package http

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"html/template"
	"net/http"
	"path/filepath"
	"strings"
	txttpl "text/template"
	"time"

	"github.com/gomarkdown/markdown"
	"github.com/gomarkdown/markdown/html"
	"github.com/gomarkdown/markdown/parser"
	"github.com/mediocregopher/blog.mediocregopher.com/srv/gmi"
	"github.com/mediocregopher/blog.mediocregopher.com/srv/http/apiutil"
	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
	"github.com/mediocregopher/blog.mediocregopher.com/srv/post/asset"
	"github.com/mediocregopher/mediocre-go-lib/v2/mctx"
)

func (a *api) postPreprocessFuncImage(args ...string) (string, error) {

	var (
		id    = args[0]
		descr = "TODO"
	)

	if len(args) > 1 {
		descr = args[1]
	}

	tpl := txttpl.New("image.html")

	tpl.Funcs(txttpl.FuncMap{
		"AssetURL": func(id string) string {
			return a.assetURL(id, false)
		},
	})

	tpl = txttpl.Must(tpl.Parse(mustReadTplFile("image.html")))

	tplPayload := struct {
		ID        string
		Descr     string
		Resizable bool
	}{
		ID:        id,
		Descr:     descr,
		Resizable: asset.IsImageResizable(id),
	}

	buf := new(bytes.Buffer)
	if err := tpl.ExecuteTemplate(buf, "image.html", tplPayload); err != nil {
		return "", err
	}

	return buf.String(), nil
}

type postTplPayload struct {
	post.StoredPost
	SeriesPrevious, SeriesNext *post.StoredPost
	Body                       template.HTML
}

func (a *api) postPreprocessFuncs() post.PreprocessFunctions {
	return post.PreprocessFunctions{
		BlogURL: func(path string) string {
			return a.blogURL(a.params.PublicURL, path, false)
		},
		BlogHTTPURL: func(path string) string {
			return a.blogURL(a.params.PublicURL, path, true)
		},
		BlogGeminiURL: func(path string) string {
			return a.blogURL(a.params.GeminiPublicURL, path, true)
		},
		AssetURL: func(id string) string {
			return a.assetURL(id, false)
		},
		PostURL: func(id string) string {
			return a.postURL(id, false)
		},
		StaticURL: func(path string) string {
			path = filepath.Join("static", path)
			return a.blogURL(a.params.PublicURL, path, false)
		},
		Image: a.postPreprocessFuncImage,
	}
}

func (a *api) postToPostTplPayload(storedPost post.StoredPost) (postTplPayload, error) {

	preprocessFuncs := a.postPreprocessFuncs()

	bodyBuf := new(bytes.Buffer)

	if err := storedPost.PreprocessBody(bodyBuf, preprocessFuncs); err != nil {
		return postTplPayload{}, fmt.Errorf("preprocessing post body: %w", err)
	}

	if storedPost.Format == post.FormatGemtext {

		prevBodyBuf := bodyBuf
		bodyBuf = new(bytes.Buffer)

		err := gmi.GemtextToMarkdown(
			bodyBuf, prevBodyBuf, a.params.GeminiGatewayURL,
		)

		if err != nil {
			return postTplPayload{}, fmt.Errorf("converting gemtext to markdown: %w", err)
		}
	}

	// this helps the markdown renderer properly parse pages which end in a
	// `</script>` tag... I don't know why.
	_, _ = bodyBuf.WriteString("\n")

	parserExt := parser.CommonExtensions | parser.AutoHeadingIDs
	parser := parser.NewWithExtensions(parserExt)

	htmlFlags := html.HrefTargetBlank
	htmlRenderer := html.NewRenderer(html.RendererOptions{Flags: htmlFlags})

	renderedBody := markdown.ToHTML(bodyBuf.Bytes(), parser, htmlRenderer)

	tplPayload := postTplPayload{
		StoredPost: storedPost,
		Body:       template.HTML(renderedBody),
	}

	if series := storedPost.Series; series != "" {

		seriesPosts, err := a.params.PostStore.GetBySeries(series)
		if err != nil {
			return postTplPayload{}, fmt.Errorf(
				"fetching posts for series %q: %w", series, err,
			)
		}

		var foundThis bool

		for i := range seriesPosts {

			seriesPost := seriesPosts[i]

			if seriesPost.ID == storedPost.ID {
				foundThis = true
				continue
			}

			if !foundThis {
				tplPayload.SeriesNext = &seriesPost
				continue
			}

			tplPayload.SeriesPrevious = &seriesPost
			break
		}
	}

	return tplPayload, nil
}

func (a *api) getPostsHandler() http.Handler {

	tpl := a.mustParseBasedTpl("posts.html")
	getPostHandler := a.getPostHandler()
	const pageCount = 20

	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		id := filepath.Base(r.URL.Path)

		if id != "/" {
			getPostHandler.ServeHTTP(rw, r)
			return
		}

		page, err := apiutil.StrToInt(r.FormValue("p"), 0)
		if err != nil {
			apiutil.BadRequest(
				rw, r, fmt.Errorf("invalid page number: %w", err),
			)
			return
		}

		tag := r.FormValue("tag")

		var (
			posts   []post.StoredPost
			hasMore bool
		)

		if tag == "" {
			posts, hasMore, err = a.params.PostStore.Get(page, pageCount)
		} else {
			posts, err = a.params.PostStore.GetByTag(tag)
		}

		if err != nil {
			apiutil.InternalServerError(
				rw, r, fmt.Errorf("fetching page %d of posts: %w", page, err),
			)
			return
		}

		tags, err := a.params.PostStore.GetTags()
		if err != nil {
			apiutil.InternalServerError(
				rw, r, fmt.Errorf("fething tags: %w", err),
			)
			return
		}

		tplPayload := struct {
			Posts              []post.StoredPost
			PrevPage, NextPage int
			Tags               []string
		}{
			Posts:    posts,
			PrevPage: -1,
			NextPage: -1,
			Tags:     tags,
		}

		if page > 0 {
			tplPayload.PrevPage = page - 1
		}

		if hasMore {
			tplPayload.NextPage = page + 1
		}

		executeTemplate(rw, r, tpl, tplPayload)
	})
}

func (a *api) getPostHandler() http.Handler {

	tpl := a.mustParseBasedTpl("post.html")

	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		id := strings.TrimSuffix(filepath.Base(r.URL.Path), ".html")

		storedPost, err := a.params.PostStore.GetByID(id)

		if errors.Is(err, post.ErrPostNotFound) {
			http.Error(rw, "Post not found", 404)
			return
		} else if err != nil {
			apiutil.InternalServerError(
				rw, r, fmt.Errorf("fetching post with id %q: %w", id, err),
			)
			return
		}

		tplPayload, err := a.postToPostTplPayload(storedPost)

		if err != nil {
			apiutil.InternalServerError(
				rw, r, fmt.Errorf(
					"generating template payload for post with id %q: %w",
					id, err,
				),
			)
			return
		}

		executeTemplate(
			rw, r, tpl, tplPayload,
			executeTemplateWithTitlePrefix(storedPost.Title),
		)
	})
}

func (a *api) managePostsHandler() http.Handler {

	tpl := a.mustParseBasedTpl("posts-manage.html")
	const pageCount = 20

	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		page, err := apiutil.StrToInt(r.FormValue("p"), 0)
		if err != nil {
			apiutil.BadRequest(
				rw, r, fmt.Errorf("invalid page number: %w", err),
			)
			return
		}

		posts, hasMore, err := a.params.PostStore.Get(page, pageCount)
		if err != nil {
			apiutil.InternalServerError(
				rw, r, fmt.Errorf("fetching page %d of posts: %w", page, err),
			)
			return
		}

		tplPayload := struct {
			Posts              []post.StoredPost
			PrevPage, NextPage int
		}{
			Posts:    posts,
			PrevPage: -1,
			NextPage: -1,
		}

		if page > 0 {
			tplPayload.PrevPage = page - 1
		}

		if hasMore {
			tplPayload.NextPage = page + 1
		}

		executeTemplate(rw, r, tpl, tplPayload)
	})
}

func (a *api) editPostHandler(isDraft bool) http.Handler {

	tpl := a.mustParseBasedTpl("post-edit.html")

	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		id := filepath.Base(r.URL.Path)

		if id == "/" && !isDraft {
			http.Error(rw, "Post id required", 400)
			return
		}

		var (
			storedPost post.StoredPost
			err        error
		)

		if id != "/" {

			if isDraft {
				storedPost.Post, err = a.params.PostDraftStore.GetByID(id)
			} else {
				storedPost, err = a.params.PostStore.GetByID(id)
			}

			if errors.Is(err, post.ErrPostNotFound) {
				http.Error(rw, "Post not found", 404)
				return
			} else if err != nil {
				apiutil.InternalServerError(
					rw, r, fmt.Errorf("fetching post with id %q: %w", id, err),
				)
				return
			}
		}

		tags, err := a.params.PostStore.GetTags()
		if err != nil {
			apiutil.InternalServerError(rw, r, fmt.Errorf("fetching tags: %w", err))
			return
		}

		tplPayload := struct {
			Post    post.StoredPost
			Tags    []string
			IsDraft bool
			Formats []post.Format
		}{
			Post:    storedPost,
			Tags:    tags,
			IsDraft: isDraft,
			Formats: post.Formats,
		}

		executeTemplate(rw, r, tpl, tplPayload)
	})
}

func postFromPostReq(r *http.Request) (post.Post, error) {

	formatStr := r.PostFormValue("format")
	if formatStr == "" {
		return post.Post{}, errors.New("format is required")
	}

	format, err := post.FormatFromString(formatStr)
	if err != nil {
		return post.Post{}, fmt.Errorf("parsing format: %w", err)
	}

	p := post.Post{
		ID:          r.PostFormValue("id"),
		Title:       r.PostFormValue("title"),
		Description: r.PostFormValue("description"),
		Tags:        strings.Fields(r.PostFormValue("tags")),
		Series:      r.PostFormValue("series"),
		Format:      format,
	}

	// textareas encode newlines as CRLF for historical reasons
	p.Body = r.PostFormValue("body")
	p.Body = strings.ReplaceAll(p.Body, "\r\n", "\n")
	p.Body = strings.TrimSpace(p.Body)

	if p.ID == "" ||
		p.Title == "" ||
		p.Body == "" ||
		len(p.Tags) == 0 {
		return post.Post{}, errors.New("id, ritle, tags, and body are all required")
	}

	return p, nil
}

func (a *api) storeAndPublishPost(ctx context.Context, p post.Post) error {

	first, err := a.params.PostStore.Set(p, time.Now())

	if err != nil {
		return fmt.Errorf("storing post with id %q: %w", p.ID, err)
	}

	if !first {
		return nil
	}

	a.params.Logger.Info(ctx, "publishing blog post to mailing list")
	urlStr := a.postURL(p.ID, true)

	if err := a.params.MailingList.Publish(p.Title, urlStr); err != nil {
		return fmt.Errorf("publishing post to mailing list: %w", err)
	}

	if err := a.params.PostDraftStore.Delete(p.ID); err != nil {
		return fmt.Errorf("deleting draft: %w", err)
	}

	return nil
}

func (a *api) postPostHandler() http.Handler {

	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		ctx := r.Context()

		p, err := postFromPostReq(r)
		if err != nil {
			apiutil.BadRequest(rw, r, err)
			return
		}

		ctx = mctx.Annotate(ctx, "postID", p.ID)

		if err := a.storeAndPublishPost(ctx, p); err != nil {
			apiutil.InternalServerError(
				rw, r, fmt.Errorf("storing/publishing post with id %q: %w", p.ID, err),
			)
			return
		}

		a.executeRedirectTpl(rw, r, a.editPostURL(p.ID, false))
	})
}

func (a *api) deletePostHandler(isDraft bool) http.Handler {

	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		id := filepath.Base(r.URL.Path)

		if id == "/" {
			apiutil.BadRequest(rw, r, errors.New("id is required"))
			return
		}

		var err error

		if isDraft {
			err = a.params.PostDraftStore.Delete(id)
		} else {
			err = a.params.PostStore.Delete(id)
		}

		if errors.Is(err, post.ErrPostNotFound) {
			http.Error(rw, "Post not found", 404)
			return
		} else if err != nil {
			apiutil.InternalServerError(
				rw, r, fmt.Errorf("deleting post with id %q: %w", id, err),
			)
			return
		}

		if isDraft {
			a.executeRedirectTpl(rw, r, a.manageDraftPostsURL(false))
		} else {
			a.executeRedirectTpl(rw, r, a.managePostsURL(false))
		}
	})
}

func (a *api) previewPostHandler() http.Handler {

	tpl := a.mustParseBasedTpl("post.html")

	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		p, err := postFromPostReq(r)
		if err != nil {
			apiutil.BadRequest(rw, r, err)
			return
		}

		storedPost := post.StoredPost{
			Post:        p,
			PublishedAt: time.Now(),
		}

		tplPayload, err := a.postToPostTplPayload(storedPost)

		if err != nil {
			apiutil.InternalServerError(
				rw, r, fmt.Errorf("generating template payload: %w", err),
			)
			return
		}

		executeTemplate(rw, r, tpl, tplPayload)
	})
}