package keymgr

import "ssh-access-tui/internal/model"

// AllocatedForward is a model.Forward together with the local port it will
// be bound to on the user's machine.
type AllocatedForward struct {
	model.Forward
	LocalPort int
}

// localPortBase is where fallback local ports are handed out from once a
// forward's natural remote port is already taken locally by another
// forward. Chosen high enough to avoid colliding with well-known ports the
// user's own machine might already be using.
const localPortBase = 20000

// AllocateLocalPorts assigns every forward a local port, all of which the
// user opens at once over a single ssh connection (one LocalForward line
// per forward — see RenderClientConfig). This is the actual answer to
// "avoid collisions when forwarding everything simultaneously": many hosts
// commonly expose the same remote port (e.g. 22, or an app port like 7888
// repeated across ten hosts), but only one of them can bind to that same
// port number locally. Each forward keeps its remote port as the local
// port when that's still free (so the common case reads naturally, e.g.
// remote 7888 -> local 7888), and falls back to the next free port from
// localPortBase upward on collision. Assignment is a pure function of the
// input order and set, so re-exporting an unchanged host list reproduces
// the same local ports.
func AllocateLocalPorts(forwards []model.Forward) []AllocatedForward {
	used := make(map[int]bool, len(forwards))
	next := localPortBase
	out := make([]AllocatedForward, 0, len(forwards))
	for _, f := range forwards {
		lp := f.Port
		if lp <= 0 || lp > 65535 || used[lp] {
			for used[next] {
				next++
			}
			lp = next
			next++
		}
		used[lp] = true
		out = append(out, AllocatedForward{Forward: f, LocalPort: lp})
	}
	return out
}