package main

import (
	"container/heap"
	"context"
	"crypto/sha256"
	"encoding/json"
	"fmt"
	logger "log"
	"net/http"
	"os"
	"strings"
	"sync"
	"time"

	"git.cs.kau.se/rasmoste/ct-sans/internal/chunk"
	"git.cs.kau.se/rasmoste/ct-sans/internal/merkle"
	"git.cs.kau.se/rasmoste/ct-sans/internal/x509"
	"github.com/google/certificate-transparency-go/client"
	"github.com/google/certificate-transparency-go/jsonclient"
	"github.com/google/certificate-transparency-go/scanner"
	"gitlab.torproject.org/rgdd/ct/pkg/metadata"
)

func collect(opts options) error {
	b, err := os.ReadFile(fmt.Sprintf("%s/%s", opts.Directory, opts.metadataFile))
	if err != nil {
		return err
	}
	var md metadata.Metadata
	if err := json.Unmarshal(b, &md); err != nil {
		return err
	}

	var await sync.WaitGroup
	defer await.Wait()
	ctx, cancel := context.WithCancel(context.Background())
	go func() {
		await.Add(1)
		defer await.Done()
		handleSignals(ctx, cancel)

		//
		// Sometimes some worker in scanner.Fetcher isn't shutdown
		// properly despite the parent context (including getRanges)
		// being done.  The below is an ugly hack to avoid hanging.
		//
		wait := time.Second * 5 // TODO: 15s
		logger.Printf("INFO: about to exit, please wait %v...\n", wait)
		select {
		case <-time.After(wait):
			os.Exit(0)
		}
	}()

	metricsCh := make(chan metrics)
	defer close(metricsCh)
	go func() {
		await.Add(1)
		defer await.Done()
		handleMetrics(ctx, opts, logs(md), metricsCh)
	}()

	defer cancel()
	var wg sync.WaitGroup
	defer wg.Wait()
	for _, log := range logs(md) {
		go func(log metadata.Log) {
			wg.Add(1)
			defer wg.Done()

			id, _ := log.Key.ID()
			th, err := readState(opts, id[:])
			if err != nil {
				logger.Printf("ERROR: %s: %v\n", *log.Description, err)
				cancel()
				return
			}
			sth, err := readSnapshot(opts, id[:])
			if err != nil {
				logger.Printf("ERROR: %s: %v\n", *log.Description, err)
				cancel()
				return
			}
			cli, err := client.New(string(log.URL),
				&http.Client{Transport: &http.Transport{IdleConnTimeout: 120 * time.Second}},
				jsonclient.Options{UserAgent: opts.HTTPAgent},
			)
			if err != nil {
				logger.Printf("ERROR: %s: %v\n", *log.Description, err)
				cancel()
				return
			}
			fetcher := scanner.NewFetcher(cli, &scanner.FetcherOptions{
				BatchSize:     int(opts.BatchSize),
				StartIndex:    th.TreeSize,
				EndIndex:      int64(sth.TreeSize),
				ParallelFetch: int(opts.WorkersPerLog),
			})
			if uint64(th.TreeSize) == sth.TreeSize {
				metricsCh <- metrics{Description: *log.Description, End: th.TreeSize, Done: true}
				return
			}

			//
			// Sequencer that waits for sufficiently large chunks
			// before verifying inclusion proofs and persisting an
			// intermediate tree head (size and root hash) as well
			// as the SANs that were observed up until that point.
			//
			chunksCh := make(chan *chunk.Chunk)
			defer close(chunksCh)
			cctx, fetchDone := context.WithCancel(ctx)
			defer fetchDone()
			go func() {
				wg.Add(1)
				defer wg.Done()
				sequence(cctx, cancel, opts, log, th.TreeSize, cli, chunksCh, metricsCh)
			}()

			//
			// Callback that puts downloaded certificates into a
			// chunk that a single sequencer can verify and persist
			//
			callback := func(eb scanner.EntryBatch) {
				leafHashes := [][sha256.Size]byte{}
				for i := 0; i < len(eb.Entries); i++ {
					leafHashes = append(leafHashes, merkle.HashLeafNode(eb.Entries[i].LeafInput))
				}
				sans, errs := x509.SANsFromLeafEntries(eb.Start, eb.Entries)
				for _, err := range errs {
					logger.Printf("NOTICE: %s: %v", *log.Description, err)
				}
				chunksCh <- &chunk.Chunk{eb.Start, leafHashes, sans}
			}

			if err := fetcher.Run(ctx, callback); err != nil {
				logger.Printf("ERROR: %s: %v\n", *log.Description, err)
				cancel()
				return
			}
			for len(chunksCh) > 0 {
				select {
				case <-ctx.Done():
					return // some Go routine cancelled due to an error, die
				case <-time.After(time.Second):
				}
			}
		}(log)
	}

	logger.Printf("INFO: collect is up-and-running, ctrl+C to exit\n")
	time.Sleep(3 * time.Second) // ensure that Go routines had time to spawn
	return nil
}

func sequence(ctx context.Context, cancel context.CancelFunc,
	opts options, log metadata.Log, nextIndex int64, cli *client.LogClient,
	chunksCh chan *chunk.Chunk, metricsCh chan metrics) {
	desc := *log.Description

	h := &chunk.ChunkHeap{}
	heap.Init(h)
	for {
		select {
		case <-ctx.Done():
			if h.Sequence(nextIndex) {
				c := h.TPop()
				if _, err := persist(c, opts, log, cli, 0, metricsCh); err != nil {
					logger.Printf("ERROR: %s: %v\n", desc, err)
				}
			}
			return
		case c, ok := <-chunksCh:
			if ok {
				h.TPush(c)
			}
			if !h.Sequence(nextIndex) {
				continue
			}

			c = h.TPop()
			putBack, err := persist(c, opts, log, cli, int64(opts.PersistSize), metricsCh)
			if err != nil {
				cancel()
				logger.Printf("ERROR: %s: %v\n", desc, err)
				return
			}
			if putBack {
				h.TPush(c)
				continue
			}

			nextIndex += int64(len(c.LeafHashes))
		}
	}
}

func persist(c *chunk.Chunk,
	opts options, log metadata.Log, cli *client.LogClient, minSequence int64,
	metricsCh chan metrics) (bool, error) {
	logID, _ := log.Key.ID()
	desc := *log.Description

	chunkSize := int64(len(c.LeafHashes))
	if chunkSize == 0 {
		return false, nil // nothing to persist
	}
	if chunkSize < minSequence {
		return true, nil // wait for more leaves
	}

	// Read persisted tree state from disk
	oldTH, err := readState(opts, logID[:])
	if err != nil {
		return false, err
	}
	if oldTH.TreeSize != c.Start {
		return false, fmt.Errorf("disk state says next index is %d, in-memory says %d", oldTH.TreeSize, c.Start)
	}

	// Read signed tree head from disk
	sth, err := readSnapshot(opts, logID[:])
	if err != nil {
		return false, err
	}

	//
	// Derive next intermediate tree state instead of verying all inclusions
	//
	// Independent context because we need to run inclusion and consistency
	// queries after the parent context is cancelled to persist on shutdown
	//
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	newTH := treeHead{TreeSize: c.Start + chunkSize}
	p, err := cli.GetProofByHash(ctx, c.LeafHashes[0][:], uint64(newTH.TreeSize))
	if err != nil {
		return true, nil // try again later
	}
	if p.LeafIndex != c.Start {
		return false, fmt.Errorf("log says proof for entry %d is at index %d", c.Start, p.LeafIndex)
	}
	if newTH.RootHash, err = merkle.TreeHeadFromRangeProof(c.LeafHashes, uint64(c.Start), proof(p.AuditPath)); err != nil {
		return false, err
	}

	// Check that new tree state is consistent with what we stored on disk
	var hashes [][]byte
	if oldTH.TreeSize > 0 {
		if hashes, err = cli.GetSTHConsistency(ctx, uint64(oldTH.TreeSize), uint64(newTH.TreeSize)); err != nil {
			return true, nil // try again later
		}
	}
	if err := merkle.VerifyConsistency(uint64(oldTH.TreeSize), uint64(newTH.TreeSize), oldTH.RootHash, newTH.RootHash, proof(hashes)); err != nil {
		return false, fmt.Errorf("%d %x is inconsistent with on-disk state: %v", newTH.TreeSize, newTH.RootHash, err)
	}

	// Check that new tree state is consistent with the signed tree head
	if hashes, err = cli.GetSTHConsistency(ctx, uint64(newTH.TreeSize), sth.TreeSize); err != nil {
		return true, nil // try again later
	}
	if err := merkle.VerifyConsistency(uint64(newTH.TreeSize), sth.TreeSize, newTH.RootHash, sth.SHA256RootHash, proof(hashes)); err != nil {
		return false, fmt.Errorf("%d %x is inconsistent with signed tree head: %v", newTH.TreeSize, newTH.RootHash, err)
	}

	// Persist SANs to disk
	fp, err := os.OpenFile(fmt.Sprintf("%s/%x/%s", opts.logDirectory, logID, opts.sansFile), os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
	if err != nil {
		return false, err
	}
	defer fp.Close()
	if _, err := fp.WriteString(strings.Join(c.SANs, "\n") + "\n"); err != nil {
		return false, err
	}
	if err := fp.Sync(); err != nil {
		return false, err
	}

	// Persist new tree state to disk
	b, err := json.Marshal(&newTH)
	if err != nil {
		return false, err
	}
	if err := os.WriteFile(fmt.Sprintf("%s/%x/%s", opts.logDirectory, logID, opts.stateFile), b, 0644); err != nil {
		return false, err
	}

	// Output metrics
	metricsCh <- metrics{
		Description: desc,
		NumEntries:  newTH.TreeSize - oldTH.TreeSize,
		Timestamp:   time.Now().Unix(),
		Start:       newTH.TreeSize,
		End:         int64(sth.TreeSize),
		Done:        uint64(newTH.TreeSize) == sth.TreeSize,
	}
	logger.Printf("DEBUG: %s: persisted [%d, %d]\n", desc, oldTH.TreeSize, newTH.TreeSize)
	return false, nil
}