package fibonacci

import (
	"backoff/utilities"
	"context"
	"fmt"
	"math/big"
	"testing"
	"time"
)

func wouldOverflow(a, b int64) (product int64, overflows bool) {
	results := new(big.Int).Mul(big.NewInt(a), big.NewInt(b))
	return results.Int64(), results.IsInt64()
}

func fibonacci(n int64) int64 {
	switch {
	case n <= 0:
		return 0
	case n == 1:
		return 1
	default:
		var a, b int64 = 0, 1
		for i := int64(2); i <= n; i++ {
			a, b = b, a+b
		}
		return b
	}
}

func TestFibonacciResultsArray(t *testing.T) {
	for n, got := range TheFibonacciSequence {
		want := fibonacci(int64(n))
		if want != got {
			t.Fatalf("error for input %d: wanted %d; got %d\n", n, want, got)
		}
	}
}

func TestFibonacciFunc(t *testing.T) {
	for n := range len(TheFibonacciSequence) {
		want := fibonacci(int64(n))
		got := fibonacci(int64(n))
		if want != got {
			t.Fatalf("error for input %d: wanted %d; got %d\n", n, want, got)
		}
	}
}

func TestFibonacciBackoffNextDoesNotOverflow(t *testing.T) {
	backoff := FibonacciBackoff{}
	for n, want := range TheFibonacciSequence {
		got := backoff.Next()
		if time.Duration(want) != got {
			t.Fatalf("error for %d: wanted %s; got %s\n", n, time.Duration(want), time.Duration(got))
		}
	}
	backoff.Reset()
	if want, got := int64(0), backoff.Iteration; want != got {
		t.Fatalf("error: wanted %d; got %d after Reset()\n", want, got)
	}
	var previous time.Duration
	backoff.PauseMultiplier = time.Second
	for input, output := range TheFibonacciSequence {
		var want time.Duration
		switch _, overflows := utilities.ProductWouldOverflowInt64(output, backoff.PauseMultiplier.Nanoseconds()); overflows {
		case true:
			want = previous
		default:
			want = time.Duration(output) * backoff.PauseMultiplier
		}
		got := backoff.Next()
		if want != got {
			t.Fatalf("error for %d (iteration=%d); wanted %s; got %s\n", input, backoff.Iteration, want, got)
		}
		previous = got
	}
}

func TestFibonacciBackoffIterationLimit(t *testing.T) {
	backoff := FibonacciBackoff{MaxIteration: 5}
	for input, output := range TheFibonacciSequence {
		want := time.Duration(output)
		if input >= int(backoff.MaxIteration) {
			if backoff.Iteration > backoff.MaxIteration {
				t.Fatalf("error: backoff.Iteration %d > max %d (%+v)\n", backoff.Iteration, backoff.MaxIteration, backoff)
			}
			want = time.Duration(fibonacci(5))
		}
		got := backoff.Next()
		if want != got {
			t.Fatalf("error for %d: wanted %s; got %s\n", input, want, got)
		}

	}
}

func TestFibonacciPauseLimit(t *testing.T) {
	backoff := FibonacciBackoff{MaxPause: time.Second}
	for input := range TheFibonacciSequence {
		if got := backoff.Next(); got > time.Second {
			t.Fatalf("error for %d: expected max %s; got %s\n", input, time.Second, got)
		}
	}
	// test with jitter
	backoff.Reset()
	backoff.Jitter = time.Millisecond * 100
	backoff.PauseMultiplier = time.Second
	max := time.Second + backoff.Jitter
	min := time.Second - backoff.Jitter
	for input := range TheFibonacciSequence {
		if got := backoff.Next(); input > 0 && (got > max || got < min) {
			t.Fatalf("error for %d: expected value in range %s - %s; got %s\n", input, min, max, got)
		}
	}
	fmt.Printf("finished\n")
}

func TestFibonacciBackoffAfter(t *testing.T) {
	backoff := FibonacciBackoff{Iteration: 1, PauseMultiplier: time.Millisecond}
	for i := 1; i <= 5; i++ {
		want := time.Duration(fibonacci(int64(i))) * time.Millisecond
		min, max := want-time.Millisecond*10, want+time.Millisecond*10
		got := func() (took time.Duration) {
			start := time.Now()
			defer func() { took = time.Since(start) }()
			<-backoff.After(context.Background())
			return
		}()
		if got > max || got < min {
			t.Fatalf("error: wanted value in range %s-%s; got %s\n", min, max, got)
		}
	}
}