// 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"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"time"
	"unicode"
	"unicode/utf8"

	"github.com/bytesparadise/libasciidoc"
	"github.com/bytesparadise/libasciidoc/pkg/configuration"
	"github.com/bytesparadise/libasciidoc/pkg/types"
)

// isTitle returns the title level if the lines seem to form a title,
// zero otherwise. Input lines may inclide trailing newlines.
func isTitle(line1, line2 []byte) int {
	// This is a very naïve method, we should target graphemes (thus at least
	// NFC normalize the lines first) and account for wide characters.
	diff := utf8.RuneCount(line1) - utf8.RuneCount(line2)
	if len(line2) < 2 || diff < -1 || diff > 1 {
		return 0
	}

	// "Don't be fooled by back-to-back delimited blocks."
	// Still gets fooled by other things, though.
	if bytes.IndexFunc(line1, func(r rune) bool {
		return unicode.IsLetter(r) || unicode.IsNumber(r)
	}) < 0 {
		return 0
	}

	// The underline must be homogenous.
	for _, r := range bytes.TrimRight(line2, "\r\n") {
		if r != line2[0] {
			return 0
		}
	}
	return 1 + strings.IndexByte("=-~^+", line2[0])
}

func writeLine(w *io.PipeWriter, cur, next []byte) []byte {
	if level := isTitle(cur, next); level > 0 {
		w.Write(append(bytes.Repeat([]byte{'='}, level), ' '))
		next = nil
	}
	w.Write(cur)
	return next
}

// ConvertTitles converts AsciiDoc two-line (underlined) titles to single-line.
func ConvertTitles(w *io.PipeWriter, input []byte) {
	var last []byte
	for _, cur := range bytes.SplitAfter(input, []byte{'\n'}) {
		last = writeLine(w, last, cur)
	}
	writeLine(w, last, nil)
}

// entry contains all context information about a single page.
type entry struct {
	path      string         // path
	mtime     time.Time      // modification time
	metadata  types.Metadata // metadata
	document  []byte         // inner document with expanded LinkWords
	backlinks []string       // what documents link back here
}

var extRE = regexp.MustCompile(`\.[^/.]*$`)

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>", resultPath(e.path), 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 {
			link.backlinks = append(link.backlinks, name)
			return []byte(makeLink(m, string(match)))
		}
		return match
	})
}

func main() {
	if len(os.Args) < 3 {
		log.Fatalf("usage: %s TEMPLATE GLOB...\n", os.Args[0])
	}

	// Read the common page header.
	header, err := ioutil.ReadFile(os.Args[1])
	if err != nil {
		log.Fatalln(err)
	}

	// Create a map from document names to their page entries.
	entries := map[string]*entry{}
	for _, glob := range os.Args[2:] {
		matches, err := filepath.Glob(glob)
		if err != nil {
			log.Fatalf("%s: %s\n", glob, err)
		}
		for _, path := range matches {
			name := stripExtension(filepath.Base(path))
			if conflict, ok := entries[name]; ok {
				log.Fatalf("%s: conflicts with %s\n", name, conflict.path)
			}
			entries[name] = &entry{path: path}
		}
	}

	tagRE := regexp.MustCompile(`<[^<>]+>`)
	for name, e := range entries {
		f, err := os.Open(e.path)
		if err != nil {
			log.Fatalln(err)
		}

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

		input, err := ioutil.ReadAll(f)
		if err != nil {
			log.Fatalln(err)
		}

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

		config := configuration.NewConfiguration(
			configuration.WithHeaderFooter(false),
			configuration.WithFilename(e.path),
			configuration.WithLastUpdated(e.mtime),
		)

		buf := bytes.NewBuffer(nil)
		e.metadata, err = libasciidoc.ConvertToHTML(pr, buf, config)
		if err != nil {
			log.Fatalln(err)
		}

		// Expand LinkWords anywhere between <tags>.
		// We want something like the inverse of Regexp.ReplaceAllStringFunc.
		raw, last, expanded := buf.Bytes(), 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.document = expanded.Bytes()
	}

	for name, e := range entries {
		f, err := os.Create(resultPath(e.path))
		if err != nil {
			log.Fatalln(err)
		}

		_, _ = f.Write(header)

		title := e.metadata.Title
		if title == "" {
			title = name
		}

		_, _ = f.WriteString(fmt.Sprintf("<title>%s</title>\n", title))
		_, _ = f.WriteString(fmt.Sprintf("<h1>%s</h1>\n", title))

		sort.Strings(e.backlinks)

		backlinks := []string{}
		for _, name := range e.backlinks {
			backlinks = append(backlinks, makeLink(&entries, name))
		}

		if len(backlinks) > 0 {
			_, _ = f.WriteString(fmt.Sprintf("<p id=links>Links here: %s</p>\n",
				strings.Join(backlinks, ", ")))
		}

		_, _ = f.Write(e.document)
		_, _ = f.WriteString(fmt.Sprintf("<p id=footer>Last updated: %s"+
			" &mdash; <a href='%s'>Source</p>\n",
			e.metadata.LastUpdated, e.path))
	}
}