package role

import (
	"slices"
	"strings"
)

type MissingPermissionError struct {
	Key string
}

func (e MissingPermissionError) Error() string {
	return ErrMissingPermission.Error() + ": " + e.Key
}

func (e MissingPermissionError) Is(target error) bool {
	return target == ErrMissingPermission
}

type GrantSet struct {
	scopes map[string]Scope
}

func (r Role) GrantSet() GrantSet {
	scopes := make(map[string]Scope, len(r.Grants))
	for _, grant := range r.Grants {
		permission, err := resolveGrantKey(grant.Key)
		if err != nil || permission.OwnerOnly && !r.Locked {
			continue
		}
		scope := effectiveScope(permission.Kind, grant.Scope)
		if held, present := scopes[grant.Key]; present {
			scope = mostRestrictive(held, scope)
		}
		scopes[grant.Key] = scope
	}
	return GrantSet{scopes: scopes}
}

func effectiveScope(kind Kind, scope Scope) Scope {
	if scope == ScopeAll {
		return ScopeAll
	}
	if scope == ScopeOwn && kind == KindScoped {
		return ScopeOwn
	}
	return ScopeNone
}

func scopeRank(scope Scope) int {
	switch scope {
	case ScopeAll:
		return 2
	case ScopeOwn:
		return 1
	default:
		return 0
	}
}

func mostRestrictive(left Scope, right Scope) Scope {
	if scopeRank(left) <= scopeRank(right) {
		return left
	}
	return right
}

func (g GrantSet) ScopeFor(key string, typeKey string) Scope {
	if typeKey == "" {
		return g.wildcard(key)
	}
	composite := key + typeSeparator + typeKey
	if _, _, err := ParseTypedKey(composite); err != nil {
		return ScopeNone
	}
	if scope, present := g.scopes[composite]; present {
		return scope
	}
	return g.wildcard(key)
}

func (g GrantSet) wildcard(key string) Scope {
	if isTypedKey(key) {
		return ScopeNone
	}
	scope, present := g.scopes[key]
	if !present {
		return ScopeNone
	}
	return scope
}

func (g GrantSet) Permits(key string, typeKey string, callerID uint32, createdBy uint32) bool {
	return ScopePermits(g.ScopeFor(key, typeKey), callerID, createdBy)
}

func ScopePermits(scope Scope, callerID uint32, createdBy uint32) bool {
	switch scope {
	case ScopeAll:
		return true
	case ScopeOwn:
		return callerID != 0 && callerID == createdBy
	default:
		return false
	}
}

func (g GrantSet) HoldsFor(key string, typeKey string) bool {
	return g.ScopeFor(key, typeKey) != ScopeNone
}

func (g GrantSet) Holds(key string) bool {
	return g.HoldsFor(key, "")
}

func (g GrantSet) HoldsAll(key string) bool {
	return g.ScopeFor(key, "") == ScopeAll
}

type EscalationError struct {
	Key string
}

func (e EscalationError) Error() string {
	return ErrEscalation.Error() + ": " + e.Key
}

func (e EscalationError) Is(target error) bool {
	return target == ErrEscalation
}

func (g GrantSet) Covers(other GrantSet, typeKeys []string) error {
	sortedTypeKeys := slices.Sorted(slices.Values(typeKeys))
	for _, permission := range catalogue {
		if scopeRank(other.ScopeFor(permission.Key, "")) > scopeRank(g.ScopeFor(permission.Key, "")) {
			return EscalationError{Key: permission.Key}
		}
		if !permission.PerType() {
			continue
		}
		for _, typeKey := range sortedTypeKeys {
			if scopeRank(other.ScopeFor(permission.Key, typeKey)) > scopeRank(g.ScopeFor(permission.Key, typeKey)) {
				return EscalationError{Key: permission.Key + typeSeparator + typeKey}
			}
		}
	}
	return nil
}

func (g GrantSet) Effective() []Grant {
	effective := []Grant{}
	for _, permission := range catalogue {
		if scope := g.wildcard(permission.Key); scope != ScopeNone {
			effective = append(effective, Grant{Key: permission.Key, Scope: scope})
		}
		if permission.PerType() {
			effective = append(effective, g.typedGrants(permission.Key)...)
		}
	}
	return effective
}

func (g GrantSet) typedGrants(key string) []Grant {
	prefix := key + typeSeparator
	composites := []string{}
	for composite := range g.scopes {
		if strings.HasPrefix(composite, prefix) {
			composites = append(composites, composite)
		}
	}
	slices.Sort(composites)
	typed := make([]Grant, 0, len(composites))
	for _, composite := range composites {
		typed = append(typed, Grant{Key: composite, Scope: g.scopes[composite]})
	}
	return typed
}

func (r Role) EffectiveGrants() []Grant {
	return r.GrantSet().Effective()
}