import { mkdir, readFile, rename, writeFile } from "node:fs/promises";
import { dirname } from "node:path";

import {
  deserializeClientRecord,
  serializeClientRecord,
  type ClientRecord,
  type SerializedClientRecord,
  type ServerPersistenceData
} from "./persistence.js";

export const SERVER_PERSISTENCE_VERSION = 1;

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

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

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

export interface ServerStoreLoadResult {
  readonly version: number;
  readonly persistedAt?: number;
  readonly clients: Map<string, ClientRecord>;
}

export interface YonexusServerStore {
  readonly filePath: string;
  load(): Promise<ServerStoreLoadResult>;
  save(clients: Iterable<ClientRecord>): Promise<void>;
}

export function createYonexusServerStore(filePath: string): YonexusServerStore {
  return {
    filePath,
    load: async () => loadServerStore(filePath),
    save: async (clients) => saveServerStore(filePath, clients)
  };
}

export async function loadServerStore(filePath: string): Promise<ServerStoreLoadResult> {
  try {
    const raw = await readFile(filePath, "utf8");
    const parsed = JSON.parse(raw) as ServerPersistenceData;
    assertPersistenceDataShape(parsed, filePath);

    const clients = new Map<string, ClientRecord>();
    for (const serialized of parsed.clients) {
      assertSerializedClientRecordShape(serialized, filePath);
      clients.set(serialized.identifier, deserializeClientRecord(serialized));
    }

    return {
      version: parsed.version,
      persistedAt: parsed.persistedAt,
      clients
    };
  } catch (error) {
    if (isFileNotFoundError(error)) {
      return {
        version: SERVER_PERSISTENCE_VERSION,
        clients: new Map()
      };
    }

    if (error instanceof YonexusServerStoreError) {
      throw error;
    }

    throw new YonexusServerStoreCorruptionError(
      `Failed to load Yonexus.Server persistence file: ${filePath}`,
      error
    );
  }
}

export async function saveServerStore(
  filePath: string,
  clients: Iterable<ClientRecord>
): Promise<void> {
  const payload: ServerPersistenceData = {
    version: SERVER_PERSISTENCE_VERSION,
    persistedAt: Math.floor(Date.now() / 1000),
    clients: Array.from(clients, (record) => serializeClientRecord(record))
  };

  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 YonexusServerStoreError(
      `Failed to save Yonexus.Server persistence file: ${filePath}`,
      error
    );
  }
}

function assertPersistenceDataShape(
  value: unknown,
  filePath: string
): asserts value is ServerPersistenceData {
  if (!value || typeof value !== "object") {
    throw new YonexusServerStoreCorruptionError(
      `Persistence file is not a JSON object: ${filePath}`
    );
  }

  const candidate = value as Partial<ServerPersistenceData>;
  if (candidate.version !== SERVER_PERSISTENCE_VERSION) {
    throw new YonexusServerStoreCorruptionError(
      `Unsupported persistence version in ${filePath}: ${String(candidate.version)}`
    );
  }

  if (!Array.isArray(candidate.clients)) {
    throw new YonexusServerStoreCorruptionError(
      `Persistence file has invalid clients array: ${filePath}`
    );
  }

  if (
    candidate.persistedAt !== undefined &&
    (!Number.isInteger(candidate.persistedAt) || candidate.persistedAt < 0)
  ) {
    throw new YonexusServerStoreCorruptionError(
      `Persistence file has invalid persistedAt value: ${filePath}`
    );
  }
}

function assertSerializedClientRecordShape(
  value: unknown,
  filePath: string
): asserts value is SerializedClientRecord {
  if (!value || typeof value !== "object") {
    throw new YonexusServerStoreCorruptionError(
      `Persistence file contains a non-object client record: ${filePath}`
    );
  }

  const candidate = value as Partial<SerializedClientRecord>;
  if (typeof candidate.identifier !== "string" || candidate.identifier.trim().length === 0) {
    throw new YonexusServerStoreCorruptionError(
      `Persistence file contains a client record with invalid identifier: ${filePath}`
    );
  }

  if (typeof candidate.pairingStatus !== "string" || typeof candidate.status !== "string") {
    throw new YonexusServerStoreCorruptionError(
      `Persistence file contains a client record with invalid state fields: ${filePath}`
    );
  }

  if (!Number.isInteger(candidate.createdAt) || !Number.isInteger(candidate.updatedAt)) {
    throw new YonexusServerStoreCorruptionError(
      `Persistence file contains a client record with invalid timestamps: ${filePath}`
    );
  }
}

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