/**
 * Model registry — single source of truth for available models.
 *
 * Backends register their models during initialization. Frontends read
 * from the registry to build dynamic model pickers, resolve aliases,
 * and query capabilities. No model names are hardcoded outside this
 * system and the backend-specific model definition files.
 */

import type { ReasoningEffortLevel } from "../types.js";

// ── Types ────────────────────────────────────────────────────────────────────

export type ModelInfo = {
  /** Canonical model ID as registered by the backend. */
  id: string;
  /** Human-readable display name for UIs (e.g. "Sonnet 4.6"). */
  displayName: string;
  /** Short description for setup wizard (e.g. "fast, balanced"). */
  description?: string;
  /** Aliases that resolve to this model. */
  aliases: string[];
  /** Provider identifier (e.g. "anthropic", "openai"). */
  provider: string;
  /** Reasoning/effort levels this model accepts. */
  supportedReasoningLevels?: ReasoningEffortLevel[];
  /** Backend-reported default reasoning level, when available. */
  defaultReasoningLevel?: ReasoningEffortLevel;
  /** Model to fall back to on overload/timeout. */
  fallback?: string;
};

// ── Registry state ──────────────────────────────────────────────────────────

const models = new Map<string, ModelInfo>();
const aliasIndex = new Map<string, string>();
const providerPrefixes: string[] = [];

/**
 * Register a provider-specific prefix that the fuzzy
 * alias resolver will strip when matching family names. Backends call
 * this during initialization so core stays provider-agnostic.
 */
export function registerProviderPrefix(prefix: string): void {
  const lower = prefix.toLowerCase();
  if (!providerPrefixes.includes(lower)) {
    providerPrefixes.push(lower);
  }
}

function resolveGenericFamilyAlias(input: string): string | null {
  const trimmed = input.trim().toLowerCase();
  if (!trimmed) return null;

  let base = trimmed;
  for (const prefix of providerPrefixes) {
    if (base.startsWith(prefix)) {
      base = base.slice(prefix.length);
      break;
    }
  }

  const tokens = base.replace(/\./g, "-").split("-").filter(Boolean);
  if (tokens.length === 0) return null;

  let boundary = tokens.length;
  while (boundary > 0 && /^\d+$/.test(tokens[boundary - 1] ?? "")) {
    boundary -= 1;
  }

  const family = tokens.slice(
    0,
    boundary === tokens.length ? tokens.length : boundary,
  );
  if (family.length === 0) return null;

  return family.join("-");
}

// ── Registration ────────────────────────────────────────────────────────────

/** Register one or more models. Idempotent — re-registration overwrites. */
export function registerModels(infos: ModelInfo[]): void {
  for (const info of infos) {
    // Clear stale aliases from any previous registration of this model ID
    const prev = models.get(info.id);
    if (prev) {
      aliasIndex.delete(prev.id.toLowerCase());
      for (const alias of prev.aliases) {
        aliasIndex.delete(alias.toLowerCase());
      }
    }
    models.set(info.id, info);
    // Index the canonical ID itself as an alias
    aliasIndex.set(info.id.toLowerCase(), info.id);
    for (const alias of info.aliases) {
      aliasIndex.set(alias.toLowerCase(), info.id);
    }
  }
}

// ── Queries ─────────────────────────────────────────────────────────────────

/** Get a model by canonical ID. */
export function getModel(id: string): ModelInfo | undefined {
  return models.get(id);
}

/** List all registered models, optionally filtered by provider. Returned in registration order. */
export function getModels(provider?: string): ModelInfo[] {
  const result = [...models.values()];
  if (provider) {
    return result.filter((m) => m.provider === provider);
  }
  return result;
}

/**
 * Resolve a user input (alias or full ID) to the canonical model ID.
 * Returns the input unchanged if no match is found (passthrough for
 * unknown/custom model names).
 */
export function resolveModelId(input: string): string {
  const lower = input.trim().toLowerCase();
  const direct = aliasIndex.get(lower);
  if (direct) return direct;

  const genericAlias = resolveGenericFamilyAlias(input);
  if (genericAlias) {
    const resolved = aliasIndex.get(genericAlias);
    if (resolved) return resolved;
  }

  return input.trim();
}

/**
 * Resolve a user input to the full ModelInfo, or undefined if not found.
 */
export function resolveModel(input: string): ModelInfo | undefined {
  const id = resolveModelId(input);
  return models.get(id);
}

/** Get the fallback model ID for a given model, or null if none configured. */
export function getFallbackModel(modelId: string): string | null {
  return resolveModel(modelId)?.fallback ?? null;
}

/**
 * Get the default model. Prefers the canonical "default" model ID if
 * registered, otherwise returns the first registered model, otherwise
 * falls back to the literal string "default".
 */
export function getDefaultModel(): string {
  if (models.has("default")) return "default";
  const first = models.values().next();
  if (!first.done) return first.value.id;
  return "default";
}

// ── Provider-scoped clearing ────────────────────────────────────────────────

/** Remove all models for a specific provider (and their aliases). */
export function clearModelsByProvider(provider: string): void {
  for (const [id, info] of models) {
    if (info.provider !== provider) continue;
    aliasIndex.delete(id.toLowerCase());
    for (const alias of info.aliases) {
      aliasIndex.delete(alias.toLowerCase());
    }
    models.delete(id);
  }
}

/** Clear the entire registry. For tests only. */
export function clearModels(): void {
  models.clear();
  aliasIndex.clear();
  providerPrefixes.length = 0;
}