package loki

import (
	"errors"
	"strconv"
	"time"
)

// Send sends the message to the loki server.
// If the client is disabled, it returns error.
// If the entries channel is full, the message is discarded and returns error.
func (client *Client) Send(msg string, timestamp time.Time) error {
	if !client.IsEnabled() {
		client.missedMessages++
		return errors.New("client disabled")
	}

	if client.addToEntries(timestamp, msg) {
		if client.missedMessages > 0 {
			client.addToEntries(time.Now(), strconv.FormatInt(client.missedMessages, 10)+" messages missed")
			client.missedMessages = 0
		}
	} else {
		client.missedMessages++
		return errors.New("channel is full")
	}

	return nil
}

// addToEntries attempts to add a log entry to the entries channel.
// It returns true if the entry was added successfully, and false otherwise.
func (client *Client) addToEntries(timestamp time.Time, msg string) bool {
	select {
	case client.entries <- logEntry{
		Ts:   timestamp,
		Line: msg,
	}:
		return true
	default:
		return false
	}
}

// run manages the sending of log batches to Loki.
// It collects log entries into batches and sends them either when a batch is full,
// or when the maximum wait time has elapsed.
func (client *Client) run() {
	if !client.IsEnabled() {
		client.drainEntries()
		return
	}

	client.waitGroup.Add(1)
	defer client.waitGroup.Done()

	var batch []logEntry
	maxWait := time.NewTimer(client.config.BatchWait)

	for {
		select {
		case <-client.quit:
			for len(client.entries) > 0 {
				entry := <-client.entries
				batch = append(batch, entry)
			}
			batch = client.processMissedMessages(batch)
			client.processBatch(batch)
			return

		case entry := <-client.entries:
			batch = append(batch, entry)
			if len(batch) >= client.config.BatchEntriesNumber {
				batch = client.processBatch(batch)
				maxWait.Reset(client.config.BatchWait)
			}

		case <-maxWait.C:
			batch = client.processBatch(batch)
			maxWait.Reset(client.config.BatchWait)
		}
	}
}

func (client *Client) drainEntries() {
	for len(client.entries) > 0 {
		<-client.entries
	}
}

func (client *Client) processBatch(batch []logEntry) []logEntry {
	if len(batch) > 0 {
		client.sendLogs(batch)
		batch = batch[:0]
	}
	return batch
}

func (client *Client) processMissedMessages(batch []logEntry) []logEntry {
	if client.missedMessages > 0 {
		batch = append(batch, logEntry{
			Ts:   time.Now(),
			Line: strconv.FormatInt(client.missedMessages, 10) + " messages missed",
		})
		client.missedMessages = 0
	}
	return batch
}