package dbUtils

import (
	"context"
	"errors"
	"io"
	"sync"

	common "git.mic.pp.ua/anderson/nettools/common"
)

var (
	ErrPipeClosed = errors.New("pipe is closed")
	ErrPipeFull   = errors.New("pipe is full")
)

// IPipe provides Pipe Interface. Pipe is a data structure
// in which u can write and from which u can read chunks
// of data. Almost like buffer
type IPipe interface {
	io.Closer
	Write(ctx context.Context, data ...[]byte) (n int, err error)
	WaitWrite(ctx context.Context, data ...[]byte) (n int, err error)
	Read(ctx context.Context) (data [][]byte, isOpen bool, err error)
	WaitRead(ctx context.Context) (data [][]byte, isOpen bool, err error)

	Cap() int
	Grow(n int)
	Len() int
	Reset()
}

// Pipe implements IPipe interface
type Pipe struct {
	IPipe
	data [][]byte
	cap  int

	signalWritten *sync.Cond
	signalRed     *sync.Cond
	lock          *sync.RWMutex

	isClosed  bool
	closeChan chan struct{}
}

// New creates new Pipe and returns pointer to it
// Set sizeLimit = -1 for no limit
// discard
func New(sizeLimit int) *Pipe {
	return &Pipe{
		data: [][]byte{},
		cap:  sizeLimit,

		signalWritten: sync.NewCond(new(sync.Mutex)),
		signalRed:     sync.NewCond(new(sync.Mutex)),
		lock:          &sync.RWMutex{},

		isClosed: false,
	}
}

// =========================
// Write

func (p *Pipe) write(data [][]byte) (overflow [][]byte, err error) {
	if p.isClosed {
		return data, ErrPipeClosed
	}
	if p.data == nil {
		p.data = make([][]byte, 0, p.cap)
		if len(data) > p.cap {
			copy(p.data, data[:p.cap])
			return data[p.cap:], ErrPipeFull
		}
		copy(p.data, data)
		return [][]byte{}, nil
	}

	spaceLeft := p.cap - len(p.data)
	if spaceLeft < 0 {
		return [][]byte{}, ErrPipeClosed
	}
	if spaceLeft < len(data) {
		err = ErrPipeFull
		overflow = make([][]byte, len(data)-spaceLeft)
		copy(overflow, data[spaceLeft:])
		data = data[:spaceLeft]
	}
	p.data = append(p.data, data...)
	return overflow, err
}

// WaitWrite waits for pipe too free if there isn't enough space and then
// saves chunks into the pipe and returns the overflow.
// May return ErrPipeClosed and ErrPipeFull as an error
func (p *Pipe) WaitWrite(ctx context.Context, data ...[]byte) (overflow [][]byte, err error) {
	if data == nil {
		return nil, nil
	}
	return overflow, common.ExecTask(ctx, func(ctx context.Context) error {
		p.lock.Lock()
		for len(data) < p.cap && len(data)+len(p.data) > p.cap {
			p.lock.Unlock()
			p.signalRed.Wait()
			p.lock.Lock()
			break
		}
		overflow, err = p.write(data)
		p.lock.Unlock()
		p.signalWritten.Signal()
		return err
	})
}

// Write saves chunks into the pipe and returns the overflow.
// May return ErrPipeClosed and ErrPipeFull as an error
func (p *Pipe) Write(ctx context.Context, data ...[]byte) (overflow [][]byte, err error) {
	if data == nil {
		return nil, nil
	}
	return overflow, common.ExecTask(ctx, func(ctx context.Context) error {
		p.lock.Lock()
		overflow, err = p.write(data)
		p.lock.Unlock()
		p.signalWritten.Signal()
		return err
	})
}

// =========================
// Read

// waitRead is an internal function that reads and waits for data,
// but it doesn't handle context cancel or closing pipe
// Extended with WaitRead function
func (p *Pipe) waitRead() (data [][]byte, isOpen bool, err error) {
	p.lock.RLock()
	for len(p.data) == 0 {
		if p.isClosed {
			return p.data, false, io.EOF
		}
		p.lock.RUnlock()
		p.signalWritten.Wait()
		p.lock.RLock()
	}
	isOpen = !p.isClosed
	data = make([][]byte, len(p.data))
	copy(data, p.data)
	p.data = nil
	p.lock.RUnlock()
	p.signalRed.Signal()
	return p.data, isOpen, nil
}

// WaitRead
// when pipe is empty -- waits for some data to be
// written. Then reads all the chunks from the
// pipe and resets pipe data after reading.
// Also returns if pipe is open and
// may return io.EOF as an error if there is no data
// and the pipe was closed. Also, may return ErrPipeClosed
// if pipe is closed during reading and there is no data in the pipe
func (p *Pipe) WaitRead(ctx context.Context) (data [][]byte, isOpen bool, err error) {
	errChan := make(chan error)
	go func() {
		data, isOpen, err = p.waitRead()
		if err != nil {
			errChan <- err
		}
		close(errChan)
	}()

	for {
		select {
		case <-ctx.Done():
			return data, isOpen, ctx.Err()
		case err := <-errChan:
			return data, isOpen, err
		case <-p.closeChan:
			p.lock.RLock()
			if len(p.data) == 0 {
				p.lock.RUnlock()
				return data, isOpen, ErrPipeClosed
			}
			p.lock.RUnlock()
		}
	}
}

// Read reads all the chunks from the pipe
// and resets pipe data after reading.
// Also returns if pipe is open and
// may return io.EOF as an error if there is no data
// and the pipe was closed
func (p *Pipe) Read(ctx context.Context) (data [][]byte, isOpen bool, err error) {
	return data, isOpen, common.ExecTask(ctx, func(ctx context.Context) error {
		p.lock.RLock()
		isOpen = !p.isClosed
		if len(p.data) == 0 {
			return io.EOF
		}
		data = make([][]byte, len(p.data))
		copy(data, p.data)
		p.data = nil
		p.lock.RUnlock()
		p.signalRed.Signal()
		return nil
	})
}

// =========================
// Boring boilerplate bellow

func (p *Pipe) Cap() int {
	p.lock.RLock()
	defer p.lock.RUnlock()
	return p.cap
}

func (p *Pipe) Len() int {
	p.lock.RLock()
	defer p.lock.RUnlock()
	return len(p.data)
}

func (p *Pipe) LenCap() (length int, capacity int) {
	p.lock.RLock()
	defer p.lock.RUnlock()
	return len(p.data), p.cap
}

func (p *Pipe) Grow(n int) {
	p.lock.Lock()
	p.cap += n
	p.lock.Unlock()
}

func (p *Pipe) Reset() {
	p.lock.Lock()
	p.data = [][]byte{}
	p.lock.Unlock()
	p.signalRed.Signal()
}

func (p *Pipe) Close() error {
	p.lock.Lock()
	p.isClosed = true
	p.lock.Unlock()
	close(p.closeChan)
	return nil
}

func (p *Pipe) GetData() *[][]byte {
	return &p.data
}