/**
 * @coreci/byom/router — BYOM routing shim (REQ-008, REQ-009, G-001).
 *
 * `routeInference(db, secrets, tenantId, payload)` resolves the tenant's
 * validated BYOM endpoint, fetches the API key from the secret manager, and
 * POSTs the OpenAI-compatible chat completion request to `{url}/v1/chat/completions`
 * (D-001). On 200 → returns the parsed ChatCompletionResponse. On
 * unconfigured/unreachable → throws ByomUnconfiguredError / ByomUnreachableError
 * (REQ-009, Edge 1) so the API gateway can return a clear actionable error and
 * NO inference is attempted.
 *
 * [G-001] Scope note: in M1 there is no M3 chat orchestrator to drive inference,
 * so the control plane exposes `POST /api/byom/test-inference` (Admin only) as a
 * plan-time proxy to satisfy REQ-008 ("100% of LLM inference calls routed to
 * BYOM, verified via outbound traffic log"). This shim is the single egress
 * point for that proxy and for the future M3 orchestrator. Marked for M3
 * deprecation of the proxy endpoint — the shim itself persists.
 *
 * REQ-009 error semantics:
 *   - ByomUnconfiguredError → no validated BYOM endpoint for the tenant → 400.
 *   - ByomUnreachableError  → endpoint unreachable OR rejected the key (401/403
 *     is treated as unreachable for the operator, since a previously-validated
 *     endpoint returning 401/403 means the key was revoked or the endpoint
 *     moved) → 503.
 */

import type { DbClient } from "@coreci/db";
import type { SecretProvider } from "@coreci/secrets";
import type { ChatCompletionRequest, ChatCompletionResponse } from "./types.js";
import { getEndpoint, BYOM_SECRET_NAME } from "./repository.js";

/** Thrown when no validated BYOM endpoint exists for the tenant (REQ-009 → 400). */
export class ByomUnconfiguredError extends Error {
  constructor(tenantId: string) {
    super(
      `BYOM is not configured for tenant ${tenantId}. Configure a BYOM endpoint in the dashboard before sending prompts.`,
    );
    this.name = "ByomUnconfiguredError";
  }
}

/** Thrown when the BYOM endpoint is unreachable or rejected the key (REQ-009, Edge 1 → 503). */
export class ByomUnreachableError extends Error {
  override readonly cause: unknown | undefined;
  constructor(message: string, cause?: unknown) {
    super(message);
    this.name = "ByomUnreachableError";
    this.cause = cause;
  }
}

/**
 * Route an inference call to the tenant's configured BYOM endpoint (REQ-008).
 *
 * 1. Resolve the tenant's validated endpoint. If none → ByomUnconfiguredError.
 * 2. Resolve the API key via secrets.get → unwrap.
 * 3. POST to `{endpoint.url}/v1/chat/completions` with Authorization: Bearer.
 * 4. On 200 → return parsed ChatCompletionResponse.
 *    On connection error → ByomUnreachableError.
 *    On 401/403 → ByomUnreachableError (treated as unreachable for the operator).
 */
export async function routeInference(
  db: DbClient,
  secrets: SecretProvider,
  tenantId: string,
  payload: ChatCompletionRequest,
): Promise<ChatCompletionResponse> {
  const endpoint = await getEndpoint(db, tenantId);
  if (!endpoint) {
    throw new ByomUnconfiguredError(tenantId);
  }

  const key = await secrets.get(tenantId, BYOM_SECRET_NAME);
  const url = joinChatCompletions(endpoint.url);

  let res: Response;
  try {
    res = await fetch(url, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        Authorization: `Bearer ${key.unwrap()}`,
      },
      body: JSON.stringify(payload),
    });
  } catch (err) {
    throw new ByomUnreachableError(
      `BYOM endpoint at ${endpoint.url} is unreachable: ${err instanceof Error ? err.message : String(err)}`,
      err,
    );
  }

  if (res.status === 401 || res.status === 403) {
    let detail: string;
    try {
      detail = await res.text();
    } catch {
      detail = `HTTP ${res.status}`;
    }
    throw new ByomUnreachableError(
      `BYOM endpoint at ${endpoint.url} rejected the API key (HTTP ${res.status}). The key may have been revoked or the endpoint moved. ${detail}`,
    );
  }

  if (!res.ok) {
    let detail: string;
    try {
      detail = await res.text();
    } catch {
      detail = `HTTP ${res.status}`;
    }
    throw new ByomUnreachableError(
      `BYOM endpoint at ${endpoint.url} returned HTTP ${res.status}: ${detail}`,
    );
  }

  let body: unknown;
  try {
    body = await res.json();
  } catch (err) {
    throw new ByomUnreachableError(
      `BYOM endpoint at ${endpoint.url} returned 200 but the body was not valid JSON: ${
        err instanceof Error ? err.message : String(err)
      }`,
      err,
    );
  }
  return body as ChatCompletionResponse;
}

/** Join a base URL with `/v1/chat/completions` (mirrors validator.ts). */
function joinChatCompletions(baseUrl: string): string {
  const trimmed = baseUrl.replace(/\/+$/, "");
  if (trimmed.endsWith("/v1/chat/completions")) return trimmed;
  if (trimmed.endsWith("/v1")) return `${trimmed}/chat/completions`;
  return `${trimmed}/v1/chat/completions`;
}