// One place that turns whatever the API threw into something an operator can
// act on. Before this existed, every list screen surfaced the raw status text
// ("Internal Server Error", "Too Many Requests", "Bad Request") — which names
// the failure but never the fix — and, worse, rendered its empty state *next
// to* the error, so "the load failed" and "there is nothing here" looked
// identical. An operator can't tell an empty audit log from a broken one.

import { ArcadiaError } from "@crema/arcadia-core-client"

export type LoadError = {
  /** Plain-language headline. Never a raw HTTP status. */
  title: string
  /** What to do about it. Empty when there's genuinely nothing to suggest. */
  detail: string
  status?: number
  /** Set for 429s — seconds until it's worth retrying. Drives auto-retry. */
  retryAfterSec?: number
  /** True when retrying might plausibly work (5xx, 429, network). */
  retryable: boolean
  /** Field-level validation messages, flattened from Ecto's error tree. */
  fields?: string[]
}

/** Flatten Ecto's nested `{tenant: {slug: ["has already been taken"]}}`. */
function flattenFieldErrors(details: unknown): string[] {
  const lines: string[] = []
  const walk = (obj: unknown, prefix: string) => {
    if (Array.isArray(obj)) {
      lines.push(prefix ? `${prefix}: ${obj.join(", ")}` : obj.join(", "))
    } else if (obj && typeof obj === "object") {
      for (const [k, v] of Object.entries(obj)) {
        walk(v, prefix ? `${prefix}.${k}` : k)
      }
    }
  }
  walk(details, "")
  return lines
}

export function describeError(err: unknown, context = "load"): LoadError {
  // Network / CORS / server down — fetch rejects before any status exists.
  if (err instanceof TypeError || (err instanceof Error && /fetch/i.test(err.message))) {
    return {
      title: "Can't reach arcadia",
      detail:
        "The API didn't respond. Check the service is running and that this host is allowed to call it, then retry.",
      retryable: true,
    }
  }

  if (!(err instanceof ArcadiaError)) {
    return {
      title: `Couldn't ${context}`,
      detail: err instanceof Error && err.message ? err.message : "An unexpected error occurred.",
      retryable: true,
    }
  }

  const fields = err.details ? flattenFieldErrors(err.details) : undefined

  switch (true) {
    case err.status === 401:
      return {
        title: "Your session has expired",
        detail: "Sign in again to continue.",
        status: 401,
        retryable: false,
      }

    case err.status === 403:
      return {
        title: "You don't have access to this",
        detail:
          "Your account lacks the role this screen needs. A platform administrator can grant it.",
        status: 403,
        retryable: false,
      }

    case err.status === 404:
      return {
        title: "Not found",
        detail: "It may have been deleted, or the endpoint isn't available on this deployment.",
        status: 404,
        retryable: false,
      }

    case err.status === 422:
      return {
        title: "That didn't validate",
        detail: fields?.length ? "" : err.message,
        status: 422,
        retryable: false,
        fields,
      }

    case err.status === 429:
      return {
        title: "Too many requests",
        detail: "arcadia is rate-limiting this console. It'll retry automatically.",
        status: 429,
        retryAfterSec: 30,
        retryable: true,
      }

    case err.status >= 500:
      return {
        title: "arcadia hit a server error",
        detail: `The request failed on the server${
          err.requestId ? ` (request ${err.requestId})` : ""
        }. Retry, and if it persists check the service logs.`,
        status: err.status,
        retryable: true,
      }

    default:
      return {
        title: `Couldn't ${context}`,
        // Prefer the server's own message over the bare status line.
        detail: fields?.length ? "" : err.message,
        status: err.status,
        retryable: err.status >= 500,
        fields,
      }
  }
}

/** One-line form, for toasts and inside dialogs. */
export function errorMessage(err: unknown, context = "save"): string {
  const d = describeError(err, context)
  const parts = [d.title]
  if (d.fields?.length) parts.push(d.fields.join("; "))
  else if (d.detail) parts.push(d.detail)
  return parts.join(" — ")
}