dayphase/src/index.js

Determines the dayphase based on hour boundaries. It allows flexible time segmentation for different cultural or system-defined day phases.

/* *******************************************************
 * dayphase
 *
 * @license
 *
 * Apache-2.0
 *
 * Copyright 2015-2025 Alex Stevovich
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @meta
 *
 * package_name: dayphase
 * file_name: src/index.js
 * purpose: {{PURPOSE}}
 *
 * @system
 *
 * generated_on: 2025-03-15T05:55:23.877Z
 * certified_version: 1.0.0
 * file_uuid: 20cc4895-87f4-4045-83dc-4b7e9d310571
 * file_size: 2178 bytes
 * file_hash: aef7b316193eb3ba0a738e0efb36a0928478cef66d8eb35454139128925a957f
 * mast_hash: e33e31aa9447acaf3dafcceaedec49debfe8fd092b26e6a40182b7fb2f390c94
 * generated_by: preamble on npm!
 *
 * [Preamble Metadata]
 ********************************************************/
function dayphase(phases = [4, 17, 21], hour = new Date().getHours()) {
    // Validate phases
    if (
        !Array.isArray(phases) ||
        phases.length === 0 ||
        phases.some((n) => n < 0 || n > 24)
    ) {
        throw new Error(
            'phases must be an ordered array of numbers between 0 and 24.',
        );
    }

    // Validate hour
    if (
        typeof hour !== 'number' ||
        !Number.isInteger(hour) ||
        hour < 0 ||
        hour > 24
    ) {
        throw new Error('hour must be an integer between 0 and 24.');
    }

    // If hour is before the first phase OR after last phase, return 0
    if (hour < phases[0] || hour > phases[phases.length - 1]) {
        return 0;
    }

    // Find the correct phase index using findIndex (simpler than for-loop)
    const index = phases.findIndex((phase) => hour < phase);

    return index !== -1 ? index : phases.length - 1;
}

export default dayphase;