package onlyoffice

import (
	"archive/zip"
	"bytes"
	"encoding/json"
	"encoding/xml"
	"fmt"
	"io"
	"regexp"
	"strings"
)

// DocxComment is one Word comment. Anchor is matched against the plain text of
// a paragraph (entity-decoded, runs concatenated), so it survives text split
// across runs. At most one comment is placed per paragraph.
type DocxComment struct {
	Anchor string `json:"anchor"`
	Text   string `json:"text"`
}

var (
	docxParaRe = regexp.MustCompile(`(?s)<w:p\b[^>]*>.*?</w:p>`)
	docxPPrRe  = regexp.MustCompile(`(?s)^<w:p\b[^>]*>\s*<w:pPr>.*?</w:pPr>`)
	docxOpenRe = regexp.MustCompile(`^<w:p\b[^>]*>`)
	docxTextRe = regexp.MustCompile(`(?s)<w:t\b[^>]*>(.*?)</w:t>`)
)

// ParseDocxComments decodes a JSON array of comments.
func ParseDocxComments(data []byte) ([]DocxComment, error) {
	var comments []DocxComment
	if err := json.Unmarshal(data, &comments); err != nil {
		return nil, fmt.Errorf("decode comments: %w", err)
	}
	return comments, nil
}

// DocxParagraphs returns the concatenated text of every paragraph in a .docx
// document.xml-free input (it takes the raw document.xml bytes).
func DocxParagraphs(documentXML []byte) []string {
	out := make([]string, 0, 64)
	for _, p := range docxParaRe.FindAllString(string(documentXML), -1) {
		if txt := strings.TrimSpace(docxPlain(p)); txt != "" {
			out = append(out, txt)
		}
	}
	return out
}

// InjectDocxComments returns a copy of the .docx with real Word comments added,
// each anchored to the first paragraph whose text contains the comment's Anchor.
// The author name is written into every comment. It reports how many comments
// were applied; anchors that match nothing are skipped.
func InjectDocxComments(src []byte, author string, comments []DocxComment) ([]byte, int, error) {
	parts, order, err := readDocxZip(src)
	if err != nil {
		return nil, 0, err
	}
	doc, ok := parts["word/document.xml"]
	if !ok {
		return nil, 0, fmt.Errorf("not a docx: word/document.xml missing")
	}
	if author == "" {
		author = "Comment"
	}

	used := make([]bool, len(comments))
	id := 0
	newDoc := docxParaRe.ReplaceAllStringFunc(string(doc), func(p string) string {
		txt := docxPlain(p)
		for i, c := range comments {
			if used[i] || c.Anchor == "" || !strings.Contains(txt, c.Anchor) {
				continue
			}
			used[i] = true
			p = docxAddMarkers(p, id)
			id++
			break
		}
		return p
	})

	applied := make([]DocxComment, 0, len(comments))
	for i, c := range comments {
		if used[i] {
			applied = append(applied, c)
		}
	}
	parts["word/document.xml"] = []byte(newDoc)
	parts["word/comments.xml"] = docxBuildComments(author, applied)
	parts["[Content_Types].xml"] = docxAddContentType(parts["[Content_Types].xml"])
	if rels, ok := parts["word/_rels/document.xml.rels"]; ok {
		parts["word/_rels/document.xml.rels"] = docxAddRel(rels)
	} else {
		parts["word/_rels/document.xml.rels"] = docxDefaultRels()
		order = append(order, "word/_rels/document.xml.rels")
	}
	if !containsStr(order, "word/comments.xml") {
		order = append(order, "word/comments.xml")
	}

	out, err := writeDocxZip(parts, order)
	if err != nil {
		return nil, 0, err
	}
	return out, len(applied), nil
}

func docxAddMarkers(p string, id int) string {
	start := fmt.Sprintf(`<w:commentRangeStart w:id="%d"/>`, id)
	end := fmt.Sprintf(`<w:commentRangeEnd w:id="%d"/><w:r><w:commentReference w:id="%d"/></w:r>`, id, id)
	if loc := docxPPrRe.FindStringIndex(p); loc != nil {
		p = p[:loc[1]] + start + p[loc[1]:]
	} else if loc := docxOpenRe.FindStringIndex(p); loc != nil {
		p = p[:loc[1]] + start + p[loc[1]:]
	}
	if i := strings.LastIndex(p, "</w:p>"); i >= 0 {
		p = p[:i] + end + p[i:]
	}
	return p
}

func docxPlain(p string) string {
	var b strings.Builder
	for _, m := range docxTextRe.FindAllStringSubmatch(p, -1) {
		b.WriteString(docxUnescape(m[1]))
	}
	return b.String()
}

func docxUnescape(s string) string {
	var out strings.Builder
	d := xml.NewDecoder(strings.NewReader("<x>" + s + "</x>"))
	for {
		tok, err := d.Token()
		if err != nil {
			break
		}
		if cd, ok := tok.(xml.CharData); ok {
			out.Write(cd)
		}
	}
	return out.String()
}

func docxBuildComments(author string, comments []DocxComment) []byte {
	var b strings.Builder
	b.WriteString(`<?xml version="1.0" encoding="UTF-8" standalone="yes"?>` + "\n")
	b.WriteString(`<w:comments xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main">`)
	for i, c := range comments {
		fmt.Fprintf(&b, `<w:comment w:id="%d" w:author="%s" w:initials="%s" w:date="%s"><w:p><w:r><w:t xml:space="preserve">%s</w:t></w:r></w:p></w:comment>`,
			i, docxEscape(author), docxInitials(author), "2026-10-07T12:00:00Z", docxEscape(c.Text))
	}
	b.WriteString(`</w:comments>`)
	return []byte(b.String())
}

func docxEscape(s string) string {
	var b bytes.Buffer
	_ = xml.EscapeText(&b, []byte(s))
	return b.String()
}

// docxInitials derives up to two initials from an author name.
func docxInitials(author string) string {
	var out []rune
	for _, f := range strings.Fields(author) {
		if r := []rune(f); len(r) > 0 {
			out = append(out, r[0])
		}
		if len(out) == 2 {
			break
		}
	}
	return strings.ToUpper(string(out))
}

func docxAddContentType(ct []byte) []byte {
	if len(ct) == 0 || strings.Contains(string(ct), "/word/comments.xml") {
		return ct
	}
	const override = `<Override PartName="/word/comments.xml" ContentType="application/vnd.openxmlformats-officedocument.wordprocessingml.comments+xml"/>`
	return []byte(strings.Replace(string(ct), "</Types>", override+"</Types>", 1))
}

func docxAddRel(rels []byte) []byte {
	if strings.Contains(string(rels), "relationships/comments") {
		return rels
	}
	const rel = `<Relationship Id="rIdComments" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/comments" Target="comments.xml"/>`
	return []byte(strings.Replace(string(rels), "</Relationships>", rel+"</Relationships>", 1))
}

func docxDefaultRels() []byte {
	return []byte(`<?xml version="1.0" encoding="UTF-8" standalone="yes"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rIdComments" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/comments" Target="comments.xml"/></Relationships>`)
}

func readDocxZip(data []byte) (map[string][]byte, []string, error) {
	zr, err := zip.NewReader(bytes.NewReader(data), int64(len(data)))
	if err != nil {
		return nil, nil, err
	}
	parts := make(map[string][]byte, len(zr.File))
	order := make([]string, 0, len(zr.File))
	for _, f := range zr.File {
		rc, err := f.Open()
		if err != nil {
			return nil, nil, err
		}
		b, err := io.ReadAll(rc)
		rc.Close()
		if err != nil {
			return nil, nil, err
		}
		parts[f.Name] = b
		order = append(order, f.Name)
	}
	return parts, order, nil
}

func writeDocxZip(parts map[string][]byte, order []string) ([]byte, error) {
	var buf bytes.Buffer
	zw := zip.NewWriter(&buf)
	written := map[string]bool{}
	for _, name := range order {
		data, ok := parts[name]
		if !ok || written[name] {
			continue
		}
		w, err := zw.Create(name)
		if err != nil {
			return nil, err
		}
		if _, err := w.Write(data); err != nil {
			return nil, err
		}
		written[name] = true
	}
	if err := zw.Close(); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

func containsStr(xs []string, s string) bool {
	for _, x := range xs {
		if x == s {
			return true
		}
	}
	return false
}