package main import ( "database/sql" "fmt" "math" "math/rand" ) var ( index map[int]System ) type System struct { x, y, z float64 planets int name string } func (e System) Store(db *sql.DB) { _, err := db.Exec(` insert into planets (name, x, y, z, planets) values (?, ?, ?, ?, ?) ;`, e.name, e.x, e.y, e.z, e.planets) if err != nil { log_error("%v", err) } } func (e System) String() string { return fmt.Sprintf("", e.name, e.x, e.y, e.z, e.planets) } func countPlanets() (int, error) { row := db.QueryRow(`select count(*) from planets`) var n int err := row.Scan(&n) return n, err } func sq(x float64) float64 { return x * x } func dist3d(x1, y1, z1, x2, y2, z2 float64) float64 { return math.Sqrt(sq(x1-x2) + sq(y1-y2) + sq(z1-z2)) } func planetDistance(p1, p2 System) float64 { return dist3d(p1.x, p1.y, p1.z, p2.x, p2.y, p2.z) } func indexPlanets(db *sql.DB) map[int]System { rows, err := db.Query(`select * from planets`) if err != nil { log_error("unable to select all planets: %v", err) return nil } defer rows.Close() index = make(map[int]System, 551) for rows.Next() { var id int p := System{} if err := rows.Scan(&id, &p.name, &p.x, &p.y, &p.z, &p.planets); err != nil { log_info("unable to scan planet row: %v", err) continue } index[id] = p } return index } func randomPlanet() (*System, error) { n := len(index) if n == 0 { return nil, fmt.Errorf("no planets are known to exist") } pick := rand.Intn(n) planet := index[pick] return &planet, nil }