/**
 * Model resolution, scoping, and initial selection
 */

import type { ThinkingLevel } from "@mariozechner/pi-agent-core";
import { type Api, type KnownProvider, type Model, modelsAreEqual } from "@mariozechner/pi-ai";
import chalk from "chalk";
import { isValidThinkingLevel } from "../cli/args.js";
import type { ModelRegistry } from "./model-registry.js";

/** Default model IDs for each known provider */
export const defaultModelPerProvider: Record<KnownProvider, string> = {
	anthropic: "claude-sonnet-4-5",
	openai: "gpt-5.1-codex",
	google: "gemini-2.5-pro",
	"google-gemini-cli": "gemini-2.5-pro",
	"google-antigravity": "gemini-3-pro-high",
	"github-copilot": "gpt-4o",
	openrouter: "openai/gpt-5.1-codex",
	xai: "grok-4-fast-non-reasoning",
	groq: "openai/gpt-oss-120b",
	cerebras: "zai-glm-4.6",
	zai: "glm-4.6",
	mistral: "devstral-medium-latest",
};

export interface ScopedModel {
	model: Model<Api>;
	thinkingLevel: ThinkingLevel;
}

/**
 * Helper to check if a model ID looks like an alias (no date suffix)
 * Dates are typically in format: -20241022 or -20250929
 */
function isAlias(id: string): boolean {
	// Check if ID ends with -latest
	if (id.endsWith("-latest")) return true;

	// Check if ID ends with a date pattern (-YYYYMMDD)
	const datePattern = /-\d{8}$/;
	return !datePattern.test(id);
}

/**
 * Try to match a pattern to a model from the available models list.
 * Returns the matched model or undefined if no match found.
 */
function tryMatchModel(modelPattern: string, availableModels: Model<Api>[]): Model<Api> | undefined {
	// Check for provider/modelId format (provider is everything before the first /)
	const slashIndex = modelPattern.indexOf("/");
	if (slashIndex !== -1) {
		const provider = modelPattern.substring(0, slashIndex);
		const modelId = modelPattern.substring(slashIndex + 1);
		const providerMatch = availableModels.find(
			(m) => m.provider.toLowerCase() === provider.toLowerCase() && m.id.toLowerCase() === modelId.toLowerCase(),
		);
		if (providerMatch) {
			return providerMatch;
		}
		// No exact provider/model match - fall through to other matching
	}

	// Check for exact ID match (case-insensitive)
	const exactMatch = availableModels.find((m) => m.id.toLowerCase() === modelPattern.toLowerCase());
	if (exactMatch) {
		return exactMatch;
	}

	// No exact match - fall back to partial matching
	const matches = availableModels.filter(
		(m) =>
			m.id.toLowerCase().includes(modelPattern.toLowerCase()) ||
			m.name?.toLowerCase().includes(modelPattern.toLowerCase()),
	);

	if (matches.length === 0) {
		return undefined;
	}

	// Separate into aliases and dated versions
	const aliases = matches.filter((m) => isAlias(m.id));
	const datedVersions = matches.filter((m) => !isAlias(m.id));

	if (aliases.length > 0) {
		// Prefer alias - if multiple aliases, pick the one that sorts highest
		aliases.sort((a, b) => b.id.localeCompare(a.id));
		return aliases[0];
	} else {
		// No alias found, pick latest dated version
		datedVersions.sort((a, b) => b.id.localeCompare(a.id));
		return datedVersions[0];
	}
}

export interface ParsedModelResult {
	model: Model<Api> | undefined;
	thinkingLevel: ThinkingLevel;
	warning: string | undefined;
}

/**
 * Parse a pattern to extract model and thinking level.
 * Handles models with colons in their IDs (e.g., OpenRouter's :exacto suffix).
 *
 * Algorithm:
 * 1. Try to match full pattern as a model
 * 2. If found, return it with "off" thinking level
 * 3. If not found and has colons, split on last colon:
 *    - If suffix is valid thinking level, use it and recurse on prefix
 *    - If suffix is invalid, warn and recurse on prefix with "off"
 *
 * @internal Exported for testing
 */
export function parseModelPattern(pattern: string, availableModels: Model<Api>[]): ParsedModelResult {
	// Try exact match first
	const exactMatch = tryMatchModel(pattern, availableModels);
	if (exactMatch) {
		return { model: exactMatch, thinkingLevel: "off", warning: undefined };
	}

	// No match - try splitting on last colon if present
	const lastColonIndex = pattern.lastIndexOf(":");
	if (lastColonIndex === -1) {
		// No colons, pattern simply doesn't match any model
		return { model: undefined, thinkingLevel: "off", warning: undefined };
	}

	const prefix = pattern.substring(0, lastColonIndex);
	const suffix = pattern.substring(lastColonIndex + 1);

	if (isValidThinkingLevel(suffix)) {
		// Valid thinking level - recurse on prefix and use this level
		const result = parseModelPattern(prefix, availableModels);
		if (result.model) {
			// Only use this thinking level if no warning from inner recursion
			// (if there was an invalid suffix deeper, we already have "off")
			return {
				model: result.model,
				thinkingLevel: result.warning ? "off" : suffix,
				warning: result.warning,
			};
		}
		return result;
	} else {
		// Invalid suffix - recurse on prefix with "off" and warn
		const result = parseModelPattern(prefix, availableModels);
		if (result.model) {
			return {
				model: result.model,
				thinkingLevel: "off",
				warning: `Invalid thinking level "${suffix}" in pattern "${pattern}". Using "off" instead.`,
			};
		}
		return result;
	}
}

/**
 * Resolve model patterns to actual Model objects with optional thinking levels
 * Format: "pattern:level" where :level is optional
 * For each pattern, finds all matching models and picks the best version:
 * 1. Prefer alias (e.g., claude-sonnet-4-5) over dated versions (claude-sonnet-4-5-20250929)
 * 2. If no alias, pick the latest dated version
 *
 * Supports models with colons in their IDs (e.g., OpenRouter's model:exacto).
 * The algorithm tries to match the full pattern first, then progressively
 * strips colon-suffixes to find a match.
 */
export async function resolveModelScope(patterns: string[], modelRegistry: ModelRegistry): Promise<ScopedModel[]> {
	const availableModels = await modelRegistry.getAvailable();
	const scopedModels: ScopedModel[] = [];

	for (const pattern of patterns) {
		const { model, thinkingLevel, warning } = parseModelPattern(pattern, availableModels);

		if (warning) {
			console.warn(chalk.yellow(`Warning: ${warning}`));
		}

		if (!model) {
			console.warn(chalk.yellow(`Warning: No models match pattern "${pattern}"`));
			continue;
		}

		// Avoid duplicates
		if (!scopedModels.find((sm) => modelsAreEqual(sm.model, model))) {
			scopedModels.push({ model, thinkingLevel });
		}
	}

	return scopedModels;
}

export interface InitialModelResult {
	model: Model<Api> | undefined;
	thinkingLevel: ThinkingLevel;
	fallbackMessage: string | undefined;
}

/**
 * Find the initial model to use based on priority:
 * 1. CLI args (provider + model)
 * 2. First model from scoped models (if not continuing/resuming)
 * 3. Restored from session (if continuing/resuming)
 * 4. Saved default from settings
 * 5. First available model with valid API key
 */
export async function findInitialModel(options: {
	cliProvider?: string;
	cliModel?: string;
	scopedModels: ScopedModel[];
	isContinuing: boolean;
	defaultProvider?: string;
	defaultModelId?: string;
	defaultThinkingLevel?: ThinkingLevel;
	modelRegistry: ModelRegistry;
}): Promise<InitialModelResult> {
	const {
		cliProvider,
		cliModel,
		scopedModels,
		isContinuing,
		defaultProvider,
		defaultModelId,
		defaultThinkingLevel,
		modelRegistry,
	} = options;

	let model: Model<Api> | undefined;
	let thinkingLevel: ThinkingLevel = "off";

	// 1. CLI args take priority
	if (cliProvider && cliModel) {
		const found = modelRegistry.find(cliProvider, cliModel);
		if (!found) {
			console.error(chalk.red(`Model ${cliProvider}/${cliModel} not found`));
			process.exit(1);
		}
		return { model: found, thinkingLevel: "off", fallbackMessage: undefined };
	}

	// 2. Use first model from scoped models (skip if continuing/resuming)
	if (scopedModels.length > 0 && !isContinuing) {
		return {
			model: scopedModels[0].model,
			thinkingLevel: scopedModels[0].thinkingLevel,
			fallbackMessage: undefined,
		};
	}

	// 3. Try saved default from settings
	if (defaultProvider && defaultModelId) {
		const found = modelRegistry.find(defaultProvider, defaultModelId);
		if (found) {
			model = found;
			if (defaultThinkingLevel) {
				thinkingLevel = defaultThinkingLevel;
			}
			return { model, thinkingLevel, fallbackMessage: undefined };
		}
	}

	// 4. Try first available model with valid API key
	const availableModels = await modelRegistry.getAvailable();

	if (availableModels.length > 0) {
		// Try to find a default model from known providers
		for (const provider of Object.keys(defaultModelPerProvider) as KnownProvider[]) {
			const defaultId = defaultModelPerProvider[provider];
			const match = availableModels.find((m) => m.provider === provider && m.id === defaultId);
			if (match) {
				return { model: match, thinkingLevel: "off", fallbackMessage: undefined };
			}
		}

		// If no default found, use first available
		return { model: availableModels[0], thinkingLevel: "off", fallbackMessage: undefined };
	}

	// 5. No model found
	return { model: undefined, thinkingLevel: "off", fallbackMessage: undefined };
}

/**
 * Restore model from session, with fallback to available models
 */
export async function restoreModelFromSession(
	savedProvider: string,
	savedModelId: string,
	currentModel: Model<Api> | undefined,
	shouldPrintMessages: boolean,
	modelRegistry: ModelRegistry,
): Promise<{ model: Model<Api> | undefined; fallbackMessage: string | undefined }> {
	const restoredModel = modelRegistry.find(savedProvider, savedModelId);

	// Check if restored model exists and has a valid API key
	const hasApiKey = restoredModel ? !!(await modelRegistry.getApiKey(restoredModel)) : false;

	if (restoredModel && hasApiKey) {
		if (shouldPrintMessages) {
			console.log(chalk.dim(`Restored model: ${savedProvider}/${savedModelId}`));
		}
		return { model: restoredModel, fallbackMessage: undefined };
	}

	// Model not found or no API key - fall back
	const reason = !restoredModel ? "model no longer exists" : "no API key available";

	if (shouldPrintMessages) {
		console.error(chalk.yellow(`Warning: Could not restore model ${savedProvider}/${savedModelId} (${reason}).`));
	}

	// If we already have a model, use it as fallback
	if (currentModel) {
		if (shouldPrintMessages) {
			console.log(chalk.dim(`Falling back to: ${currentModel.provider}/${currentModel.id}`));
		}
		return {
			model: currentModel,
			fallbackMessage: `Could not restore model ${savedProvider}/${savedModelId} (${reason}). Using ${currentModel.provider}/${currentModel.id}.`,
		};
	}

	// Try to find any available model
	const availableModels = await modelRegistry.getAvailable();

	if (availableModels.length > 0) {
		// Try to find a default model from known providers
		let fallbackModel: Model<Api> | undefined;
		for (const provider of Object.keys(defaultModelPerProvider) as KnownProvider[]) {
			const defaultId = defaultModelPerProvider[provider];
			const match = availableModels.find((m) => m.provider === provider && m.id === defaultId);
			if (match) {
				fallbackModel = match;
				break;
			}
		}

		// If no default found, use first available
		if (!fallbackModel) {
			fallbackModel = availableModels[0];
		}

		if (shouldPrintMessages) {
			console.log(chalk.dim(`Falling back to: ${fallbackModel.provider}/${fallbackModel.id}`));
		}

		return {
			model: fallbackModel,
			fallbackMessage: `Could not restore model ${savedProvider}/${savedModelId} (${reason}). Using ${fallbackModel.provider}/${fallbackModel.id}.`,
		};
	}

	// No models available
	return { model: undefined, fallbackMessage: undefined };
}
