// Package session owns the daemon's in-memory state of truth and persists a
// snapshot on every change. Transitions go through the pure statemachine. It
// also owns per-session evidence stats: it accumulates active-window time while
// Active, logs raw focus events, and seals each session into the audit chain.
package session

import (
	"context"
	"errors"
	"fmt"
	"log"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"

	"antidrift/internal/ai"
	"antidrift/internal/domain"
	"antidrift/internal/enforce"
	"antidrift/internal/evidence"
	"antidrift/internal/knowledge"
	"antidrift/internal/statemachine"
	"antidrift/internal/store"
	"antidrift/internal/tasks"

	"github.com/google/uuid"
)

const (
	unavailableTitle = "(evidence unavailable)"
	sessionRetention = 30 * 24 * time.Hour
)

const coachTimeout = 60 * time.Second

const (
	coachIdle    = "idle"
	coachPending = "pending"
	coachReady   = "ready"
	coachError   = "error"
)

const tasksTimeout = 30 * time.Second

const (
	tasksIdle    = "idle"
	tasksPending = "pending"
	tasksReady   = "ready"
	tasksError   = "error"
)

const knowledgeTimeout = 10 * time.Second

const (
	knowledgeIdle    = "idle"
	knowledgePending = "pending"
	knowledgeReady   = "ready"
	knowledgeAbsent  = "absent"
	knowledgeError   = "error"
)

const reflectionTimeout = 30 * time.Second

const reflectionHistoryN = 5

// reflectionTopBuckets caps how many per-window time buckets the finished-session
// block lists for the reviewer, keeping the prompt compact.
const reflectionTopBuckets = 3

const (
	reflectionIdle    = "idle"
	reflectionPending = "pending"
	reflectionReady   = "ready"
	reflectionAbsent  = "absent"
)

var ErrNotPlanning = errors.New("session: coaching is only available while planning")

var ErrNotActive = errors.New("session: only available while a commitment is active")

// Controller holds runtime state and the active commitment behind a mutex.
type Controller struct {
	mu             sync.Mutex
	runtimeState   domain.RuntimeState
	commitment     *domain.Commitment
	deadline       time.Time
	snapshotPath   string
	auditPath      string
	sessionsDir    string
	clock          func() time.Time
	onChange       func()
	latestWindow   evidence.WindowSnapshot
	stats          *EvidenceStats
	outcomePending string
	coach          ai.Coach
	coachStatus    string
	coachProposal  *ai.Proposal
	coachErr       string
	coachGen       int

	tasksProvider tasks.Provider
	tasksStatus   string
	tasksList     []tasks.Task
	tasksGen      int

	knowledgeSrc    knowledge.Source
	knowledgeStatus string
	knowledgeText   string // cached grounding the coach reads
	knowledgePath   string // selected path; "" = adapter default
	knowledgeChars  int
	knowledgeGen    int

	reviewer         ai.Reviewer
	reflectionStatus string
	reflectionRecap  string
	carryForward     string // latest-wins takeaway; grounds the next coach
	reflectionGen    int

	allowedClasses   []string                // durable: the active session's allowed window classes
	enforcementLevel domain.EnforcementLevel // durable: block enables window-minimize enforcement
	guard            enforce.Guard
	judge            ai.DriftJudge
	driftStatus      string
	driftReason      string
	driftGen         int
	nudgeEpoch       int // identifies the current on-task stretch; nudge staleness guard
	lastJudgedAt     time.Time
	judgedClasses    map[string]ai.Verdict

	nudge        ai.Nudger
	recentTitles []string // in-memory ring of recent distinct titles this session
	nudgeMessage string   // current soft advisory ("" = none)
	lastNudgedAt time.Time
}

// New loads any persisted snapshot, prunes stale session logs, and rebuilds
// in-memory stats from the raw log if a live session was interrupted.
func New(snapshotPath string) (*Controller, error) {
	s, err := store.Load(snapshotPath)
	if err != nil {
		return nil, err
	}
	dir := filepath.Dir(snapshotPath)
	c := &Controller{
		runtimeState:     s.RuntimeState,
		commitment:       s.Commitment,
		snapshotPath:     snapshotPath,
		auditPath:        filepath.Join(dir, "audit.jsonl"),
		sessionsDir:      filepath.Join(dir, "sessions"),
		clock:            time.Now,
		outcomePending:   s.OutcomePending,
		reflectionStatus: s.ReflectionStatus,
		reflectionRecap:  s.ReflectionRecap,
		carryForward:     s.CarryForward,
	}
	if s.DeadlineUnixSecs > 0 {
		c.deadline = time.Unix(s.DeadlineUnixSecs, 0)
	}
	if c.runtimeState == "" {
		c.runtimeState = domain.RuntimeLocked
	}
	_ = store.PruneOlderThan(c.sessionsDir, sessionRetention, c.clock())
	if c.runtimeState == domain.RuntimeActive && s.SessionID != "" {
		c.allowedClasses = s.AllowedWindowClasses
		c.enforcementLevel = s.EnforcementLevel
		// Drift state is not persisted: recompute fresh after restart to avoid
		// stale interrupts. This also initializes judgedClasses (the pipeline
		// writes to it) so a restored Active session never panics on a nil map.
		c.resetDriftLocked()
		c.replayStats(s.SessionID)
	}
	return c, nil
}

// SetClock overrides the time source (tests only). Call before starting a
// session.
func (c *Controller) SetClock(f func() time.Time) {
	c.mu.Lock()
	c.clock = f
	c.mu.Unlock()
}

// SetOnChange registers a callback fired after an evidence-driven state change
// (focus updates). It is invoked with the mutex released.
func (c *Controller) SetOnChange(f func()) {
	c.mu.Lock()
	c.onChange = f
	c.mu.Unlock()
}

func (c *Controller) notify() {
	c.mu.Lock()
	f := c.onChange
	c.mu.Unlock()
	if f != nil {
		f()
	}
}

// State returns the current broadcastable state. Safe for concurrent use.
func (c *Controller) State() State {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.stateLocked()
}

// Deadline returns the active commitment deadline, or the zero time.
func (c *Controller) Deadline() time.Time {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.deadline
}

func (c *Controller) persistLocked() error {
	snap := store.Snapshot{
		RuntimeState:   c.runtimeState,
		Commitment:     c.commitment,
		OutcomePending: c.outcomePending,
	}
	if !c.deadline.IsZero() {
		snap.DeadlineUnixSecs = c.deadline.Unix()
	}
	if c.stats != nil {
		snap.SessionID = c.stats.SessionID
	}
	snap.AllowedWindowClasses = c.allowedClasses
	snap.EnforcementLevel = c.enforcementLevel
	snap.ReflectionStatus = c.reflectionStatus
	snap.ReflectionRecap = c.reflectionRecap
	snap.CarryForward = c.carryForward
	return store.Save(c.snapshotPath, snap)
}

// EnterPlanning moves Locked -> Planning.
func (c *Controller) EnterPlanning() error {
	c.mu.Lock()
	defer c.mu.Unlock()
	next, err := statemachine.TransitionRuntime(c.runtimeState, statemachine.EnterPlanning)
	if err != nil {
		return err
	}
	c.runtimeState = next
	c.resetCoachLocked()
	c.startTasksFetchLocked()
	c.startKnowledgeFetchLocked()
	return c.persistLocked()
}

// SetCoach injects the AI coach. Mirrors SetOnChange. A nil coach makes
// RequestCoach degrade gracefully.
func (c *Controller) SetCoach(coach ai.Coach) {
	c.mu.Lock()
	c.coach = coach
	c.mu.Unlock()
}

// resetCoachLocked returns coach state to idle and invalidates any in-flight
// request. Caller holds mu.
func (c *Controller) resetCoachLocked() {
	c.coachStatus = coachIdle
	c.coachProposal = nil
	c.coachErr = ""
	c.coachGen++
}

// SetTasks injects the Tasks provider. Mirrors SetCoach. A nil provider keeps
// the planning tasks list absent.
func (c *Controller) SetTasks(p tasks.Provider) {
	c.mu.Lock()
	c.tasksProvider = p
	c.mu.Unlock()
}

// startTasksFetchLocked kicks off an asynchronous Today() fetch when a provider
// is set. Mirrors RequestCoach: generation-guarded, discards stale or
// post-planning results, and notifies on completion. Caller holds mu.
func (c *Controller) startTasksFetchLocked() {
	c.tasksList = nil
	if c.tasksProvider == nil {
		c.tasksStatus = tasksIdle
		return
	}
	c.tasksGen++
	gen := c.tasksGen
	c.tasksStatus = tasksPending
	provider := c.tasksProvider
	go func() {
		ctx, cancel := context.WithTimeout(context.Background(), tasksTimeout)
		defer cancel()
		list, err := provider.Today(ctx)

		c.mu.Lock()
		if gen != c.tasksGen || c.runtimeState != domain.RuntimePlanning {
			c.mu.Unlock()
			return // stale or left planning: discard
		}
		if err != nil {
			c.tasksStatus = tasksError
			c.tasksList = nil
		} else {
			c.tasksStatus = tasksReady
			c.tasksList = list
		}
		c.mu.Unlock()
		c.notify()
	}()
}

// SetKnowledge injects the Knowledge source. Mirrors SetTasks. A nil source
// keeps the planning knowledge view absent and the coach ungrounded.
func (c *Controller) SetKnowledge(s knowledge.Source) {
	c.mu.Lock()
	c.knowledgeSrc = s
	c.mu.Unlock()
}

// SetKnowledgePath selects an explicit profile path (session-only; not
// persisted). While planning, it re-loads immediately so the indicator and the
// cached grounding update. An empty path resets to the adapter default.
func (c *Controller) SetKnowledgePath(path string) {
	c.mu.Lock()
	c.knowledgePath = strings.TrimSpace(path)
	planning := c.runtimeState == domain.RuntimePlanning
	if planning {
		c.startKnowledgeFetchLocked()
	}
	c.mu.Unlock()
	if planning {
		c.notify()
	}
}

// startKnowledgeFetchLocked kicks off an asynchronous Load when a source is set.
// Mirrors startTasksFetchLocked: generation-guarded, discards stale or
// post-planning results, and notifies on completion. The loaded text is cached
// in knowledgeText for the coach to read. Caller holds mu.
func (c *Controller) startKnowledgeFetchLocked() {
	c.knowledgeText = ""
	c.knowledgeChars = 0
	if c.knowledgeSrc == nil {
		c.knowledgeStatus = knowledgeIdle
		return
	}
	c.knowledgeGen++
	gen := c.knowledgeGen
	c.knowledgeStatus = knowledgePending
	src := c.knowledgeSrc
	path := c.knowledgePath
	go func() {
		ctx, cancel := context.WithTimeout(context.Background(), knowledgeTimeout)
		defer cancel()
		prof, err := src.Load(ctx, path)

		c.mu.Lock()
		if gen != c.knowledgeGen || c.runtimeState != domain.RuntimePlanning {
			c.mu.Unlock()
			return // stale or left planning: discard
		}
		if err != nil {
			c.knowledgeStatus = knowledgeError
			c.knowledgeText = ""
			c.knowledgeChars = 0
			if prof.Path != "" {
				c.knowledgePath = prof.Path
			}
		} else if prof.Text == "" {
			c.knowledgeStatus = knowledgeAbsent
			c.knowledgeText = ""
			c.knowledgeChars = 0
			c.knowledgePath = prof.Path
		} else {
			c.knowledgeStatus = knowledgeReady
			c.knowledgeText = prof.Text
			c.knowledgeChars = len(prof.Text)
			c.knowledgePath = prof.Path
		}
		c.mu.Unlock()
		c.notify()
	}()
}

// SetReviewer injects the AI reviewer. A nil reviewer keeps reflection idle and
// leaves the coach ungrounded by any carry-forward.
func (c *Controller) SetReviewer(r ai.Reviewer) {
	c.mu.Lock()
	c.reviewer = r
	c.mu.Unlock()
}

// startReflectionFetchLocked kicks off an asynchronous reflection when a
// reviewer is set, on entering Review. Unlike the tasks/knowledge fetches, the
// completion guard is generation-only (not state-gated): the carry-forward must
// still apply if the user clicks End before the reviewer returns. A superseded
// review (a later session's fetch) bumps the generation and discards this one.
// The recap and carry-forward are cleared up front so a failed/slow reviewer
// never leaves stale data from the previous session. Caller holds mu.
func (c *Controller) startReflectionFetchLocked() {
	c.reflectionRecap = ""
	c.carryForward = ""
	if c.reviewer == nil {
		c.reflectionStatus = reflectionIdle
		return
	}
	c.reflectionGen++
	gen := c.reflectionGen
	c.reflectionStatus = reflectionPending
	reviewer := c.reviewer
	finished := c.buildReflectionFinishedLocked()
	// Read the history synchronously, here under the lock, on purpose: it must
	// happen-before End appends the just-finished session to the audit chain, so
	// that session is excluded from "recent history" and not double-counted (it
	// is already carried in `finished`). Moving this into the goroutine would
	// race with End's append and reintroduce that double-count. The read is
	// bounded to reflectionHistoryN summaries and runs once per Review entry, not
	// on any hot path.
	history := buildReflectionHistory(c.auditPath)
	go func() {
		ctx, cancel := context.WithTimeout(context.Background(), reflectionTimeout)
		defer cancel()
		refl, err := reviewer.Review(ctx, finished, history)

		c.mu.Lock()
		if gen != c.reflectionGen {
			c.mu.Unlock()
			return // superseded review: discard
		}
		if err != nil || strings.TrimSpace(refl.Recap) == "" {
			c.reflectionStatus = reflectionAbsent
			c.reflectionRecap = ""
			c.carryForward = ""
		} else {
			c.reflectionStatus = reflectionReady
			c.reflectionRecap = refl.Recap
			c.carryForward = refl.CarryForward
		}
		_ = c.persistLocked()
		c.mu.Unlock()
		c.notify()
	}()
}

// buildReflectionFinishedLocked renders the just-finished session as a compact
// block for the reviewer. Caller holds mu; c.stats/c.commitment are still set
// (End clears them, but enterReview runs before End). Reuses bucketViews for the
// per-window totals, already sorted desc by seconds.
func (c *Controller) buildReflectionFinishedLocked() string {
	var na, sc string
	if c.commitment != nil {
		na, sc = c.commitment.NextAction, c.commitment.SuccessCondition
	}
	outcome := c.outcomePending
	if outcome == "" {
		outcome = "completed"
	}
	var b strings.Builder
	fmt.Fprintf(&b, "Next action: %s\n", na)
	fmt.Fprintf(&b, "Success condition: %s\n", sc)
	fmt.Fprintf(&b, "Outcome: %s\n", outcome)
	if c.stats != nil {
		fmt.Fprintf(&b, "Context switches: %d\n", c.stats.SwitchCount)
		for i, bv := range bucketViews(c.stats.Buckets) {
			if i >= reflectionTopBuckets {
				break
			}
			fmt.Fprintf(&b, "- %s · %s: %dm\n", bv.Class, bv.Title, bv.Seconds/60)
		}
	}
	return strings.TrimRight(b.String(), "\n")
}

// buildReflectionHistory renders the last few prior sessions as compact lines.
// The just-finished session is not yet in the chain (End appends it), so it is
// not double-counted. Returns "" when there is no usable history.
func buildReflectionHistory(auditPath string) string {
	sums, err := store.RecentSessions(auditPath, reflectionHistoryN)
	if err != nil || len(sums) == 0 {
		return ""
	}
	var b strings.Builder
	for _, s := range sums {
		top := ""
		if len(s.Buckets) > 0 {
			top = fmt.Sprintf(", top %s %dm", s.Buckets[0].Class, s.Buckets[0].Seconds/60)
		}
		fmt.Fprintf(&b, "- %s: %s (%d switches%s)\n", s.Outcome, s.NextAction, s.SwitchCount, top)
	}
	return strings.TrimRight(b.String(), "\n")
}

// AllowedClassesForTest exposes the session allowed classes for tests.
func (c *Controller) AllowedClassesForTest() []string {
	c.mu.Lock()
	defer c.mu.Unlock()
	return append([]string(nil), c.allowedClasses...)
}

// EnforcementLevelForTest exposes the active session's enforcement level. Tests
// only.
func (c *Controller) EnforcementLevelForTest() domain.EnforcementLevel {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.enforcementLevel
}

// composedGroundingLocked combines the standing profile (knowledge port) with
// the latest carry-forward takeaway into the single free-form grounding string
// the coach already accepts. Caller holds mu.
func (c *Controller) composedGroundingLocked() string {
	g := c.knowledgeText
	if c.carryForward != "" {
		if g != "" {
			g += "\n\n"
		}
		g += "Last session's takeaway: " + c.carryForward
	}
	return g
}

// RequestCoach starts an async coach call for intent. Returns ErrNotPlanning if
// not in planning; otherwise never a hard error (failures surface as coach
// state). The proposal is ephemeral and never persisted.
func (c *Controller) RequestCoach(intent string) error {
	c.mu.Lock()
	if c.runtimeState != domain.RuntimePlanning {
		c.mu.Unlock()
		return ErrNotPlanning
	}
	if c.coach == nil {
		c.coachStatus = coachError
		c.coachErr = "coach unavailable"
		c.coachProposal = nil
		c.mu.Unlock()
		c.notify()
		return nil
	}
	c.coachGen++
	gen := c.coachGen
	c.coachStatus = coachPending
	c.coachErr = ""
	c.coachProposal = nil
	coach := c.coach
	grounding := c.composedGroundingLocked()
	c.mu.Unlock()
	c.notify()

	go func() {
		ctx, cancel := context.WithTimeout(context.Background(), coachTimeout)
		defer cancel()
		prop, err := coach.Coach(ctx, intent, grounding)

		c.mu.Lock()
		if gen != c.coachGen || c.runtimeState != domain.RuntimePlanning {
			c.mu.Unlock()
			return // stale or left planning: discard
		}
		if err != nil {
			c.coachStatus = coachError
			c.coachErr = coachErrorMessage(err)
			c.coachProposal = nil
		} else {
			c.coachStatus = coachReady
			c.coachProposal = &prop
			c.coachErr = ""
		}
		c.mu.Unlock()
		c.notify()
	}()
	return nil
}

func coachErrorMessage(err error) string {
	switch {
	case errors.Is(err, ai.ErrEmptyResponse), errors.Is(err, ai.ErrNoJSON), errors.Is(err, ai.ErrInvalidProposal):
		return "coach returned an unusable response"
	case errors.Is(err, context.DeadlineExceeded):
		return "coach timed out"
	default:
		return "coach unavailable"
	}
}

// StartManualCommitment validates input, activates a new commitment, mints a
// session, seeds evidence stats from the latest window, and moves Planning ->
// Active.
func (c *Controller) StartManualCommitment(nextAction, successCondition string, timebox time.Duration, allowedClasses []string, level domain.EnforcementLevel) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	commitment, err := domain.NewManual(nextAction, successCondition, timebox)
	if err != nil {
		return err
	}
	commitment.State, err = statemachine.TransitionCommitment(commitment.State, statemachine.CommitmentActivate)
	if err != nil {
		return err
	}
	next, err := statemachine.TransitionRuntime(c.runtimeState, statemachine.ActivateAccepted)
	if err != nil {
		return err
	}
	now := c.clock()
	c.runtimeState = next
	c.commitment = &commitment
	c.deadline = now.Add(timebox)
	c.outcomePending = ""
	c.resetCoachLocked()
	c.allowedClasses = append([]string(nil), allowedClasses...)
	c.enforcementLevel = level
	c.resetDriftLocked()

	sessionID := "session-" + uuid.Must(uuid.NewV7()).String()
	c.stats = &EvidenceStats{
		SessionID:   sessionID,
		StartedUnix: now.Unix(),
		Buckets:     map[bucketKey]time.Duration{},
	}
	seed := c.latestWindow
	_ = store.AppendFocus(c.sessionsDir, sessionID, focusEvent(now, seed))
	c.applyEvent(now, seed)
	return c.persistLocked()
}

// Complete moves Active -> Review with a "completed" outcome.
func (c *Controller) Complete() error { return c.enterReview("completed") }

// Expire moves Active -> Review with an "expired" outcome (timebox elapsed).
func (c *Controller) Expire() error { return c.enterReview("expired") }

func (c *Controller) enterReview(outcome string) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	next, err := statemachine.TransitionRuntime(c.runtimeState, statemachine.CompleteForReview)
	if err != nil {
		return err
	}
	if c.commitment != nil {
		completed, err := statemachine.TransitionCommitment(c.commitment.State, statemachine.Complete)
		if err != nil {
			return err
		}
		c.commitment.State = completed
	}
	// Flush the final open segment, then freeze accounting.
	if c.stats != nil && c.stats.hasLast {
		c.stats.Buckets[c.stats.lastKey] += c.clock().Sub(c.stats.lastFocusAt)
		c.stats.hasLast = false
	}
	c.runtimeState = next
	c.outcomePending = outcome
	c.startReflectionFetchLocked()
	return c.persistLocked()
}

// End moves Review -> Locked, writes the session summary to the audit chain,
// and clears the commitment and stats.
func (c *Controller) End() error {
	c.mu.Lock()
	defer c.mu.Unlock()
	next, err := statemachine.TransitionRuntime(c.runtimeState, statemachine.EndWorkPeriod)
	if err != nil {
		return err
	}
	if c.stats != nil {
		if err := store.AppendSession(c.auditPath, c.buildSummaryLocked()); err != nil {
			// State integrity over audit completeness: the transition still
			// completes. Surfaced for the operator; no auto-retry in M1.
			log.Printf("session: audit append failed: %v", err)
		}
	}
	c.runtimeState = next
	c.commitment = nil
	c.deadline = time.Time{}
	c.stats = nil
	c.outcomePending = ""
	c.allowedClasses = nil
	c.enforcementLevel = ""
	c.resetDriftLocked()
	return c.persistLocked()
}

func (c *Controller) buildSummaryLocked() store.SessionSummary {
	buckets := make([]store.BucketTotal, 0, len(c.stats.Buckets))
	for k, d := range c.stats.Buckets {
		buckets = append(buckets, store.BucketTotal{Class: k.Class, Title: k.Title, Seconds: int64(d.Seconds())})
	}
	sort.Slice(buckets, func(i, j int) bool { return buckets[i].Seconds > buckets[j].Seconds })
	outcome := c.outcomePending
	if outcome == "" {
		outcome = "completed"
	}
	var na, sc string
	if c.commitment != nil {
		na, sc = c.commitment.NextAction, c.commitment.SuccessCondition
	}
	return store.SessionSummary{
		SessionID:   c.stats.SessionID,
		NextAction:  na,
		SuccessCond: sc,
		Outcome:     outcome,
		StartedUnix: c.stats.StartedUnix,
		EndedUnix:   c.clock().Unix(),
		SwitchCount: c.stats.SwitchCount,
		Buckets:     buckets,
	}
}