/**
 * earth-now.co
 * Author:  Simon-Pierre Boucher
 * Contact: contact@spboucher.ai
 * File:    packages/widget/src/render.ts
 * Purpose: Pure, DOM-free widget helpers — config resolution, model payload parsing, display text building (unit-testable)
 */

import {
  type CounterModel,
  type CounterWindow,
  formatRate,
  formatValue,
  rateAt,
  windowValue,
} from "@earth-now/counter";

/** Default API origin the widget talks to when data-api is not provided. */
export const DEFAULT_API = "https://www.earth-now.co";

export interface WidgetConfig {
  metricId: string;
  window: CounterWindow;
  lang: string;
  api: string;
}

/**
 * Resolve a widget config from a DOMStringMap-like object
 * (data-earth-now-metric / data-window / data-lang / data-api).
 * Returns null when no metric id is declared.
 */
export function resolveConfig(dataset: Partial<Record<string, string>>): WidgetConfig | null {
  const metricId = dataset["earthNowMetric"]?.trim();
  if (!metricId) return null;
  const w = dataset["window"];
  const window: CounterWindow =
    w === "today" || w === "ytd" || w === "session" || w === "total" ? w : "total";
  return {
    metricId,
    window,
    lang: dataset["lang"] ?? "en",
    api: (dataset["api"] ?? DEFAULT_API).replace(/\/+$/, ""),
  };
}

/** URL of the CounterModel endpoint for a config. */
export function modelUrl(config: WidgetConfig): string {
  return `${config.api}/v1/metrics/${encodeURIComponent(config.metricId)}/model`;
}

/**
 * Validate a fetched JSON payload into a CounterModel.
 * Accepts either the model itself or an `{ model: ... }` envelope.
 * Throws a descriptive error on anything malformed — the caller renders "data pending".
 */
export function parseModelPayload(json: unknown): CounterModel {
  const candidate =
    typeof json === "object" && json !== null && "model" in json
      ? (json as { model: unknown }).model
      : json;
  if (typeof candidate !== "object" || candidate === null)
    throw new Error("earth-now widget: model payload is not an object");
  const m = candidate as Partial<CounterModel>;
  if (typeof m.metricId !== "string") throw new Error("earth-now widget: model missing metricId");
  if (typeof m.anchorValue !== "number" || !Number.isFinite(m.anchorValue))
    throw new Error("earth-now widget: model missing finite anchorValue");
  if (typeof m.anchorTime !== "string" || Number.isNaN(Date.parse(m.anchorTime)))
    throw new Error("earth-now widget: model missing valid anchorTime");
  if (typeof m.rateFn !== "object" || m.rateFn === null || typeof m.rateFn.kind !== "string")
    throw new Error("earth-now widget: model missing rateFn");
  if (typeof m.displayHints !== "object" || m.displayHints === null)
    throw new Error("earth-now widget: model missing displayHints");
  return m as CounterModel;
}

export interface DisplayText {
  /** Formatted counter value (applySigFigs false — the ticker animates the trailing digits). */
  value: string;
  /** Formatted instantaneous rate incl. cadence suffix, e.g. "4.3/s". */
  rate: string;
  /** Display unit label from the model's display hints. */
  unit: string;
}

/**
 * Compute the text a widget shows at instant tMs — pure, time is a parameter.
 * "session" windows use the caller-provided session start (widget load time).
 */
export function buildDisplayText(
  model: CounterModel,
  tMs: number,
  config: WidgetConfig,
  sessionStartMs?: number,
): DisplayText {
  const v = windowValue(model, tMs, config.window, sessionStartMs);
  const opts = { locale: config.lang, applySigFigs: false };
  return {
    value: formatValue(v, model.displayHints, opts),
    rate: formatRate(rateAt(model, tMs), model.displayHints, { locale: config.lang }),
    unit: model.displayHints.unit,
  };
}