package api

import (
	"errors"
	"fmt"
	"html/template"
	"net/http"
	"path/filepath"
	"strings"

	"github.com/gomarkdown/markdown"
	"github.com/gomarkdown/markdown/html"
	"github.com/gomarkdown/markdown/parser"
	"github.com/mediocregopher/blog.mediocregopher.com/srv/api/apiutil"
	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
)

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

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

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

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

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

		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
		}

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

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

		renderedBody := markdown.ToHTML([]byte(storedPost.Body), parser, htmlRenderer)

		tplPayload := struct {
			post.StoredPost
			SeriesPrevious, SeriesNext *post.StoredPost
			Body                       template.HTML
		}{
			StoredPost: storedPost,
			Body:       template.HTML(renderedBody),
		}

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

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

			var foundThis bool

			for i := range seriesPosts {

				seriesPost := seriesPosts[i]

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

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

				tplPayload.SeriesNext = &seriesPost
				break
			}
		}

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

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

	tpl := a.mustParseBasedTpl("posts.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.WithOrderDesc().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() http.Handler {

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

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

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

		var storedPost post.StoredPost

		if id != "/" {

			var err error
			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
			}
		}

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

func (a *api) deletePostHandler() 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
		}

		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
		}

		a.executeRedirectTpl(rw, r, "posts/")

	})
}