package engine

import (
	"context"
	"errors"
	"sync"
	"sync/atomic"
	"testing"
	"time"

	"tower/internal/collectors"
	"tower/internal/model"
)

type fakeStore struct {
	mu sync.Mutex

	upsertCalls int
	lastNow     time.Time
	lastIssues  []model.Issue
}

func (s *fakeStore) Upsert(now time.Time, issues []model.Issue) {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.upsertCalls++
	s.lastNow = now
	// Deep-ish copy: slice copy is enough for our tests.
	s.lastIssues = append([]model.Issue(nil), issues...)
}

func (s *fakeStore) Snapshot(now time.Time) []model.Issue {
	s.mu.Lock()
	defer s.mu.Unlock()
	return append([]model.Issue(nil), s.lastIssues...)
}

func (s *fakeStore) UpsertCount() int {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.upsertCalls
}

type fakeCollector struct {
	name     string
	interval time.Duration

	// delay simulates work. If ctx is canceled/timeout hits, Collect returns ctx.Err().
	delay time.Duration

	issuesFn func(call int64) []model.Issue

	calls  atomic.Int64
	callCh chan time.Time
}

func (c *fakeCollector) Name() string { return c.name }
func (c *fakeCollector) Interval() time.Duration {
	return c.interval
}

func (c *fakeCollector) Collect(ctx context.Context) ([]model.Issue, collectors.Status, error) {
	call := c.calls.Add(1)
	if c.callCh != nil {
		select {
		case c.callCh <- time.Now():
		default:
		}
	}

	if c.delay > 0 {
		t := time.NewTimer(c.delay)
		defer t.Stop()
		select {
		case <-ctx.Done():
			var st collectors.Status
			return nil, st, ctx.Err()
		case <-t.C:
		}
	}

	var st collectors.Status
	if c.issuesFn != nil {
		return c.issuesFn(call), st, nil
	}
	return nil, st, nil
}

func recvSnapshot(t *testing.T, ch <-chan Snapshot, within time.Duration) Snapshot {
	t.Helper()
	select {
	case s := <-ch:
		return s
	case <-time.After(within):
		t.Fatalf("timed out waiting for snapshot")
		return Snapshot{}
	}
}

func TestEngine_UpsertAndSnapshotsEmitted(t *testing.T) {
	st := &fakeStore{}
	c := &fakeCollector{
		name:     "c1",
		interval: 100 * time.Millisecond,
		issuesFn: func(call int64) []model.Issue {
			return []model.Issue{{
				ID:       "id-1",
				Priority: model.PriorityP1,
				Title:    "hello",
				LastSeen: time.Now(),
			}}
		},
	}

	e := New(st, []CollectorConfig{{Collector: c, Timeout: 200 * time.Millisecond}}, 0)
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	defer e.Stop()

	e.Start(ctx)

	snap := recvSnapshot(t, e.Snapshots(), 300*time.Millisecond)
	if st.UpsertCount() < 1 {
		t.Fatalf("expected store.Upsert to be called")
	}
	if len(snap.Issues) != 1 || snap.Issues[0].ID != "id-1" {
		t.Fatalf("expected snapshot to contain issue id-1; got %+v", snap.Issues)
	}
	if _, ok := snap.Collectors["c1"]; !ok {
		t.Fatalf("expected collector health entry for c1")
	}
}

func TestEngine_CollectorTimeoutCancelsLongCollect(t *testing.T) {
	st := &fakeStore{}
	c := &fakeCollector{
		name:     "slow",
		interval: time.Hour,
		delay:    200 * time.Millisecond,
	}

	e := New(st, []CollectorConfig{{Collector: c, Timeout: 20 * time.Millisecond}}, 0)
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	defer e.Stop()

	e.Start(ctx)

	snap := recvSnapshot(t, e.Snapshots(), 400*time.Millisecond)
	ch, ok := snap.Collectors["slow"]
	if !ok {
		t.Fatalf("expected collector health entry for slow")
	}
	if ch.LastError == nil {
		t.Fatalf("expected LastError to be set")
	}
	if !errors.Is(ch.LastError, context.DeadlineExceeded) {
		t.Fatalf("expected context deadline exceeded; got %v", ch.LastError)
	}
	if st.UpsertCount() < 1 {
		t.Fatalf("expected store.Upsert to be called")
	}
}

func TestEngine_RefreshNowTriggersImmediateCollect(t *testing.T) {
	st := &fakeStore{}
	callCh := make(chan time.Time, 10)
	c := &fakeCollector{
		name:     "r",
		interval: 200 * time.Millisecond,
		callCh:   callCh,
	}

	e := New(st, []CollectorConfig{{Collector: c, Timeout: time.Second}}, 0)
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	defer e.Stop()

	e.Start(ctx)

	// First collect happens immediately.
	select {
	case <-callCh:
	case <-time.After(200 * time.Millisecond):
		t.Fatalf("timed out waiting for initial collect")
	}

	// Trigger refresh; should happen well before the 200ms interval.
	time.Sleep(10 * time.Millisecond)
	e.RefreshNow()

	select {
	case <-callCh:
		// ok
	case <-time.After(120 * time.Millisecond):
		t.Fatalf("expected RefreshNow to trigger a collect quickly")
	}
}

func TestEngine_MultipleCollectorsRunOnIntervals(t *testing.T) {
	st := &fakeStore{}
	fast := &fakeCollector{name: "fast", interval: 30 * time.Millisecond}
	slow := &fakeCollector{name: "slow", interval: 80 * time.Millisecond}

	e := New(st, []CollectorConfig{{Collector: fast, Timeout: time.Second}, {Collector: slow, Timeout: time.Second}}, 0)
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	e.Start(ctx)
	// Let it run a bit.
	time.Sleep(220 * time.Millisecond)
	e.Stop()

	fastCalls := fast.calls.Load()
	slowCalls := slow.calls.Load()

	// Includes initial collect.
	if fastCalls < 4 {
		t.Fatalf("expected fast collector to be called multiple times; got %d", fastCalls)
	}
	if slowCalls < 2 {
		t.Fatalf("expected slow collector to be called multiple times; got %d", slowCalls)
	}
}