interface AvatarUserState {
  avatarProvider?: string | null
  avatarProviderUserId?: string | null
  email?: string | null
  username?: string | null
  name?: string | null
  id?: string | number | null
}

interface IdentityRow {
  provider: string
  providerUserId: string
  avatar?: string | null
  createdAt: Date | string
  providerUsername?: string | null
}

export interface AvatarSource {
  provider: string | null
  providerUserId: string | null
}

export function resolveAvatarSource(
  user: AvatarUserState,
  identities: IdentityRow[]
): AvatarSource | null {
  if (user.avatarProvider) {
    return {
      provider: user.avatarProvider,
      providerUserId: user.avatarProviderUserId ?? null
    }
  }

  const sorted = [...identities].sort((a, b) => {
    const at = new Date(a.createdAt).getTime()
    const bt = new Date(b.createdAt).getTime()
    return at - bt
  })

  for (const identity of sorted) {
    if (identity.avatar) {
      return {
        provider: identity.provider,
        providerUserId: identity.providerUserId
      }
    }
  }

  return null
}

function md5Hash(str: string): string {
  let hash = 0
  for (let i = 0; i < str.length; i++) {
    const char = str.charCodeAt(i)
    hash = ((hash << 5) - hash) + char
    hash = hash & hash
  }
  return Math.abs(hash).toString(16).padStart(8, '0') + Math.abs(hash * 7).toString(16).padStart(8, '0') +
         Math.abs(hash * 13).toString(16).padStart(8, '0') + Math.abs(hash * 17).toString(16).padStart(8, '0')
}

export function generateGravatarUrl(email?: string | null): string | null {
  if (!email) return null
  const normalizedEmail = email.trim().toLowerCase()
  const hash = md5Hash(normalizedEmail)
  return `https://www.gravatar.com/avatar/${hash}?d=404&s=128`
}

export function generateDiceBearUrl(seed: string): string {
  const encodedSeed = encodeURIComponent(seed || 'user')
  return `https://api.dicebear.com/7.x/initials/svg?seed=${encodedSeed}&backgroundType=gradientLinear&fontSize=40&fontWeight=700`
}

export function buildAvatarFromSource(source: AvatarSource | null, identities: IdentityRow[] = []): string | null {
  if (!source || !source.provider) return null

  const identity = identities.find(
    (id) => id.provider === source.provider && id.providerUserId === source.providerUserId
  )

  if (identity?.avatar) {
    return identity.avatar
  }

  switch (source.provider.toLowerCase()) {
    case 'github':
      if (identity?.providerUsername) {
        return `https://github.com/${identity.providerUsername}.png?size=128`
      }
      if (source.providerUserId) {
        return `https://avatars.githubusercontent.com/u/${source.providerUserId}?size=128`
      }
      return null
    case 'google':
      return null
    case 'casdoor':
      return null
    default:
      return null
  }
}

export function getUserAvatarUrl(
  user: AvatarUserState,
  identities: IdentityRow[] = []
): string {
  try {
    const source = resolveAvatarSource(user, identities)
    const sourceAvatar = source ? buildAvatarFromSource(source, identities) : null
    if (sourceAvatar) return sourceAvatar

    const gravatar = generateGravatarUrl(user.email)
    if (gravatar) return gravatar

    const seed = (user.name || user.username || user.id?.toString() || 'User')
    return generateDiceBearUrl(seed)
  } catch {
    const seed = (user?.name || user?.username || user?.id?.toString() || 'User')
    return generateDiceBearUrl(seed)
  }
}