// Package writer handles persistence of scraped chapters and metadata.
//
// Directory layout:
//
//	static/books/
//	├── {book-slug}/
//	│   ├── metadata.yaml
//	│   ├── vol-0/          (no volume grouping)
//	│   │   ├── 1-50/
//	│   │   │   ├── chapter-1.md
//	│   │   │   └── …
//	│   │   └── 51-100/
//	│   │       └── …
//	│   └── vol-1/
//	│       └── …
package writer

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"github.com/libnovel/scraper/internal/scraper"
	"gopkg.in/yaml.v3"
)

const chaptersPerFolder = 50

// Writer persists scraped content under a configurable root directory.
type Writer struct {
	root string // e.g. "./static/books"
}

// New creates a Writer that stores files under root.
func New(root string) *Writer {
	return &Writer{root: root}
}

// ─── Metadata ─────────────────────────────────────────────────────────────────

// WriteMetadata serialises meta to static/books/{slug}/metadata.yaml.
// It creates the directory if it does not exist and overwrites any existing file.
func (w *Writer) WriteMetadata(meta scraper.BookMeta) error {
	dir := w.bookDir(meta.Slug)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return fmt.Errorf("writer: mkdir %s: %w", dir, err)
	}

	path := filepath.Join(dir, "metadata.yaml")
	f, err := os.Create(path)
	if err != nil {
		return fmt.Errorf("writer: create metadata %s: %w", path, err)
	}
	defer f.Close()

	enc := yaml.NewEncoder(f)
	enc.SetIndent(2)
	if err := enc.Encode(meta); err != nil {
		return fmt.Errorf("writer: encode metadata: %w", err)
	}
	return enc.Close()
}

// ReadMetadata reads the metadata.yaml for slug if it exists.
// Returns (zero-value, false, nil) when the file does not exist.
func (w *Writer) ReadMetadata(slug string) (scraper.BookMeta, bool, error) {
	path := filepath.Join(w.bookDir(slug), "metadata.yaml")
	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return scraper.BookMeta{}, false, nil
		}
		return scraper.BookMeta{}, false, fmt.Errorf("writer: read metadata %s: %w", path, err)
	}

	var meta scraper.BookMeta
	if err := yaml.Unmarshal(data, &meta); err != nil {
		return scraper.BookMeta{}, true, fmt.Errorf("writer: unmarshal metadata %s: %w", path, err)
	}
	return meta, true, nil
}

// ─── Chapters ─────────────────────────────────────────────────────────────────

// ChapterExists returns true if the markdown file for ref already exists on disk.
func (w *Writer) ChapterExists(slug string, ref scraper.ChapterRef) bool {
	_, err := os.Stat(w.chapterPath(slug, ref))
	return err == nil
}

// WriteChapter writes chapter.Text to the appropriate markdown file.
// The parent directories are created on demand.
func (w *Writer) WriteChapter(slug string, chapter scraper.Chapter) error {
	path := w.chapterPath(slug, chapter.Ref)
	dir := filepath.Dir(path)

	if err := os.MkdirAll(dir, 0o755); err != nil {
		return fmt.Errorf("writer: mkdir %s: %w", dir, err)
	}

	// Build the markdown document.
	var sb strings.Builder
	sb.WriteString("# ")
	sb.WriteString(chapter.Ref.Title)
	sb.WriteString("\n\n")
	sb.WriteString(chapter.Text)
	sb.WriteString("\n")

	if err := os.WriteFile(path, []byte(sb.String()), 0o644); err != nil {
		return fmt.Errorf("writer: write chapter %s: %w", path, err)
	}
	return nil
}

// ─── Path helpers ─────────────────────────────────────────────────────────────

// bookDir returns the root directory for a book slug.
func (w *Writer) bookDir(slug string) string {
	return filepath.Join(w.root, slug)
}

// chapterPath computes the full file path for a chapter.
//
//	vol-{volume}/{folderRange}/chapter-{number}.md
//
// Example: vol-0/1-50/chapter-1.md, vol-0/51-100/chapter-51.md
func (w *Writer) chapterPath(slug string, ref scraper.ChapterRef) string {
	vol := ref.Volume // 0 == no volume grouping
	volDir := fmt.Sprintf("vol-%d", vol)

	// Folder group: chapters 1-50 → "1-50", 51-100 → "51-100", …
	lo := ((ref.Number-1)/chaptersPerFolder)*chaptersPerFolder + 1
	hi := lo + chaptersPerFolder - 1
	rangeDir := fmt.Sprintf("%d-%d", lo, hi)

	filename := fmt.Sprintf("chapter-%d.md", ref.Number)

	return filepath.Join(w.bookDir(slug), volDir, rangeDir, filename)
}