import { platform } from 'os';
import slash from 'slash';

const VOLUME = /^([A-Z]:)/i;
const IS_WINDOWS = platform() === 'win32';
const noop = () => null;
function matches(pattern, importee) {
    if (pattern instanceof RegExp) {
        return pattern.test(importee);
    }
    if (importee.length < pattern.length) {
        return false;
    }
    if (importee === pattern) {
        return true;
    }
    const importeeStartsWithKey = importee.indexOf(pattern) === 0;
    const importeeHasSlashAfterKey = importee.substring(pattern.length)[0] === '/';
    return importeeStartsWithKey && importeeHasSlashAfterKey;
}
function normalizeId(id) {
    if (typeof id === 'string' && (IS_WINDOWS || VOLUME.test(id))) {
        return slash(id.replace(VOLUME, ''));
    }
    return id;
}
function getEntries({ entries }) {
    if (!entries) {
        return [];
    }
    if (Array.isArray(entries)) {
        return entries;
    }
    return Object.entries(entries).map(([key, value]) => {
        return { find: key, replacement: value };
    });
}
function getCustomResolver({ customResolver }, options) {
    if (typeof customResolver === 'function') {
        return customResolver;
    }
    if (customResolver && typeof customResolver.resolveId === 'function') {
        return customResolver.resolveId;
    }
    if (typeof options.customResolver === 'function') {
        return options.customResolver;
    }
    if (options.customResolver && typeof options.customResolver.resolveId === 'function') {
        return options.customResolver.resolveId;
    }
    return null;
}
function alias(options = {}) {
    const entries = getEntries(options);
    if (entries.length === 0) {
        return {
            name: 'alias',
            resolveId: noop
        };
    }
    return {
        name: 'alias',
        buildStart(inputOptions) {
            return Promise.all([...entries, options].map(({ customResolver }) => customResolver &&
                typeof customResolver === 'object' &&
                typeof customResolver.buildStart === 'function' &&
                customResolver.buildStart.call(this, inputOptions))).then(() => {
                // enforce void return value
            });
        },
        resolveId(importee, importer) {
            const importeeId = normalizeId(importee);
            const importerId = normalizeId(importer);
            // First match is supposed to be the correct one
            const matchedEntry = entries.find((entry) => matches(entry.find, importeeId));
            if (!matchedEntry || !importerId) {
                return null;
            }
            const updatedId = normalizeId(importeeId.replace(matchedEntry.find, matchedEntry.replacement));
            const customResolver = getCustomResolver(matchedEntry, options);
            if (customResolver) {
                return customResolver.call(this, updatedId, importerId, {});
            }
            return this.resolve(updatedId, importer, { skipSelf: true }).then((resolved) => {
                let finalResult = resolved;
                if (!finalResult) {
                    finalResult = { id: updatedId };
                }
                return finalResult;
            });
        }
    };
}

export default alias;