/**
 * MI Provider Abstraction — swappable AI backends for Mycelial Intelligence.
 *
 * Normalises Ollama, Gemini, Anthropic, and OpenAI-compatible endpoints into
 * a single stream interface. The registry auto-detects available providers
 * from environment variables at startup.
 */

export interface MiMessage {
	role: "system" | "user" | "assistant";
	content: string;
	images?: string[];
}

export interface MiStreamChunk {
	content: string;
	done: boolean;
}

export interface MiModelConfig {
	/** Unique ID used in API requests (e.g. "gemini-flash") */
	id: string;
	/** Provider key (e.g. "ollama", "gemini") */
	provider: string;
	/** Model name as the provider expects it (e.g. "gemini-2.5-flash") */
	providerModel: string;
	/** Display label for UI */
	label: string;
	/** Group header in model selector */
	group: string;
}

export interface MiProvider {
	id: string;
	isAvailable(): boolean;
	stream(messages: MiMessage[], model: string): AsyncGenerator<MiStreamChunk>;
}

// ── Model Registry ──

const MODEL_REGISTRY: MiModelConfig[] = [
	{ id: "gemini-flash", provider: "gemini", providerModel: "gemini-2.5-flash", label: "Gemini Flash", group: "Gemini" },
	{ id: "gemini-pro", provider: "gemini", providerModel: "gemini-2.5-pro", label: "Gemini Pro", group: "Gemini" },
	{ id: "llama3.2", provider: "ollama", providerModel: "llama3.2:3b", label: "Llama 3.2 (3B)", group: "Local" },
	{ id: "llama3.1", provider: "ollama", providerModel: "llama3.1:8b", label: "Llama 3.1 (8B)", group: "Local" },
	{ id: "qwen2.5-coder", provider: "ollama", providerModel: "qwen2.5-coder:7b", label: "Qwen Coder", group: "Local" },
	{ id: "mistral-small", provider: "ollama", providerModel: "mistral-small:24b", label: "Mistral Small", group: "Local" },
];

// ── Ollama Provider ──

class OllamaProvider implements MiProvider {
	id = "ollama";
	#url: string;

	constructor() {
		this.#url = process.env.OLLAMA_URL || "http://localhost:11434";
	}

	isAvailable(): boolean {
		return true; // Ollama is always "available" — fails at call time if offline
	}

	async *stream(messages: MiMessage[], model: string): AsyncGenerator<MiStreamChunk> {
		const res = await fetch(`${this.#url}/api/chat`, {
			method: "POST",
			headers: { "Content-Type": "application/json" },
			body: JSON.stringify({ model, messages, stream: true }),
		});

		if (!res.ok) {
			const errText = await res.text().catch(() => "");
			throw new Error(`Ollama error ${res.status}: ${errText}`);
		}

		if (!res.body) throw new Error("No response body from Ollama");

		const reader = res.body.getReader();
		const decoder = new TextDecoder();
		let buffer = "";

		while (true) {
			const { done, value } = await reader.read();
			if (done) break;

			buffer += decoder.decode(value, { stream: true });
			const lines = buffer.split("\n");
			buffer = lines.pop() || "";

			for (const line of lines) {
				if (!line.trim()) continue;
				try {
					const data = JSON.parse(line);
					yield {
						content: data.message?.content || "",
						done: !!data.done,
					};
				} catch {
					// skip malformed lines
				}
			}
		}

		// Process remaining buffer
		if (buffer.trim()) {
			try {
				const data = JSON.parse(buffer);
				yield { content: data.message?.content || "", done: true };
			} catch {
				// ignore
			}
		}
	}
}

// ── Gemini Provider ──

class GeminiProvider implements MiProvider {
	id = "gemini";

	isAvailable(): boolean {
		return !!(process.env.GEMINI_API_KEY);
	}

	async *stream(messages: MiMessage[], model: string): AsyncGenerator<MiStreamChunk> {
		const apiKey = process.env.GEMINI_API_KEY;
		if (!apiKey) throw new Error("GEMINI_API_KEY not configured");

		const { GoogleGenerativeAI } = await import("@google/generative-ai");
		const genAI = new GoogleGenerativeAI(apiKey);

		// Extract system instruction from messages
		const systemMsg = messages.find((m) => m.role === "system");
		const chatMessages = messages.filter((m) => m.role !== "system");

		const geminiModel = genAI.getGenerativeModel({
			model,
			...(systemMsg ? { systemInstruction: { role: "user", parts: [{ text: systemMsg.content }] } } : {}),
		});

		// Convert messages to Gemini format
		const history = chatMessages.slice(0, -1).map((m) => ({
			role: m.role === "assistant" ? "model" : "user",
			parts: [{ text: m.content }],
		}));

		const lastMsg = chatMessages[chatMessages.length - 1];
		if (!lastMsg) throw new Error("No messages to send");

		const chat = geminiModel.startChat({ history });
		const result = await chat.sendMessageStream(lastMsg.content);

		for await (const chunk of result.stream) {
			const text = chunk.text();
			if (text) {
				yield { content: text, done: false };
			}
		}
		yield { content: "", done: true };
	}
}

// ── Anthropic Provider (stub) ──

class AnthropicProvider implements MiProvider {
	id = "anthropic";

	isAvailable(): boolean {
		return !!(process.env.ANTHROPIC_API_KEY);
	}

	async *stream(_messages: MiMessage[], _model: string): AsyncGenerator<MiStreamChunk> {
		throw new Error("Anthropic provider not yet implemented — add @anthropic-ai/sdk");
	}
}

// ── OpenAI-Compatible Provider (stub) ──

class OpenAICompatProvider implements MiProvider {
	id = "openai-compat";

	isAvailable(): boolean {
		return !!(process.env.OPENAI_COMPAT_URL && process.env.OPENAI_COMPAT_KEY);
	}

	async *stream(_messages: MiMessage[], _model: string): AsyncGenerator<MiStreamChunk> {
		throw new Error("OpenAI-compatible provider not yet implemented");
	}
}

// ── Provider Registry ──

export class MiProviderRegistry {
	#providers = new Map<string, MiProvider>();

	constructor() {
		this.register(new OllamaProvider());
		this.register(new GeminiProvider());
		this.register(new AnthropicProvider());
		this.register(new OpenAICompatProvider());
	}

	register(provider: MiProvider): void {
		this.#providers.set(provider.id, provider);
	}

	/** Look up a model by its friendly ID and return the provider + provider-model. */
	resolveModel(modelId: string): { provider: MiProvider; providerModel: string } | null {
		const config = MODEL_REGISTRY.find((m) => m.id === modelId);
		if (!config) return null;

		const provider = this.#providers.get(config.provider);
		if (!provider || !provider.isAvailable()) return null;

		return { provider, providerModel: config.providerModel };
	}

	/** Get provider directly by provider ID (for fallback when modelId is a raw provider model name). */
	getProviderById(providerId: string): MiProvider | null {
		const provider = this.#providers.get(providerId);
		return provider && provider.isAvailable() ? provider : null;
	}

	/** All models whose provider is currently available. */
	getAvailableModels(): MiModelConfig[] {
		return MODEL_REGISTRY.filter((m) => {
			const p = this.#providers.get(m.provider);
			return p && p.isAvailable();
		});
	}

	/** MI_MODEL env or first available model. */
	getDefaultModel(): string {
		const envModel = process.env.MI_MODEL;
		if (envModel) {
			// Check if it's a registry ID
			if (MODEL_REGISTRY.find((m) => m.id === envModel)) return envModel;
			// It might be a raw provider model name — find the registry entry
			const entry = MODEL_REGISTRY.find((m) => m.providerModel === envModel);
			if (entry) return entry.id;
			// Unknown — return as-is for backward compat (Ollama will handle it)
			return envModel;
		}
		// First available
		const available = this.getAvailableModels();
		return available[0]?.id || "llama3.2";
	}

	/**
	 * Stream from any provider and normalize to NDJSON `{message:{content:"..."}}` format
	 * matching Ollama's wire format — zero changes needed in the client parser.
	 */
	streamToNDJSON(gen: AsyncGenerator<MiStreamChunk>): ReadableStream {
		const encoder = new TextEncoder();
		return new ReadableStream({
			async pull(controller) {
				try {
					const { value, done: iterDone } = await gen.next();
					if (iterDone) {
						controller.close();
						return;
					}
					const payload = JSON.stringify({
						message: { role: "assistant", content: value.content },
						done: value.done,
					});
					controller.enqueue(encoder.encode(payload + "\n"));
					if (value.done) controller.close();
				} catch (err: any) {
					controller.error(err);
				}
			},
		});
	}
}

/** Singleton registry, ready at import time. */
export const miRegistry = new MiProviderRegistry();