package sync

import (
	"fmt"
	"path/filepath"
	"strings"
	"time"

	"github.com/databricks/cli/libs/fileset"
	"github.com/databricks/cli/libs/notebook"
)

// SnapshotState keeps track of files on the local filesystem and their corresponding
// entries in WSFS.
type SnapshotState struct {
	// Map of local file names to their last recorded modified time. Files found
	// to have a newer mtime have their content synced to their remote version.
	LastModifiedTimes map[string]time.Time `json:"last_modified_times"`

	// Map of local file names to corresponding remote names.
	// For example: A notebook named "foo.py" locally would be stored as "foo"
	// in WSFS, and the entry would be: {"foo.py": "foo"}
	LocalToRemoteNames map[string]string `json:"local_to_remote_names"`

	// Inverse of LocalToRemoteNames. Together they form a 1:1 mapping where all
	// the remote names and local names are unique.
	RemoteToLocalNames map[string]string `json:"remote_to_local_names"`
}

// Convert an array of files on the local file system to a SnapshotState representation.
func NewSnapshotState(localFiles []fileset.File) (*SnapshotState, error) {
	fs := &SnapshotState{
		LastModifiedTimes:  make(map[string]time.Time),
		LocalToRemoteNames: make(map[string]string),
		RemoteToLocalNames: make(map[string]string),
	}

	// Expect no files to have a duplicate entry in the input array.
	seen := make(map[string]fileset.File)
	for _, f := range localFiles {
		if _, ok := seen[f.Relative]; !ok {
			seen[f.Relative] = f
		} else {
			return nil, fmt.Errorf("expected only one entry per file. Found duplicate entries for file: %s", f.Relative)
		}
	}

	// Compute the new state.
	for _, f := range localFiles {
		// Compute the remote name the file will have in WSFS
		remoteName := filepath.ToSlash(f.Relative)
		isNotebook, _, err := notebook.Detect(f.Absolute)
		if err != nil {
			// Ignore this file if we're unable to determine the notebook type.
			// Trying to upload such a file to the workspace would fail anyway.
			continue
		}
		if isNotebook {
			ext := filepath.Ext(remoteName)
			remoteName = strings.TrimSuffix(remoteName, ext)
		}

		// Add the file to snapshot state
		fs.LastModifiedTimes[f.Relative] = f.Modified()
		if existingLocalName, ok := fs.RemoteToLocalNames[remoteName]; ok {
			return nil, fmt.Errorf("both %s and %s point to the same remote file location %s. Please remove one of them from your local project", existingLocalName, f.Relative, remoteName)
		}

		fs.LocalToRemoteNames[f.Relative] = remoteName
		fs.RemoteToLocalNames[remoteName] = f.Relative
	}
	return fs, nil
}

// Consistency checks for the sync files state representation. These are invariants
// that downstream code for computing changes to apply to WSFS depends on.
//
// Invariants:
//  1. All entries in LastModifiedTimes have a corresponding entry in LocalToRemoteNames
//     and vice versa.
//  2. LocalToRemoteNames and RemoteToLocalNames together form a 1:1 mapping of
//     local <-> remote file names.
func (fs *SnapshotState) validate() error {
	// Validate invariant (1)
	for localName := range fs.LastModifiedTimes {
		if _, ok := fs.LocalToRemoteNames[localName]; !ok {
			return fmt.Errorf("invalid sync state representation. Local file %s is missing the corresponding remote file", localName)
		}
	}
	for localName := range fs.LocalToRemoteNames {
		if _, ok := fs.LastModifiedTimes[localName]; !ok {
			return fmt.Errorf("invalid sync state representation. Local file %s is missing it's last modified time", localName)
		}
	}

	// Validate invariant (2)
	for localName, remoteName := range fs.LocalToRemoteNames {
		if _, ok := fs.RemoteToLocalNames[remoteName]; !ok {
			return fmt.Errorf("invalid sync state representation. Remote file %s is missing the corresponding local file", remoteName)
		}
		if fs.RemoteToLocalNames[remoteName] != localName {
			return fmt.Errorf("invalid sync state representation. Inconsistent values found. Local file %s points to %s. Remote file %s points to %s", localName, remoteName, remoteName, fs.RemoteToLocalNames[remoteName])
		}
	}
	for remoteName, localName := range fs.RemoteToLocalNames {
		if _, ok := fs.LocalToRemoteNames[localName]; !ok {
			return fmt.Errorf("invalid sync state representation. local file %s is missing the corresponding remote file", localName)
		}
		if fs.LocalToRemoteNames[localName] != remoteName {
			return fmt.Errorf("invalid sync state representation. Inconsistent values found. Remote file %s points to %s. Local file %s points to %s", remoteName, localName, localName, fs.LocalToRemoteNames[localName])
		}
	}
	return nil
}