package main

import (
	"bytes"
	"log/slog"
	"os"
	"path"
	"path/filepath"
	"slices"
	"strings"
	"time"

	"github.com/adrg/frontmatter"
	mapset "github.com/deckarep/golang-set/v2"
	"github.com/pkg/errors"
	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
	htmlrenderer "github.com/yuin/goldmark/renderer/html"
)

type PostMatter struct {
	Date        time.Time `toml:"date"`
	Description string    `toml:"description"`
	Title       string    `toml:"title"`
	Taxonomies  struct {
		Tags []string `toml:"tags"`
	} `toml:"taxonomies"`
}

type Post struct {
	Input    string
	Output   string
	Basename string
	URL      string
	Content  string
	PostMatter
}

type Tags mapset.Set[string]

var markdown = goldmark.New(
	goldmark.WithRendererOptions(
		htmlrenderer.WithUnsafe(),
	),
	goldmark.WithExtensions(
		extension.GFM,
		extension.Footnote,
		extension.Typographer,
	),
)

func getPost(filename string) (*PostMatter, []byte, error) {
	matter := PostMatter{}
	content, err := os.Open(filename)
	defer content.Close()
	if err != nil {
		return nil, nil, errors.WithMessagef(err, "could not open post %s", filename)
	}
	rest, err := frontmatter.MustParse(content, &matter)
	if err != nil {
		return nil, nil, errors.WithMessagef(err, "could not parse front matter of post %s", filename)
	}

	return &matter, rest, nil
}

func renderMarkdown(content []byte) (string, error) {
	var buf bytes.Buffer
	if err := markdown.Convert(content, &buf); err != nil {
		return "", errors.WithMessage(err, "could not convert markdown content")
	}
	return buf.String(), nil
}

func readPosts(root string, inputDir string, outputDir string) ([]Post, Tags, error) {
	tags := mapset.NewSet[string]()
	posts := []Post{}
	subdir := filepath.Join(root, inputDir)
	files, err := os.ReadDir(subdir)
	if err != nil {
		return nil, nil, errors.WithMessagef(err, "could not read post directory %s", subdir)
	}
	outputReplacer := strings.NewReplacer(root, outputDir, ".md", "/index.html")
	urlReplacer := strings.NewReplacer(root, "", ".md", "/")
	for _, f := range files {
		pathFromRoot := filepath.Join(subdir, f.Name())
		if !f.IsDir() && path.Ext(pathFromRoot) == ".md" {
			output := outputReplacer.Replace(pathFromRoot)
			url := urlReplacer.Replace(pathFromRoot)
			slog.Debug("reading post", "post", pathFromRoot)
			matter, content, err := getPost(pathFromRoot)
			if err != nil {
				return nil, nil, err
			}

			for _, tag := range matter.Taxonomies.Tags {
				tags.Add(strings.ToLower(tag))
			}

			slog.Debug("rendering markdown in post", "post", pathFromRoot)
			html, err := renderMarkdown(content)
			if err != nil {
				return nil, nil, err
			}
			post := Post{
				Input:      pathFromRoot,
				Output:     output,
				Basename:   filepath.Base(url),
				URL:        url,
				PostMatter: *matter,
				Content:    html,
			}

			posts = append(posts, post)
		}
	}
	slices.SortFunc(posts, func(a, b Post) int {
		return b.Date.Compare(a.Date)
	})
	return posts, tags, nil
}