import type { Scene } from '@/types/scene'

const FILE_VERSION = 1
const MAGIC = 'animatr-project'

export interface ProjectFile {
  magic: typeof MAGIC
  fileVersion: number
  savedAt: string
  scene: Scene
}

export function serializeProject(scene: Scene): string {
  const payload: ProjectFile = {
    magic: MAGIC,
    fileVersion: FILE_VERSION,
    savedAt: new Date().toISOString(),
    scene,
  }
  return JSON.stringify(payload, null, 2)
}

export class ProjectFileError extends Error {
  constructor(message: string) {
    super(message)
    this.name = 'ProjectFileError'
  }
}

export function parseProject(text: string): Scene {
  let data: unknown
  try {
    data = JSON.parse(text)
  } catch {
    throw new ProjectFileError('File is not valid JSON.')
  }
  if (!data || typeof data !== 'object') {
    throw new ProjectFileError('File is empty or not an object.')
  }
  const obj = data as Record<string, unknown>
  if (obj.magic !== MAGIC) {
    throw new ProjectFileError('Not an Animatr project file (magic missing).')
  }
  const scene = obj.scene
  if (!scene || typeof scene !== 'object') {
    throw new ProjectFileError('Project file has no scene.')
  }
  const s = scene as Record<string, unknown>
  if (!s.canvas || typeof s.canvas !== 'object') {
    throw new ProjectFileError('Scene data incomplete: canvas missing.')
  }
  if (!Array.isArray(s.layers)) {
    throw new ProjectFileError('Scene data incomplete: layers missing.')
  }
  if (!Array.isArray(s.assets)) {
    throw new ProjectFileError('Scene data incomplete: assets missing.')
  }
  return scene as Scene
}

export function downloadProject(scene: Scene, filename = 'projekt.animatr.json') {
  const source = serializeProject(scene)
  const blob = new Blob([source], { type: 'application/json' })
  const url = URL.createObjectURL(blob)
  const a = document.createElement('a')
  a.href = url
  a.download = filename
  document.body.appendChild(a)
  a.click()
  document.body.removeChild(a)
  setTimeout(() => URL.revokeObjectURL(url), 1000)
}

export function pickProjectFile(): Promise<File | null> {
  return new Promise((resolve) => {
    const input = document.createElement('input')
    input.type = 'file'
    input.accept = '.json,application/json'
    input.onchange = () => {
      const f = input.files?.[0]
      resolve(f ?? null)
    }
    input.oncancel = () => resolve(null)
    input.click()
  })
}

export async function readProjectFile(file: File): Promise<Scene> {
  const text = await file.text()
  return parseProject(text)
}