import type { ClawdbotConfig } from "../config/config.js";
import { DEFAULT_MODEL, DEFAULT_PROVIDER } from "./defaults.js";
import {
  buildModelAliasIndex,
  modelKey,
  parseModelRef,
  resolveModelRefFromString,
} from "./model-selection.js";

type ModelCandidate = {
  provider: string;
  model: string;
};

type FallbackAttempt = {
  provider: string;
  model: string;
  error: string;
};

function isAbortError(err: unknown): boolean {
  if (!err || typeof err !== "object") return false;
  const name = "name" in err ? String(err.name) : "";
  if (name === "AbortError") return true;
  const message =
    "message" in err && typeof err.message === "string"
      ? err.message.toLowerCase()
      : "";
  return message.includes("aborted");
}

function buildAllowedModelKeys(
  cfg: ClawdbotConfig | undefined,
  defaultProvider: string,
): Set<string> | null {
  const rawAllowlist = cfg?.agent?.allowedModels ?? [];
  if (rawAllowlist.length === 0) return null;
  const keys = new Set<string>();
  for (const raw of rawAllowlist) {
    const parsed = parseModelRef(String(raw ?? ""), defaultProvider);
    if (!parsed) continue;
    keys.add(modelKey(parsed.provider, parsed.model));
  }
  return keys.size > 0 ? keys : null;
}

function resolveFallbackCandidates(params: {
  cfg: ClawdbotConfig | undefined;
  provider: string;
  model: string;
}): ModelCandidate[] {
  const provider = params.provider.trim() || DEFAULT_PROVIDER;
  const model = params.model.trim() || DEFAULT_MODEL;
  const aliasIndex = buildModelAliasIndex({
    cfg: params.cfg ?? {},
    defaultProvider: DEFAULT_PROVIDER,
  });
  const allowlist = buildAllowedModelKeys(params.cfg, DEFAULT_PROVIDER);
  const seen = new Set<string>();
  const candidates: ModelCandidate[] = [];

  const addCandidate = (candidate: ModelCandidate, enforceAllowlist: boolean) => {
    if (!candidate.provider || !candidate.model) return;
    const key = modelKey(candidate.provider, candidate.model);
    if (seen.has(key)) return;
    if (enforceAllowlist && allowlist && !allowlist.has(key)) return;
    seen.add(key);
    candidates.push(candidate);
  };

  addCandidate({ provider, model }, false);

  for (const raw of params.cfg?.agent?.modelFallbacks ?? []) {
    const resolved = resolveModelRefFromString({
      raw: String(raw ?? ""),
      defaultProvider: DEFAULT_PROVIDER,
      aliasIndex,
    });
    if (!resolved) continue;
    addCandidate(resolved.ref, true);
  }

  return candidates;
}

export async function runWithModelFallback<T>(params: {
  cfg: ClawdbotConfig | undefined;
  provider: string;
  model: string;
  run: (provider: string, model: string) => Promise<T>;
  onError?: (attempt: {
    provider: string;
    model: string;
    error: unknown;
    attempt: number;
    total: number;
  }) => void | Promise<void>;
}): Promise<{
  result: T;
  provider: string;
  model: string;
  attempts: FallbackAttempt[];
}> {
  const candidates = resolveFallbackCandidates(params);
  const attempts: FallbackAttempt[] = [];
  let lastError: unknown;

  for (let i = 0; i < candidates.length; i += 1) {
    const candidate = candidates[i] as ModelCandidate;
    try {
      const result = await params.run(candidate.provider, candidate.model);
      return {
        result,
        provider: candidate.provider,
        model: candidate.model,
        attempts,
      };
    } catch (err) {
      if (isAbortError(err)) throw err;
      lastError = err;
      attempts.push({
        provider: candidate.provider,
        model: candidate.model,
        error: err instanceof Error ? err.message : String(err),
      });
      await params.onError?.({
        provider: candidate.provider,
        model: candidate.model,
        error: err,
        attempt: i + 1,
        total: candidates.length,
      });
    }
  }

  if (attempts.length <= 1 && lastError) throw lastError;
  const summary =
    attempts.length > 0
      ? attempts
          .map(
            (attempt) =>
              `${attempt.provider}/${attempt.model}: ${attempt.error}`,
          )
          .join(" | ")
      : "unknown";
  throw new Error(
    `All models failed (${attempts.length || candidates.length}): ${summary}`,
    { cause: lastError instanceof Error ? lastError : undefined },
  );
}