package churl

// This file is a copy of `net/url/parse.go`, with some modifications to make it work for ClickHouse HA URLs.
// Most private fuctions and constants are copied as-is from Go 1.25.7.
// The reason is that the origin `Parse()` func does not support multiple hosts in the Host part after Go 1.26.
// See the original issue to more details: https://github.com/golang/go/issues/75859

import (
	"errors"
	"fmt"
	"net/netip"
	neturl "net/url"
	"strings"
)

type encoding int

const (
	encodePath encoding = 1 + iota
	encodePathSegment
	encodeHost
	encodeZone
	encodeUserPassword
	encodeQueryComponent
	encodeFragment
)

const upperhex = "0123456789ABCDEF"

func Parse(rawURL string) (*neturl.URL, error) {
	// Cut off #frag
	u, frag, _ := strings.Cut(rawURL, "#")
	url, err := parse(u, false)
	if err != nil {
		return nil, &neturl.Error{Op: "parse", URL: u, Err: err}
	}
	if frag == "" {
		return url, nil
	}
	if err = setFragment(url, frag); err != nil {
		return nil, &neturl.Error{Op: "parse", URL: rawURL, Err: err}
	}
	return url, nil
}

func parse(rawURL string, viaRequest bool) (*neturl.URL, error) {
	var rest string
	var err error

	if stringContainsCTLByte(rawURL) {
		return nil, errors.New("net/url: invalid control character in URL")
	}

	if rawURL == "" && viaRequest {
		return nil, errors.New("empty url")
	}
	url := new(neturl.URL)

	if rawURL == "*" {
		url.Path = "*"
		return url, nil
	}

	// Split off possible leading "http:", "mailto:", etc.
	// Cannot contain escaped characters.
	if url.Scheme, rest, err = getScheme(rawURL); err != nil {
		return nil, err
	}
	url.Scheme = strings.ToLower(url.Scheme)

	if strings.HasSuffix(rest, "?") && strings.Count(rest, "?") == 1 {
		url.ForceQuery = true
		rest = rest[:len(rest)-1]
	} else {
		rest, url.RawQuery, _ = strings.Cut(rest, "?")
	}

	if !strings.HasPrefix(rest, "/") {
		if url.Scheme != "" {
			// We consider rootless paths per RFC 3986 as opaque.
			url.Opaque = rest
			return url, nil
		}
		if viaRequest {
			return nil, errors.New("invalid URI for request")
		}

		// Avoid confusion with malformed schemes, like cache_object:foo/bar.
		// See golang.org/issue/16822.
		//
		// RFC 3986, §3.3:
		// In addition, a URI reference (Section 4.1) may be a relative-path reference,
		// in which case the first path segment cannot contain a colon (":") character.
		if segment, _, _ := strings.Cut(rest, "/"); strings.Contains(segment, ":") {
			// First path segment has colon. Not allowed in relative URL.
			return nil, errors.New("first path segment in URL cannot contain colon")
		}
	}

	if (url.Scheme != "" || !viaRequest && !strings.HasPrefix(rest, "///")) && strings.HasPrefix(rest, "//") {
		var authority string
		authority, rest = rest[2:], ""
		if i := strings.Index(authority, "/"); i >= 0 {
			authority, rest = authority[:i], authority[i:]
		}
		url.User, url.Host, err = parseAuthority(authority)
		if err != nil {
			return nil, err
		}
	} else if url.Scheme != "" && strings.HasPrefix(rest, "/") {
		// OmitHost is set to true when rawURL has an empty host (authority).
		// See golang.org/issue/46059.
		url.OmitHost = true
	}

	// Set Path and, optionally, RawPath.
	// RawPath is a hint of the encoding of Path. We don't want to set it if
	// the default escaping of Path is equivalent, to help make sure that people
	// don't rely on it in general.
	if err := setPath(url, rest); err != nil {
		return nil, err
	}
	return url, nil
}

func getScheme(rawURL string) (scheme, path string, err error) {
	for i := 0; i < len(rawURL); i++ {
		c := rawURL[i]
		switch {
		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z':
		// do nothing
		case '0' <= c && c <= '9' || c == '+' || c == '-' || c == '.':
			if i == 0 {
				return "", rawURL, nil
			}
		case c == ':':
			if i == 0 {
				return "", "", errors.New("missing protocol scheme")
			}
			return rawURL[:i], rawURL[i+1:], nil
		default:
			// we have encountered an invalid character,
			// so there is no valid scheme
			return "", rawURL, nil
		}
	}
	return "", rawURL, nil
}

func parseAuthority(authority string) (user *neturl.Userinfo, host string, err error) {
	i := strings.LastIndex(authority, "@")
	if i < 0 {
		host, err = parseHost(authority)
	} else {
		host, err = parseHost(authority[i+1:])
	}
	if err != nil {
		return nil, "", err
	}
	if i < 0 {
		return nil, host, nil
	}
	userinfo := authority[:i]
	if !validUserinfo(userinfo) {
		return nil, "", errors.New("net/url: invalid userinfo")
	}
	if !strings.Contains(userinfo, ":") {
		if userinfo, err = unescape(userinfo, encodeUserPassword); err != nil {
			return nil, "", err
		}
		user = neturl.User(userinfo)
	} else {
		username, password, _ := strings.Cut(userinfo, ":")
		if username, err = unescape(username, encodeUserPassword); err != nil {
			return nil, "", err
		}
		if password, err = unescape(password, encodeUserPassword); err != nil {
			return nil, "", err
		}
		user = neturl.UserPassword(username, password)
	}
	return user, host, nil
}

func parseHost(host string) (string, error) {
	if openBracketIdx := strings.LastIndex(host, "["); openBracketIdx != -1 {
		// Parse an IP-Literal in RFC 3986 and RFC 6874.
		// E.g., "[fe80::1]", "[fe80::1%25en0]", "[fe80::1]:80".
		closeBracketIdx := strings.LastIndex(host, "]")
		if closeBracketIdx < 0 {
			return "", errors.New("missing ']' in host")
		}

		colonPort := host[closeBracketIdx+1:]
		if !validOptionalPort(colonPort) {
			return "", fmt.Errorf("invalid port %q after host", colonPort)
		}
		unescapedColonPort, err := unescape(colonPort, encodeHost)
		if err != nil {
			return "", err
		}

		hostname := host[openBracketIdx+1 : closeBracketIdx]
		var unescapedHostname string
		// RFC 6874 defines that %25 (%-encoded percent) introduces
		// the zone identifier, and the zone identifier can use basically
		// any %-encoding it likes. That's different from the host, which
		// can only %-encode non-ASCII bytes.
		// We do impose some restrictions on the zone, to avoid stupidity
		// like newlines.
		zoneIdx := strings.Index(hostname, "%25")
		if zoneIdx >= 0 {
			hostPart, err := unescape(hostname[:zoneIdx], encodeHost)
			if err != nil {
				return "", err
			}
			zonePart, err := unescape(hostname[zoneIdx:], encodeZone)
			if err != nil {
				return "", err
			}
			unescapedHostname = hostPart + zonePart
		} else {
			var err error
			unescapedHostname, err = unescape(hostname, encodeHost)
			if err != nil {
				return "", err
			}
		}

		// Per RFC 3986, only a host identified by a valid
		// IPv6 address can be enclosed by square brackets.
		// This excludes any IPv4, but notably not IPv4-mapped addresses.
		addr, err := netip.ParseAddr(unescapedHostname)
		if err != nil {
			return "", fmt.Errorf("invalid host: %w", err)
		}
		if addr.Is4() {
			return "", errors.New("invalid IP-literal")
		}
		return "[" + unescapedHostname + "]" + unescapedColonPort, nil
	} else if i := strings.LastIndex(host, ":"); i != -1 {
		colonPort := host[i:]
		if !validOptionalPort(colonPort) {
			return "", fmt.Errorf("invalid port %q after host", colonPort)
		}
	}

	var err error
	if host, err = unescape(host, encodeHost); err != nil {
		return "", err
	}
	return host, nil
}

func validUserinfo(s string) bool {
	for _, r := range s {
		if 'A' <= r && r <= 'Z' {
			continue
		}
		if 'a' <= r && r <= 'z' {
			continue
		}
		if '0' <= r && r <= '9' {
			continue
		}
		switch r {
		case '-', '.', '_', ':', '~', '!', '$', '&', '\'',
			'(', ')', '*', '+', ',', ';', '=', '%':
			continue
		case '@':
			// `RFC 3986 section 3.2.1` does not allow '@' in userinfo.
			// It is a delimiter between userinfo and host.
			// However, URLs are diverse, and in some cases,
			// the userinfo may contain an '@' character,
			// for example, in "http://username:p@ssword@google.com",
			// the string "username:p@ssword" should be treated as valid userinfo.
			// Ref:
			//   https://go.dev/issue/3439
			//   https://go.dev/issue/22655
			continue
		default:
			return false
		}
	}
	return true
}

func validOptionalPort(port string) bool {
	if port == "" {
		return true
	}
	if port[0] != ':' {
		return false
	}
	for _, b := range port[1:] {
		if b < '0' || b > '9' {
			return false
		}
	}
	return true
}

func unescape(s string, mode encoding) (string, error) {
	// Count %, check that they're well-formed.
	n := 0
	hasPlus := false
	for i := 0; i < len(s); {
		switch s[i] {
		case '%':
			n++
			if i+2 >= len(s) || !ishex(s[i+1]) || !ishex(s[i+2]) {
				s = s[i:]
				if len(s) > 3 {
					s = s[:3]
				}
				return "", neturl.EscapeError(s)
			}
			// Per https://tools.ietf.org/html/rfc3986#page-21
			// in the host component %-encoding can only be used
			// for non-ASCII bytes.
			// But https://tools.ietf.org/html/rfc6874#section-2
			// introduces %25 being allowed to escape a percent sign
			// in IPv6 scoped-address literals. Yay.
			if mode == encodeHost && unhex(s[i+1]) < 8 && s[i:i+3] != "%25" {
				return "", neturl.EscapeError(s[i : i+3])
			}
			if mode == encodeZone {
				// RFC 6874 says basically "anything goes" for zone identifiers
				// and that even non-ASCII can be redundantly escaped,
				// but it seems prudent to restrict %-escaped bytes here to those
				// that are valid host name bytes in their unescaped form.
				// That is, you can use escaping in the zone identifier but not
				// to introduce bytes you couldn't just write directly.
				// But Windows puts spaces here! Yay.
				v := unhex(s[i+1])<<4 | unhex(s[i+2])
				if s[i:i+3] != "%25" && v != ' ' && shouldEscape(v, encodeHost) {
					return "", neturl.EscapeError(s[i : i+3])
				}
			}
			i += 3
		case '+':
			hasPlus = mode == encodeQueryComponent
			i++
		default:
			if (mode == encodeHost || mode == encodeZone) && s[i] < 0x80 && shouldEscape(s[i], mode) {
				return "", neturl.InvalidHostError(s[i : i+1])
			}
			i++
		}
	}

	if n == 0 && !hasPlus {
		return s, nil
	}

	var t strings.Builder
	t.Grow(len(s) - 2*n)
	for i := 0; i < len(s); i++ {
		switch s[i] {
		case '%':
			t.WriteByte(unhex(s[i+1])<<4 | unhex(s[i+2]))
			i += 2
		case '+':
			if mode == encodeQueryComponent {
				t.WriteByte(' ')
			} else {
				t.WriteByte('+')
			}
		default:
			t.WriteByte(s[i])
		}
	}
	return t.String(), nil
}

func escape(s string, mode encoding) string {
	spaceCount, hexCount := 0, 0
	for _, c := range []byte(s) {
		if shouldEscape(c, mode) {
			if c == ' ' && mode == encodeQueryComponent {
				spaceCount++
			} else {
				hexCount++
			}
		}
	}

	if spaceCount == 0 && hexCount == 0 {
		return s
	}

	var buf [64]byte
	var t []byte

	required := len(s) + 2*hexCount
	if required <= len(buf) {
		t = buf[:required]
	} else {
		t = make([]byte, required)
	}

	if hexCount == 0 {
		copy(t, s)
		for i := 0; i < len(s); i++ {
			if s[i] == ' ' {
				t[i] = '+'
			}
		}
		return string(t)
	}

	j := 0
	for _, c := range []byte(s) {
		switch {
		case c == ' ' && mode == encodeQueryComponent:
			t[j] = '+'
			j++
		case shouldEscape(c, mode):
			t[j] = '%'
			t[j+1] = upperhex[c>>4]
			t[j+2] = upperhex[c&15]
			j += 3
		default:
			t[j] = c
			j++
		}
	}
	return string(t)
}

func shouldEscape(c byte, mode encoding) bool {
	// §2.3 Unreserved characters (alphanum)
	if 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || '0' <= c && c <= '9' {
		return false
	}

	if mode == encodeHost || mode == encodeZone {
		// §3.2.2 Host allows
		//	sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="
		// as part of reg-name.
		// We add : because we include :port as part of host.
		// We add [ ] because we include [ipv6]:port as part of host.
		// We add < > because they're the only characters left that
		// we could possibly allow, and Parse will reject them if we
		// escape them (because hosts can't use %-encoding for
		// ASCII bytes).
		switch c {
		case '!', '$', '&', '\'', '(', ')', '*', '+', ',', ';', '=', ':', '[', ']', '<', '>', '"':
			return false
		}
	}

	switch c {
	case '-', '_', '.', '~': // §2.3 Unreserved characters (mark)
		return false

	case '$', '&', '+', ',', '/', ':', ';', '=', '?', '@': // §2.2 Reserved characters (reserved)
		// Different sections of the URL allow a few of
		// the reserved characters to appear unescaped.
		switch mode {
		case encodePath: // §3.3
			// The RFC allows : @ & = + $ but saves / ; , for assigning
			// meaning to individual path segments. This package
			// only manipulates the path as a whole, so we allow those
			// last three as well. That leaves only ? to escape.
			return c == '?'

		case encodePathSegment: // §3.3
			// The RFC allows : @ & = + $ but saves / ; , for assigning
			// meaning to individual path segments.
			return c == '/' || c == ';' || c == ',' || c == '?'

		case encodeUserPassword: // §3.2.1
			// The RFC allows ';', ':', '&', '=', '+', '$', and ',' in
			// userinfo, so we must escape only '@', '/', and '?'.
			// The parsing of userinfo treats ':' as special so we must escape
			// that too.
			return c == '@' || c == '/' || c == '?' || c == ':'

		case encodeQueryComponent: // §3.4
			// The RFC reserves (so we must escape) everything.
			return true

		case encodeFragment: // §4.1
			// The RFC text is silent but the grammar allows
			// everything, so escape nothing.
			return false
		}
	}

	if mode == encodeFragment {
		// RFC 3986 §2.2 allows not escaping sub-delims. A subset of sub-delims are
		// included in reserved from RFC 2396 §2.2. The remaining sub-delims do not
		// need to be escaped. To minimize potential breakage, we apply two restrictions:
		// (1) we always escape sub-delims outside of the fragment, and (2) we always
		// escape single quote to avoid breaking callers that had previously assumed that
		// single quotes would be escaped. See issue #19917.
		switch c {
		case '!', '(', ')', '*':
			return false
		}
	}

	// Everything else must be escaped.
	return true
}

func ishex(c byte) bool {
	switch {
	case '0' <= c && c <= '9':
		return true
	case 'a' <= c && c <= 'f':
		return true
	case 'A' <= c && c <= 'F':
		return true
	}
	return false
}

func unhex(c byte) byte {
	switch {
	case '0' <= c && c <= '9':
		return c - '0'
	case 'a' <= c && c <= 'f':
		return c - 'a' + 10
	case 'A' <= c && c <= 'F':
		return c - 'A' + 10
	default:
		panic("invalid hex character")
	}
}

func stringContainsCTLByte(s string) bool {
	for i := 0; i < len(s); i++ {
		b := s[i]
		if b < ' ' || b == 0x7f {
			return true
		}
	}
	return false
}

func setFragment(u *neturl.URL, f string) error {
	frag, err := unescape(f, encodeFragment)
	if err != nil {
		return err
	}
	u.Fragment = frag
	if escf := escape(frag, encodeFragment); f == escf {
		// Default encoding is fine.
		u.RawFragment = ""
	} else {
		u.RawFragment = f
	}
	return nil
}

func setPath(u *neturl.URL, p string) error {
	path, err := unescape(p, encodePath)
	if err != nil {
		return err
	}
	u.Path = path
	if escp := escape(path, encodePath); p == escp {
		// Default encoding is fine.
		u.RawPath = ""
	} else {
		u.RawPath = p
	}
	return nil
}