// Command catalog-diff compiles a host's Puppet catalog in two environments
// and reports what changes between them.
package main

import (
	"context"
	"errors"
	"fmt"
	"io"
	"math/rand"
	"os"
	"sync"
	"time"

	"github.com/spf13/cobra"

	"git.unkin.net/unkin/puppet-catalog-tools/internal/catalog"
	"git.unkin.net/unkin/puppet-catalog-tools/internal/config"
	"git.unkin.net/unkin/puppet-catalog-tools/internal/puppetdb"
	"git.unkin.net/unkin/puppet-catalog-tools/internal/puppetserver"
)

var version = "dev"

// Exit codes, also documented in --help and the README.
const (
	exitSame      = 0 // compiled, no differences
	exitCompile   = 1 // catalog compilation failed
	exitDifferent = 2 // compiled, differences present
	exitTransport = 3 // transport, auth, environment-mismatch or usage error
)

// maxRetry bounds --retry: past this the backoff is already pinned at its
// ceiling and the run outlives any review it could inform.
const maxRetry = 20

const longHelp = `Compile a host's Puppet catalog in a base environment and in the environment
built from the branch under test, then diff the two.

Branch names are converted to environment names the way g10k deploys them:
every character outside [0-9A-Za-z_] becomes "_". Use --environment to bypass
that conversion.

Exit codes:
  0  catalogs compiled, no differences
  1  catalog compilation failed in one or both environments
  2  catalogs compiled, differences present
  3  transport, auth, environment-mismatch or usage error

--testonly compiles the test environment only and returns 0, 1 or 3 (never 2).`

type options struct {
	branch          string
	environment     string
	base            string
	testonly        bool
	jsonOut         bool
	server          string
	puppetdb        string
	cert            string
	key             string
	cacert          string
	timeout         time.Duration
	retry           int
	includeClasses  bool
	ignoreResources []string
	ignoreAttrs     []string
	datatypeChanges bool
	detailAdd       bool
	sourceFileLine  bool
}

// exitError carries the exit code a failure should produce.
type exitError struct {
	code int
	err  error
}

func (e *exitError) Error() string {
	if e == nil {
		return "<nil>"
	}
	if e.err == nil {
		return fmt.Sprintf("failed with exit code %d", e.code)
	}
	return e.err.Error()
}

func (e *exitError) Unwrap() error {
	if e == nil {
		return nil
	}
	return e.err
}

func fail(code int, format string, args ...any) *exitError {
	return &exitError{code: code, err: fmt.Errorf(format, args...)}
}

func main() {
	cfg, err := config.Load()
	if err != nil {
		fmt.Fprintln(os.Stderr, "config error:", err)
		os.Exit(exitTransport)
	}

	opts := &options{}
	root := &cobra.Command{
		Use:           "catalog-diff <hostname>",
		Short:         "Diff a host's Puppet catalog between two environments",
		Long:          longHelp,
		Args:          cobra.ExactArgs(1),
		Version:       version,
		SilenceUsage:  true,
		SilenceErrors: true,
		RunE: func(cmd *cobra.Command, args []string) error {
			return run(cmd.Context(), cmd.OutOrStdout(), args[0], opts)
		},
	}

	f := root.Flags()
	f.StringVarP(&opts.branch, "branch", "b", "", "branch under test (required unless --environment is given)")
	f.StringVar(&opts.environment, "environment", "", "explicit puppet environment name, bypasses branch name conversion")
	f.StringVar(&opts.base, "base", cfg.BaseEnvironment, "base environment to diff against")
	f.BoolVar(&opts.testonly, "testonly", false, "compile the test environment only; no output, result via exit code")
	f.BoolVar(&opts.jsonOut, "json", false, "machine-readable output")
	f.StringVar(&opts.server, "server", cfg.ServerURL, "puppetserver base URL")
	f.StringVar(&opts.puppetdb, "puppetdb", cfg.PuppetDBURL, "PuppetDB base URL")
	f.StringVar(&opts.cert, "cert", cfg.Cert, "client certificate PEM (CATALOG_DIFF_CERT)")
	f.StringVar(&opts.key, "key", cfg.Key, "client private key PEM (CATALOG_DIFF_KEY)")
	f.StringVar(&opts.cacert, "cacert", cfg.CACert, "CA bundle PEM used to verify puppetserver (CATALOG_DIFF_CACERT)")
	f.DurationVar(&opts.timeout, "timeout", 10*time.Minute, "per-compile timeout")
	f.IntVar(&opts.retry, "retry", 2, "retries for transient compile or transport failures")
	f.BoolVar(&opts.includeClasses, "include-classes", false, "diff Class resources, which manage nothing themselves")
	f.StringArrayVar(&opts.ignoreResources, "ignore", nil, "ignore resources matching Type[Title] (glob), repeatable")
	f.StringArrayVar(&opts.ignoreAttrs, "ignore-attr", nil, "ignore a parameter on every resource, repeatable")
	f.BoolVar(&opts.datatypeChanges, "display-datatype-changes", false, "report changes where only the datatype differs (28 vs \"28\")")
	f.BoolVar(&opts.detailAdd, "display-detail-add", false, "expand the parameters of added resources")
	f.BoolVar(&opts.sourceFileLine, "display-source-file-line", false, "print the manifest file and line each change came from")

	root.AddCommand(configCmd())

	if err := root.Execute(); err != nil {
		// errSilent only carries an exit code; the diff is already printed.
		if !errors.Is(err, errSilent) {
			fmt.Fprintln(os.Stderr, "error:", err)
		}
		var ee *exitError
		if errors.As(err, &ee) {
			os.Exit(ee.code)
		}
		os.Exit(exitTransport)
	}
}

func configCmd() *cobra.Command {
	cmd := &cobra.Command{Use: "config", Short: "Manage configuration"}
	cmd.AddCommand(&cobra.Command{
		Use:   "init",
		Short: "Write a default config file to " + config.Path(),
		RunE: func(_ *cobra.Command, _ []string) error {
			path, err := config.WriteDefault()
			if err != nil {
				return err
			}
			fmt.Println("Config written to", path)
			return nil
		},
	})
	cmd.AddCommand(&cobra.Command{
		Use:   "show",
		Short: "Print the active configuration",
		RunE: func(_ *cobra.Command, _ []string) error {
			cfg, err := config.Load()
			if err != nil {
				return err
			}
			fmt.Printf("config file      : %s\n", config.Path())
			fmt.Printf("server_url       : %s\n", cfg.ServerURL)
			fmt.Printf("puppetdb_url     : %s\n", cfg.PuppetDBURL)
			fmt.Printf("cert             : %s\n", cfg.Cert)
			fmt.Printf("key              : %s\n", cfg.Key)
			fmt.Printf("cacert           : %s\n", cfg.CACert)
			fmt.Printf("base_environment : %s\n", cfg.BaseEnvironment)
			return nil
		},
	})
	return cmd
}

// validate rejects flag values the rest of the run cannot act on. A negative
// retry count would skip the compile loop entirely and a non-positive timeout
// cancels every request before it is sent, so both are usage errors.
func validate(opts *options) error {
	if opts.retry < 0 {
		return fail(exitTransport, "--retry must be zero or more, got %d", opts.retry)
	}
	if opts.retry > maxRetry {
		return fail(exitTransport, "--retry must be at most %d, got %d", maxRetry, opts.retry)
	}
	if opts.timeout <= 0 {
		return fail(exitTransport, "--timeout must be positive, got %s", opts.timeout)
	}
	return nil
}

// resolveEnvironment turns the flags into the environment to test.
func resolveEnvironment(opts *options) (string, error) {
	if opts.environment != "" && opts.branch != "" {
		return "", fail(exitTransport, "--branch and --environment are mutually exclusive")
	}
	if opts.environment != "" {
		if !catalog.ValidEnvironmentName(opts.environment) {
			return "", fail(exitTransport, "%q is not a valid puppet environment name (must match [a-z0-9_]+)", opts.environment)
		}
		return opts.environment, nil
	}
	if opts.branch == "" {
		return "", fail(exitTransport, "one of --branch or --environment is required")
	}
	env := catalog.BranchToEnvironment(opts.branch)
	if !catalog.ValidEnvironmentName(env) {
		return "", fail(exitTransport,
			"branch %q deploys as environment %q, which puppet rejects (environment names must match [a-z0-9_]+). "+
				"Rename the branch or pass --environment", opts.branch, env)
	}
	return env, nil
}

func run(ctx context.Context, out io.Writer, hostname string, opts *options) error {
	if ctx == nil {
		ctx = context.Background()
	}

	if err := validate(opts); err != nil {
		return err
	}

	testEnv, err := resolveEnvironment(opts)
	if err != nil {
		return err
	}
	if !catalog.ValidEnvironmentName(opts.base) {
		return fail(exitTransport, "%q is not a valid base environment name (must match [a-z0-9_]+)", opts.base)
	}
	if testEnv == opts.base && !opts.testonly {
		return fail(exitTransport, "test and base environments are both %q; there is nothing to diff", testEnv)
	}

	tlsCfg, err := puppetserver.TLSConfig(opts.cert, opts.key, opts.cacert)
	if err != nil {
		return &exitError{code: exitTransport, err: err}
	}

	server := puppetserver.New(opts.server, tlsCfg, opts.timeout)
	facts := puppetdb.New(opts.puppetdb, opts.timeout)
	facts.Warn = func(msg string, _ int) { fmt.Fprintln(os.Stderr, "warning:", msg) }

	healthCtx, cancel := context.WithTimeout(ctx, 30*time.Second)
	defer cancel()
	if err := server.Health(healthCtx); err != nil {
		return &exitError{code: exitTransport, err: err}
	}

	factValues, err := facts.Facts(ctx, hostname)
	if err != nil {
		return &exitError{code: exitTransport, err: err}
	}

	if opts.testonly {
		_, err := compile(ctx, server, hostname, testEnv, factValues, opts)
		return err
	}

	// Both compilations are independent, so run them together: one host costs
	// one compile's wall clock rather than two. The first failure cancels its
	// sibling — a quick manifest error should not wait out a full compile.
	compileCtx, abandon := context.WithCancel(ctx)
	defer abandon()

	var (
		wg               sync.WaitGroup
		testCat, baseCat *catalog.Catalog
		testErr, baseErr error
	)
	wg.Add(2)
	go func() {
		defer wg.Done()
		testCat, testErr = compile(compileCtx, server, hostname, testEnv, factValues, opts)
		if testErr != nil {
			abandon()
		}
	}()
	go func() {
		defer wg.Done()
		baseCat, baseErr = compile(compileCtx, server, hostname, opts.base, factValues, opts)
		if baseErr != nil {
			abandon()
		}
	}()
	wg.Wait()

	// Report the test environment's failure first: it is the one under review,
	// unless it only stopped because the base compile failed first.
	switch {
	case testErr != nil && baseErr != nil:
		if abandoned(ctx, testErr) {
			return baseErr
		}
		return testErr
	case testErr != nil:
		return testErr
	case baseErr != nil:
		return baseErr
	}

	normOpts := catalog.Options{
		IncludeClasses:  opts.includeClasses,
		IgnoreResources: opts.ignoreResources,
		IgnoreAttrs:     opts.ignoreAttrs,
	}
	changes := catalog.Diff(
		catalog.Normalize(baseCat, normOpts),
		catalog.Normalize(testCat, normOpts),
		catalog.DiffOptions{DisplayDatatypeChanges: opts.datatypeChanges},
	)
	report := catalog.NewReport(hostname, opts.base, testEnv, changes)

	if opts.jsonOut {
		err = catalog.RenderJSON(out, report)
	} else {
		err = catalog.RenderText(out, report, catalog.RenderOptions{
			Colour:         isTerminal(os.Stdout),
			DetailAdd:      opts.detailAdd,
			SourceFileLine: opts.sourceFileLine,
		})
	}
	if err != nil {
		return &exitError{code: exitTransport, err: err}
	}
	if len(changes) > 0 {
		return &exitError{code: exitDifferent, err: errSilent}
	}
	return nil
}

// errSilent marks an exit code that carries no message of its own: the diff
// itself has already been printed.
var errSilent = errors.New("differences present")

// abandoned reports whether err is only the fallout of cancelling a compile
// because its sibling failed first, rather than a failure in its own right.
func abandoned(ctx context.Context, err error) bool {
	return ctx.Err() == nil && errors.Is(err, context.Canceled)
}

// compile runs one compilation, retrying transient failures, and maps the
// final failure onto an exit code.
func compile(ctx context.Context, server *puppetserver.Client, hostname, environment string, facts map[string]any, opts *options) (*catalog.Catalog, error) {
	var lastErr error
	for attempt := 0; attempt <= opts.retry; attempt++ {
		if attempt > 0 {
			// The cancellation, not the error that earned the retry, is why
			// this compile stopped.
			if err := sleepCtx(ctx, backoff(attempt)); err != nil {
				if lastErr != nil {
					err = fmt.Errorf("%w while retrying after: %v", err, lastErr)
				}
				return nil, &exitError{code: exitTransport, err: err}
			}
		}
		cat, err := server.Compile(ctx, puppetserver.CompileRequest{
			Certname:     hostname,
			Environment:  environment,
			Facts:        facts,
			TrustedFacts: puppetserver.TrustedFacts(hostname),
		})
		if err == nil {
			return cat, nil
		}
		lastErr = err
		if !transient(err) {
			break
		}
	}

	if lastErr == nil {
		return nil, &exitError{code: exitTransport, err: fmt.Errorf("no compile was attempted for %s in %s", hostname, environment)}
	}
	var compileErr *puppetserver.CompileError
	if errors.As(lastErr, &compileErr) {
		return nil, &exitError{code: exitCompile, err: lastErr}
	}
	return nil, &exitError{code: exitTransport, err: lastErr}
}

// transient reports whether a failure is worth retrying: a transport error, a
// server-side 5xx, or a compile the compiler's own PuppetDB query broke. A
// manifest that does not compile, an environment mismatch and an unusable
// response shape are all settled answers and are not retried.
func transient(err error) bool {
	var mismatch *puppetserver.EnvironmentMismatchError
	if errors.As(err, &mismatch) {
		return false
	}
	var respErr *puppetserver.ResponseError
	if errors.As(err, &respErr) {
		return false
	}
	var compileErr *puppetserver.CompileError
	if errors.As(err, &compileErr) {
		return compileErr.Transient()
	}
	return true
}

// backoff grows exponentially from 2s and adds up to 50% jitter, so parallel
// compiles do not retry in lockstep against an autoscaling compiler pool. The
// shift is capped: an unbounded one overflows into a negative delay.
func backoff(attempt int) time.Duration {
	const (
		start = 2 * time.Second
		limit = 30 * time.Second
	)
	d := limit
	if attempt >= 1 && attempt < 32 {
		if shifted := start << (attempt - 1); shifted > 0 && shifted < limit {
			d = shifted
		}
	}
	return d + time.Duration(rand.Int63n(int64(d/2)))
}

func sleepCtx(ctx context.Context, d time.Duration) error {
	timer := time.NewTimer(d)
	defer timer.Stop()
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-timer.C:
		return nil
	}
}

func isTerminal(f *os.File) bool {
	info, err := f.Stat()
	if err != nil {
		return false
	}
	return info.Mode()&os.ModeCharDevice != 0
}