// Command vulncheck runs govulncheck over the module and fails on each
// vulnerability that the code calls, the required check "Vulnerabilities"
// of docs/agentic-workflow.md, with the levels of docs/risk-analysis.md.
//
// With -base it fails only on those the branch brings: called at HEAD,
// not called at the merge base with that ref. So a vulnerability found
// anew in the standard library of main stops no unrelated branch; the
// nightly build checks main in full.
//
//	go run ./tools/vulncheck                   # main, in full
//	go run ./tools/vulncheck -base origin/main # a branch, only its own
//
// It is a development tool, not part of the werkdock binary.
package main

import (
	"bufio"
	"bytes"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"io"
	"os"
	"os/exec"
	"sort"
	"strings"
)

// The Go toolchain of the module downloads it on first use; it runs on a
// newer Go than the module's, but checks the standard library of the
// module's own toolchain.
const govulncheck = "golang.org/x/vuln/cmd/govulncheck@v1.8.0"

const exceptionsFile = "tools/vulnerability-exceptions.txt"

// vuln is one OSV entry as far as the verdict needs it.
// Calls holds each vulnerable symbol that the code calls, as
// "module@version package.function", so that a branch that calls another
// symbol of the same advisory, or moves to another affected version, is
// not mistaken for its merge base.
type vuln struct {
	ID      string
	Summary string
	Fixed   string
	Calls   map[string]bool
}

func main() {
	base := flag.String("base", "", "ref whose merge base with HEAD is the baseline; empty checks in full")
	flag.Parse()
	if err := run(*base, os.Stdout); err != nil {
		fmt.Fprintln(os.Stderr, "vulncheck:", err)
		os.Exit(1)
	}
}

func run(base string, out io.Writer) error {
	exceptions, err := readExceptions(exceptionsFile)
	if err != nil {
		return err
	}
	head, err := scan(".")
	if err != nil {
		return err
	}
	var baseline map[string]vuln
	if base != "" {
		if baseline, err = scanMergeBase(base); err != nil {
			return err
		}
	}
	failing := verdict(head, baseline, exceptions)
	for _, v := range failing {
		fmt.Fprintf(out, "%s: %s; fixed in %s; https://pkg.go.dev/vuln/%s\n", v.ID, v.Summary, v.Fixed, v.ID)
	}
	if len(failing) > 0 {
		return fmt.Errorf("%d called vulnerabilities; fix them, or add an exception with its reason to %s",
			len(failing), exceptionsFile)
	}
	fmt.Fprintln(out, "vulncheck: no called vulnerability")
	return nil
}

// verdict returns the called vulnerabilities of head without an exception,
// and with a baseline only those with a call that the baseline lacks,
// sorted by id.
func verdict(head, baseline map[string]vuln, exceptions map[string]string) []vuln {
	var failing []vuln
	for id, v := range head {
		if len(v.Calls) == 0 || exceptions[id] != "" {
			continue
		}
		if baseline != nil && !bringsCall(v, baseline[id]) {
			continue
		}
		failing = append(failing, v)
	}
	sort.Slice(failing, func(i, j int) bool { return failing[i].ID < failing[j].ID })
	return failing
}

func bringsCall(head, base vuln) bool {
	for call := range head.Calls {
		if !base.Calls[call] {
			return true
		}
	}
	return false
}

func scan(dir string) (map[string]vuln, error) {
	cmd := exec.Command("go", "run", govulncheck, "-format", "json", "./...")
	cmd.Dir = dir
	cmd.Stderr = os.Stderr
	stdout, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("govulncheck in %s: %w", dir, err)
	}
	return parse(bytes.NewReader(stdout))
}

// scanMergeBase scans an export of the merge base, which writes nothing into the repository.
func scanMergeBase(ref string) (map[string]vuln, error) {
	mergeBase, err := exec.Command("git", "merge-base", "HEAD", ref).Output()
	if err != nil {
		return nil, fmt.Errorf("merge base with %s: %w", ref, err)
	}
	dir, err := os.MkdirTemp("", "vulncheck-")
	if err != nil {
		return nil, err
	}
	defer os.RemoveAll(dir)
	export := exec.Command("sh", "-c", `git archive "$1" | tar -x -C "$2"`, "sh", strings.TrimSpace(string(mergeBase)), dir)
	if out, err := export.CombinedOutput(); err != nil {
		return nil, fmt.Errorf("export of the merge base: %w: %s", err, out)
	}
	return scan(dir)
}

// parse reads govulncheck's JSON stream: one "osv" object per entry, and
// "finding" objects whose first trace frame names a function when the
// code calls the vulnerable symbol.
func parse(r io.Reader) (map[string]vuln, error) {
	type frame struct {
		Module   string `json:"module"`
		Version  string `json:"version"`
		Package  string `json:"package"`
		Function string `json:"function"`
	}
	var msg struct {
		OSV *struct {
			ID      string `json:"id"`
			Summary string `json:"summary"`
		} `json:"osv"`
		Finding *struct {
			OSV          string  `json:"osv"`
			FixedVersion string  `json:"fixed_version"`
			Trace        []frame `json:"trace"`
		} `json:"finding"`
	}
	vulns := map[string]vuln{}
	dec := json.NewDecoder(r)
	for {
		msg.OSV, msg.Finding = nil, nil
		if err := dec.Decode(&msg); errors.Is(err, io.EOF) {
			return vulns, nil
		} else if err != nil {
			return nil, fmt.Errorf("govulncheck output: %w", err)
		}
		if o := msg.OSV; o != nil {
			v := vulns[o.ID]
			v.ID, v.Summary = o.ID, o.Summary
			vulns[o.ID] = v
		}
		if f := msg.Finding; f != nil {
			v := vulns[f.OSV]
			v.ID = f.OSV
			if f.FixedVersion != "" {
				v.Fixed = f.FixedVersion
			}
			if len(f.Trace) > 0 && f.Trace[0].Function != "" {
				t := f.Trace[0]
				if v.Calls == nil {
					v.Calls = map[string]bool{}
				}
				v.Calls[t.Module+"@"+t.Version+" "+t.Package+"."+t.Function] = true
			}
			vulns[f.OSV] = v
		}
	}
}

// readExceptions reads "ID reason" lines; '#' starts a comment.
// An exception without a reason is an error, since the reason is what the
// human approves.
func readExceptions(path string) (map[string]string, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	return parseExceptions(f)
}

func parseExceptions(r io.Reader) (map[string]string, error) {
	exceptions := map[string]string{}
	sc := bufio.NewScanner(r)
	for n := 1; sc.Scan(); n++ {
		line := strings.TrimSpace(sc.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		id, reason, _ := strings.Cut(line, " ")
		if strings.TrimSpace(reason) == "" {
			return nil, fmt.Errorf("%s:%d: exception %s without a reason", exceptionsFile, n, id)
		}
		exceptions[id] = strings.TrimSpace(reason)
	}
	return exceptions, sc.Err()
}