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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() {
-        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}`);
-        }
-    }
-}