1 files changed, 126 insertions, 0 deletions
diff --git a/internal/system/op.go b/internal/system/op.go
new file mode 100644
index 00000000..c3f93cdb
--- /dev/null
+++ b/internal/system/op.go
@@ -0,0 +1,126 @@
+package system
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+
+	"git.ophivana.moe/cat/fortify/internal/state"
+)
+
+const (
+	// Process type is unconditionally reverted on exit.
+	Process = state.EnableLength + 1
+	// User type is reverted at final launcher exit.
+	User = state.EnableLength
+)
+
+type Criteria struct {
+	*state.Enablements
+}
+
+func (ec *Criteria) hasType(o Op) bool {
+	// nil criteria: revert everything except User
+	if ec.Enablements == nil {
+		return o.Type() != User
+	}
+
+	return ec.Has(o.Type())
+}
+
+// Op is a reversible system operation.
+type Op interface {
+	// Type returns Op's enablement type.
+	Type() state.Enablement
+
+	// apply the Op
+	apply(sys *I) error
+	// revert reverses the Op if criteria is met
+	revert(sys *I, ec *Criteria) error
+
+	Is(o Op) bool
+	Path() string
+	String() string
+}
+
+func TypeString(e state.Enablement) string {
+	switch e {
+	case User:
+		return "User"
+	case Process:
+		return "Process"
+	default:
+		return e.String()
+	}
+}
+
+type I struct {
+	uid int
+	ops []Op
+
+	state [2]bool
+	lock  sync.Mutex
+}
+
+func (sys *I) UID() int {
+	return sys.uid
+}
+
+func (sys *I) Commit() error {
+	sys.lock.Lock()
+	defer sys.lock.Unlock()
+
+	if sys.state[0] {
+		panic("sys instance committed twice")
+	}
+	sys.state[0] = true
+
+	sp := New(sys.uid)
+	sp.ops = make([]Op, 0, len(sys.ops)) // prevent copies during commits
+	defer func() {
+		// sp is set to nil when all ops are applied
+		if sp != nil {
+			// rollback partial commit
+			if err := sp.Revert(&Criteria{nil}); err != nil {
+				fmt.Println("fortify: errors returned reverting partial commit:", err)
+			}
+		}
+	}()
+
+	for _, o := range sys.ops {
+		if err := o.apply(sys); err != nil {
+			return err
+		} else {
+			// register partial commit
+			sp.ops = append(sp.ops, o)
+		}
+	}
+
+	// disarm partial commit rollback
+	sp = nil
+	return nil
+}
+
+func (sys *I) Revert(ec *Criteria) error {
+	sys.lock.Lock()
+	defer sys.lock.Unlock()
+
+	if sys.state[1] {
+		panic("sys instance reverted twice")
+	}
+	sys.state[1] = true
+
+	// collect errors
+	errs := make([]error, len(sys.ops))
+
+	for i := range sys.ops {
+		errs[i] = sys.ops[len(sys.ops)-i-1].revert(sys, ec)
+	}
+
+	// errors.Join filters nils
+	return errors.Join(errs...)
+}
+
+func New(uid int) *I {
+	return &I{uid: uid}
+}