import { StructOfArr } from "./types.ts";
import { zip } from "./utils.ts";

export class Rule<V extends string[]> {
    private separators: ({ kind: "word", word: string } | { kind: "end" })[];
    private vars: V;

    public constructor(separators: string[], vars: V) {
        this.separators = separators.map(word => ({ kind: "word", word }));
        this.vars = vars;
        this.separators.push({ kind: "end" });
    }

    public get(text: string): StructOfArr<V, string> | null {
        const first_sep = this.separators[0] ?? "";
        if (first_sep.kind === "end") {
            if (text.length > 0) return null;
            else return {} as StructOfArr<V, string>;
        }
        let [val, rest] = split_once(text, first_sep.word);
        if (rest === null) return null;
        const result = {} as Record<string, string>;
        for (const [key, sep] of zip(this.vars, this.separators.slice(1))) {
            if (sep.kind === "end") {
                result[key] = rest;
                break;
            }
            [val, rest] = split_once(rest, sep.word);
            if (rest === null) return null;
            result[key] = val;
        }
        return result as StructOfArr<V, string>;
    }
}

function split_once(text: string, separator: string) {
    const cursor = text.indexOf(separator);
    if (cursor === -1) return [text, null] as const;
    const left = text.slice(0, cursor);
    const right = text.slice(cursor + separator.length);
    return [left, right] as const;
}