package storage

import (
	"context"
	"errors"
	"time"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"

	"github.com/alchemistkay/guestguard/internal/domain"
)

// MessageRepo owns the scheduled_messages + message_deliveries pair.
// Tier 2 Block F.
type MessageRepo struct {
	pool *pgxpool.Pool
}

func NewMessageRepo(db *DB) *MessageRepo {
	return &MessageRepo{pool: db.Pool}
}

type CreateMessageParams struct {
	EventID     uuid.UUID
	SendAt      time.Time
	Audience    domain.MessageAudience
	Channel     domain.MessageChannel
	TemplateKey *string
	Subject     *string
	Body        string
	Status      domain.MessageStatus
	CreatedBy   *uuid.UUID
}

// Create inserts a row and returns the persisted message.
func (r *MessageRepo) Create(ctx context.Context, p CreateMessageParams) (*domain.ScheduledMessage, error) {
	const q = `
        INSERT INTO scheduled_messages
            (event_id, send_at, audience, channel, template_key, subject, body, status, created_by)
        VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
        RETURNING id, event_id, send_at, audience, channel, template_key, subject, body,
                  status, sent_at, recipient_count, created_by, created_at, updated_at
    `
	row := r.pool.QueryRow(ctx, q,
		p.EventID, p.SendAt, p.Audience, p.Channel, p.TemplateKey, p.Subject,
		p.Body, p.Status, p.CreatedBy,
	)
	return scanMessage(row)
}

// CreateBatch inserts many messages in one transaction. Used by the
// auto-reminder seeding path on event creation.
func (r *MessageRepo) CreateBatch(ctx context.Context, msgs []domain.ScheduledMessage) error {
	if len(msgs) == 0 {
		return nil
	}
	tx, err := r.pool.Begin(ctx)
	if err != nil {
		return err
	}
	defer tx.Rollback(ctx)

	const q = `
        INSERT INTO scheduled_messages
            (event_id, send_at, audience, channel, template_key, subject, body, status)
        VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
    `
	for _, m := range msgs {
		if _, err := tx.Exec(ctx, q,
			m.EventID, m.SendAt, m.Audience, m.Channel,
			m.TemplateKey, m.Subject, m.Body, m.Status,
		); err != nil {
			return err
		}
	}
	return tx.Commit(ctx)
}

// Get returns a single message by id, scoped to the event so a hostile
// editor on event A can't peek at event B.
func (r *MessageRepo) Get(ctx context.Context, eventID, msgID uuid.UUID) (*domain.ScheduledMessage, error) {
	const q = `
        SELECT id, event_id, send_at, audience, channel, template_key, subject, body,
               status, sent_at, recipient_count, created_by, created_at, updated_at
        FROM scheduled_messages
        WHERE id = $1 AND event_id = $2
    `
	m, err := scanMessage(r.pool.QueryRow(ctx, q, msgID, eventID))
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, domain.ErrMessageNotFound
		}
		return nil, err
	}
	return m, nil
}

// ListByEvent returns every message for the event, newest first.
func (r *MessageRepo) ListByEvent(ctx context.Context, eventID uuid.UUID) ([]domain.ScheduledMessage, error) {
	rows, err := r.pool.Query(ctx, `
        SELECT id, event_id, send_at, audience, channel, template_key, subject, body,
               status, sent_at, recipient_count, created_by, created_at, updated_at
        FROM scheduled_messages
        WHERE event_id = $1
        ORDER BY created_at DESC
    `, eventID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := []domain.ScheduledMessage{}
	for rows.Next() {
		m, err := scanMessage(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, *m)
	}
	return out, rows.Err()
}

type UpdateMessageParams struct {
	SendAt   *time.Time
	Audience *domain.MessageAudience
	Channel  *domain.MessageChannel
	Subject  *string
	Body     *string
}

// Update patches a scheduled message. Refuses unless status='scheduled'
// or 'draft' — once a message is sending/sent/cancelled, edits are not
// safe. Returns ErrMessageNotEditable when the state forbids the edit.
func (r *MessageRepo) Update(ctx context.Context, eventID, msgID uuid.UUID, p UpdateMessageParams) (*domain.ScheduledMessage, error) {
	tx, err := r.pool.Begin(ctx)
	if err != nil {
		return nil, err
	}
	defer tx.Rollback(ctx)

	var status domain.MessageStatus
	if err := tx.QueryRow(ctx, `
        SELECT status FROM scheduled_messages
        WHERE id = $1 AND event_id = $2
        FOR UPDATE
    `, msgID, eventID).Scan(&status); err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, domain.ErrMessageNotFound
		}
		return nil, err
	}
	if status != domain.StatusScheduled && status != domain.StatusDraft {
		return nil, domain.ErrMessageNotEditable
	}

	const upd = `
        UPDATE scheduled_messages
        SET send_at    = COALESCE($3, send_at),
            audience   = COALESCE($4, audience),
            channel    = COALESCE($5, channel),
            subject    = COALESCE($6, subject),
            body       = COALESCE($7, body),
            updated_at = now()
        WHERE id = $1 AND event_id = $2
        RETURNING id, event_id, send_at, audience, channel, template_key, subject, body,
                  status, sent_at, recipient_count, created_by, created_at, updated_at
    `
	m, err := scanMessage(tx.QueryRow(ctx, upd,
		msgID, eventID, p.SendAt, p.Audience, p.Channel, p.Subject, p.Body,
	))
	if err != nil {
		return nil, err
	}
	if err := tx.Commit(ctx); err != nil {
		return nil, err
	}
	return m, nil
}

// Cancel marks a still-scheduled message as cancelled. A sending/sent
// message can't be cancelled.
func (r *MessageRepo) Cancel(ctx context.Context, eventID, msgID uuid.UUID) error {
	tag, err := r.pool.Exec(ctx, `
        UPDATE scheduled_messages
        SET status = 'cancelled', updated_at = now()
        WHERE id = $1 AND event_id = $2
          AND status IN ('draft', 'scheduled')
    `, msgID, eventID)
	if err != nil {
		return err
	}
	if tag.RowsAffected() == 0 {
		return domain.ErrMessageNotEditable
	}
	return nil
}

// PromoteToScheduled flips a draft / future-scheduled row to "send right
// now" by setting send_at and (if needed) status. Powers the
// /messages/{id}/send-now endpoint.
func (r *MessageRepo) PromoteToScheduled(ctx context.Context, eventID, msgID uuid.UUID) error {
	tag, err := r.pool.Exec(ctx, `
        UPDATE scheduled_messages
        SET send_at = now(),
            status  = 'scheduled',
            updated_at = now()
        WHERE id = $1 AND event_id = $2
          AND status IN ('draft', 'scheduled')
    `, msgID, eventID)
	if err != nil {
		return err
	}
	if tag.RowsAffected() == 0 {
		return domain.ErrMessageNotEditable
	}
	return nil
}

// ListDue returns up to `limit` messages whose send_at has passed. The
// scheduler worker calls this every poll interval.
func (r *MessageRepo) ListDue(ctx context.Context, limit int) ([]domain.ScheduledMessage, error) {
	if limit <= 0 || limit > 200 {
		limit = 50
	}
	rows, err := r.pool.Query(ctx, `
        SELECT id, event_id, send_at, audience, channel, template_key, subject, body,
               status, sent_at, recipient_count, created_by, created_at, updated_at
        FROM scheduled_messages
        WHERE status = 'scheduled' AND send_at <= now()
        ORDER BY send_at ASC
        LIMIT $1
    `, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := []domain.ScheduledMessage{}
	for rows.Next() {
		m, err := scanMessage(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, *m)
	}
	return out, rows.Err()
}

// ClaimForSending atomically transitions a single message from
// 'scheduled' to 'sending', returning whether the claim succeeded. Used
// by the worker to avoid two replicas double-sending the same message.
func (r *MessageRepo) ClaimForSending(ctx context.Context, msgID uuid.UUID) (bool, error) {
	tag, err := r.pool.Exec(ctx, `
        UPDATE scheduled_messages
        SET status = 'sending', updated_at = now()
        WHERE id = $1 AND status = 'scheduled'
    `, msgID)
	if err != nil {
		return false, err
	}
	return tag.RowsAffected() == 1, nil
}

// MarkSent flips a 'sending' message to 'sent', recording how many
// recipients the worker actually addressed.
func (r *MessageRepo) MarkSent(ctx context.Context, msgID uuid.UUID, recipientCount int) error {
	_, err := r.pool.Exec(ctx, `
        UPDATE scheduled_messages
        SET status = 'sent',
            sent_at = now(),
            recipient_count = $2,
            updated_at = now()
        WHERE id = $1
    `, msgID, recipientCount)
	return err
}

// MarkFailed parks a message in 'failed' state with no recipients
// dispatched. Used when the worker can't even compose the message
// (event went away, etc.).
func (r *MessageRepo) MarkFailed(ctx context.Context, msgID uuid.UUID) error {
	_, err := r.pool.Exec(ctx, `
        UPDATE scheduled_messages
        SET status = 'failed', updated_at = now()
        WHERE id = $1
    `, msgID)
	return err
}

// RecordDelivery upserts one per-recipient outcome.
func (r *MessageRepo) RecordDelivery(ctx context.Context, d domain.MessageDelivery) error {
	_, err := r.pool.Exec(ctx, `
        INSERT INTO message_deliveries (message_id, guest_id, status, sent_at, error)
        VALUES ($1, $2, $3, $4, $5)
        ON CONFLICT (message_id, guest_id) DO UPDATE SET
            status = EXCLUDED.status,
            sent_at = EXCLUDED.sent_at,
            error = EXCLUDED.error
    `, d.MessageID, d.GuestID, d.Status, d.SentAt, d.Error)
	return err
}

// DeliveryCounts returns "X of Y delivered" for the per-message line in
// the UI without pulling every delivery row.
type DeliveryStats struct {
	Sent   int `json:"sent"`
	Failed int `json:"failed"`
	Total  int `json:"total"`
}

func (r *MessageRepo) DeliveryStats(ctx context.Context, msgID uuid.UUID) (DeliveryStats, error) {
	var s DeliveryStats
	err := r.pool.QueryRow(ctx, `
        SELECT
          count(*) FILTER (WHERE status = 'sent')   AS sent,
          count(*) FILTER (WHERE status IN ('failed','bounced','skipped')) AS failed,
          count(*) AS total
        FROM message_deliveries
        WHERE message_id = $1
    `, msgID).Scan(&s.Sent, &s.Failed, &s.Total)
	return s, err
}

// MessageRecipient is one guest the audience filter resolved to for a
// given message. The notifier renders the body per recipient using
// these fields so {{guest_name}}, {{rsvp_link}}, etc. land correctly.
type MessageRecipient struct {
	GuestID   uuid.UUID
	Name      string
	Email     string
	Phone     string
	TokenHash string // for link reconstruction (host pairs this with the raw token)
}

// LoadRecipients returns the audience-filtered slice of guests for a
// message. Only guests with an email (when channel includes email) or
// phone (when channel includes sms) are returned — others go on the
// skipped pile at delivery time.
func (r *MessageRepo) LoadRecipients(ctx context.Context, eventID uuid.UUID, audience domain.MessageAudience) ([]MessageRecipient, error) {
	// Build the WHERE clause based on audience. We always include
	// guests on the event; the audience condition adds an inner join /
	// filter on rsvps.
	var where string
	switch audience {
	case domain.AudienceAll:
		where = ""
	case domain.AudiencePending:
		where = "AND NOT EXISTS (SELECT 1 FROM rsvps r WHERE r.guest_id = g.id)"
	case domain.AudienceAttending:
		where = "AND EXISTS (SELECT 1 FROM rsvps r WHERE r.guest_id = g.id AND r.response = 'attending')"
	case domain.AudienceDeclined:
		where = "AND EXISTS (SELECT 1 FROM rsvps r WHERE r.guest_id = g.id AND r.response = 'declined')"
	case domain.AudienceMaybe:
		where = "AND EXISTS (SELECT 1 FROM rsvps r WHERE r.guest_id = g.id AND r.response = 'maybe')"
	default:
		return nil, domain.ErrInvalidAudience
	}
	q := `
        SELECT g.id, g.name, COALESCE(g.email,''), COALESCE(g.phone,''),
               COALESCE(t.token_hash, '')
        FROM guests g
        LEFT JOIN tokens t ON t.guest_id = g.id
        WHERE g.event_id = $1
        ` + where + `
        ORDER BY g.created_at ASC
    `
	rows, err := r.pool.Query(ctx, q, eventID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := []MessageRecipient{}
	for rows.Next() {
		var rec MessageRecipient
		if err := rows.Scan(&rec.GuestID, &rec.Name, &rec.Email, &rec.Phone, &rec.TokenHash); err != nil {
			return nil, err
		}
		out = append(out, rec)
	}
	return out, rows.Err()
}

// CountRecipients is the fast-path of LoadRecipients used by the UI's
// "X guests will receive this" preview before send.
func (r *MessageRepo) CountRecipients(ctx context.Context, eventID uuid.UUID, audience domain.MessageAudience) (int, error) {
	recs, err := r.LoadRecipients(ctx, eventID, audience)
	if err != nil {
		return 0, err
	}
	return len(recs), nil
}

func scanMessage(s rowScanner) (*domain.ScheduledMessage, error) {
	var m domain.ScheduledMessage
	err := s.Scan(
		&m.ID, &m.EventID, &m.SendAt, &m.Audience, &m.Channel,
		&m.TemplateKey, &m.Subject, &m.Body,
		&m.Status, &m.SentAt, &m.RecipientCount, &m.CreatedBy,
		&m.CreatedAt, &m.UpdatedAt,
	)
	if err != nil {
		return nil, err
	}
	return &m, nil
}