sleepy_agent_ios/SleepyAgent/Inference/Bridge/LlmEngineBridge.mm

//
//  LlmEngineBridge.mm
//  SleepyAgent
//
//  Objective-C++ implementation of LiteRT-LM bridge
//

#import "LlmEngineBridge.h"
#include <memory>
#include <string>
#include <vector>

// TODO: Include actual LiteRT-LM headers when available
// These are placeholder includes - replace with actual paths
// #include "litert_lm/engine.h"
// #include "litert_lm/conversation.h"
// #include "litert_lm/content.h"

NSString *const kLiteRTLMErrorDomain = @"com.sleepyagent.litert.lm";

// MARK: - Private Interface

@interface LlmEngineBridge () {
    // TODO: Replace with actual LiteRT-LM C++ types
    // std::unique_ptr<litert::lm::Engine> _engine;
    // std::unique_ptr<litert::lm::Conversation> _conversation;
    
    // Stub: Just track state for now
    BOOL _isInitialized;
    NSString *_modelPath;
    LiteRTAccelerator _accelerator;
    NSMutableArray<NSDictionary *> *_history;
}
@end

// MARK: - Response Stream Implementation

@interface LiteRTResponseStream () {
    NSMutableArray<NSString *> *_chunks;
    NSInteger _currentIndex;
    BOOL _isComplete;
}
@end

@implementation LiteRTResponseStream

- (instancetype)init {
    self = [super init];
    if (self) {
        _chunks = [NSMutableArray array];
        _currentIndex = 0;
        _isComplete = NO;
    }
    return self;
}

- (void)addChunk:(NSString *)chunk {
    [_chunks addObject:chunk];
}

- (void)markComplete {
    _isComplete = YES;
}

- (nullable NSString *)nextChunk {
    if (_currentIndex < _chunks.count) {
        return _chunks[_currentIndex++];
    }
    return nil;
}

- (BOOL)hasMore {
    return _currentIndex < _chunks.count || !_isComplete;
}

- (void)close {
    _chunks = nil;
    _isComplete = YES;
}

@end

// MARK: - LlmEngineBridge Implementation

@implementation LlmEngineBridge

- (nullable instancetype)initWithModelPath:(NSString *)modelPath
                               accelerator:(LiteRTAccelerator)accelerator
                                     error:(NSError **)error {
    self = [super init];
    if (self) {
        _modelPath = [modelPath copy];
        _accelerator = accelerator;
        _history = [NSMutableArray array];
        
        // Check if model file exists
        if (![[NSFileManager defaultManager] fileExistsAtPath:modelPath]) {
            if (error) {
                *error = [NSError errorWithDomain:kLiteRTLMErrorDomain
                                             code:404
                                         userInfo:@{NSLocalizedDescriptionKey: 
                                                    [NSString stringWithFormat:@"Model file not found: %@", modelPath]}];
            }
            return nil;
        }
        
        // TODO: Initialize actual LiteRT-LM engine
        //
        // Example implementation:
        // auto config = litert::lm::EngineConfig{
        //     .model_path = [modelPath UTF8String],
        //     .max_num_tokens = 8192
        // };
        //
        // auto accel = (accelerator == LiteRTAcceleratorMetal) 
        //     ? litert::HwAccelerators::kGpu 
        //     : litert::HwAccelerators::kCpu;
        //
        // auto result = litert::lm::Engine::Create(config, accel);
        // if (!result.ok()) {
        //     if (error) {
        //         *error = [NSError errorWithDomain:kLiteRTLMErrorDomain
        //                                      code:1
        //                                  userInfo:@{NSLocalizedDescriptionKey: 
        //                                             @(result.status().message().data())}];
        //     }
        //     return nil;
        // }
        // _engine = std::move(*result);
        //
        // // Create conversation for KV cache
        // auto conv_config = litert::lm::ConversationConfig{};
        // auto conv_result = _engine->CreateConversation(conv_config);
        // if (conv_result.ok()) {
        //     _conversation = std::move(*conv_result);
        // }
        
        // Stub: Simulate successful initialization
        _isInitialized = YES;
    }
    return self;
}

- (nullable NSString *)generateResponse:(NSString *)prompt
                                  error:(NSError **)error {
    if (!_isInitialized) {
        if (error) {
            *error = [NSError errorWithDomain:kLiteRTLMErrorDomain
                                         code:2
                                     userInfo:@{NSLocalizedDescriptionKey: @"Engine not initialized"}];
        }
        return nil;
    }
    
    // TODO: Implement actual generation with LiteRT-LM
    //
    // Example:
    // auto contents = litert::lm::Contents::FromText([prompt UTF8String]);
    // auto response = _conversation->SendMessage(contents);
    // if (response.ok()) {
    //     return [NSString stringWithUTF8String:response->text().c_str()];
    // } else {
    //     if (error) {
    //         *error = [NSError errorWithDomain:kLiteRTLMErrorDomain
    //                                      code:3
    //                                  userInfo:@{NSLocalizedDescriptionKey: 
    //                                             @(response.status().message().data())}];
    //     }
    //     return nil;
    // }
    
    // Stub: Return placeholder response
    return [NSString stringWithFormat:@"[STUB] LiteRT-LM Swift APIs are coming soon. "
            @"This is a placeholder response for prompt: %@", prompt];
}

- (nullable LiteRTResponseStream *)generateResponseStream:(NSString *)prompt
                                                    error:(NSError **)error {
    if (!_isInitialized) {
        if (error) {
            *error = [NSError errorWithDomain:kLiteRTLMErrorDomain
                                         code:2
                                     userInfo:@{NSLocalizedDescriptionKey: @"Engine not initialized"}];
        }
        return nil;
    }
    
    LiteRTResponseStream *stream = [[LiteRTResponseStream alloc] init];
    
    // TODO: Implement actual streaming with LiteRT-LM
    //
    // Example:
    // auto contents = litert::lm::Contents::FromText([prompt UTF8String]);
    // auto async_response = _conversation->SendMessageAsync(contents);
    //
    // for (const auto& chunk : async_response) {
    //     [stream addChunk:@(chunk.text().c_str())];
    // }
    // [stream markComplete];
    
    // Stub: Simulate streaming with placeholder
    NSArray *words = @[@"LiteRT-LM", @"on", @"iOS", @"requires", @"C++", 
                       @"integration.", @"Swift", @"APIs", @"are", @"'coming", 
                       @"soon'", @"per", @"Google.", @"See", @"LITERT_INTEGRATION.md",
                       @"for", @"details."];
    
    for (NSString *word in words) {
        [stream addChunk:[word stringByAppendingString:@" "]];
    }
    [stream markComplete];
    
    return stream;
}

- (void)addToHistory:(NSString *)message
                role:(NSString *)role {
    [_history addObject:@{@"role": role, @"message": message}];
    
    // TODO: Add to LiteRT-LM conversation history
    // if (_conversation) {
    //     auto role_str = [role isEqualToString:@"user"] 
    //         ? litert::lm::Role::kUser 
    //         : litert::lm::Role::kAssistant;
    //     _conversation->AddMessage(role_str, [message UTF8String]);
    // }
}

- (void)clearHistory {
    [_history removeAllObjects];
    
    // TODO: Reset LiteRT-LM conversation
    // if (_engine) {
    //     auto conv_config = litert::lm::ConversationConfig{};
    //     auto conv_result = _engine->CreateConversation(conv_config);
    //     if (conv_result.ok()) {
    //         _conversation = std::move(*conv_result);
    //     }
    // }
}

- (BOOL)isReady {
    return _isInitialized; // && _engine != nullptr;
}

- (NSInteger)maxTokens {
    return 16384; // Default, could query from model
}

- (NSInteger)estimateTokens:(NSString *)text {
    // Rough estimation: ~4 characters per token
    return text.length / 4;
    
    // TODO: Use actual tokenizer
    // if (_engine) {
    //     return _engine->EstimateTokens([text UTF8String]);
    // }
}

- (void)close {
    // TODO: Release C++ resources
    // _conversation.reset();
    // _engine.reset();
    
    _isInitialized = NO;
    _modelPath = nil;
    [_history removeAllObjects];
}

- (void)dealloc {
    [self close];
}

@end