import { readFileSync, writeFileSync } from "node:fs";

export interface ConfigStore {
  read(): Record<string, unknown>;
  write(root: Record<string, unknown>): void;
}

export type ConfigSource =
  | {
      configPath: string;
      configStore?: never;
    }
  | {
      configPath?: never;
      configStore: ConfigStore;
    };

function cloneConfig(root: Record<string, unknown>): Record<string, unknown> {
  return JSON.parse(JSON.stringify(root)) as Record<string, unknown>;
}

function ensureConfigRoot(value: unknown, source: string): Record<string, unknown> {
  if (!value || typeof value !== "object" || Array.isArray(value)) {
    throw new Error(`Invalid config.json shape at ${source}`);
  }
  return value as Record<string, unknown>;
}

export function createFileConfigStore(configPath: string): ConfigStore {
  return {
    read() {
      const raw = readFileSync(configPath, "utf-8");
      return ensureConfigRoot(JSON.parse(raw) as unknown, configPath);
    },
    write(root) {
      writeFileSync(configPath, `${JSON.stringify(root, null, 2)}\n`, "utf-8");
    },
  };
}

export function createMemoryConfigStore(
  initialRoot: Record<string, unknown>,
): ConfigStore & { snapshot(): Record<string, unknown> } {
  let current = cloneConfig(initialRoot);

  return {
    read() {
      return cloneConfig(current);
    },
    write(root) {
      current = cloneConfig(root);
    },
    snapshot() {
      return cloneConfig(current);
    },
  };
}

export function getConfigStore(source: ConfigSource): ConfigStore {
  if (source.configStore) {
    return source.configStore;
  }
  return createFileConfigStore(source.configPath);
}