// Package main is a command-lint tool `zs` called Zen Static for generating static websites
package main

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"os/exec"
	"os/signal"
	"path/filepath"
	"strings"
	"syscall"
	"text/template"
	"time"

	embed "github.com/13rac1/goldmark-embed"
	d2 "github.com/FurqanSoftware/goldmark-d2"
	chromahtml "github.com/alecthomas/chroma/v2/formatters/html"
	ignore "github.com/sabhiram/go-gitignore"
	log "github.com/sirupsen/logrus"
	"github.com/spf13/cobra"
	"github.com/spf13/viper"
	fences "github.com/stefanfritsch/goldmark-fences"
	"github.com/yuin/goldmark"
	highlighting "github.com/yuin/goldmark-highlighting/v2"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/renderer/html"
	"go.abhg.dev/goldmark/anchor"
	"go.abhg.dev/goldmark/wikilink"
	"go.mills.io/static"
	"golang.org/x/sync/errgroup"
	"gopkg.in/yaml.v2"
)

const (
	// ZSDIR is the default directory for storing layouts and extensions
	ZSDIR = ".zs"

	// ZSCONFIG is the default configuration name (without extension)
	ZSCONFIG = "config"

	// ZSIGNORE is the default ignore file
	ZSIGNORE = ".zsignore"

	// PUBDIR is the default directory for publishing final built content
	PUBDIR = ".pub"

	// DefaultIgnore is the default set of ignore patterns if no .zsignore
	DefaultIgnore = `*~
*.bak

COPYING
Dockerfile
LICENSE
Makefile
README.md`
)

// Ignore holds a set of patterns to ignore from parsing a .zsignore file
var Ignore *ignore.GitIgnore

// Parser holds a configured global instance of the goldmark markdown parser
var Parser goldmark.Markdown

var (
	configFile        string
	enabledExtensions []string
)

// Extensions is a mapping of name to extension and the default set of extensions enabled
// which can be overridden with -e/--extension or the extensions key
// in ia config file such as .zs/config.yml
var Extensions = map[string]goldmark.Extender{
	"table":          extension.Table,
	"strikethrough":  extension.Strikethrough,
	"linkify":        extension.Linkify,
	"tasklist":       extension.TaskList,
	"definitionlist": extension.DefinitionList,
	"footnote":       extension.Footnote,
	"typography":     extension.Typographer,
	"cjk":            extension.CJK,
	"highlighting": highlighting.NewHighlighting(
		highlighting.WithStyle("github"),
		highlighting.WithFormatOptions(
			chromahtml.WithLineNumbers(true),
		),
	),
	"anchor":   &anchor.Extender{Texter: anchor.Text(" ")},
	"d2":       &d2.Extender{},
	"embed":    embed.New(),
	"fences":   &fences.Extender{},
	"wikilink": &wikilink.Extender{},
}

// Vars holds a map of global variables
type Vars map[string]string

// MapKeys returns a slice of keys from a map
func MapKeys[K comparable, V any](m map[K]V) []K {
	r := make([]K, 0, len(m))
	for k := range m {
		r = append(r, k)
	}
	return r
}

// NewTicker is a function that wraps a time.Ticker and ticks immediately instead of waiting for the first interval
func NewTicker(d time.Duration) *time.Ticker {
	ticker := time.NewTicker(d)
	oc := ticker.C
	nc := make(chan time.Time, 1)
	go func() {
		nc <- time.Now()
		for tm := range oc {
			nc <- tm
		}
	}()
	ticker.C = nc
	return ticker
}

// RootCmd is the base command when called without any subcommands
var RootCmd = &cobra.Command{
	Use:     "zs",
	Version: FullVersion(),
	Short:   "zs the zen static site generator",
	Long: `zs is an extremely minimal static site generator written in Go.

  - Keep your texts in markdown, or HTML format right in the main directory of your blog/site.
  - Keep all service files (extensions, layout pages, deployment scripts etc) in the .zs subdirectory.
  - Define variables in the header of the content files using YAML front matter:
  - Use placeholders for variables and plugins in your markdown or html files, e.g. {{ title }} or {{ command arg1 arg2 }}.
  - Write extensions in any language you like and put them into the .zs sub-directory.
  - Everything the extensions prints to stdout becomes the value of the placeholder.
`,
	PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
		debug, err := cmd.Flags().GetBool("debug")
		if err != nil {
			return fmt.Errorf("error getting debug flag: %w", err)
		}

		if debug {
			log.SetLevel(log.DebugLevel)
		} else {
			log.SetLevel(log.InfoLevel)
		}

		var extensions []goldmark.Extender
		for _, name := range viper.GetStringSlice("extensions") {
			if extender, valid := Extensions[name]; valid {
				extensions = append(extensions, extender)
			} else {
				log.Warnf("invalid extension: %s", name)
			}
		}

		Parser = goldmark.New(
			goldmark.WithExtensions(extensions...),
			goldmark.WithParserOptions(
				parser.WithAttribute(),
				parser.WithAutoHeadingID(),
			),
			goldmark.WithRendererOptions(
				html.WithHardWraps(),
				html.WithXHTML(),
				html.WithUnsafe(),
			),
		)

		return nil
	},
}

// BuildCmd is the build sub-command that performs whole builds or single builds
var BuildCmd = &cobra.Command{
	Use:   "build [<file>]",
	Short: "Builds the whole site or a single file",
	Long:  `The build command builds the entire site or a single file if specified.`,
	Args:  cobra.RangeArgs(0, 1),
	RunE: func(cmd *cobra.Command, args []string) error {
		if len(args) == 0 {
			ctx := context.Background()
			if err := buildAll(ctx, false); err != nil {
				return fmt.Errorf("error building site: %w", err)
			}
			return nil
		}

		if err := build(args[0], os.Stdout, globals()); err != nil {
			return fmt.Errorf("error building file %q", args[0])
		}

		return nil
	},
}

// ServeCmd is the serve sub-command that performs whole builds or single builds
var ServeCmd = &cobra.Command{
	Use:   "serve [flags]",
	Short: "Serves the site and rebuilds automatically",
	Long:  `The serve command serves the site and watches for rebuilds automatically`,
	Args:  cobra.RangeArgs(0, 1),
	RunE: func(cmd *cobra.Command, args []string) error {
		var wg errgroup.Group

		ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
		defer cancel()

		bind, err := cmd.Flags().GetString("bind")
		if err != nil {
			return fmt.Errorf("error getting bind flag: %w", err)
		}

		root, err := cmd.Flags().GetString("root")
		if err != nil {
			return fmt.Errorf("error getting root flag: %w", err)
		}

		wg.Go(func() error {
			if err := serve(ctx, bind, root); err != nil {
				return fmt.Errorf("error serving site: %w", err)
			}
			return nil
		})

		if err := wg.Wait(); err != nil {
			return fmt.Errorf("error running serve: %w", err)
		}

		return nil
	},
}

// VarCmd is the var sub-command that performs whole builds or single builds
var VarCmd = &cobra.Command{
	Use:     "var <file> [<var>...]",
	Aliases: []string{"vars"},
	Short:   "Display variables for the specified file",
	Long: `The var command extracts and display sll teh variables defined in a file.
If the name of variables (optional) are passed as additional arguments, only those variables
are display instead of all variables (the default behavior).`,
	Args: cobra.MinimumNArgs(1),
	RunE: func(cmd *cobra.Command, args []string) error {
		s := ""

		vars, _, err := getVars(args[0], Vars{})
		if err != nil {
			return fmt.Errorf("error getting variables from %s: %w", args[0], err)
		}

		if len(args) > 1 {
			for _, a := range args[1:] {
				s = s + vars[a] + "\n"
			}
		} else {
			for k, v := range vars {
				s = s + k + ":" + v + "\n"
			}
		}
		fmt.Println(strings.TrimSpace(s))

		return nil
	},
}

// WatchCmd is the watch sub-command that performs whole builds or single builds
var WatchCmd = &cobra.Command{
	Use:   "watch",
	Short: "Watches for file changes and rebuilds modified files",
	Long:  `The watch command watches for any changes to files and rebuilds them automatically`,
	Args:  cobra.RangeArgs(0, 1),
	RunE: func(cmd *cobra.Command, args []string) error {
		var wg errgroup.Group

		ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
		defer cancel()

		wg.Go(func() error {
			if err := buildAll(ctx, true); err != nil {
				return fmt.Errorf("error watching for changes: %w", err)
			}
			return nil
		})

		if err := wg.Wait(); err != nil {
			return fmt.Errorf("error running watch: %w", err)
		}

		return nil
	},
}

// renameExt renames extension (if any) from oldext to newext
// If oldext is an empty string - extension is extracted automatically.
// If path has no extension - new extension is appended
func renameExt(path, oldext, newext string) string {
	if oldext == "" {
		oldext = filepath.Ext(path)
	}
	if oldext == "" || strings.HasSuffix(path, oldext) {
		return strings.TrimSuffix(path, oldext) + newext
	}
	return path
}

// globals returns list of global OS environment variables that start
// with ZS_ prefix as Vars, so the values can be used inside templates
func globals() Vars {
	vars := Vars{
		"title":       viper.GetString("title"),
		"description": viper.GetString("description"),
		"keywords":    viper.GetString("keywords"),
	}

	if viper.GetBool("production") {
		vars["production"] = "1"
	}

	for _, e := range os.Environ() {
		pair := strings.Split(e, "=")
		if strings.HasPrefix(pair[0], "ZS_") {
			vars[strings.ToLower(pair[0][3:])] = pair[1]
		}
	}
	return vars
}

// run executes a command or a script. Vars define the command environment,
// each zs var is converted into OS environment variable with ZS_ prefix
// prepended.  Additional variable $ZS contains path to the zs binary. Command
// stderr is printed to zs stderr, command output is returned as a string.
func run(vars Vars, cmd string, args ...string) (string, error) {
	// First check if partial exists (.html)
	if b, err := ioutil.ReadFile(filepath.Join(ZSDIR, cmd+".html")); err == nil {
		return string(b), nil
	}

	var errbuf, outbuf bytes.Buffer
	c := exec.Command(cmd, args...)
	env := []string{"ZS=" + os.Args[0], "ZS_OUTDIR=" + PUBDIR}
	env = append(env, os.Environ()...)
	for k, v := range vars {
		if k != "content" {
			env = append(env, "ZS_"+strings.ToUpper(k)+"="+v)
		}
	}
	c.Env = env
	c.Stdout = &outbuf
	c.Stderr = &errbuf

	if err := c.Run(); err != nil {
		log.Errorf("error running command: %s", cmd)
		log.Error(errbuf.String())
		return "", err
	}

	return string(outbuf.Bytes()), nil
}

// getVars returns list of variables defined in a text file and actual file
// content following the variables declaration. Header is separated from
// content by an empty line. Header can be either YAML or JSON.
// If no empty newline is found - file is treated as content-only.
func getVars(path string, globals Vars) (Vars, string, error) {
	if Ignore.MatchesPath(path) {
		return nil, "", nil
	}

	b, err := ioutil.ReadFile(path)
	if err != nil {
		return nil, "", err
	}
	s := string(b)

	// Pick some default values for content-dependent variables
	v := Vars{}
	title := strings.Replace(strings.Replace(path, "_", " ", -1), "-", " ", -1)
	v["title"] = strings.ToTitle(title)
	v["description"] = ""
	v["file"] = path
	v["url"] = path[:len(path)-len(filepath.Ext(path))] + ".html"
	v["output"] = filepath.Join(PUBDIR, v["url"])

	// Override default values with globals
	for name, value := range globals {
		v[name] = value
	}

	// Add layout if none is specified
	if _, ok := v["layout"]; !ok {
		v["layout"] = "layout.html"
	}

	delim := "\n---\n"
	sep := strings.Index(s, delim)
	if sep == -1 {
		return v, s, nil
	}

	header := s[:sep]
	body := s[sep+len(delim):]

	vars := Vars{}
	if err := yaml.Unmarshal([]byte(header), &vars); err != nil {
		log.WithError(err).Warn("failed to parse header")
		return v, s, nil
	}
	// Override default values + globals with the ones defines in the file
	for key, value := range vars {
		v[key] = value
	}
	if strings.HasPrefix(v["url"], "./") {
		v["url"] = v["url"][2:]
	}
	return v, body, nil
}

// Render expanding zs plugins and variables
func render(s string, vars Vars) (string, error) {
	openingDelimiter := "{{"
	closingDelimiter := "}}"

	out := &bytes.Buffer{}
	for {
		from := strings.Index(s, openingDelimiter)
		if from == -1 {
			out.WriteString(s)
			return out.String(), nil
		}

		to := strings.Index(s, closingDelimiter)
		if to == -1 {
			return "", fmt.Errorf("closing delimiter not found")
		}

		out.WriteString(s[:from])
		cmd := s[from+len(openingDelimiter) : to]
		s = s[to+len(closingDelimiter):]
		m := strings.Fields(strings.TrimSpace(cmd))
		if len(m) == 1 {
			log.Debugf("vars: #%v", vars)
			if v, ok := vars[m[0]]; ok {
				out.WriteString(v)
				continue
			}
		}
		if _, err := exec.LookPath(m[0]); err == nil {
			if res, err := run(vars, m[0], m[1:]...); err == nil {
				out.WriteString(res)
			} else {
				log.WithError(err).Warnf("error running command: %s", m[0])
			}
		}
	}

}

// Renders markdown with the given layout into html expanding all the macros
func buildMarkdown(path string, w io.Writer, vars Vars) error {
	v, body, err := getVars(path, vars)
	if err != nil {
		return err
	}

	content, err := render(body, v)
	if err != nil {
		return err
	}

	buf := &bytes.Buffer{}
	if err := Parser.Convert([]byte(content), buf); err != nil {
		return err
	}
	v["content"] = buf.String()

	if w == nil {
		out, err := os.Create(filepath.Join(PUBDIR, renameExt(path, "", ".html")))
		if err != nil {
			return err
		}
		defer out.Close()
		w = out
	}

	return buildHTML(filepath.Join(ZSDIR, v["layout"]), w, v)
}

// Renders text file expanding all variable macros inside it
func buildHTML(path string, w io.Writer, vars Vars) error {
	v, body, err := getVars(path, vars)
	if err != nil {
		return err
	}
	if body, err = render(body, v); err != nil {
		return err
	}
	tmpl, err := template.New("").Delims("<%", "%>").Parse(body)
	if err != nil {
		return err
	}
	if w == nil {
		f, err := os.Create(filepath.Join(PUBDIR, path))
		if err != nil {
			return err
		}
		defer f.Close()
		w = f
	}
	return tmpl.Execute(w, vars)
}

// Copies file as is from path to writer
func buildRaw(path string, w io.Writer) error {
	in, err := os.Open(path)
	if err != nil {
		return err
	}
	defer in.Close()
	if w == nil {
		out, err := os.Create(filepath.Join(PUBDIR, path))
		if err != nil {
			return err
		}
		defer out.Close()
		w = out
	}
	_, err = io.Copy(w, in)
	return err
}

func build(path string, w io.Writer, vars Vars) error {
	if Ignore.MatchesPath(path) {
		return nil
	}

	ext := filepath.Ext(path)
	if ext == ".md" || ext == ".mkd" {
		return buildMarkdown(path, w, vars)
	} else if ext == ".html" || ext == ".xml" {
		return buildHTML(path, w, vars)
	} else {
		return buildRaw(path, w)
	}
}

func buildAll(ctx context.Context, watch bool) error {
	ticker := NewTicker(time.Second)
	defer ticker.Stop()

	lastModified := time.Unix(0, 0)
	modified := false

	vars := globals()
	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
			os.Mkdir(PUBDIR, 0755)
			filepath.Walk(".", func(path string, info os.FileInfo, err error) error {
				// rebuild if changes to .zs/ or .zsignore
				if (filepath.Base(path) == ZSIGNORE || filepath.Dir(path) == ZSDIR) && info.ModTime().After(lastModified) {
					if filepath.Base(path) == ZSIGNORE {
						Ignore = ParseIgnoreFile(path)
					}
					// reset lastModified to 0 so everything rebuilds
					lastModified = time.Unix(0, 0)
					return nil
				}

				// ignore hidden files and directories and ignored patterns
				if filepath.Base(path)[0] == '.' || strings.HasPrefix(path, ".") || Ignore.MatchesPath(path) {
					return nil
				}

				// inform user about fs walk errors, but continue iteration
				if err != nil {
					log.WithError(err).Warn("error walking directory")
					return nil
				}

				if info.IsDir() {
					os.Mkdir(filepath.Join(PUBDIR, path), 0755)
					return nil
				} else if info.ModTime().After(lastModified) {
					if !modified {
						// First file in this build cycle is about to be modified
						if _, err := exec.LookPath("prehook"); err == nil {
							if _, err := run(vars, "prehook"); err != nil {
								log.WithError(err).Warn("error running prehook")
							}
							modified = true
						}
					}
					log.Debugf("build: %s", path)
					return build(path, nil, vars)
				}
				return nil
			})
			if modified {
				// At least one file in this build cycle has been modified
				if _, err := exec.LookPath("posthook"); err == nil {
					if _, err := run(vars, "posthook"); err != nil {
						log.WithError(err).Warn("error running posthook")
					}
					modified = false
				}
			}
			if !watch {
				return nil
			}
			lastModified = time.Now()
		}
	}
}

// serve runs a static web server and builds and continuously watches for changes to rebuild
func serve(ctx context.Context, bind, root string) error {
	os.Mkdir(root, 0755)

	svr, err := static.NewServer(
		static.WithBind(bind),
		static.WithDir(true),
		static.WithRoot(root),
		static.WithSPA(true),
	)
	if err != nil {
		return err
	}

	go svr.Run(ctx)
	go buildAll(ctx, true)

	<-ctx.Done()

	return nil
}

func ensureFirstPath(p string) {
	paths := strings.Split(os.Getenv("PATH"), string(os.PathListSeparator))
	if len(paths) > 0 && paths[0] != p {
		paths = append([]string{p}, paths...)
		os.Setenv("PATH", strings.Join(paths, string(os.PathListSeparator)))
	}
}

func init() {
	cobra.OnInitialize(initConfig)

	RootCmd.PersistentFlags().BoolP("debug", "D", false, "enable debug logging $($ZS_DEBUG)")
	RootCmd.PersistentFlags().StringVarP(&configFile, "config", "c", "", "config file (default: .zs/config.yml)")
	RootCmd.PersistentFlags().StringSliceP("extensions", "e", MapKeys(Extensions), "override and enable specific extensions")
	RootCmd.PersistentFlags().BoolP("production", "p", false, "enable production mode ($ZS_PRODUCTION)")
	RootCmd.PersistentFlags().StringP("title", "t", "", "site title ($ZS_TITLE)")
	RootCmd.PersistentFlags().StringP("description", "d", "", "site description ($ZS_DESCRIPTION)")
	RootCmd.PersistentFlags().StringP("keywords", "k", "", "site keywords ($ZS_KEYWORDS)")

	viper.BindPFlag("debug", RootCmd.PersistentFlags().Lookup("debug"))
	viper.SetDefault("debug", false)

	viper.BindPFlag("extensions", RootCmd.PersistentFlags().Lookup("extensions"))
	viper.SetDefault("extensions", MapKeys(Extensions))

	viper.BindPFlag("production", RootCmd.PersistentFlags().Lookup("production"))
	viper.SetDefault("production", false)

	viper.BindPFlag("title", RootCmd.PersistentFlags().Lookup("title"))
	viper.SetDefault("title", "")

	viper.BindPFlag("description", RootCmd.PersistentFlags().Lookup("description"))
	viper.SetDefault("description", "")

	viper.BindPFlag("keywords", RootCmd.PersistentFlags().Lookup("keywords"))
	viper.SetDefault("keywords", "")

	ServeCmd.Flags().StringP("bind", "b", ":8000", "set the [<address>]:<port> to listen on")
	ServeCmd.Flags().StringP("root", "r", PUBDIR, "set the root directory to serve")

	RootCmd.AddCommand(BuildCmd)
	RootCmd.AddCommand(ServeCmd)
	RootCmd.AddCommand(VarCmd)
	RootCmd.AddCommand(WatchCmd)

	// prepend .zs to $PATH, so plugins will be found before OS commands
	w, _ := os.Getwd()
	ensureFirstPath(filepath.Join(w, ZSDIR))
}

// initConfig reads in config file and ENV variables if set.
func initConfig() {
	if configFile == "" {
		// Use config file from .zs/config.yml
		viper.AddConfigPath(ZSDIR)
		viper.SetConfigName(ZSCONFIG)
	} else {
		// Use config file from the flag.
		viper.SetConfigFile(configFile)
	}

	// from the environment
	viper.SetEnvPrefix("ZS")
	viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
	viper.AutomaticEnv() // read in environment variables that match

	// If a config file is found, read it in.
	if err := viper.ReadInConfig(); err != nil {
		if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
			log.WithError(err).Warnf("error reading config %s (using defaults)", viper.ConfigFileUsed())
		}
	}
}

// ParseIgnoreFile parsers a .zsignore file or uses the default if an error occurred
func ParseIgnoreFile(fn string) *ignore.GitIgnore {
	obj, err := ignore.CompileIgnoreFile(ZSIGNORE)
	if err != nil {
		if !errors.Is(err, os.ErrNotExist) {
			log.WithError(err).Warnf("error parsing .zsignore: %s (using defaults)s", fn)
		}
		return ignore.CompileIgnoreLines(DefaultIgnore)
	}

	return obj
}

func main() {
	// prepend .zs to $PATH, so plugins will be found before OS commands
	cwd, err := os.Getwd()
	if err != nil {
		log.WithError(err).Fatal("error getting current working directory")
	}
	ensureFirstPath(filepath.Join(cwd, ZSDIR))

	// initializes Ignore (.zsignore) patterns
	Ignore = ParseIgnoreFile(ZSIGNORE)

	if err := RootCmd.Execute(); err != nil {
		log.WithError(err).Error("error executing command")
		os.Exit(1)
	}
}