// Implemented locally rather than imported from @wrnexus/core: compiler modules
// are bundled into the Node-only VS Code extension, which contains no other
// packages, so a runtime import of core would break the editor compiler.
const HTML_ESCAPES: Record<string, string> = {
  "&": "&amp;",
  "<": "&lt;",
  ">": "&gt;",
  '"': "&quot;",
  "'": "&#39;",
};

function escapeHtml(value: string): string {
  return value.replace(/[&<>"']/g, (character) => HTML_ESCAPES[character]!);
}

const SAFE_ISLAND_NAME = /^[A-Za-z0-9_-]+$/;

function isSafeIslandName(name: string): boolean {
  return SAFE_ISLAND_NAME.test(name);
}

export type IslandStrategy = "only" | "load" | "visible" | "idle";

export interface IslandDiagnostic {
  code: "WRN-ISLAND-PROPS";
  message: string;
  severity: "error";
}

const STRATEGIES: Record<string, IslandStrategy> = {
  "client:only": "only",
  "client:load": "load",
  "client:visible": "visible",
  "client:idle": "idle",
};

export function parseIslandStrategy(directives: string[]): IslandStrategy {
  for (const directive of directives) {
    const match = STRATEGIES[directive];
    if (match) return match;
  }
  return "only";
}

function unsupportedProp(value: unknown): boolean {
  const type = typeof value;
  if (type === "function" || type === "symbol" || type === "bigint" || type === "undefined") {
    return true;
  }
  if (value === null || type !== "object") return false;
  if (Array.isArray(value)) return (value as unknown[]).some(unsupportedProp);
  const proto = Object.getPrototypeOf(value);
  if (proto !== Object.prototype && proto !== null) return true;
  return Object.values(value as Record<string, unknown>).some(unsupportedProp);
}

/**
 * Interprets an island attribute value with JSX semantics.
 *
 * `title="Revenue"` is a string, `start={3}` is a number, `flag` alone is
 * `true`. Without this every prop arrives as a string, so `start={3}` would be
 * `"3"` and arithmetic in the island silently concatenates.
 *
 * Returns `dynamic` for a `{…}` value that is not JSON: such expressions are
 * evaluated at runtime and cannot cross the serialization boundary.
 */
export function islandPropValue(raw: string | undefined): { value: unknown } | { dynamic: string } {
  if (raw === undefined || raw === "") return { value: true };
  const expression = /^\{([\s\S]*)\}$/.exec(raw);
  if (!expression) return { value: raw };
  const inner = expression[1]!.trim();
  try {
    return { value: JSON.parse(inner) as unknown };
  } catch {
    return { dynamic: inner };
  }
}

export function serializeIslandProps(
  componentName: string,
  props: Record<string, unknown>,
): { json: string } | { diagnostic: IslandDiagnostic } {
  const offenders = Object.entries(props)
    .filter(([, value]) => unsupportedProp(value))
    .map(([key]) => key);

  if (offenders.length > 0) {
    return {
      diagnostic: {
        code: "WRN-ISLAND-PROPS",
        severity: "error",
        message:
          `Island '${componentName}' received non-serializable prop(s): ${offenders.join(", ")}. ` +
          `Island props cross a serialization boundary and must be JSON-safe ` +
          `(no functions, symbols, bigints, undefined, or class instances).`,
      },
    };
  }

  return { json: JSON.stringify(props) };
}

export function renderIslandMarker(input: {
  name: string;
  strategy: IslandStrategy;
  propsJson: string;
}): string {
  // The name becomes a path segment when the browser fetches
  // /__wrnexus/island/<name>.js, so reuse the framework's conservative charset
  // rather than relying on escaping alone.
  if (!isSafeIslandName(input.name)) {
    throw new Error(
      `Island name '${input.name}' is not a safe identifier. ` +
        `Island names may only contain letters, digits, underscores, and hyphens.`,
    );
  }

  return (
    `<div data-wrn-island="${escapeHtml(input.name)}"` +
    ` data-wrn-island-strategy="${input.strategy}"` +
    ` data-wrn-island-props="${escapeHtml(input.propsJson)}"></div>`
  );
}

/**
 * Local binding names introduced by island imports.
 *
 * Codegen sees only component tag names, so it needs the set of names that came
 * from `.tsx` imports to tell an island apart from a `.wrn` component.
 */
export function islandNamesFrom(
  imports: Array<{ kind?: "island"; declaration: { defaultImport?: string } }>,
): Set<string> {
  const names = new Set<string>();
  for (const entry of imports) {
    if (entry.kind !== "island") continue;
    const local = entry.declaration.defaultImport;
    if (local) names.add(local);
  }
  return names;
}