package main

import (
	"fmt"
	"sync"
	"time"
)

// RingBuf implements an indefinitely writable circular buffer with a fixed size. Old data is overridden if write circle loops. Somewhat threadsafe.
type RingBuf struct {
	sync.RWMutex
	data     []byte
	writePos int
	written  int
	loop     bool
}

// NewRingBuf initializes a new RingBuf with a fixed size > 0
func NewRingBuf(size int) *RingBuf {
	if size <= 0 {
		return nil
	}
	rb := &RingBuf{
		data:     make([]byte, size),
		writePos: 0,
		written:  0,
		loop:     false,
	}
	return rb
}

func (rb *RingBuf) WriteLine(in string) (int, error) {
	return rb.Write([]byte(fmt.Sprintf("[%s]: %s\n", time.Now().Format("2006-01-02 15:04:05"), in)))
}

func (rb *RingBuf) WriteError(err error) (int, error) {
	return rb.Write([]byte(fmt.Sprintf("[%s]: ⚠️ %s\n", time.Now().Format("2006-01-02 15:04:05"), err.Error())))
}

// Write writes all data from input buf to RingBuf, overriding looped data
func (rb *RingBuf) Write(buf []byte) (int, error) {
	rb.Lock()
	defer rb.Unlock()

	inLen := len(buf)
	bufLen := len(rb.data)

	if !rb.loop && rb.written < bufLen {
		rb.written = rb.written + inLen
		rb.loop = rb.written >= bufLen
	}

	// throw away bytes which would get looped over if input bigger than data
	if inLen > bufLen {
		buf = buf[inLen-bufLen:]
	}

	// Copy to data field
	bytesToEnd := bufLen - rb.writePos
	copy(rb.data[rb.writePos:], buf)
	if len(buf) > bytesToEnd {
		copy(rb.data, buf[bytesToEnd:])
	}
	// Move writePos
	rb.writePos = ((rb.writePos + len(buf)) % bufLen)
	return inLen, nil
}

// Size returns the maximum size of the RingBuf
func (rb *RingBuf) Size() int {
	return len(rb.data)
}

// Bytes returns content of RingBuf. DON'T WRITE TO SLICE!
func (rb *RingBuf) Bytes() []byte {
	rb.RLock()
	defer rb.RUnlock()

	bufLen := len(rb.data)
	if rb.loop {
		out := make([]byte, bufLen)
		if rb.writePos == 0 {
			copy(out, rb.data)
		} else {
			copy(out, rb.data[rb.writePos:])
			copy(out[bufLen-rb.writePos:], rb.data[:rb.writePos])
		}
		return out
	}
	out := make([]byte, rb.writePos)
	copy(out, rb.data[:rb.writePos])
	return out
}

// Restart restarts RingBuf from 0
func (rb *RingBuf) Restart() {
	rb.writePos = 0
	rb.written = 0
	rb.loop = false
}

// String returns content of RingBuf as string
func (rb *RingBuf) String() string {
	return string(rb.Bytes())
}