package main

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

	"git.cs.kau.se/rasmoste/ct-sans/internal/chunk"
	"git.cs.kau.se/rasmoste/ct-sans/internal/utils"
	ct "github.com/google/certificate-transparency-go"
	"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/merkle"
	"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
	}

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

	var wg sync.WaitGroup
	defer wg.Wait()

	go func() {
		wg.Add(1)
		defer wg.Done()

		sigs := make(chan os.Signal, 1)
		defer close(sigs)

		signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
		select {
		case <-sigs:
			fmt.Fprintf(os.Stderr, "INFO: received shutdown signal, please wait...\n")
			cancel()
		case <-ctx.Done():
		}
	}()

	for _, log := range utils.Logs(md) {
		go func(log metadata.Log) {
			wg.Add(1)
			defer wg.Done()

			chunks := make(chan *chunk.Chunk)
			defer close(chunks)

			id, _ := log.Key.ID()
			th, err := readState(opts, id[:])
			if err != nil {
				fmt.Fprintf(os.Stderr, "ERROR: %s: %v\n", *log.Description, err)
				cancel()
				return
			}
			sth, err := readSnapshot(opts, id[:])
			if err != nil {
				fmt.Fprintf(os.Stderr, "ERROR: %s: %v\n", *log.Description, err)
				cancel()
				return
			}

			cli, err := client.New(string(log.URL), &http.Client{}, jsonclient.Options{UserAgent: "wip2"})
			if err != nil {
				fmt.Fprintf(os.Stderr, "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),
				Continuous:    false,
			})

			//
			// 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 := []string{"example.com"} // TODO: fixme
				chunks <- &chunk.Chunk{eb.Start, leafHashes, sans}
			}

			//
			// 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.
			//
			go func() {
				wg.Add(1)
				defer wg.Done()
				defer fmt.Fprintf(os.Stderr, "INFO: %s: shutdown sequencer\n", *log.Description)

				h := &chunk.ChunkHeap{}
				heap.Init(h)
				curr := th.TreeSize
				for {
					select {
					case <-ctx.Done():
						if h.Sequence(curr) {
							c := h.TPop()
							if _, err := persistChunk(cli, opts, id[:], 0, c); err != nil {
								fmt.Fprintf(os.Stderr, "ERROR: %s: %v\n", err)
							}
						}
						return
					case c, ok := <-chunks:
						if ok {
							h.TPush(c)
						}
						if !h.Sequence(curr) {
							continue
						}

						c = h.TPop()
						putBack, err := persistChunk(cli, opts, id[:], int64(opts.persistSize), c)
						if err != nil {
							cancel()
							fmt.Fprintf(os.Stderr, "ERROR: %s: %v\n", *log.Description, err)
							return
						}
						if putBack {
							h.TPush(c)
							continue
						}

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

			if err := fetcher.Run(ctx, callback); err != nil {
				fmt.Fprintf(os.Stderr, "ERROR: %s: %v\n", *log.Description, err)
				cancel()
				return
			}

			fmt.Fprintf(os.Stderr, "INFO: %s: fetch completed\n", *log.Description)
			for len(chunks) > 0 {
				select {
				case <-ctx.Done():
					return
				case <-time.After(1 * time.Second):
					fmt.Fprintf(os.Stderr, "DEBUG: %s: waiting for chunks to be consumed\n", *log.Description)
				}
			}
		}(log)
		break
	}

	time.Sleep(1 * time.Second)
	return fmt.Errorf("TODO")
}

type treeHead struct {
	TreeSize int64             `json:"tree_size"`
	RootHash [sha256.Size]byte `json:root_hash"`
}

func readState(opts options, logID []byte) (treeHead, error) {
	if _, err := os.Stat(fmt.Sprintf("%s/%x/%s", opts.logDirectory, logID, opts.stateFile)); err != nil {
		return treeHead{0, sha256.Sum256(nil)}, nil
	}
	b, err := os.ReadFile(fmt.Sprintf("%s/%x/%s", opts.logDirectory, logID, opts.stateFile))
	if err != nil {
		return treeHead{}, err
	}
	var th treeHead
	if err := json.Unmarshal(b, &th); err != nil {
		return treeHead{}, err
	}
	return th, nil
}

func readSnapshot(opts options, logID []byte) (ct.SignedTreeHead, error) {
	b, err := os.ReadFile(fmt.Sprintf("%s/%x/%s", opts.logDirectory, logID, opts.sthFile))
	if err != nil {
		return ct.SignedTreeHead{}, err
	}
	var sth ct.SignedTreeHead
	if err := json.Unmarshal(b, &sth); err != nil {
		return ct.SignedTreeHead{}, err
	}
	return sth, nil
}

func persistChunk(cli *client.LogClient, opts options, logID []byte, minSequence int64, c *chunk.Chunk) (bool, error) {
	if len(c.LeafHashes) == 0 {
		return false, nil // nothing to persist
	}
	if int64(len(c.LeafHashes)) < minSequence {
		return true, nil // wait for more leaves
	}

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

	// Derive next intermediate tree state to persist
	//
	// 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()
	p, err := cli.GetProofByHash(ctx, c.LeafHashes[0][:], uint64(c.Start+int64(len(c.LeafHashes))))
	if err != nil {
		fmt.Fprintf(os.Stderr, "WARNING: %x: %v\n", logID, err)
		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)
	}
	// TODO: ranged inclusion verify + consistency proof

	// 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 intermediate log state to disk
	b, err := json.Marshal(&treeHead{c.Start + int64(len(c.LeafHashes)), [sha256.Size]byte{}})
	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
	}

	fmt.Fprintf(os.Stderr, "DEBUG: %x: persist: start=%d end=%d\n", logID, c.Start, c.Start+int64(len(c.LeafHashes)))
	return false, nil
}