package youtube

import (
	"context"
	"time"

	"golang.org/x/time/rate"
)

// globalFetchGate is the process-wide rate limiter for outbound timedtext/caption
// fetches. A single instance is shared by ALL Adapter instances (the scheduler's
// per-user runners + the web click-path) so they cannot collectively exceed the
// per-egress-IP cap. ADR-014 item 2: the gate serialises/limits concurrent caption
// fetches regardless of how many users or goroutines are upstream. The 429 is per
// IP, not per user — so the gate is process-wide, not per-withUser, not per-video.
//
// Default 2s/req (burst 1): the first fetch passes immediately, subsequent fetches
// are spaced at least 2s apart. Production overrides via SetFetchRate from config.
var globalFetchGate = rate.NewLimiter(rate.Every(2*time.Second), 1)

// SetFetchRate replaces the process-wide gate's rate with one token per interval.
// Call once at startup from config (TAPIR_FETCH_RATE). A non-positive interval
// installs an unlimited gate (rate.Inf) — used in dev/tests so nothing throttles.
func SetFetchRate(interval time.Duration) {
	if interval <= 0 {
		globalFetchGate = rate.NewLimiter(rate.Inf, 1)
		return
	}
	globalFetchGate = rate.NewLimiter(rate.Every(interval), 1)
}

// WaitFetchGate blocks until the process-wide gate allows one timedtext fetch,
// respecting ctx cancellation. Called from httpDo before every live outbound
// caption fetch so the scheduler and the click-path share the same egress budget.
func WaitFetchGate(ctx context.Context) error {
	return globalFetchGate.Wait(ctx)
}