// (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 gosec

import (
	"encoding/json"
	"fmt"
	"go/ast"
	"os"
	"strconv"
)

// Score type used by severity and confidence values
type Score int

const (
	// Low severity or confidence
	Low Score = iota
	// Medium severity or confidence
	Medium
	// High severity or confidence
	High
)

// Cwe id and url
type Cwe struct {
	ID  string
	URL string
}

// GetCwe creates a cwe object for a given RuleID
func GetCwe(id string) Cwe {
	return Cwe{ID: id, URL: fmt.Sprintf("https://cwe.mitre.org/data/definitions/%s.html", id)}
}

// IssueToCWE maps gosec rules to CWEs
var IssueToCWE = map[string]Cwe{
	"G101": GetCwe("798"),
	"G102": GetCwe("200"),
	"G103": GetCwe("242"),
	"G104": GetCwe("703"),
	"G106": GetCwe("322"),
	"G107": GetCwe("88"),
	"G109": GetCwe("190"),
	"G110": GetCwe("409"),
	"G201": GetCwe("89"),
	"G202": GetCwe("89"),
	"G203": GetCwe("79"),
	"G204": GetCwe("78"),
	"G301": GetCwe("276"),
	"G302": GetCwe("276"),
	"G303": GetCwe("377"),
	"G304": GetCwe("22"),
	"G305": GetCwe("22"),
	"G401": GetCwe("326"),
	"G402": GetCwe("295"),
	"G403": GetCwe("310"),
	"G404": GetCwe("338"),
	"G501": GetCwe("327"),
	"G502": GetCwe("327"),
	"G503": GetCwe("327"),
	"G504": GetCwe("327"),
	"G505": GetCwe("327"),
}

// Issue is returned by a gosec rule if it discovers an issue with the scanned code.
type Issue struct {
	Severity   Score  `json:"severity"`   // issue severity (how problematic it is)
	Confidence Score  `json:"confidence"` // issue confidence (how sure we are we found it)
	Cwe        Cwe    `json:"cwe"`        // Cwe associated with RuleID
	RuleID     string `json:"rule_id"`    // Human readable explanation
	What       string `json:"details"`    // Human readable explanation
	File       string `json:"file"`       // File name we found it in
	Code       string `json:"code"`       // Impacted code line
	Line       string `json:"line"`       // Line number in file
	Col        string `json:"column"`     // Column number in line
}

// MetaData is embedded in all gosec rules. The Severity, Confidence and What message
// will be passed through to reported issues.
type MetaData struct {
	ID         string
	Severity   Score
	Confidence Score
	What       string
}

// MarshalJSON is used convert a Score object into a JSON representation
func (c Score) MarshalJSON() ([]byte, error) {
	return json.Marshal(c.String())
}

// String converts a Score into a string
func (c Score) String() string {
	switch c {
	case High:
		return "HIGH"
	case Medium:
		return "MEDIUM"
	case Low:
		return "LOW"
	}
	return "UNDEFINED"
}

func codeSnippet(file *os.File, start int64, end int64, n ast.Node) (string, error) {
	if n == nil {
		return "", fmt.Errorf("Invalid AST node provided")
	}

	size := (int)(end - start)    // Go bug, os.File.Read should return int64 ...
	_, err := file.Seek(start, 0) // #nosec
	if err != nil {
		return "", fmt.Errorf("move to the beginning of file: %v", err)
	}

	buf := make([]byte, size)
	if nread, err := file.Read(buf); err != nil || nread != size {
		return "", fmt.Errorf("Unable to read code")
	}
	return string(buf), nil
}

// NewIssue creates a new Issue
func NewIssue(ctx *Context, node ast.Node, ruleID, desc string, severity Score, confidence Score) *Issue {
	var code string
	fobj := ctx.FileSet.File(node.Pos())
	name := fobj.Name()

	start, end := fobj.Line(node.Pos()), fobj.Line(node.End())
	line := strconv.Itoa(start)
	if start != end {
		line = fmt.Sprintf("%d-%d", start, end)
	}

	col := strconv.Itoa(fobj.Position(node.Pos()).Column)

	// #nosec
	if file, err := os.Open(fobj.Name()); err == nil {
		defer file.Close()
		s := (int64)(fobj.Position(node.Pos()).Offset) // Go bug, should be int64
		e := (int64)(fobj.Position(node.End()).Offset) // Go bug, should be int64
		code, err = codeSnippet(file, s, e, node)
		if err != nil {
			code = err.Error()
		}
	}

	return &Issue{
		File:       name,
		Line:       line,
		Col:        col,
		RuleID:     ruleID,
		What:       desc,
		Confidence: confidence,
		Severity:   severity,
		Code:       code,
		Cwe:        IssueToCWE[ruleID],
	}
}