// Copyright 2025 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import Foundation

/// **[Public Preview]** A multimodal model (like Gemini) that generates content using
/// server-managed prompt templates.
///
/// > Warning: This API is a public preview and may be subject to change.
///
/// When using server prompt templates, prompts, system instructions, tools, and model
/// configurations are defined and stored server-side in the Firebase console or via the Firebase AI
/// Logic REST API. Client applications only pass a template identifier and any runtime input
/// variables required by the template.
///
/// Benefits of this approach include:
/// - Protecting prompts and system instructions from exposure in client code.
/// - Updating prompts, schemas, and configurations without releasing a new app version.
///
/// > Tip: We recommend versioning your template IDs (for example, `my-template-v1-0-0`) and using
/// [Firebase Remote Config](https://firebase.google.com/docs/ai-logic/server-prompt-templates/versioning-with-remote-config)
/// to dynamically manage template IDs in client requests.
///
/// For more details, see the
/// [Server Prompt Templates
/// guide](https://firebase.google.com/docs/ai-logic/server-prompt-templates/get-started).
public final class TemplateGenerativeModel: Sendable {
  let generativeAIService: GenerativeAIService
  let apiConfig: APIConfig

  /// A list of tools the model may use to generate the next response.
  let tools: [TemplateTool]?

  /// Tool configuration for any ``TemplateTool`` specified in the request.
  let toolConfig: TemplateToolConfig?

  /// Configuration parameters for sending requests to the backend.
  let requestOptions: RequestOptions

  init(firebaseInfo: FirebaseInfo, apiConfig: APIConfig, tools: [TemplateTool]?,
       toolConfig: TemplateToolConfig?, requestOptions: RequestOptions,
       urlSession: URLSession = GenAIURLSession.default) {
    generativeAIService = GenerativeAIService(
      firebaseInfo: firebaseInfo,
      urlSession: urlSession
    )
    self.apiConfig = apiConfig
    self.tools = tools
    self.toolConfig = toolConfig
    self.requestOptions = requestOptions
  }

  /// **[Public Preview]** Generates content from a prompt template and inputs.
  ///
  /// > Warning: This API is a public preview and may be subject to change.
  ///
  /// - Parameters:
  ///   - templateID: The ID of the server prompt template to use (for example,
  ///     `"my-template-v1-0-0"`).
  ///   - inputs: A dictionary of variable names and values to substitute into the template's
  ///     Handlebars placeholders (such as `{{variable}}`) or `input.schema`. Supported value types
  ///     include `String`, `Int`, `Double`, `Float`, `Bool`, arrays, and nested dictionaries;
  ///     defaults to no inputs.
  /// - Returns: The content generated by the model.
  /// - Throws: A ``GenerateContentError`` if the request failed, or an `EncodingError` if `inputs`
  ///   cannot be encoded.
  public func generateContent(templateID: String,
                              inputs: [String: Any] = [:]) async throws
    -> GenerateContentResponse {
    return try await generateContentWithHistory(
      history: [],
      template: templateID,
      inputs: TemplateInput.inputs(from: inputs)
    )
  }

  /// **[Public Preview]** Generates content from a prompt template and inputs, with streaming
  /// responses.
  ///
  /// > Warning: This API is a public preview and may be subject to change.
  ///
  /// - Parameters:
  ///   - templateID: The ID of the server prompt template to use (for example,
  ///     `"my-template-v1-0-0"`).
  ///   - inputs: A dictionary of variable names and values to substitute into the template's
  ///     Handlebars placeholders (such as `{{variable}}`) or `input.schema`. Supported value types
  ///     include `String`, `Int`, `Double`, `Float`, `Bool`, arrays, and nested dictionaries;
  ///     defaults to no inputs.
  /// - Returns: An `AsyncThrowingStream` that yields `GenerateContentResponse` objects.
  /// - Throws: A ``GenerateContentError`` if the request failed, or an `EncodingError` if `inputs`
  ///   cannot be encoded.
  @available(macOS 12.0, watchOS 8.0, *)
  public func generateContentStream(templateID: String, inputs: [String: Any] = [:]) throws
    -> AsyncThrowingStream<GenerateContentResponse, Error> {
    return try generateContentStreamWithHistory(
      history: [],
      template: templateID,
      inputs: TemplateInput.inputs(from: inputs)
    )
  }

  /// **[Public Preview]** Creates a new chat conversation using this model with the provided
  /// template, inputs, and history.
  ///
  /// > Warning: This API is a public preview and may be subject to change.
  ///
  /// The template's model, system instructions, and configurations apply to every turn
  /// automatically, while the returned ``TemplateChat`` tracks conversation history.
  ///
  /// > Important: The referenced server prompt template must include the `{{history}}` tag in its
  /// content, which indicates where the conversation turns managed by the client SDK should be
  /// injected.
  ///
  /// For more details, see
  /// [Multi-turn interactions with server prompt templates](https://firebase.google.com/docs/ai-logic/server-prompt-templates/multi-turn-interactions).
  ///
  /// - Parameters:
  ///   - templateID: The ID of the server prompt template to use.
  ///   - inputs: A dictionary of variable names and values to substitute into the template; the
  ///     same inputs are sent with every turn of the conversation. Defaults to no inputs.
  ///   - history: The previous conversation history to seed the chat session with.
  /// - Returns: A new ``TemplateChat`` instance.
  public func startChat(templateID: String,
                        inputs: [String: Any] = [:],
                        history: [ModelContent] = []) -> TemplateChat {
    return TemplateChat(
      model: self,
      templateID: templateID,
      inputs: inputs,
      history: history
    )
  }

  // MARK: - Internal

  func templateGenerateContentRequest(template: String, inputs: [String: TemplateInput],
                                      history: [ModelContent],
                                      stream: Bool) throws -> TemplateGenerateContentRequest {
    try history.throwIfError()
    // Normalize an empty tools array to `nil` so that an empty `"tools"` array is not sent.
    let internalTools = try tools?.map { try $0.toInternal() }
    return TemplateGenerateContentRequest(
      template: template,
      inputs: inputs,
      history: history,
      projectID: generativeAIService.firebaseInfo.projectID,
      stream: stream,
      apiConfig: apiConfig,
      options: requestOptions,
      tools: (internalTools?.isEmpty ?? true) ? nil : internalTools,
      toolConfig: toolConfig
    )
  }

  /// Generates content from a prompt template, inputs, and history.
  ///
  /// - Parameters:
  ///   - history: The conversation history to use.
  ///   - template: The prompt template to use.
  ///   - inputs: The variables to substitute into the template.
  /// - Returns: The content generated by the model.
  /// - Throws: A ``GenerateContentError`` if the request failed.
  func generateContentWithHistory(history: [ModelContent], template: String,
                                  inputs: [String: TemplateInput]) async throws
    -> GenerateContentResponse {
    let request = try templateGenerateContentRequest(
      template: template,
      inputs: inputs,
      history: history,
      stream: false
    )

    return try await generativeAIService.loadRequest(request: request)
  }

  /// Generates a stream of content from a prompt template, inputs, and history.
  ///
  /// - Parameters:
  ///   - history: The conversation history to use.
  ///   - template: The prompt template to use.
  ///   - inputs: The variables to substitute into the template.
  /// - Returns: An `AsyncThrowingStream` that yields `GenerateContentResponse` objects.
  /// - Throws: A ``GenerateContentError`` if the request failed.
  @available(macOS 12.0, watchOS 8.0, *)
  func generateContentStreamWithHistory(history: [ModelContent], template: String,
                                        inputs: [String: TemplateInput]) throws
    -> AsyncThrowingStream<GenerateContentResponse, Error> {
    let request = try templateGenerateContentRequest(
      template: template,
      inputs: inputs,
      history: history,
      stream: true
    )

    return generativeAIService.loadRequestStream(request: request)
  }
}