bam (Thing subclasses: several steps, one file)

1 files changed, 309 insertions, 0 deletions

diff --git a/src/data/cacheable-object.js b/src/data/cacheable-object.js
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+++ b/src/data/cacheable-object.js
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+// Generally extendable class for caching properties and handling dependencies,
+// with a few key properties:
+//
+// 1) The behavior of every property is defined by its descriptor, which is a
+//    static value stored on the subclass (all instances share the same property
+//    descriptors).
+//
+//  1a) Additional properties may not be added past the time of object
+//      construction, and attempts to do so (including externally setting a
+//      property name which has no corresponding descriptor) will throw a
+//      TypeError. (This is done via an Object.seal(this) call after a newly
+//      created instance defines its own properties according to the descriptor
+//      on its constructor class.)
+//
+// 2) Properties may have two flags set: update and expose. Properties which
+//    update are provided values from the external. Properties which expose
+//    provide values to the external, generally dependent on other update
+//    properties (within the same object).
+//
+//  2a) Properties may be flagged as both updating and exposing. This is so
+//      that the same name may be used for both "output" and "input".
+//
+// 3) Exposed properties have values which are computations dependent on other
+//    properties, as described by a `compute` function on the descriptor.
+//    Depended-upon properties are explicitly listed on the descriptor next to
+//    this function, and are only provided as arguments to the function once
+//    listed.
+//
+//  3a) An exposed property may depend only upon updating properties, not other
+//      exposed properties (within the same object). This is to force the
+//      general complexity of a single object to be fairly simple: inputs
+//      directly determine outputs, with the only in-between step being the
+//      `compute` function, no multiple-layer dependencies. Note that this is
+//      only true within a given object - externally, values provided to one
+//      object's `update` may be (and regularly are) the exposed values of
+//      another object.
+//
+//  3b) If a property both updates and exposes, it is automatically regarded as
+//      a dependancy. (That is, its exposed value will depend on the value it is
+//      updated with.) Rather than a required `compute` function, these have an
+//      optional `transform` function, which takes the update value as its first
+//      argument and then the usual key-value dependencies as its second. If no
+//      `transform` function is provided, the expose value is the same as the
+//      update value.
+//
+// 4) Exposed properties are cached; that is, if no depended-upon properties are
+//    updated, the value of an exposed property is not recomputed.
+//
+//  4a) The cache for an exposed property is invalidated as soon as any of its
+//      dependencies are updated, but the cache itself is lazy: the exposed
+//      value will not be recomputed until it is again accessed. (Likewise, an
+//      exposed value won't be computed for the first time until it is first
+//      accessed.)
+//
+// 5) Updating a property may optionally apply validation checks before passing,
+//    declared by a `validate` function on the `update` block. This function
+//    should either throw an error (e.g. TypeError) or return false if the value
+//    is invalid.
+//
+// 6) Objects do not expect all updating properties to be provided at once.
+//    Incomplete objects are deliberately supported and enabled.
+//
+//  6a) The default value for every updating property is null; undefined is not
+//      accepted as a property value under any circumstances (it always errors).
+//      However, this default may be overridden by specifying a `default` value
+//      on a property's `update` block. (This value will be checked against
+//      the property's validate function.) Note that a property may always be
+//      updated to null, even if the default is non-null. (Null always bypasses
+//      the validate check.)
+//
+//  6b) It's required by the external consumer of an object to determine whether
+//      or not the object is ready for use (within the larger program). This is
+//      convenienced by the static CacheableObject.listAccessibleProperties()
+//      function, which provides a mapping of exposed property names to whether
+//      or not their dependencies are yet met.
+
+import { color, ENABLE_COLOR } from '../util/cli.js';
+
+import { inspect as nodeInspect } from 'util';
+
+function inspect(value) {
+    return nodeInspect(value, {colors: ENABLE_COLOR});
+}
+
+export default class CacheableObject {
+    static instance = Symbol('CacheableObject `this` instance');
+
+    #propertyUpdateValues = Object.create(null);
+    #propertyUpdateCacheInvalidators = Object.create(null);
+
+    /*
+    // Note the constructor doesn't take an initial data source. Due to a quirk
+    // of JavaScript, private members can't be accessed before the superclass's
+    // constructor is finished processing - so if we call the overridden
+    // update() function from inside this constructor, it will error when
+    // writing to private members. Pretty bad!
+    //
+    // That means initial data must be provided by following up with update()
+    // after constructing the new instance of the Thing (sub)class.
+    */
+
+    constructor() {
+        this.#defineProperties();
+        this.#initializeUpdatingPropertyValues();
+
+        if (CacheableObject.DEBUG_SLOW_TRACK_INVALID_PROPERTIES) {
+            return new Proxy(this, {
+                get: (obj, key) => {
+                    if (!Object.hasOwn(obj, key)) {
+                        if (key !== 'constructor') {
+                            CacheableObject._invalidAccesses.add(`(${obj.constructor.name}).${key}`);
+                        }
+                    }
+                    return obj[key];
+                }
+            });
+        }
+    }
+
+    #initializeUpdatingPropertyValues() {
+        for (const [ property, descriptor ] of Object.entries(this.constructor.propertyDescriptors)) {
+            const { flags, update } = descriptor;
+
+            if (!flags.update) {
+                continue;
+            }
+
+            if (update?.default) {
+                this[property] = update?.default;
+            } else {
+                this[property] = null;
+            }
+        }
+    }
+
+    #defineProperties() {
+        if (!this.constructor.propertyDescriptors) {
+            throw new Error(`Expected constructor ${this.constructor.name} to define propertyDescriptors`);
+        }
+
+        for (const [ property, descriptor ] of Object.entries(this.constructor.propertyDescriptors)) {
+            const { flags } = descriptor;
+
+            const definition = {
+                configurable: false,
+                enumerable: true
+            };
+
+            if (flags.update) {
+                definition.set = this.#getUpdateObjectDefinitionSetterFunction(property);
+            }
+
+            if (flags.expose) {
+                definition.get = this.#getExposeObjectDefinitionGetterFunction(property);
+            }
+
+            Object.defineProperty(this, property, definition);
+        }
+
+        Object.seal(this);
+    }
+
+    #getUpdateObjectDefinitionSetterFunction(property) {
+        const { update } = this.#getPropertyDescriptor(property);
+        const validate = update?.validate;
+        const allowNull = update?.allowNull;
+
+        return (newValue) => {
+            const oldValue = this.#propertyUpdateValues[property];
+
+            if (newValue === undefined) {
+                throw new ValueError(`Properties cannot be set to undefined`);
+            }
+
+            if (newValue === oldValue) {
+                return;
+            }
+
+            if (newValue !== null && validate) {
+                try {
+                    const result = validate(newValue);
+                    if (result === undefined) {
+                        throw new TypeError(`Validate function returned undefined`);
+                    } else if (result !== true) {
+                        throw new TypeError(`Validation failed for value ${newValue}`);
+                    }
+                } catch (error) {
+                    error.message = `Property ${color.green(property)} (${inspect(this[property])} -> ${inspect(newValue)}): ${error.message}`;
+                    throw error;
+                }
+            }
+
+            this.#propertyUpdateValues[property] = newValue;
+            this.#invalidateCachesDependentUpon(property);
+        };
+    }
+
+    #getUpdatePropertyValidateFunction(property) {
+        const descriptor = this.#getPropertyDescriptor(property);
+    }
+
+    #getPropertyDescriptor(property) {
+        return this.constructor.propertyDescriptors[property];
+    }
+
+    #invalidateCachesDependentUpon(property) {
+        for (const invalidate of this.#propertyUpdateCacheInvalidators[property] || []) {
+            invalidate();
+        }
+    }
+
+    #getExposeObjectDefinitionGetterFunction(property) {
+        const { flags } = this.#getPropertyDescriptor(property);
+        const compute = this.#getExposeComputeFunction(property);
+
+        if (compute) {
+            let cachedValue;
+            const checkCacheValid = this.#getExposeCheckCacheValidFunction(property);
+            return () => {
+                if (checkCacheValid()) {
+                    return cachedValue;
+                } else {
+                    return (cachedValue = compute());
+                }
+            };
+        } else if (!flags.update && !compute) {
+            throw new Error(`Exposed property ${property} does not update and is missing compute function`);
+        } else {
+            return () => this.#propertyUpdateValues[property];
+        }
+    }
+
+    #getExposeComputeFunction(property) {
+        const { flags, expose } = this.#getPropertyDescriptor(property);
+
+        const compute = expose?.compute;
+        const transform = expose?.transform;
+
+        if (flags.update && !transform) {
+            return null;
+        } else if (flags.update && compute) {
+            throw new Error(`Updating property ${property} has compute function, should be formatted as transform`);
+        } else if (!flags.update && !compute) {
+            throw new Error(`Exposed property ${property} does not update and is missing compute function`);
+        }
+
+        const dependencyKeys = expose.dependencies || [];
+        const dependencyGetters = dependencyKeys.map(key => () => [key, this.#propertyUpdateValues[key]]);
+        const getAllDependencies = () => Object.fromEntries(dependencyGetters.map(f => f())
+            .concat([[this.constructor.instance, this]]));
+
+        if (flags.update) {
+            return () => transform(this.#propertyUpdateValues[property], getAllDependencies());
+        } else {
+            return () => compute(getAllDependencies());
+        }
+    }
+
+    #getExposeCheckCacheValidFunction(property) {
+        const { flags, expose } = this.#getPropertyDescriptor(property);
+
+        let valid = false;
+
+        const invalidate = () => {
+            valid = false;
+        };
+
+        const dependencyKeys = new Set(expose?.dependencies);
+
+        if (flags.update) {
+            dependencyKeys.add(property);
+        }
+
+        for (const key of dependencyKeys) {
+            if (this.#propertyUpdateCacheInvalidators[key]) {
+                this.#propertyUpdateCacheInvalidators[key].push(invalidate);
+            } else {
+                this.#propertyUpdateCacheInvalidators[key] = [invalidate];
+            }
+        }
+
+        return () => {
+            if (!valid) {
+                valid = true;
+                return false;
+            } else {
+                return true;
+            }
+        };
+    }
+
+    static DEBUG_SLOW_TRACK_INVALID_PROPERTIES = false;
+    static _invalidAccesses = new Set();
+
+    static showInvalidAccesses() {
+        if (!this.DEBUG_SLOW_TRACK_INVALID_PROPERTIES) {
+            return;
+        }
+
+        if (!this._invalidAccesses.size) {
+            return;
+        }
+
+        console.log(`${this._invalidAccesses.size} unique invalid accesses:`);
+        for (const line of this._invalidAccesses) {
+            console.log(` - ${line}`);
+        }
+    }
+}