// Package main provides onion-grab, a tool that visits a list of domains over
// HTTPS to see if they have Onion-Location configured.
//
// Install:
//
//	$ go install git.cs.kau.se/rasmoste/onion-grab@latest
//
// Usage:
//
//	$ onion-grab -h
package main

import (
	"bufio"
	"context"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"sync"
	"syscall"
	"time"

	"git.cs.kau.se/rasmoste/onion-grab/internal/onionloc"
	"git.cs.kau.se/rasmoste/onion-grab/internal/options"
	"git.cs.kau.se/rasmoste/onion-grab/internal/qna"
)

func main() {
	opts := options.Parse()
	cli := &http.Client{
		Transport: &http.Transport{
			DisableKeepAlives:      true,
			MaxResponseHeaderBytes: opts.MaxResponse * 1024 * 1024,
		},
	}

	fp, err := os.OpenFile(opts.InputFile, os.O_RDONLY, 0644)
	if err != nil {
		log.Printf("ERROR: %v", err)
		os.Exit(1)
	}
	defer fp.Close()

	questionCh := make(chan qna.Question)
	defer close(questionCh)

	answerCh := make(chan qna.Answer)
	defer close(answerCh)

	var wg sync.WaitGroup
	defer wg.Wait()

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	log.Printf("INFO: starting await handler, ctrl+C to exit\n")
	go func() {
		wg.Add(1)
		defer wg.Done()
		awaitHandler(ctx, cancel)
	}()

	log.Printf("INFO: starting %d workers with rate-limit %d requests/s\n", opts.NumWorkers, opts.Limit)
	for i := 0; i < opts.NumWorkers; i++ {
		go func() {
			wg.Add(1)
			defer wg.Done()
			workHandler(ctx, opts, cli, questionCh, answerCh)
		}()
	}

	log.Printf("INFO: starting work aggregator\n")
	go func() {
		wg.Add(1)
		defer wg.Done()
		workAggregator(ctx, opts, answerCh)
	}()

	log.Printf("INFO: generating work\n")
	nextLine, readAll := workGenerator(ctx, opts, fp, questionCh)
	if !readAll {
		notice := fmt.Sprintf("only read up until line %d", nextLine)
		if opts.StartLineInclusive != 0 {
			notice += fmt.Sprintf(" (line %d relative to start)", nextLine-opts.StartLineInclusive)
		}
		log.Printf("NOTICE: %s\n", notice)
	}
}

func awaitHandler(ctx context.Context, cancel context.CancelFunc) {
	sigs := make(chan os.Signal, 1)
	defer close(sigs)

	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
	select {
	case <-sigs:
	case <-ctx.Done():
	}
	cancel()
}

func workHandler(ctx context.Context, opts options.Options, cli *http.Client, questionCh chan qna.Question, answerCh chan qna.Answer) {
	for {
		select {
		case <-ctx.Done():
			return
		case question := <-questionCh:
			work(ctx, &opts, cli, question, answerCh)
		}
	}
}

func work(ctx context.Context, opts *options.Options, cli *http.Client, question qna.Question, answerCh chan qna.Answer) {
	cctx, cancel := context.WithTimeout(ctx, opts.Timeout)
	defer cancel()

	answer := qna.Answer{Domain: question.Domain}
	req, err := http.NewRequestWithContext(cctx, http.MethodGet, "https://"+question.Domain, nil)
	if err != nil {
		answer.ReqErr = err
		answerCh <- answer
		return
	}

	rsp, err := cli.Do(req)
	if err != nil {
		answer.DoErr = err
		answerCh <- answer
		return
	}
	defer rsp.Body.Close()

	onion, ok := onionloc.HTTP(rsp)
	if ok {
		answer.HTTP = onion
	}
	onion, ok = onionloc.HTML(rsp)
	if ok {
		answer.HTML = onion
	}
	answerCh <- answer
}

func workAggregator(ctx context.Context, opts options.Options, answerCh chan qna.Answer) {
	p := qna.Progress{}
	handleAnswer := func(a qna.Answer) {
		p.AddAnswer(a)
		if a.HTTP != "" || a.HTML != "" {
			fmt.Printf("%s\n", a.String())
		}
	}

	metrics := time.NewTicker(opts.MetricsInterval)
	defer metrics.Stop()
	for {
		select {
		case <-ctx.Done():
			log.Printf("INFO: about to exit, reading remaining answers\n")
			for {
				select {
				case a := <-answerCh:
					handleAnswer(a)
				case <-time.After(opts.Timeout + time.Second):
					log.Printf("INFO: metrics@aggregator: summary: \n\n%s\n\n", p.String())
					return
				}
			}
		case a := <-answerCh:
			handleAnswer(a)
		case <-metrics.C:
			log.Printf("INFO: metrics@aggregator: \n\n%s\n\n", p.String())
		}
	}
}

func workGenerator(ctx context.Context, opts options.Options, fp *os.File, questionCh chan qna.Question) (int64, bool) {
	scanner := bufio.NewScanner(fp)
	buf := make([]byte, 0, opts.MaxFileBuffer*1024*1024)
	scanner.Buffer(buf, opts.MaxFileBuffer*1024*1024)

	// roll-up to the requested start line
	nextLine := int64(0)
	if opts.StartLineInclusive > nextLine {
		for scanner.Scan() {
			nextLine++
			select {
			case <-ctx.Done():
				return nextLine, false
			default:
			}

			if nextLine == opts.StartLineInclusive {
				break
			}
		}
	}

	// initialize metrics
	metrics := time.NewTicker(opts.MetricsInterval)
	defer metrics.Stop()
	startTime := time.Now().Unix()
	latestTime := startTime
	latestCount := opts.StartLineInclusive

	// initialize rate-limit
	limit := time.NewTicker(time.Second)
	defer limit.Stop()
	readCount := 0

	for scanner.Scan() {
		if opts.EndLineExclusive > 0 && nextLine == opts.EndLineExclusive {
			break
		}

		if readCount == opts.Limit {
			select {
			case <-ctx.Done():
				return nextLine, false
			case <-limit.C:
				readCount = 0
			}
		}

		select {
		case <-ctx.Done():
			return nextLine, false
		case questionCh <- qna.Question{Domain: trimWildcard(scanner.Text())}:
			nextLine++
			readCount++
		case <-metrics.C:
			now := time.Now().Unix()
			currRate := float64(nextLine-latestCount) / float64(now-latestTime)
			avgRate := float64(nextLine-opts.StartLineInclusive) / float64(now-startTime)

			str := fmt.Sprintf("  Current rate: %.1f sites/s\n", currRate)
			str += fmt.Sprintf("  Average rate: %.1f sites/s\n", avgRate)
			str += fmt.Sprintf("     Next line: %d\n", nextLine)
			log.Printf("INFO: metrics@generator:\n\n%s\n\n", str)

			latestCount = nextLine
			latestTime = now
		}
	}

	select {
	case <-ctx.Done():
	case <-time.After(opts.Timeout + time.Second):
	}
	return nextLine, true
}

func trimWildcard(san string) string {
	if len(san) >= 2 && san[:2] == "*." {
		return san[2:]
	}
	return san
}