/**
 * Four-quadrant RPC message model. Channels and messages are
 * decoupled: HTTP is the client→server physical channel, SSE the server→client one; logical
 * messages are channel-independent, and the wire full form is a four-member discriminated union.
 * api/ contract layer: zero Node dependencies, importable from the browser.
 */

import type { z as zCore } from 'zod'
type ZodIssue = zCore.core.$ZodIssue
import type { Branded } from '@deepseek-ai/dsh-brand'
import type { SessionId } from '@deepseek-ai/dsh-session/types'

/**
 * Message correlation id: the initiator mints it on a request; a response
 * echoes the matching request's rpcId and never mints a new one.
 */
export type RpcId = Branded<'rpc-id'>

/**
 * Brands a string as RpcId (same precedent as core `SessionId()`). Minted by the initiator:
 * client-request → client mints; server-request → host mints (answerable frames get a stable
 * logical id, pure pushes mint a fresh one each time).
 * @param id - Raw id string (implementations mint UUIDs; tests may pass fixtures).
 * @returns The same string, branded (compile-time cast, zero runtime cost).
 */
export function RpcId(id: string): RpcId {
  return id as RpcId
}

/** Error code → details type map (a second table isomorphic to RpcMethodMap). New code = one row here + one branch in the error schema. */
export interface RpcErrorDetailsMap {
  'bad-request': { issues: ZodIssue[] }
  'session-not-found': { sessionId: SessionId }
  'agent-busy': { reason: string }
  'internal': {}
}

/** Closed error-code union (the keys of RpcErrorDetailsMap). */
export type RpcErrorCode = keyof RpcErrorDetailsMap

/**
 * Distributive union expanded from the map: code is the discriminant, so
 * `switch (error.code)` narrows details. details is required (internal uses an explicit {}).
 */
export type RpcError = {
  [C in RpcErrorCode]: { code: C; message: string; details: RpcErrorDetailsMap[C] }
}[RpcErrorCode]

/** Business success/failure result: the result slot of a unary response; methods never throw business errors. */
export type RpcResult<T> = { ok: true; value: T } | { ok: false; error: RpcError }

/**
 * Signature-layer narrow form, request side (domain-interface view, shared by
 * both directions): rpcId is explicit in the signature, never mixed into the
 * business payload; the type tag and method are filled in by the carrier layer.
 */
export interface RpcRequest<P> {
  rpcId: RpcId
  payload: P
}

/** Signature-layer narrow form, response side: rpcId always echoes the matching request. */
export interface RpcResponse<T> {
  rpcId: RpcId
  result: RpcResult<T>
}

// ---- Wire full forms: four named members of a discriminated union (discriminant = the four `type` literals) ----

/** Call initiated by the client (wire carrier: POST /api/<method> body). */
export interface ClientRequest {
  type: 'client-request'
  rpcId: RpcId
  method: string
  payload: unknown
}

/** Response to a ClientRequest (wire carrier: the HTTP response body of that POST); rpcId echoed. */
export interface ServerResponse {
  type: 'server-response'
  rpcId: RpcId
  result: RpcResult<unknown>
}

/**
 * Message initiated by the server (wire carrier: SSE frame). Answerable interactions
 * (approval/question requested — stable rpcId, reused on replay) and pure pushes
 * (session/event etc. — rpcId identifies that one push) share this shape; whether a
 * response is expected is determined statically by method (a strict dichotomy, no third kind).
 */
export interface ServerRequest {
  type: 'server-request'
  rpcId: RpcId
  method: string
  payload: unknown
}

/** Response to a ServerRequest (wire carrier: POST /api/respond body); rpcId echoed, never minted anew. */
export interface ClientResponse {
  type: 'client-response'
  rpcId: RpcId
  result: RpcResult<unknown>
}

/** Authoritative wire full-form union; narrow via `switch (message.type)`. */
export type RpcMessage = ClientRequest | ServerResponse | ServerRequest | ClientResponse

/**
 * Carrier receipt (not an RpcMessage — it belongs to the carrier layer, same
 * discipline as "HTTP status describes only the carrier"): the HTTP response
 * body of the POST carrying a client-response. Late/duplicate responses yield not-pending.
 */
export type RpcReceipt = { accepted: true } | { accepted: false; reason: 'not-pending' | 'bad-response' }