import type { Db } from "./driver.ts";

const SAFE = /^[A-Za-z_][A-Za-z0-9_]*$/;
const ident = (value: string) => {
  if (!SAFE.test(value)) throw new TypeError(`Unsafe ledger identifier: ${value}`);
  return value;
};

export interface LedgerOptions {
  db: () => Db;
  table: string;
  subjectColumn?: string;
  amountColumn?: string;
  kindColumn?: string;
  reasonColumn?: string;
  referenceColumn?: string;
}

export function defineLedger(options: LedgerOptions) {
  const table = ident(options.table);
  const subject = ident(options.subjectColumn ?? "subject_id");
  const amount = ident(options.amountColumn ?? "amount");
  const kind = ident(options.kindColumn ?? "kind");
  const reason = ident(options.reasonColumn ?? "reason");
  const reference = ident(options.referenceColumn ?? "ref");
  const positive = (value: number) => {
    if (!Number.isSafeInteger(value) || value < 1)
      throw new RangeError("ledger amount must be a positive safe integer");
  };
  const write = async (
    subjectId: string,
    delta: number,
    entryKind: string,
    entryReason: string,
    ref = "",
  ) => {
    if (!subjectId.trim()) throw new TypeError("ledger subject cannot be empty");
    await options
      .db()
      .exec(
        `INSERT INTO ${table} (${subject},${amount},${kind},${reason},${reference}) VALUES (?,?,?,?,?)`,
        [subjectId, delta, entryKind, entryReason, ref],
      );
  };
  const balance = async (subjectId: string, db = options.db()) => {
    const row = await db.one<{ balance: number | string | null }>(
      `SELECT COALESCE(SUM(${amount}),0) AS balance FROM ${table} WHERE ${subject} = ?`,
      [subjectId],
    );
    return Number(row?.balance ?? 0);
  };
  return {
    balance,
    async credit(subjectId: string, value: number, entryReason: string, ref = "") {
      positive(value);
      await write(subjectId, value, "credit", entryReason, ref);
    },
    async debit(subjectId: string, value: number, entryReason: string, ref = "") {
      positive(value);
      return options.db().tx(async (db) => {
        if ((await balance(subjectId, db)) < value) return false;
        await db.exec(
          `INSERT INTO ${table} (${subject},${amount},${kind},${reason},${reference}) VALUES (?,?,?,?,?)`,
          [subjectId, -value, "debit", entryReason, ref],
        );
        return true;
      });
    },
    refund: (subjectId: string, value: number, entryReason: string, ref = "") => {
      positive(value);
      return write(subjectId, value, "refund", entryReason, ref);
    },
    entries: (subjectId: string) =>
      options.db().all(`SELECT * FROM ${table} WHERE ${subject} = ? ORDER BY id DESC`, [subjectId]),
  };
}