// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.

package license

import (
	"fmt"
	"go/ast"
	"regexp"
	"strings"
	"time"

	"golang.org/x/tools/go/analysis"
)

var Analyzer = &analysis.Analyzer{
	Name: "license",
	Doc:  "check the license header.",
	Run:  run,
}

var EEAnalyzer = &analysis.Analyzer{
	Name: "enterpriseLicense",
	Doc:  "check the license header for enterprise code.",
	Run:  run,
}

const defaultLicenseYear = 2015

var (
	ignoreFilesPattern       string
	licenseYear              int
	sourceAvailablePackageRe = regexp.MustCompile("/enterprise")
)

const (
	licenseLine1Format          = "// Copyright (c) %d-present Mattermost, Inc. All Rights Reserved."
	defaultLicenseLine2         = "// See LICENSE.txt for license information."
	enterpriseLicenseLine2      = "// See ENTERPRISE-LICENSE.txt and SOURCE-CODE-LICENSE.txt for license information."
	sourceAvailableLicenseLine2 = "// See LICENSE.enterprise for license information."
)

// buildHeaders are allowed to precede the license headers.
var buildHeaders = []string{
	"//go:generate",
	"//go:build",
}

// generatedHeaders indicate files to automatically ignore.
var generatedHeaders = []string{
	"// Code generated by mockery",
	"// Code generated by MockGen. DO NOT EDIT.",
	"by go-bindata DO NOT EDIT. (@generated)",
	"// This file is automatically generated. Do not modify it manually.",
}

func init() {
	Analyzer.Flags.StringVar(&ignoreFilesPattern, "ignore", "", "Comma separated list of files to ignore")
	Analyzer.Flags.IntVar(&licenseYear, "year", defaultLicenseYear, "Year to use in license header (2015-present)")
	EEAnalyzer.Flags.StringVar(&ignoreFilesPattern, "ignore", "", "Comma separated list of files to ignore")
	EEAnalyzer.Flags.IntVar(&licenseYear, "year", defaultLicenseYear, "Year to use in license header (2015-present)")
}

func run(pass *analysis.Pass) (interface{}, error) {
	var ignoreFiles []string
	if ignoreFilesPattern != "" {
		ignoreFiles = strings.Split(ignoreFilesPattern, ",")
	}

	// Validate license year
	if licenseYear == 0 {
		licenseYear = defaultLicenseYear
	}

	currentYear := time.Now().Year()
	if licenseYear < defaultLicenseYear || licenseYear > currentYear {
		return nil, fmt.Errorf("license year must be between %d and %d", defaultLicenseYear, currentYear)
	}

	expectedLine1 := fmt.Sprintf(licenseLine1Format, licenseYear)
	expectedLine2 := defaultLicenseLine2

	if pass.Analyzer.Name == "enterpriseLicense" {
		// Closed source enterprise license
		expectedLine2 = enterpriseLicenseLine2
	} else if sourceAvailablePackageRe.MatchString(pass.Pkg.Path()) {
		// Source available license
		expectedLine2 = sourceAvailableLicenseLine2
	}

	for _, file := range pass.Files {
		checkFile(pass, file, ignoreFiles, expectedLine1, expectedLine2)
	}
	return nil, nil
}

func checkFile(pass *analysis.Pass, file *ast.File, ignoreFiles []string, expectedLine1 string, expectedLine2 string) {
	fileObj := pass.Fset.File(file.Pos())

	// Ignore files specified via -ignore
	if fileIsIgnored(fileObj.Name(), ignoreFiles) {
		return
	}

	if len(file.Comments) == 0 {
		pass.Reportf(file.Pos(), "License not found")
		return
	}

	if len(file.Comments[0].List) == 0 {
		pass.Reportf(file.Pos(), "License not found or wrong")
		return
	}

	// Ignore known generated files.
	for _, header := range generatedHeaders {
		if strings.Contains(file.Comments[0].List[0].Text, header) {
			return
		}
	}

	// Allow the first comment block to be entirely build directives. If found,
	// the next comment block will be required to be a license and must naturally
	// be separated by an empty line (otherwise it would be the same comment block).
	commentGroup := 0

	foundBuildHeader := false
	allBuildHeaders := true
	for _, commentText := range file.Comments[commentGroup].List {
		isBuildHeader := false
		for _, buildHeader := range buildHeaders {
			if strings.HasPrefix(commentText.Text, buildHeader) {
				isBuildHeader = true
				break
			}
		}

		if isBuildHeader {
			foundBuildHeader = true
		} else {
			allBuildHeaders = false
		}
	}

	if foundBuildHeader && !allBuildHeaders {
		pass.Reportf(file.Pos(), "Must be an empty line between the build directive and the license")
		return
	} else if foundBuildHeader && allBuildHeaders {
		commentGroup++
	}

	if len(file.Comments) < commentGroup+1 {
		pass.Reportf(file.Pos(), "License not found")
		return
	}

	if len(file.Comments[commentGroup].List) < 2 {
		pass.Reportf(file.Pos(), "License not found or wrong")
		return
	}

	if file.Comments[commentGroup].List[0].Text != expectedLine1 {
		pass.Reportf(file.Comments[commentGroup].List[0].Pos(), "License copywright wrong, expected: %s", expectedLine1)
		return
	}

	if file.Comments[commentGroup].List[1].Text != expectedLine2 {
		pass.Reportf(file.Comments[commentGroup].List[1].Pos(), "License reference wrong, expected %s", expectedLine2)
		return
	}
}

func fileIsIgnored(file string, ignoreFiles []string) bool {
	for _, f := range ignoreFiles {
		if strings.HasSuffix(file, f) {
			return true
		}
	}
	return false
}