package process

import (
	"context"
	"encoding/json"
	"testing"
	"time"

	"github.com/nats-io/nats.go/jetstream"
)

type ledgerMsg struct {
	jetstream.Msg
	subject string
	seq     uint64
	pending uint64
	stored  time.Time
	times   uint64
}

func (m ledgerMsg) Subject() string { return m.subject }
func (m ledgerMsg) Metadata() (*jetstream.MsgMetadata, error) {
	return &jetstream.MsgMetadata{Sequence: jetstream.SequencePair{Stream: m.seq, Consumer: m.seq}, NumPending: m.pending, Timestamp: m.stored, NumDelivered: max(m.times, 1)}, nil
}

func TestConsumerLedgerKeepsTheFactsAfterEachMessage(t *testing.T) {
	kept := map[string][]byte{}
	now := time.Date(2026, 11, 12, 9, 0, 0, 0, time.UTC)
	l := NewConsumerLedger("EVENTS", "n1_m", func(_ context.Context, key string, value []byte) error { kept[key] = value; return nil }, func() time.Time { return now }, nil)
	read := func() ConsumerFacts {
		var f ConsumerFacts
		if err := json.Unmarshal(kept["n1_m"], &f); err != nil {
			t.Fatal(err)
		}
		return f
	}
	a, b := ledgerMsg{subject: "mesh.seat.s.event.a", seq: 7, pending: 1}, ledgerMsg{subject: "mesh.seat.s.event.b", seq: 8, pending: 0}
	l.Delivered(a)
	now = now.Add(time.Minute)
	l.Delivered(b)
	if f := read(); f.Pending != 0 || !f.OldestUnacknowledged.Equal(now.Add(-time.Minute)) {
		t.Errorf("after two deliveries: %+v, want pending 0 and the first one's delivery as the oldest unacknowledged", f)
	}
	// A message delivered again keeps its first delivery's time (A-187): asked again in this run, and after a restart, where the
	// new ledger knows none, the time the bus stored it.
	now = now.Add(time.Minute)
	l.Delivered(ledgerMsg{subject: a.subject, seq: 7, pending: 0, times: 2})
	if f := read(); !f.OldestUnacknowledged.Equal(now.Add(-2 * time.Minute)) {
		t.Errorf("after a delivery again: %+v, want the first delivery kept as the oldest unacknowledged", f)
	}
	stored := now.Add(-time.Hour)
	again := NewConsumerLedger("EVENTS", "n1_m", func(_ context.Context, key string, value []byte) error { kept[key] = value; return nil }, func() time.Time { return now }, nil)
	again.Delivered(ledgerMsg{subject: a.subject, seq: 7, stored: stored, times: 3})
	if f := read(); !f.OldestUnacknowledged.Equal(stored) {
		t.Errorf("after a restart's delivery again: %+v, want the time the bus stored it", f)
	}
	now = now.Add(-time.Minute)
	at := now.Add(-time.Hour)
	l.Applied(a, at)
	if f := read(); f.Acknowledged != 7 || f.LastEvent != "mesh.seat.s.event.a" || !f.LastAt.Equal(at) || !f.OldestUnacknowledged.Equal(now) {
		t.Errorf("after the first applied: %+v, want sequence 7, its event and at, and the second one's delivery as the oldest", f)
	}
	l.Applied(b, time.Time{})
	if f := read(); f.Acknowledged != 8 || !f.OldestUnacknowledged.IsZero() {
		t.Errorf("after both applied: %+v, want sequence 8 and none unacknowledged", f)
	}
}