// Human error copy. Maps error codes / shapes / thrown values to a single
// plain sentence a person can act on. Used by the root ErrorBoundary and
// available to any route that catches a failure (e.g. a fetch reject).
//
// Ported/generalised from arcadia-personal-cloud-web's `acceptErrorMessage`:
// switch on a known machine `code`, else flatten field-validation errors,
// else fall back to the raw message or a friendly default.

import { isRouteErrorResponse } from "react-router"

/** A known machine error code → the human sentence we show for it. Extend
 *  this map as the app grows real backend error codes. */
const CODE_MESSAGES: Record<string, string> = {
  network_error: "Couldn't reach the server. Check your connection and try again.",
  timeout: "That took too long to respond. Try again in a moment.",
  unauthorized: "Your session has expired. Sign in again to continue.",
  forbidden: "You don't have access to that.",
  not_found: "We couldn't find what you were looking for.",
  rate_limited: "Too many requests just now. Give it a few seconds.",
  server_error: "Something went wrong on our end. Try again shortly.",
}

type ErrorShape = {
  error?: string
  code?: string
  message?: string
  errors?: Record<string, string[] | string>
}

/** Turn any caught value into one human sentence. */
export function humanErrorMessage(err: unknown): string {
  // React Router route-error responses (thrown Responses / 404s etc.).
  if (isRouteErrorResponse(err)) {
    if (err.status === 404) return CODE_MESSAGES.not_found
    if (err.status === 401) return CODE_MESSAGES.unauthorized
    if (err.status === 403) return CODE_MESSAGES.forbidden
    if (err.status === 429) return CODE_MESSAGES.rate_limited
    if (err.status >= 500) return CODE_MESSAGES.server_error
    return err.statusText || "That request couldn't be completed."
  }

  const d = (
    err && typeof err === "object" ? err : {}
  ) as ErrorShape
  const code = d.code ?? d.error
  if (code && CODE_MESSAGES[code]) return CODE_MESSAGES[code]

  // arcadia-style field validation: { errors: { field: [msg...] } } —
  // flatten into a single readable line so the user knows what to fix.
  if (d.errors && typeof d.errors === "object") {
    const lines: string[] = []
    for (const [field, msgs] of Object.entries(d.errors)) {
      const label = field.replace(/_/g, " ")
      const arr = Array.isArray(msgs) ? msgs : [String(msgs)]
      for (const m of arr) lines.push(`${label} ${m}`)
    }
    if (lines.length) return lines.join("; ")
  }

  if (err instanceof Error && err.message) return err.message
  if (typeof d.message === "string" && d.message) return d.message

  return "An unexpected error occurred. Please try again."
}

/** Short heading to pair with {@link humanErrorMessage} in a boundary/card. */
export function humanErrorTitle(err: unknown): string {
  if (isRouteErrorResponse(err)) {
    if (err.status === 404) return "Page not found"
    return "Something went wrong"
  }
  return "Something went wrong"
}