import { runtimeThemeContract, runtimeGradientGroups, type RuntimeThemeToken } from "./contract"
import { invalidateThemeRequest } from "./requests"

type SavedProperty = { property: string; value: string; priority: string }
const applied = new WeakMap<HTMLElement, { properties: SavedProperty[]; scope: string | null }>()
const isRecord = (value: unknown): value is Record<string, unknown> =>
  typeof value === "object" && value !== null && !Array.isArray(value)

/** Restore the host's previous inline values and scope. */
export function resetRuntimeTheme(root: HTMLElement) {
  invalidateThemeRequest(root)
  const previous = applied.get(root)
  if (!previous) return
  for (const { property, value, priority } of previous.properties) {
    if (value) root.style.setProperty(property, value, priority)
    else root.style.removeProperty(property)
  }
  if (previous.scope === null) root.removeAttribute("data-hm-theme")
  else root.setAttribute("data-hm-theme", previous.scope)
  applied.delete(root)
}

/** Validate without touching the DOM (editors/loaders can preserve their last valid value). */
export function isRuntimeTheme(theme: unknown): theme is import("./contract").RuntimeTheme {
  if (!isRecord(theme) || theme.schemaVersion !== 1 || !isRecord(theme.tokens)) return false
  const tokens = theme.tokens
  for (const group of runtimeGradientGroups) {
    const count = group.filter(key => Object.hasOwn(tokens, key)).length
    if (count !== 0 && count !== group.length) return false
  }
  for (const [key, value] of Object.entries(tokens)) {
    if (!Object.hasOwn(runtimeThemeContract, key) || typeof value !== "string") return false
    const definition = runtimeThemeContract[key as RuntimeThemeToken]
    const valid = definition.type === "radius"
      ? /^(?:[2-9]|1[0-2])px$/.test(value)
      : /^#[0-9a-fA-F]{6}$/.test(value)
    if (!valid) return false
  }
  return true
}

/** Atomic validation. Invalid documents release the previous override to host/default. */
export function applyRuntimeTheme(root: HTMLElement, theme: unknown): boolean {
  if (!isRuntimeTheme(theme)) { resetRuntimeTheme(root); return false }
  const values: (readonly [string, string])[] = Object.entries(theme.tokens).map(([key, value]) =>
    [runtimeThemeContract[key as RuntimeThemeToken].property, value!] as const)
  // Reviewed Gray default comes from the existing palette. Retain custom cancel
  // overrides without changing the public token or the full Default preset.
  const cancel = theme.tokens["color.action.cancel"]
  if (cancel && cancel.toLowerCase() !== runtimeThemeContract["color.action.cancel"].defaultValue)
    values.push(["--hm-button-cancel-runtime-ink", cancel])
  resetRuntimeTheme(root)
  const scope = root.getAttribute("data-hm-theme")
  const properties = values.map(([property]) => ({
    property, value: root.style.getPropertyValue(property), priority: root.style.getPropertyPriority(property),
  }))
  root.setAttribute("data-hm-theme", "runtime")
  for (const [property, value] of values) root.style.setProperty(property, value)
  applied.set(root, { properties, scope })
  return true
}