Transform [Message] to History struct

Author: sebsto

Examples/ios-math-solver/Sources/MathSolverViewModel.swift

@@ -113,7 +113,7 @@ final class MathSolverViewModel: ObservableObject, @unchecked Sendable {
 
         // Make the streaming request
         Task {
-            var messages: [Message] = []
+            var messages: History = []
             do {
                 // Process the stream
                 let response = try await bedrockService.converseStream(with: promptBuilder)

Examples/text_chat/Sources/TextChat.swift

@@ -48,7 +48,7 @@ struct TextChat {
         var request: ConverseRequestBuilder? = nil
 
         // we keep track of the history of the conversation
-        var history: [Message] = []
+        var history: History = []
 
         // while the user doesn't type "exit" or "quit"
         while true {

Examples/web-playground/backend/Sources/PlaygroundAPI/Types/Chat.swift

@@ -21,7 +21,7 @@ extension Message: @retroactive ResponseCodable {}
 
 struct ChatInput: Codable {
     let prompt: String?
-    let history: [Message]?
+    let history: History?
     let imageFormat: ImageBlock.Format?
     let imageBytes: String?
     let documentName: String?

Sources/Converse/BedrockService+Converse.swift

@@ -42,7 +42,7 @@ extension BedrockService {
     /// - Returns: A Message containing the model's response
     public func converse(
         with model: BedrockModel,
-        conversation: [Message],
+        conversation: History,
         maxTokens: Int? = nil,
         temperature: Double? = nil,
         topP: Double? = nil,

Sources/Converse/BedrockService+ConverseStreaming.swift

@@ -43,7 +43,7 @@ extension BedrockService {
     ///            or the low-level stream provided by the AWS SDK.
     public func converseStream(
         with model: BedrockModel,
-        conversation: [Message],
+        conversation: History,
         maxTokens: Int? = nil,
         temperature: Double? = nil,
         topP: Double? = nil,

Sources/Converse/ContentBlocks/History.swift

@@ -24,15 +24,15 @@ import Foundation
 
 public struct ConverseRequest {
     let model: BedrockModel
-    let messages: [Message]
+    let messages: History
     let inferenceConfig: InferenceConfig?
     let toolConfig: ToolConfig?
     let systemPrompts: [String]?
     let maxReasoningTokens: Int?
 
     init(
         model: BedrockModel,
-        messages: [Message] = [],
+        messages: History,
         maxTokens: Int?,
         temperature: Double?,
         topP: Double?,

Sources/Converse/ConverseRequest.swift

@@ -24,7 +24,7 @@ public struct ConverseRequestBuilder: Sendable {
     public private(set) var model: BedrockModel
     private var parameters: ConverseParameters
 
-    public private(set) var history: [Message]
+    public private(set) var history: History
     public private(set) var tools: [Tool]?
 
     public private(set) var prompt: String?
@@ -88,8 +88,11 @@ public struct ConverseRequestBuilder: Sendable {
     // MARK - builder methods
 
     // MARK - builder methods - history
-
     public func withHistory(_ history: [Message]) throws -> ConverseRequestBuilder {
+        try withHistory(.init(history))
+    }
+
+    public func withHistory(_ history: History) throws -> ConverseRequestBuilder {
         if let lastMessage = history.last {
             guard lastMessage.role == .assistant else {
                 throw BedrockLibraryError.ConverseRequestBuilder("Last message in history must be from assistant.")

Sources/Converse/ConverseRequestBuilder.swift

@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Bedrock Library open source project
+//
+// Copyright (c) 2025 Amazon.com, Inc. or its affiliates
+//                    and the Swift Bedrock Library project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift Bedrock Library project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+public struct History: Codable, Sendable {
+    private var messages: [Message] = []
+    
+    public init() {}
+    
+    public init(_ message: Message) {
+        messages = [message]
+    }
+    
+    public init(_ messages: [Message]) {
+        self.messages = messages
+    }
+    
+    public init(_ messages: Message...) {
+        self.messages = messages
+    }
+    
+    public mutating func append(_ message: Message) {
+        messages.append(message)
+    }
+    
+    /// Essentials functions from Array that History needs
+    public var count: Int { messages.count }
+    
+    public subscript(index: Int) -> Message {
+        messages[index]
+    }
+
+    public var last : Message? {
+        messages.last
+    }
+
+    public static func + (lhs: History, rhs: [Message]) -> History {
+        var result = lhs
+        result.messages.append(contentsOf: rhs)
+        return result
+    }
+}
+
+/// Collection
+extension History: Collection {
+    public var startIndex: Int { messages.startIndex }
+    public var endIndex: Int { messages.endIndex }
+    public func index(after i: Int) -> Int { messages.index(after: i) }
+}
+
+/// CustomString Convertible
+extension History: CustomStringConvertible {
+    public var description: String {
+        var result = "\(self.count) turns:\n"
+        for message in self {
+            result += "\(message)\n"
+        }
+        return result
+    }
+}
+
+/// ExpressibleByArrayLiteral
+extension History: ExpressibleByArrayLiteral {
+    public init(arrayLiteral elements: Message...) {
+        self.messages = elements
+    }
+}