package parse

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

// ExtractDOCX reads a .docx file and returns its plain text.
// DOCX is a ZIP archive; we unzip word/document.xml, walk <w:t> nodes
// for text, and emit a newline at each <w:p> boundary.
func ExtractDOCX(r io.Reader) (string, error) {
	data, err := io.ReadAll(r)
	if err != nil {
		return "", fmt.Errorf("read docx: %w", err)
	}
	zr, err := zip.NewReader(bytes.NewReader(data), int64(len(data)))
	if err != nil {
		return "", fmt.Errorf("open docx zip: %w", err)
	}
	var docFile *zip.File
	for _, f := range zr.File {
		if f.Name == "word/document.xml" {
			docFile = f
			break
		}
	}
	if docFile == nil {
		return "", errors.New("word/document.xml not found in docx")
	}
	rc, err := docFile.Open()
	if err != nil {
		return "", fmt.Errorf("open document.xml: %w", err)
	}
	defer rc.Close()
	return parseDocXML(rc)
}

func parseDocXML(r io.Reader) (string, error) {
	dec := xml.NewDecoder(r)
	var sb strings.Builder
	var inText bool
	for {
		tok, err := dec.Token()
		if err == io.EOF {
			break
		}
		if err != nil {
			return "", fmt.Errorf("parse document.xml: %w", err)
		}
		switch t := tok.(type) {
		case xml.StartElement:
			if t.Name.Local == "t" {
				inText = true
			}
		case xml.EndElement:
			if t.Name.Local == "t" {
				inText = false
			}
			if t.Name.Local == "p" {
				sb.WriteByte('\n')
			}
		case xml.CharData:
			if inText {
				sb.Write([]byte(t))
			}
		}
	}
	return strings.TrimSpace(sb.String()), nil
}