package lua

import (
	"encoding/json"
	"os"
)

// Kernel action grants are OPERATOR policy, persisted separately from both
// plugin state and the endpoint/visibility overrides.
//
// Why a separate file rather than reusing .access.json:
//
//   - .access.json is a flat map[string]string ("name" or "name#path" -> spec).
//     Kernel grants are a list plus a boolean, so folding them in would either
//     change the shape of a file an older binary still reads, or force an
//     encoding that cannot round-trip. An upgrade must not corrupt a running
//     deployment's restrictions.
//   - The two answer different questions — "who may call this endpoint" vs
//     "what may this plugin do to the kernel" — and an operator looking at one
//     should not have to parse the other.
//
// Shape: { "<plugin>": { "actions": ["reload", ...], "all_read": true } }

const kernelPermsFileName = ".kernel-perms.json"

func (ps *Plugins) kernelPermsFile() string {
	if ps.dir == "" {
		return ""
	}
	return ps.dir + string(os.PathSeparator) + kernelPermsFileName
}

// LoadKernelPermissions reads the persisted grants. A missing file is the normal
// fresh-install state (nothing granted); a corrupt file is logged and ignored
// rather than fatal — losing a grant is recoverable, refusing to boot is not.
func (ps *Plugins) LoadKernelPermissions() error {
	path := ps.kernelPermsFile()
	if path == "" {
		return nil
	}
	b, err := os.ReadFile(path)
	if os.IsNotExist(err) {
		return nil
	}
	if err != nil {
		return err
	}
	raw := map[string]jsonPermission{}
	if err := json.Unmarshal(b, &raw); err != nil {
		return err
	}
	ps.mu.Lock()
	defer ps.mu.Unlock()
	if ps.kernelPerms == nil {
		ps.kernelPerms = kernelPermissionSet{}
	}
	for name, jp := range raw {
		ps.kernelPerms[name] = jp.unmarshal()
	}
	return nil
}

// saveKernelPermissionsLocked flushes the grant map. Caller holds ps.mu.
//
// Grants drop unknown action names on write. If an operator authorized an action
// that a later release removed, keeping the name would leave a stale entry that
// nothing can ever satisfy — and it would reappear in the UI as if it were live.
func (ps *Plugins) saveKernelPermissionsLocked() {
	path := ps.kernelPermsFile()
	if path == "" {
		return
	}
	out := map[string]jsonPermission{}
	for name, perm := range ps.kernelPerms {
		valid := make([]string, 0, len(perm.Actions))
		for _, a := range perm.Actions {
			if _, ok := LookupKernelAction(a); ok {
				valid = append(valid, a)
			}
		}
		if len(valid) == 0 && !perm.AllRead {
			continue // nothing granted: presence would be a lie
		}
		out[name] = KernelPermission{Actions: valid, AllRead: perm.AllRead}.marshal()
	}
	if len(out) == 0 {
		_ = os.Remove(path)
		return
	}
	writeJSONAtomic(path, out)
}