package com.h.pixeldroid.fragments.feeds.uncachedFeeds.accountLists

import androidx.paging.PagingSource
import com.h.pixeldroid.api.PixelfedAPI
import com.h.pixeldroid.objects.Account
import retrofit2.HttpException
import java.io.IOException

class FollowersPagingSource(
    private val api: PixelfedAPI,
    private val accessToken: String,
    private val accountId: String,
    private val following: Boolean
) : PagingSource<Int, Account>() {
    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, Account> {
        val position = params.key
        return try {
            val response =
            // Pixelfed and Mastodon don't implement this in the same fashion. Pixelfed uses
            // Laravel's paging mechanism, while Mastodon uses the Link header for pagination.
                // No need to know which is which, they should ignore the non-relevant argument
                if(following) {
                    api.followers(account_id = accountId,
                        authorization = "Bearer $accessToken",
                        limit = params.loadSize,
                        page = position?.toString(),
                        max_id = position?.toString())
                } else {
                    api.following(account_id = accountId,
                        authorization = "Bearer $accessToken",
                        limit = params.loadSize,
                        page = position?.toString(),
                        max_id = position?.toString())
                }

            val accounts = if(response.isSuccessful){
                response.body().orEmpty()
            } else {
                throw HttpException(response)
            }

            val nextPosition = if(response.headers()["Link"] != null){
                //Header is of the form:
                // Link: <https://mastodon.social/api/v1/accounts/1/followers?limit=2&max_id=7628164>; rel="next", <https://mastodon.social/api/v1/accounts/1/followers?limit=2&since_id=7628165>; rel="prev"
                // So we want the first max_id value. In case there are arguments after
                // the max_id in the URL, we make sure to stop at the first '?'
                response.headers()["Link"]
                    .orEmpty()
                    .substringAfter("max_id=")
                    .substringBefore('?')
                    .substringBefore('>')
                    .toIntOrNull() ?: 0
            } else {
                params.key?.plus(1) ?: 2
            }

            LoadResult.Page(
                data = accounts,
                prevKey = null,
                nextKey = if (accounts.isEmpty()) null else nextPosition
            )
        } catch (exception: IOException) {
            LoadResult.Error(exception)
        } catch (exception: HttpException) {
            LoadResult.Error(exception)
        }
    }
}