package builder

import (
	"fmt"
	"html/template"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/fsnotify/fsnotify"
	"nebbet.no/internal/db"
)

// Builder orchestrates the markdown → HTML build pipeline.
type Builder struct {
	ContentDir   string
	OutputDir    string
	TemplateDir  string
	ComponentDir string
	LibDir       string
	MetaDB       *db.MetaDB
	SearchDB     *db.SearchDB
	tmpl         *template.Template
}

func New(contentDir, outputDir string, meta *db.MetaDB, search *db.SearchDB) *Builder {
	return &Builder{
		ContentDir:   contentDir,
		OutputDir:    outputDir,
		TemplateDir:  "templates",
		ComponentDir: "components",
		LibDir:       "lib",
		MetaDB:       meta,
		SearchDB:     search,
	}
}

// PageData is passed to HTML templates.
type PageData struct {
	Title            string
	Content          template.HTML
	// ImportMapTag is the full <script type="importmap">…</script> block,
	// pre-rendered as safe HTML so the JSON inside is never entity-escaped.
	ImportMapTag     template.HTML
	ComponentScripts []string
	Date             string
	Tags             []string
	Path             string
}

// BuildAll performs a full site build.
func (b *Builder) BuildAll() error {
	if err := b.loadTemplates(); err != nil {
		return fmt.Errorf("load templates: %w", err)
	}
	importMap, err := GenerateImportMap(b.LibDir)
	if err != nil {
		return fmt.Errorf("importmap: %w", err)
	}
	return filepath.WalkDir(b.ContentDir, func(path string, d os.DirEntry, err error) error {
		if err != nil || d.IsDir() || !strings.HasSuffix(path, ".md") {
			return err
		}
		return b.BuildFile(path, importMap)
	})
}

// BuildFile converts a single markdown file and updates both databases.
func (b *Builder) BuildFile(mdPath, importMap string) error {
	data, err := os.ReadFile(mdPath)
	if err != nil {
		return err
	}

	fm, body := ParseFrontmatter(string(data))
	if fm.Draft {
		fmt.Printf("skip draft: %s\n", mdPath)
		return nil
	}

	htmlBody, err := MarkdownToHTML(body)
	if err != nil {
		return fmt.Errorf("markdown: %w", err)
	}
	htmlBody = ProcessComponents(htmlBody)
	scripts := FindComponentScripts(htmlBody, b.ComponentDir)

	// Derive URL path and output file path from content-relative path.
	rel, _ := filepath.Rel(b.ContentDir, mdPath)
	urlPath := "/" + filepath.ToSlash(strings.TrimSuffix(rel, ".md"))
	// /index → /  and  /section/index → /section
	switch {
	case urlPath == "/index":
		urlPath = "/"
	case strings.HasSuffix(urlPath, "/index"):
		urlPath = strings.TrimSuffix(urlPath, "/index")
	}
	outPath := filepath.Join(b.OutputDir, filepath.FromSlash(
		strings.TrimSuffix(filepath.ToSlash(rel), ".md")+".html"))

	if err := os.MkdirAll(filepath.Dir(outPath), 0755); err != nil {
		return err
	}

	var importMapTag template.HTML
	if importMap != "" {
		importMapTag = template.HTML(
			"<script type=\"importmap\">" + importMap + "</script>")
	}
	page := PageData{
		Title:            fm.Title,
		Content:          template.HTML(htmlBody),
		ImportMapTag:     importMapTag,
		ComponentScripts: scripts,
		Date:             fm.Date,
		Tags:             fm.Tags,
		Path:             urlPath,
	}

	tmplName := fm.Layout + ".html"
	f, err := os.Create(outPath)
	if err != nil {
		return err
	}
	defer f.Close()
	if err := b.tmpl.ExecuteTemplate(f, tmplName, page); err != nil {
		return fmt.Errorf("template %s: %w", tmplName, err)
	}

	if err := b.MetaDB.UpsertPage(db.PageMeta{
		Path:      urlPath,
		HTMLPath:  outPath,
		Title:     fm.Title,
		Date:      fm.Date,
		Tags:      fm.Tags,
		UpdatedAt: time.Now(),
	}); err != nil {
		return fmt.Errorf("meta db: %w", err)
	}
	if err := b.SearchDB.IndexPage(db.SearchPage{
		Path:    urlPath,
		Title:   fm.Title,
		Content: StripHTML(htmlBody),
	}); err != nil {
		return fmt.Errorf("search db: %w", err)
	}

	fmt.Printf("built  %s → %s\n", mdPath, outPath)
	return nil
}

// RemovePage deletes the built HTML and removes the page from both databases.
func (b *Builder) RemovePage(mdPath string) error {
	rel, _ := filepath.Rel(b.ContentDir, mdPath)
	urlPath := "/" + filepath.ToSlash(strings.TrimSuffix(rel, ".md"))
	switch {
	case urlPath == "/index":
		urlPath = "/"
	case strings.HasSuffix(urlPath, "/index"):
		urlPath = strings.TrimSuffix(urlPath, "/index")
	}
	outPath := filepath.Join(b.OutputDir, filepath.FromSlash(
		strings.TrimSuffix(filepath.ToSlash(rel), ".md")+".html"))

	_ = os.Remove(outPath)
	_ = b.MetaDB.DeletePage(urlPath)
	_ = b.SearchDB.DeletePage(urlPath)
	fmt.Printf("removed %s\n", outPath)
	return nil
}

func (b *Builder) loadTemplates() error {
	tmpl, err := template.ParseGlob(filepath.Join(b.TemplateDir, "*.html"))
	if err != nil {
		return err
	}
	b.tmpl = tmpl
	return nil
}

// Watch monitors source directories and rebuilds on changes.
// A 150 ms debounce prevents redundant rebuilds when many files change at once.
func (b *Builder) Watch() error {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return err
	}
	defer watcher.Close()

	// Add all dirs (including nested content subdirs) to watcher.
	watchDirs := []string{b.ContentDir, b.TemplateDir, b.ComponentDir, b.LibDir, "styles"}
	for _, dir := range watchDirs {
		if err := addDirRecursive(watcher, dir); err != nil && !os.IsNotExist(err) {
			return err
		}
	}

	fmt.Println("watching for changes — Ctrl+C to stop")

	var (
		debounce  = time.NewTimer(0)
		pendingMD = ""   // non-empty → rebuild only this file
		fullBuild = false
	)
	<-debounce.C // drain initial tick

	for {
		select {
		case event, ok := <-watcher.Events:
			if !ok {
				return nil
			}
			if !event.Has(fsnotify.Write) && !event.Has(fsnotify.Create) && !event.Has(fsnotify.Remove) {
				continue
			}

			// If a new directory appears, start watching it.
			if event.Has(fsnotify.Create) {
				if info, err := os.Stat(event.Name); err == nil && info.IsDir() {
					_ = watcher.Add(event.Name)
				}
			}

			isMD := strings.HasSuffix(event.Name, ".md")
			isContentMD := isMD && strings.HasPrefix(
				filepath.ToSlash(event.Name),
				filepath.ToSlash(b.ContentDir),
			)

			if isContentMD && !fullBuild {
				if event.Has(fsnotify.Remove) {
					b.RemovePage(event.Name)
					pendingMD = ""
				} else if pendingMD == "" {
					pendingMD = event.Name
				} else if pendingMD != event.Name {
					// Multiple different md files → full rebuild.
					fullBuild = true
					pendingMD = ""
				}
			} else {
				// Templates, styles, components, lib, or multiple md changed.
				fullBuild = true
				pendingMD = ""
			}

			debounce.Reset(150 * time.Millisecond)

		case <-debounce.C:
			importMap, _ := GenerateImportMap(b.LibDir)
			if fullBuild {
				if err := b.loadTemplates(); err == nil {
					_ = b.BuildAll()
				}
				fullBuild = false
			} else if pendingMD != "" {
				if err := b.loadTemplates(); err == nil {
					_ = b.BuildFile(pendingMD, importMap)
				}
				pendingMD = ""
			}

		case err, ok := <-watcher.Errors:
			if !ok {
				return nil
			}
			fmt.Fprintf(os.Stderr, "watch error: %v\n", err)
		}
	}
}

func addDirRecursive(w *fsnotify.Watcher, root string) error {
	return filepath.WalkDir(root, func(path string, d os.DirEntry, err error) error {
		if err != nil {
			return nil // skip unreadable entries
		}
		if d.IsDir() {
			return w.Add(path)
		}
		return nil
	})
}