// ==UserScript==
// @name         Deep Space Communications Relay Tab Completion
// @namespace    https://hollymcfarland.com
// @version      2026-08-16
// @description  Tab complete known definitions
// @author       You
// @match        https://dscr.dixonary.co.uk/
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    document.addEventListener("keydown", (event) => {
        // Only listen to tab
        if (event.key !== "Tab") return;

        // Only listen when message box focused
        const inputEl = document.querySelector("#message-input");
        if (document.activeElement !== inputEl) return;

        // Don't tab out of input box
        event.preventDefault();

        const input = inputEl.value;
        const cursorPos = inputEl.selectionStart;

        // I don't even want to _think_ about how to handle tab completion if you have a range selected
        if (cursorPos !== inputEl.selectionEnd) return;

        // Character behind cursor should be non-whitespace
        // Character after cursor should at least not be a letter
        // Hopefully this accounts for _most_ reasonable signal definitions
        if (!(/\S/.test(input[cursorPos-1]) && (input.length === cursorPos || /[^A-Z]/.test(input[cursorPos])))) return;

        // Everything from most recent word boundary to the cursor position should be a reasonable estimate of "current signal"
        const currentSignal = /[\w-_]+?$/.exec(input.slice(0, cursorPos).toUpperCase())[0];

        const signals = JSON.parse(localStorage.getItem("dict")).map((s) => (s.value));

        const matches = signals.filter((s) => (s.startsWith(currentSignal)));

        // Give up if current signal isn't a prefix of any signal
        if (!matches.length) return;

        // Longest common prefix algorithm
        // After loop, i contains number of additional characters (after currentSignal.length) that are shared by all matches
        matches.sort();
        console.log(matches);
        let i = 0;
        for (; i<matches[0].length; i++) {
            const idx = i + currentSignal.length;
            const [first, last] = [matches[0][idx], matches[matches.length-1][idx]];
            if (first === undefined || last === undefined || first !== last) break;
        }

        const addedCharacters = matches[0].slice(currentSignal.length, currentSignal.length+i);

        // Put new computed value back into text box and reposition cursor to match
        inputEl.value = input.slice(0, cursorPos) + addedCharacters + input.slice(cursorPos);
        inputEl.selectionStart = cursorPos + i;
        inputEl.selectionEnd = cursorPos + i;
    });
})();