import { applyFinalCodexGpt56ContextCap } from "./context-cap-policy";
import { readModelCache, writeModelCache } from "./model-cache";
import { isRetiredModel, isRetiredModelKey } from "./model-retirements";
import { applyGeneratedModelPolicies, enrichModelThinking } from "./model-thinking";
import { type GeneratedProvider, getBundledModels } from "./models";
import type { Api, Model, Provider } from "./types";

const DEFAULT_CACHE_TTL_MS = 2 * 60 * 60 * 1000;
const NON_AUTHORITATIVE_RETRY_MS = 5 * 60 * 1000;

/**
 * Controls when dynamic endpoint models should be fetched.
 */
export type ModelRefreshStrategy = "online" | "offline" | "online-if-uncached";

/**
 * Hook for loading and mapping models.dev fallback data into canonical model objects.
 */
export interface ModelsDevFallback<TApi extends Api = Api, TPayload = unknown> {
	/** Fetches raw fallback payload (for example from models.dev). */
	fetch(): Promise<TPayload>;
	/** Maps payload into provider models. */
	map(payload: TPayload, providerId: Provider): readonly Model<TApi>[];
}

/**
 * Configuration for provider model resolution.
 */
export interface ModelManagerOptions<TApi extends Api = Api, TModelsDevPayload = unknown> {
	/** Provider id used for static lookup and cache namespacing. */
	providerId: Provider;
	/** Optional static list override. When omitted, bundled models.json is used. */
	staticModels?: readonly Model<TApi>[];
	/** Optional override for the cache database path. Default: <agent-dir>/models.db. */
	cacheDbPath?: string;
	/** Maximum cache age in milliseconds before considered stale. Default: 24h. */
	cacheTtlMs?: number;
	/** Optional dynamic endpoint fetcher. */
	fetchDynamicModels?: () => Promise<readonly Model<TApi>[] | null>;
	/** Optional models.dev fallback hook. */
	modelsDev?: ModelsDevFallback<TApi, TModelsDevPayload>;
	/** Clock override for deterministic tests. */
	now?: () => number;
	/** Optional guard that must permit cache publication. Default: writes are permitted. */
	canPublishCache?: () => boolean;
}

/**
 * Resolution result.
 *
 * `stale` is false when the resolved catalog is authoritative for the selected provider:
 * - dynamic endpoint data was fetched in this call,
 * - a still-fresh authoritative cache was reused in `online-if-uncached` mode, or
 * - the provider has no dynamic fetcher configured.
 */
export interface ModelResolutionResult<TApi extends Api = Api> {
	models: Model<TApi>[];
	stale: boolean;
}

/**
 * Stateful facade over provider model resolution.
 */
export interface ModelManager<TApi extends Api = Api> {
	refresh(strategy?: ModelRefreshStrategy): Promise<ModelResolutionResult<TApi>>;
}

/**
 * Creates a reusable provider model manager.
 */
export function createModelManager<TApi extends Api = Api, TModelsDevPayload = unknown>(
	options: ModelManagerOptions<TApi, TModelsDevPayload>,
): ModelManager<TApi> {
	return {
		refresh(strategy: ModelRefreshStrategy = "online-if-uncached") {
			return resolveProviderModels(options, strategy);
		},
	};
}

/**
 * Cheap fast path for trusted model sources (bundled literals, our own cache rows).
 * Skips per-field validation; only guards against catastrophically corrupt rows.
 */
function passModelList<TApi extends Api>(value: unknown): Model<TApi>[] {
	if (!Array.isArray(value)) {
		return [];
	}
	const out: Model<TApi>[] = [];
	for (const item of value) {
		if (item === null || typeof item !== "object") {
			continue;
		}
		const candidate = item as { id?: unknown; provider?: unknown };
		if (typeof candidate.id !== "string") {
			continue;
		}
		if (typeof candidate.provider === "string" && isRetiredModelKey(candidate.provider, candidate.id)) {
			continue;
		}
		out.push(enrichModelThinking(item as Model<TApi>));
	}
	applyGeneratedModelPolicies(out as Model<Api>[]);
	return applyFinalCodexGpt56ContextCap(out);
}

/**
 * Resolves provider models with source precedence:
 * static -> models.dev -> cache -> dynamic.
 *
 * Later sources override earlier ones by model id.
 */
export async function resolveProviderModels<TApi extends Api = Api, TModelsDevPayload = unknown>(
	options: ModelManagerOptions<TApi, TModelsDevPayload>,
	strategy: ModelRefreshStrategy = "online-if-uncached",
): Promise<ModelResolutionResult<TApi>> {
	const now = options.now ?? Date.now;
	const ttlMs = options.cacheTtlMs ?? DEFAULT_CACHE_TTL_MS;
	const dbPath = options.cacheDbPath;
	const staticModels = passModelList<TApi>(
		options.staticModels ?? getBundledModels(options.providerId as GeneratedProvider),
	);
	const cache = readModelCache<TApi>(options.providerId, ttlMs, now, dbPath);
	const dynamicFetcher = options.fetchDynamicModels;
	const hasDynamicFetcher = typeof dynamicFetcher === "function";
	const hasAuthoritativeCache = (cache?.authoritative ?? false) || !hasDynamicFetcher;
	const cacheAgeMs = cache ? now() - cache.updatedAt : Number.POSITIVE_INFINITY;
	const shouldFetchFromNetwork = shouldFetchRemoteSources(
		strategy,
		cache?.fresh ?? false,
		hasAuthoritativeCache,
		cacheAgeMs,
	);
	const staticFingerprint = fingerprintStatic(staticModels);

	// Cold-start fast path: when a fresh, authoritative cache exists, the network
	// fetch is skipped, AND the static catalog slice is byte-identical to what
	// was merged in last time, the cache row IS the authoritative merge result.
	// Re-running `mergeDynamicModels(static, cache)` would just rebuild the same
	// objects (~800ms in the steady-state cold-start profile for `skc -p hi`).
	if (
		!shouldFetchFromNetwork &&
		cache?.fresh &&
		hasAuthoritativeCache &&
		cache.staticFingerprint === staticFingerprint &&
		cache.staticFingerprint.length > 0
	) {
		const cachedModels = passModelList<TApi>(cache.models);
		if (!hasStaticTransportDrift(staticModels, cachedModels)) {
			return { models: cachedModels, stale: false };
		}
		const repairedModels = mergeDynamicModels(staticModels, cachedModels);
		if (options.canPublishCache?.() ?? true) {
			writeModelCache(options.providerId, now(), repairedModels, true, staticFingerprint, dbPath);
		}
		return { models: repairedModels, stale: false };
	}

	const [fetchedModelsDevModels, fetchedDynamicModels] = shouldFetchFromNetwork
		? await Promise.all([fetchModelsDev(options), dynamicFetcher ? fetchDynamicModels(dynamicFetcher) : null])
		: [null, null];
	const modelsDevModels = normalizeModelList<TApi>(fetchedModelsDevModels ?? []);
	const shouldUseFreshCacheAsAuthoritative =
		strategy === "online-if-uncached" && (cache?.fresh ?? false) && hasAuthoritativeCache;
	const dynamicFetchSucceeded = fetchedDynamicModels !== null;
	const cacheModels = dynamicFetchSucceeded ? [] : normalizeModelList<TApi>(cache?.models ?? []);
	const dynamicModels = fetchedDynamicModels ?? [];
	const mergedWithCache = mergeDynamicModels(mergeModelSources(staticModels, modelsDevModels), cacheModels);
	const models = applyFinalCodexGpt56ContextCap(mergeDynamicModels(mergedWithCache, dynamicModels));
	const dynamicAuthoritative = !hasDynamicFetcher || dynamicFetchSucceeded || shouldUseFreshCacheAsAuthoritative;
	if (shouldFetchFromNetwork) {
		if (dynamicFetchSucceeded) {
			const snapshotModels = applyFinalCodexGpt56ContextCap(
				mergeDynamicModels(mergeModelSources(staticModels, modelsDevModels), dynamicModels),
			);
			if (options.canPublishCache?.() ?? true) {
				writeModelCache(options.providerId, now(), snapshotModels, true, staticFingerprint, dbPath);
			}
		} else {
			// Dynamic fetch failed — update cache with a non-authoritative snapshot so
			// stale state remains visible while retry backoff still applies.
			const latestCache = readModelCache<TApi>(options.providerId, ttlMs, now, dbPath);
			if (options.canPublishCache?.() ?? true) {
				writeModelCache(
					options.providerId,
					now(),
					applyFinalCodexGpt56ContextCap(
						mergeDynamicModels(
							mergeModelSources(staticModels, modelsDevModels),
							normalizeModelList<TApi>(latestCache?.models ?? cache?.models ?? []),
						),
					),
					false,
					staticFingerprint,
					dbPath,
				);
			}
		}
	}
	return {
		models,
		stale: !dynamicAuthoritative,
	};
}

async function fetchModelsDev<TApi extends Api, TModelsDevPayload>(
	options: ModelManagerOptions<TApi, TModelsDevPayload>,
): Promise<Model<TApi>[] | null> {
	if (!options.modelsDev) {
		return null;
	}

	try {
		const payload = await options.modelsDev.fetch();
		return normalizeModelList<TApi>(options.modelsDev.map(payload, options.providerId));
	} catch {
		return null;
	}
}

async function fetchDynamicModels<TApi extends Api>(
	fetcher: () => Promise<readonly Model<TApi>[] | null>,
): Promise<Model<TApi>[] | null> {
	try {
		const models = await fetcher();
		if (models === null) {
			return null;
		}
		return normalizeModelList<TApi>(models);
	} catch {
		return null;
	}
}

function shouldFetchRemoteSources(
	strategy: ModelRefreshStrategy,
	hasFreshCache: boolean,
	hasAuthoritativeCache: boolean,
	cacheAgeMs: number,
): boolean {
	if (strategy === "offline") {
		return false;
	}
	if (strategy === "online") {
		return true;
	}
	// online-if-uncached: skip fetch if cache is fresh.
	// For non-authoritative caches (dynamic fetch previously failed),
	// use a shorter retry interval instead of retrying every startup.
	if (!hasFreshCache) {
		return true;
	}
	if (!hasAuthoritativeCache) {
		return cacheAgeMs >= NON_AUTHORITATIVE_RETRY_MS;
	}
	return false;
}

function hasStaticTransportDrift<TApi extends Api>(
	staticModels: readonly Model<TApi>[],
	cachedModels: readonly Model<TApi>[],
): boolean {
	if (staticModels.length === 0 || cachedModels.length === 0) return false;
	const cachedById = new Map(cachedModels.map(model => [model.id, model]));
	for (const staticModel of staticModels) {
		const cachedModel = cachedById.get(staticModel.id);
		if (!cachedModel) continue;
		if (cachedModel.api !== staticModel.api) return true;
	}
	return false;
}

function mergeModelSources<TApi extends Api>(...sources: readonly (readonly Model<TApi>[])[]): Model<TApi>[] {
	// Strip out empty/missing sources up front. The hot path is `(static, [])`
	// (modelsDev disabled / failed) — a single non-empty source means we can
	// skip the Map churn entirely and just hand back the array.
	const nonEmpty = sources.filter(source => source.length > 0);
	if (nonEmpty.length === 0) return [];
	if (nonEmpty.length === 1) return [...nonEmpty[0]];
	const merged = new Map<string, Model<TApi>>();
	for (const source of nonEmpty) {
		for (const model of source) {
			if (!model?.id) continue;
			merged.set(model.id, model);
		}
	}
	return Array.from(merged.values());
}

function mergeDynamicModels<TApi extends Api>(
	baseModels: readonly Model<TApi>[],
	dynamicModels: readonly Model<TApi>[],
): Model<TApi>[] {
	// Empty-side fast paths: `mergeDynamicModels(base, [])` is the common shape
	// after we've already merged the first pair, and `(...)` with no base
	// happens for providers without static catalogs.
	if (dynamicModels.length === 0) return baseModels.length === 0 ? [] : [...baseModels];
	if (baseModels.length === 0) return [...dynamicModels];
	const merged = new Map<string, Model<TApi>>(baseModels.map(model => [model.id, model]));
	for (const dynamicModel of dynamicModels) {
		if (!dynamicModel?.id) {
			continue;
		}
		const existingModel = merged.get(dynamicModel.id);
		if (!existingModel) {
			merged.set(dynamicModel.id, dynamicModel);
			continue;
		}
		merged.set(dynamicModel.id, mergeDynamicModel(existingModel, dynamicModel));
	}
	return Array.from(merged.values());
}

/**
 * Stable, low-collision fingerprint of a static catalog slice. Cached by
 * reference so repeat calls in the same process (e.g. multiple cold-start
 * arms calling `resolveProviderModels` with the same `staticModels` array)
 * skip the JSON+hash work after the first call.
 */
const kStaticFingerprint = Symbol("model-manager.staticFingerprint");
type ModelArrayWithFingerprint = readonly Model<Api>[] & { [kStaticFingerprint]?: string };
function fingerprintStatic<TApi extends Api>(models: readonly Model<TApi>[]): string {
	if (models.length === 0) return "empty";
	const tagged = models as ModelArrayWithFingerprint;
	const cached = tagged[kStaticFingerprint];
	if (cached !== undefined) return cached;
	// `Bun.hash` returns a `bigint`; base36 keeps the string short for the
	// SQLite column without sacrificing distinguishability.
	const fingerprint = Bun.hash(JSON.stringify(models)).toString(36);
	tagged[kStaticFingerprint] = fingerprint;
	return fingerprint;
}

function mergeDynamicModel<TApi extends Api>(existingModel: Model<TApi>, dynamicModel: Model<TApi>): Model<TApi> {
	const supportsImage = existingModel.input.includes("image") || dynamicModel.input.includes("image");
	// The static catalog is authoritative for transport: `api` (and its
	// api-specific `baseUrl`). Dynamic discovery enumerates ids via a single
	// hardcoded api (e.g. fetchOpenAICompatibleModels always tags
	// `openai-completions`), so spreading it blindly would clobber catalog
	// entries that route through a different format — e.g. opencode-go
	// qwen3.7-max is `anthropic-messages` but would be downgraded to
	// `openai-completions` and 401 with `not supported for format oa-compat`
	// (issue #489). Keep the existing api, and only take the dynamic baseUrl
	// when the api matches (same transport, same URL shape).
	const baseUrl = existingModel.api === dynamicModel.api ? dynamicModel.baseUrl : existingModel.baseUrl;
	const merged = enrichModelThinking({
		...existingModel,
		...dynamicModel,
		api: existingModel.api,
		baseUrl,
		name: preferDiscoveryName(dynamicModel.name, existingModel.name, dynamicModel.id),
		reasoning: existingModel.reasoning || dynamicModel.reasoning,
		input: supportsImage ? ["text", "image"] : ["text"],
		cost: {
			input: preferDiscoveryCost(dynamicModel.cost.input, existingModel.cost.input),
			output: preferDiscoveryCost(dynamicModel.cost.output, existingModel.cost.output),
			cacheRead: preferDiscoveryCost(dynamicModel.cost.cacheRead, existingModel.cost.cacheRead),
			cacheWrite: preferDiscoveryCost(dynamicModel.cost.cacheWrite, existingModel.cost.cacheWrite),
		},
		contextWindow: preferDiscoveryLimit(dynamicModel.contextWindow, existingModel.contextWindow),
		maxTokens: preferDiscoveryLimit(dynamicModel.maxTokens, existingModel.maxTokens),
		headers: dynamicModel.headers ? { ...existingModel.headers, ...dynamicModel.headers } : existingModel.headers,
		compat: dynamicModel.compat ?? existingModel.compat,
		contextPromotionTarget: dynamicModel.contextPromotionTarget ?? existingModel.contextPromotionTarget,
	});
	const policyModels = [merged as Model<Api>];
	applyGeneratedModelPolicies(policyModels);
	return policyModels[0] as Model<TApi>;
}

function preferDiscoveryCost(discoveryCost: number, fallbackCost: number): number {
	if (Number.isFinite(discoveryCost) && discoveryCost > 0) {
		return discoveryCost;
	}
	return fallbackCost;
}

function preferDiscoveryName(discoveryName: string, fallbackName: string, modelId: string): string {
	const normalizedDiscoveryName = discoveryName.trim();
	if (normalizedDiscoveryName.length === 0) {
		return fallbackName;
	}
	if (normalizedDiscoveryName === modelId && fallbackName !== modelId) {
		return fallbackName;
	}
	return normalizedDiscoveryName;
}

function preferDiscoveryLimit(discoveryLimit: number, fallbackLimit: number): number {
	if (!Number.isFinite(discoveryLimit) || discoveryLimit <= 0) {
		return fallbackLimit;
	}
	if (discoveryLimit === 4096 && fallbackLimit > discoveryLimit) {
		return fallbackLimit;
	}
	return discoveryLimit;
}

function normalizeModelList<TApi extends Api>(value: unknown): Model<TApi>[] {
	if (!Array.isArray(value)) {
		return [];
	}
	const models: Model<TApi>[] = [];
	for (const item of value) {
		if (isModelLike(item) && !isRetiredModel(item)) {
			models.push(enrichModelThinking(item as Model<TApi>));
		}
	}
	return applyFinalCodexGpt56ContextCap(models);
}

function isModelLike(value: unknown): value is Model<Api> {
	if (!isRecord(value)) {
		return false;
	}
	const v = value as {
		id?: unknown;
		name?: unknown;
		api?: unknown;
		provider?: unknown;
		baseUrl?: unknown;
		reasoning?: unknown;
		input?: unknown;
		cost?: unknown;
		contextWindow?: unknown;
		maxTokens?: unknown;
	};
	if (typeof v.id !== "string" || v.id.length === 0) {
		return false;
	}
	if (typeof v.name !== "string" || v.name.length === 0) {
		return false;
	}
	if (typeof v.api !== "string" || v.api.length === 0) {
		return false;
	}
	if (typeof v.provider !== "string" || v.provider.length === 0) {
		return false;
	}
	if (typeof v.baseUrl !== "string" || v.baseUrl.length === 0) {
		return false;
	}
	if (typeof v.reasoning !== "boolean") {
		return false;
	}
	if (!isModelInputArray(v.input)) {
		return false;
	}
	if (!isModelCost(v.cost)) {
		return false;
	}
	// Finite positive: NaN > 0 is false, +Infinity < Infinity is false.
	const cw = v.contextWindow;
	if (typeof cw !== "number" || !(cw > 0 && cw < Infinity)) {
		return false;
	}
	const mt = v.maxTokens;
	if (typeof mt !== "number" || !(mt > 0 && mt < Infinity)) {
		return false;
	}
	return true;
}

function isRecord(value: unknown): value is Record<string, unknown> {
	return typeof value === "object" && value !== null;
}

function isModelInputArray(value: unknown): value is ("text" | "image")[] {
	if (!Array.isArray(value) || value.length === 0) {
		return false;
	}
	for (let i = 0; i < value.length; i++) {
		const item = value[i];
		if (item !== "text" && item !== "image") {
			return false;
		}
	}
	return true;
}

function isModelCost(value: unknown): value is Model<Api>["cost"] {
	if (!isRecord(value)) {
		return false;
	}
	const c = value as {
		input?: unknown;
		output?: unknown;
		cacheRead?: unknown;
		cacheWrite?: unknown;
	};
	// Finite (NaN-safe): -Infinity < x < Infinity rejects NaN and both infinities.
	// Preserves original behavior: 0 and negatives remain valid.
	const ci = c.input;
	if (typeof ci !== "number" || !(ci > -Infinity && ci < Infinity)) {
		return false;
	}
	const co = c.output;
	if (typeof co !== "number" || !(co > -Infinity && co < Infinity)) {
		return false;
	}
	const cr = c.cacheRead;
	if (typeof cr !== "number" || !(cr > -Infinity && cr < Infinity)) {
		return false;
	}
	const cw = c.cacheWrite;
	if (typeof cw !== "number" || !(cw > -Infinity && cw < Infinity)) {
		return false;
	}
	return true;
}