package dev.joserg.jpa;

import static org.springframework.data.domain.ScrollPosition.offset;

import java.util.function.Function;

import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.ScrollPosition;
import org.springframework.data.domain.Slice;
import org.springframework.data.domain.SliceImpl;
import org.springframework.data.domain.Sort;
import org.springframework.data.domain.Window;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
import org.springframework.data.repository.query.FluentQuery.FetchableFluentQuery;

public interface SliceSpecificationExecutor<T> extends JpaSpecificationExecutor<T> {

  default Window<T> findAllWindowed(Specification<T> spec, Sort sort, int limit, ScrollPosition scrollPosition) {
    return this.findBy(spec, toWindow(sort, limit, scrollPosition));
  }

  default Window<T> findAllWindowed(Specification<T> spec, Sort sort, ScrollPosition scrollPosition) {
    return this.findBy(spec, toWindow(sort, scrollPosition));
  }

  default Window<T> findAllWindowed(Specification<T> spec, ScrollPosition scrollPosition) {
    return this.findAllWindowed(spec, Sort.unsorted(), scrollPosition);
  }

  default Slice<T> findAllSliced(Specification<T> spec, Pageable pageable) {
    final var window = pageable.isUnpaged()
        ? this.findAllWindowed(spec, pageable.getSort(), offset())
        : this.findAllWindowed(spec, pageable.getSort(), pageable.getPageSize(), this.getInclusiveStartingOffset(pageable));
    return new SliceImpl<>(window.getContent(), pageable, window.hasNext());
  }

  private ScrollPosition getInclusiveStartingOffset(Pageable pageable) {
    return pageable.getOffset() == 0
        ? ScrollPosition.offset()
        : offset(pageable.getOffset() - 1);
  }

  private static <T> Function<FetchableFluentQuery<T>, Window<T>> toWindow(Sort sort, int limit, ScrollPosition scrollPosition) {
    return fetchableFluentQuery -> fetchableFluentQuery.sortBy(sort).limit(limit).scroll(scrollPosition);
  }

  private static <T> Function<FetchableFluentQuery<T>, Window<T>> toWindow(Sort sort, ScrollPosition scrollPosition) {
    return fetchableFluentQuery -> fetchableFluentQuery.sortBy(sort).scroll(scrollPosition);
  }

}