// Wiki 贡献级差异：页面身份是 slug，语义拆成「正文 / 来源文档 / 引用分块 / 出边 / 入边 / 目录」。
//
// 为什么不能只比页面级：删除一篇与别人共同贡献同一页的文档后，页面还在、名字还在，
// 只有那篇文档的正文与引用被摘掉。页面级差异会把这种"语义重算"显示成"无变化"，
// 操作员据此会误判撤销没有生效。这里把每类语义单独取集合再比，撤销的那份贡献
// 必须能在 sources/citations/links/content 上被指出来。
//
// 边界：本包只读归档里的 wiki_pages 行，**不重算** WeKnora 的实体/概念/边。
// 语义重算发生在源侧，治理侧能做的是把源侧算完的结果如实比对与保留。
package librarydiff

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"sort"
	"strings"
)

// volatileWikiFields 是每次保存都会变、但不代表页面语义变化的列。
var volatileWikiFields = []string{"updated_at", "updated_by", "created_at", "view_count"}

type WikiContribution struct {
	Slug     string `json:"slug"`
	Title    string `json:"title"`
	PageType string `json:"page_type"`
	Status   string `json:"status"` // added | updated | removed
	// Changed 是发生变化（或被删除）的语义类别：content / sources / citations /
	// out_links / in_links / category / status / page_type。撤销一份贡献时，
	// sources 与 citations 必须出现，正文没变也要标出来。
	Changed          []string `json:"changed"`
	SourcesAdded     []string `json:"sources_added"`
	SourcesRemoved   []string `json:"sources_removed"`
	CitationsBefore  int      `json:"citations_before"`
	CitationsAfter   int      `json:"citations_after"`
	CitationsAdded   []string `json:"citations_added,omitempty"`
	CitationsRemoved []string `json:"citations_removed,omitempty"`
	LinksAdded       []string `json:"links_added,omitempty"`
	LinksRemoved     []string `json:"links_removed,omitempty"`
	// ContentDigestBefore/After 让证据可以复核"正文真的变了"，而不是只凭长度。
	ContentDigestBefore string `json:"content_digest_before,omitempty"`
	ContentDigestAfter  string `json:"content_digest_after,omitempty"`
}

type WikiResult struct {
	State   string `json:"state"` // computed
	Added   int    `json:"added"`
	Updated int    `json:"updated"`
	Removed int    `json:"removed"`
	// SourcesAdded/Removed 是所有页面来源变化的合计，便于一眼看到"撤销了谁的贡献"。
	SourcesAdded   int                `json:"sources_added"`
	SourcesRemoved int                `json:"sources_removed"`
	BaseCount      int                `json:"base_count"`
	TargetCount    int                `json:"target_count"`
	Pages          []WikiContribution `json:"pages"`
}

type wikiPage struct {
	slug      string
	title     string
	pageType  string
	status    string
	content   string
	sources   []string
	citations []string
	outLinks  []string
	inLinks   []string
	category  string
}

// CompareWiki 以 base 为基准（当前生产版本），target 为拟发布版本，逐页比对语义。
func CompareWiki(base, target []map[string]any) (WikiResult, error) {
	basePages, err := indexWiki(base)
	if err != nil {
		return WikiResult{}, err
	}
	targetPages, err := indexWiki(target)
	if err != nil {
		return WikiResult{}, err
	}
	result := WikiResult{State: "computed", Pages: []WikiContribution{},
		BaseCount: len(basePages), TargetCount: len(targetPages)}
	for slug, next := range targetPages {
		previous, ok := basePages[slug]
		if !ok {
			result.Added++
			result.Pages = append(result.Pages, WikiContribution{
				Slug: next.slug, Title: next.title, PageType: next.pageType, Status: "added",
				Changed: []string{"added"}, SourcesAdded: next.sources,
				CitationsAfter: len(next.citations), ContentDigestAfter: digestOf(next.content),
			})
			result.SourcesAdded += len(next.sources)
			continue
		}
		change, changed := diffWikiPage(previous, next)
		if !changed {
			continue
		}
		result.Updated++
		result.SourcesAdded += len(change.SourcesAdded)
		result.SourcesRemoved += len(change.SourcesRemoved)
		result.Pages = append(result.Pages, change)
	}
	for slug, previous := range basePages {
		if _, ok := targetPages[slug]; ok {
			continue
		}
		result.Removed++
		result.Pages = append(result.Pages, WikiContribution{
			Slug: previous.slug, Title: previous.title, PageType: previous.pageType, Status: "removed",
			Changed: []string{"removed"}, SourcesRemoved: previous.sources,
			CitationsBefore: len(previous.citations), ContentDigestBefore: digestOf(previous.content),
		})
		result.SourcesRemoved += len(previous.sources)
	}
	sort.Slice(result.Pages, func(i, j int) bool { return result.Pages[i].Slug < result.Pages[j].Slug })
	return result, nil
}

func diffWikiPage(previous, next wikiPage) (WikiContribution, bool) {
	change := WikiContribution{Slug: next.slug, Title: next.title, PageType: next.pageType, Status: "updated",
		CitationsBefore: len(previous.citations), CitationsAfter: len(next.citations),
		ContentDigestBefore: digestOf(previous.content), ContentDigestAfter: digestOf(next.content)}
	change.SourcesAdded, change.SourcesRemoved = setDiff(next.sources, previous.sources), setDiff(previous.sources, next.sources)
	change.CitationsAdded, change.CitationsRemoved = setDiff(next.citations, previous.citations), setDiff(previous.citations, next.citations)
	change.LinksAdded, change.LinksRemoved = setDiff(next.outLinks, previous.outLinks), setDiff(previous.outLinks, next.outLinks)
	if previous.content != next.content {
		change.Changed = append(change.Changed, "content")
	}
	if len(change.SourcesAdded)+len(change.SourcesRemoved) > 0 {
		change.Changed = append(change.Changed, "sources")
	}
	if len(change.CitationsAdded)+len(change.CitationsRemoved) > 0 {
		change.Changed = append(change.Changed, "citations")
	}
	if len(change.LinksAdded)+len(change.LinksRemoved) > 0 {
		change.Changed = append(change.Changed, "out_links")
	}
	if added, removed := setDiff(next.inLinks, previous.inLinks), setDiff(previous.inLinks, next.inLinks); len(added)+len(removed) > 0 {
		change.Changed = append(change.Changed, "in_links")
	}
	if previous.category != next.category {
		change.Changed = append(change.Changed, "category")
	}
	if previous.status != next.status {
		change.Changed = append(change.Changed, "status")
	}
	if previous.pageType != next.pageType {
		change.Changed = append(change.Changed, "page_type")
	}
	return change, len(change.Changed) > 0
}

func indexWiki(rows []map[string]any) (map[string]wikiPage, error) {
	pages := make(map[string]wikiPage, len(rows))
	for _, row := range rows {
		slug, _ := row["slug"].(string)
		slug = strings.TrimSpace(slug)
		if slug == "" {
			return nil, errors.New("wiki row without slug")
		}
		if _, exists := pages[slug]; exists {
			return nil, fmt.Errorf("duplicate wiki slug %s", slug)
		}
		page := wikiPage{slug: slug}
		page.title, _ = row["title"].(string)
		page.pageType, _ = row["page_type"].(string)
		page.status, _ = row["status"].(string)
		page.content, _ = row["content"].(string)
		var err error
		if page.sources, err = stringList(row["source_refs"]); err != nil {
			return nil, fmt.Errorf("wiki %s source_refs: %w", slug, err)
		}
		if page.citations, err = stringList(row["chunk_refs"]); err != nil {
			return nil, fmt.Errorf("wiki %s chunk_refs: %w", slug, err)
		}
		if page.outLinks, err = stringList(row["out_links"]); err != nil {
			return nil, fmt.Errorf("wiki %s out_links: %w", slug, err)
		}
		if page.inLinks, err = stringList(row["in_links"]); err != nil {
			return nil, fmt.Errorf("wiki %s in_links: %w", slug, err)
		}
		category, err := stringList(row["category_path"])
		if err != nil {
			return nil, fmt.Errorf("wiki %s category_path: %w", slug, err)
		}
		if folder, ok := row["folder_id"].(string); ok && folder != "" {
			category = append(category, folder)
		}
		page.category = strings.Join(category, "/")
		pages[slug] = page
	}
	return pages, nil
}

// stringList 同时接受 JSON 数组与字符串化数组；其他形状一律报错，
// 避免"读不出来就当空集合"把撤销误判成没有来源。
func stringList(value any) ([]string, error) {
	switch typed := value.(type) {
	case nil:
		return nil, nil
	case []string:
		return append([]string{}, typed...), nil
	case []any:
		out := make([]string, 0, len(typed))
		for _, item := range typed {
			text, ok := item.(string)
			if !ok {
				return nil, fmt.Errorf("non-string item %T", item)
			}
			out = append(out, text)
		}
		return out, nil
	case string:
		if strings.TrimSpace(typed) == "" {
			return nil, nil
		}
		var out []string
		if err := json.Unmarshal([]byte(typed), &out); err != nil {
			return nil, err
		}
		return out, nil
	default:
		return nil, fmt.Errorf("unsupported value %T", value)
	}
}

// setDiff 返回 left 有、right 没有的元素（升序）。
func setDiff(left, right []string) []string {
	seen := make(map[string]bool, len(right))
	for _, item := range right {
		seen[item] = true
	}
	out := make([]string, 0)
	for _, item := range left {
		if seen[item] {
			continue
		}
		seen[item] = true
		out = append(out, item)
	}
	sort.Strings(out)
	return out
}

func digestOf(text string) string {
	sum := sha256.Sum256([]byte(text))
	return hex.EncodeToString(sum[:])
}

// changedLabels 把语义类别翻成给操作员看的词，界面不用各自维护一份。
func ChangedLabels(changed []string) []string {
	labels := map[string]string{
		"content": "正文", "sources": "来源文档", "citations": "引用分块",
		"out_links": "出边", "in_links": "入边", "category": "目录",
		"status": "状态", "page_type": "页面类型", "added": "新增", "removed": "整页撤销",
	}
	out := make([]string, 0, len(changed))
	for _, name := range changed {
		if label, ok := labels[name]; ok {
			out = append(out, label)
		} else {
			out = append(out, name)
		}
	}
	return out
}