package orchestrator

import (
	"context"
	"log"
	"math/rand"
	"time"

	"github.com/jmoiron/sqlx"

	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/fabric"
	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/models"
	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/store"
)

// Ticker drives the topic state machine. Every TickInterval it scans
// for topics with timestamps that have crossed a transition boundary
// and applies the transition atomically per topic.
//
// State transitions handled by the ticker:
//
//	created       → signup_open      (when now >= signup_open_at)
//	                                  + post Fabric announcement
//	signup_open   → signup_closed    (when now >= signup_close_at, allocator succeeded)
//	              → cancelled         (allocator returned CancelReason)
//	signup_closed → debating         (when now >= debate_start_at; opens round 0)
//
// NOT handled by the ticker (driven elsewhere):
//
//	debating      → completed         driven by POST /api/topics/{id}/verdict
//	                                  (judge submits; handler flips status).
//	                                  The "judging" sub-state is implicit:
//	                                  status==debating AND now>=debate_end_at.
//
// Per-topic transitions use SELECT FOR UPDATE so concurrent ticker
// instances (or future replicas) don't double-fire.
type Ticker struct {
	db        *sqlx.DB
	topics    *store.TopicStore
	signups   *store.SignupStore
	camps     *store.CampStore
	rounds    *store.RoundStore
	announcer *fabric.Announcer
	interval  time.Duration
	rng       *rand.Rand
}

func NewTicker(
	db *sqlx.DB,
	topics *store.TopicStore,
	signups *store.SignupStore,
	camps *store.CampStore,
	rounds *store.RoundStore,
	announcer *fabric.Announcer,
	interval time.Duration,
) *Ticker {
	if interval <= 0 {
		interval = 15 * time.Second
	}
	return &Ticker{
		db:        db,
		topics:    topics,
		signups:   signups,
		camps:     camps,
		rounds:    rounds,
		announcer: announcer,
		interval:  interval,
		rng:       rand.New(rand.NewSource(time.Now().UnixNano())),
	}
}

// Run blocks until ctx is cancelled. Caller goroutines it.
func (t *Ticker) Run(ctx context.Context) {
	log.Printf("orchestrator: ticker started (interval=%s, announce=%v)", t.interval, t.announcer.Enabled())
	tk := time.NewTicker(t.interval)
	defer tk.Stop()
	// First tick immediately so startup is responsive — don't wait
	// 15s for the first scan.
	t.tickOnce(ctx)
	for {
		select {
		case <-ctx.Done():
			log.Printf("orchestrator: ticker stopped")
			return
		case <-tk.C:
			t.tickOnce(ctx)
		}
	}
}

// tickOnce scans + applies. Errors are logged per topic; one topic
// failing doesn't stall the others.
func (t *Ticker) tickOnce(ctx context.Context) {
	now := time.Now()

	// 1. created → signup_open
	if err := t.transitionByStatus(ctx, now,
		models.TopicStatusCreated, "signup_open_at",
		func(ctx context.Context, tx *sqlx.Tx, topicID string) error {
			topic, err := t.topics.GetByID(ctx, topicID)
			if err != nil {
				return err
			}
			if _, err := tx.ExecContext(ctx,
				`UPDATE topics SET status = ? WHERE id = ?`,
				models.TopicStatusSignupOpen, topicID); err != nil {
				return err
			}
			// Announcement is best-effort, outside the tx (network call).
			go t.broadcastAnnouncement(topic)
			return nil
		}); err != nil {
		log.Printf("orchestrator: created→signup_open scan: %v", err)
	}

	// 2. signup_open → signup_closed | cancelled
	if err := t.transitionByStatus(ctx, now,
		models.TopicStatusSignupOpen, "signup_close_at",
		func(ctx context.Context, tx *sqlx.Tx, topicID string) error {
			signups, err := t.signups.ListByTopic(ctx, topicID)
			if err != nil {
				return err
			}
			res := Allocate(signups, t.rng)
			if res.CancelReason != "" {
				_, err := tx.ExecContext(ctx,
					`UPDATE topics SET status = ?, cancelled_reason = ? WHERE id = ?`,
					models.TopicStatusCancelled, res.CancelReason, topicID)
				log.Printf("orchestrator: topic %s cancelled at signup_close: %s",
					topicID, res.CancelReason)
				return err
			}
			if err := t.camps.WriteAllocation(ctx, tx, topicID, res.Allocation); err != nil {
				return err
			}
			_, err = tx.ExecContext(ctx,
				`UPDATE topics SET status = ? WHERE id = ?`,
				models.TopicStatusSignupClosed, topicID)
			log.Printf("orchestrator: topic %s allocated pro=%s con=%s judge=%s",
				topicID,
				res.Allocation[models.CampPro], res.Allocation[models.CampCon], res.Allocation[models.CampJudge])
			return err
		}); err != nil {
		log.Printf("orchestrator: signup_open→signup_closed scan: %v", err)
	}

	// 3. signup_closed → debating (opens round 0)
	if err := t.transitionByStatus(ctx, now,
		models.TopicStatusSignupClosed, "debate_start_at",
		func(ctx context.Context, tx *sqlx.Tx, topicID string) error {
			if _, err := tx.ExecContext(ctx,
				`UPDATE topics SET status = ? WHERE id = ?`,
				models.TopicStatusDebating, topicID); err != nil {
				return err
			}
			// Round 0 inserted within the tx — if commit fails we don't
			// leak a half-state.
			_, err := tx.ExecContext(ctx,
				`INSERT INTO rounds (id, topic_id, round_no) VALUES (UUID(), ?, 0)`,
				topicID)
			log.Printf("orchestrator: topic %s entered debating; round 0 opened", topicID)
			return err
		}); err != nil {
		log.Printf("orchestrator: signup_closed→debating scan: %v", err)
	}

	// Note: there's no explicit `debating → judging` transition in v1.
	// The verdict handler enforces "status==debating AND now>=debate_end_at"
	// as its preconditions; that's equivalent to a "judging" gate without
	// adding a new enum value. Migration 002 will introduce the explicit
	// 'judging' state when we want richer UI (e.g. "Awaiting verdict"
	// distinct from "In debate"); until then this comment serves as the
	// state-machine documentation for future maintainers.
}

// transitionByStatus is the shared "scan + per-row tx + apply" pattern.
// Picks all topics in `currentStatus` whose `dueColumn` <= now, opens a
// tx with SELECT FOR UPDATE, re-checks status (someone else may have
// already moved it), calls apply, commits. Errors per topic logged.
func (t *Ticker) transitionByStatus(ctx context.Context, now time.Time,
	currentStatus models.TopicStatus, dueColumn string,
	apply func(context.Context, *sqlx.Tx, string) error) error {

	// Pull candidate IDs first (no lock); we lock per row inside the loop.
	var ids []string
	q := "SELECT id FROM topics WHERE status = ? AND " + dueColumn + " <= ? LIMIT 50"
	if err := t.db.SelectContext(ctx, &ids, q, currentStatus, now); err != nil {
		return err
	}
	for _, id := range ids {
		if err := t.applyOne(ctx, id, currentStatus, apply); err != nil {
			log.Printf("orchestrator: apply topic=%s: %v", id, err)
		}
	}
	return nil
}

func (t *Ticker) applyOne(ctx context.Context, topicID string,
	expected models.TopicStatus,
	apply func(context.Context, *sqlx.Tx, string) error) error {

	tx, err := t.db.BeginTxx(ctx, nil)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback() }() // safe no-op after commit

	var actual models.TopicStatus
	if err := tx.GetContext(ctx, &actual,
		`SELECT status FROM topics WHERE id = ? FOR UPDATE`, topicID); err != nil {
		return err
	}
	if actual != expected {
		// Already transitioned by some other process — skip.
		return nil
	}
	if err := apply(ctx, tx, topicID); err != nil {
		return err
	}
	return tx.Commit()
}

func (t *Ticker) broadcastAnnouncement(topic *models.Topic) {
	if topic == nil {
		return
	}
	if err := t.announcer.PostTopicAnnouncement(
		context.Background(),
		topic.ID, topic.Title, topic.Summary,
		topic.SignupOpenAt, topic.SignupCloseAt,
		topic.DebateStartAt, topic.DebateEndAt,
		topic.VerdictSchemaID,
	); err != nil {
		log.Printf("orchestrator: announce topic=%s failed: %v", topic.ID, err)
	}
}