package tldr

import (
	"sort"

	"github.com/bwmarrin/discordgo"
)

type MessageFetcher interface {
	ChannelMessages(channelID string, limit int, beforeID, afterID, aroundID string, options ...discordgo.RequestOption) ([]*discordgo.Message, error)
}

// FetchAfter pages forward from afterID and returns up to limit messages,
// oldest first. Discord returns the messages immediately following the ID,
// so paging with the newest ID of each batch walks toward the present.
func FetchAfter(f MessageFetcher, channelID, afterID string, limit int) ([]*discordgo.Message, error) {
	var all []*discordgo.Message
	after := afterID

	for len(all) < limit {
		want := min(100, limit-len(all))
		batch, err := f.ChannelMessages(channelID, want, "", after, "")
		if err != nil {
			return nil, err
		}
		if len(batch) == 0 {
			break
		}

		newest := batch[0].ID
		for _, m := range batch {
			if CompareIDs(m.ID, newest) > 0 {
				newest = m.ID
			}
		}
		all = append(all, batch...)
		after = newest

		if len(batch) < want {
			break
		}
	}

	sort.Slice(all, func(i, j int) bool { return CompareIDs(all[i].ID, all[j].ID) < 0 })
	return all, nil
}