// Program hswg is a static website generator employing libasciidoc with added
// support for two-line/underlined titles, and postprocessing "wiki" InterLinks.
package main

import (
	"bytes"
	"encoding/binary"
	"encoding/xml"
	"fmt"
	"html/template"
	"io"
	"io/ioutil"
	"log"
	"os"
	"os/signal"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/bytesparadise/libasciidoc/pkg/configuration"
	"github.com/bytesparadise/libasciidoc/pkg/parser"
	"github.com/bytesparadise/libasciidoc/pkg/renderer/sgml/html5"
	"github.com/bytesparadise/libasciidoc/pkg/types"
	"github.com/bytesparadise/libasciidoc/pkg/validator"
)

// Metadata contains select metadata about a rendered document.
type Metadata struct {
	types.Metadata

	// Note that this includes entries from the front-matter
	// (see parser.ApplySubstitutions <- parser.ParseDocument).
	Attributes types.Attributes
}

// IsDraft returns whether the document is marked as a draft, and should not
// be linked anywhere else.
func (m *Metadata) IsDraft() bool { return m.Attributes.Has("draft") }

// Attr is a shortcut for retrieving document attributes by name.
func (m *Metadata) Attr(name string) string {
	return m.Attributes.GetAsStringWithDefault(name, "")
}

// AttrList is similar to Attr, but splits the result at commas,
// and trims whitespace around array elements.
func (m *Metadata) AttrList(name string) []string {
	if !m.Attributes.Has(name) {
		return nil
	}

	res := strings.Split(m.Attr(name), ",")
	for i := range res {
		res[i] = strings.TrimSpace(res[i])
	}
	return res
}

// Render converts an io.Reader with an AsciiDoc document to HTML. So long as
// the file could be read at all, it will always return a non-empty document.
func Render(r io.Reader, config *configuration.Configuration) (
	html *bytes.Buffer, meta Metadata, err error) {
	html = bytes.NewBuffer(nil)

	var input []byte
	if input, err = ioutil.ReadAll(r); err != nil {
		return
	}

	pr, pw := io.Pipe()
	go func() {
		defer pw.Close()
		ConvertTitles(pw, input)
	}()

	// io.Copy(os.Stdout, pr)
	// return

	var doc *types.Document
	var preprocessed string
	// TODO(p): Ensure that this doesn't pose a security risk.
	if preprocessed, err = parser.Preprocess(pr, config); err != nil {
		// Render it raw below.
	} else if doc, err = parser.ParseDocument(
		strings.NewReader(preprocessed), config); err == nil {
		doctype := config.Attributes.GetAsStringWithDefault(
			types.AttrDocType, "article")
		problems, verr := validator.Validate(doc, doctype)
		if verr != nil {
			fmt.Fprintln(os.Stderr, verr)
		}
		for _, problem := range problems {
			fmt.Fprintln(os.Stderr, problem.Message)
		}
		meta.Metadata, err = html5.Render(doc, config, html)
	}
	if err != nil {
		// Fallback: output all the text sanitized for direct inclusion.
		html.Reset()

		_, _ = html.WriteString("<pre>")
		for _, line := range bytes.Split(input, []byte{'\n'}) {
			_ = xml.EscapeText(html, line)
			_, _ = html.WriteString("\n")
		}
		_, _ = html.WriteString("</pre>")
	}
	meta.Attributes = config.Attributes
	return
}

// Entry contains all context information about a single page.
type Entry struct {
	Metadata                        // metadata
	PathSource      string          // path to source AsciiDoc
	PathDestination string          // path to destination HTML
	mtime           time.Time       // modification time
	raw             []byte          // raw inner document
	Content         template.HTML   // inner document with expanded LinkWords
	backlinks       map[string]bool // what documents link back here
	Backlinks       []template.HTML
}

// Published returns the date when the entry was published, or nil if unknown.
func (e *Entry) Published() *time.Time {
	if d, ok := e.Attributes.GetAsString("date"); !ok {
		return nil
	} else if t, err := time.Parse(time.RFC3339, d); err == nil {
		return &t
	} else if t, err := time.Parse("2006-01-02", d); err == nil {
		return &t
	} else {
		log.Printf("%s: date: %s\n", e.PathSource, err)
		return nil
	}
}

var (
	globs = []string{"*.adoc", "*.asciidoc"}
	extRE = regexp.MustCompile(`\.[^/.]*$`)
)

func pathToName(path string) string {
	return stripExtension(filepath.Base(path))
}

func stripExtension(path string) string {
	return extRE.ReplaceAllString(path, "")
}

func resultPath(path string) string {
	if m := extRE.FindStringIndex(path); m != nil {
		return path[:m[0]] + ".html"
	}
	return path + ".html"
}

func makeLink(m *map[string]*Entry, name string) string {
	e := (*m)[name]
	return fmt.Sprintf("<a href='%s'>%s</a>",
		filepath.Clean(e.PathDestination), name)
}

var linkWordRE = regexp.MustCompile(`\b\p{Lu}\p{L}*\b`)

func expand(m *map[string]*Entry, name string, chunk []byte) []byte {
	return linkWordRE.ReplaceAllFunc(chunk, func(match []byte) []byte {
		if link, ok := (*m)[string(match)]; ok && string(match) != name &&
			!link.IsDraft() {
			link.backlinks[name] = true
			return []byte(makeLink(m, string(match)))
		}
		return match
	})
}

var tagRE = regexp.MustCompile(`<[^<>]+>`)

func renderEntry(name string, e *Entry) error {
	f, err := os.Open(e.PathSource)
	if err != nil {
		return err
	}

	if i, err := f.Stat(); err != nil {
		return err
	} else {
		e.mtime = i.ModTime()
	}

	var html *bytes.Buffer
	if html, e.Metadata, err = Render(f, configuration.NewConfiguration(
		configuration.WithFilename(e.PathSource),
		configuration.WithLastUpdated(e.mtime),
		configuration.WithAttribute("toc", "preamble"),
		configuration.WithAttribute("toc-title", "<h2>Contents</h2>"),
		configuration.WithAttribute("source-highlighter", "chroma"),
	)); err != nil {
		return err
	}

	// Every page needs to have a title.
	if e.Title == "" {
		e.Title = name
	}

	e.raw = html.Bytes()
	return nil
}

func makeEntry(path string) *Entry {
	return &Entry{
		PathSource:      path,
		PathDestination: resultPath(path),
	}
}

// loadEntries creates a map from document names to their page entries.
func loadEntries(dirname string) (map[string]*Entry, error) {
	entries := map[string]*Entry{}
	for _, glob := range globs {
		matches, err := filepath.Glob(filepath.Join(dirname, glob))
		if err != nil {
			return nil, fmt.Errorf("%s: %s", dirname, err)
		}
		for _, path := range matches {
			name := pathToName(path)
			if conflict, ok := entries[name]; ok {
				return nil, fmt.Errorf("%s: conflicts with %s",
					name, conflict.PathSource)
			}
			entries[name] = makeEntry(path)
		}
	}
	return entries, nil
}

func writeEntry(e *Entry, t *template.Template,
	entries *map[string]*Entry) error {
	f, err := os.Create(e.PathDestination)
	if err != nil {
		return err
	}

	backlinks := []string{}
	for name := range e.backlinks {
		backlinks = append(backlinks, name)
	}
	sort.Strings(backlinks)
	for _, name := range backlinks {
		e.Backlinks =
			append(e.Backlinks, template.HTML(makeLink(entries, name)))
	}

	return t.Execute(f, e)
}

func writeIndex(path string, t *template.Template,
	entries *map[string]*Entry) error {
	// Reorder entries reversely, primarily by date, secondarily by filename.
	ordered := []*Entry{}
	for _, e := range *entries {
		ordered = append(ordered, e)
	}

	sort.Slice(ordered, func(i, j int) bool {
		a, b := ordered[i], ordered[j]
		p1, p2 := a.Published(), b.Published()
		if p1 == nil && p2 != nil {
			return true
		}
		if p1 == nil && p2 == nil {
			return a.PathSource > b.PathSource
		}
		if p2 == nil {
			return false
		}
		if p1.Equal(*p2) {
			return a.PathSource > b.PathSource
		}
		return p2.Before(*p1)
	})

	f, err := os.Create(path)
	if err != nil {
		return err
	}

	// TODO(p): Splitting content to categories would be nice. Or tags.
	return t.Execute(f, ordered)
}

func finalizeEntries(entries *map[string]*Entry, t *template.Template,
	indexPath string, indexT *template.Template) {
	// The initial render of a large amount of entries is resource-intensive.
	var wg sync.WaitGroup
	for name, e := range *entries {
		e.backlinks = map[string]bool{}
		if e.raw != nil {
			continue
		}

		wg.Add(1)
		go func(name string, e *Entry) {
			defer wg.Done()
			if err := renderEntry(name, e); err != nil {
				log.Printf("%s: %s\n", name, err)
			}
		}(name, e)
	}

	wg.Wait()

	for name, e := range *entries {
		// Expand LinkWords anywhere between <tags>.
		// We want something like the inverse of Regexp.ReplaceAllStringFunc.
		raw, last, expanded := e.raw, 0, bytes.NewBuffer(nil)
		for _, where := range tagRE.FindAllIndex(raw, -1) {
			_, _ = expanded.Write(expand(entries, name, raw[last:where[0]]))
			_, _ = expanded.Write(raw[where[0]:where[1]])
			last = where[1]
		}
		_, _ = expanded.Write(expand(entries, name, raw[last:]))
		e.Content = template.HTML(expanded.String())
	}
	for name, e := range *entries {
		// Don't overwrite failed renders.
		if e.raw == nil {
			continue
		}
		if err := writeEntry(e, t, entries); err != nil {
			log.Printf("%s: %s\n", name, err)
		}
	}
	if err := writeIndex(indexPath, indexT, entries); err != nil {
		log.Printf("%s: %s\n", indexPath, err)
	}
}

type watchEvent struct {
	path    string // the path of the target
	present bool   // if not, the file has been removed
}

func dispatchEvents(dirname string, r io.Reader, ch chan<- *watchEvent) error {
	var e syscall.InotifyEvent
	for {
		// FIXME(p): This has to respect the machine's endianness.
		// Perhaps use the unsafe package.
		err := binary.Read(r, binary.LittleEndian, &e)
		if err == io.EOF {
			return nil
		}
		if err != nil {
			return err
		}

		base := make([]byte, e.Len)
		if e.Len != 0 {
			if n, err := r.Read(base); err != nil {
				return err
			} else if n < int(e.Len) {
				return fmt.Errorf("short read")
			}
		}

		switch {
		case e.Mask&syscall.IN_IGNORED != 0:
			return fmt.Errorf("watch removed by kernel")
		case e.Mask&syscall.IN_Q_OVERFLOW != 0:
			log.Println("inotify: queue overflowed")
			ch <- nil
			continue
		case e.Len == 0:
			continue
		}

		basename, interesting := string(base[:bytes.IndexByte(base, 0)]), false
		for _, glob := range globs {
			if matches, _ := filepath.Match(glob, basename); matches {
				interesting = true
			}
		}
		if !interesting {
			continue
		}

		event := &watchEvent{path: filepath.Join(dirname, basename)}
		if e.Mask&syscall.IN_MODIFY != 0 || e.Mask&syscall.IN_MOVED_TO != 0 ||
			e.Mask&syscall.IN_CLOSE_WRITE != 0 {
			event.present = true
			ch <- event
		}
		if e.Mask&syscall.IN_DELETE != 0 || e.Mask&syscall.IN_MOVED_FROM != 0 {
			event.present = false
			ch <- event
		}
	}
}

func watchDirectory(dirname string) (<-chan *watchEvent, error) {
	inotifyFD, err := syscall.InotifyInit1(0)
	if err != nil {
		return nil, err
	}

	// We're ignoring IN_CREATE, as it doesn't seem to be useful,
	// and we're leaving out IN_MODIFY since VIM always triggers IN_CLOSE_WRITE,
	// saving us from having to coalesce plentiful similar events.
	_, err = syscall.InotifyAddWatch(inotifyFD, dirname, syscall.IN_ONLYDIR|
		syscall.IN_MOVE|syscall.IN_DELETE|syscall.IN_CLOSE_WRITE)
	if err != nil {
		return nil, err
	}

	inotifyFile := os.NewFile(uintptr(inotifyFD), "inotify")
	buf := make([]byte, syscall.SizeofInotifyEvent+syscall.PathMax+1)
	ch := make(chan *watchEvent)
	go func() {
		// Trigger an initial rendering run.
		ch <- nil

		defer close(ch)
		for {
			n, err := inotifyFile.Read(buf)
			if err != nil {
				log.Println(err)
				return
			}
			err = dispatchEvents(dirname, bytes.NewReader(buf[:n]), ch)
			if err != nil {
				log.Printf("inotify: %s\n", err)
				return
			}
		}
	}()
	return ch, nil
}

var funcs = template.FuncMap{
	"contains": func(needle string, haystack []string) bool {
		for _, el := range haystack {
			if el == needle {
				return true
			}
		}
		return false
	},
}

func singleFile() {
	html, meta, err := Render(os.Stdin, configuration.NewConfiguration())
	if err != nil {
		log.Println(err)
	} else if meta.Title != "" {
		_, _ = os.Stdout.WriteString("<h1>")
		_ = xml.EscapeText(os.Stdout, []byte(meta.Title))
		_, _ = os.Stdout.WriteString("</h1>\n")
	}
	_, _ = io.Copy(os.Stdout, html)
}

func main() {
	if len(os.Args) < 2 {
		singleFile()
		return
	}
	if len(os.Args) != 4 {
		log.Fatalf("usage: %s TEMPLATE INDEX DIRECTORY\n", os.Args[0])
	}

	argTemplate, argIndex, argDirectory := os.Args[1], os.Args[2], os.Args[3]

	// Read a template for entries.
	header, err := ioutil.ReadFile(argTemplate)
	if err != nil {
		log.Fatalln(err)
	}
	tmplEntry, err := template.New("entry").Funcs(funcs).Parse(string(header))
	if err != nil {
		log.Fatalln(err)
	}

	// Read a template for the index from the standard input.
	index, err := ioutil.ReadAll(os.Stdin)
	if err != nil {
		log.Fatalln(err)
	}
	tmplIndex, err := template.New("index").Funcs(funcs).Parse(string(index))
	if err != nil {
		log.Fatalln(err)
	}

	// Re-render as needed, avoid having to trigger anything manually.
	var entries map[string]*Entry
	directoryWatch, err := watchDirectory(argDirectory)
	if err != nil {
		log.Fatalln(err)
	}

	signals := make(chan os.Signal, 1)
	signal.Notify(signals, syscall.SIGINT, syscall.SIGHUP, syscall.SIGTERM)
	for {
		select {
		case <-signals:
			os.Exit(0)
		case event, ok := <-directoryWatch:
			if !ok {
				os.Exit(1)
			}

			if event == nil {
				log.Println("reloading all files")
				if entries, err = loadEntries(argDirectory); err != nil {
					log.Println(err)
				}
			} else if event.present {
				log.Printf("updating %s\n", event.path)
				entries[pathToName(event.path)] = makeEntry(event.path)
			} else {
				log.Printf("removing %s\n", event.path)
				delete(entries, pathToName(event.path))
				os.Remove(resultPath(event.path))
			}

			finalizeEntries(&entries, tmplEntry, argIndex, tmplIndex)
			log.Println("done")
		}
	}
}