// Copyright 2021 The Go 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 main

import (
	"fmt"
	"os"
	"strings"
	"time"

	"golang.org/x/tools/go/packages"
	"golang.org/x/tools/go/ssa"
	"golang.org/x/vulndb/cmd/vulnreport/internal/vulnentries"
	"golang.org/x/vulndb/internal/derrors"
	"golang.org/x/vulndb/internal/report"
	"golang.org/x/vulndb/internal/semver"
)

// exportedFunctions returns a set of vulnerable functions exported by a set of packages
// from the same module.
func exportedFunctions(pkgs []*packages.Package, r *report.Report) (_ map[string]bool, err error) {
	defer derrors.Wrap(&err, "exportedFunctions(%q)", pkgs[0].PkgPath)

	if pkgs[0].Module != nil && !affected(r, pkgs[0].Module.Version) {
		fmt.Fprintf(os.Stderr, "version %s of module %s is not affected by this vuln\n",
			pkgs[0].Module.Version, pkgs[0].Module.Path)
		return map[string]bool{}, nil
	}

	entries, err := vulnentries.Functions(pkgs, r)
	if err != nil {
		return nil, err
	}
	// Return the name of all entry points.
	// Note that "main" and "init" are both possible entries.
	// Both have clear meanings: "main" means that invoking
	// the program is a problem, and "init" means that very likely
	// some global state is altered, and so every exported function
	// is vulnerable. For now, we leave it to consumers to use this
	// information as they wish.
	names := map[string]bool{}
	for _, e := range entries {
		if pkgPath(e) == pkgs[0].PkgPath {
			names[symbolName(e)] = true
		}
	}
	return names, nil
}

func symbolName(fn *ssa.Function) string {
	recv := fn.Signature.Recv()
	if recv == nil {
		return fn.Name()
	}
	recvType := recv.Type().String()
	// Remove package path from type.
	i := strings.LastIndexByte(recvType, '.')
	if i < 0 {
		return recvType + "." + fn.Name()
	}
	return recvType[i+1:] + "." + fn.Name()
}

// pkgPath returns the path of the f's enclosing package, if any.
// Otherwise, returns "".
//
// Copy of golang.org/x/vuln/internal/vulncheck/source.go:pkgPath.
func pkgPath(f *ssa.Function) string {
	if f.Package() != nil && f.Package().Pkg != nil {
		return f.Package().Pkg.Path()
	}
	return ""
}

func affected(r *report.Report, version string) bool {
	// Generate dummy osv entry just so we
	// can check semver ranges.
	o := r.GenerateOSVEntry("", time.Now())
	for _, a := range o.Affected {
		if semver.AffectsSemver(a.Ranges, version) {
			return true
		}
	}
	return false
}