package lighthouse

import (
	"context"
	"math"
	"strconv"
	"strings"
)

// presencePrefix marks a presence channel.
const presencePrefix = "presence:"

// ParseChannel returns the authorizer namespace of channel, the WinterCMS
// parseChannel rule:
//
//   - a "presence:presence:" prefix yields "" (deny);
//   - one "presence:" prefix is stripped, and presence is reported true;
//   - more than three ":"-separated segments yield "" (deny);
//   - otherwise the namespace is the first segment.
//
// The lookup is byte-exact: no case folding or Unicode normalization.
func ParseChannel(channel string) (namespace string, presence bool) {
	presence = strings.HasPrefix(channel, presencePrefix)
	if strings.HasPrefix(channel, presencePrefix+presencePrefix) {
		return "", presence
	}
	name := strings.TrimPrefix(channel, presencePrefix)
	parts := strings.Split(name, ":")
	if len(parts) > 3 {
		return "", presence
	}
	return parts[0], presence
}

// ChannelID returns segment 1 of channel (0 when it is missing) converted
// with PHP's (int) cast, as the WinterCMS authorizers read
// explode(':', $channel)[1]. "5abc" is 5, "abc" is 0, "1e3" is 1000, and
// out-of-range values saturate. For "presence:collection:5" segment 1 is
// "collection", so the id is 0.
func ChannelID(channel string) int64 {
	parts := strings.SplitN(channel, ":", 3)
	if len(parts) < 2 {
		return 0
	}
	return PHPInt(parts[1])
}

// PHPInt converts s the way PHP 8's (int) cast converts a string: leading
// whitespace and a sign are allowed, the longest numeric prefix (digits,
// an optional fraction and exponent) is used, integers saturate at the
// int64 bounds, and non-finite floats become 0.
func PHPInt(s string) int64 {
	i := 0
	for i < len(s) && isPHPSpace(s[i]) {
		i++
	}
	start := i
	if i < len(s) && (s[i] == '+' || s[i] == '-') {
		i++
	}
	digitsStart := i
	for i < len(s) && isDigit(s[i]) {
		i++
	}
	intDigits := i - digitsStart
	isFloat := false
	if i < len(s) && s[i] == '.' {
		j := i + 1
		for j < len(s) && isDigit(s[j]) {
			j++
		}
		if intDigits > 0 || j > i+1 {
			isFloat = true
			i = j
		}
	}
	if intDigits == 0 && !isFloat {
		return 0
	}
	if i < len(s) && (s[i] == 'e' || s[i] == 'E') {
		j := i + 1
		if j < len(s) && (s[j] == '+' || s[j] == '-') {
			j++
		}
		k := j
		for k < len(s) && isDigit(s[k]) {
			k++
		}
		if k > j {
			isFloat = true
			i = k
		}
	}
	num := s[start:i]
	if !isFloat {
		n, err := strconv.ParseInt(num, 10, 64)
		if err != nil {
			if strings.HasPrefix(num, "-") {
				return math.MinInt64
			}
			return math.MaxInt64
		}
		return n
	}
	f, _ := strconv.ParseFloat(num, 64)
	switch {
	case math.IsInf(f, 0) || math.IsNaN(f):
		return 0
	case f >= math.MaxInt64:
		return math.MaxInt64
	case f <= math.MinInt64:
		return math.MinInt64
	default:
		return int64(f)
	}
}

func isPHPSpace(c byte) bool {
	return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\v' || c == '\f'
}

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

// FormatChannels lowercases each channel (ASCII, as PHP strtolower) and
// prefixes lowercase(namespace)+":" unless the namespace is empty or the
// channel already starts with that prefix.
func FormatChannels(namespace string, channels []string) []string {
	out := make([]string, len(channels))
	prefix := ""
	if namespace != "" && namespace != "0" {
		prefix = asciiLower(namespace) + ":"
	}
	for i, ch := range channels {
		name := asciiLower(ch)
		if prefix != "" && !strings.HasPrefix(name, prefix) {
			name = prefix + name
		}
		out[i] = name
	}
	return out
}

func asciiLower(s string) string {
	b := []byte(s)
	for i, c := range b {
		if c >= 'A' && c <= 'Z' {
			b[i] = c + ('a' - 'A')
		}
	}
	return string(b)
}

type clientIDKey struct{}

// WithClientID returns ctx carrying the realtime client id of a subscribe
// request. Drivers call it before invoking an Authorizer.
func WithClientID(ctx context.Context, id string) context.Context {
	if ctx == nil {
		ctx = context.Background()
	}
	return context.WithValue(ctx, clientIDKey{}, id)
}

// ClientID returns the realtime client id placed in ctx by the driver, or
// "" outside a subscribe request.
func ClientID(ctx context.Context) string {
	if ctx == nil {
		return ""
	}
	id, _ := ctx.Value(clientIDKey{}).(string)
	return id
}