package sync

import (
	"bufio"
	"context"
	"encoding/json"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"time"

	"crypto/md5"
	"encoding/hex"

	"github.com/databricks/bricks/git"
	"github.com/databricks/bricks/project"
)

// Bump it up every time a potentially breaking change is made to the snapshot schema
const LatestSnapshotVersion = "v1"

// A snapshot is a persistant store of knowledge bricks cli has about state of files
// in the remote repo. We use the last modified times (mtime) of files to determine
// whether a files need to be updated in the remote repo.
//
// 1. Any stale files in the remote repo are updated. That is if the last modified
// time recorded in the snapshot is less than the actual last modified time of the file
//
// 2. Any files present in snapshot but absent locally are deleted from remote path
//
// Changing either the databricks workspace (ie Host) or the remote path (ie RemotePath)
// local files are being synced to will make bricks cli switch to a different
// snapshot for persisting/loading sync state
type Snapshot struct {
	// version for snapshot schema. Only snapshots matching the latest snapshot
	// schema version are used and older ones are invalidated (by deleting them)
	Version string `json:"version"`

	// hostname of the workspace this snapshot is for
	Host string `json:"host"`

	// Path in workspace for project repo
	RemotePath string `json:"remote_path"`

	// Map of all files present in the remote repo with the:
	// key: relative file path from project root
	// value: last time the remote instance of this file was updated
	LastUpdatedTimes map[string]time.Time `json:"last_modified_times"`

	// This map maps local file names to their remote names
	// eg. notebook named "foo.py" locally would be stored as "foo", thus this
	// map will contain an entry "foo.py" -> "foo"
	LocalToRemoteNames map[string]string `json:"local_to_remote_names"`

	// Inverse of localToRemoteNames. Together the form a bijective mapping (ie
	// there is a 1:1 unique mapping between local and remote name)
	RemoteToLocalNames map[string]string `json:"remote_to_local_names"`
}

type diff struct {
	put    []string
	delete []string
}

const syncSnapshotDirName = "sync-snapshots"

func GetFileName(host, remotePath string) string {
	hash := md5.Sum([]byte(host + remotePath))
	hashString := hex.EncodeToString(hash[:])
	return hashString[:16] + ".json"
}

// Compute path of the snapshot file on the local machine
// The file name for unique for a tuple of (host, remotePath)
// precisely it's the first 16 characters of md5(concat(host, remotePath))
func (s *Snapshot) getPath(ctx context.Context) (string, error) {
	prj := project.Get(ctx)
	cacheDir, err := prj.CacheDir()
	if err != nil {
		return "", err
	}
	snapshotDir := filepath.Join(cacheDir, syncSnapshotDirName)
	if _, err := os.Stat(snapshotDir); os.IsNotExist(err) {
		err = os.Mkdir(snapshotDir, os.ModeDir|os.ModePerm)
		if err != nil {
			return "", fmt.Errorf("failed to create config directory: %s", err)
		}
	}
	fileName := GetFileName(s.Host, s.RemotePath)
	return filepath.Join(snapshotDir, fileName), nil
}

func newSnapshot(ctx context.Context, remotePath string) (*Snapshot, error) {
	prj := project.Get(ctx)

	// Get host this snapshot is for
	wsc := prj.WorkspacesClient()

	// TODO: The host may be late-initialized in certain Azure setups where we
	// specify the workspace by its resource ID. tracked in: https://databricks.atlassian.net/browse/DECO-194
	host := wsc.Config.Host
	if host == "" {
		return nil, fmt.Errorf("failed to resolve host for snapshot")
	}

	return &Snapshot{
		Version:            LatestSnapshotVersion,
		Host:               host,
		RemotePath:         remotePath,
		LastUpdatedTimes:   make(map[string]time.Time),
		LocalToRemoteNames: make(map[string]string),
		RemoteToLocalNames: make(map[string]string),
	}, nil
}

func (s *Snapshot) storeSnapshot(ctx context.Context) error {
	snapshotPath, err := s.getPath(ctx)
	if err != nil {
		return err
	}
	f, err := os.OpenFile(snapshotPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
	if err != nil {
		return fmt.Errorf("failed to create/open persisted sync snapshot file: %s", err)
	}
	defer f.Close()

	// persist snapshot to disk
	bytes, err := json.MarshalIndent(s, "", "  ")
	if err != nil {
		return fmt.Errorf("failed to json marshal in-memory snapshot: %s", err)
	}
	_, err = f.Write(bytes)
	if err != nil {
		return fmt.Errorf("failed to write sync snapshot to disk: %s", err)
	}
	return nil
}

func (s *Snapshot) loadSnapshot(ctx context.Context) error {
	snapshotPath, err := s.getPath(ctx)
	if err != nil {
		return err
	}
	// Snapshot file not found. We do not load anything
	if _, err := os.Stat(snapshotPath); os.IsNotExist(err) {
		return nil
	}

	snapshotCopy := Snapshot{}

	bytes, err := os.ReadFile(snapshotPath)
	if err != nil {
		return fmt.Errorf("failed to read sync snapshot from disk: %s", err)
	}
	err = json.Unmarshal(bytes, &snapshotCopy)
	if err != nil {
		return fmt.Errorf("failed to json unmarshal persisted snapshot: %s", err)
	}
	// invalidate old snapshot with schema versions
	if snapshotCopy.Version != LatestSnapshotVersion {

		log.Printf("Did not load existing snapshot because its version is %s while the latest version is %s", s.Version, LatestSnapshotVersion)
		return nil
	}
	*s = snapshotCopy
	return nil
}

func (d diff) IsEmpty() bool {
	return len(d.put) == 0 && len(d.delete) == 0
}

func (d diff) String() string {
	if d.IsEmpty() {
		return "no changes"
	}
	var changes []string
	if len(d.put) > 0 {
		changes = append(changes, fmt.Sprintf("PUT: %s", strings.Join(d.put, ", ")))
	}
	if len(d.delete) > 0 {
		changes = append(changes, fmt.Sprintf("DELETE: %s", strings.Join(d.delete, ", ")))
	}
	return strings.Join(changes, ", ")
}

func getNotebookDetails(path string) (isNotebook bool, typeOfNotebook string, err error) {
	isNotebook = false
	typeOfNotebook = ""

	isPythonFile, err := regexp.Match(`\.py$`, []byte(path))
	if err != nil {
		return
	}
	if isPythonFile {
		f, err := os.Open(path)
		if err != nil {
			return false, "", err
		}
		defer f.Close()
		scanner := bufio.NewScanner(f)
		ok := scanner.Scan()
		if !ok {
			return false, "", scanner.Err()
		}
		// A python file is a notebook if it starts with the following magic string
		isNotebook = strings.Contains(scanner.Text(), "# Databricks notebook source")
		return isNotebook, "PYTHON", nil
	}
	return false, "", nil
}

func (s *Snapshot) diff(all []git.File) (change diff, err error) {
	currentFilenames := map[string]bool{}
	lastModifiedTimes := s.LastUpdatedTimes
	remoteToLocalNames := s.RemoteToLocalNames
	localToRemoteNames := s.LocalToRemoteNames
	for _, f := range all {
		// create set of current files to figure out if removals are needed
		currentFilenames[f.Relative] = true
		// get current modified timestamp
		modified := f.Modified()
		lastSeenModified, seen := lastModifiedTimes[f.Relative]

		if !seen || modified.After(lastSeenModified) {
			change.put = append(change.put, f.Relative)
			lastModifiedTimes[f.Relative] = modified

			// Keep track of remote names of local files so we can delete them later
			isNotebook, typeOfNotebook, err := getNotebookDetails(f.Absolute)
			if err != nil {
				return change, err
			}
			remoteName := f.Relative
			if isNotebook && typeOfNotebook == "PYTHON" {
				remoteName = strings.TrimSuffix(f.Relative, `.py`)
			}

			// If the remote handle of a file changes, we want to delete the old
			// remote version of that file to avoid duplicates.
			// This can happen if a python notebook is converted to a python
			// script or vice versa
			oldRemoteName, ok := localToRemoteNames[f.Relative]
			if ok && oldRemoteName != remoteName {
				change.delete = append(change.delete, oldRemoteName)
				delete(remoteToLocalNames, oldRemoteName)
			}
			// We cannot allow two local files in the project to point to the same
			// remote path
			oldLocalName, ok := remoteToLocalNames[remoteName]
			if ok && oldLocalName != f.Relative {
				return change, fmt.Errorf("both %s and %s point to the same remote file location %s. Please remove one of them from your local project", oldLocalName, f.Relative, remoteName)
			}
			localToRemoteNames[f.Relative] = remoteName
			remoteToLocalNames[remoteName] = f.Relative
		}
	}
	// figure out files in the snapshot.lastModifiedTimes, but not on local
	// filesystem. These will be deleted
	for localName := range lastModifiedTimes {
		_, exists := currentFilenames[localName]
		if exists {
			continue
		}

		// TODO: https://databricks.atlassian.net/browse/DECO-429
		// Add error wrapper giving instructions like this for all errors here :)
		remoteName, ok := localToRemoteNames[localName]
		if !ok {
			return change, fmt.Errorf("missing remote path for local path: %s. Please try syncing again after deleting .databricks/sync-snapshots dir from your project root", localName)
		}

		// add them to a delete batch
		change.delete = append(change.delete, remoteName)
	}
	// and remove them from the snapshot
	for _, remoteName := range change.delete {
		// we do note assert that remoteName exists in remoteToLocalNames since it
		// will be missing for files with remote name changed
		localName := remoteToLocalNames[remoteName]

		delete(lastModifiedTimes, localName)
		delete(remoteToLocalNames, remoteName)
		delete(localToRemoteNames, localName)
	}
	return
}