// Package wsutil provides a small, reusable WebSocket gateway client for
// stateful IM channels (KOOK, QQ OneBot, and similar). It owns the transport
// mechanics that those channels share — dialing a gateway, running a read loop,
// sending an application-level heartbeat, and reconnecting with exponential
// backoff (optionally splicing resume parameters onto the gateway URL) — while
// leaving the platform-specific signaling to the adapter via Handler hooks.
//
// It depends only on the standard library plus github.com/gorilla/websocket and
// internal/logger, never on a specific channel adapter.
package wsutil

import "time"

// Backoff is a resettable exponential backoff delay scheduler. It yields delays
// starting at base and doubling up to cap (for example 2s, 4s, 8s, ... capped at
// 60s), which is the WebSocket gateway reconnect pattern used by stateful IM
// channels. It is safe for concurrent use by a single goroutine.
type Backoff struct {
	base     time.Duration
	max      time.Duration
	attempts int
}

// NewBackoff creates a backoff with the given base and cap. A non-positive base
// defaults to 1s and a non-positive cap to 60s.
func NewBackoff(base, cap time.Duration) *Backoff {
	if base <= 0 {
		base = time.Second
	}
	if cap <= 0 {
		cap = 60 * time.Second
	}
	return &Backoff{base: base, max: cap}
}

// Next returns the delay to sleep before the next attempt and advances the
// internal attempt counter. It never exceeds the configured cap.
func (b *Backoff) Next() time.Duration {
	var d time.Duration
	if b.attempts >= 60 {
		d = b.max
	} else {
		d = b.base << uint(b.attempts)
	}
	if d > b.max || d <= 0 {
		d = b.max
	}
	b.attempts++
	return d
}

// Reset restores the backoff to its initial state after a successful connect, so
// a later drop starts the ramp over from the base delay.
func (b *Backoff) Reset() { b.attempts = 0 }