package blog

import (
	"bytes"
	"html/template"
	"strings"
	"time"

	chromahtml "github.com/alecthomas/chroma/v2/formatters/html"
	highlighting "github.com/yuin/goldmark-highlighting/v2"
	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/renderer/html"
	"gopkg.in/yaml.v3"
)

// FrontMatter is the YAML block at the top of a post file.
type FrontMatter struct {
	Title       string   `yaml:"title"`
	Date        string   `yaml:"date"`
	Tags        []string `yaml:"tags"`
	Slug        string   `yaml:"slug"`
	Draft       bool     `yaml:"draft"`
	Description string   `yaml:"description"`
}

// Post is a parsed blog post with rendered HTML content.
type Post struct {
	FrontMatter
	ParsedDate time.Time
	Content    template.HTML
	Slug       string
}

// RenderMarkdown converts a markdown string to HTML.
func RenderMarkdown(src string) (template.HTML, error) {
	md := goldmark.New(
		goldmark.WithExtensions(
			extension.GFM,
			extension.Footnote,
			extension.DefinitionList,
			extension.Strikethrough,
			extension.Table,
			highlighting.NewHighlighting(
				highlighting.WithFormatOptions(
					chromahtml.WithClasses(true),
				),
			),
		),
		goldmark.WithParserOptions(
			parser.WithAutoHeadingID(),
		),
		goldmark.WithRendererOptions(
			html.WithXHTML(),
		),
	)
	var buf bytes.Buffer
	if err := md.Convert([]byte(src), &buf); err != nil {
		return "", err
	}
	return template.HTML(buf.String()), nil
}

// ParsePost parses raw markdown bytes (with optional YAML frontmatter) into a Post.
// filename is the bare filename (e.g. "my-post.md") used to derive the slug if not set.
func ParsePost(raw []byte, filename string) (*Post, error) {
	content := string(raw)
	var fm FrontMatter
	var markdownContent string

	if strings.HasPrefix(content, "---") {
		// Find closing ---
		rest := content[3:]
		idx := strings.Index(rest, "\n---")
		if idx >= 0 {
			fmRaw := rest[:idx]
			if err := yaml.Unmarshal([]byte(fmRaw), &fm); err != nil {
				return nil, err
			}
			markdownContent = strings.TrimSpace(rest[idx+4:])
		} else {
			markdownContent = content
		}
	} else {
		markdownContent = content
	}

	htmlContent, err := RenderMarkdown(markdownContent)
	if err != nil {
		return nil, err
	}

	slug := fm.Slug
	if slug == "" {
		slug = strings.TrimSuffix(filename, ".md")
	}

	var parsedDate time.Time
	if fm.Date != "" {
		for _, layout := range []string{"2006-01-02", "2006-01-02T15:04:05Z07:00"} {
			if t, err := time.Parse(layout, fm.Date); err == nil {
				parsedDate = t
				break
			}
		}
	}

	return &Post{
		FrontMatter: fm,
		ParsedDate:  parsedDate,
		Content:     htmlContent,
		Slug:        slug,
	}, nil
}