import { mkdir, readFile, rename, writeFile } from "node:fs/promises";
import { dirname } from "node:path";
import { generateKeyPair, type KeyPair } from "../crypto/keypair.js";

export const CLIENT_STATE_VERSION = 1;

export interface YonexusClientState {
  identifier: string;
  privateKey?: string;
  secret?: string;
  publicKey?: string;
  pairedAt?: number;
  authenticatedAt?: number;
  updatedAt: number;
}

export interface YonexusClientStateFile extends YonexusClientState {
  version: number;
}

export class YonexusClientStateError extends Error {
  override readonly cause?: unknown;

  constructor(message: string, cause?: unknown) {
    super(message);
    this.name = "YonexusClientStateError";
    this.cause = cause;
  }
}

export class YonexusClientStateCorruptionError extends YonexusClientStateError {
  constructor(message: string, cause?: unknown) {
    super(message, cause);
    this.name = "YonexusClientStateCorruptionError";
  }
}

export interface YonexusClientStateStore {
  readonly filePath: string;
  load(identifier: string): Promise<YonexusClientState>;
  save(state: YonexusClientState): Promise<void>;
}

export function createYonexusClientStateStore(filePath: string): YonexusClientStateStore {
  return {
    filePath,
    load: async (identifier) => loadYonexusClientState(filePath, identifier),
    save: async (state) => saveYonexusClientState(filePath, state)
  };
}

export async function loadYonexusClientState(
  filePath: string,
  identifier: string
): Promise<YonexusClientState> {
  try {
    const raw = await readFile(filePath, "utf8");
    const parsed = JSON.parse(raw) as YonexusClientStateFile;
    assertClientStateShape(parsed, filePath);

    return {
      identifier: parsed.identifier,
      privateKey: parsed.privateKey,
      publicKey: parsed.publicKey,
      secret: parsed.secret,
      pairedAt: parsed.pairedAt,
      authenticatedAt: parsed.authenticatedAt,
      updatedAt: parsed.updatedAt
    };
  } catch (error) {
    if (isFileNotFoundError(error)) {
      return createInitialClientState(identifier);
    }

    if (error instanceof YonexusClientStateError) {
      throw error;
    }

    throw new YonexusClientStateCorruptionError(
      `Failed to load Yonexus.Client state file: ${filePath}`,
      error
    );
  }
}

export async function saveYonexusClientState(
  filePath: string,
  state: YonexusClientState
): Promise<void> {
  const normalizedState = {
    ...state,
    identifier: state.identifier.trim(),
    updatedAt: state.updatedAt || Math.floor(Date.now() / 1000)
  } satisfies YonexusClientState;

  const payload: YonexusClientStateFile = {
    version: CLIENT_STATE_VERSION,
    ...normalizedState
  };

  const tempPath = `${filePath}.tmp`;

  try {
    await mkdir(dirname(filePath), { recursive: true });
    await writeFile(tempPath, `${JSON.stringify(payload, null, 2)}\n`, "utf8");
    await rename(tempPath, filePath);
  } catch (error) {
    throw new YonexusClientStateError(
      `Failed to save Yonexus.Client state file: ${filePath}`,
      error
    );
  }
}

export function createInitialClientState(identifier: string): YonexusClientState {
  const normalizedIdentifier = identifier.trim();
  return {
    identifier: normalizedIdentifier,
    updatedAt: Math.floor(Date.now() / 1000)
  };
}

export function hasClientSecret(state: YonexusClientState): boolean {
  return typeof state.secret === "string" && state.secret.length > 0;
}

export function hasClientKeyPair(state: YonexusClientState): boolean {
  return (
    typeof state.privateKey === "string" &&
    state.privateKey.length > 0 &&
    typeof state.publicKey === "string" &&
    state.publicKey.length > 0
  );
}

/**
 * Ensure the client state has a valid key pair.
 * If no key pair exists, generates a new Ed25519 key pair.
 * Returns the (possibly updated) state and whether a new key was generated.
 */
export async function ensureClientKeyPair(
  state: YonexusClientState,
  stateStore: YonexusClientStateStore
): Promise<{ state: YonexusClientState; generated: boolean }> {
  if (hasClientKeyPair(state)) {
    return { state, generated: false };
  }

  const keyPair = await generateKeyPair();
  const updatedState: YonexusClientState = {
    ...state,
    privateKey: keyPair.privateKey,
    publicKey: keyPair.publicKey,
    updatedAt: Math.floor(Date.now() / 1000)
  };

  await stateStore.save(updatedState);
  return { state: updatedState, generated: true };
}

function assertClientStateShape(
  value: unknown,
  filePath: string
): asserts value is YonexusClientStateFile {
  if (!value || typeof value !== "object") {
    throw new YonexusClientStateCorruptionError(
      `State file is not a JSON object: ${filePath}`
    );
  }

  const candidate = value as Partial<YonexusClientStateFile>;
  if (candidate.version !== CLIENT_STATE_VERSION) {
    throw new YonexusClientStateCorruptionError(
      `Unsupported client state version in ${filePath}: ${String(candidate.version)}`
    );
  }

  if (typeof candidate.identifier !== "string" || candidate.identifier.trim().length === 0) {
    throw new YonexusClientStateCorruptionError(
      `Client state file has invalid identifier: ${filePath}`
    );
  }

  const updatedAt = candidate.updatedAt;
  if (typeof updatedAt !== "number" || !Number.isInteger(updatedAt) || updatedAt < 0) {
    throw new YonexusClientStateCorruptionError(
      `Client state file has invalid updatedAt value: ${filePath}`
    );
  }
}

function isFileNotFoundError(error: unknown): error is NodeJS.ErrnoException {
  return (
    typeof error === "object" &&
    error !== null &&
    "code" in error &&
    (error as { code?: unknown }).code === "ENOENT"
  );
}