[Feat] Calculator 구현

Calculator/Calculator/App/AppContainer.swift

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+//
+//  AppContainer.swift
+//  Calculator
+//
+//  Created by 안치욱 on 12/26/25.
+//
+
+
+struct AppContainer {
+    let engine: CalculatorEngine
+
+    init(engine: CalculatorEngine = DefaultCalculatorEngine()) {
+        self.engine = engine
+    }
+
+    func makeCalculatorViewModel() -> CalculatorViewModel {
+        CalculatorViewModel(engine: engine)
+    }
+}

Calculator/Calculator/App/CalculatorApp.swift

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+//
+//  CalculatorApp.swift
+//  Calculator
+//
+//  Created by 안치욱 on 12/26/25.
+//
+
+
+import SwiftUI
+
+@main
+struct CalculatorApp: App {
+    private let container = AppContainer()
+
+    var body: some Scene {
+        WindowGroup {
+            CalculatorView(viewModel: container.makeCalculatorViewModel())
+        }
+    }
+}

Calculator/Calculator/Assets.xcassets/AccentColor.colorset/Contents.json

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+{
+  "colors" : [
+    {
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

Calculator/Calculator/Assets.xcassets/AppIcon.appiconset/Contents.json

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+{
+  "images" : [
+    {
+      "idiom" : "universal",
+      "platform" : "ios",
+      "size" : "1024x1024"
+    },
+    {
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ],
+      "idiom" : "universal",
+      "platform" : "ios",
+      "size" : "1024x1024"
+    },
+    {
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "tinted"
+        }
+      ],
+      "idiom" : "universal",
+      "platform" : "ios",
+      "size" : "1024x1024"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

Calculator/Calculator/Assets.xcassets/Contents.json

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+{
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

Calculator/Calculator/Domain/CalculatorEngine.swift

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+//
+//  CalculatorEngine.swift
+//  Calculator
+//
+//  Created by 안치욱 on 12/26/25.
+//
+
+
+public protocol CalculatorEngine {
+    func reduce(state: CalculatorState, action: CalculatorAction) -> CalculatorState
+}

Calculator/Calculator/Domain/CalculatorTypes.swift

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+//
+//  CalculatorTypes.swift
+//  Calculator
+//
+//  Created by 안치욱 on 12/26/25.
+//
+
+
+import Foundation
+
+public enum Operation: Equatable {
+    case add, sub, mul, div
+}
+
+public enum CalculatorAction: Equatable {
+    case digit(Int)
+    case dot
+    case op(Operation)
+    case equals
+    case clear
+    case delete
+    case toggleSign
+    case percent
+}
+
+public struct CalculatorState: Equatable {
+    public var display: String = "0"
+
+    public var entry: String = "0"
+
+    public var accumulator: Decimal? = nil
+
+    public var pendingOp: Operation? = nil
+
+    public var isEnteringNewNumber: Bool = true
+
+    public var error: String? = nil
+
+    public init() {}
+}

Calculator/Calculator/Domain/DefaultCalculatorEngine.swift

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+//
+//  DefaultCalculatorEngine.swift
+//  Calculator
+//
+//  Created by 안치욱 on 12/26/25.
+//
+
+
+import Foundation
+
+public struct DefaultCalculatorEngine: CalculatorEngine {
+    public init() {}
+
+    public func reduce(state: CalculatorState, action: CalculatorAction) -> CalculatorState {
+        var s = state
+        s.error = nil
+
+        switch action {
+        case .clear:
+            return CalculatorState()
+
+        case .digit(let n):
+            return handleDigit(&s, n)
+
+        case .dot:
+            return handleDot(&s)
+
+        case .delete:
+            return handleDelete(&s)
+
+        case .toggleSign:
+            return handleToggleSign(&s)
+
+        case .percent:
+            return handlePercent(&s)
+
+        case .op(let op):
+            return handleOp(&s, op)
+
+        case .equals:
+            return handleEquals(&s)
+        }
+    }
+}
+
+private extension DefaultCalculatorEngine {
+
+    func handleDigit(_ s: inout CalculatorState, _ n: Int) -> CalculatorState {
+        guard (0...9).contains(n) else { return s }
+
+        if s.isEnteringNewNumber {
+            s.entry = "\(n)"
+            s.isEnteringNewNumber = false
+        } else {
+            if s.entry == "0" { s.entry = "\(n)" }
+            else if s.entry == "-0" { s.entry = "-\(n)" }
+            else { s.entry += "\(n)" }
+        }
+        s.display = s.entry
+        return s
+    }
+
+    func handleDot(_ s: inout CalculatorState) -> CalculatorState {
+        if s.isEnteringNewNumber {
+            s.entry = "0."
+            s.isEnteringNewNumber = false
+        } else if !s.entry.contains(".") {
+            s.entry += "."
+        }
+        s.display = s.entry
+        return s
+    }
+
+    func handleDelete(_ s: inout CalculatorState) -> CalculatorState {
+        guard !s.isEnteringNewNumber else { return s }
+
+        if s.entry.count <= 1 || (s.entry.count == 2 && s.entry.hasPrefix("-")) {
+            s.entry = "0"
+            s.isEnteringNewNumber = true
+        } else {
+            s.entry.removeLast()
+            if s.entry.last == "." { s.entry.removeLast() } // "12." 방지
+            if s.entry == "-" { s.entry = "0"; s.isEnteringNewNumber = true }
+        }
+        s.display = s.entry
+        return s
+    }
+
+    func handleToggleSign(_ s: inout CalculatorState) -> CalculatorState {
+        if s.entry == "0" { return s }
+        if s.entry.hasPrefix("-") { s.entry.removeFirst() }
+        else { s.entry = "-" + s.entry }
+        s.display = s.entry
+        return s
+    }
+
+    func handlePercent(_ s: inout CalculatorState) -> CalculatorState {
+        guard let v = Decimal(string: s.entry) else { return s }
+        let r = v / 100
+        s.entry = format(r)
+        s.display = s.entry
+        return s
+    }
+
+    func handleOp(_ s: inout CalculatorState, _ op: Operation) -> CalculatorState {
+        guard let current = Decimal(string: s.entry) else { return s }
+
+        if s.accumulator == nil {
+            s.accumulator = current
+        } else if let acc = s.accumulator, let pending = s.pendingOp, !s.isEnteringNewNumber {
+            guard let result = apply(pending, acc, current) else { return setError(&s) }
+            s.accumulator = result
+            s.entry = format(result)
+            s.display = s.entry
+        } else {
+
+        }
+
+        s.pendingOp = op
+        s.isEnteringNewNumber = true
+        return s
+    }
+
+    func handleEquals(_ s: inout CalculatorState) -> CalculatorState {
+        guard let acc = s.accumulator, let pending = s.pendingOp else {
+            s.display = s.entry
+            s.isEnteringNewNumber = true
+            return s
+        }
+        guard let current = Decimal(string: s.entry) else { return s }
+
+        guard let result = apply(pending, acc, current) else { return setError(&s) }
+        s.accumulator = result
+        s.pendingOp = nil
+        s.entry = format(result)
+        s.display = s.entry
+        s.isEnteringNewNumber = true
+        return s
+    }
+
+    func apply(_ op: Operation, _ a: Decimal, _ b: Decimal) -> Decimal? {
+        switch op {
+        case .add: return a + b
+        case .sub: return a - b
+        case .mul: return a * b
+        case .div:
+            if b == 0 { return nil }
+            return a / b
+        }
+    }
+
+    func setError(_ s: inout CalculatorState) -> CalculatorState {
+        s.error = "Error"
+        s.display = "Error"
+        s.entry = "0"
+        s.accumulator = nil
+        s.pendingOp = nil
+        s.isEnteringNewNumber = true
+        return s
+    }
+
+    func format(_ d: Decimal) -> String {
+        let ns = d as NSDecimalNumber
+        var str = ns.stringValue
+
+        if str == "-0" { str = "0" }
+        return str
+    }
+}

Calculator/Calculator/Presentation/CalculatorViewModel.swift

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+//
+//  CalculatorViewModel.swift
+//  Calculator
+//
+//  Created by 안치욱 on 12/26/25.
+//
+
+
+import SwiftUI
+
+import Combine
+
+
+@MainActor
+final class CalculatorViewModel: ObservableObject {
+    @Published private(set) var state: CalculatorState
+
+    private let engine: CalculatorEngine
+
+    init(engine: CalculatorEngine, initial: CalculatorState = .init()) {
+        self.engine = engine
+        self.state = initial
+    }
+
+    func send(_ action: CalculatorAction) {
+        state = engine.reduce(state: state, action: action)
+    }
+}