// Copyright (c) 2024 Mattermost Community Enterprise
// Access Control Implementation (PAP + PDP)

package access_control

import (
	"net/http"
	"strings"
	"sync"

	"github.com/mattermost/mattermost/server/public/model"
	"github.com/mattermost/mattermost/server/public/shared/mlog"
	"github.com/mattermost/mattermost/server/public/shared/request"
	"github.com/mattermost/mattermost/server/v8/channels/store"
)

// AccessControlConfig holds configuration for the access control service
type AccessControlConfig struct {
	Store  store.Store
	Config func() *model.Config
	Logger mlog.LoggerIFace
}

// AccessControlImpl implements the AccessControlServiceInterface (PAP + PDP)
type AccessControlImpl struct {
	store  store.Store
	config func() *model.Config
	logger mlog.LoggerIFace

	// In-memory storage for policies
	policies map[string]*model.AccessControlPolicy
	mutex    sync.RWMutex

	// CEL engine initialized flag
	initialized bool
}

// NewAccessControlInterface creates a new access control interface
func NewAccessControlInterface(cfg *AccessControlConfig) *AccessControlImpl {
	return &AccessControlImpl{
		store:    cfg.Store,
		config:   cfg.Config,
		logger:   cfg.Logger,
		policies: make(map[string]*model.AccessControlPolicy),
	}
}

// PAP Methods (Policy Administration Point)

// Init initializes the policy administration point
func (ac *AccessControlImpl) Init(rctx request.CTX) *model.AppError {
	ac.mutex.Lock()
	defer ac.mutex.Unlock()

	if ac.initialized {
		return nil
	}

	// Initialize CEL engine (in production, this would set up the CEL environment)
	ac.logger.Info("Initializing Access Control Policy Administration Point")

	ac.initialized = true
	return nil
}

// GetPolicyRuleAttributes retrieves the attributes of the given policy for a specific action
func (ac *AccessControlImpl) GetPolicyRuleAttributes(rctx request.CTX, policyID string, action string) (map[string][]string, *model.AppError) {
	ac.mutex.RLock()
	defer ac.mutex.RUnlock()

	policy, ok := ac.policies[policyID]
	if !ok {
		return nil, model.NewAppError("GetPolicyRuleAttributes", "access_control.policy_not_found", map[string]any{"PolicyId": policyID}, "", http.StatusNotFound)
	}

	attributes := make(map[string][]string)

	for _, rule := range policy.Rules {
		// Check if this rule applies to the requested action
		appliesToAction := false
		for _, ruleAction := range rule.Actions {
			if ruleAction == action || ruleAction == "*" {
				appliesToAction = true
				break
			}
		}

		if appliesToAction {
			// Extract attributes from expression (simplified implementation)
			// In production, this would use the CEL parser
			extractedAttrs := extractAttributesFromExpression(rule.Expression)
			for attrName, attrValues := range extractedAttrs {
				attributes[attrName] = append(attributes[attrName], attrValues...)
			}
		}
	}

	return attributes, nil
}

// CheckExpression checks the validity of the given CEL expression
func (ac *AccessControlImpl) CheckExpression(rctx request.CTX, expression string) ([]model.CELExpressionError, *model.AppError) {
	var errors []model.CELExpressionError

	if expression == "" {
		errors = append(errors, model.CELExpressionError{
			Line:    1,
			Column:  1,
			Message: "Expression cannot be empty",
		})
		return errors, nil
	}

	// Basic syntax validation (simplified - in production would use CEL parser)
	// Check for balanced parentheses
	parenCount := 0
	for i, c := range expression {
		if c == '(' {
			parenCount++
		} else if c == ')' {
			parenCount--
		}
		if parenCount < 0 {
			errors = append(errors, model.CELExpressionError{
				Line:    1,
				Column:  i + 1,
				Message: "Unbalanced parentheses: unexpected ')'",
			})
		}
	}
	if parenCount > 0 {
		errors = append(errors, model.CELExpressionError{
			Line:    1,
			Column:  len(expression),
			Message: "Unbalanced parentheses: missing ')'",
		})
	}

	// Check for valid operators
	validOperators := []string{"&&", "||", "==", "!=", "in", "contains", "startsWith", "endsWith"}
	hasValidOperator := false
	for _, op := range validOperators {
		if strings.Contains(expression, op) {
			hasValidOperator = true
			break
		}
	}

	// If expression has no operators, it might be a simple attribute reference which is valid
	if !hasValidOperator && !strings.Contains(expression, ".") && !strings.Contains(expression, "subject") && !strings.Contains(expression, "resource") {
		errors = append(errors, model.CELExpressionError{
			Line:    1,
			Column:  1,
			Message: "Expression should reference subject or resource attributes",
		})
	}

	return errors, nil
}

// ExpressionToVisualAST converts the given expression to a visual AST
func (ac *AccessControlImpl) ExpressionToVisualAST(rctx request.CTX, expression string) (*model.VisualExpression, *model.AppError) {
	// Simplified implementation - in production would parse CEL expression properly
	visual := &model.VisualExpression{
		Conditions: []model.Condition{},
	}

	// Split by && for AND conditions
	parts := strings.Split(expression, "&&")
	for _, part := range parts {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}

		condition := model.Condition{
			Attribute: part,
			Operator:  "exists",
			Value:     true,
		}

		visual.Conditions = append(visual.Conditions, condition)
	}

	return visual, nil
}

// NormalizePolicy normalizes the given policy by restoring ids back to names
func (ac *AccessControlImpl) NormalizePolicy(rctx request.CTX, policy *model.AccessControlPolicy) (*model.AccessControlPolicy, *model.AppError) {
	// In production, this would resolve IDs to names in expressions
	// For now, return the policy as-is
	return policy, nil
}

// QueryUsersForExpression evaluates the given expression and returns matching users
func (ac *AccessControlImpl) QueryUsersForExpression(rctx request.CTX, expression string, opts model.SubjectSearchOptions) ([]*model.User, int64, *model.AppError) {
	if ac.store == nil {
		return nil, 0, model.NewAppError("QueryUsersForExpression", "access_control.store_not_available", nil, "", http.StatusInternalServerError)
	}

	// Simplified implementation - in production would evaluate CEL expression
	// For now, return users based on basic search
	users, err := ac.store.User().Search(rctx, "", opts.Term, &model.UserSearchOptions{
		Limit: opts.Limit,
	})
	if err != nil {
		return nil, 0, model.NewAppError("QueryUsersForExpression", "access_control.query_failed", nil, err.Error(), http.StatusInternalServerError)
	}

	return users, int64(len(users)), nil
}

// QueryUsersForResource finds users that match to the resource
func (ac *AccessControlImpl) QueryUsersForResource(rctx request.CTX, resourceID, action string, opts model.SubjectSearchOptions) ([]*model.User, int64, *model.AppError) {
	ac.mutex.RLock()
	defer ac.mutex.RUnlock()

	// Find policies that apply to this resource
	var applicableExpressions []string
	for _, policy := range ac.policies {
		if !policy.Active {
			continue
		}

		// Check if policy type matches resource type
		// In production, would check policy.Type against resource type
		for _, rule := range policy.Rules {
			for _, ruleAction := range rule.Actions {
				if ruleAction == action || ruleAction == "*" {
					applicableExpressions = append(applicableExpressions, rule.Expression)
				}
			}
		}
	}

	if len(applicableExpressions) == 0 {
		return nil, 0, nil
	}

	// Combine expressions and query
	combinedExpression := strings.Join(applicableExpressions, " || ")
	return ac.QueryUsersForExpression(rctx, combinedExpression, opts)
}

// GetChannelMembersToRemove retrieves channel members that need to be removed
func (ac *AccessControlImpl) GetChannelMembersToRemove(rctx request.CTX, channelID string) ([]*model.ChannelMember, *model.AppError) {
	// In production, this would evaluate access control policies against channel members
	// and return those who no longer have access
	return nil, nil
}

// SavePolicy saves the given access control policy
func (ac *AccessControlImpl) SavePolicy(rctx request.CTX, policy *model.AccessControlPolicy) (*model.AccessControlPolicy, *model.AppError) {
	ac.mutex.Lock()
	defer ac.mutex.Unlock()

	if policy.ID == "" {
		policy.ID = model.NewId()
	}

	// Validate policy
	if appErr := policy.IsValid(); appErr != nil {
		return nil, appErr
	}

	// Validate expressions
	for _, rule := range policy.Rules {
		errors, appErr := ac.CheckExpression(rctx, rule.Expression)
		if appErr != nil {
			return nil, appErr
		}
		if len(errors) > 0 {
			return nil, model.NewAppError("SavePolicy", "access_control.invalid_expression", map[string]any{"Errors": errors}, "", http.StatusBadRequest)
		}
	}

	now := model.GetMillis()
	if policy.CreateAt == 0 {
		policy.CreateAt = now
	}
	policy.Revision++

	ac.policies[policy.ID] = policy

	ac.logger.Info("Saved access control policy",
		mlog.String("policy_id", policy.ID),
		mlog.String("name", policy.Name),
	)

	return policy, nil
}

// GetPolicy retrieves the access control policy with the given ID
func (ac *AccessControlImpl) GetPolicy(rctx request.CTX, id string) (*model.AccessControlPolicy, *model.AppError) {
	ac.mutex.RLock()
	defer ac.mutex.RUnlock()

	policy, ok := ac.policies[id]
	if !ok {
		return nil, model.NewAppError("GetPolicy", "access_control.policy_not_found", map[string]any{"PolicyId": id}, "", http.StatusNotFound)
	}

	return policy, nil
}

// DeletePolicy deletes the access control policy with the given ID
func (ac *AccessControlImpl) DeletePolicy(rctx request.CTX, id string) *model.AppError {
	ac.mutex.Lock()
	defer ac.mutex.Unlock()

	if _, ok := ac.policies[id]; !ok {
		return model.NewAppError("DeletePolicy", "access_control.policy_not_found", map[string]any{"PolicyId": id}, "", http.StatusNotFound)
	}

	delete(ac.policies, id)

	ac.logger.Info("Deleted access control policy",
		mlog.String("policy_id", id),
	)

	return nil
}

// PDP Methods (Policy Decision Point)

// AccessEvaluation evaluates an access request and returns a decision
func (ac *AccessControlImpl) AccessEvaluation(rctx request.CTX, accessRequest model.AccessRequest) (model.AccessDecision, *model.AppError) {
	ac.mutex.RLock()
	defer ac.mutex.RUnlock()

	decision := model.AccessDecision{
		Decision: false,
		Context:  make(map[string]any),
	}

	// Find applicable policies
	for _, policy := range ac.policies {
		if !policy.Active {
			continue
		}

		// Check if policy type matches resource type
		if policy.Type != "" && policy.Type != accessRequest.Resource.Type {
			continue
		}

		// Evaluate rules
		for _, rule := range policy.Rules {
			// Check if action matches
			actionMatches := false
			for _, ruleAction := range rule.Actions {
				if ruleAction == accessRequest.Action || ruleAction == "*" {
					actionMatches = true
					break
				}
			}

			if !actionMatches {
				continue
			}

			// Evaluate expression (simplified)
			allowed := ac.evaluateExpression(rule.Expression, accessRequest)
			if allowed {
				decision.Decision = true
				decision.Context["matched_policy"] = policy.ID
				decision.Context["matched_rule"] = rule.Expression
				return decision, nil
			}
		}
	}

	return decision, nil
}

// Helper functions

func extractAttributesFromExpression(expression string) map[string][]string {
	attributes := make(map[string][]string)

	// Simple extraction of attribute references like "subject.attr" or "resource.attr"
	parts := strings.Fields(expression)
	for _, part := range parts {
		part = strings.Trim(part, "()")
		if strings.HasPrefix(part, "subject.") {
			attrName := strings.TrimPrefix(part, "subject.")
			attrName = strings.Split(attrName, "==")[0]
			attrName = strings.Split(attrName, "!=")[0]
			attrName = strings.TrimSpace(attrName)
			if attrName != "" {
				attributes["subject."+attrName] = []string{}
			}
		} else if strings.HasPrefix(part, "resource.") {
			attrName := strings.TrimPrefix(part, "resource.")
			attrName = strings.Split(attrName, "==")[0]
			attrName = strings.Split(attrName, "!=")[0]
			attrName = strings.TrimSpace(attrName)
			if attrName != "" {
				attributes["resource."+attrName] = []string{}
			}
		}
	}

	return attributes
}

func (ac *AccessControlImpl) evaluateExpression(expression string, request model.AccessRequest) bool {
	// Simplified expression evaluation
	// In production, this would use the CEL engine

	// Default: if expression references subject.id, check if it matches
	if strings.Contains(expression, "subject.id") {
		if strings.Contains(expression, "==") {
			parts := strings.Split(expression, "==")
			if len(parts) == 2 {
				expected := strings.TrimSpace(parts[1])
				expected = strings.Trim(expected, "\"'")
				if request.Subject.ID == expected {
					return true
				}
			}
		}
	}

	// Check for "true" expression (always allow)
	if strings.TrimSpace(expression) == "true" {
		return true
	}

	// Check for subject type matching
	if strings.Contains(expression, "subject.type") && strings.Contains(expression, request.Subject.Type) {
		return true
	}

	// Default deny
	return false
}