const caseInsensitiveAttributes = {
    autocomplete: ['form'],
    charset: ['meta', 'script'],
    contenteditable: null,
    crossorigin: ['audio', 'img', 'link', 'script', 'video'],
    dir: null,
    draggable: null,
    dropzone: null,
    formmethod: ['button', 'input'],
    inputmode: ['input', 'textarea'],
    kind: ['track'],
    method: ['form'],
    preload: ['audio', 'video'],
    referrerpolicy: null,
    sandbox: ['iframe'],
    spellcheck: null,
    scope: ['th'],
    shape: ['area'],
    sizes: ['link'],
    step: ['input'],
    translate: null,
    type: [
        'a',
        'link',
        'button',
        'embed',
        'object',
        'script',
        'source',
        'style',
        'input',
        'menu',
        'menuitem'
    ],
    wrap: ['textarea']
};

// https://html.spec.whatwg.org/#invalid-value-default
/** @typedef { [key: string]: { tag: null | string[], default: string, valid: string[] } } */
const invalidValueDefault = {
    crossorigin: {
        tag: null,
        default: 'anonymous',
        valid: ['', 'anonymous', 'use-credentials']
    },
    // https://html.spec.whatwg.org/#referrer-policy-attributes
    // The attribute's invalid value default and missing value default are both the empty string state.
    referrerpolicy: {
        tag: null,
        default: '',
        valid: ['', 'url', 'origin', 'no-referrer', 'no-referrer-when-downgrade', 'same-origin', 'origin-when-cross-origin', 'strict-origin-when-cross-origin', 'unsafe-url']
    },
    // https://html.spec.whatwg.org/#lazy-loading-attributes
    loading: {
        tag: ['img', 'iframe'],
        default: 'eager',
        valid: ['lazy', 'eager']
    },
    // https://html.spec.whatwg.org/#the-img-element
    // https://html.spec.whatwg.org/#image-decoding-hint
    decoding: {
        tag: ['img'],
        default: 'auto',
        valid: ['auto', 'sync', 'async']
    },
    // https://html.spec.whatwg.org/#the-track-element
    kind: {
        tag: ['track'],
        default: 'metadata',
        valid: ['subtitles', 'captions', 'descriptions', 'chapters', 'metadata']
    },
    type: {
        tag: ['button'],
        default: 'submit',
        valid: ['submit', 'reset', 'button']
    },
    wrap: {
        tag: ['textarea'],
        default: 'soft',
        valid: ['soft', 'hard']
    },
    // https://html.spec.whatwg.org/#the-hidden-attribute
    hidden: {
        tag: null,
        default: 'hidden',
        valid: ['hidden', 'until-found']
    },
    // https://html.spec.whatwg.org/#autocapitalization
    autocapitalize: {
        tag: null,
        default: 'sentences',
        valid: ['none', 'off', 'on', 'sentences', 'words', 'characters']
    },
    // https://html.spec.whatwg.org/#the-marquee-element
    behavior: {
        tag: ['marquee'],
        default: 'scroll',
        valid: ['scroll', 'slide', 'alternate']
    },
    direction: {
        tag: ['marquee'],
        default: 'left',
        valid: ['left', 'right', 'up', 'down']
    }
};

export function onAttrs() {
    return (attrs, node) => {
        const newAttrs = attrs;

        Object.entries(attrs).forEach(([attrName, attrValue]) => {
            let newAttrValue = attrValue;

            if (
                Object.hasOwnProperty.call(caseInsensitiveAttributes, attrName)
                && (
                    caseInsensitiveAttributes[attrName] === null
                    || caseInsensitiveAttributes[attrName].includes(node.tag)
                )
            ) {
                newAttrValue = typeof attrValue.toLowerCase === 'function' ? attrValue.toLowerCase() : attrValue;
            }

            if (
                Object.hasOwnProperty.call(invalidValueDefault, attrName)
            ) {
                const meta = invalidValueDefault[attrName];
                if (meta.tag === null || (node && node.tag && meta.tag.includes(node.tag))) {
                    if (!meta.valid.includes(newAttrValue)) {
                        newAttrValue = meta.default;
                    }
                }
            }

            newAttrs[attrName] = newAttrValue;
        });

        return newAttrs;
    };
}