package storage

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"time"

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

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

type RSVPRepo struct {
	pool *pgxpool.Pool
}

func NewRSVPRepo(db *DB) *RSVPRepo {
	return &RSVPRepo{pool: db.Pool}
}

type CreateRSVPParams struct {
	GuestID           uuid.UUID
	Response          domain.RSVPResponse
	PlusOnes          int
	DietaryNotes      *string
	DeviceFingerprint map[string]any
	IPAddress         string
	RiskScore         *int
}

func (r *RSVPRepo) Create(ctx context.Context, p CreateRSVPParams) (*domain.RSVP, error) {
	var fpJSON []byte
	if p.DeviceFingerprint != nil {
		b, err := json.Marshal(p.DeviceFingerprint)
		if err != nil {
			return nil, fmt.Errorf("marshal fingerprint: %w", err)
		}
		fpJSON = b
	}

	var ip *string
	if p.IPAddress != "" {
		ip = &p.IPAddress
	}

	const q = `
        INSERT INTO rsvps (guest_id, response, plus_ones, dietary_notes,
                           device_fingerprint, ip_address, risk_score)
        VALUES ($1, $2, $3, $4, $5, $6::inet, $7)
        RETURNING id, guest_id, response, plus_ones, dietary_notes,
                  submitted_at, device_fingerprint, ip_address::text, risk_score,
                  edit_count
    `

	row := r.pool.QueryRow(ctx, q,
		p.GuestID, p.Response, p.PlusOnes, p.DietaryNotes,
		fpJSON, ip, p.RiskScore,
	)

	rs, err := scanRSVP(row)
	if err != nil {
		var pgErr *pgconn.PgError
		if errors.As(err, &pgErr) && pgErr.Code == "23505" {
			return nil, domain.ErrRSVPAlreadySubmitted
		}
		return nil, err
	}
	return rs, nil
}

// GetByGuest returns the RSVP submitted by `guestID`, or ErrRSVPNotFound when
// none exists yet. Used by /access/{token} to surface the current submission
// so the frontend can show an edit form, and by PATCH /rsvp to load the row
// being revised.
func (r *RSVPRepo) GetByGuest(ctx context.Context, guestID uuid.UUID) (*domain.RSVP, error) {
	const q = `
        SELECT id, guest_id, response, plus_ones, dietary_notes,
               submitted_at, device_fingerprint, ip_address::text, risk_score,
               edit_count
        FROM rsvps WHERE guest_id = $1
    `
	rs, err := scanRSVP(r.pool.QueryRow(ctx, q, guestID))
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, domain.ErrRSVPNotFound
		}
		return nil, err
	}
	return rs, nil
}

type UpdateRSVPParams struct {
	GuestID           uuid.UUID
	Response          domain.RSVPResponse
	PlusOnes          int
	DietaryNotes      *string
	DeviceFingerprint map[string]any
	IPAddress         string
	RiskScore         *int
}

// Update applies a revision to the guest's RSVP. The previous values are
// snapshotted into rsvp_revisions inside the same transaction so the history
// is consistent — either both the snapshot and the new state land, or neither
// does. Returns ErrRSVPEditLimitReached if the guest has already hit
// MaxRSVPEdits; the row itself is left untouched.
func (r *RSVPRepo) Update(ctx context.Context, p UpdateRSVPParams) (*domain.RSVP, error) {
	var fpJSON []byte
	if p.DeviceFingerprint != nil {
		b, err := json.Marshal(p.DeviceFingerprint)
		if err != nil {
			return nil, fmt.Errorf("marshal fingerprint: %w", err)
		}
		fpJSON = b
	}

	var ip *string
	if p.IPAddress != "" {
		ip = &p.IPAddress
	}

	tx, err := r.pool.Begin(ctx)
	if err != nil {
		return nil, err
	}
	defer tx.Rollback(ctx)

	// SELECT ... FOR UPDATE locks the row so two concurrent edits can't both
	// snapshot the same prior state and both increment edit_count past the cap.
	var (
		rsvpID       uuid.UUID
		prevResp     domain.RSVPResponse
		prevPlusOnes int
		prevDietary  *string
		editCount    int
	)
	err = tx.QueryRow(ctx, `
        SELECT id, response, plus_ones, dietary_notes, edit_count
        FROM rsvps WHERE guest_id = $1
        FOR UPDATE
    `, p.GuestID).Scan(&rsvpID, &prevResp, &prevPlusOnes, &prevDietary, &editCount)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, domain.ErrRSVPNotFound
		}
		return nil, err
	}
	if editCount >= domain.MaxRSVPEdits {
		return nil, domain.ErrRSVPEditLimitReached
	}

	if _, err := tx.Exec(ctx, `
        INSERT INTO rsvp_revisions (rsvp_id, prev_response, prev_plus_ones, prev_dietary)
        VALUES ($1, $2, $3, $4)
    `, rsvpID, prevResp, prevPlusOnes, prevDietary); err != nil {
		return nil, fmt.Errorf("snapshot revision: %w", err)
	}

	const upd = `
        UPDATE rsvps
        SET response = $2,
            plus_ones = $3,
            dietary_notes = $4,
            device_fingerprint = COALESCE($5, device_fingerprint),
            ip_address = COALESCE($6::inet, ip_address),
            risk_score = COALESCE($7, risk_score),
            submitted_at = now(),
            edit_count = edit_count + 1
        WHERE guest_id = $1
        RETURNING id, guest_id, response, plus_ones, dietary_notes,
                  submitted_at, device_fingerprint, ip_address::text, risk_score,
                  edit_count
    `
	row := tx.QueryRow(ctx, upd,
		p.GuestID, p.Response, p.PlusOnes, p.DietaryNotes,
		fpJSON, ip, p.RiskScore,
	)
	rs, err := scanRSVP(row)
	if err != nil {
		return nil, err
	}
	if err := tx.Commit(ctx); err != nil {
		return nil, err
	}
	return rs, nil
}

// ListRevisions returns every prior state of an RSVP, newest first. Empty
// slice (not nil) when there are no revisions, so the JSON encodes as `[]`.
func (r *RSVPRepo) ListRevisions(ctx context.Context, rsvpID uuid.UUID) ([]domain.RSVPRevision, error) {
	const q = `
        SELECT id, rsvp_id, prev_response, prev_plus_ones, prev_dietary, changed_at
        FROM rsvp_revisions
        WHERE rsvp_id = $1
        ORDER BY changed_at DESC
    `
	rows, err := r.pool.Query(ctx, q, rsvpID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	out := []domain.RSVPRevision{}
	for rows.Next() {
		var rev domain.RSVPRevision
		if err := rows.Scan(
			&rev.ID, &rev.RSVPID, &rev.PrevResponse,
			&rev.PrevPlusOnes, &rev.PrevDietary, &rev.ChangedAt,
		); err != nil {
			return nil, err
		}
		out = append(out, rev)
	}
	return out, rows.Err()
}

// RSVPActivity is a denormalised RSVP entry for the activity feed —
// includes the guest's name so the API can hand it to the frontend
// without a separate lookup.
type RSVPActivity struct {
	GuestID     uuid.UUID
	GuestName   string
	Response    string
	PlusOnes    int
	SubmittedAt time.Time
}

// ListRecentByEvent returns the most recent RSVPs for an event, newest first.
func (r *RSVPRepo) ListRecentByEvent(ctx context.Context, eventID uuid.UUID, limit int) ([]RSVPActivity, error) {
	if limit <= 0 || limit > 200 {
		limit = 50
	}
	const q = `
        SELECT r.guest_id, g.name, r.response, r.plus_ones, r.submitted_at
        FROM rsvps r
        JOIN guests g ON g.id = r.guest_id
        WHERE g.event_id = $1
        ORDER BY r.submitted_at DESC
        LIMIT $2
    `
	rows, err := r.pool.Query(ctx, q, eventID, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var out []RSVPActivity
	for rows.Next() {
		var a RSVPActivity
		if err := rows.Scan(&a.GuestID, &a.GuestName, &a.Response, &a.PlusOnes, &a.SubmittedAt); err != nil {
			return nil, err
		}
		out = append(out, a)
	}
	return out, rows.Err()
}

func scanRSVP(s rowScanner) (*domain.RSVP, error) {
	var (
		rs     domain.RSVP
		fpJSON []byte
		ip     *string
	)
	err := s.Scan(
		&rs.ID, &rs.GuestID, &rs.Response, &rs.PlusOnes, &rs.DietaryNotes,
		&rs.SubmittedAt, &fpJSON, &ip, &rs.RiskScore, &rs.EditCount,
	)
	if err != nil {
		return nil, err
	}
	if len(fpJSON) > 0 {
		_ = json.Unmarshal(fpJSON, &rs.DeviceFingerprint)
	}
	if ip != nil {
		rs.IPAddress = ip
	}
	return &rs, nil
}