArrayUtils.cdc"
+
+pub struct Token {
+    pub let id: Int
+    pub(set) var balance: Int
+
+    init(id: Int, balance: Int) {
+        self.id = id
+        self.balance = balance
+    }
+}
+
+pub(set) var arrayUtils = ArrayUtils()
+
+pub fun testRange() {
+    // Act
+    var range = arrayUtils.range(0, 10)
+
+    // Assert
+    var expected: [Int] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+    var i: Int = 0
+    while i < expected.length {
+        Test.assert(expected[i] == range[i])
+        i = i + 1
+    }
+}
+
+pub fun testReverseRange() {
+    // Act
+    var range = arrayUtils.reverse(arrayUtils.range(0, 10))
+
+    // Assert
+    var expected: [Int] = [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
+    var i: Int = 0
+    while i < expected.length {
+        Test.assert(expected[i] == range[i])
+        i = i + 1
+    }
+}
+
+pub fun testTransform() {
+    // Arrange
+    let tokens = [
+        Token(id: 0, balance: 10),
+        Token(id: 1, balance: 5),
+        Token(id: 2, balance: 15)
+    ]
+
+    // Act
+    arrayUtils.transform(&tokens as &[AnyStruct], fun (t: AnyStruct): AnyStruct {
+        var token = t as! Token
+        token.balance = token.balance * 2
+        return token
+    })
+
+    // Assert
+    Test.assert(tokens[0].balance == 20)
+    Test.assert(tokens[1].balance == 10)
+    Test.assert(tokens[2].balance == 30)
+}
+
+pub fun testIterate() {
+    // Arrange
+    let tokens = [
+        Token(id: 0, balance: 10),
+        Token(id: 1, balance: 5),
+        Token(id: 2, balance: 15),
+        Token(id: 3, balance: 22),
+        Token(id: 4, balance: 31)
+    ]
+
+    // Act
+    arrayUtils.iterate(tokens as [AnyStruct], fun (t: AnyStruct): Bool {
+        var token = t as! Token
+        return token.id <= 2
+    })
+}
+
+pub fun testMap() {
+    // Arrange
+    let tokens = [
+        Token(id: 0, balance: 10),
+        Token(id: 1, balance: 5),
+        Token(id: 2, balance: 15)
+    ]
+
+    // Act
+    let mapped = arrayUtils.map(tokens as [AnyStruct], fun (t: AnyStruct): AnyStruct {
+        var token = t as! Token
+        token.balance = token.balance - 2
+        return token
+    })
+
+    // Assert
+    Test.assert((mapped[0] as! Token).balance == 8)
+    Test.assert((mapped[1] as! Token).balance == 3)
+    Test.assert((mapped[2] as! Token).balance == 13)
+}
+
+pub fun testMapStrings() {
+    // Arrange
+    let strings = ["Peter", "John", "Mark"]
+
+    // Act
+    let mapped = arrayUtils.mapStrings(strings, fun (s: String): String {
+        return "Hello, ".concat(s).concat("!")
+    })
+
+    // Assert
+    Test.assert(mapped[0] == "Hello, Peter!")
+    Test.assert(mapped[1] == "Hello, John!")
+    Test.assert(mapped[2] == "Hello, Mark!")
+}
+
+pub fun testReduce() {
+    // Arrange
+    let tokens = [
+        Token(id: 0, balance: 10),
+        Token(id: 1, balance: 5),
+        Token(id: 2, balance: 15)
+    ]
+    let initial = Token(id: 5, balance: 0) as AnyStruct
+
+    // Act
+    let token = arrayUtils.reduce(tokens as [AnyStruct], initial, fun (acc: AnyStruct, t: AnyStruct): AnyStruct {
+        var token = t as! Token
+        var accToken = acc as! Token
+        accToken.balance = accToken.balance + token.balance
+        return accToken
+    })
+
+    // Assert
+    Test.assert((token as! Token).balance == 30)
+}