import {
  resolveDesignSystem,
  validateDesignSystem,
  type DesignSystem,
  type DesignDiagnostic,
} from "@wrnexus/design-system";

export type DecisionLock = string;
const forbidden = new Set(["__proto__", "prototype", "constructor"]);
export function decisionPath(path: string): string[] {
  if (typeof path !== "string" || path.length > 512 || !path.startsWith("/"))
    throw Error("WRN-STUDIO-LOCK-PATH: use a JSON pointer.");
  const parts = path
    .slice(1)
    .split("/")
    .map((p) => {
      if (/~(?![01])/u.test(p)) throw Error("Invalid pointer escape.");
      return p.replace(/~1/g, "/").replace(/~0/g, "~");
    });
  if (
    !["tokens", "modes", "densities", "recipes", "name", "id", "version", "defaultMode"].includes(
      parts[0]!,
    ) ||
    parts.some((p) => !p || forbidden.has(p)) ||
    parts.length > 8
  )
    throw Error("WRN-STUDIO-LOCK-PATH: unsupported decision path.");
  return parts;
}
export const pointerPart = (value: string) => value.replace(/~/g, "~0").replace(/\//g, "~1");
export function readDecision(value: unknown, path: string): unknown {
  let current = value;
  for (const part of decisionPath(path)) {
    if (!current || typeof current !== "object" || !Object.hasOwn(current, part)) return undefined;
    current = (current as Record<string, unknown>)[part];
  }
  return current;
}
export function writeDecision(system: DesignSystem, path: string, value: unknown) {
  const parts = decisionPath(path);
  let target = system as unknown as Record<string, unknown>;
  for (const part of parts.slice(0, -1)) {
    if (!Object.hasOwn(target, part)) target[part] = {};
    if (!target[part] || typeof target[part] !== "object" || Array.isArray(target[part]))
      throw Error("WRN-STUDIO-PATCH: parent must be an object.");
    target = target[part] as Record<string, unknown>;
  }
  const last = parts.at(-1)!;
  if (value === undefined) delete target[last];
  else target[last] = structuredClone(value);
}
export function validateLocks(locks: unknown): asserts locks is DecisionLock[] {
  if (
    !Array.isArray(locks) ||
    locks.length > 128 ||
    locks.some((p) => typeof p !== "string") ||
    new Set(locks).size !== locks.length
  )
    throw Error("WRN-STUDIO-LOCKS: provide up to 128 unique decision paths.");
  for (const path of locks) decisionPath(path);
}
function references(value: unknown, result = new Set<string>()) {
  if (value && typeof value === "object") {
    if ("ref" in value && typeof value.ref === "string") result.add(value.ref);
    else for (const child of Object.values(value)) references(child, result);
  }
  return result;
}
function tokenNames(system: DesignSystem, path: string) {
  const [kind, layer, name] = decisionPath(path);
  const names = new Set<string>();
  if (kind === "tokens")
    for (const token of Object.keys(system.tokens)) if (!layer || token === layer) names.add(token);
  if (kind === "modes" || kind === "densities") {
    const layers = system[kind] ?? {};
    for (const [key, tokens] of Object.entries(layers))
      if (!layer || key === layer)
        for (const token of Object.keys(tokens)) if (!name || name === token) names.add(token);
  }
  if (kind === "recipes") references(readDecision(system, path), names);
  return names;
}
function configurations(a: DesignSystem, b: DesignSystem) {
  const modes = [
    undefined,
    ...new Set([...Object.keys(a.modes ?? {}), ...Object.keys(b.modes ?? {})]),
  ];
  const densities = [
    undefined,
    ...new Set([...Object.keys(a.densities ?? {}), ...Object.keys(b.densities ?? {})]),
  ];
  if (modes.length * densities.length > 128)
    throw Error("WRN-STUDIO-LOCK-LIMIT: too many lock configurations.");
  return modes.flatMap((mode) => densities.map((density) => ({ mode, density })));
}
/** Locks protect raw decisions and effective referenced values, including aliases and modes. */
export function checkDecisionLocks(
  before: DesignSystem,
  after: DesignSystem,
  locks: DecisionLock[],
): DesignDiagnostic[] {
  validateLocks(locks);
  if (!locks.length) return [];
  const diagnostics: DesignDiagnostic[] = [];
  const fail = (path: string, message: string) =>
    diagnostics.push({ code: "WRN-STUDIO-LOCK", path, message });
  const configurationsList = configurations(before, after);
  const resolve = (system: DesignSystem, mode?: string, density?: string) =>
    resolveDesignSystem(system, {
      mode: mode && Object.hasOwn(system.modes ?? {}, mode) ? mode : undefined,
      density: density && Object.hasOwn(system.densities ?? {}, density) ? density : undefined,
    }).tokens;
  const pairs = configurationsList.map(({ mode, density }) => ({
    mode,
    density,
    before: resolve(before, mode, density),
    after: resolve(after, mode, density),
  }));
  for (const path of locks) {
    if (JSON.stringify(readDecision(before, path)) !== JSON.stringify(readDecision(after, path))) {
      fail(path, "This decision is locked. Unlock it before changing or removing it.");
      continue;
    }
    const names = tokenNames(before, path);
    let changed = false;
    for (const pair of pairs) {
      const parts = decisionPath(path);
      if (parts[0] === "modes" && parts[1] && pair.mode !== parts[1]) continue;
      if (parts[0] === "densities" && parts[1] && pair.density !== parts[1]) continue;
      for (const name of names)
        if (
          JSON.stringify({ type: pair.before[name]?.type, value: pair.before[name]?.value }) !==
          JSON.stringify({ type: pair.after[name]?.type, value: pair.after[name]?.value })
        ) {
          changed = true;
          break;
        }
      if (changed) break;
    }
    if (changed)
      fail(path, "A referenced token or mode changes the effective value of this locked decision.");
  }
  return diagnostics;
}
/** Local directions copy lock dependencies; arbitrary provider patches must pass checks unchanged. */
export function preserveDecisionLocks(
  before: DesignSystem,
  after: DesignSystem,
  locks: DecisionLock[],
) {
  validateLocks(locks);
  const next = structuredClone(after);
  const names = new Set<string>();
  for (const path of locks) {
    writeDecision(next, path, readDecision(before, path));
    for (const name of tokenNames(before, path)) names.add(name);
  }
  // The default selection is part of an effective token/recipe decision.
  if (names.size) next.defaultMode = before.defaultMode;
  for (const name of names) {
    for (const token of [
      before.tokens[name],
      ...Object.values(before.modes ?? {}).map((t) => t[name]),
      ...Object.values(before.densities ?? {}).map((t) => t[name]),
    ])
      for (const ref of references(token)) names.add(ref);
    writeDecision(next, "/tokens/" + pointerPart(name), before.tokens[name]);
    for (const kind of ["modes", "densities"] as const)
      for (const layer of new Set([
        ...Object.keys(before[kind] ?? {}),
        ...Object.keys(next[kind] ?? {}),
      ]))
        writeDecision(
          next,
          `/${kind}/${pointerPart(layer)}/${pointerPart(name)}`,
          before[kind]?.[layer]?.[name],
        );
  }
  if (validateDesignSystem(next).length)
    throw Error("WRN-STUDIO-LOCK: locked decisions cannot be combined with this direction.");
  const failures = checkDecisionLocks(before, next, locks);
  if (failures.length) throw Error(failures.map((d) => d.message).join(" "));
  return next;
}
export async function designRevision(system: DesignSystem, locks: DecisionLock[] = []) {
  validateLocks(locks);
  const bytes = new TextEncoder().encode(JSON.stringify({ system, locks: [...locks].sort() }));
  return [...new Uint8Array(await crypto.subtle.digest("SHA-256", bytes))]
    .map((b) => b.toString(16).padStart(2, "0"))
    .join("");
}