system: isolate app/system into generic implementation

This improves maintainability and extensibility of system operations, makes writing tests for them possible, and operations now apply and revert in order, instead of being bunched up into their own categories.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

internal/system/xhost.go

@@ -0,0 +1,54 @@
+package system
+
+import (
+	"fmt"
+
+	"git.ophivana.moe/cat/fortify/internal/fmsg"
+	"git.ophivana.moe/cat/fortify/internal/state"
+	"git.ophivana.moe/cat/fortify/internal/verbose"
+	"git.ophivana.moe/cat/fortify/xcb"
+)
+
+// ChangeHosts appends an X11 ChangeHosts command Op.
+func (sys *I) ChangeHosts(username string) {
+	sys.lock.Lock()
+	defer sys.lock.Unlock()
+
+	sys.ops = append(sys.ops, XHost(username))
+}
+
+type XHost string
+
+func (x XHost) Type() state.Enablement {
+	return state.EnableX
+}
+
+func (x XHost) apply(_ *I) error {
+	verbose.Printf("inserting entry %s to X11\n", x)
+	return fmsg.WrapErrorSuffix(xcb.ChangeHosts(xcb.HostModeInsert, xcb.FamilyServerInterpreted, "localuser\x00"+string(x)),
+		fmt.Sprintf("cannot insert entry %s to X11:", x))
+}
+
+func (x XHost) revert(_ *I, ec *Criteria) error {
+	if ec.hasType(x) {
+		verbose.Printf("deleting entry %s from X11\n", x)
+		return fmsg.WrapErrorSuffix(xcb.ChangeHosts(xcb.HostModeDelete, xcb.FamilyServerInterpreted, "localuser\x00"+string(x)),
+			fmt.Sprintf("cannot delete entry %s from X11:", x))
+	} else {
+		verbose.Printf("skipping entry %s in X11\n", x)
+		return nil
+	}
+}
+
+func (x XHost) Is(o Op) bool {
+	x0, ok := o.(XHost)
+	return ok && x == x0
+}
+
+func (x XHost) Path() string {
+	return string(x)
+}
+
+func (x XHost) String() string {
+	return string("SI:localuser:" + x)
+}