// Structs and functions for unmarshaling NCX files in e-pub archives

package main

import (
	"fmt"
	"encoding/xml"
	"net/url"
	"sort"
)

// A URI for content
type Content struct {
	Src string `xml:"src,attr"`
}

// A content label and URI pair
type NavPoint struct {
	Label   string  `xml:"navLabel>text"`
	Content Content `xml:"content"`
	Order   int     `xml:"playOrder,attr"`
}

// A series of navigation points
type Ncx struct {
	XMLName   xml.Name   `xml:"ncx"`
	Title     string     `xml:"docTitle>text"`
	NavPoints []NavPoint `xml:"navMap>navPoint"`
}

// Parse an NCX file
func ParseNcx(content string) *Ncx {
	dest := &Ncx{}

	// Unmarshal XHTML
	if err := xml.Unmarshal([]byte(content), &dest); err != nil {
		fmt.Printf("error: %s\n", err)
	}

	// Sort navigation points
	sort.Slice(dest.NavPoints, func(i, j int) bool {
		return dest.NavPoints[i].Order < dest.NavPoints[j].Order
	})

	return dest
}

// Build a table of contents from an NCX file
func ReadTableOfContents(content string) []string {
	ncx := ParseNcx(content)

	var toc []string

	for _, point := range ncx.NavPoints {
		src, err := url.QueryUnescape(point.Content.Src)
		if err != nil {
			fmt.Printf("error: %s\n", err)
		}

		toc = append(toc, src)
	}

	return toc
}