package design

import (
	"bytes"
	"compress/gzip"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"strings"
	"time"
)

const CanvasDataPrefix = "SHAKKERDATA://"

type CanvasSnapshot struct {
	ProjectID   string       `json:"projectId"`
	Version     string       `json:"version"`
	SnapshotID  string       `json:"snapshotId"`
	Viewport    Viewport     `json:"viewport"`
	Nodes       []Node       `json:"nodes"`
	Connections []Connection `json:"connections"`
	UpdatedAt   string       `json:"updatedAt"`
}

func EncodeCanvasSnapshot(project Project) (string, error) {
	snapshot := CanvasSnapshot{
		ProjectID:   project.ID,
		Version:     project.Version,
		SnapshotID:  project.SnapshotID,
		Viewport:    project.Viewport,
		Nodes:       append([]Node(nil), project.Nodes...),
		Connections: append([]Connection(nil), project.Connections...),
		UpdatedAt:   project.UpdatedAt.UTC().Format(time.RFC3339Nano),
	}

	payload, err := json.Marshal(snapshot)
	if err != nil {
		return "", err
	}

	var compressed bytes.Buffer
	writer := gzip.NewWriter(&compressed)
	if _, err := writer.Write(payload); err != nil {
		_ = writer.Close()
		return "", err
	}
	if err := writer.Close(); err != nil {
		return "", err
	}

	return CanvasDataPrefix + base64.StdEncoding.EncodeToString(compressed.Bytes()), nil
}

func DecodeCanvasSnapshot(canvas string) (CanvasSnapshot, error) {
	canvas = strings.TrimSpace(canvas)
	if !strings.HasPrefix(canvas, CanvasDataPrefix) {
		return CanvasSnapshot{}, fmt.Errorf("%w: canvas snapshot must use %s prefix", ErrInvalidInput, CanvasDataPrefix)
	}

	raw, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(canvas, CanvasDataPrefix))
	if err != nil {
		return CanvasSnapshot{}, err
	}
	reader, err := gzip.NewReader(bytes.NewReader(raw))
	if err != nil {
		return CanvasSnapshot{}, err
	}
	defer reader.Close()

	payload, err := io.ReadAll(reader)
	if err != nil {
		return CanvasSnapshot{}, err
	}

	var snapshot CanvasSnapshot
	if err := json.Unmarshal(payload, &snapshot); err != nil {
		return CanvasSnapshot{}, err
	}
	return snapshot, nil
}

func CanvasVersion(now time.Time) string {
	if now.IsZero() {
		now = time.Now()
	}
	return fmt.Sprintf("%d", now.UnixMilli())
}