package lua

import "strings"

// One vocabulary for "who may see / read / call this".
//
// Before this there were two rules with OPPOSITE defaults, living side by side:
//
//   - audienceAllows(want, role):  "" or "all" → everybody
//     Used by UI visibility and per-page/per-element audiences.
//   - HTTPHandler.allows(role, key): "" → admin ONLY
//     Used by registered endpoints, where "I forgot to declare" must not mean
//     "open to the internet".
//
// Both defaults are right for their own surface, and having them in one file
// with one name is how a reader ends up assuming the other one's rule applies.
// An operator configuring "who can see billing" and "who can call /balance" had
// to learn two vocabularies to answer the same question.
//
// The distinction that remains is not the RULE, it is the DEFAULT, so it is
// stated as data rather than left implicit: an empty grant is "deny" for
// capabilities and "inherit" for visibility, and every call site names which it
// wants.

// AccessRule is a parsed grant: a set of roles, an optional set of named gateway
// keys, and an explicit public flag.
//
// Keys REPLACE roles rather than adding to them. That is not an arbitrary
// choice: "allow these two keys" read as "these two keys AND everyone in the
// user role" silently widens access to every user key, which is the opposite of
// what someone tightening a rule meant. `keys = { "@alice" }` therefore means
// exactly alice.
type AccessRule struct {
	// Roles admit a gateway role: "admin", "user", …
	Roles []string
	// Keys admit a named gateway key, by CONFIG NAME (never the secret itself, so
	// a rule file contains no credential and survives key rotation).
	Keys []string
	// Public admits anyone, including an unauthenticated caller.
	Public bool
}

// AccessAll is the grant that admits everyone.
func AccessAll() AccessRule { return AccessRule{Public: true} }

// ParseAccessRule reads the one grant syntax the plugin API accepts:
//
//	"admin"                        roles
//	"admin, user"                  roles
//	"@alice, @bob"                 named keys, replacing the role rule
//	"user, @alice"                 the named keys plus the roles (union)
//	"public"                       anyone
//	"all"                          anyone (the older spelling of public)
//	""                             empty — meaning depends on the caller
//
// An "@name" token is a key, anything else is a role. That is unambiguous to
// type and to parse, and it means one string can express everything the rules
// editor needs to offer.
//
// "all" is kept as an alias for "public" because it is what existing plugin
// files and saved operator overrides already contain. Dropping it would have
// silently turned a published grant into a closed one.
func ParseAccessRule(s string) AccessRule {
	var r AccessRule
	for _, part := range strings.Split(s, ",") {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		if strings.EqualFold(part, "public") || strings.EqualFold(part, "all") {
			r.Public = true
			continue
		}
		if strings.HasPrefix(part, "@") {
			if k := strings.TrimSpace(strings.TrimPrefix(part, "@")); k != "" {
				r.Keys = append(r.Keys, k)
			}
			continue
		}
		r.Roles = append(r.Roles, part)
	}
	return r
}

// Rule renders the grant back to the syntax ParseAccessRule accepts. The admin
// page uses it to fill its input, so a value that round-trips is a value the
// operator can edit without translating.
func (r AccessRule) Rule() string {
	var parts []string
	for _, k := range r.Keys {
		parts = append(parts, "@"+k)
	}
	for _, role := range r.Roles {
		parts = append(parts, role)
	}
	if r.Public {
		parts = append(parts, "public")
	}
	return strings.Join(parts, ", ")
}

// Empty reports whether the grant names nobody.
func (r AccessRule) Empty() bool {
	return len(r.Roles) == 0 && len(r.Keys) == 0 && !r.Public
}

// AllowsCapability reports whether a CAPABILITY (an endpoint, a callable
// function) is reachable. Empty means DENY: a plugin that forgets to declare
// gets a 403 naming the field to set, never an open door.
//
// Admin is always admitted. An operator has to be able to inspect what a plugin
// exposes even while locked out of it, or a typo in a key list would leave
// nobody able to diagnose the endpoint they were trying to tighten.
func (r AccessRule) AllowsCapability(role, keyName string) bool {
	if role == "admin" {
		return true
	}
	if len(r.Keys) > 0 {
		// A non-empty key list REPLACES the role rule (see the type comment).
		// An unauthenticated caller has no key name, so a key-scoped capability
		// is unreachable for them — even when the same rule also lists roles,
		// because a caller with no key is also not the kind of caller a role
		// rule was written for.
		if keyName == "" {
			return false
		}
		for _, k := range r.Keys {
			if strings.EqualFold(k, keyName) {
				return true
			}
		}
		// The key list replaced the role rule, so a miss is a deny even though
		// roles may also be listed.
		return false
	}
	if r.Public {
		return true
	}
	for _, want := range r.Roles {
		if strings.EqualFold(want, role) {
			return true
		}
	}
	return false
}

// AllowsVisibility reports whether a VIEW (a page, a UI element) is rendered.
// Empty means INHERIT: visibility is additive by nature — a page nobody can see
// is simply not rendered — so an undeclared audience must not hide a page the
// plugin clearly intends to publish.
func (r AccessRule) AllowsVisibility(role string) bool {
	if r.Empty() || r.Public {
		return true
	}
	if role == "admin" && len(r.Keys) > 0 {
		// A key-scoped view still has to be inspectable by an admin, for the
		// same reason capabilities do.
		return true
	}
	for _, want := range r.Roles {
		if strings.EqualFold(want, role) {
			return true
		}
	}
	return false
}

// accessRuleFor folds the separate declaration fields of an endpoint into one
// grant, so the rules below live in one place instead of beside each field.
//
// It is a plain fold, deliberately. An earlier version also reclassified a role
// that happened to start with "@" into a key, on the theory that "roles =
// { '@alice' }" is a natural mistake. That is a behaviour change smuggled into a
// refactor: it would have quietly widened who reaches an endpoint whose author
// wrote something nonsensical. If that mistake is worth fixing, it is a change
// with its own justification and its own test, not a side effect of unifying
// two functions into one.
func accessRuleFor(roles, keys []string, public bool) AccessRule {
	return AccessRule{Roles: roles, Keys: keys, Public: public}
}