// Package slots defines the sixteen code slots each player has. Slots 1-3 hold
// the built-in example programs and are read-only; slots 4-16 belong to the
// player, who saves source code in them and picks one when launching a ship.
package slots

import (
	"io/fs"
	"strings"

	"halcyon/examples"
)

const Count = 16

// builtin lists the example programs, in slot order (slot 1 is the first).
var builtin = []string{"echo", "telemetry", "pursue"}

// FirstUser is the first slot a player can write to.
var FirstUser = len(builtin) + 1

type Slot struct {
	Number  int
	Name    string
	Source  string
	Builtin bool
}

// Valid reports whether n is one of the sixteen slots.
func Valid(n int) bool { return n >= 1 && n <= Count }

// Builtin returns the example that occupies slot n, if it is one of the first three.
func Builtin(n int) (Slot, bool) {
	if n < 1 || n > len(builtin) {
		return Slot{}, false
	}
	src, err := fs.ReadFile(examples.FS, builtin[n-1]+".s")
	if err != nil {
		return Slot{}, false
	}
	return Slot{Number: n, Name: strings.ToUpper(builtin[n-1]), Source: string(src), Builtin: true}, true
}