scratch-vm/src/engine/execute.js

const BlockUtility = require('./block-utility');
const BlocksExecuteCache = require('./blocks-execute-cache');
const log = require('../util/log');
const Thread = require('./thread');
const {Map} = require('immutable');
const cast = require('../util/cast');

/**
 * Single BlockUtility instance reused by execute for every pritimive ran.
 * @const
 */
const blockUtility = new BlockUtility();

/**
 * Profiler frame name for block functions.
 * @const {string}
 */
const blockFunctionProfilerFrame = 'blockFunction';

/**
 * Profiler frame ID for 'blockFunction'.
 * @type {number}
 */
let blockFunctionProfilerId = -1;

/**
 * Utility function to determine if a value is a Promise.
 * @param {*} value Value to check for a Promise.
 * @return {boolean} True if the value appears to be a Promise.
 */
const isPromise = function (value) {
    return (
        value !== null &&
        typeof value === 'object' &&
        typeof value.then === 'function'
    );
};

/**
 * Handle any reported value from the primitive, either directly returned
 * or after a promise resolves.
 * @param {*} resolvedValue Value eventually returned from the primitive.
 * @param {!Sequencer} sequencer Sequencer stepping the thread for the ran
 * primitive.
 * @param {!Thread} thread Thread containing the primitive.
 * @param {!string} currentBlockId Id of the block in its thread for value from
 * the primitive.
 * @param {!string} opcode opcode used to identify a block function primitive.
 * @param {!boolean} isHat Is the current block a hat?
 */
// @todo move this to callback attached to the thread when we have performance
// metrics (dd)
const handleReport = function (
    resolvedValue, sequencer, thread, currentBlockId, opcode, isHat) {
    thread.pushReportedValue(resolvedValue);
    if (isHat) {
        // Hat predicate was evaluated.
        if (sequencer.runtime.getIsEdgeActivatedHat(opcode)) {
            // If this is an edge-activated hat, only proceed if the value is
            // true and used to be false, or the stack was activated explicitly
            // via stack click
            if (!thread.stackClick) {
                const oldEdgeValue = sequencer.runtime.updateEdgeActivatedValue(
                    currentBlockId,
                    resolvedValue
                );
                const edgeWasActivated = !oldEdgeValue && resolvedValue;
                if (!edgeWasActivated) {
                    sequencer.retireThread(thread);
                }
            }
        } else if (!resolvedValue) {
            // Not an edge-activated hat: retire the thread
            // if predicate was false.
            sequencer.retireThread(thread);
        }
    } else {
        // In a non-hat, report the value visually if necessary if
        // at the top of the thread stack.
        if (typeof resolvedValue !== 'undefined' && thread.atStackTop()) {
            if (thread.stackClick) {
                sequencer.runtime.visualReport(currentBlockId, resolvedValue);
            }
            if (thread.updateMonitor) {
                const targetId = sequencer.runtime.monitorBlocks.getBlock(currentBlockId).targetId;
                if (targetId && !sequencer.runtime.getTargetById(targetId)) {
                    // Target no longer exists
                    return;
                }
                sequencer.runtime.requestUpdateMonitor(Map({
                    id: currentBlockId,
                    spriteName: targetId ? sequencer.runtime.getTargetById(targetId).getName() : null,
                    value: resolvedValue
                }));
            }
        }
        // Finished any yields.
        thread.status = Thread.STATUS_RUNNING;
    }
};

/**
 * A convenience constant to help make use of the recursiveCall argument easier
 * to read.
 * @const {boolean}
 */
const RECURSIVE = true;

/**
 * A execute.js internal representation of a block to reduce the time spent in
 * execute as the same blocks are called the most.
 *
 * With the help of the Blocks class create a mutable copy of block
 * information. The members of BlockCached derived values of block information
 * that does not need to be reevaluated until a change in Blocks. Since Blocks
 * handles where the cache instance is stored, it drops all cache versions of a
 * block when any change happens to it. This way we can quickly execute blocks
 * and keep perform the right action according to the current block information
 * in the editor.
 *
 * @param {Blocks} blockContainer the related Blocks instance
 * @param {object} cached default set of cached values
 */
class BlockCached {
    constructor (blockContainer, cached) {
        /**
         * Block operation code for this block.
         * @type {string}
         */
        this.opcode = cached.opcode;

        /**
         * Original block object containing argument values for static fields.
         * @type {object}
         */
        this.fields = cached.fields;

        /**
         * Original block object containing argument values for executable inputs.
         * @type {object}
         */
        this.inputs = cached.inputs;

        /**
         * Procedure mutation.
         * @type {?object}
         */
        this.mutation = cached.mutation;

        /**
         * Is the opcode a hat (event responder) block.
         * @type {boolean}
         */
        this._isHat = false;

        /**
         * The block opcode's implementation function.
         * @type {?function}
         */
        this._blockFunction = null;

        /**
         * Is the block function defined for this opcode?
         * @type {boolean}
         */
        this._definedBlockFunction = false;

        /**
         * Is this block a block with no function but a static value to return.
         * @type {boolean}
         */
        this._isShadowBlock = false;

        /**
         * The static value of this block if it is a shadow block.
         * @type {?any}
         */
        this._shadowValue = null;

        /**
         * A copy of the block's fields that may be modified.
         * @type {object}
         */
        this._fields = Object.assign({}, this.fields);

        /**
         * A copy of the block's inputs that may be modified.
         * @type {object}
         */
        this._inputs = Object.assign({}, this.inputs);

        /**
         * An arguments object for block implementations. All executions of this
         * specific block will use this objecct.
         * @type {object}
         */
        this._argValues = {
            mutation: this.mutation
        };

        const {runtime} = blockUtility.sequencer;

        const {opcode, fields, inputs} = this;

        // Assign opcode isHat and blockFunction data to avoid dynamic lookups.
        this._isHat = runtime.getIsHat(opcode);
        this._blockFunction = runtime.getOpcodeFunction(opcode);
        this._definedBlockFunction = typeof this._blockFunction !== 'undefined';

        // Store the current shadow value if there is a shadow value.
        const fieldKeys = Object.keys(fields);
        this._isShadowBlock = (
            !this._definedBlockFunction &&
            fieldKeys.length === 1 &&
            Object.keys(inputs).length === 0
        );
        this._shadowValue = this._isShadowBlock && fields[fieldKeys[0]].value;

        // Store the static fields onto _argValues.
        for (const fieldName in fields) {
            if (
                fieldName === 'VARIABLE' ||
                fieldName === 'LIST' ||
                fieldName === 'BROADCAST_OPTION'
            ) {
                this._argValues[fieldName] = {
                    id: fields[fieldName].id,
                    name: fields[fieldName].value
                };
            } else {
                this._argValues[fieldName] = fields[fieldName].value;
            }
        }

        // Remove custom_block. It is not part of block execution.
        delete this._inputs.custom_block;

        if ('BROADCAST_INPUT' in this._inputs) {
            // BROADCAST_INPUT is called BROADCAST_OPTION in the args and is an
            // object with an unchanging shape.
            this._argValues.BROADCAST_OPTION = {
                id: null,
                name: null
            };

            // We can go ahead and compute BROADCAST_INPUT if it is a shadow
            // value.
            const broadcastInput = this._inputs.BROADCAST_INPUT;
            if (broadcastInput.block === broadcastInput.shadow) {
                // Shadow dropdown menu is being used.
                // Get the appropriate information out of it.
                const shadow = blockContainer.getBlock(broadcastInput.shadow);
                const broadcastField = shadow.fields.BROADCAST_OPTION;
                this._argValues.BROADCAST_OPTION.id = broadcastField.id;
                this._argValues.BROADCAST_OPTION.name = broadcastField.value;

                // Evaluating BROADCAST_INPUT here we do not need to do so
                // later.
                delete this._inputs.BROADCAST_INPUT;
            }
        }
    }
}

/**
 * Execute a block.
 * @param {!Sequencer} sequencer Which sequencer is executing.
 * @param {!Thread} thread Thread which to read and execute.
 * @param {boolean} recursiveCall is execute called from another execute call?
 */
const execute = function (sequencer, thread, recursiveCall) {
    const runtime = sequencer.runtime;

    // sequencer and thread are the same objects during a recursive set of
    // execute operations.
    if (recursiveCall !== RECURSIVE) {
        blockUtility.sequencer = sequencer;
        blockUtility.thread = thread;
    }

    // Current block to execute is the one on the top of the stack.
    const currentBlockId = thread.peekStack();
    const currentStackFrame = thread.peekStackFrame();

    let blockContainer = thread.blockContainer;
    let blockCached = BlocksExecuteCache.getCached(blockContainer, currentBlockId, BlockCached);
    if (blockCached === null) {
        blockContainer = runtime.flyoutBlocks;
        blockCached = BlocksExecuteCache.getCached(blockContainer, currentBlockId, BlockCached);
        // Stop if block or target no longer exists.
        if (blockCached === null) {
            // No block found: stop the thread; script no longer exists.
            sequencer.retireThread(thread);
            return;
        }
    }

    const opcode = blockCached.opcode;
    const inputs = blockCached._inputs;
    const blockFunction = blockCached._blockFunction;
    const isHat = blockCached._isHat;

    // Hats and single-field shadows are implemented slightly differently
    // from regular blocks.
    // For hats: if they have an associated block function, it's treated as a
    // predicate; if not, execution will proceed as a no-op. For single-field
    // shadows: If the block has a single field, and no inputs, immediately
    // return the value of the field.
    if (!blockCached._definedBlockFunction) {
        if (!opcode) {
            log.warn(`Could not get opcode for block: ${currentBlockId}`);
            return;
        }

        if (recursiveCall === RECURSIVE && blockCached._isShadowBlock) {
            // One field and no inputs - treat as arg.
            thread.pushReportedValue(blockCached._shadowValue);
            thread.status = Thread.STATUS_RUNNING;
        } else if (isHat) {
            // Skip through the block (hat with no predicate).
            return;
        } else {
            log.warn(`Could not get implementation for opcode: ${opcode}`);
        }
        thread.requestScriptGlowInFrame = true;
        return;
    }

    // Update values for arguments (inputs).
    const argValues = blockCached._argValues;

    // Fields are set during blockCached initialization.

    // Recursively evaluate input blocks.
    for (const inputName in inputs) {
        const input = inputs[inputName];
        const inputBlockId = input.block;
        // Is there no value for this input waiting in the stack frame?
        if (inputBlockId !== null && currentStackFrame.waitingReporter === null) {
            // If there's not, we need to evaluate the block.
            // Push to the stack to evaluate the reporter block.
            thread.pushStack(inputBlockId);
            // Save name of input for `Thread.pushReportedValue`.
            currentStackFrame.waitingReporter = inputName;
            // Actually execute the block.
            execute(sequencer, thread, RECURSIVE);
            if (thread.status === Thread.STATUS_PROMISE_WAIT) {
                // Create a reported value on the stack frame to store the
                // already built values.
                currentStackFrame.reported = {};
                // Waiting for the block to resolve, store the current argValues
                // onto a member of the currentStackFrame that can be used once
                // the nested block resolves to rebuild argValues up to this
                // point.
                for (const _inputName in inputs) {
                    // We are waiting on the nested block at inputName so we
                    // don't need to store any more inputs.
                    if (_inputName === inputName) break;
                    if (_inputName === 'BROADCAST_INPUT') {
                        currentStackFrame.reported[_inputName] = argValues.BROADCAST_OPTION.name;
                    } else {
                        currentStackFrame.reported[_inputName] = argValues[_inputName];
                    }
                }
                return;
            }

            // Execution returned immediately,
            // and presumably a value was reported, so pop the stack.
            currentStackFrame.waitingReporter = null;
            thread.popStack();
        }

        let inputValue;
        if (currentStackFrame.waitingReporter === null) {
            inputValue = currentStackFrame.justReported;
            currentStackFrame.justReported = null;
        } else if (currentStackFrame.waitingReporter === inputName) {
            inputValue = currentStackFrame.justReported;
            currentStackFrame.waitingReporter = null;
            currentStackFrame.justReported = null;
            // We have rebuilt argValues with all the stored values in the
            // currentStackFrame from the nested block's promise resolving.
            // Using the reported value from the block we waited on, unset the
            // value. The next execute needing to store reported values will
            // creates its own temporary storage.
            currentStackFrame.reported = null;
        } else if (typeof currentStackFrame.reported[inputName] !== 'undefined') {
            inputValue = currentStackFrame.reported[inputName];
        }

        if (inputName === 'BROADCAST_INPUT') {
            const broadcastInput = inputs[inputName];
            // Check if something is plugged into the broadcast block, or
            // if the shadow dropdown menu is being used.
            if (broadcastInput.block !== broadcastInput.shadow) {
                // Something is plugged into the broadcast input.
                // Cast it to a string. We don't need an id here.
                argValues.BROADCAST_OPTION.id = null;
                argValues.BROADCAST_OPTION.name = cast.toString(inputValue);
            }
        } else {
            argValues[inputName] = inputValue;
        }
    }

    let primitiveReportedValue = null;
    if (runtime.profiler !== null) {
        if (blockFunctionProfilerId === -1) {
            blockFunctionProfilerId = runtime.profiler.idByName(blockFunctionProfilerFrame);
        }
        // The method commented below has its code inlined underneath to reduce
        // the bias recorded for the profiler's calls in this time sensitive
        // execute function.
        //
        // runtime.profiler.start(blockFunctionProfilerId, opcode);
        runtime.profiler.records.push(
            runtime.profiler.START, blockFunctionProfilerId, opcode, performance.now());
    }
    primitiveReportedValue = blockFunction(argValues, blockUtility);
    if (runtime.profiler !== null) {
        // runtime.profiler.stop(blockFunctionProfilerId);
        runtime.profiler.records.push(runtime.profiler.STOP, performance.now());
    }

    if (recursiveCall !== RECURSIVE && typeof primitiveReportedValue === 'undefined') {
        // No value reported - potentially a command block.
        // Edge-activated hats don't request a glow; all commands do.
        thread.requestScriptGlowInFrame = true;
    }

    // If it's a promise, wait until promise resolves.
    if (isPromise(primitiveReportedValue)) {
        if (thread.status === Thread.STATUS_RUNNING) {
            // Primitive returned a promise; automatically yield thread.
            thread.status = Thread.STATUS_PROMISE_WAIT;
        }
        // Promise handlers
        primitiveReportedValue.then(resolvedValue => {
            handleReport(resolvedValue, sequencer, thread, currentBlockId, opcode, isHat);
            if (typeof resolvedValue === 'undefined') {
                let stackFrame;
                let nextBlockId;
                do {
                    // In the case that the promise is the last block in the current thread stack
                    // We need to pop out repeatedly until we find the next block.
                    const popped = thread.popStack();
                    if (popped === null) {
                        return;
                    }
                    nextBlockId = thread.target.blocks.getNextBlock(popped);
                    if (nextBlockId !== null) {
                        // A next block exists so break out this loop
                        break;
                    }
                    // Investigate the next block and if not in a loop,
                    // then repeat and pop the next item off the stack frame
                    stackFrame = thread.peekStackFrame();
                } while (stackFrame !== null && !stackFrame.isLoop);

                thread.pushStack(nextBlockId);
            } else {
                thread.popStack();
            }
        }, rejectionReason => {
            // Promise rejected: the primitive had some error.
            // Log it and proceed.
            log.warn('Primitive rejected promise: ', rejectionReason);
            thread.status = Thread.STATUS_RUNNING;
            thread.popStack();
        });
    } else if (thread.status === Thread.STATUS_RUNNING) {
        if (recursiveCall === RECURSIVE) {
            // In recursive calls (where execute calls execute) handleReport
            // simplifies to just calling thread.pushReportedValue.
            thread.pushReportedValue(primitiveReportedValue);
        } else {
            handleReport(primitiveReportedValue, sequencer, thread, currentBlockId, opcode, isHat);
        }
    }
};

module.exports = execute;