import type { ViteUserConfig } from 'astro'

import type { ConfigSerialized } from './user-options'

function resolveVirtualModuleId<T extends string>(id: T): `\0${T}` {
  return `\0${id}`
}

/** Vite plugin that exposes user config via virtual modules. */
export function vitePluginUserConfig(
  config: ConfigSerialized,
): NonNullable<ViteUserConfig['plugins']>[number] {
  /** Map of virtual module names to their code contents as strings. */
  const modules = new Map<string, string>()

  /** Mapping names prefixed with `\0` to their original form. */
  const resolutionMap = new Map<string, string>()

  for (const [key, value] of [
    [
      'virtual:starlight-theme-nova/user-config',
      `export default ${JSON.stringify(config)}`,
    ],
  ]) {
    modules.set(key, value)
    resolutionMap.set(resolveVirtualModuleId(key), key)
  }

  return {
    name: 'vite-plugin-starlight-theme-nova-user-config',
    resolveId(id): string | void {
      if (modules.has(id)) {
        return resolveVirtualModuleId(id)
      }
    },
    load(id): string | void {
      const resolution = resolutionMap.get(id)
      if (resolution) return modules.get(resolution)
    },
  }
}