package nuapi

import (
	"context"
	"fmt"
	"os"
	"slices"
)

type ChapterEntryTraverser func(ctx context.Context, api *Api, novelID NovelID, pageCount int, out chan<- NovelChapterEntry)

// TraverseAscending returns a ChapterEntryTraverser which traverses entries from oldest to newest chapter
func TraverseAscending() ChapterEntryTraverser {
	return func(ctx context.Context, api *Api, novelID NovelID, pageCount int, out chan<- NovelChapterEntry) {
		defer close(out)

		for pageIndex := pageCount; pageIndex > 0; pageIndex-- {
			if ctx.Err() != nil {
				break
			}

			entries, err := api.getChapterEntriesByPageIndex(novelID, pageIndex)
			if err != nil {
				if Verbose {
					fmt.Fprintln(os.Stderr, err)
				}
				return
			}

			slices.Reverse(entries)

			for _, entry := range entries {
				out <- entry
			}
		}
	}
}

// TraverseDescending returns a ChapterEntryTraverser which traverses entries from newest to oldest chapter
func TraverseDescending() ChapterEntryTraverser {
	return func(ctx context.Context, api *Api, novelID NovelID, pageCount int, out chan<- NovelChapterEntry) {
		defer close(out)

		for pageIndex := 1; pageIndex <= pageCount; pageIndex++ {
			if ctx.Err() != nil {
				break
			}

			entries, err := api.getChapterEntriesByPageIndex(novelID, pageIndex)
			if err != nil {
				if Verbose {
					fmt.Fprintln(os.Stderr, err)
				}
				return
			}

			for _, entry := range entries {
				out <- entry
			}
		}
	}
}