package content

import (
	"bytes"
	"context"
	"io"
	"os"
	"path"
	"path/filepath"
	"slices"
	"strings"
	"time"

	"go.alanpearce.eu/x/log"

	"github.com/adrg/frontmatter"
	mapset "github.com/deckarep/golang-set/v2"
	fences "github.com/stefanfritsch/goldmark-fences"
	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
	htmlrenderer "github.com/yuin/goldmark/renderer/html"
	"gitlab.com/tozd/go/errors"
)

type PostMatter struct {
	Date        time.Time
	Description string
	Title       string
	Taxonomies  struct {
		Tags []string
	}
}

type Post struct {
	Input    string
	Output   string
	Basename string
	URL      string
	*PostMatter

	content []byte
}

type Config struct {
	Root    string
	PostDir string
}

type Collection struct {
	config *Config

	Posts []Post
	Tags  mapset.Set[string]
}

var markdown = goldmark.New(
	goldmark.WithRendererOptions(
		htmlrenderer.WithUnsafe(),
	),
	goldmark.WithExtensions(
		extension.GFM,
		extension.Footnote,
		extension.Typographer,
		&fences.Extender{},
	),
)

var postOutputReplacer = strings.NewReplacer(
	"index.md", "index.html",
	".md", "/index.html",
)
var postURLReplacer = strings.NewReplacer(
	"index.md", "",
	".md", "/",
)

func (cc *Collection) GetPost(filename string) (*Post, error) {
	fp := filepath.Join(cc.config.Root, cc.config.PostDir, filename)
	url := path.Join("/", cc.config.PostDir, postURLReplacer.Replace(filename)) + "/"
	post := &Post{
		Input:      fp,
		Output:     path.Join(cc.config.PostDir, postOutputReplacer.Replace(filename)),
		Basename:   filepath.Base(url),
		URL:        url,
		PostMatter: &PostMatter{},
	}

	err := parse(fp, post)
	if err != nil {
		return nil, err
	}

	return post, nil
}

var pageOutputReplacer = strings.NewReplacer(
	"index.md", "index.html",
	".md", ".html",
)
var pageURLReplacer = strings.NewReplacer(
	"index.md", "",
	".md", "",
)

func (cc *Collection) GetPage(filename string) (*Post, error) {
	fp := filepath.Join(cc.config.Root, filename)
	url := path.Join("/", pageURLReplacer.Replace(filename))
	post := &Post{
		Input:      fp,
		Output:     pageOutputReplacer.Replace(filename),
		Basename:   filepath.Base(url),
		URL:        url,
		PostMatter: &PostMatter{},
	}

	err := parse(fp, post)
	if err != nil {
		return nil, err
	}

	return post, nil
}

func parse(fp string, post *Post) error {
	content, err := os.Open(fp)
	if err != nil {
		return errors.WithMessagef(err, "could not open post %s", fp)
	}
	defer content.Close()

	post.content, err = frontmatter.Parse(content, post.PostMatter)
	if err != nil {
		return errors.WithMessagef(
			err,
			"could not parse front matter of post %s",
			fp,
		)
	}

	return nil
}

// implements templ.Component
func (p *Post) Render(_ context.Context, w io.Writer) error {
	return markdown.Convert(p.content, w)
}

func (p *Post) RenderString() (string, error) {
	var buf bytes.Buffer
	if err := p.Render(context.Background(), &buf); err != nil {
		return "", errors.WithMessage(err, "could not convert markdown content")
	}

	return buf.String(), nil
}

func NewContentCollection(config *Config, log *log.Logger) (*Collection, error) {
	cc := &Collection{
		Posts:  []Post{},
		Tags:   mapset.NewSet[string](),
		config: config,
	}

	log.Debug("reading posts", "root", config.Root, "input_dir", config.PostDir)
	subdir := filepath.Join(config.Root, config.PostDir)
	files, err := os.ReadDir(subdir)
	if err != nil {
		return nil, errors.WithMessagef(err, "could not read post directory %s", subdir)
	}
	for _, f := range files {
		fn := f.Name()
		if !f.IsDir() && path.Ext(fn) == ".md" {
			log.Debug("reading post", "post", fn)
			post, err := cc.GetPost(fn)
			if err != nil {
				return nil, err
			}

			for _, tag := range post.PostMatter.Taxonomies.Tags {
				cc.Tags.Add(strings.ToLower(tag))
			}

			cc.Posts = append(cc.Posts, *post)
		}
	}
	slices.SortFunc(cc.Posts, func(a, b Post) int {
		return b.Date.Compare(a.Date)
	})

	return cc, nil
}