package platform

import (
	"encoding/json"
	"errors"
	"fmt"
)

const canvasOperationsProtocol = 1

type canvasOperation struct {
	ID        string                     `json:"id"`
	Type      string                     `json:"type"`
	CanvasID  string                     `json:"canvas_id"`
	ElementID string                     `json:"element_id"`
	Record    json.RawMessage            `json:"record,omitempty"`
	Patch     map[string]json.RawMessage `json:"patch,omitempty"`
}
type canvasOperationBatch struct {
	ProtocolVersion  int               `json:"protocol_version"`
	RequestID        string            `json:"request_id"`
	ExpectedVersions map[string]int64  `json:"expected_versions"`
	Operations       []canvasOperation `json:"operations"`
}

var errInvalidCanvasOperation = errors.New("invalid_canvas_operation")

// applyCanvasOperations stages a complete batch. Input snapshots are never mutated.
// HTTP/auth/version/idempotency are checked by the transaction coordinator.
func applyCanvasOperations(initial map[string]canvasSnapshot, operations []canvasOperation) (map[string]canvasSnapshot, error) {
	if len(operations) == 0 || len(operations) > 2500 {
		return nil, errInvalidCanvasOperation
	}
	documents := make(map[string]map[string]json.RawMessage, len(initial))
	for id, snapshot := range initial {
		var document map[string]json.RawMessage
		if json.Unmarshal(snapshot.Document, &document) != nil {
			return nil, errInvalidCanvasOperation
		}
		documents[id] = document
	}
	seen := map[string]bool{}
	for _, operation := range operations {
		if !uuidSlugPattern.MatchString(operation.ID) || seen[operation.ID] || !canvasID.MatchString(operation.ElementID) {
			return nil, errInvalidCanvasOperation
		}
		seen[operation.ID] = true
		document := documents[operation.CanvasID]
		if document == nil {
			return nil, errInvalidCanvasOperation
		}
		collection := ""
		switch operation.Type {
		case "node.create", "node.patch", "node.delete":
			collection = "nodes"
		case "edge.create", "edge.patch", "edge.delete":
			collection = "edges"
		default:
			return nil, errInvalidCanvasOperation
		}
		var records []map[string]json.RawMessage
		if json.Unmarshal(document[collection], &records) != nil {
			return nil, errInvalidCanvasOperation
		}
		index := -1
		for i, record := range records {
			var id string
			_ = json.Unmarshal(record["id"], &id)
			if id == operation.ElementID {
				index = i
				break
			}
		}
		switch operation.Type {
		case "node.create", "edge.create":
			if index >= 0 || len(operation.Record) == 0 || len(operation.Patch) != 0 {
				return nil, fmt.Errorf("%w: create conflict", errInvalidCanvasOperation)
			}
			var record map[string]json.RawMessage
			var id string
			if json.Unmarshal(operation.Record, &record) != nil || json.Unmarshal(record["id"], &id) != nil || id != operation.ElementID {
				return nil, errInvalidCanvasOperation
			}
			records = append(records, record)
		case "node.delete", "edge.delete":
			if index < 0 || len(operation.Record) != 0 || len(operation.Patch) != 0 {
				return nil, fmt.Errorf("%w: missing delete target", errInvalidCanvasOperation)
			}
			records = append(records[:index], records[index+1:]...)
		case "node.patch", "edge.patch":
			if index < 0 || len(operation.Record) != 0 || len(operation.Patch) == 0 {
				return nil, errInvalidCanvasOperation
			}
			for field, value := range operation.Patch {
				allowed := field == "data" || collection == "nodes" && (field == "position" || field == "width" || field == "height") || collection == "edges" && (field == "source" || field == "target" || field == "sourceHandle" || field == "targetHandle")
				if !allowed {
					return nil, errInvalidCanvasOperation
				}
				if field == "data" {
					// Merge individual data fields; a geometry-only patch never rolls back titles/assets.
					var before, patch map[string]json.RawMessage
					if json.Unmarshal(records[index][field], &before) != nil || json.Unmarshal(value, &patch) != nil || patch == nil {
						return nil, errInvalidCanvasOperation
					}
					if before == nil {
						before = map[string]json.RawMessage{}
					}
					for key, item := range patch {
						if string(item) == "null" {
							delete(before, key)
						} else {
							before[key] = item
						}
					}
					encoded, err := json.Marshal(before)
					if err != nil {
						return nil, err
					}
					records[index][field] = encoded
				} else {
					records[index][field] = append(json.RawMessage(nil), value...)
				}
			}
		}
		encoded, err := json.Marshal(records)
		if err != nil {
			return nil, err
		}
		document[collection] = encoded
	}
	result := make(map[string]canvasSnapshot, len(initial))
	for id, document := range documents {
		raw, err := json.Marshal(document)
		if err != nil {
			return nil, err
		}
		normalized, valid := normalizeCanvas(raw)
		if !valid {
			return nil, errInvalidCanvasOperation
		}
		snapshot := initial[id]
		snapshot.Document = normalized
		snapshot.Version++
		result[id] = snapshot
	}
	return result, nil
}