package pacer

import (
	"context"
	"testing"
	"time"
)

func TestPacer_Instant(t *testing.T) {
	p := New(100, 0) // 100/s, no ramp
	ctx, cancel := context.WithTimeout(context.Background(), 200*time.Millisecond)
	defer cancel()

	ch, stop := p.Tick(ctx)
	defer stop()

	var count int
	for range ch {
		count++
		if count > 25 {
			// Should fire ~20 times in 200ms at 100/s
			break
		}
	}
	if count < 15 {
		t.Errorf("instant pacer: expected ≥15 ticks in 200ms, got %d", count)
	}
}

func TestPacer_RampLinear(t *testing.T) {
	// This test uses a mock clock that advances with each call.
	// Total wall clock needed: 100ms (ramp) + 200ms (steady) = 300ms.
	p := New(100, 100*time.Millisecond) // 100/s, 100ms ramp
	clockMs := 0
	p.Clock = func() time.Time {
		clockMs += 10 // each p.Clock call advances 10ms
		return time.Date(2000, 1, 1, 0, 0, 0, clockMs*1_000_000, time.UTC)
	}

	ctx, cancel := context.WithTimeout(context.Background(), 500*time.Millisecond)
	defer cancel()

	ch, stop := p.Tick(ctx)
	defer stop()

	var count int
	for range ch {
		count++
		if count > 50 {
			break
		}
	}
	// With mock clock: ramp phase (100ms) + steady phase (~200ms of ticks)
	// At 100/s, 1 tick per 10ms. In 300ms mock time, should get ~30 ticks.
	if count < 20 {
		t.Errorf("ramp pacer: expected ≥20 ticks in 300ms mock time, got %d", count)
	}
}

func TestPacer_Overshoot(t *testing.T) {
	// rate=0 should return a ticker that essentially never fires.
	p := New(0, 0)
	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
	defer cancel()

	ch, stop := p.Tick(ctx)
	defer stop()

	select {
	case _, ok := <-ch:
		if ok {
			t.Error("channel should be closed for rate=0")
		}
	case <-time.After(60 * time.Millisecond):
		// expected — no ticks fired
	}
}

func TestPacer_ContextCancel(t *testing.T) {
	p := New(10_000, 0) // fast rate
	ctx, cancel := context.WithCancel(context.Background())

	ch, stop := p.Tick(ctx)

	// Cancel immediately
	cancel()
	stop()

	// Channel should close (no tick sent after cancel)
	select {
	case _, ok := <-ch:
		if ok {
			t.Error("channel should be closed after context cancel")
		}
	case <-time.After(50 * time.Millisecond):
		// ok — closed within 50ms
	}
}