Support multiple chat templates per model

Sources/Tokenizers/Tokenizer.swift

@@ -125,7 +125,8 @@ public protocol Tokenizer {
         chatTemplate: String?,
         addGenerationPrompt: Bool,
         truncation: Bool,
-        maxLength: Int?
+        maxLength: Int?,
+        tools: [[String: Any]]?
     ) throws -> [Int]
 }
 
@@ -323,12 +324,35 @@ public class PreTrainedTokenizer: Tokenizer {
 
     public func applyChatTemplate(
         messages: [[String: String]],
-        chatTemplate: String?,
+        chatTemplate: String? = nil,
         addGenerationPrompt: Bool = false,
         truncation: Bool = false,
-        maxLength: Int?
+        maxLength: Int? = nil,
+        tools: [[String: Any]]? = nil
     ) throws -> [Int] {
-        let template = try Template(chatTemplate ?? tokenizerConfig.chatTemplate?.stringValue ?? defaultChatTemplate)
+        var chatTemplateFromConfig: String?
+        if let chatTemplateValue = tokenizerConfig.chatTemplate {
+            if let chatTemplateStringValue = chatTemplateValue.stringValue {
+                chatTemplateFromConfig = chatTemplateStringValue
+            } else if let chatTemplateArrayValue = chatTemplateValue.arrayValue {
+                // If a list of chat templates is specified, convert them to a dict
+                let templateDict = Dictionary<String, String>(uniqueKeysWithValues: chatTemplateArrayValue.compactMap { template in
+                    guard let name = template[dynamicMember: "name"]?.stringValue,
+                          let templateString = template[dynamicMember: "template"]?.stringValue else {
+                        return nil
+                    }
+                    return (name, templateString)
+                })
+                // Choose the appropriate template
+                if let tools = tools, !tools.isEmpty, let toolUseTemplate = templateDict["tool_use"] {
+                    chatTemplateFromConfig = toolUseTemplate
+                } else {
+                    chatTemplateFromConfig = templateDict["default"]
+                }
+            }
+        }
+
+        let template = try Template(chatTemplate ?? chatTemplateFromConfig ?? defaultChatTemplate)
         var context: [String: Any] = [
             "messages": messages,
             "add_generation_prompt": addGenerationPrompt