// Copyright 2018 The Goma Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package acl

import (
	"context"
	"fmt"
	"strings"
	"sync"

	"github.com/golang/protobuf/proto"
	"golang.org/x/oauth2"
	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"

	"go.chromium.org/goma/server/auth"
	"go.chromium.org/goma/server/auth/account"
	"go.chromium.org/goma/server/log"
	pb "go.chromium.org/goma/server/proto/auth"
)

// AuthDB provides authentication database; user groups.
type AuthDB interface {
	IsMember(ctx context.Context, email, group string) bool
}

// Checker checks token.
type Checker struct {
	AuthDB
	account.Pool

	mu     sync.RWMutex
	config *pb.ACL

	accounts map[string]account.Account
}

// Set sets config in the checker.
func (c *Checker) Set(ctx context.Context, config *pb.ACL) error {
	c.mu.Lock()
	defer c.mu.Unlock()

	if c.Pool == nil {
		c.Pool = account.Empty{}
	}
	if c.accounts == nil {
		c.accounts = make(map[string]account.Account)
	}

	logger := log.FromContext(ctx)

	seen := make(map[string]bool)

	for _, g := range config.Groups {
		if g.ServiceAccount == "" {
			continue
		}
		if seen[g.ServiceAccount] {
			continue
		}
		sa, err := c.Pool.New(g.ServiceAccount)
		if err != nil {
			return fmt.Errorf("service account %q: %v", g.ServiceAccount, err)
		}
		seen[g.ServiceAccount] = true
		if sa.Equals(c.accounts[g.ServiceAccount]) {
			// no diff
			logger.Infof("service account %s: no change", g.ServiceAccount)
			continue
		}
		logger.Infof("service account %s: update", g.ServiceAccount)
		c.accounts[g.ServiceAccount] = sa
	}
	for sa := range c.accounts {
		if !seen[sa] {
			logger.Infof("service account %s: deleted", sa)
			delete(c.accounts, sa)
		}
	}
	logger.Infof("acl updated")
	c.config = proto.Clone(config).(*pb.ACL)
	return nil
}

// CheckToken checks token and returns group id and token used for backend API.
func (c *Checker) CheckToken(ctx context.Context, token *oauth2.Token, tokenInfo *auth.TokenInfo) (string, *oauth2.Token, error) {
	c.mu.RLock()
	defer c.mu.RUnlock()

	logger := log.FromContext(ctx)

	for _, g := range c.config.GetGroups() {
		if !checkGroup(ctx, tokenInfo, g, c.AuthDB) {
			continue
		}

		logger.Debugf("in group:%s", g.Id)
		if g.Reject {
			logger.Errorf("group:%s rejected", g.Id)
			return g.Id, nil, grpc.Errorf(codes.PermissionDenied, "access rejected")
		}
		if g.ServiceAccount == "" {
			logger.Debugf("group:%s use EUC", g.Id)
			return g.Id, token, nil
		}

		sa := c.accounts[g.ServiceAccount]
		if sa == nil {
			logger.Errorf("group:%s service account not found: %s", g.Id, g.ServiceAccount)
			return g.Id, nil, grpc.Errorf(codes.Internal, "service account not found: %s", g.ServiceAccount)
		}
		saToken, err := sa.Token(ctx)
		if err != nil {
			logger.Errorf("group:%s service account:%s error:%v", g.Id, g.ServiceAccount, err)
			return g.Id, nil, grpc.Errorf(codes.Internal, "service account:%s error:%v", g.ServiceAccount, err)
		}
		logger.Debugf("group:%s use service account:%s", g.Id, g.ServiceAccount)
		return g.Id, saToken, nil
	}
	logger.Errorf("no acl match")
	return "", nil, grpc.Errorf(codes.PermissionDenied, "access rejected")
}

func checkGroup(ctx context.Context, tokenInfo *auth.TokenInfo, g *pb.Group, authDB AuthDB) bool {
	logger := log.FromContext(ctx)
	logger.Debugf("checking group:%s", g.Id)
	if g.Audience != "" {
		if tokenInfo.Audience != g.Audience {
			logger.Debugf("audience mismatch: %s != %s", tokenInfo.Audience, g.Audience)
			return false
		}
	}
	if len(g.Emails) == 0 && len(g.Domains) == 0 && authDB != nil {
		if !authDB.IsMember(ctx, tokenInfo.Email, g.Id) {
			logger.Debugf("not member in authdb group:%s", g.Id)
			return false
		}
		return true
	}
	if !match(tokenInfo.Email, g.Emails, g.Domains) {
		logger.Debugf("emails/domains mismatch: client email not in group %s", g.Id)
		return false
	}
	return true
}

func match(email string, emails, domains []string) bool {
	for _, e := range emails {
		if email == e {
			return true
		}
	}
	for _, d := range domains {
		if strings.HasSuffix(email, "@"+d) {
			return true
		}
	}
	return false
}