interface CommandNode {
    flags?: {command_node_type?: number};
    children?: number[];
    redirectNode?: number;
    extraNodeData?: {name?: string; parser?: string; properties?: {type?: number | string}};
}
interface CommandTree {nodes: CommandNode[]; rootIndex: number}
const trees = new WeakMap<object, CommandTree>();

export function remember_command_tree(instance: object, packet: unknown): void {
    const tree = packet as CommandTree;
    if (tree && Array.isArray(tree.nodes) && Number.isSafeInteger(tree.rootIndex)
        && tree.nodes.length <= 100_000 && tree.nodes[tree.rootIndex]) trees.set(instance, tree);
}

export function local_command_completion(instance: object, input: string, players: string[]): {matches: string[]; start: number; length: number} {
    const start = input.search(/\S*$/);
    const offset = start === 0 && input.startsWith('/') ? 1 : start;
    const result = {matches: [] as string[], start: offset, length: input.length - offset};
    const tree = trees.get(instance);
    if (!tree || !input.startsWith('/')) return result;
    // Walk complete arguments; only the final (possibly empty) token is being completed.
    const tokens = input.slice(1, start || 1).trim().split(/\s+/).filter(Boolean);
    let parents = [tree.rootIndex];
    const children = (index: number): number[] => {
        const node = tree.nodes[index];
        const redirect = node?.redirectNode;
        return Number.isSafeInteger(redirect) ? tree.nodes[redirect!]?.children ?? [] : node?.children ?? [];
    };
    for (const token of tokens) {
        const next: number[] = [];
        for (const parent of parents) {
            for (const index of children(parent)) {
                const node = tree.nodes[index];
                if (node?.flags?.command_node_type === 1 && node.extraNodeData?.name === token) next.push(index);
                else if (node?.flags?.command_node_type === 2) {
                    const parser = node.extraNodeData?.parser;
                    const kind = node.extraNodeData?.properties?.type;
                    // Quoted and greedy strings need Brigadier parsing; leave their suggestions to the server.
                    if (token.includes('"') || parser === 'minecraft:message' || parser === 'brigadier:string' && (kind === 2 || kind === 'greedy_phrase')) continue;
                    next.push(index);
                }
            }
        }
        parents = [...new Set(next)].slice(0, 256);
    }
    const prefix = input.slice(offset).toLowerCase();
    for (const parent of parents) {
        for (const index of children(parent)) {
            const node = tree.nodes[index];
            const data = node?.extraNodeData;
            const suggestions = node?.flags?.command_node_type === 1 ? [data?.name]
                : data?.parser === 'brigadier:bool' ? ['true', 'false']
                    : data?.parser === 'minecraft:entity' || data?.parser === 'minecraft:game_profile' ? players : [];
            for (const match of suggestions) {
                if (typeof match === 'string' && match.length && match.length <= 256
                    && match.toLowerCase().startsWith(prefix) && !result.matches.includes(match)) result.matches.push(match);
                if (result.matches.length >= 100) return result;
            }
        }
    }
    return result;
}