package useCases

import (
	"RenewCMS/internal/domain/article"
	"RenewCMS/internal/domain/author"
	"RenewCMS/internal/domain/image"
	"RenewCMS/internal/domain/site"
	"crypto/sha256"
	"encoding/hex"
	"slices"
	"strconv"
	"strings"
)

type purgeGroup struct {
	kept      image.Image
	keptUsage int
	mergedIds []uint32
}

type purgePlan struct {
	groups      []purgeGroup
	copies      int
	articles    int
	fingerprint string
}

type purgePlanner struct {
	imageRepository   image.Repository
	articleRepository article.Repository
	sites             site.Repository
	authors           author.Repository
}

func (p *purgePlanner) plan() (purgePlan, error) {
	duplicates, err := p.imageRepository.ListDuplicates()
	if err != nil {
		return purgePlan{}, err
	}
	articles, err := p.articleRepository.FindByFilters(article.Filters{})
	if err != nil {
		return purgePlan{}, err
	}

	siteUsage, err := imageUsageCount(p.sites, p.authors)
	if err != nil {
		return purgePlan{}, err
	}

	groups := []purgeGroup{}
	copies := 0
	touched := map[uint32]bool{}
	for _, members := range groupByHash(duplicates) {
		group, planned := planGroup(members, articles, siteUsage)
		if !planned {
			continue
		}
		groups = append(groups, group)
		copies += len(group.mergedIds)
		for _, id := range articlesUsingCopies(group, members, articles) {
			touched[id] = true
		}
	}
	slices.SortFunc(groups, func(a, b purgeGroup) int { return int(a.kept.ID) - int(b.kept.ID) })

	return purgePlan{groups: groups, copies: copies, articles: len(touched), fingerprint: fingerprintOf(groups)}, nil
}

func groupByHash(images []image.Image) [][]image.Image {
	byHash := map[string][]image.Image{}
	hashes := []string{}
	for _, img := range images {
		if img.SHA256 == "" {
			continue
		}
		if _, seen := byHash[img.SHA256]; !seen {
			hashes = append(hashes, img.SHA256)
		}
		byHash[img.SHA256] = append(byHash[img.SHA256], img)
	}
	groups := make([][]image.Image, 0, len(hashes))
	for _, hash := range hashes {
		groups = append(groups, byHash[hash])
	}
	return groups
}

func usageOf(img image.Image, articles []article.Article) int {
	storedName := image.StoredName(img.Path)
	used := 0
	for _, a := range articles {
		if strings.Contains(a.Body, storedName) {
			used++
		}
	}
	return used
}

func planGroup(members []image.Image, articles []article.Article, siteUsage map[uint32]int) (purgeGroup, bool) {
	usage := make(map[uint32]int, len(members))
	anyUsed := false
	for _, member := range members {
		usage[member.ID] = usageOf(member, articles) + siteUsage[member.ID]
		anyUsed = anyUsed || usage[member.ID] > 0
	}
	if !anyUsed {
		return purgeGroup{}, false
	}

	kept := members[0]
	for _, member := range members[1:] {
		if isBetterToKeep(member, kept, usage) {
			kept = member
		}
	}

	mergedIds := []uint32{}
	for _, member := range members {
		if member.ID != kept.ID {
			mergedIds = append(mergedIds, member.ID)
		}
	}
	slices.Sort(mergedIds)
	return purgeGroup{kept: kept, keptUsage: usage[kept.ID], mergedIds: mergedIds}, true
}

func isBetterToKeep(candidate, current image.Image, usage map[uint32]int) bool {
	if usage[candidate.ID] != usage[current.ID] {
		return usage[candidate.ID] > usage[current.ID]
	}
	if !candidate.CreatedAt.Equal(current.CreatedAt) {
		return candidate.CreatedAt.Before(current.CreatedAt)
	}
	return candidate.ID < current.ID
}

func articlesUsingCopies(group purgeGroup, members []image.Image, articles []article.Article) []uint32 {
	mergedNames := []string{}
	for _, member := range members {
		if member.ID != group.kept.ID {
			mergedNames = append(mergedNames, image.StoredName(member.Path))
		}
	}
	ids := []uint32{}
	for _, a := range articles {
		for _, name := range mergedNames {
			if strings.Contains(a.Body, name) {
				ids = append(ids, a.ID)
				break
			}
		}
	}
	return ids
}

func fingerprintOf(groups []purgeGroup) string {
	var builder strings.Builder
	for _, group := range groups {
		builder.WriteString(strconv.FormatUint(uint64(group.kept.ID), 10))
		builder.WriteString(":")
		for position, id := range group.mergedIds {
			if position > 0 {
				builder.WriteString(",")
			}
			builder.WriteString(strconv.FormatUint(uint64(id), 10))
		}
		builder.WriteString(";")
	}
	sum := sha256.Sum256([]byte(builder.String()))
	return hex.EncodeToString(sum[:])
}