package main

import (
	"bytes"
	"context"
	"crypto/sha256"
	"crypto/x509"
	"encoding/json"
	"errors"
	"fmt"
	logger "log"
	"net/http"
	"os"
	"time"

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

func snapshot(opts options) error {
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	if err := os.MkdirAll(opts.Directory, os.ModePerm); err != nil {
		return err
	}

	logger.Printf("INFO: updating metadata file\n")
	source := metadata.NewHTTPSource(metadata.HTTPSourceOptions{Name: "google"})
	msg, sig, md, err := source.Load(ctx)
	if err != nil {
		return err
	}
	if err := os.WriteFile(fmt.Sprintf("%s/%s", opts.Directory, opts.metadataFile), msg, 0644); err != nil {
		return err
	}
	if err := os.WriteFile(fmt.Sprintf("%s/%s", opts.Directory, opts.metadataSignatureFile), sig, 0644); err != nil {
		return err
	}
	timestamp := []byte(fmt.Sprintf("%d", time.Now().Unix()))
	if err := os.WriteFile(fmt.Sprintf("%s/%s", opts.Directory, opts.metadataTimestampFile), timestamp, 0644); err != nil {
		return err
	}

	logger.Printf("INFO: updating signed tree heads\n")
	for _, log := range logs(md) {
		id, _ := log.Key.ID()
		der, _ := x509.MarshalPKIXPublicKey(log.Key)
		dir := fmt.Sprintf("%s/%x", opts.logDirectory, id)
		sthFile := fmt.Sprintf("%s/%s", dir, opts.sthFile)
		if err := os.MkdirAll(dir, os.ModePerm); err != nil {
			return fmt.Errorf("%s: %v", log.Description, err)
		}

		// Fetch next STH
		cli, err := client.New(string(log.URL), &http.Client{}, jsonclient.Options{PublicKeyDER: der, UserAgent: opts.HTTPAgent})
		if err != nil {
			return fmt.Errorf("%s: %v", *log.Description, err)
		}
		nextSTH, err := cli.GetSTH(ctx)
		if err != nil {
			return fmt.Errorf("%s: %v", *log.Description, err)
		}
		nextSTHBytes, err := json.Marshal(nextSTH)
		if err != nil {
			return fmt.Errorf("%s: %v", *log.Description, err)
		}
		//
		// It's a bit ugly that ct.SignedTreeHead contains fields that
		// are not populated.  Doesn't cause any prolems here, however.
		//

		// Bootstrap log if we don't have any STH yet
		if _, err := os.Stat(sthFile); err != nil {
			if !errors.Is(err, os.ErrNotExist) {
				return fmt.Errorf("%s: %v", *log.Description, err)
			}
			if err := os.WriteFile(sthFile, nextSTHBytes, 0644); err != nil {
				return fmt.Errorf("%s: %v", *log.Description, err)
			}

			logger.Printf("INFO: bootstrapped %s at tree size %d\n", *log.Description, nextSTH.TreeSize)
			continue
		}

		// Otherwise: update an existing STH
		currSTHBytes, err := os.ReadFile(sthFile)
		if err != nil {
			return fmt.Errorf("%s: %v", *log.Description, err)
		}
		var currSTH ct.SignedTreeHead
		if err := json.Unmarshal(currSTHBytes, &currSTH); err != nil {
			return fmt.Errorf("%s: %v", *log.Description, err)
		}
		if nextSTH.TreeSize < currSTH.TreeSize {
			return fmt.Errorf("%s: next tree size is smaller: %s", *log.Description, nextSTHBytes)
		}
		if nextSTH.TreeSize == currSTH.TreeSize {
			if !bytes.Equal(nextSTH.SHA256RootHash[:], currSTH.SHA256RootHash[:]) {
				return fmt.Errorf("%s: split-view: %s", *log.Description, nextSTHBytes)
			}

			logger.Printf("INFO: %s is already up-to-date at size %d\n", *log.Description, nextSTH.TreeSize)
			continue
		}
		hashes, err := cli.GetSTHConsistency(ctx, currSTH.TreeSize, nextSTH.TreeSize)
		if err != nil {
			return fmt.Errorf("%s: %v", *log.Description, err)
		}
		if err := merkle.VerifyConsistency(currSTH.TreeSize,
			nextSTH.TreeSize,
			[sha256.Size]byte(currSTH.SHA256RootHash),
			[sha256.Size]byte(nextSTH.SHA256RootHash),
			proof(hashes)); err != nil {
			return fmt.Errorf("%s: inconsistent tree: %v", *log.Description, err)
		}
		if err := os.WriteFile(sthFile, nextSTHBytes, 0644); err != nil {
			return fmt.Errorf("%s: %v", *log.Description, err)
		}
		logger.Printf("INFO: updated %s to tree size %d\n", *log.Description, nextSTH.TreeSize)
	}
	return nil
}

// logs select logs that count towards CT-compliance checks.  Logs that don't
// have a description are skipped after printing a warning.
func logs(md metadata.Metadata) (logs []metadata.Log) {
	for _, operators := range md.Operators {
		for _, log := range operators.Logs {
			if log.Description == nil {
				fmt.Fprintf(os.Stderr, "WARNING: skipping log without description")
				continue
			}
			if log.State == nil {
				continue // skip logs with unknown states
			}
			if log.State.Name == metadata.LogStatePending {
				continue // pending logs do not count towards CT-compliance
			}
			if log.State.Name == metadata.LogStateRetired {
				continue // retired logs are not necessarily reachable
			}
			if log.State.Name == metadata.LogStateRejected {
				continue // rejected logs do not count towards CT-compliance
			}

			logs = append(logs, log)
		}
	}
	return
}

// proof formats hashes so that they can be passed to the merkle package
func proof(hashes [][]byte) (p [][sha256.Size]byte) {
	for _, hash := range hashes {
		var h [sha256.Size]byte
		copy(h[:], hash)
		p = append(p, h)
	}
	return
}