import type { Plugin, UserConfig } from 'vite';

const DEFAULT_DICTIONARY = '_-abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';

function counter(dictionary: string = DEFAULT_DICTIONARY) {
    const sequence: string[] = [dictionary[0]];
    return () => {
        const str = sequence.join('');
        let carry = 0;
        for (let i = 0; i < sequence.length; i++) {
            const index = dictionary.indexOf(sequence[i]) + carry + 1;
            if (index < dictionary.length) {
                sequence[i] = dictionary[index];
                /**
                 * Make sure the following rules are not violated:
                 * 1. The first character cannot be a number
                 * 2. The second character cannot be a number if the first is a dash
                 * 3. The dash cannot be the only character
                 *
                 * https://www.w3.org/TR/CSS21/syndata.html#characters
                 */
                const [c1, c2] = sequence;
                if (
                    (c1 >= '0' && c1 <= '9') ||
                    (c1 === '-' && (c2 >= '0' && c2 <= '9')) ||
                    (c1 === '-' && sequence.length === 1)
                ) {
                    i--;
                    continue;
                }
                carry = 0;
                break;
            } else {
                sequence[i] = dictionary[0];
                carry = 1;
            }
        }
        if (carry) {
            sequence.push(dictionary[0]);
        }
        return str;
    };
};

export interface OptimizeCssModuleOptions {
    dictionary?: string;
}

export function optimizeCssModules(options?: OptimizeCssModuleOptions): Plugin {
    const next = counter(options?.dictionary);
    const map: Map<string, string> = new Map();

    return {
        name: 'optimize-css-modules',
        apply: 'build',
        config: () => ({
            css: {
                modules: {
                    generateScopedName: (name: string, fileName: string) => {
                        const key = fileName + name;
                        let hash = map.get(key);
                        if (!hash) {
                            map.set(key, (hash = next()));
                        }
                        return hash;
                    }
                }
            }
        })
    };
};