package wsutil

import (
	"net/url"
	"sort"
	"strings"
)

// AppendQuery returns rawURL with the given query parameters added, preserving
// any existing query string. Parameters with an empty value are omitted. It is
// used by stateful gateway clients to splice resume parameters (resume/sn/
// session_id) and access tokens onto a gateway URL before reconnecting. Keys are
// appended in sorted order so the result is deterministic for tests.
func AppendQuery(rawURL string, params map[string]string) string {
	if len(params) == 0 {
		return rawURL
	}
	u, err := url.Parse(rawURL)
	if err != nil {
		return appendNaive(rawURL, params)
	}

	keys := make([]string, 0, len(params))
	for k := range params {
		keys = append(keys, k)
	}
	sort.Strings(keys)

	pairs := existingPairs(u.Query())
	for _, k := range keys {
		if params[k] == "" {
			continue
		}
		pairs = append(pairs, url.QueryEscape(k)+"="+url.QueryEscape(params[k]))
	}
	u.RawQuery = strings.Join(pairs, "&")
	return u.String()
}

// existingPairs flattens url.Values into ordered "k=v" pairs so that appending
// new parameters produces a deterministic query string. Multi-valued keys keep
// their original value order.
func existingPairs(v url.Values) []string {
	keys := make([]string, 0, len(v))
	for k := range v {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	pairs := make([]string, 0, len(v))
	for _, k := range keys {
		for _, val := range v[k] {
			pairs = append(pairs, url.QueryEscape(k)+"="+url.QueryEscape(val))
		}
	}
	return pairs
}

// appendNaive appends query parameters to a URL that could not be parsed, using
// '?' or '&' based on what is already present.
func appendNaive(rawURL string, params map[string]string) string {
	sep := "?"
	if strings.Contains(rawURL, "?") {
		sep = "&"
	}
	var b strings.Builder
	b.WriteString(rawURL)
	b.WriteString(sep)
	keys := make([]string, 0, len(params))
	for k := range params {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	first := true
	for _, k := range keys {
		if params[k] == "" {
			continue
		}
		if !first {
			b.WriteString("&")
		}
		first = false
		b.WriteString(url.QueryEscape(k) + "=" + url.QueryEscape(params[k]))
	}
	return b.String()
}