package bookfile

import (
	"archive/zip"
	"errors"
	"fmt"
	"io"
	"path"
	"sort"
	"strconv"
	"strings"
)

var ErrNotZip = errors.New("not a readable zip")
var ErrUnsafeZip = errors.New("unsafe zip entry")

func unsafeEntry(n string) bool {
	return strings.HasPrefix(n, "/") || strings.Contains(n, "..") || strings.ContainsRune(n, '\\') || strings.ContainsAny(n, "\n\r")
}

func isImage(name string) bool {
	switch strings.ToLower(path.Ext(name)) {
	case ".jpg", ".jpeg", ".png", ".webp", ".gif", ".avif":
		return true
	}
	return false
}

// junkEntry: macOS 打包混入的资源叉垃圾(__MACOSX/ 目录与 ._* AppleDouble),不是页
func junkEntry(name string) bool {
	if strings.HasPrefix(strings.ToLower(name), "__macosx/") {
		return true
	}
	return strings.HasPrefix(path.Base(name), "._")
}

func PageIndex(f io.ReaderAt, size int64) ([]string, error) {
	zr, err := zip.NewReader(f, size)
	if err != nil {
		return nil, ErrNotZip
	}
	var names []string
	for _, zf := range zr.File {
		if unsafeEntry(zf.Name) {
			return nil, fmt.Errorf("%w: %s", ErrUnsafeZip, zf.Name)
		}
		if junkEntry(zf.Name) {
			continue
		}
		if isImage(zf.Name) {
			names = append(names, zf.Name)
		}
	}
	sort.Slice(names, func(i, j int) bool { return NaturalLess(names[i], names[j]) })
	return names, nil
}

func ReadEntry(f io.ReaderAt, size int64, name string) ([]byte, error) {
	zr, err := zip.NewReader(f, size)
	if err != nil {
		return nil, ErrNotZip
	}
	for _, zf := range zr.File {
		if zf.Name == name {
			rc, err := zf.Open()
			if err != nil {
				return nil, err
			}
			defer rc.Close()
			return io.ReadAll(io.LimitReader(rc, 64<<20))
		}
	}
	return nil, errors.New("no such entry")
}

func NaturalLess(a, b string) bool {
	i, j := 0, 0
	for i < len(a) && j < len(b) {
		da, db := isDigit(a[i]), isDigit(b[j])
		switch {
		case da && db:
			si, sj := i, j
			for i < len(a) && isDigit(a[i]) {
				i++
			}
			for j < len(b) && isDigit(b[j]) {
				j++
			}
			na, _ := strconv.Atoi(a[si:i])
			nb, _ := strconv.Atoi(b[sj:j])
			if na != nb {
				return na < nb
			}
			if a[si:i] != b[sj:j] {
				return a[si:i] < b[sj:j]
			}
		case !da && !db:
			if a[i] != b[j] {
				return a[i] < b[j]
			}
			i++
			j++
		default:
			return da // 数字段排在字母前
		}
	}
	return j < len(b)
}

func isDigit(c byte) bool { return c >= '0' && c <= '9' }