package docs

import (
	"bytes"
	"fmt"
	"io/fs"
	"os"
	"strings"

	"bookhoard/templates"

	"github.com/yuin/goldmark"
	highlighting "github.com/yuin/goldmark-highlighting"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/renderer/html"
	"golang.org/x/text/cases"
	"golang.org/x/text/language"
)

type DocsHandler struct {
	markdown goldmark.Markdown
	docsPath string
	docsFS   fs.FS
}

func NewDocsHandler(docsPath string) *DocsHandler {
	// Create goldmark renderer with syntax highlighting
	md := goldmark.New(
		goldmark.WithExtensions(
			extension.GFM,
			extension.Table,
			highlighting.NewHighlighting(
				// Chroma renders code blocks with inline styles, so the
				// palette ships with the HTML — no client-side highlighter
				// needed. The docs are read on dark themes most of the time;
				// code blocks keep a dark surface under light themes too.
				highlighting.WithStyle("github-dark"),
			),
		),
		goldmark.WithParserOptions(
			parser.WithAutoHeadingID(),
		),
		goldmark.WithRendererOptions(
			html.WithHardWraps(),
			html.WithXHTML(),
			html.WithUnsafe(),
		),
	)

	return &DocsHandler{
		markdown: md,
		docsPath: docsPath,
		docsFS:   os.DirFS(docsPath),
	}
}

// LoadDocument loads and renders a markdown document
func (h *DocsHandler) LoadDocument(docPath string) (*templates.Document, error) {
	// Clean the path
	docPath = strings.TrimPrefix(docPath, "/")
	docPath = strings.TrimSuffix(docPath, "/")

	// Default to INDEX.md if root
	if docPath == "" || docPath == "docs" {
		docPath = "index.md"
	} else {
		// Remove /docs prefix if present
		docPath = strings.TrimPrefix(docPath, "docs/")

		// Add .md if not present
		if !strings.HasSuffix(docPath, ".md") {
			docPath += ".md"
		}
	}

	// Read the markdown file
	content, err := fs.ReadFile(h.docsFS, docPath)
	if err != nil {
		return nil, fmt.Errorf("failed to read document: %w", err)
	}

	// Convert markdown to HTML
	var buf bytes.Buffer
	context := parser.NewContext()
	if err := h.markdown.Convert(content, &buf, parser.WithContext(context)); err != nil {
		return nil, fmt.Errorf("failed to convert markdown: %w", err)
	}

	// Extract title from first heading
	title := h.extractTitle(content)

	// Generate table of contents
	toc := h.generateTOC(content)

	// Generate breadcrumb
	breadcrumb := h.generateBreadcrumb(docPath)

	// Determine category
	category := h.getCategory(docPath)

	return &templates.Document{
		Title:      title,
		Content:    buf.String(),
		TOC:        toc,
		Breadcrumb: breadcrumb,
		Category:   category,
		SourceFile: docPath,
	}, nil
}

// extractTitle extracts the first heading from markdown content
func (h *DocsHandler) extractTitle(content []byte) string {
	lines := bytes.Split(content, []byte("\n"))
	for _, line := range lines {
		line = bytes.TrimSpace(line)
		if bytes.HasPrefix(line, []byte("# ")) {
			return string(bytes.TrimPrefix(line, []byte("# ")))
		}
	}
	return "Documentation"
}

// generateTOC generates a table of contents from markdown headings
func (h *DocsHandler) generateTOC(content []byte) []templates.TOCItem {
	var toc []templates.TOCItem
	lines := bytes.Split(content, []byte("\n"))

	for _, line := range lines {
		line = bytes.TrimSpace(line)
		if bytes.HasPrefix(line, []byte("#")) && !bytes.HasPrefix(line, []byte("# ")) {
			// Count heading level
			level := 0
			for _, c := range line {
				if c == '#' {
					level++
				} else {
					break
				}
			}

			if level > 1 && level <= 4 { // Only ## ### ####
				title := strings.TrimSpace(string(bytes.TrimLeft(line, "#")))
				anchor := h.slugify(title)

				toc = append(toc, templates.TOCItem{
					Level:  level,
					Title:  title,
					Anchor: anchor,
				})
			}
		}
	}

	return toc
}

// generateBreadcrumb generates breadcrumb navigation. Only "Docs" links out:
// directory segments have no landing pages, so they render as plain text
// (URL left empty). The current page is omitted — the h1 below shows it.
func (h *DocsHandler) generateBreadcrumb(docPath string) []templates.BreadcrumbItem {
	parts := strings.Split(strings.TrimSuffix(docPath, ".md"), "/")
	breadcrumb := []templates.BreadcrumbItem{
		{Title: "Docs", URL: "/docs"},
	}

	for i, part := range parts {
		if part == "" {
			continue
		}
		if i == len(parts)-1 {
			break // current page
		}
		breadcrumb = append(breadcrumb, templates.BreadcrumbItem{
			Title: cases.Title(language.English).String(strings.ReplaceAll(part, "-", " ")),
		})
	}

	return breadcrumb
}

// getCategory determines the category of a document. It reuses the nav
// routing (placeDoc) so search results and breadcrumbs name sections exactly
// as the sidebar does.
func (h *DocsHandler) getCategory(docPath string) string {
	return placeDoc(docPath).section
}

// slugify converts a string to a URL-safe slug
func (h *DocsHandler) slugify(s string) string {
	s = strings.ToLower(s)
	s = strings.ReplaceAll(s, " ", "-")
	s = strings.ReplaceAll(s, "/", "-")

	// Remove non-alphanumeric characters (except hyphens)
	var result strings.Builder
	for _, c := range s {
		if (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9') || c == '-' {
			result.WriteRune(c)
		}
	}

	return result.String()
}

// ListDocuments returns all markdown files in the docs directory
func (h *DocsHandler) ListDocuments() ([]string, error) {
	var docs []string

	err := fs.WalkDir(h.docsFS, ".", func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		if strings.HasSuffix(path, ".md") {
			docs = append(docs, strings.TrimSuffix(path, ".md"))
		}
		return nil
	})

	return docs, err
}

// SearchDoc represents a document for search indexing
type SearchDoc struct {
	ID      string `json:"id"`
	Title   string `json:"title"`
	Content string `json:"content"`
	URL     string `json:"url"`
}

// GenerateSearchIndex generates a search index for all documentation
func (h *DocsHandler) GenerateSearchIndex() ([]SearchDoc, error) {
	docs, err := h.ListDocuments()
	if err != nil {
		return nil, fmt.Errorf("failed to list documents: %w", err)
	}

	var searchDocs []SearchDoc
	for _, path := range docs {
		doc, err := h.LoadDocument(path)
		if err != nil {
			continue
		}

		// Strip HTML tags for better search
		content := h.stripHTML(doc.Content)

		searchDocs = append(searchDocs, SearchDoc{
			ID:      path,
			Title:   doc.Title,
			Content: content,
			URL:     "/docs/" + strings.TrimSuffix(path, ".md"),
		})
	}

	return searchDocs, nil
}

// stripHTML removes HTML tags from string
func (h *DocsHandler) stripHTML(html string) string {
	var result strings.Builder
	inTag := false
	for _, r := range html {
		if r == '<' {
			inTag = true
			continue
		}
		if r == '>' {
			inTag = false
			continue
		}
		if !inTag {
			result.WriteRune(r)
		}
	}
	return result.String()
}