scratch-vm/src/serialization/sb2.js

/**
 * @fileoverview
 * Partial implementation of an SB2 JSON importer.
 * Parses provided JSON and then generates all needed
 * scratch-vm runtime structures.
 */

const Blocks = require('../engine/blocks');
const RenderedTarget = require('../sprites/rendered-target');
const Sprite = require('../sprites/sprite');
const Color = require('../util/color');
const log = require('../util/log');
const uid = require('../util/uid');
const StringUtil = require('../util/string-util');
const specMap = require('./sb2_specmap');
const Variable = require('../engine/variable');

const {loadCostume} = require('../import/load-costume.js');
const {loadSound} = require('../import/load-sound.js');
const {deserializeCostume, deserializeSound} = require('./deserialize-assets.js');

/**
 * Convert a Scratch 2.0 procedure string (e.g., "my_procedure %s %b %n")
 * into an argument map. This allows us to provide the expected inputs
 * to a mutated procedure call.
 * @param {string} procCode Scratch 2.0 procedure string.
 * @return {object} Argument map compatible with those in sb2specmap.
 */
const parseProcedureArgMap = function (procCode) {
    const argMap = [
        {} // First item in list is op string.
    ];
    const INPUT_PREFIX = 'input';
    let inputCount = 0;
    // Split by %n, %b, %s.
    const parts = procCode.split(/(?=[^\\]%[nbs])/);
    for (let i = 0; i < parts.length; i++) {
        const part = parts[i].trim();
        if (part.substring(0, 1) === '%') {
            const argType = part.substring(1, 2);
            const arg = {
                type: 'input',
                inputName: INPUT_PREFIX + (inputCount++)
            };
            if (argType === 'n') {
                arg.inputOp = 'math_number';
            } else if (argType === 's') {
                arg.inputOp = 'text';
            }
            argMap.push(arg);
        }
    }
    return argMap;
};

/**
 * Generate a list of "argument IDs" for procdefs and caller mutations.
 * IDs just end up being `input0`, `input1`, ... which is good enough.
 * @param {string} procCode Scratch 2.0 procedure string.
 * @return {Array.<string>} Array of argument id strings.
 */
const parseProcedureArgIds = function (procCode) {
    return parseProcedureArgMap(procCode)
        .map(arg => arg.inputName)
        .filter(name => name); // Filter out unnamed inputs which are labels
};

/**
 * Flatten a block tree into a block list.
 * Children are temporarily stored on the `block.children` property.
 * @param {Array.<object>} blocks list generated by `parseBlockList`.
 * @return {Array.<object>} Flattened list to be passed to `blocks.createBlock`.
 */
const flatten = function (blocks) {
    let finalBlocks = [];
    for (let i = 0; i < blocks.length; i++) {
        const block = blocks[i];
        finalBlocks.push(block);
        if (block.children) {
            finalBlocks = finalBlocks.concat(flatten(block.children));
        }
        delete block.children;
    }
    return finalBlocks;
};

/**
 * Parse any list of blocks from SB2 JSON into a list of VM-format blocks.
 * Could be used to parse a top-level script,
 * a list of blocks in a branch (e.g., in forever),
 * or a list of blocks in an argument (e.g., move [pick random...]).
 * @param {Array.<object>} blockList SB2 JSON-format block list.
 * @param {Function} addBroadcastMsg function to update broadcast message name map
 * @param {Function} getVariableId function to retreive a variable's ID based on name
 * @param {ImportedExtensionsInfo} extensions - (in/out) parsed extension information will be stored here.
 * @return {Array.<object>} Scratch VM-format block list.
 */
const parseBlockList = function (blockList, addBroadcastMsg, getVariableId, extensions) {
    const resultingList = [];
    let previousBlock = null; // For setting next.
    for (let i = 0; i < blockList.length; i++) {
        const block = blockList[i];
        // eslint-disable-next-line no-use-before-define
        const parsedBlock = parseBlock(block, addBroadcastMsg, getVariableId, extensions);
        if (typeof parsedBlock === 'undefined') continue;
        if (previousBlock) {
            parsedBlock.parent = previousBlock.id;
            previousBlock.next = parsedBlock.id;
        }
        previousBlock = parsedBlock;
        resultingList.push(parsedBlock);
    }
    return resultingList;
};

/**
 * Parse a Scratch object's scripts into VM blocks.
 * This should only handle top-level scripts that include X, Y coordinates.
 * @param {!object} scripts Scripts object from SB2 JSON.
 * @param {!Blocks} blocks Blocks object to load parsed blocks into.
 * @param {Function} addBroadcastMsg function to update broadcast message name map
 * @param {Function} getVariableId function to retreive a variable's ID based on name
 * @param {ImportedExtensionsInfo} extensions - (in/out) parsed extension information will be stored here.
 */
const parseScripts = function (scripts, blocks, addBroadcastMsg, getVariableId, extensions) {
    for (let i = 0; i < scripts.length; i++) {
        const script = scripts[i];
        const scriptX = script[0];
        const scriptY = script[1];
        const blockList = script[2];
        const parsedBlockList = parseBlockList(blockList, addBroadcastMsg, getVariableId, extensions);
        if (parsedBlockList[0]) {
            // Adjust script coordinates to account for
            // larger block size in scratch-blocks.
            // @todo: Determine more precisely the right formulas here.
            parsedBlockList[0].x = scriptX * 1.5;
            parsedBlockList[0].y = scriptY * 2.2;
            parsedBlockList[0].topLevel = true;
            parsedBlockList[0].parent = null;
        }
        // Flatten children and create add the blocks.
        const convertedBlocks = flatten(parsedBlockList);
        for (let j = 0; j < convertedBlocks.length; j++) {
            blocks.createBlock(convertedBlocks[j]);
        }
    }
};

/**
 * Create a callback for assigning fixed IDs to imported variables
 * Generator stores the global variable mapping in a closure
 * @param {!string} targetId the id of the target to scope the variable to
 * @return {string} variable ID
 */
const generateVariableIdGetter = (function () {
    let globalVariableNameMap = {};
    const namer = (targetId, name) => `${targetId}-${name}`;
    return function (targetId, topLevel) {
        // Reset the global variable map if topLevel
        if (topLevel) globalVariableNameMap = {};
        return function (name) {
            if (topLevel) { // Store the name/id pair in the globalVariableNameMap
                globalVariableNameMap[name] = namer(targetId, name);
                return globalVariableNameMap[name];
            }
            // Not top-level, so first check the global name map
            if (globalVariableNameMap[name]) return globalVariableNameMap[name];
            return namer(targetId, name);
        };
    };
}());

const globalBroadcastMsgStateGenerator = (function () {
    let broadcastMsgNameMap = {};
    const allBroadcastFields = [];
    const emptyStringName = uid();
    return function (topLevel) {
        if (topLevel) broadcastMsgNameMap = {};
        return {
            broadcastMsgMapUpdater: function (name, field) {
                name = name.toLowerCase();
                if (name === '') {
                    name = emptyStringName;
                }
                broadcastMsgNameMap[name] = `broadcastMsgId-${name}`;
                allBroadcastFields.push(field);
                return broadcastMsgNameMap[name];
            },
            globalBroadcastMsgs: broadcastMsgNameMap,
            allBroadcastFields: allBroadcastFields,
            emptyMsgName: emptyStringName
        };
    };
}());

/**
 * Parse a single "Scratch object" and create all its in-memory VM objects.
 * TODO: parse the "info" section, especially "savedExtensions"
 * @param {!object} object - From-JSON "Scratch object:" sprite, stage, watcher.
 * @param {!Runtime} runtime - Runtime object to load all structures into.
 * @param {ImportedExtensionsInfo} extensions - (in/out) parsed extension information will be stored here.
 * @param {boolean} topLevel - Whether this is the top-level object (stage).
 * @param {?object} zip - Optional zipped assets for local file import
 * @return {!Promise.<Array.<Target>>} Promise for the loaded targets when ready, or null for unsupported objects.
 */
const parseScratchObject = function (object, runtime, extensions, topLevel, zip) {
    if (!object.hasOwnProperty('objName')) {
        // Watcher/monitor - skip this object until those are implemented in VM.
        // @todo
        return Promise.resolve(null);
    }
    // Blocks container for this object.
    const blocks = new Blocks();
    // @todo: For now, load all Scratch objects (stage/sprites) as a Sprite.
    const sprite = new Sprite(blocks, runtime);
    // Sprite/stage name from JSON.
    if (object.hasOwnProperty('objName')) {
        sprite.name = object.objName;
    }
    // Costumes from JSON.
    const costumePromises = [];
    if (object.hasOwnProperty('costumes')) {
        for (let i = 0; i < object.costumes.length; i++) {
            const costumeSource = object.costumes[i];
            const costume = {
                name: costumeSource.costumeName,
                bitmapResolution: costumeSource.bitmapResolution || 1,
                rotationCenterX: costumeSource.rotationCenterX,
                rotationCenterY: costumeSource.rotationCenterY,
                // TODO we eventually want this next property to be called
                // md5ext to reflect what it actually contains, however this
                // will be a very extensive change across many repositories
                // and should be done carefully and altogether
                md5: costumeSource.baseLayerMD5,
                skinId: null
            };
            const md5ext = costumeSource.baseLayerMD5;
            const idParts = StringUtil.splitFirst(md5ext, '.');
            const md5 = idParts[0];
            const ext = idParts[1].toLowerCase();
            costume.dataFormat = ext;
            costume.assetId = md5;
            // If there is no internet connection, or if the asset is not in storage
            // for some reason, and we are doing a local .sb2 import, (e.g. zip is provided)
            // the file name of the costume should be the baseLayerID followed by the file ext
            const assetFileName = `${costumeSource.baseLayerID}.${ext}`;
            costumePromises.push(deserializeCostume(costume, runtime, zip, assetFileName)
                .then(() => loadCostume(costume.md5, costume, runtime)));
        }
    }
    // Sounds from JSON
    const soundPromises = [];
    if (object.hasOwnProperty('sounds')) {
        for (let s = 0; s < object.sounds.length; s++) {
            const soundSource = object.sounds[s];
            const sound = {
                name: soundSource.soundName,
                format: soundSource.format,
                rate: soundSource.rate,
                sampleCount: soundSource.sampleCount,
                // TODO we eventually want this next property to be called
                // md5ext to reflect what it actually contains, however this
                // will be a very extensive change across many repositories
                // and should be done carefully and altogether
                // (for example, the audio engine currently relies on this
                // property to be named 'md5')
                md5: soundSource.md5,
                data: null
            };
            const md5ext = soundSource.md5;
            const idParts = StringUtil.splitFirst(md5ext, '.');
            const md5 = idParts[0];
            const ext = idParts[1].toLowerCase();
            sound.dataFormat = ext;
            sound.assetId = md5;
            // If there is no internet connection, or if the asset is not in storage
            // for some reason, and we are doing a local .sb2 import, (e.g. zip is provided)
            // the file name of the sound should be the soundID (provided from the project.json)
            // followed by the file ext
            const assetFileName = `${soundSource.soundID}.${ext}`;
            soundPromises.push(deserializeSound(sound, runtime, zip, assetFileName)
                .then(() => loadSound(sound, runtime)));
        }
    }

    // Create the first clone, and load its run-state from JSON.
    const target = sprite.createClone();

    const getVariableId = generateVariableIdGetter(target.id, topLevel);

    const globalBroadcastMsgObj = globalBroadcastMsgStateGenerator(topLevel);
    const addBroadcastMsg = globalBroadcastMsgObj.broadcastMsgMapUpdater;

    // Load target properties from JSON.
    if (object.hasOwnProperty('variables')) {
        for (let j = 0; j < object.variables.length; j++) {
            const variable = object.variables[j];
            const newVariable = new Variable(
                getVariableId(variable.name),
                variable.name,
                Variable.SCALAR_TYPE,
                variable.isPersistent
            );
            newVariable.value = variable.value;
            target.variables[newVariable.id] = newVariable;
        }
    }

    // If included, parse any and all scripts/blocks on the object.
    if (object.hasOwnProperty('scripts')) {
        parseScripts(object.scripts, blocks, addBroadcastMsg, getVariableId, extensions);
    }

    // Update stage specific blocks (e.g. sprite clicked <=> stage clicked)
    blocks.updateTargetSpecificBlocks(topLevel); // topLevel = isStage

    if (object.hasOwnProperty('lists')) {
        for (let k = 0; k < object.lists.length; k++) {
            const list = object.lists[k];
            // @todo: monitor properties.
            const newVariable = new Variable(
                getVariableId(list.listName),
                list.listName,
                Variable.LIST_TYPE,
                false
            );
            newVariable.value = list.contents;
            target.variables[newVariable.id] = newVariable;
        }
    }
    if (object.hasOwnProperty('scratchX')) {
        target.x = object.scratchX;
    }
    if (object.hasOwnProperty('scratchY')) {
        target.y = object.scratchY;
    }
    if (object.hasOwnProperty('direction')) {
        target.direction = object.direction;
    }
    if (object.hasOwnProperty('isDraggable')) {
        target.draggable = object.isDraggable;
    }
    if (object.hasOwnProperty('scale')) {
        // SB2 stores as 1.0 = 100%; we use % in the VM.
        target.size = object.scale * 100;
    }
    if (object.hasOwnProperty('visible')) {
        target.visible = object.visible;
    }
    if (object.hasOwnProperty('currentCostumeIndex')) {
        target.currentCostume = Math.round(object.currentCostumeIndex);
    }
    if (object.hasOwnProperty('rotationStyle')) {
        if (object.rotationStyle === 'none') {
            target.rotationStyle = RenderedTarget.ROTATION_STYLE_NONE;
        } else if (object.rotationStyle === 'leftRight') {
            target.rotationStyle = RenderedTarget.ROTATION_STYLE_LEFT_RIGHT;
        } else if (object.rotationStyle === 'normal') {
            target.rotationStyle = RenderedTarget.ROTATION_STYLE_ALL_AROUND;
        }
    }
    if (object.hasOwnProperty('tempoBPM')) {
        target.tempo = object.tempoBPM;
    }
    if (object.hasOwnProperty('videoAlpha')) {
        // SB2 stores alpha as opacity, where 1.0 is opaque.
        // We convert to a percentage, and invert it so 100% is full transparency.
        target.videoTransparency = 100 - (100 * object.videoAlpha);
    }
    if (object.hasOwnProperty('info')) {
        if (object.info.hasOwnProperty('videoOn')) {
            if (object.info.videoOn) {
                target.videoState = RenderedTarget.VIDEO_STATE.ON;
            }
        }
    }

    target.isStage = topLevel;

    Promise.all(costumePromises).then(costumes => {
        sprite.costumes = costumes;
    });

    Promise.all(soundPromises).then(sounds => {
        sprite.sounds = sounds;
    });

    // The stage will have child objects; recursively process them.
    const childrenPromises = [];
    if (object.children) {
        for (let m = 0; m < object.children.length; m++) {
            childrenPromises.push(parseScratchObject(object.children[m], runtime, extensions, false, zip));
        }
    }

    return Promise.all(
        costumePromises.concat(soundPromises)
    ).then(() =>
        Promise.all(
            childrenPromises
        ).then(children => {
            // Need create broadcast msgs as variables after
            // all other targets have finished processing.
            if (target.isStage) {
                const allBroadcastMsgs = globalBroadcastMsgObj.globalBroadcastMsgs;
                const allBroadcastMsgFields = globalBroadcastMsgObj.allBroadcastFields;
                const oldEmptyMsgName = globalBroadcastMsgObj.emptyMsgName;
                if (allBroadcastMsgs[oldEmptyMsgName]) {
                    // Find a fresh 'messageN'
                    let currIndex = 1;
                    while (allBroadcastMsgs[`message${currIndex}`]) {
                        currIndex += 1;
                    }
                    const newEmptyMsgName = `message${currIndex}`;
                    // Add the new empty message name to the broadcast message
                    // name map, and assign it the old id.
                    // Then, delete the old entry in map.
                    allBroadcastMsgs[newEmptyMsgName] = allBroadcastMsgs[oldEmptyMsgName];
                    delete allBroadcastMsgs[oldEmptyMsgName];
                    // Now update all the broadcast message fields with
                    // the new empty message name.
                    for (let i = 0; i < allBroadcastMsgFields.length; i++) {
                        if (allBroadcastMsgFields[i].value === '') {
                            allBroadcastMsgFields[i].value = newEmptyMsgName;
                        }
                    }
                }
                // Traverse the broadcast message name map and create
                // broadcast messages as variables on the stage (which is this
                // target).
                for (const msgName in allBroadcastMsgs) {
                    const msgId = allBroadcastMsgs[msgName];
                    const newMsg = new Variable(
                        msgId,
                        msgName,
                        Variable.BROADCAST_MESSAGE_TYPE,
                        false
                    );
                    target.variables[newMsg.id] = newMsg;
                }
            }
            let targets = [target];
            for (let n = 0; n < children.length; n++) {
                targets = targets.concat(children[n]);
            }
            return targets;
        })
    );
};

/**
 * Top-level handler. Parse provided JSON,
 * and process the top-level object (the stage object).
 * @param {!object} json SB2-format JSON to load.
 * @param {!Runtime} runtime Runtime object to load all structures into.
 * @param {boolean=} optForceSprite If set, treat as sprite (Sprite2).
 * @param {?object} zip Optional zipped assets for local file import
 * @return {Promise.<ImportedProject>} Promise that resolves to the loaded targets when ready.
 */
const sb2import = function (json, runtime, optForceSprite, zip) {
    const extensions = {
        extensionIDs: new Set(),
        extensionURLs: new Map()
    };
    return parseScratchObject(json, runtime, extensions, !optForceSprite, zip)
        .then(targets => ({
            targets,
            extensions
        }));
};

/**
 * Given the sb2 block, inspect the specmap for a translation method or object.
 * @param {!object} block a sb2 formatted block
 * @return {object} specmap block to parse this opcode
 */
const specMapBlock = function (block) {
    const opcode = block[0];
    const mapped = opcode && specMap[opcode];
    if (!mapped) {
        log.warn(`Couldn't find SB2 block: ${opcode}`);
        return null;
    }
    if (typeof mapped === 'function') {
        return mapped(block);
    }
    return mapped;
};

/**
 * Parse a single SB2 JSON-formatted block and its children.
 * @param {!object} sb2block SB2 JSON-formatted block.
 * @param {Function} addBroadcastMsg function to update broadcast message name map
 * @param {Function} getVariableId function to retrieve a variable's ID based on name
 * @param {ImportedExtensionsInfo} extensions - (in/out) parsed extension information will be stored here.
 * @return {object} Scratch VM format block, or null if unsupported object.
 */
const parseBlock = function (sb2block, addBroadcastMsg, getVariableId, extensions) {
    const blockMetadata = specMapBlock(sb2block);
    if (!blockMetadata) {
        return;
    }
    const oldOpcode = sb2block[0];
    // If the block is from an extension, record it.
    const dotIndex = blockMetadata.opcode.indexOf('.');
    if (dotIndex >= 0) {
        const extension = blockMetadata.opcode.substring(0, dotIndex);
        extensions.extensionIDs.add(extension);
    }
    // Block skeleton.
    const activeBlock = {
        id: uid(), // Generate a new block unique ID.
        opcode: blockMetadata.opcode, // Converted, e.g. "motion_movesteps".
        inputs: {}, // Inputs to this block and the blocks they point to.
        fields: {}, // Fields on this block and their values.
        next: null, // Next block.
        shadow: false, // No shadow blocks in an SB2 by default.
        children: [] // Store any generated children, flattened in `flatten`.
    };
    // For a procedure call, generate argument map from proc string.
    if (oldOpcode === 'call') {
        blockMetadata.argMap = parseProcedureArgMap(sb2block[1]);
    }
    // Look at the expected arguments in `blockMetadata.argMap.`
    // The basic problem here is to turn positional SB2 arguments into
    // non-positional named Scratch VM arguments.
    for (let i = 0; i < blockMetadata.argMap.length; i++) {
        const expectedArg = blockMetadata.argMap[i];
        const providedArg = sb2block[i + 1]; // (i = 0 is opcode)
        // Whether the input is obscuring a shadow.
        let shadowObscured = false;
        // Positional argument is an input.
        if (expectedArg.type === 'input') {
            // Create a new block and input metadata.
            const inputUid = uid();
            activeBlock.inputs[expectedArg.inputName] = {
                name: expectedArg.inputName,
                block: null,
                shadow: null
            };
            if (typeof providedArg === 'object' && providedArg) {
                // Block or block list occupies the input.
                let innerBlocks;
                if (typeof providedArg[0] === 'object' && providedArg[0]) {
                    // Block list occupies the input.
                    innerBlocks = parseBlockList(providedArg, addBroadcastMsg, getVariableId, extensions);
                } else {
                    // Single block occupies the input.
                    innerBlocks = [parseBlock(providedArg, addBroadcastMsg, getVariableId, extensions)];
                }
                let previousBlock = null;
                for (let j = 0; j < innerBlocks.length; j++) {
                    if (j === 0) {
                        innerBlocks[j].parent = activeBlock.id;
                    } else {
                        innerBlocks[j].parent = previousBlock;
                    }
                    previousBlock = innerBlocks[j].id;
                }
                // Obscures any shadow.
                shadowObscured = true;
                activeBlock.inputs[expectedArg.inputName].block = (
                    innerBlocks[0].id
                );
                activeBlock.children = (
                    activeBlock.children.concat(innerBlocks)
                );
            }
            // Generate a shadow block to occupy the input.
            if (!expectedArg.inputOp) {
                // No editable shadow input; e.g., for a boolean.
                continue;
            }
            // Each shadow has a field generated for it automatically.
            // Value to be filled in the field.
            let fieldValue = providedArg;
            // Shadows' field names match the input name, except for these:
            let fieldName = expectedArg.inputName;
            if (expectedArg.inputOp === 'math_number' ||
                expectedArg.inputOp === 'math_whole_number' ||
                expectedArg.inputOp === 'math_positive_number' ||
                expectedArg.inputOp === 'math_integer' ||
                expectedArg.inputOp === 'math_angle') {
                fieldName = 'NUM';
                // Fields are given Scratch 2.0 default values if obscured.
                if (shadowObscured) {
                    fieldValue = 10;
                }
            } else if (expectedArg.inputOp === 'text') {
                fieldName = 'TEXT';
                if (shadowObscured) {
                    fieldValue = '';
                }
            } else if (expectedArg.inputOp === 'colour_picker') {
                // Convert SB2 color to hex.
                fieldValue = Color.decimalToHex(providedArg);
                fieldName = 'COLOUR';
                if (shadowObscured) {
                    fieldValue = '#990000';
                }
            } else if (expectedArg.inputOp === 'event_broadcast_menu') {
                fieldName = 'BROADCAST_OPTION';
                if (shadowObscured) {
                    fieldValue = '';
                }
            } else if (expectedArg.inputOp === 'music.menu.DRUM') {
                if (shadowObscured) {
                    fieldValue = 1;
                }
            } else if (expectedArg.inputOp === 'music.menu.INSTRUMENT') {
                if (shadowObscured) {
                    fieldValue = 1;
                }
            } else if (expectedArg.inputOp === 'videoSensing.menu.MOTION_DIRECTION') {
                if (shadowObscured) {
                    fieldValue = 1;
                } else if (fieldValue === 'motion') {
                    fieldValue = 1;
                } else if (fieldValue === 'direction') {
                    fieldValue = 2;
                }
            } else if (expectedArg.inputOp === 'videoSensing.menu.STAGE_SPRITE') {
                if (shadowObscured) {
                    fieldValue = 2;
                } else if (fieldValue === 'Stage') {
                    fieldValue = 1;
                } else if (fieldValue === 'this sprite') {
                    fieldValue = 2;
                }
            } else if (shadowObscured) {
                // Filled drop-down menu.
                fieldValue = '';
            }
            const fields = {};
            fields[fieldName] = {
                name: fieldName,
                value: fieldValue
            };
            // event_broadcast_menus have some extra properties to add to the
            // field and a different value than the rest
            if (expectedArg.inputOp === 'event_broadcast_menu') {
                if (!shadowObscured) {
                    // Need to update the broadcast message name map with
                    // the value of this field.
                    // Also need to provide the fields[fieldName] object,
                    // so that we can later update its value property, e.g.
                    // if sb2 message name is empty string, we will later
                    // replace this field's value with messageN
                    // once we can traverse through all the existing message names
                    // and come up with a fresh messageN.
                    const broadcastId = addBroadcastMsg(fieldValue, fields[fieldName]);
                    fields[fieldName].id = broadcastId;
                }
                fields[fieldName].variableType = expectedArg.variableType;
            }
            activeBlock.children.push({
                id: inputUid,
                opcode: expectedArg.inputOp,
                inputs: {},
                fields: fields,
                next: null,
                topLevel: false,
                parent: activeBlock.id,
                shadow: true
            });
            activeBlock.inputs[expectedArg.inputName].shadow = inputUid;
            // If no block occupying the input, alias to the shadow.
            if (!activeBlock.inputs[expectedArg.inputName].block) {
                activeBlock.inputs[expectedArg.inputName].block = inputUid;
            }
        } else if (expectedArg.type === 'field') {
            // Add as a field on this block.
            activeBlock.fields[expectedArg.fieldName] = {
                name: expectedArg.fieldName,
                value: providedArg
            };

            if (expectedArg.fieldName === 'VARIABLE' || expectedArg.fieldName === 'LIST') {
                // Add `id` property to variable fields
                activeBlock.fields[expectedArg.fieldName].id = getVariableId(providedArg);
            } else if (expectedArg.fieldName === 'BROADCAST_OPTION') {
                // Add the name in this field to the broadcast msg name map.
                // Also need to provide the fields[fieldName] object,
                // so that we can later update its value property, e.g.
                // if sb2 message name is empty string, we will later
                // replace this field's value with messageN
                // once we can traverse through all the existing message names
                // and come up with a fresh messageN.
                const broadcastId = addBroadcastMsg(providedArg, activeBlock.fields[expectedArg.fieldName]);
                activeBlock.fields[expectedArg.fieldName].id = broadcastId;
            }
            const varType = expectedArg.variableType;
            if (typeof varType === 'string') {
                activeBlock.fields[expectedArg.fieldName].variableType = varType;
            }
        }
    }

    // Updates for blocks that have new menus (e.g. in Looks)
    switch (oldOpcode) {
    case 'comeToFront':
        activeBlock.fields.FRONT_BACK = {
            name: 'FRONT_BACK',
            value: 'front'
        };
        break;
    case 'goBackByLayers:':
        activeBlock.fields.FORWARD_BACKWARD = {
            name: 'FORWARD_BACKWARD',
            value: 'backward'
        };
        break;
    case 'backgroundIndex':
        activeBlock.fields.NUMBER_NAME = {
            name: 'NUMBER_NAME',
            value: 'number'
        };
        break;
    case 'sceneName':
        activeBlock.fields.NUMBER_NAME = {
            name: 'NUMBER_NAME',
            value: 'name'
        };
        break;
    case 'costumeIndex':
        activeBlock.fields.NUMBER_NAME = {
            name: 'NUMBER_NAME',
            value: 'number'
        };
        break;
    }

    // Special cases to generate mutations.
    if (oldOpcode === 'stopScripts') {
        // Mutation for stop block: if the argument is 'other scripts',
        // the block needs a next connection.
        if (sb2block[1] === 'other scripts in sprite' ||
            sb2block[1] === 'other scripts in stage') {
            activeBlock.mutation = {
                tagName: 'mutation',
                hasnext: 'true',
                children: []
            };
        }
    } else if (oldOpcode === 'procDef') {
        // Mutation for procedure definition:
        // store all 2.0 proc data.
        const procData = sb2block.slice(1);
        // Create a new block and input metadata.
        const inputUid = uid();
        const inputName = 'custom_block';
        activeBlock.inputs[inputName] = {
            name: inputName,
            block: inputUid,
            shadow: inputUid
        };
        activeBlock.children = [{
            id: inputUid,
            opcode: 'procedures_prototype',
            inputs: {},
            fields: {},
            next: null,
            shadow: true,
            children: [],
            mutation: {
                tagName: 'mutation',
                proccode: procData[0], // e.g., "abc %n %b %s"
                argumentnames: JSON.stringify(procData[1]), // e.g. ['arg1', 'arg2']
                argumentids: JSON.stringify(parseProcedureArgIds(procData[0])),
                argumentdefaults: JSON.stringify(procData[2]), // e.g., [1, 'abc']
                warp: procData[3], // Warp mode, e.g., true/false.
                children: []
            }
        }];
    } else if (oldOpcode === 'call') {
        // Mutation for procedure call:
        // string for proc code (e.g., "abc %n %b %s").
        activeBlock.mutation = {
            tagName: 'mutation',
            children: [],
            proccode: sb2block[1],
            argumentids: JSON.stringify(parseProcedureArgIds(sb2block[1]))
        };
    } else if (oldOpcode === 'getParam') {
        // Assign correct opcode based on the block shape.
        switch (sb2block[2]) {
        case 'r':
            activeBlock.opcode = 'argument_reporter_string_number';
            break;
        case 'b':
            activeBlock.opcode = 'argument_reporter_boolean';
            break;
        }
    }
    return activeBlock;
};

module.exports = {
    deserialize: sb2import
};