import { Timestamp, timestampCompare } from "../common.ts";

export type CausalTreeOp<T> = T & { at: Timestamp; parent?: CausalTreeOp<T> };
// parent is referred to via timestamp instead of reference here
// makes the api simpler
export type WeakCausalTreeOp<T> = T & { at: Timestamp; parent?: Timestamp };
export type AnyCausalTreeOp<T> = CausalTreeOp<T> | WeakCausalTreeOp<T>;

export class CausalTree<T> {
  operations: CausalTreeOp<T>[] = [];
  clock: number = 0;

  /** WARN: mutates 'op' for performance (in-place conversion from weak op to strong) */
  apply(op: AnyCausalTreeOp<T>): number {
    const opParent = op.parent;
    const parentOpIdx = this.operations.findIndex(
      Array.isArray(opParent)
        ? it => timestampCompare(it.at, opParent) === 0
        : it => it === opParent,
    );
    if (opParent && parentOpIdx === -1) throw new Error("parent was not found in op log");

    let idx = parentOpIdx + 1;
    for (; idx < this.operations.length; idx++) {
      const curr = this.operations[idx];
      if (timestampCompare(curr.at, op.at) < 0) break;
    }

    const storedOp = op as CausalTreeOp<T>;
    storedOp.parent = this.operations[parentOpIdx];
    this.operations.splice(idx, 0, storedOp);
    this.clock = Math.max(this.clock, storedOp.at[1]);

    return idx;
  }

  static toWeakOp<T>(op: CausalTreeOp<T>): WeakCausalTreeOp<T> {
    return { ...op, parent: op.parent?.at };
  }
}