package database

import (
	"RenewCMS/internal/domain/article"
	entity "RenewCMS/internal/infrastructure/persistence/models"
	"slices"

	"gorm.io/gorm"
)

const (
	articleSlugIndexName         = "idx_articles_site_slug"
	articleSlugBackfillBatchSize = 500
	articleSlugIndexStatement    = "CREATE UNIQUE INDEX idx_articles_site_slug ON articles (site_id, slug)"
)

type slugOwner struct {
	siteID uint32
	slug   string
}

type slugAssignment struct {
	id   uint32
	slug string
}

func BackfillArticleSlugs(db *gorm.DB) error {
	var rows []entity.Article
	if err := db.Unscoped().Select("id", "site_id", "title", "slug", "deleted_at").Order("id ASC").Find(&rows).Error; err != nil {
		return err
	}
	assignments := planSlugAssignments(rows)
	for batch := range slices.Chunk(assignments, articleSlugBackfillBatchSize) {
		if err := writeSlugAssignments(db, batch); err != nil {
			return err
		}
	}
	return nil
}

func writeSlugAssignments(db *gorm.DB, batch []slugAssignment) error {
	return db.Transaction(func(tx *gorm.DB) error {
		for _, assignment := range batch {
			if err := tx.Unscoped().Model(&entity.Article{}).Where("id = ?", assignment.id).UpdateColumn("slug", assignment.slug).Error; err != nil {
				return err
			}
		}
		return nil
	})
}

func planSlugAssignments(rows []entity.Article) []slugAssignment {
	assignments := []slugAssignment{}
	claimed := map[slugOwner]bool{}
	pending := []entity.Article{}
	for _, row := range rows {
		if row.DeletedAt.Valid {
			if tombstone := article.Tombstone(row.ID); row.Slug != tombstone {
				assignments = append(assignments, slugAssignment{row.ID, tombstone})
			}
			continue
		}
		owner := slugOwner{row.SiteID, row.Slug}
		if row.Slug == "" || claimed[owner] {
			pending = append(pending, row)
			continue
		}
		claimed[owner] = true
	}
	for _, row := range pending {
		base := row.Slug
		attempt := 2
		if base == "" {
			base = snapshotSlug(row.Title)
			attempt = 1
		}
		slug := firstFreeSnapshotSlug(claimed, row.SiteID, base, attempt)
		claimed[slugOwner{row.SiteID, slug}] = true
		assignments = append(assignments, slugAssignment{row.ID, slug})
	}
	return assignments
}

func firstFreeSnapshotSlug(claimed map[slugOwner]bool, siteID uint32, base string, attempt int) string {
	for ; ; attempt++ {
		candidate := snapshotSlugWithSuffix(base, attempt)
		if !claimed[slugOwner{siteID, candidate}] {
			return candidate
		}
	}
}

func ensureArticleSlugIndex(db *gorm.DB) error {
	if db.Migrator().HasIndex(&entity.Article{}, articleSlugIndexName) {
		return nil
	}
	return db.Exec(articleSlugIndexStatement).Error
}