package main

import (
	"errors"
	"fmt"
	"html/template"
	"log"
	"net/http"
	"path/filepath"
	"regexp"
	"slices"
	"sort"
	"strings"
)

// Wiki pages are markdown in {repo}.wiki.git, paths in the git tree. Rendered
// here rather than by cgit: clean URLs, an index from ls-tree, and a history
// link out to cgit.

// A wiki path component, for reading and writing alike.
var wikiNameRE = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]*$`)

const maxWikiDepth = 8

func (f *Forge) wikiDir(path string) string {
	return filepath.Join(f.store.reposDir, path+".wiki.git")
}

// wikiFiles maps a URL to the tree paths it could mean: the page itself, then
// that name as a directory. index.md is served at the root of the wiki and of
// any subdirectory.
func wikiFiles(page string) ([]string, bool) {
	page = strings.TrimPrefix(page, "/")
	page = strings.TrimSuffix(page, ".md")
	if page == "" || strings.HasSuffix(page, "/") {
		page += "index"
		if !validWikiPage(page) {
			return nil, false
		}
		return []string{page + ".md"}, true
	}
	if !validWikiPage(page) {
		return nil, false
	}
	return []string{page + ".md", page + "/index.md"}, true
}

func validWikiPage(page string) bool {
	parts := strings.Split(page, "/")
	if len(parts) > maxWikiDepth {
		return false
	}
	for _, part := range parts {
		if !wikiNameRE.MatchString(part) {
			return false
		}
	}
	return true
}

// wikiPage is the reverse: a tree path as it appears in a URL. Only a whole
// index component is dropped: myindex.md is a page called myindex.
func wikiPage(file string) string {
	page := strings.TrimSuffix(file, ".md")
	if page == "index" {
		return ""
	}
	if rest, ok := strings.CutSuffix(page, "/index"); ok {
		return rest + "/"
	}
	return page
}

type wikiView struct {
	Path     string // the repository
	Page     string // the page, "" for the root
	File     string // the path in the tree
	Rendered template.HTML
	Pages    []string
	Missing  bool // no such page yet
	Empty    bool // no pages at all yet
	Can      bool // may edit
}

type wikiEdit struct {
	Path    string
	Page    string
	File    string
	Body    string
	Base    string // the blob this edit started from, for the compare and swap
	Preview template.HTML
}

// handleWiki routes everything under {repo}/wiki.
func (f *Forge) handleWiki(w http.ResponseWriter, r *http.Request, path string, repo Repo, rest string) {
	if repo.Wiki == featDisabled {
		f.fail(w, r, http.StatusNotFound, "this repository has its wiki turned off")
		return
	}
	page := strings.TrimPrefix(strings.TrimPrefix(rest, "wiki"), "/")
	files, ok := wikiFiles(page)
	if !ok {
		f.fail(w, r, http.StatusNotFound, "that is not a usable page name")
		return
	}

	// Without javascript a form cannot put a name into a path, so it arrives
	// as a query.
	if isGet(r) && r.URL.Query().Get("page") != "" {
		wanted, ok := wikiFiles(r.URL.Query().Get("page"))
		if !ok {
			f.fail(w, r, http.StatusBadRequest,
				"a page name is letters, digits, dot, dash, and underscore, with / for a subdirectory")
			return
		}
		http.Redirect(w, r, "/"+path+"/wiki/"+wikiPage(wanted[0])+"?edit", http.StatusSeeOther)
		return
	}

	switch {
	case isGet(r) && r.URL.Query().Has("edit"):
		// Editing is always the page itself, never the directory behind it.
		f.wikiForm(w, r, path, repo, files[0], "", "")
	case isGet(r):
		f.wikiShow(w, r, path, repo, files)
	case r.Method == http.MethodPost:
		if f.checkPost(w, r) {
			f.wikiSave(w, r, path, repo, files[0])
		}
	default:
		f.fail(w, r, http.StatusNotFound, "no such page")
	}
}

func (f *Forge) wikiShow(w http.ResponseWriter, r *http.Request, path string, repo Repo, files []string) {
	dir := f.wikiDir(path)
	view := wikiView{
		Path: path, Page: wikiPage(files[0]), File: files[0],
		Can: f.viewer(r).CanWiki(repo),
	}

	head, err := resolveRef(dir, branch)
	if err != nil {
		// An empty wiki and a missing repository must not read the same.
		f.problem(w, r, http.StatusInternalServerError, err)
		return
	}
	if head == "" {
		view.Empty, view.Missing = true, true
	} else {
		view.Pages = f.wikiPages(dir, head)
		view.Missing = true
		for _, file := range files {
			if body, err := catFile(dir, head+":"+file); err == nil {
				view.Page, view.File = wikiPage(file), file
				view.Rendered = renderMarkdown(string(body))
				view.Missing = false
				break
			}
		}
	}

	d := f.page(r)
	d.Repo = f.repoBar(r, path, "", "wiki", repo)
	d.Data = view
	// A wiki with no pages at all is a state, not a 404.
	status := http.StatusOK
	if view.Missing && !view.Empty {
		status = http.StatusNotFound
	}
	f.render(w, "wiki.html", status, d)
}

// wikiPages is the index, straight out of the tree.
func (f *Forge) wikiPages(dir, head string) []string {
	paths, err := listTreeRecursive(dir, head)
	if err != nil {
		log.Printf("wiki: %v", err)
		return nil
	}
	pages := []string{}
	for _, p := range paths {
		if !strings.HasSuffix(p, ".md") {
			continue
		}
		// A push can put a name here that reading refuses, or one that reads
		// back as another file; a link that does not open its file is worse
		// than none.
		page := wikiPage(p)
		files, ok := wikiFiles(page)
		if !ok || !slices.Contains(files, p) {
			continue
		}
		pages = append(pages, page)
	}
	sort.Strings(pages)
	return pages
}

func (f *Forge) wikiForm(w http.ResponseWriter, r *http.Request, path string, repo Repo, file, body, message string) {
	if !f.viewer(r).CanWiki(repo) {
		f.fail(w, r, http.StatusForbidden, "you may not edit this wiki")
		return
	}
	dir := f.wikiDir(path)
	base, err := f.wikiBlob(dir, file)
	if err != nil {
		f.problem(w, r, http.StatusInternalServerError, err)
		return
	}
	// An editor opened empty over a page would save it away.
	if body == "" && base != "" {
		current, err := catFile(dir, base)
		if err != nil {
			f.problem(w, r, http.StatusInternalServerError, err)
			return
		}
		body = string(current)
	}

	d := f.page(r)
	d.Repo = f.repoBar(r, path, "", "wiki", repo)
	d.Error = message
	d.Data = wikiEdit{Path: path, Page: wikiPage(file), File: file, Body: body, Base: base}
	f.render(w, "wiki-edit.html", http.StatusOK, d)
}

// wikiBlob is the page's blob id now. The editor carries it back and wikiSave
// compares it inside the commit: a compare and swap on the page, not the
// branch.
func (f *Forge) wikiBlob(dir, file string) (string, error) {
	head, err := resolveRef(dir, branch)
	if err != nil {
		return "", err
	}
	return blobIn(dir, head, file)
}

// blobIn is the id of one path's blob in one commit, or "" when the repository
// is empty or the commit does not hold that path.
func blobIn(dir, commit, file string) (string, error) {
	if commit == "" {
		return "", nil
	}
	return resolveRef(dir, commit+":"+file)
}

// errStale is the comparison failing inside the commit.
var errStale = errors.New("the page changed while it was being edited")

func (f *Forge) wikiSave(w http.ResponseWriter, r *http.Request, path string, repo Repo, file string) {
	if !f.viewer(r).CanWiki(repo) {
		f.fail(w, r, http.StatusForbidden, "you may not edit this wiki")
		return
	}
	body := strings.ReplaceAll(r.PostFormValue("body"), "\r\n", "\n")
	base := r.PostFormValue("base")

	if len(body) > maxBody {
		f.fail(w, r, http.StatusBadRequest, "that page is too big")
		return
	}
	if r.PostFormValue("action") == "preview" {
		d := f.page(r)
		d.Repo = f.repoBar(r, path, "", "wiki", repo)
		d.Data = wikiEdit{
			Path: path, Page: wikiPage(file), File: file, Body: body, Base: base,
			Preview: renderMarkdown(body),
		}
		f.render(w, "wiki-edit.html", http.StatusOK, d)
		return
	}

	dir := f.wikiDir(path)
	verb := "update"
	if base == "" {
		verb = "create"
	}
	if !strings.HasSuffix(body, "\n") {
		body += "\n"
	}
	// Compared inside the commit, or both saves of one page would land.
	err := commitWith(dir, f.actor(r), f.store.forgeAuthor(), func(commit string) ([]change, string, error) {
		now, err := blobIn(dir, commit, file)
		if err != nil {
			return nil, "", err
		}
		if now != base {
			return nil, "", errStale
		}
		return []change{{path: file, data: []byte(body)}}, fmt.Sprintf("wiki: %s %s", verb, file), nil
	})
	if errors.Is(err, errStale) {
		f.wikiForm(w, r, path, repo, file, body,
			"somebody else changed this page while you were editing it. open it again in another window, merge your text in, and save")
		return
	}
	if err != nil {
		f.problem(w, r, http.StatusInternalServerError, err)
		return
	}
	http.Redirect(w, r, "/"+path+"/wiki/"+wikiPage(file), http.StatusSeeOther)
}