// This file is part of gmnhg.

// gmnhg is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// gmnhg is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with gmnhg. If not, see <https://www.gnu.org/licenses/>.

// gmnhg converts Hugo content files to a Gemini site. This program is
// to be started in the top level directory of a Hugo site (the one
// containing config.toml).
//
// gmngh will read layout template files (with .gotmpl extension) and
// then apply them to content files ending with .md by the following
// algorithm (file names are relative to layouts/gmnhg):
//
// 1. If the .md file specifies its own layout, the relevant layout file
// is applied. If not, the default template is applied (single). If the
// layout file does not exist, the file is skipped. Draft posts are not
// rendered. _index.md files are also skipped.
//
// 2. For every top-level content directory an index.gmi is generated,
// the corresponding template is taken from top/{directory_name}.gotmpl.
// If there's no matching template, the index won't be rendered.
//
// 3. The very top index.gmi is generated from index.gotmpl.
//
// The program will then copy static files from static/ directory to the
// output dir.
//
// Templates are passed the following data:
//
// 1. Single pages are given .Post, which contains the entire post
// rendered, .Metadata, which contains the metadata crawled from it (see
// HugoMetadata), and .Link, which contains the filename relative to
// content dir (with .md replaced with .gmi).
//
// 2. Directory index pages are passed .Posts, which is a slice over
// post metadata crawled (see HugoMetadata), and .Dirname, which is
// directory name relative to content dir.
//
// 3. The top-level index.gmi is passed with the .PostData map whose
// keys are top-level content directories names and values are slices
// over the same post props as specified in 1.
//
// This program provides some extra template functions, documented in
// templates.go.
package main

import (
	"bytes"
	"errors"
	"flag"
	"io"
	"io/ioutil"
	"os"
	"path"
	"path/filepath"
	"regexp"
	"strings"
	"text/template"

	gemini "git.tdem.in/tdemin/gmnhg"
)

const defaultTemplate = "single"

const (
	contentBase  = "content/"
	templateBase = "layouts/gmnhg/"
	staticBase   = "static/"
	outputBase   = "output/"
)

var (
	tmplNameRegex     = regexp.MustCompile(templateBase + `(\w+)\.gotmpl`)
	contentNameRegex  = regexp.MustCompile(contentBase + `([\w-_ ]+)\.md`)
	topLevelPostRegex = regexp.MustCompile(contentBase + `([\w-_ ]+)/([\w-_ ]+)\.md`)
)

// TODO: more meaningful errors

type post struct {
	Post     []byte
	Metadata gemini.HugoMetadata
	Link     string
}

func copyFile(dst, src string) error {
	input, err := os.Open(src)
	if err != nil {
		return err
	}
	defer input.Close()
	if p := path.Dir(dst); p != "" {
		if err := os.MkdirAll(p, 0755); err != nil {
			return err
		}
	}
	output, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer output.Close()
	if _, err := io.Copy(output, input); err != nil {
		return err
	}
	return nil
}

func writeFile(dst string, contents []byte) error {
	if p := path.Dir(dst); p != "" {
		if err := os.MkdirAll(p, 0755); err != nil {
			return err
		}
	}
	output, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer output.Close()
	if _, err := output.Write(contents); err != nil {
		return err
	}
	return nil
}

func main() {
	var outputDir, workingDir string
	flag.StringVar(&outputDir, "output", outputBase, "output directory (will be created if missing)")
	flag.StringVar(&workingDir, "working", "", "working directory (defaults to current directory)")
	flag.Parse()

	if workingDir != "" {
		if err := os.Chdir(workingDir); err != nil {
			panic(err)
		}
	}

	if fileInfo, err := os.Stat("config.toml"); os.IsNotExist(err) || fileInfo.IsDir() {
		panic("config.toml either doesn't exist or is a directory; not in a Hugo site dir?")
	}

	// build templates
	templates := make(map[string]*template.Template)
	if _, err := os.Stat(templateBase); !os.IsNotExist(err) {
		if err := filepath.Walk(templateBase, func(path string, info os.FileInfo, err error) error {
			if err != nil {
				return err
			}
			if info.IsDir() {
				return nil
			}
			name := tmplNameRegex.FindStringSubmatch(path)
			if name == nil || len(name) != 2 {
				return nil
			}
			tmplName := name[1]
			contents, err := ioutil.ReadFile(path)
			if err != nil {
				return err
			}
			tmpl, err := template.New(tmplName).Funcs(funcMap).Parse(string(contents))
			if err != nil {
				return err
			}
			templates[tmplName] = tmpl
			return nil
		}); err != nil {
			panic(err)
		}
	}

	// render posts to Gemtext and collect top level posts data
	posts := make(map[string]*post, 0)
	topLevelPosts := make(map[string][]*post)
	if err := filepath.Walk(contentBase, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if n := info.Name(); info.IsDir() || !strings.HasSuffix(n, ".md") || n == "_index.md" {
			return nil
		}
		fileContent, err := ioutil.ReadFile(path)
		if err != nil {
			return err
		}
		gemText, metadata, err := gemini.RenderMarkdown(fileContent, gemini.WithoutMetadata)
		// skip drafts from rendering
		if errors.Is(err, gemini.ErrPostIsDraft) {
			return nil
		} else if err != nil {
			return err
		}
		key := strings.TrimPrefix(strings.TrimSuffix(path, ".md"), contentBase) + ".gmi"
		p := post{
			Post:     gemText,
			Link:     key,
			Metadata: metadata,
		}
		posts[key] = &p
		if matches := topLevelPostRegex.FindStringSubmatch(path); matches != nil {
			topLevelPosts[matches[1]] = append(topLevelPosts[matches[1]], &p)
		}
		return nil
	}); err != nil {
		panic(err)
	}

	// clean up output dir beforehand
	if _, err := os.Stat(outputDir); os.IsNotExist(err) {
		if err := os.MkdirAll(outputDir, 0755); err != nil {
			panic(err)
		}
	} else {
		dir, err := ioutil.ReadDir(outputDir)
		if err != nil {
			panic(err)
		}
		for _, d := range dir {
			os.RemoveAll(path.Join(outputDir, d.Name()))
		}
	}

	var singleTemplate = defaultSingleTemplate
	if tmpl, hasTmpl := templates["single"]; hasTmpl {
		singleTemplate = tmpl
	}

	// render posts to files
	for fileName, post := range posts {
		var tmpl = singleTemplate
		if pl := post.Metadata.PostLayout; pl != "" {
			t, ok := templates[pl]
			if !ok {
				// no point trying to render pages with no layout
				continue
			}
			tmpl = t
		}
		buf := bytes.Buffer{}
		if err := tmpl.Execute(&buf, &post); err != nil {
			panic(err)
		}
		if err := writeFile(path.Join(outputDir, fileName), buf.Bytes()); err != nil {
			panic(err)
		}
	}
	// render indexes for top-level dirs
	for dirname, posts := range topLevelPosts {
		tmpl, hasTmpl := templates["top/"+dirname]
		if !hasTmpl {
			continue
		}
		buf := bytes.Buffer{}
		if err := tmpl.Execute(&buf, map[string]interface{}{
			"Posts":   posts,
			"Dirname": dirname,
		}); err != nil {
			panic(err)
		}
		if err := writeFile(path.Join(outputDir, dirname, "index.gmi"), buf.Bytes()); err != nil {
			panic(err)
		}
	}
	// render index page
	var indexTmpl = defaultIndexTemplate
	if t, hasIndexTmpl := templates["index"]; hasIndexTmpl {
		indexTmpl = t
	}
	buf := bytes.Buffer{}
	if err := indexTmpl.Execute(&buf, map[string]interface{}{"PostData": topLevelPosts}); err != nil {
		panic(err)
	}
	if err := writeFile(path.Join(outputDir, "index.gmi"), buf.Bytes()); err != nil {
		panic(err)
	}

	// copy static files to output dir unmodified
	if err := filepath.Walk(staticBase, func(p string, info os.FileInfo, err error) error {
		if info.IsDir() {
			return nil
		}
		return copyFile(path.Join(outputDir, strings.TrimPrefix(p, staticBase)), p)
	}); err != nil {
		panic(err)
	}
}