package licensing

import (
	"context"
	"io"
	"math"
	"os"
	"path/filepath"
	"strings"

	"golang.org/x/xerrors"

	"github.com/aquasecurity/trivy/pkg/fanal/analyzer"
	"github.com/aquasecurity/trivy/pkg/fanal/types"
	"github.com/aquasecurity/trivy/pkg/licensing"
	"github.com/aquasecurity/trivy/pkg/log"
	"github.com/aquasecurity/trivy/pkg/set"
	xio "github.com/aquasecurity/trivy/pkg/x/io"
)

const version = 1

var (
	skipDirs = []string{
		"node_modules/",  // node scan will pick these up
		"usr/share/doc/", // dpkg will pick these up

		// Some heuristic exclusion
		"usr/lib",
		"usr/local/include",
		"usr/include",
		"usr/lib/python",
		"usr/local/go",
		"opt/yarn",
		"usr/lib/gems",
		"usr/src/wordpress",
	}

	acceptedExtensions = set.NewCaseInsensitive(
		".asp",
		".aspx",
		".bas",
		".bat",
		".b",
		".c",
		".cue",
		".cgi",
		".cs",
		".css",
		".fish",
		".html",
		".h",
		".ini",
		".java",
		".js",
		".jsx",
		".markdown",
		".md",
		".py",
		".php",
		".pl",
		".r",
		".rb",
		".sh",
		".sql",
		".ts",
		".tsx",
		".txt",
		".vue",
		".zsh",
	)

	acceptedFileNames = set.NewCaseInsensitive(
		"license",
		"licence",
		"copyright",
	)
)

func init() {
	analyzer.RegisterAnalyzer(newLicenseFileAnalyzer())
}

// licenseFileAnalyzer is an analyzer for file headers and license files
type licenseFileAnalyzer struct {
	classifierConfidenceLevel float64
}

func newLicenseFileAnalyzer() *licenseFileAnalyzer {
	return &licenseFileAnalyzer{}
}

func (a *licenseFileAnalyzer) Analyze(ctx context.Context, input analyzer.AnalysisInput) (*analyzer.AnalysisResult, error) {
	ctx = log.WithContextPrefix(ctx, "license")
	log.DebugContext(ctx, "License scanning", log.FilePath(input.FilePath))

	// need files to be text based, readable files
	readable, err := isHumanReadable(input.Content, input.Info.Size())
	if err != nil || !readable {
		return nil, nil
	}
	lf, err := licensing.Classify(input.FilePath, input.Content, a.classifierConfidenceLevel)
	if err != nil {
		return nil, xerrors.Errorf("license classification error: %w", err)
	} else if len(lf.Findings) == 0 {
		return nil, nil
	}

	return &analyzer.AnalysisResult{
		Licenses: []types.LicenseFile{*lf},
	}, nil
}

func (a *licenseFileAnalyzer) Init(opt analyzer.AnalyzerOptions) error {
	a.classifierConfidenceLevel = opt.LicenseScannerOption.ClassifierConfidenceLevel
	return nil
}

func (a *licenseFileAnalyzer) Required(filePath string, _ os.FileInfo) bool {
	for _, skipDir := range skipDirs {
		if strings.Contains(filePath, skipDir) {
			return false
		}
	}
	if acceptedExtensions.Contains(filepath.Ext(filePath)) {
		return true
	}

	return acceptedFileNames.Contains(filepath.Base(filePath))
}

func isHumanReadable(content xio.ReadSeekerAt, fileSize int64) (bool, error) {
	headSize := int(math.Min(float64(fileSize), 300))
	head := make([]byte, headSize)
	if _, err := content.Read(head); err != nil {
		return false, err
	}
	if _, err := content.Seek(0, io.SeekStart); err != nil {
		return false, err
	}

	// cf. https://github.com/file/file/blob/f2a6e7cb7db9b5fd86100403df6b2f830c7f22ba/src/encoding.c#L151-L228
	for _, b := range head {
		if b < 7 || b == 11 || (13 < b && b < 27) || (27 < b && b < 0x20) || b == 0x7f {
			return false, nil
		}
	}

	return true, nil
}

func (a *licenseFileAnalyzer) Type() analyzer.Type {
	return analyzer.TypeLicenseFile
}

func (a *licenseFileAnalyzer) Version() int {
	return version
}