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>

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}
+}