// (c) Copyright 2016 Hewlett Packard Enterprise Development LP
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package rules

import (
	"fmt"
	"go/ast"

	"github.com/GoASTScanner/gas"
)

type insecureConfigTLS struct {
	MinVersion   int16
	MaxVersion   int16
	requiredType string
	goodCiphers  []string
}

func stringInSlice(a string, list []string) bool {
	for _, b := range list {
		if b == a {
			return true
		}
	}
	return false
}

func (t *insecureConfigTLS) processTLSCipherSuites(n ast.Node, c *gas.Context) *gas.Issue {
	tlsConfig := gas.MatchCompLit(n, c, t.requiredType)
	if tlsConfig == nil {
		return nil
	}

	for _, expr := range tlsConfig.Elts {
		if keyvalExpr, ok := expr.(*ast.KeyValueExpr); ok {
			if keyname, ok := keyvalExpr.Key.(*ast.Ident); ok && keyname.Name == "CipherSuites" {
				if ciphers, ok := keyvalExpr.Value.(*ast.CompositeLit); ok {
					for _, cipher := range ciphers.Elts {
						if ident, ok := cipher.(*ast.SelectorExpr); ok {
							if !stringInSlice(ident.Sel.Name, t.goodCiphers) {
								str := fmt.Sprintf("TLS Bad Cipher Suite: %s", ident.Sel.Name)
								return gas.NewIssue(c, n, str, gas.High, gas.High)
							}
						}
					}
				}
			}
		}
	}
	return nil
}

func (t *insecureConfigTLS) processTlsConfVal(n *ast.KeyValueExpr, c *gas.Context) *gas.Issue {
	if ident, ok := n.Key.(*ast.Ident); ok {
		switch ident.Name {
		case "InsecureSkipVerify":
			if node, ok := n.Value.(*ast.Ident); ok {
				if node.Name != "false" {
					return gas.NewIssue(c, n, "TLS InsecureSkipVerify set true.", gas.High, gas.High)
				}
			} else {
				// TODO(tk): symbol tab look up to get the actual value
				return gas.NewIssue(c, n, "TLS InsecureSkipVerify may be true.", gas.High, gas.Low)
			}

		case "PreferServerCipherSuites":
			if node, ok := n.Value.(*ast.Ident); ok {
				if node.Name == "false" {
					return gas.NewIssue(c, n, "TLS PreferServerCipherSuites set false.", gas.Medium, gas.High)
				}
			} else {
				// TODO(tk): symbol tab look up to get the actual value
				return gas.NewIssue(c, n, "TLS PreferServerCipherSuites may be false.", gas.Medium, gas.Low)
			}

		case "MinVersion":
			if ival, ierr := gas.GetInt(n.Value); ierr == nil {
				if (int16)(ival) < t.MinVersion {
					return gas.NewIssue(c, n, "TLS MinVersion too low.", gas.High, gas.High)
				}
				// TODO(tk): symbol tab look up to get the actual value
				return gas.NewIssue(c, n, "TLS MinVersion may be too low.", gas.High, gas.Low)
			}

		case "MaxVersion":
			if ival, ierr := gas.GetInt(n.Value); ierr == nil {
				if (int16)(ival) < t.MaxVersion {
					return gas.NewIssue(c, n, "TLS MaxVersion too low.", gas.High, gas.High)
				}
				// TODO(tk): symbol tab look up to get the actual value
				return gas.NewIssue(c, n, "TLS MaxVersion may be too low.", gas.High, gas.Low)
			}

		case "CipherSuites":
			if ret := t.processTLSCipherSuites(n, c); ret != nil {
				return ret
			}

		}

	}
	return nil
}

func (t *insecureConfigTLS) Match(n ast.Node, c *gas.Context) (gi *gas.Issue, err error) {
	if node := gas.MatchCompLit(n, c, t.requiredType); node != nil {
		for _, elt := range node.Elts {
			if kve, ok := elt.(*ast.KeyValueExpr); ok {
				gi = t.processTlsConfVal(kve, c)
				if gi != nil {
					break
				}
			}
		}
	}
	return
}

// NewModernTlsCheck see: https://wiki.mozilla.org/Security/Server_Side_TLS#Modern_compatibility
func NewModernTlsCheck(conf gas.Config) (gas.Rule, []ast.Node) {
	return &insecureConfigTLS{
		requiredType: "tls.Config",
		MinVersion:   0x0303, // TLS 1.2 only
		MaxVersion:   0x0303,
		goodCiphers: []string{
			"TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
			"TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
			"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
			"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
		},
	}, []ast.Node{(*ast.CompositeLit)(nil)}
}

// NewIntermediateTlsCheck see: https://wiki.mozilla.org/Security/Server_Side_TLS#Intermediate_compatibility_.28default.29
func NewIntermediateTlsCheck(conf gas.Config) (gas.Rule, []ast.Node) {
	return &insecureConfigTLS{
		requiredType: "tls.Config",
		MinVersion:   0x0301, // TLS 1.2, 1.1, 1.0
		MaxVersion:   0x0303,
		goodCiphers: []string{
			"TLS_RSA_WITH_AES_128_CBC_SHA",
			"TLS_RSA_WITH_AES_256_CBC_SHA",
			"TLS_RSA_WITH_AES_128_GCM_SHA256",
			"TLS_RSA_WITH_AES_256_GCM_SHA384",
			"TLS_ECDHE_ECDSA_WITH_RC4_128_SHA",
			"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA",
			"TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA",
			"TLS_ECDHE_RSA_WITH_RC4_128_SHA",
			"TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA",
			"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA",
			"TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA",
			"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
			"TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
			"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
			"TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
		},
	}, []ast.Node{(*ast.CompositeLit)(nil)}
}

// NewCompatTlsCheck see: https://wiki.mozilla.org/Security/Server_Side_TLS#Old_compatibility_.28default.29
func NewCompatTlsCheck(conf gas.Config) (gas.Rule, []ast.Node) {
	return &insecureConfigTLS{
		requiredType: "tls.Config",
		MinVersion:   0x0301, // TLS 1.2, 1.1, 1.0
		MaxVersion:   0x0303,
		goodCiphers: []string{
			"TLS_RSA_WITH_RC4_128_SHA",
			"TLS_RSA_WITH_3DES_EDE_CBC_SHA",
			"TLS_RSA_WITH_AES_128_CBC_SHA",
			"TLS_RSA_WITH_AES_256_CBC_SHA",
			"TLS_RSA_WITH_AES_128_GCM_SHA256",
			"TLS_RSA_WITH_AES_256_GCM_SHA384",
			"TLS_ECDHE_ECDSA_WITH_RC4_128_SHA",
			"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA",
			"TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA",
			"TLS_ECDHE_RSA_WITH_RC4_128_SHA",
			"TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA",
			"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA",
			"TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA",
			"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
			"TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
			"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
			"TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
		},
	}, []ast.Node{(*ast.CompositeLit)(nil)}
}