package pfile

import (
	"bufio"
	"bytes"
	"compress/gzip"
	"encoding/binary"
	"io"
	"net"
	"os"
	"sync"
	"time"

	"git.crumpington.com/public/jldb/lib/errs"
	"git.crumpington.com/public/jldb/mdb/change"
)

type File struct {
	lock sync.RWMutex
	f    *os.File
	page dataPage
}

func Open(path string) (*File, error) {
	f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0600)
	if err != nil {
		return nil, errs.IO.WithErr(err)
	}

	pf := &File{f: f}
	pf.page = newDataPage()

	return pf, nil
}

func (pf *File) Close() error {
	pf.lock.Lock()
	defer pf.lock.Unlock()

	if err := pf.f.Close(); err != nil {
		return errs.IO.WithErr(err)
	}
	return nil
}

// ----------------------------------------------------------------------------
// Writing
// ----------------------------------------------------------------------------

func (pf *File) ApplyChanges(changes []change.Change) error {
	pf.lock.Lock()
	defer pf.lock.Unlock()

	return pf.applyChanges(changes)
}

func (pf *File) applyChanges(changes []change.Change) error {
	for _, change := range changes {
		if len(change.WritePageIDs) > 0 {
			if err := pf.writeChangePages(change); err != nil {
				return err
			}
		}

		for _, id := range change.ClearPageIDs {
			if err := pf.writePage(emptyPage, id); err != nil {
				return err
			}
		}
	}

	if err := pf.f.Sync(); err != nil {
		return errs.IO.WithErr(err)
	}

	return nil
}

func (pf *File) writeChangePages(change change.Change) error {
	page := pf.page

	header := page.Header()

	header.PageType = pageTypeHead
	header.CollectionID = change.CollectionID
	header.ItemID = change.ItemID
	header.DataSize = uint64(len(change.Data))

	pageIDs := change.WritePageIDs
	data := change.Data

	for len(change.Data) > 0 && len(pageIDs) > 0 {
		pageID := pageIDs[0]
		pageIDs = pageIDs[1:]

		if len(pageIDs) > 0 {
			header.NextPage = pageIDs[0]
		} else {
			header.NextPage = 0
		}

		n := page.Write(data)
		data = data[n:]

		page.Header().CRC = page.ComputeCRC()

		if err := pf.writePage(page, pageID); err != nil {
			return err
		}

		// All but first page has pageTypeData.
		header.PageType = pageTypeData
	}

	if len(pageIDs) > 0 {
		return errs.Unexpected.WithMsg("Too many pages provided for given data.")
	}

	if len(data) > 0 {
		return errs.Unexpected.WithMsg("Not enough pages for given data.")
	}

	return nil
}

func (pf *File) writePage(page dataPage, id uint64) error {
	if _, err := pf.f.WriteAt(page, int64(id*pageSize)); err != nil {
		return errs.IO.WithErr(err)
	}
	return nil
}

// ----------------------------------------------------------------------------
// Reading
// ----------------------------------------------------------------------------

func (pf *File) iterate(each func(pageID uint64, page dataPage) error) error {
	pf.lock.RLock()
	defer pf.lock.RUnlock()

	page := pf.page

	fi, err := pf.f.Stat()
	if err != nil {
		return errs.IO.WithErr(err)
	}

	fileSize := fi.Size()
	if fileSize%pageSize != 0 {
		return errs.Corrupt.WithMsg("File size isn't a multiple of page size.")
	}

	maxPage := uint64(fileSize / pageSize)
	if _, err := pf.f.Seek(0, io.SeekStart); err != nil {
		return errs.IO.WithErr(err)
	}

	r := bufio.NewReaderSize(pf.f, 1024*1024)

	for pageID := uint64(0); pageID < maxPage; pageID++ {
		if _, err := r.Read(page); err != nil {
			return errs.IO.WithErr(err)
		}

		if err := page.Validate(); err != nil {
			return err
		}
		if err := each(pageID, page); err != nil {
			return err
		}
	}

	return nil
}

func (pf *File) readData(id uint64, buf *bytes.Buffer) error {
	page := pf.page

	// The head page.
	if err := pf.readPage(page, id); err != nil {
		return err
	}

	remaining := int(page.Header().DataSize)

	for {
		data := page.Data()
		if len(data) > remaining {
			data = data[:remaining]
		}

		buf.Write(data)
		remaining -= len(data)

		if page.Header().NextPage == 0 {
			break
		}

		if err := pf.readPage(page, page.Header().NextPage); err != nil {
			return err
		}
	}

	if remaining != 0 {
		return errs.Corrupt.WithMsg("Incorrect data size. %d remaining.", remaining)
	}

	return nil
}

func (pf *File) readPage(p dataPage, id uint64) error {
	if _, err := pf.f.ReadAt(p, int64(id*pageSize)); err != nil {
		return errs.IO.WithErr(err)
	}
	return p.Validate()
}

// ----------------------------------------------------------------------------
// Send / Recv
// ----------------------------------------------------------------------------

func (pf *File) Send(conn net.Conn, timeout time.Duration) error {
	pf.lock.RLock()
	defer pf.lock.RUnlock()

	if _, err := pf.f.Seek(0, io.SeekStart); err != nil {
		return errs.IO.WithErr(err)
	}

	fi, err := pf.f.Stat()
	if err != nil {
		return errs.IO.WithErr(err)
	}

	remaining := fi.Size()

	conn.SetWriteDeadline(time.Now().Add(timeout))
	if err := binary.Write(conn, binary.LittleEndian, remaining); err != nil {
		return err
	}

	buf := make([]byte, 1024*1024)
	w, err := gzip.NewWriterLevel(conn, 3)
	if err != nil {
		return errs.Unexpected.WithErr(err)
	}
	defer w.Close()

	for remaining > 0 {
		n, err := pf.f.Read(buf)
		if err != nil {
			return errs.IO.WithErr(err)
		}

		conn.SetWriteDeadline(time.Now().Add(timeout))
		if _, err := w.Write(buf[:n]); err != nil {
			return errs.IO.WithErr(err)
		}

		remaining -= int64(n)
		w.Flush()
	}

	return nil
}

func Recv(conn net.Conn, filePath string, timeout time.Duration) error {
	defer conn.Close()

	f, err := os.Create(filePath)
	if err != nil {
		return errs.IO.WithErr(err)
	}
	defer f.Close()

	remaining := uint64(0)
	if err := binary.Read(conn, binary.LittleEndian, &remaining); err != nil {
		return err
	}

	r, err := gzip.NewReader(conn)
	if err != nil {
		return errs.Unexpected.WithErr(err)
	}
	defer r.Close()

	buf := make([]byte, 1024*1024)
	for remaining > 0 {

		conn.SetReadDeadline(time.Now().Add(timeout))

		n, err := io.ReadFull(r, buf)
		if err != nil && n == 0 {
			return errs.IO.WithErr(err)
		}
		remaining -= uint64(n)

		if _, err := f.Write(buf[:n]); err != nil {
			return errs.IO.WithErr(err)
		}
	}

	if err := f.Sync(); err != nil {
		return errs.IO.WithErr(err)
	}

	return nil
}