package session

import (
	"context"
	"errors"
	"path/filepath"
	"testing"
	"time"

	"antidrift/internal/ai"
	"antidrift/internal/domain"
	"antidrift/internal/evidence"
	"antidrift/internal/store"
)

func newTestController(t *testing.T) (*Controller, string) {
	t.Helper()
	path := filepath.Join(t.TempDir(), "state.json")
	c, err := New(path)
	if err != nil {
		t.Fatalf("new controller: %v", err)
	}
	return c, path
}

func TestHappyPathDrivesStates(t *testing.T) {
	c, _ := newTestController(t)
	if c.State().RuntimeState != domain.RuntimeLocked {
		t.Fatalf("should start Locked")
	}
	if err := c.EnterPlanning(); err != nil {
		t.Fatalf("enter planning: %v", err)
	}
	if err := c.StartManualCommitment("Port session", "session tests pass", 25*time.Minute); err != nil {
		t.Fatalf("start commitment: %v", err)
	}
	st := c.State()
	if st.RuntimeState != domain.RuntimeActive {
		t.Fatalf("should be Active, got %s", st.RuntimeState)
	}
	if st.Commitment == nil || st.Commitment.NextAction != "Port session" {
		t.Fatalf("active commitment missing: %+v", st.Commitment)
	}
	if st.Commitment.DeadlineUnixSecs <= time.Now().Unix() {
		t.Fatalf("deadline should be in the future")
	}
	if err := c.Complete(); err != nil {
		t.Fatalf("complete: %v", err)
	}
	if c.State().RuntimeState != domain.RuntimeReview {
		t.Fatalf("should be Review after complete")
	}
	if err := c.End(); err != nil {
		t.Fatalf("end: %v", err)
	}
	if c.State().RuntimeState != domain.RuntimeLocked {
		t.Fatalf("should be Locked after end")
	}
}

func TestStartCommitmentRejectsInvalidInput(t *testing.T) {
	c, _ := newTestController(t)
	_ = c.EnterPlanning()
	if err := c.StartManualCommitment("", "x", 25*time.Minute); err == nil {
		t.Fatalf("empty next action should error")
	}
	if c.State().RuntimeState != domain.RuntimePlanning {
		t.Fatalf("failed start must not change state, got %s", c.State().RuntimeState)
	}
}

func TestStateRestoresFromSnapshot(t *testing.T) {
	path := filepath.Join(t.TempDir(), "state.json")
	first, err := New(path)
	if err != nil {
		t.Fatalf("new: %v", err)
	}
	_ = first.EnterPlanning()
	_ = first.StartManualCommitment("Persisted action", "done", 25*time.Minute)

	second, err := New(path)
	if err != nil {
		t.Fatalf("reopen: %v", err)
	}
	st := second.State()
	if st.RuntimeState != domain.RuntimeActive {
		t.Fatalf("restored state should be Active, got %s", st.RuntimeState)
	}
	if st.Commitment == nil || st.Commitment.NextAction != "Persisted action" {
		t.Fatalf("restored commitment missing: %+v", st.Commitment)
	}
}

func TestRestoredCommitmentKeepsDeadline(t *testing.T) {
	path := filepath.Join(t.TempDir(), "state.json")
	first, err := New(path)
	if err != nil {
		t.Fatalf("new: %v", err)
	}
	_ = first.EnterPlanning()
	_ = first.StartManualCommitment("Keep deadline", "done", 25*time.Minute)
	want := first.State().Commitment.DeadlineUnixSecs

	second, err := New(path)
	if err != nil {
		t.Fatalf("reopen: %v", err)
	}
	got := second.State().Commitment
	if got == nil || got.DeadlineUnixSecs != want {
		t.Fatalf("restored deadline: got %+v want %d", got, want)
	}
}

// fakeClock returns successive instants on demand.
type fakeClock struct{ now time.Time }

func (f *fakeClock) advance(d time.Duration) { f.now = f.now.Add(d) }
func (f *fakeClock) fn() func() time.Time    { return func() time.Time { return f.now } }

func snap(class, title string) evidence.WindowSnapshot {
	return evidence.WindowSnapshot{Class: class, Title: title, Health: evidence.EvidenceHealth{Available: true}}
}

func bucketSeconds(t *testing.T, st State, class, title string) int64 {
	t.Helper()
	if st.Evidence == nil {
		t.Fatalf("expected evidence projection")
	}
	for _, b := range st.Evidence.Buckets {
		if b.Class == class && b.Title == title {
			return b.Seconds
		}
	}
	return -1
}

func TestAccumulatesBucketsAndSwitches(t *testing.T) {
	c, _ := newTestController(t)
	clk := &fakeClock{now: time.Unix(1000, 0)}
	c.SetClock(clk.fn())
	c.RecordWindow(snap("code", "antidrift")) // latest window before start

	_ = c.EnterPlanning()
	_ = c.StartManualCommitment("work", "done", 25*time.Minute) // seeds at t=1000 with code/antidrift

	clk.advance(10 * time.Second)
	c.RecordWindow(snap("firefox", "docs")) // credits 10s to code/antidrift, switch -> firefox
	clk.advance(20 * time.Second)
	c.RecordWindow(snap("code", "antidrift")) // credits 20s to firefox/docs, switch back

	st := c.State()
	if got := bucketSeconds(t, st, "code", "antidrift"); got != 10 {
		t.Errorf("code bucket = %d, want 10", got)
	}
	if got := bucketSeconds(t, st, "firefox", "docs"); got != 20 {
		t.Errorf("firefox bucket = %d, want 20", got)
	}
	if st.Evidence.SwitchCount != 2 {
		t.Errorf("switch count = %d, want 2", st.Evidence.SwitchCount)
	}
}

func TestNoAccountingOutsideActive(t *testing.T) {
	c, _ := newTestController(t)
	clk := &fakeClock{now: time.Unix(1000, 0)}
	c.SetClock(clk.fn())
	// Locked: RecordWindow must not create stats.
	c.RecordWindow(snap("code", "x"))
	if c.State().Evidence != nil {
		t.Fatalf("no session: evidence should be nil")
	}
}

func TestUnavailableAccruesToReservedBucket(t *testing.T) {
	c, _ := newTestController(t)
	clk := &fakeClock{now: time.Unix(1000, 0)}
	c.SetClock(clk.fn())
	_ = c.EnterPlanning()
	_ = c.StartManualCommitment("work", "done", 25*time.Minute) // seed: empty unavailable latestWindow
	// latestWindow was zero-value (unavailable) at seed time.
	clk.advance(5 * time.Second)
	c.RecordWindow(snap("code", "x")) // credits 5s to the reserved bucket
	st := c.State()
	if got := bucketSeconds(t, st, "", "(evidence unavailable)"); got != 5 {
		t.Errorf("unavailable bucket = %d, want 5", got)
	}
}

func TestCrashReplayRebuildsStats(t *testing.T) {
	path := filepath.Join(t.TempDir(), "state.json")
	first, _ := New(path)
	clk := &fakeClock{now: time.Unix(1000, 0)}
	first.SetClock(clk.fn())
	first.RecordWindow(snap("code", "antidrift"))
	_ = first.EnterPlanning()
	_ = first.StartManualCommitment("work", "done", 25*time.Minute)
	clk.advance(15 * time.Second)
	first.RecordWindow(snap("firefox", "docs")) // 15s -> code, switch

	// Simulate crash + restart: New replays the raw log.
	second, err := New(path)
	if err != nil {
		t.Fatalf("reopen: %v", err)
	}
	st := second.State()
	if st.RuntimeState != domain.RuntimeActive {
		t.Fatalf("restored state should be Active, got %s", st.RuntimeState)
	}
	if got := bucketSeconds(t, st, "code", "antidrift"); got != 15 {
		t.Errorf("replayed code bucket = %d, want 15", got)
	}
	if st.Evidence.SwitchCount != 1 {
		t.Errorf("replayed switch count = %d, want 1", st.Evidence.SwitchCount)
	}
}

func TestEndWritesAuditSummary(t *testing.T) {
	dir := t.TempDir()
	path := filepath.Join(dir, "state.json")
	c, _ := New(path)
	clk := &fakeClock{now: time.Unix(1000, 0)}
	c.SetClock(clk.fn())
	c.RecordWindow(snap("code", "antidrift"))
	_ = c.EnterPlanning()
	_ = c.StartManualCommitment("write plan", "plan done", 25*time.Minute)
	clk.advance(30 * time.Second)
	c.RecordWindow(snap("firefox", "docs"))
	clk.advance(10 * time.Second)
	if err := c.Complete(); err != nil { // flush: +10s to firefox/docs
		t.Fatalf("complete: %v", err)
	}
	if err := c.End(); err != nil {
		t.Fatalf("end: %v", err)
	}

	auditPath := filepath.Join(dir, "audit.jsonl")
	if err := store.VerifyChain(auditPath); err != nil {
		t.Fatalf("chain should verify: %v", err)
	}
}

type fakeCoach struct {
	prop ai.Proposal
	err  error
	gate chan struct{} // if non-nil, Coach blocks until it receives
}

func (f *fakeCoach) Coach(ctx context.Context, intent string) (ai.Proposal, error) {
	if f.gate != nil {
		<-f.gate
	}
	return f.prop, f.err
}

// waitCoachStatus polls until the coach view reaches want, or fails after 2s.
func waitCoachStatus(t *testing.T, c *Controller, want string) State {
	t.Helper()
	deadline := time.Now().Add(2 * time.Second)
	for time.Now().Before(deadline) {
		st := c.State()
		if st.Coach != nil && st.Coach.Status == want {
			return st
		}
		time.Sleep(5 * time.Millisecond)
	}
	t.Fatalf("coach status never reached %q (last: %+v)", want, c.State().Coach)
	return State{}
}

func TestRequestCoachReady(t *testing.T) {
	c, _ := newTestController(t)
	_ = c.EnterPlanning()
	c.SetCoach(&fakeCoach{prop: ai.Proposal{NextAction: "Do X", SuccessCondition: "X done", TimeboxSecs: 1500}})
	if err := c.RequestCoach("do x"); err != nil {
		t.Fatalf("request coach: %v", err)
	}
	st := waitCoachStatus(t, c, "ready")
	if st.Coach.Proposal == nil || st.Coach.Proposal.NextAction != "Do X" || st.Coach.Proposal.TimeboxSecs != 1500 {
		t.Fatalf("ready proposal wrong: %+v", st.Coach)
	}
}

func TestRequestCoachError(t *testing.T) {
	c, _ := newTestController(t)
	_ = c.EnterPlanning()
	c.SetCoach(&fakeCoach{err: errors.New("backend down")})
	if err := c.RequestCoach("x"); err != nil {
		t.Fatalf("request: %v", err)
	}
	st := waitCoachStatus(t, c, "error")
	if st.Coach.Error == "" {
		t.Fatal("error status should carry a message")
	}
}

func TestRequestCoachUnavailable(t *testing.T) {
	c, _ := newTestController(t)
	_ = c.EnterPlanning()
	if err := c.RequestCoach("x"); err != nil {
		t.Fatalf("nil coach must degrade, not error: %v", err)
	}
	st := c.State()
	if st.Coach == nil || st.Coach.Status != "error" {
		t.Fatalf("want error status for nil coach, got %+v", st.Coach)
	}
}

func TestRequestCoachWrongState(t *testing.T) {
	c, _ := newTestController(t)
	c.SetCoach(&fakeCoach{prop: ai.Proposal{NextAction: "x", SuccessCondition: "y", TimeboxSecs: 60}})
	if err := c.RequestCoach("x"); err == nil {
		t.Fatal("coaching from Locked should error")
	}
	if c.State().Coach != nil {
		t.Fatal("no coach view outside planning")
	}
}

func TestRequestCoachStaleResultDiscarded(t *testing.T) {
	c, _ := newTestController(t)
	_ = c.EnterPlanning()

	slow := &fakeCoach{prop: ai.Proposal{NextAction: "OLD", SuccessCondition: "old", TimeboxSecs: 60}, gate: make(chan struct{})}
	c.SetCoach(slow)
	_ = c.RequestCoach("first") // gen1 pending, goroutine blocks on gate

	fast := &fakeCoach{prop: ai.Proposal{NextAction: "NEW", SuccessCondition: "new", TimeboxSecs: 120}}
	c.SetCoach(fast)
	_ = c.RequestCoach("second") // gen2 -> ready NEW
	st := waitCoachStatus(t, c, "ready")
	if st.Coach.Proposal.NextAction != "NEW" {
		t.Fatalf("expected NEW, got %+v", st.Coach.Proposal)
	}

	close(slow.gate) // release gen1; it must be discarded
	time.Sleep(50 * time.Millisecond)
	if got := c.State().Coach.Proposal.NextAction; got != "NEW" {
		t.Fatalf("stale gen1 overwrote state: %q", got)
	}
}

func TestLeavingPlanningClearsCoach(t *testing.T) {
	c, _ := newTestController(t)
	_ = c.EnterPlanning()
	c.SetCoach(&fakeCoach{prop: ai.Proposal{NextAction: "x", SuccessCondition: "y", TimeboxSecs: 60}})
	_ = c.RequestCoach("x")
	waitCoachStatus(t, c, "ready")
	if err := c.StartManualCommitment("a", "b", 25*time.Minute); err != nil {
		t.Fatalf("start: %v", err)
	}
	if c.State().Coach != nil {
		t.Fatal("coach view must be gone once Active")
	}
}