/*
SGBlog -- Git-backed CGI/UCSPI blogging/phlogging/gemlogging engine
Copyright (C) 2020-2021 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as
published by the Free Software Foundation, version 3 of the License.

This program 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 Affero General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package main

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"log"
	"net/url"
	"os"
	"strconv"
	"text/template"

	"github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/plumbing"
	"github.com/go-git/go-git/v5/plumbing/object"
	"go.stargrave.org/sgblog"
)

const (
	TmplGemMenu = `{{$CR := printf "\r"}}20 text/gemini{{$CR}}
# {{.Cfg.Title}} {{if .Topic}}(topic: {{.Topic}}) {{end}}({{.Offset}}-{{.OffsetNext}})
{{if .Cfg.AboutURL}}=> {{.Cfg.AboutURL}} About{{end}}
{{if .Offset}}=> /?offset={{.OffsetPrev}}{{if .Topic}}&topic={{.Topic}}{{end}} Prev{{end}}
{{if not .LogEnded}}=> /?offset={{.OffsetNext}}{{if .Topic}}&topic={{.Topic}}{{end}} Next{{end}}

{{$datePrev := "0001-01-01" -}}
{{- range .Entries -}}
{{- $dateCur := .Commit.Author.When.Format "2006-01-02" -}}
{{- if ne $dateCur $datePrev}}{{$datePrev = $dateCur}}## {{$dateCur}}
{{end -}}
=> /{{.Commit.Hash.String}} [{{.Commit.Author.When.Format "15:04"}}] {{.Title}} ({{.LinesNum}}L){{with .CommentsNum}} ({{.}}C){{end}}{{if .Topics}}{{range .Topics}} {{.}}{{end}}{{end}}
{{end}}

{{range .Topics -}}=> /?topic={{.}} Topic: {{.}}
{{end}}
Generated by: SGBlog {{.Version}}
`
	TmplGemEntry = `{{$CR := printf "\r"}}20 text/gemini{{$CR}}
# {{.Title}}
What: {{.Commit.Hash.String}}
When: {{.When}}
{{if .Topics}}Topics:{{range .Topics}} {{.}}{{end}}{{end}}
` + "```" + `
{{.Commit.Message}}` + "```" + `
{{- if .Note}}
## Note:
` + "```" + `
{{.Note}}
` + "```" + `
{{end -}}
{{- if .Cfg.CommentsEmail}}
=> mailto:{{.Cfg.CommentsEmail}}?subject={{.TitleEscaped}} leave comment
{{end}}{{range $idx, $comment := .Comments}}
## comment {{$idx}}:
` + "```" + `
{{$comment}}
` + "```" + `
{{end}}
Generated by: SGBlog {{.Version}}
`
)

func makeGemErr(err error) {
	fmt.Print("59 " + err.Error() + "\r\n")
	log.Fatalln(err)
}

func serveGemini(cfgPath string) {
	cfg, err := readCfg(cfgPath)
	if err != nil {
		log.Fatalln(err)
	}

	headHash, err := initRepo(cfg)
	if err != nil {
		log.Fatalln(err)
	}

	scanner := bufio.NewScanner(io.LimitReader(os.Stdin, 2+1<<10))
	if !scanner.Scan() {
		makeGemErr(errors.New("no CRLF found"))
	}
	urlRaw := scanner.Text()
	u, err := url.Parse(urlRaw)
	if err != nil {
		makeGemErr(err)
	}
	if u.Scheme != "gemini" {
		makeGemErr(errors.New("only gemini:// is supported" + u.String()))
	}

	if u.Path == "/" {
		offset := 0
		if offsetRaw, exists := u.Query()["offset"]; exists {
			offset, err = strconv.Atoi(offsetRaw[0])
			if err != nil {
				makeGemErr(err)
			}
		}
		repoLog, err := repo.Log(&git.LogOptions{From: *headHash})
		if err != nil {
			makeGemErr(err)
		}
		topicsCache, err := getTopicsCache(cfg, repoLog)
		if err != nil {
			makeGemErr(err)
		}
		repoLog, err = repo.Log(&git.LogOptions{From: *headHash})
		if err != nil {
			makeGemErr(err)
		}

		commitN := 0
		var commits CommitIterNext
		var topic string
		if t, exists := u.Query()["topic"]; exists {
			topic = t[0]
			hashes := topicsCache[topic]
			if hashes == nil {
				makeGemErr(errors.New("no posts with that topic"))
			}
			if len(hashes) > offset {
				hashes = hashes[offset:]
				commitN += offset
			}
			commits = &HashesIter{hashes}
		} else {
			for i := 0; i < offset; i++ {
				if _, err = repoLog.Next(); err != nil {
					break
				}
				commitN++
			}
			commits = repoLog
		}

		logEnded := false
		entries := make([]TableMenuEntry, 0, PageEntries)
		for i := 0; i < PageEntries; i++ {
			commit, err := commits.Next()
			if err != nil {
				logEnded = true
				break
			}
			lines := msgSplit(commit.Message)
			entries = append(entries, TableMenuEntry{
				Commit:   commit,
				Title:    lines[0],
				LinesNum: len(lines) - 2,
				CommentsNum: len(sgblog.ParseComments(sgblog.GetNote(
					repo, commentsTree, commit.Hash,
				))),
				Topics: sgblog.ParseTopics(sgblog.GetNote(
					repo, topicsTree, commit.Hash,
				)),
			})
		}
		tmpl := template.Must(template.New("menu").Parse(TmplGemMenu))
		offsetPrev := offset - PageEntries
		if offsetPrev < 0 {
			offsetPrev = 0
		}
		err = tmpl.Execute(os.Stdout, struct {
			Cfg        *Cfg
			Topic      string
			Offset     int
			OffsetPrev int
			OffsetNext int
			LogEnded   bool
			Entries    []TableMenuEntry
			Topics     []string
			Version    string
		}{
			Cfg:        cfg,
			Topic:      topic,
			Offset:     offset,
			OffsetPrev: offsetPrev,
			OffsetNext: offset + PageEntries,
			LogEnded:   logEnded,
			Entries:    entries,
			Topics:     topicsCache.Topics(),
			Version:    sgblog.Version,
		})
		if err != nil {
			log.Fatalln(err)
		}
	} else if sha1DigestRe.MatchString(u.Path[1:]) {
		commit, err := repo.CommitObject(plumbing.NewHash(u.Path[1:]))
		if err != nil {
			log.Fatalln(err)
		}
		tmpl := template.Must(template.New("entry").Parse(TmplGemEntry))
		title := msgSplit(commit.Message)[0]
		err = tmpl.Execute(os.Stdout, struct {
			Title        string
			Commit       *object.Commit
			When         string
			Cfg          *Cfg
			Note         string
			Comments     []string
			Topics       []string
			Version      string
			TitleEscaped string
		}{
			Title:    title,
			Commit:   commit,
			When:     commit.Author.When.Format(sgblog.WhenFmt),
			Cfg:      cfg,
			Note:     string(sgblog.GetNote(repo, notesTree, commit.Hash)),
			Comments: sgblog.ParseComments(sgblog.GetNote(repo, commentsTree, commit.Hash)),
			Topics:   sgblog.ParseTopics(sgblog.GetNote(repo, topicsTree, commit.Hash)),
			Version:  sgblog.Version,
			TitleEscaped: url.PathEscape(fmt.Sprintf(
				"Re: %s (%s)", title, commit.Hash,
			)),
		})
		if err != nil {
			log.Fatalln(err)
		}
	} else {
		makeGemErr(errors.New("unknown URL action"))
	}
}