取得授權碼後，我們就能準備取得我們的權杖了，我們需要再透過api 先取得短期權杖，再用短期權杖取得長期權杖，並儲存下來供使用者之後使用，讓我們照著官方的使用說明來實作吧

目標

取得長期權杖，並儲存在本地端，以提供使用者之後能透過此權杖使用Instagram basic display 的api，Android 我們這邊透過MVVM 的架構，讓AccessTokenActivity能夠取得長期權杖並儲存在本地端

API:

interface ApiInstagramService {

    @FormUrlEncoded
    @POST("oauth/access_token")
    suspend fun getShortAccessTokenInfo(
        @Field("client_id") clientId: String,
        @Field("client_secret") clientSecret: String,
        @Field("code") code: String,
        @Field("grant_type") grantType: String,
        @Field("redirect_uri") redirectUri: String
    ): ShortAccessTokenInfo
}

interface GraphInstagramService {

    @GET("access_token")
    suspend fun getLongAccessTokenInfo(
        @Query("grant_type") grantType: String,
        @Query("client_secret") clientSecret: String,
        @Query("access_token") accessToken: String
    ): LongAccessTokenInfo

}

DataRepository:

    suspend fun getAccessToken(
        clientId: String,
        clientSecret: String,
        code: String,
        redirectUri: String
    ) {
        withContext(Dispatchers.IO) {
            getShortAccessToken(
                clientId,
                clientSecret,
                code,
                redirectUri
            )
        }
    }

    private suspend fun getShortAccessToken(
        clientId: String,
        clientSecret: String,
        code: String,
        redirectUri: String
    ) {
        try {
            val shortAccessTokenInfo = apiInstagramService.getShortAccessTokenInfo(
                clientId = clientId,
                clientSecret = clientSecret,
                code = code,
                grantType = "authorization_code",
                redirectUri = redirectUri
            )

            Log.d(TAG, "shortAccessTokenInfo = $shortAccessTokenInfo")

            preference.set(Constants.PREF_KEY_INSTAGRAM_USER_ID, shortAccessTokenInfo.userId)

            val currentTimeMillis: Long = System.currentTimeMillis()

            getLongAccessToken(shortAccessTokenInfo.accessToken, clientSecret, currentTimeMillis)
        } catch (exception: UnknownHostException) { // Request Api when no internet
            exception.printStackTrace()
            Log.e(TAG, "shortAccessTokenInfo exception = $exception")
            _accessTokenResult.postValue(false)
        } catch (exception: Exception) {
            exception.printStackTrace()
            Log.e(TAG, "shortAccessTokenInfo exception = $exception")
            _accessTokenResult.postValue(false)
        }
    }

    private suspend fun getLongAccessToken(
        shortAccessToken: String,
        clientSecret: String,
        currentTimeMillis: Long
    ) {
        try {
            val longAccessTokenInfo = graphInstagramService.getLongAccessTokenInfo(
                grantType = "ig_exchange_token",
                clientSecret = clientSecret,
                accessToken = shortAccessToken
            )

            val expiredTimeMillis = currentTimeMillis + longAccessTokenInfo.expiresIn

            preference.set(Constants.PREF_KEY_EXPIRED_MILLISECONDS, expiredTimeMillis)
            preference.set(Constants.PREF_KEY_ACCESS_TOKEN, longAccessTokenInfo.accessToken)

            _accessTokenResult.postValue(true)

        } catch (exception: UnknownHostException) { // Request Api when no internet
            exception.printStackTrace()
            Log.e(TAG, "getLongAccessToken exception = $exception")
            _accessTokenResult.postValue(false)
        } catch (exception: Exception) {
            exception.printStackTrace()
            Log.e(TAG, "getLongAccessToken exception = $exception")
            _accessTokenResult.postValue(false)
        }
    }

AccessTokenViewModel:

    fun getAssessToken(
        clientId: String,
        clientSecret: String,
        code: String,
        redirectUri: String
    ) {
        viewModelScope.launch {
            repository.getAccessToken(
                clientId,
                clientSecret,
                code,
                redirectUri
            )
        }
    }