package stario

import (
	"errors"
	"io"
	"sync"
)

var ErrStarBufferInvalidCapacity = errors.New("star buffer capacity must be greater than zero")
var ErrStarBufferClosed = errors.New("star buffer closed")
var ErrStarBufferWriteClosed = errors.New("star buffer write closed")

type StarBuffer struct {
	datas      []byte
	pStart     uint64
	pEnd       uint64
	size       uint64
	cap        uint64
	isClose    bool
	isWriteEnd bool
	mu         sync.Mutex
	notEmpty   *sync.Cond
	notFull    *sync.Cond
}

func NewStarBuffer(cap uint64) (*StarBuffer, error) {
	if cap == 0 {
		return nil, ErrStarBufferInvalidCapacity
	}
	rtnBuffer := &StarBuffer{
		cap:   cap,
		datas: make([]byte, cap),
	}
	rtnBuffer.notEmpty = sync.NewCond(&rtnBuffer.mu)
	rtnBuffer.notFull = sync.NewCond(&rtnBuffer.mu)
	return rtnBuffer, nil
}

func (star *StarBuffer) Free() uint64 {
	star.mu.Lock()
	defer star.mu.Unlock()
	return star.cap - star.size
}

func (star *StarBuffer) Cap() uint64 {
	star.mu.Lock()
	defer star.mu.Unlock()
	return star.cap
}

func (star *StarBuffer) Len() uint64 {
	star.mu.Lock()
	defer star.mu.Unlock()
	return star.size
}

func (star *StarBuffer) getByte() (byte, error) {
	star.mu.Lock()
	defer star.mu.Unlock()
	for star.size == 0 && !star.isWriteEnd && !star.isClose {
		star.notEmpty.Wait()
	}
	if star.size == 0 {
		return 0, io.EOF
	}
	data := star.datas[star.pStart]
	star.pStart = (star.pStart + 1) % star.cap
	star.size--
	star.notFull.Broadcast()
	return data, nil
}

func (star *StarBuffer) putByte(data byte) error {
	star.mu.Lock()
	defer star.mu.Unlock()
	for star.size == star.cap && !star.isClose && !star.isWriteEnd {
		star.notFull.Wait()
	}
	if star.isClose {
		return ErrStarBufferClosed
	}
	if star.isWriteEnd {
		return ErrStarBufferWriteClosed
	}
	star.datas[star.pEnd] = data
	star.pEnd = (star.pEnd + 1) % star.cap
	star.size++
	star.notEmpty.Broadcast()
	return nil
}

func (star *StarBuffer) EndWrite() error {
	star.mu.Lock()
	defer star.mu.Unlock()
	if star.isClose {
		return ErrStarBufferClosed
	}
	star.isWriteEnd = true
	star.notEmpty.Broadcast()
	star.notFull.Broadcast()
	return nil
}

func (star *StarBuffer) Close() error {
	star.mu.Lock()
	defer star.mu.Unlock()
	star.isClose = true
	star.isWriteEnd = true
	star.notEmpty.Broadcast()
	star.notFull.Broadcast()
	return nil
}

func (star *StarBuffer) Read(buf []byte) (int, error) {
	if buf == nil {
		return 0, errors.New("buffer is nil")
	}
	if len(buf) == 0 {
		return 0, nil
	}
	star.mu.Lock()
	defer star.mu.Unlock()
	for star.size == 0 && !star.isWriteEnd && !star.isClose {
		star.notEmpty.Wait()
	}
	if star.size == 0 {
		return 0, io.EOF
	}
	sum := minInt(len(buf), int(star.size))
	first := minInt(sum, int(star.cap-star.pStart))
	copy(buf, star.datas[star.pStart:star.pStart+uint64(first)])
	second := sum - first
	if second > 0 {
		copy(buf[first:], star.datas[:second])
	}
	star.pStart = (star.pStart + uint64(sum)) % star.cap
	star.size -= uint64(sum)
	star.notFull.Broadcast()
	return sum, nil
}

func (star *StarBuffer) Write(bts []byte) (int, error) {
	if bts == nil {
		return 0, star.EndWrite()
	}
	if len(bts) == 0 {
		return 0, nil
	}
	star.mu.Lock()
	defer star.mu.Unlock()
	sum := 0
	for sum < len(bts) {
		for star.size == star.cap && !star.isClose && !star.isWriteEnd {
			star.notFull.Wait()
		}
		if star.isClose {
			if sum == 0 {
				return 0, ErrStarBufferClosed
			}
			return sum, ErrStarBufferClosed
		}
		if star.isWriteEnd {
			if sum == 0 {
				return 0, ErrStarBufferWriteClosed
			}
			return sum, ErrStarBufferWriteClosed
		}
		space := int(star.cap - star.size)
		if space == 0 {
			continue
		}
		n := minInt(len(bts)-sum, space)
		first := minInt(n, int(star.cap-star.pEnd))
		copy(star.datas[star.pEnd:star.pEnd+uint64(first)], bts[sum:sum+first])
		second := n - first
		if second > 0 {
			copy(star.datas[:second], bts[sum+first:sum+n])
		}
		star.pEnd = (star.pEnd + uint64(n)) % star.cap
		star.size += uint64(n)
		sum += n
		star.notEmpty.Broadcast()
	}
	return sum, nil
}

func minInt(a int, b int) int {
	if a < b {
		return a
	}
	return b
}