/*
RBAC — Role-Based Access Control for Volt.

Defines roles with granular permissions, assigns users/groups to roles,
and enforces access control on all CLI/API operations.

Roles are stored as YAML in /etc/volt/rbac/. The system ships with
four built-in roles (admin, operator, deployer, viewer) and supports
custom roles.

Enforcement: Commands call rbac.Require(user, permission) before executing.
The user identity comes from:
  1. $VOLT_USER environment variable
  2. OS user (via os/user.Current())
  3. SSO token (future)

Permission model is action-based:
  - "containers.create", "containers.delete", "containers.start", etc.
  - "deploy.rolling", "deploy.canary", "deploy.rollback"
  - "config.read", "config.write"
  - "admin.*" (wildcard for full access)

Copyright (c) Armored Gates LLC. All rights reserved.
*/
package rbac

import (
	"fmt"
	"os"
	"os/user"
	"path/filepath"
	"strings"
	"sync"

	"gopkg.in/yaml.v3"
)

// ── Constants ────────────────────────────────────────────────────────────────

const (
	// DefaultRBACDir is where role and binding files are stored.
	DefaultRBACDir = "/etc/volt/rbac"

	// RolesFile stores role definitions.
	RolesFile = "roles.yaml"

	// BindingsFile stores user/group → role mappings.
	BindingsFile = "bindings.yaml"
)

// ── Built-in Roles ───────────────────────────────────────────────────────────

// Role defines a named set of permissions.
type Role struct {
	Name        string   `yaml:"name" json:"name"`
	Description string   `yaml:"description" json:"description"`
	Permissions []string `yaml:"permissions" json:"permissions"`
	BuiltIn     bool     `yaml:"builtin,omitempty" json:"builtin,omitempty"`
}

// Binding maps a user or group to a role.
type Binding struct {
	Subject     string `yaml:"subject" json:"subject"`         // username or group:name
	SubjectType string `yaml:"subject_type" json:"subject_type"` // "user" or "group"
	Role        string `yaml:"role" json:"role"`
}

// RBACConfig holds the full RBAC state.
type RBACConfig struct {
	Roles    []Role    `yaml:"roles" json:"roles"`
	Bindings []Binding `yaml:"bindings" json:"bindings"`
}

// ── Default Built-in Roles ───────────────────────────────────────────────────

var defaultRoles = []Role{
	{
		Name:        "admin",
		Description: "Full access to all operations",
		Permissions: []string{"*"},
		BuiltIn:     true,
	},
	{
		Name:        "operator",
		Description: "Manage containers, services, deployments, and view config",
		Permissions: []string{
			"containers.*",
			"vms.*",
			"services.*",
			"deploy.*",
			"compose.*",
			"logs.read",
			"events.read",
			"top.read",
			"config.read",
			"security.audit",
			"health.*",
			"network.read",
			"volumes.*",
			"images.*",
		},
		BuiltIn: true,
	},
	{
		Name:        "deployer",
		Description: "Deploy, restart, and view logs — no create/delete",
		Permissions: []string{
			"deploy.*",
			"containers.start",
			"containers.stop",
			"containers.restart",
			"containers.list",
			"containers.inspect",
			"containers.logs",
			"services.start",
			"services.stop",
			"services.restart",
			"services.status",
			"logs.read",
			"events.read",
			"health.read",
		},
		BuiltIn: true,
	},
	{
		Name:        "viewer",
		Description: "Read-only access to all resources",
		Permissions: []string{
			"containers.list",
			"containers.inspect",
			"containers.logs",
			"vms.list",
			"vms.inspect",
			"services.list",
			"services.status",
			"deploy.status",
			"deploy.history",
			"logs.read",
			"events.read",
			"top.read",
			"config.read",
			"security.audit",
			"health.read",
			"network.read",
			"volumes.list",
			"images.list",
		},
		BuiltIn: true,
	},
}

// ── Store ────────────────────────────────────────────────────────────────────

// Store manages RBAC configuration on disk.
type Store struct {
	dir string
	mu  sync.RWMutex
}

// NewStore creates an RBAC store at the given directory.
func NewStore(dir string) *Store {
	if dir == "" {
		dir = DefaultRBACDir
	}
	return &Store{dir: dir}
}

// Dir returns the RBAC directory path.
func (s *Store) Dir() string {
	return s.dir
}

// ── Role Operations ──────────────────────────────────────────────────────────

// LoadRoles reads role definitions from disk, merging with built-in defaults.
func (s *Store) LoadRoles() ([]Role, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	roles := make([]Role, len(defaultRoles))
	copy(roles, defaultRoles)

	path := filepath.Join(s.dir, RolesFile)
	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return roles, nil // Return defaults only
		}
		return nil, fmt.Errorf("rbac: read roles: %w", err)
	}

	var custom struct {
		Roles []Role `yaml:"roles"`
	}
	if err := yaml.Unmarshal(data, &custom); err != nil {
		return nil, fmt.Errorf("rbac: parse roles: %w", err)
	}

	// Merge custom roles (don't override built-ins)
	builtinNames := make(map[string]bool)
	for _, r := range defaultRoles {
		builtinNames[r.Name] = true
	}

	for _, r := range custom.Roles {
		if builtinNames[r.Name] {
			continue // Skip attempts to redefine built-in roles
		}
		roles = append(roles, r)
	}

	return roles, nil
}

// GetRole returns a role by name.
func (s *Store) GetRole(name string) (*Role, error) {
	roles, err := s.LoadRoles()
	if err != nil {
		return nil, err
	}
	for _, r := range roles {
		if r.Name == name {
			return &r, nil
		}
	}
	return nil, fmt.Errorf("rbac: role %q not found", name)
}

// CreateRole adds a new custom role.
func (s *Store) CreateRole(role Role) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	// Validate name
	if role.Name == "" {
		return fmt.Errorf("rbac: role name is required")
	}
	for _, r := range defaultRoles {
		if r.Name == role.Name {
			return fmt.Errorf("rbac: cannot redefine built-in role %q", role.Name)
		}
	}

	// Load existing custom roles
	path := filepath.Join(s.dir, RolesFile)
	var config struct {
		Roles []Role `yaml:"roles"`
	}

	data, err := os.ReadFile(path)
	if err == nil {
		yaml.Unmarshal(data, &config)
	}

	// Check for duplicate
	for _, r := range config.Roles {
		if r.Name == role.Name {
			return fmt.Errorf("rbac: role %q already exists", role.Name)
		}
	}

	config.Roles = append(config.Roles, role)
	return s.writeRoles(config.Roles)
}

// DeleteRole removes a custom role (built-in roles cannot be deleted).
func (s *Store) DeleteRole(name string) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	for _, r := range defaultRoles {
		if r.Name == name {
			return fmt.Errorf("rbac: cannot delete built-in role %q", name)
		}
	}

	path := filepath.Join(s.dir, RolesFile)
	var config struct {
		Roles []Role `yaml:"roles"`
	}

	data, err := os.ReadFile(path)
	if err != nil {
		return fmt.Errorf("rbac: role %q not found", name)
	}
	yaml.Unmarshal(data, &config)

	found := false
	filtered := make([]Role, 0, len(config.Roles))
	for _, r := range config.Roles {
		if r.Name == name {
			found = true
			continue
		}
		filtered = append(filtered, r)
	}

	if !found {
		return fmt.Errorf("rbac: role %q not found", name)
	}

	return s.writeRoles(filtered)
}

func (s *Store) writeRoles(roles []Role) error {
	if err := os.MkdirAll(s.dir, 0750); err != nil {
		return fmt.Errorf("rbac: create dir: %w", err)
	}

	config := struct {
		Roles []Role `yaml:"roles"`
	}{Roles: roles}

	data, err := yaml.Marshal(config)
	if err != nil {
		return fmt.Errorf("rbac: marshal roles: %w", err)
	}

	path := filepath.Join(s.dir, RolesFile)
	return atomicWrite(path, data)
}

// ── Binding Operations ───────────────────────────────────────────────────────

// LoadBindings reads user/group → role bindings from disk.
func (s *Store) LoadBindings() ([]Binding, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	path := filepath.Join(s.dir, BindingsFile)
	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, fmt.Errorf("rbac: read bindings: %w", err)
	}

	var config struct {
		Bindings []Binding `yaml:"bindings"`
	}
	if err := yaml.Unmarshal(data, &config); err != nil {
		return nil, fmt.Errorf("rbac: parse bindings: %w", err)
	}

	return config.Bindings, nil
}

// AssignRole binds a user or group to a role.
func (s *Store) AssignRole(subject, subjectType, roleName string) error {
	// Verify role exists
	if _, err := s.GetRole(roleName); err != nil {
		return err
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	bindings := s.loadBindingsUnsafe()

	// Check for duplicate
	for _, b := range bindings {
		if b.Subject == subject && b.SubjectType == subjectType && b.Role == roleName {
			return fmt.Errorf("rbac: %s %q is already assigned role %q", subjectType, subject, roleName)
		}
	}

	bindings = append(bindings, Binding{
		Subject:     subject,
		SubjectType: subjectType,
		Role:        roleName,
	})

	return s.writeBindings(bindings)
}

// RevokeRole removes a user/group → role binding.
func (s *Store) RevokeRole(subject, subjectType, roleName string) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	bindings := s.loadBindingsUnsafe()

	found := false
	filtered := make([]Binding, 0, len(bindings))
	for _, b := range bindings {
		if b.Subject == subject && b.SubjectType == subjectType && b.Role == roleName {
			found = true
			continue
		}
		filtered = append(filtered, b)
	}

	if !found {
		return fmt.Errorf("rbac: binding not found for %s %q → %q", subjectType, subject, roleName)
	}

	return s.writeBindings(filtered)
}

// GetUserRoles returns all roles assigned to a user (directly and via groups).
func (s *Store) GetUserRoles(username string) ([]string, error) {
	bindings, err := s.LoadBindings()
	if err != nil {
		return nil, err
	}

	roleSet := make(map[string]bool)

	// Get user's OS groups for group-based matching
	userGroups := getUserGroups(username)

	for _, b := range bindings {
		if b.SubjectType == "user" && b.Subject == username {
			roleSet[b.Role] = true
		} else if b.SubjectType == "group" {
			for _, g := range userGroups {
				if b.Subject == g {
					roleSet[b.Role] = true
				}
			}
		}
	}

	roles := make([]string, 0, len(roleSet))
	for r := range roleSet {
		roles = append(roles, r)
	}
	return roles, nil
}

func (s *Store) loadBindingsUnsafe() []Binding {
	path := filepath.Join(s.dir, BindingsFile)
	data, err := os.ReadFile(path)
	if err != nil {
		return nil
	}

	var config struct {
		Bindings []Binding `yaml:"bindings"`
	}
	yaml.Unmarshal(data, &config)
	return config.Bindings
}

func (s *Store) writeBindings(bindings []Binding) error {
	if err := os.MkdirAll(s.dir, 0750); err != nil {
		return fmt.Errorf("rbac: create dir: %w", err)
	}

	config := struct {
		Bindings []Binding `yaml:"bindings"`
	}{Bindings: bindings}

	data, err := yaml.Marshal(config)
	if err != nil {
		return fmt.Errorf("rbac: marshal bindings: %w", err)
	}

	path := filepath.Join(s.dir, BindingsFile)
	return atomicWrite(path, data)
}

// ── Authorization ────────────────────────────────────────────────────────────

// Require checks if the current user has a specific permission.
// Returns nil if authorized, error if not.
//
// Permission format: "resource.action" (e.g., "containers.create")
// Wildcard: "resource.*" matches all actions for a resource
// Admin wildcard: "*" matches everything
func Require(permission string) error {
	store := NewStore("")
	return RequireWithStore(store, permission)
}

// RequireWithStore checks authorization using a specific store (for testing).
func RequireWithStore(store *Store, permission string) error {
	username := CurrentUser()

	// Root always has full access
	if os.Geteuid() == 0 {
		return nil
	}

	// If RBAC is not configured, allow all (graceful degradation)
	if !store.isConfigured() {
		return nil
	}

	roleNames, err := store.GetUserRoles(username)
	if err != nil {
		return fmt.Errorf("rbac: failed to check roles for %q: %w", username, err)
	}

	if len(roleNames) == 0 {
		return fmt.Errorf("rbac: access denied — user %q has no assigned roles\n  Ask an admin to run: volt rbac user assign %s <role>", username, username)
	}

	// Check each role for the required permission
	roles, err := store.LoadRoles()
	if err != nil {
		return fmt.Errorf("rbac: failed to load roles: %w", err)
	}

	roleMap := make(map[string]*Role)
	for i := range roles {
		roleMap[roles[i].Name] = &roles[i]
	}

	for _, rn := range roleNames {
		role, ok := roleMap[rn]
		if !ok {
			continue
		}
		if roleHasPermission(role, permission) {
			return nil
		}
	}

	return fmt.Errorf("rbac: access denied — user %q lacks permission %q\n  Current roles: %s",
		username, permission, strings.Join(roleNames, ", "))
}

// roleHasPermission checks if a role grants a specific permission.
func roleHasPermission(role *Role, required string) bool {
	for _, perm := range role.Permissions {
		if perm == "*" {
			return true // Global wildcard
		}
		if perm == required {
			return true // Exact match
		}
		// Wildcard match: "containers.*" matches "containers.create"
		if strings.HasSuffix(perm, ".*") {
			prefix := strings.TrimSuffix(perm, ".*")
			if strings.HasPrefix(required, prefix+".") {
				return true
			}
		}
	}
	return false
}

// ── Identity ─────────────────────────────────────────────────────────────────

// CurrentUser returns the identity of the current user.
// Checks $VOLT_USER first, then falls back to OS user.
func CurrentUser() string {
	if u := os.Getenv("VOLT_USER"); u != "" {
		return u
	}
	if u, err := user.Current(); err == nil {
		return u.Username
	}
	return "unknown"
}

// getUserGroups returns the OS groups for a given username.
func getUserGroups(username string) []string {
	u, err := user.Lookup(username)
	if err != nil {
		return nil
	}
	gids, err := u.GroupIds()
	if err != nil {
		return nil
	}

	var groups []string
	for _, gid := range gids {
		g, err := user.LookupGroupId(gid)
		if err != nil {
			continue
		}
		groups = append(groups, g.Name)
	}
	return groups
}

// isConfigured returns true if RBAC has been set up (bindings file exists).
func (s *Store) isConfigured() bool {
	path := filepath.Join(s.dir, BindingsFile)
	_, err := os.Stat(path)
	return err == nil
}

// ── Helpers ──────────────────────────────────────────────────────────────────

// atomicWrite writes data to a file using tmp+rename for crash safety.
func atomicWrite(path string, data []byte) error {
	tmp := path + ".tmp"
	if err := os.WriteFile(tmp, data, 0640); err != nil {
		return err
	}
	if err := os.Rename(tmp, path); err != nil {
		os.Remove(tmp)
		return err
	}
	return nil
}

// Init initializes the RBAC directory with default configuration.
// Called by `volt rbac init`.
func (s *Store) Init() error {
	s.mu.Lock()
	defer s.mu.Unlock()

	if err := os.MkdirAll(s.dir, 0750); err != nil {
		return fmt.Errorf("rbac: create dir: %w", err)
	}

	// Write default roles file (documenting built-ins, no custom roles yet)
	rolesData := `# Volt RBAC Role Definitions
# Built-in roles (admin, operator, deployer, viewer) are always available.
# Add custom roles below.
roles: []
`
	rolesPath := filepath.Join(s.dir, RolesFile)
	if err := os.WriteFile(rolesPath, []byte(rolesData), 0640); err != nil {
		return fmt.Errorf("rbac: write roles: %w", err)
	}

	// Write empty bindings file
	bindingsData := `# Volt RBAC Bindings — user/group to role mappings
# Example:
#   bindings:
#     - subject: karl
#       subject_type: user
#       role: admin
#     - subject: developers
#       subject_type: group
#       role: deployer
bindings: []
`
	bindingsPath := filepath.Join(s.dir, BindingsFile)
	if err := os.WriteFile(bindingsPath, []byte(bindingsData), 0640); err != nil {
		return fmt.Errorf("rbac: write bindings: %w", err)
	}

	return nil
}