package atree

import (
	"fmt"

	bin "gordenko.dev/dima/bin/little"
	"gordenko.dev/dima/qb"
	"gordenko.dev/dima/qb/storage"
	"gordenko.dev/dima/qb/util"
)

type readResult struct {
	Data []byte
	Err  error
}

// INDEX PAGES

func (s *Atree) DeletePages(pageNumbers []uint32) {
	s.mutex.Lock()
	for _, pageNo := range pageNumbers {
		delete(s.pages, pageNo)
	}
	s.mutex.Unlock()
}

func (s *Atree) fetchIndexPage(pageNo uint32) ([]byte, error) {
	// buf, err := s.fetchPage(pageNo)
	// if err != nil {
	// 	return nil, err
	// }
	// if buf[pageTypeIdx] != PageTypeIndex {
	// 	return nil, fmt.Errorf("wrong pageType %d instead of %d", buf[pageTypeIdx], PageTypeIndex)
	// }
	// return buf, nil
	return nil, nil
}

func (s *Atree) fetchDataPage(pageNo uint32) ([]byte, error) {
	buf, err := s.fetchPage(pageNo)
	if err != nil {
		return nil, err
	}
	return buf, nil
}

func (s *Atree) fetchPage(pageNo uint32) ([]byte, error) {
	s.mutex.Lock()
	p, ok := s.pages[pageNo]
	if ok {
		p.ReferenceCount++
		s.mutex.Unlock()
		return p.Buf, nil
	}

	resultCh := make(chan readResult, 1)
	s.pageWaits[pageNo] = append(s.pageWaits[pageNo], resultCh)
	if len(s.pageWaits[pageNo]) == 1 {
		s.pagesToRead = append(s.pagesToRead, pageNo)
		s.mutex.Unlock()

		select {
		case s.readSignalCh <- struct{}{}:
		default:
		}
	} else {
		s.mutex.Unlock()
	}

	result := <-resultCh
	if result.Err == nil {
		result.Err = s.verifyCRC(result.Data, storage.DataPageSize)
	}
	return result.Data, result.Err
}

func (s *Atree) releasePage(pageNo uint32) {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	p, ok := s.pages[pageNo]
	if ok {
		if p.ReferenceCount > 0 {
			p.ReferenceCount--
			return
		} else {
			qb.Abort(
				qb.ReferenceCountBug,
				fmt.Errorf("call releasePage on page %d with reference count = %d",
					pageNo, p.ReferenceCount),
			)
		}
	}
}

// DATA PAGES

// READ

func (s *Atree) pageReader() {
	for {
		select {
		case <-s.readSignalCh:
			s.readPages()
		}
	}
}

func (s *Atree) readPages() {
	s.mutex.Lock()
	if len(s.pagesToRead) == 0 {
		s.mutex.Unlock()
		return
	}
	pagesToRead := s.pagesToRead
	s.pagesToRead = nil
	s.mutex.Unlock()

	for _, pageNo := range pagesToRead {
		buf := make([]byte, storage.DataPageSize)
		off := int(pageNo-1) * storage.DataPageSize
		n, err := s.file.ReadAt(buf, int64(off))
		if n != storage.DataPageSize {
			err = fmt.Errorf("read %d instead of %d", n, storage.DataPageSize)
		}

		s.mutex.Lock()
		resultChannels := s.pageWaits[pageNo]
		delete(s.pageWaits, pageNo)

		if err != nil {
			s.mutex.Unlock()
			for _, resultCh := range resultChannels {
				resultCh <- readResult{
					Err: err,
				}
			}
		} else {
			s.pages[pageNo] = &_page{
				PageNo:         pageNo,
				Buf:            buf,
				ReferenceCount: len(resultChannels),
			}
			s.mutex.Unlock()
			for _, resultCh := range resultChannels {
				resultCh <- readResult{
					Data: buf,
				}
			}
		}
	}
}

// WRITE

func (s *Atree) verifyCRC(data []byte, pageSize int) error {
	var (
		pos           = pageSize - 4
		calculatedCRC = util.CalculateCRC32(data[:pos])
		storedCRC, _  = bin.GetUint32(data[pos:])
	)
	if calculatedCRC != storedCRC {
		return fmt.Errorf("calculatedCRC %d not equal storedCRC %d",
			calculatedCRC, storedCRC)
	}
	return nil
}