package sqlite

import (
	"database/sql"
	"fmt"
	"hash/fnv"
	"io"
	"mime"
	"path/filepath"
	"time"

	"github.com/andybalholm/brotli"
	"github.com/klauspost/compress/gzip"
	"github.com/klauspost/compress/zstd"
	"go.alanpearce.eu/website/internal/buffer"
	"go.alanpearce.eu/website/internal/content"
	"go.alanpearce.eu/website/internal/storage"
	"go.alanpearce.eu/x/log"

	"gitlab.com/tozd/go/errors"
	_ "modernc.org/sqlite" // import registers db/SQL driver
)

var encodings = []string{"gzip", "br", "zstd"}

type Writer struct {
	db *sql.DB

	options *Options
	log     *log.Logger
	queries struct {
		insertURL     *sql.Stmt
		insertFile    *sql.Stmt
		insertContent *sql.Stmt
	}
}

type Options struct {
	Compress bool
}

func OpenDB(dbPath string) (*sql.DB, error) {
	return sql.Open(
		"sqlite",
		fmt.Sprintf(
			"file:%s?mode=%s&_pragma=foreign_keys(1)&_pragma=mmap_size(%d)",
			dbPath,
			"rwc",
			16*1024*1024,
		),
	)
}

func NewWriter(db *sql.DB, logger *log.Logger, opts *Options) (*Writer, error) {
	_, err := db.Exec(`
		CREATE TABLE IF NOT EXISTS url (
			url_id INTEGER PRIMARY KEY,
			path TEXT NOT NULL
		);
		CREATE UNIQUE INDEX IF NOT EXISTS url_path
			ON url (path);

		CREATE TABLE IF NOT EXISTS file (
			file_id INTEGER PRIMARY KEY,
			url_id INTEGER NOT NULL,
			content_type TEXT NOT NULL,
			last_modified INTEGER NOT NULL,
			etag TEXT NOT NULL,
			FOREIGN KEY (url_id) REFERENCES url (url_id)
		);
		CREATE UNIQUE INDEX IF NOT EXISTS file_url_content_type
			ON file (url_id, content_type);

		CREATE TABLE IF NOT EXISTS content (
			content_id INTEGER PRIMARY KEY,
			file_id INTEGER NOT NULL,
			encoding TEXT NOT NULL,
			body BLOB NOT NULL,
			FOREIGN KEY (file_id) REFERENCES file (file_id)
		);
		CREATE UNIQUE INDEX IF NOT EXISTS file_content
			ON content (file_id, encoding);
	`)
	if err != nil {
		return nil, errors.WithMessage(err, "creating tables")
	}

	w := &Writer{
		db:      db,
		log:     logger,
		options: opts,
	}

	w.queries.insertURL, err = db.Prepare(`INSERT INTO url (path) VALUES (?)`)
	if err != nil {
		return nil, errors.WithMessage(err, "preparing insert URL statement")
	}

	w.queries.insertFile, err = db.Prepare(`
		INSERT INTO file (url_id, content_type, last_modified, etag)
		VALUES (:url_id, :content_type, :last_modified, :etag)
	`)
	if err != nil {
		return nil, errors.WithMessage(err, "preparing insert file statement")
	}

	w.queries.insertContent, err = db.Prepare(`
		INSERT INTO content (file_id, encoding, body)
		VALUES (:file_id, :encoding, :body)
	`)
	if err != nil {
		return nil, errors.WithMessage(err, "preparing insert content statement")
	}

	return w, nil
}

func (s *Writer) Mkdirp(string) error {
	return nil
}

func (s *Writer) storeURL(path string) (int64, error) {
	r, err := s.queries.insertURL.Exec(path)
	if err != nil {
		return 0, errors.WithMessagef(err, "inserting URL %s into database", path)
	}

	return r.LastInsertId()
}

func (s *Writer) storeFile(urlID int64, file *storage.File) (int64, error) {
	r, err := s.queries.insertFile.Exec(
		sql.Named("url_id", urlID),
		sql.Named("content_type", file.ContentType),
		sql.Named("last_modified", file.LastModified.Unix()),
		sql.Named("etag", file.Etag),
	)
	if err != nil {
		return 0, errors.WithMessage(err, "inserting file into database")
	}

	return r.LastInsertId()
}

func (s *Writer) storeEncoding(fileID int64, encoding string, data []byte) error {
	_, err := s.queries.insertContent.Exec(
		sql.Named("file_id", fileID),
		sql.Named("encoding", encoding),
		sql.Named("body", data),
	)
	if err != nil {
		return errors.WithMessagef(
			err,
			"inserting encoding into database file_id: %d encoding: %s",
			fileID,
			encoding,
		)
	}

	return nil
}

func etag(content []byte) (string, error) {
	hash := fnv.New64a()
	hash.Write(content)

	return fmt.Sprintf(`W/"%x"`, hash.Sum(nil)), nil
}

func contentType(pathname string) string {
	return mime.TypeByExtension(filepath.Ext(pathNameToFileName(pathname)))
}

func (s *Writer) WritePost(post *content.Post, content *buffer.Buffer) error {
	s.log.Debug("storing post", "title", post.Title)
	bytes := content.Bytes()
	etag, err := etag(bytes)
	if err != nil {
		return errors.WithMessage(err, "calculating etag")
	}

	file := &storage.File{
		Path:         post.URL,
		ContentType:  contentType(post.URL),
		LastModified: post.Date,
		Etag:         etag,
	}

	return s.write(file, content)
}

func (s *Writer) Write(pathname string, content *buffer.Buffer) error {
	bytes := content.Bytes()

	etag, err := etag(bytes)
	if err != nil {
		return errors.WithMessage(err, "calculating etag")
	}

	file := &storage.File{
		Path:         pathname,
		ContentType:  contentType(pathname),
		LastModified: time.Now(),
		Etag:         etag,
	}

	return s.write(file, content)
}

func (s *Writer) write(file *storage.File, content *buffer.Buffer) error {
	s.log.Debug("storing content", "pathname", file.Path)
	bytes := content.Bytes()

	urlID, err := s.storeURL(file.Path)
	if err != nil {
		return errors.WithMessage(err, "storing URL")
	}

	fileID, err := s.storeFile(urlID, file)
	if err != nil {
		return errors.WithMessage(err, "storing file")
	}

	err = s.storeEncoding(fileID, "identity", bytes)
	if err != nil {
		return err
	}

	if s.options.Compress {
		for _, enc := range encodings {
			compressed, err := compress(enc, content)
			if err != nil {
				return errors.WithMessage(err, "compressing file")
			}

			err = s.storeEncoding(fileID, enc, compressed.Bytes())
			if err != nil {
				return err
			}

		}
	}

	return nil
}

func compress(encoding string, content *buffer.Buffer) (compressed *buffer.Buffer, err error) {
	var w io.WriteCloser
	compressed = new(buffer.Buffer)
	switch encoding {
	case "gzip":
		w = gzip.NewWriter(compressed)
	case "br":
		w = brotli.NewWriter(compressed)
	case "zstd":
		w, err = zstd.NewWriter(compressed)
		if err != nil {
			return nil, errors.WithMessage(err, "could not create zstd writer")
		}
	}
	defer w.Close()

	err = content.SeekStart()
	if err != nil {
		return nil, errors.WithMessage(err, "seeking to start of content buffer")
	}
	_, err = io.Copy(w, content)
	if err != nil {
		return nil, errors.WithMessage(err, "compressing file")
	}

	return compressed, nil
}