// Package backends implements CRUD against the `backends` table.
// Ein Backend ist ein Pool — Name, Scheme, Healthcheck, LB-Algorithm,
// WebSocket-Flag. Die konkreten Upstream-Server liegen in
// backend_servers (siehe services/backendservers).
package backends

import (
	"context"
	"errors"

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

	"git.netcell-it.de/projekte/edgeguard-native/internal/models"
)

var (
	ErrNotFound = errors.New("backend not found")
	ErrInUse    = errors.New("backend is referenced by one or more routing rules")
)

type Repo struct {
	Pool *pgxpool.Pool
}

func New(pool *pgxpool.Pool) *Repo { return &Repo{Pool: pool} }

const baseSelect = `
SELECT id, name, scheme, health_check_path, lb_algorithm, websocket, force_http1, active,
       created_at, updated_at
FROM backends
`

func (r *Repo) List(ctx context.Context) ([]models.Backend, error) {
	rows, err := r.Pool.Query(ctx, baseSelect+" ORDER BY name ASC")
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := make([]models.Backend, 0, 16)
	for rows.Next() {
		b, err := scanBackend(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, *b)
	}
	return out, rows.Err()
}

func (r *Repo) Get(ctx context.Context, id int64) (*models.Backend, error) {
	row := r.Pool.QueryRow(ctx, baseSelect+" WHERE id = $1", id)
	b, err := scanBackend(row)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, ErrNotFound
		}
		return nil, err
	}
	return b, nil
}

func (r *Repo) Create(ctx context.Context, b models.Backend) (*models.Backend, error) {
	if b.LBAlgorithm == "" {
		b.LBAlgorithm = "roundrobin"
	}
	row := r.Pool.QueryRow(ctx, `
INSERT INTO backends (name, scheme, health_check_path, lb_algorithm, websocket, force_http1, active)
VALUES ($1, $2, $3, $4, $5, $6, $7)
RETURNING id, name, scheme, health_check_path, lb_algorithm, websocket, force_http1, active,
          created_at, updated_at`,
		b.Name, b.Scheme, b.HealthCheckPath, b.LBAlgorithm, b.WebSocket, b.ForceHTTP1, b.Active)
	return scanBackend(row)
}

func (r *Repo) Update(ctx context.Context, id int64, b models.Backend) (*models.Backend, error) {
	if b.LBAlgorithm == "" {
		b.LBAlgorithm = "roundrobin"
	}
	row := r.Pool.QueryRow(ctx, `
UPDATE backends SET
   name = $1,
   scheme = $2,
   health_check_path = $3,
   lb_algorithm = $4,
   websocket = $5,
   force_http1 = $6,
   active = $7,
   updated_at = NOW()
WHERE id = $8
RETURNING id, name, scheme, health_check_path, lb_algorithm, websocket, force_http1, active,
          created_at, updated_at`,
		b.Name, b.Scheme, b.HealthCheckPath, b.LBAlgorithm, b.WebSocket, b.ForceHTTP1, b.Active, id)
	out, err := scanBackend(row)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, ErrNotFound
		}
		return nil, err
	}
	return out, nil
}

func (r *Repo) Delete(ctx context.Context, id int64) error {
	var n int
	if err := r.Pool.QueryRow(ctx,
		`SELECT COUNT(*) FROM routing_rules WHERE backend_id = $1`, id,
	).Scan(&n); err != nil {
		return err
	}
	if n > 0 {
		return ErrInUse
	}
	tag, err := r.Pool.Exec(ctx, `DELETE FROM backends WHERE id = $1`, id)
	if err != nil {
		return err
	}
	if tag.RowsAffected() == 0 {
		return ErrNotFound
	}
	return nil
}

func scanBackend(row interface{ Scan(...any) error }) (*models.Backend, error) {
	var b models.Backend
	if err := row.Scan(
		&b.ID, &b.Name, &b.Scheme,
		&b.HealthCheckPath, &b.LBAlgorithm, &b.WebSocket, &b.ForceHTTP1, &b.Active,
		&b.CreatedAt, &b.UpdatedAt,
	); err != nil {
		return nil, err
	}
	return &b, nil
}