import type { Api, Model } from "@earendil-works/pi-ai";

export const PROVIDER = "grts";
export const AUTO_ID = "auto";

/**
 * Cascade priority for `grts/auto`, answer quality first; also the display order.
 * NVIDIA sits behind Mistral: its strongest free models queue past the deadline
 * (measured twice). Keyless Kilo trails: always there, but its anonymous router
 * lands on weak models.
 */
export const BACKENDS = [
	"google",
	"zai",
	"groq",
	"mistral",
	"nvidia",
	"openrouter",
	"hetzner",
	"kilo",
] as const;
export type Backend = (typeof BACKENDS)[number];

export type GratisModel = Model<Api>;

type Input = ("text" | "image")[];

interface BackendInfo {
	label: string;
	/** Backend-specific key: step 1 of key resolution. */
	gratisEnv: string;
	/** Native env of the backend: step 2. */
	nativeEnv: string;
	/** Pi provider id for credential-store lookup: step 3. */
	nativeProvider?: string;
	/** Keyless backends register without any key. */
	keyless: boolean;
	/** Advisory cooldowns after observed 429 or quota exhaustion. */
	rateCooldownMs: number;
	quotaCooldownMs: number;
}

const MINUTE = 60_000;
const HOUR = 60 * MINUTE;

export const BACKEND_INFO: Record<Backend, BackendInfo> = {
	kilo: {
		label: "Kilo",
		gratisEnv: "GRATIS_KILO_TOKEN",
		nativeEnv: "KILO_API_KEY",
		keyless: true,
		rateCooldownMs: 5 * MINUTE,
		quotaCooldownMs: HOUR,
	},
	google: {
		label: "Google",
		gratisEnv: "GRATIS_GOOGLE_TOKEN",
		nativeEnv: "GEMINI_API_KEY",
		nativeProvider: "google",
		keyless: false,
		rateCooldownMs: MINUTE,
		quotaCooldownMs: HOUR,
	},
	nvidia: {
		label: "NVIDIA",
		gratisEnv: "GRATIS_NVIDIA_TOKEN",
		nativeEnv: "NVIDIA_API_KEY",
		nativeProvider: "nvidia",
		keyless: false,
		rateCooldownMs: MINUTE,
		quotaCooldownMs: HOUR,
	},
	openrouter: {
		label: "OpenRouter",
		gratisEnv: "GRATIS_OPENROUTER_TOKEN",
		nativeEnv: "OPENROUTER_API_KEY",
		nativeProvider: "openrouter",
		keyless: false,
		rateCooldownMs: MINUTE,
		quotaCooldownMs: HOUR,
	},
	groq: {
		label: "Groq",
		gratisEnv: "GRATIS_GROQ_TOKEN",
		nativeEnv: "GROQ_API_KEY",
		nativeProvider: "groq",
		keyless: false,
		rateCooldownMs: MINUTE,
		quotaCooldownMs: HOUR,
	},
	mistral: {
		label: "Mistral",
		gratisEnv: "GRATIS_MISTRAL_TOKEN",
		nativeEnv: "MISTRAL_API_KEY",
		nativeProvider: "mistral",
		keyless: false,
		rateCooldownMs: MINUTE,
		quotaCooldownMs: HOUR,
	},
	zai: {
		label: "Z.ai",
		gratisEnv: "GRATIS_ZAI_TOKEN",
		nativeEnv: "ZAI_API_KEY",
		nativeProvider: "zai",
		keyless: false,
		rateCooldownMs: MINUTE,
		quotaCooldownMs: HOUR,
	},
	hetzner: {
		label: "Hetzner",
		gratisEnv: "GRATIS_HETZNER_TOKEN",
		nativeEnv: "HETZNER_INFERENCE_API_KEY",
		// Pi has no built-in Hetzner provider; a models.json `hetzner` entry supplies one.
		nativeProvider: "hetzner",
		keyless: false,
		rateCooldownMs: MINUTE,
		quotaCooldownMs: HOUR,
	},
};

export const KILO_BASE_URL = "https://api.kilo.ai/api/gateway";
export const OPENROUTER_BASE_URL = "https://openrouter.ai/api/v1";
const OPENROUTER_ANTHROPIC_BASE_URL = "https://openrouter.ai/api";
const GOOGLE_BASE_URL = "https://generativelanguage.googleapis.com/v1beta";
const GROQ_BASE_URL = "https://api.groq.com/openai/v1";
const MISTRAL_BASE_URL = "https://api.mistral.ai";
const NVIDIA_BASE_URL = "https://integrate.api.nvidia.com/v1";
// General endpoint only: Coding Plan endpoints (`/api/coding/paas/v4`, `/api/anthropic`) spend plan quota.
const ZAI_BASE_URL = "https://api.z.ai/api/paas/v4";
const HETZNER_BASE_URL = "https://inference.hetzner.com/api/v1";

/** Backends whose catalog is refreshed from a live models endpoint. */
export type LiveBackend = "kilo" | "openrouter" | "nvidia" | "hetzner" | "zai";
export const LIVE_BACKENDS: readonly LiveBackend[] = [
	"kilo",
	"openrouter",
	"nvidia",
	"hetzner",
	"zai",
];

/** Live catalog endpoints; only Hetzner's requires the backend key. */
export const DISCOVERY_URL: Record<Exclude<LiveBackend, "zai">, string> = {
	kilo: `${KILO_BASE_URL}/models`,
	openrouter: `${OPENROUTER_BASE_URL}/models`,
	nvidia: `${NVIDIA_BASE_URL}/models`,
	hetzner: `${HETZNER_BASE_URL}/models`,
};
export const DISCOVERY_NEEDS_KEY: Record<
	Exclude<LiveBackend, "zai">,
	boolean
> = {
	kilo: false,
	openrouter: false,
	nvidia: false,
	hetzner: true,
};

/**
 * Gratis-maintained free set. Discovery keeps a live model only when its id
 * matches one of these and its published pricing is zero.
 */
const VIRTUAL_MODELS: Partial<Record<Backend, readonly string[]>> = {
	kilo: ["kilo-auto/free", "openrouter/free"],
	openrouter: ["openrouter/free"],
};

/** Applied only when a catalog publishes no value. */
const FALLBACK_CONTEXT_WINDOW = 32_768;
const FALLBACK_MAX_TOKENS = 8_192;

/** `grts/auto` candidates: top-ranked models per backend with a usable context. */
export const AUTO_CANDIDATES_PER_BACKEND = 4;
export const AUTO_MIN_CONTEXT_WINDOW = 131_072;

const FREE_COST = { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 };
const CAVEAT = "free tier, prompts may be logged";

const OPENROUTER_COMPAT = {
	supportsDeveloperRole: false,
	thinkingFormat: "openrouter",
} as const;

/**
 * Pi sends `reasoning: { effort: "none" }` for thinking off unless off is
 * unsupported; routers and free pools may land on models that reject that
 * ("Reasoning is mandatory"), so thinking off sends no reasoning setting.
 */
const NO_FORCED_OFF = { off: null } as const;

/** vLLM-style OpenAI servers (NVIDIA NIM, Hetzner): plain max_tokens, no store, system role only. */
const VLLM_COMPAT = {
	supportsStore: false,
	supportsDeveloperRole: false,
	supportsReasoningEffort: false,
	maxTokensField: "max_tokens",
	supportsStrictMode: false,
} as const;

/** Pi's own Z.ai GLM compatibility settings. */
const ZAI_COMPAT = {
	supportsStore: false,
	supportsDeveloperRole: false,
	supportsReasoningEffort: false,
	maxTokensField: "max_tokens",
	thinkingFormat: "zai",
	supportsStrictMode: true,
	zaiToolStream: true,
} as const;

const GOOGLE_THINKING = {
	off: null,
	minimal: "minimal",
	low: "low",
	medium: "medium",
	high: "high",
	xhigh: null,
	max: null,
} as const;
/** Newer Gemini Flash models reject MINIMAL, the level Pi uses for thinking off. */
const GOOGLE_THINKING_NO_MINIMAL = {
	...GOOGLE_THINKING,
	minimal: null,
} as const;
const GROQ_GPT_OSS_THINKING = {
	off: null,
	minimal: null,
	low: "low",
	medium: "medium",
	high: "high",
	xhigh: null,
	max: null,
} as const;

/** One curated or confirmed catalog entry before gratis naming and zero cost. */
export type ZaiEntry = Entry;

interface Entry {
	id: string;
	name: string;
	api: Api;
	baseUrl: string;
	contextWindow: number;
	maxTokens: number;
	input: Input;
	reasoning: boolean;
	compat?: GratisModel["compat"];
	thinkingLevelMap?: GratisModel["thinkingLevelMap"];
}

export function gratisModel(backend: Backend, entry: Entry): GratisModel {
	const model: GratisModel = {
		id: `${backend}/${entry.id}`,
		name: `${BACKEND_INFO[backend].label} ${entry.name} (${CAVEAT})`,
		api: entry.api,
		provider: PROVIDER,
		baseUrl: entry.baseUrl,
		reasoning: entry.reasoning,
		input: entry.input,
		cost: { ...FREE_COST },
		contextWindow: entry.contextWindow,
		maxTokens: entry.maxTokens,
	};
	if (entry.compat) model.compat = entry.compat;
	if (entry.thinkingLevelMap) model.thinkingLevelMap = entry.thinkingLevelMap;
	return model;
}

export function backendOf(model: Pick<GratisModel, "id">): Backend | undefined {
	const prefix = model.id.slice(0, model.id.indexOf("/"));
	return (BACKENDS as readonly string[]).includes(prefix)
		? (prefix as Backend)
		: undefined;
}

export function upstreamId(model: Pick<GratisModel, "id">): string {
	return model.id.slice(model.id.indexOf("/") + 1);
}

const google = (
	id: string,
	name: string,
	thinkingLevelMap?: Entry["thinkingLevelMap"],
): Entry => ({
	id,
	name,
	api: "google-generative-ai",
	baseUrl: GOOGLE_BASE_URL,
	contextWindow: 1_048_576,
	maxTokens: 65_536,
	input: ["text", "image"],
	reasoning: true,
	...(thinkingLevelMap ? { thinkingLevelMap } : {}),
});

const groq = (
	id: string,
	name: string,
	maxTokens: number,
	thinkingLevelMap?: Entry["thinkingLevelMap"],
): Entry => ({
	id,
	name,
	api: "openai-completions",
	baseUrl: GROQ_BASE_URL,
	contextWindow: 131_072,
	maxTokens,
	input: ["text"],
	reasoning: thinkingLevelMap !== undefined,
	compat: { supportsStrictMode: true },
	...(thinkingLevelMap ? { thinkingLevelMap } : {}),
});

const mistral = (
	id: string,
	name: string,
	contextWindow: number,
	maxTokens: number,
	input: Input,
	reasoning: boolean,
): Entry => ({
	id,
	name,
	api: "mistral-conversations",
	baseUrl: MISTRAL_BASE_URL,
	contextWindow,
	maxTokens,
	input,
	reasoning,
});

const openai = (
	baseUrl: string,
	compat: Entry["compat"],
	id: string,
	name: string,
	contextWindow: number,
	maxTokens: number,
	input: Input,
): Entry => ({
	id,
	name,
	api: "openai-completions",
	baseUrl,
	contextWindow,
	maxTokens,
	input,
	reasoning: true,
	compat,
});
const nvidia = openai.bind(undefined, NVIDIA_BASE_URL, VLLM_COMPAT);
const zai = openai.bind(undefined, ZAI_BASE_URL, ZAI_COMPAT);
const hetzner = openai.bind(undefined, HETZNER_BASE_URL, VLLM_COMPAT);

/** Curated static catalogs, ranked. Stale entries are fixed here, never by user config. */
const STATIC: Record<Exclude<Backend, "kilo">, readonly Entry[]> = {
	// Only models Pi's NVIDIA catalog prices at 0; priced ones (Nemotron 3 Super/Ultra) stay out.
	nvidia: [
		nvidia("moonshotai/kimi-k3", "Kimi K3", 1_048_576, 131_072, [
			"text",
			"image",
		]),
		nvidia("z-ai/glm-5.3", "GLM 5.3", 1_000_000, 131_072, ["text"]),
		nvidia("moonshotai/kimi-k2.6", "Kimi K2.6", 262_144, 262_144, [
			"text",
			"image",
		]),
		nvidia("z-ai/glm-5.3-flash", "GLM 5.3 Flash", 1_000_000, 131_072, [
			"text",
			"image",
		]),
		nvidia(
			"nvidia/nemotron-3.5-lightning-30b-a3b",
			"Nemotron 3.5 Lightning",
			262_144,
			262_144,
			["text"],
		),
		nvidia("openai/gpt-oss-20b", "GPT OSS 20B", 131_072, 32_768, ["text"]),
	],
	// Exactly the models Z.ai prices Free; "flash" alone is not proof (glm-5.3-flash is paid).
	zai: [
		zai("glm-4.7-flash", "GLM 4.7 Flash", 204_800, 131_072, ["text"]),
		zai("glm-4.5-flash", "GLM 4.5 Flash", 131_072, 98_304, ["text"]),
		zai("glm-4.6v-flash", "GLM 4.6V Flash", 128_000, 32_768, ["text", "image"]),
	],
	// Fallback only: the keyed live models list replaces it when reachable.
	hetzner: [
		hetzner("Qwen/Qwen3.6-35B-A3B-FP8", "Qwen 3.6 35B", 262_144, 65_536, [
			"text",
			"image",
		]),
		hetzner("Qwen3.8-27B", "Qwen 3.8 27B", 262_144, 65_536, ["text", "image"]),
	],
	// Concrete ids only: `-latest` aliases move to models whose thinking levels differ.
	google: [
		google("gemini-3.8-flash", "Gemini 3.8 Flash", GOOGLE_THINKING_NO_MINIMAL),
		google("gemini-3.7-flash", "Gemini 3.7 Flash", GOOGLE_THINKING_NO_MINIMAL),
		google("gemini-3.5-flash", "Gemini 3.5 Flash", GOOGLE_THINKING),
		google("gemini-3.5-flash-lite", "Gemini 3.5 Flash-Lite", GOOGLE_THINKING),
	],
	// Fallback only: live discovery replaces it when reachable.
	openrouter: [
		{
			id: "openrouter/free",
			name: "Free Models Router",
			api: "openai-completions",
			baseUrl: OPENROUTER_BASE_URL,
			contextWindow: 200_000,
			maxTokens: FALLBACK_MAX_TOKENS,
			input: ["text", "image"],
			reasoning: true,
			compat: OPENROUTER_COMPAT,
			thinkingLevelMap: NO_FORCED_OFF,
		},
	],
	groq: [
		groq("openai/gpt-oss-120b", "GPT OSS 120B", 65_536, GROQ_GPT_OSS_THINKING),
		groq("llama-3.3-70b-versatile", "Llama 3.3 70B", 32_768),
		groq("openai/gpt-oss-20b", "GPT OSS 20B", 65_536, GROQ_GPT_OSS_THINKING),
		groq("llama-3.1-8b-instant", "Llama 3.1 8B", 131_072),
	],
	mistral: [
		mistral("devstral-latest", "Devstral", 262_144, 262_144, ["text"], false),
		mistral(
			"mistral-medium-latest",
			"Mistral Medium",
			262_144,
			262_144,
			["text", "image"],
			true,
		),
		mistral(
			"mistral-small-latest",
			"Mistral Small",
			256_000,
			256_000,
			["text", "image"],
			true,
		),
		mistral(
			"mistral-large-latest",
			"Mistral Large",
			262_144,
			262_144,
			["text", "image"],
			false,
		),
		mistral("codestral-latest", "Codestral", 256_000, 4_096, ["text"], false),
	],
};

export function staticModels(backend: Backend): GratisModel[] {
	if (backend === "kilo") return [];
	return STATIC[backend].map((entry) => gratisModel(backend, entry));
}

const liveIds = (payload: unknown): string[] => {
	const data = (payload as { data?: unknown } | undefined)?.data;
	if (!Array.isArray(data)) throw new Error("catalog payload has no data");
	return data.flatMap((raw) =>
		typeof raw?.id === "string" ? [raw.id as string] : [],
	);
};

/** NVIDIA publishes bare ids: keep curated free models that are live. */
export function parseNvidiaCatalog(payload: unknown): GratisModel[] {
	const live = new Set(liveIds(payload));
	return staticModels("nvidia").filter((model) => live.has(upstreamId(model)));
}

/**
 * Hetzner's list is definitive and every model is free while experimental.
 * Known ids keep curated metadata; new ids use the published context length.
 */
export function parseHetznerCatalog(payload: unknown): GratisModel[] {
	const data = (payload as { data?: unknown } | undefined)?.data;
	if (!Array.isArray(data)) throw new Error("catalog payload has no data");
	const curated = new Map(
		staticModels("hetzner").map((model) => [upstreamId(model), model]),
	);
	return data.flatMap((raw: { id?: unknown; max_model_len?: unknown }) => {
		if (typeof raw?.id !== "string") return [];
		const known = curated.get(raw.id);
		const contextWindow =
			positive(raw.max_model_len) ??
			known?.contextWindow ??
			FALLBACK_CONTEXT_WINDOW;
		if (known) return [{ ...known, contextWindow }];
		return [
			gratisModel(
				"hetzner",
				hetzner(
					raw.id,
					raw.id,
					contextWindow,
					Math.min(FALLBACK_MAX_TOKENS, contextWindow),
					["text"],
				),
			),
		];
	});
}

export function parseCatalog(
	backend: Exclude<LiveBackend, "zai">,
	payload: unknown,
): GratisModel[] {
	if (backend === "nvidia") return parseNvidiaCatalog(payload);
	if (backend === "hetzner") return parseHetznerCatalog(payload);
	return parseLiveCatalog(backend, payload);
}

/** Model ids the NVIDIA public list currently serves, for intersecting Pi's catalog. */
export function liveModelIds(payload: unknown): Set<string> {
	return new Set(liveIds(payload));
}

/** Z.ai's first-party pricing page, served as markdown. */
export const ZAI_PRICING_URL = "https://docs.z.ai/guides/overview/pricing.md";
/** models.dev confirms cost and limits for Z.ai ids gratis does not know. */
export const MODELS_DEV_URL = "https://models.dev/api.json";

export interface ZaiPricing {
	/** Lowercased model ids whose input and output are both listed as Free. */
	free: string[];
	/** Free ids listed under Vision Models. */
	vision: Set<string>;
}

/**
 * Parse the pricing page's model tables. Returns undefined when no model table
 * is found (format changed), so callers keep their last confirmed list.
 */
export function parseZaiPricing(markdown: string): ZaiPricing | undefined {
	let section = "";
	let tables = 0;
	const free: string[] = [];
	const vision = new Set<string>();
	for (const line of markdown.split("\n")) {
		if (line.startsWith("#")) section = line;
		const cells = line.split("|").map((cell) => cell.trim());
		// | Model | Input | Cached Input | Cached Input Storage | Output |
		if (cells.length !== 7) continue;
		const [, name = "", input, , , output] = cells;
		if (name === "Model" && input === "Input" && output === "Output") {
			tables++;
			continue;
		}
		const id = name.toLowerCase();
		if (input !== "Free" || output !== "Free" || !/^glm-[a-z0-9.-]+$/.test(id))
			continue;
		free.push(id);
		if (/vision/i.test(section)) vision.add(id);
	}
	return tables > 0 ? { free, vision } : undefined;
}

/** A models.dev `zai` entry confirming cost 0 on the general endpoint. */
export function modelsDevZaiEntry(
	payload: unknown,
	id: string,
): Entry | undefined {
	const provider = (payload as { zai?: { api?: unknown; models?: unknown } })
		?.zai;
	if (provider?.api !== ZAI_BASE_URL) return undefined;
	const raw = (provider.models as Record<string, LiveModelsDev> | undefined)?.[
		id
	];
	if (raw?.cost?.input !== 0 || raw.cost?.output !== 0) return undefined;
	const inputs = strings(raw.modalities?.input);
	return zai(
		id,
		typeof raw.name === "string" ? raw.name : id,
		positive(raw.limit?.context) ?? FALLBACK_CONTEXT_WINDOW,
		positive(raw.limit?.output) ?? FALLBACK_MAX_TOKENS,
		inputs.includes("image") ? ["text", "image"] : ["text"],
	);
}

interface LiveModelsDev {
	name?: unknown;
	cost?: { input?: unknown; output?: unknown };
	limit?: { context?: unknown; output?: unknown };
	modalities?: { input?: unknown };
}

/**
 * Z.ai models the pricing page lists as Free: known ids keep curated
 * metadata; unknown ids need a models.dev confirmation (`confirmed`).
 */
export function zaiFreeModels(
	pricing: ZaiPricing,
	confirmed: ReadonlyMap<string, Entry>,
): GratisModel[] {
	const known = new Map(STATIC.zai.map((entry) => [entry.id, entry]));
	return pricing.free.flatMap((id) => {
		const entry = known.get(id) ?? confirmed.get(id);
		return entry ? [gratisModel("zai", entry)] : [];
	});
}

/** Z.ai free ids that need models.dev before they can be listed. */
export function unknownZaiIds(pricing: ZaiPricing): string[] {
	const known = new Set(STATIC.zai.map((entry) => entry.id));
	return pricing.free.filter((id) => !known.has(id));
}

/** Backends whose models come from Pi's runtime-refreshed built-in catalog. */
export type PiCatalogBackend = "google" | "groq" | "mistral" | "nvidia";
export const PI_CATALOG_BACKENDS: readonly PiCatalogBackend[] = [
	"google",
	"groq",
	"mistral",
	"nvidia",
];

const GEMINI_FLASH = /^gemini-(\d+(?:\.\d+)?)-flash(-lite)?$/;
const NOT_CHAT = /safeguard|guard|whisper|tts|embed|ocr|voxtral|moderation/i;

const version = (id: string) =>
	(/(\d+(?:\.\d+)?)/.exec(id)?.[1] ?? "0")
		.split(".")
		.map(Number)
		.reduce((sum, part, index) => sum + part / 1000 ** index, 0);

/** Pi's free rule per backend; `live` narrows NVIDIA to ids its public list serves. */
function piFree(
	backend: PiCatalogBackend,
	model: Model<Api>,
	live: ReadonlySet<string> | undefined,
): boolean {
	if (NOT_CHAT.test(model.id)) return false;
	if (backend === "google") return GEMINI_FLASH.test(model.id);
	if (backend === "mistral") return model.id.endsWith("-latest");
	if (backend === "nvidia")
		return (
			model.cost.input === 0 &&
			model.cost.output === 0 &&
			(live === undefined || live.has(model.id))
		);
	return true;
}

/**
 * Gratis models from Pi's built-in catalog for one backend, ranked: gratis's
 * known preferences first, then newer versions, then larger contexts.
 * Empty when Pi's catalog has no match, so callers fall back to the static list.
 */
export function fromPiCatalog(
	backend: PiCatalogBackend,
	catalog: readonly Model<Api>[],
	live?: ReadonlySet<string>,
): GratisModel[] {
	// Gemini Flash versions are ordered, so newest wins; elsewhere ids carry no
	// comparable version and gratis's known preferences lead.
	const preference =
		backend === "google" ? [] : STATIC[backend].map((entry) => entry.id);
	const rank = (id: string) => {
		const index = preference.indexOf(id);
		return index === -1 ? preference.length : index;
	};
	const flashLite = (id: string) => Number(id.endsWith("-lite"));
	return catalog
		.filter((model) => piFree(backend, model, live))
		.sort(
			(a, b) =>
				rank(a.id) - rank(b.id) ||
				version(b.id) - version(a.id) ||
				flashLite(a.id) - flashLite(b.id) ||
				b.contextWindow - a.contextWindow,
		)
		.map((model) =>
			gratisModel(backend, {
				id: model.id,
				name: model.name,
				api: model.api,
				baseUrl: model.baseUrl,
				contextWindow: model.contextWindow,
				maxTokens: model.maxTokens,
				input: model.input,
				reasoning: model.reasoning,
				...(model.compat ? { compat: model.compat } : {}),
				...(model.thinkingLevelMap
					? { thinkingLevelMap: model.thinkingLevelMap }
					: {}),
			}),
		);
}

interface LiveModel {
	id?: unknown;
	name?: unknown;
	context_length?: unknown;
	pricing?: { prompt?: unknown; completion?: unknown };
	isFree?: unknown;
	architecture?: { input_modalities?: unknown; output_modalities?: unknown };
	top_provider?: {
		context_length?: unknown;
		max_completion_tokens?: unknown;
	};
	supported_parameters?: unknown;
}

const positive = (value: unknown): number | undefined =>
	typeof value === "number" && Number.isFinite(value) && value > 0
		? Math.floor(value)
		: undefined;

const zeroPrice = (value: unknown): boolean =>
	(typeof value === "string" || typeof value === "number") &&
	Number(value) === 0;

const strings = (value: unknown): string[] =>
	Array.isArray(value)
		? value.filter((item): item is string => typeof item === "string")
		: [];

/**
 * Parse an OpenRouter-shaped `/models` payload into ranked free models:
 * virtual routers first, then upstream order. Anything unexpected is skipped,
 * so arbitrary churn and empty pools yield fewer models, never errors.
 */
export function parseLiveCatalog(
	backend: "kilo" | "openrouter",
	payload: unknown,
): GratisModel[] {
	const data = (payload as { data?: unknown } | undefined)?.data;
	if (!Array.isArray(data)) throw new Error("catalog payload has no data");
	const virtual = VIRTUAL_MODELS[backend] ?? [];
	const models: GratisModel[] = [];
	for (const raw of data as LiveModel[]) {
		if (typeof raw?.id !== "string") continue;
		const id = raw.id;
		const isVirtualModel = virtual.includes(id);
		if (!isVirtualModel && !id.endsWith(":free")) continue;
		if (raw.isFree === false) continue;
		if (!zeroPrice(raw.pricing?.prompt) || !zeroPrice(raw.pricing?.completion))
			continue;
		const params = strings(raw.supported_parameters);
		if (!params.includes("tools")) continue;
		const outputs = strings(raw.architecture?.output_modalities);
		if (outputs.length > 0 && !outputs.includes("text")) continue;
		const inputs = strings(raw.architecture?.input_modalities);
		const input: Input = inputs.includes("image")
			? ["text", "image"]
			: ["text"];
		const anthropic = backend === "openrouter" && id.startsWith("anthropic/");
		models.push(
			gratisModel(backend, {
				id,
				name: typeof raw.name === "string" ? raw.name : id,
				api: anthropic ? "anthropic-messages" : "openai-completions",
				baseUrl:
					backend === "kilo"
						? KILO_BASE_URL
						: anthropic
							? OPENROUTER_ANTHROPIC_BASE_URL
							: OPENROUTER_BASE_URL,
				contextWindow:
					positive(raw.top_provider?.context_length) ??
					positive(raw.context_length) ??
					FALLBACK_CONTEXT_WINDOW,
				maxTokens:
					positive(raw.top_provider?.max_completion_tokens) ??
					FALLBACK_MAX_TOKENS,
				input,
				reasoning: params.includes("reasoning"),
				...(anthropic
					? {}
					: {
							compat: OPENROUTER_COMPAT,
							...(params.includes("reasoning")
								? { thinkingLevelMap: NO_FORCED_OFF }
								: {}),
						}),
			}),
		);
	}
	const rank = (model: GratisModel) => {
		const index = virtual.indexOf(upstreamId(model));
		return index === -1 ? virtual.length : index;
	};
	// Array sort is stable, so equal ranks keep upstream order.
	return models.sort((a, b) => rank(a) - rank(b));
}