banking.bacs-processing-date

pub fn bacs_processing_dates(submission_iso: &str, after_cutoff: bool) -> BacsCycle

/// The three days of one Bacs cycle.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct BacsCycle {
    /// day 1: the file is accepted
    pub input_day: String,
    /// day 2: Bacs processes it and sends it to the receiving banks
    pub processing_day: String,
    /// day 3: the money leaves one account and arrives in the other
    pub entry_day: String,
}

fune!(banking.bacs-processing-date@^1);  // then call bacs_processing_dates(…)

use super::funejson::Value;  ← the fune runtime: the JSON value the test vectors use; fune build keeps it only where a signature takes one
use super::dates_add_business_days::add_business_days;  ← from dates.add-business-days ^1.0.0 · built alongside by fune
use super::dates_bank_holidays::bank_holidays;  ← from dates.bank-holidays ^1.0.0 · built alongside by fune
use super::dates_day_of_week::is_weekday;  ← from dates.day-of-week ^1.0.0 · built alongside by fune

fn holidays_for(years: &[i64]) -> Vec<String> {
    let mut out = Vec::new();
    for year in years {
        for holiday in bank_holidays("england-and-wales", *year) {
            out.push(holiday.date);
        }
    }
    out
}

fn cycle_with(submission_iso: &str, after_cutoff: bool, holidays: &[String]) -> BacsCycle {
    let processing_day = is_weekday(submission_iso) && !holidays.iter().any(|h| h == submission_iso);
    let input_day = if processing_day && !after_cutoff {
        submission_iso.to_string()
    } else {
        add_business_days(submission_iso, 1, holidays)
    };
    BacsCycle {
        processing_day: add_business_days(&input_day, 1, holidays),
        entry_day: add_business_days(&input_day, 2, holidays),
        input_day,
    }
}

/// The Bacs cycle a file joins. Bacs works on processing days - Monday to
/// Friday except England and Wales bank holidays - and a file joins the cycle
/// whose input day is the day it arrives, if that is a processing day and it
/// arrived before the 22:30 deadline, or the next processing day otherwise.
/// Processing is the next processing day and entry the one after.
///
/// # Panics
/// Panics on a malformed date or a year outside the published holiday data.
pub fn bacs_processing_dates(submission_iso: &str, after_cutoff: bool) -> BacsCycle {
    // is_weekday validates the date before its year is read.
    is_weekday(submission_iso);
    let year: i64 = submission_iso[0..4].parse().unwrap();
    // Only reach for next year's calendar when the cycle really runs into it,
    // so a December submission in the last published year still works as long
    // as its cycle ends inside that year.
    let mut cycle = cycle_with(submission_iso, after_cutoff, &holidays_for(&[year]));
    if cycle.entry_day[0..4] != submission_iso[0..4] {
        cycle = cycle_with(submission_iso, after_cutoff, &holidays_for(&[year, year + 1]));
    }
    cycle
}

pub fn bacs_cycle_to_value(cycle: &BacsCycle) -> Value {
    Value::obj(vec![
        ("inputDay", Value::str(&cycle.input_day)),
        ("processingDay", Value::str(&cycle.processing_day)),
        ("entryDay", Value::str(&cycle.entry_day)),
    ])
}

pub fn fune_vector(args: &[Value]) -> Value {
    bacs_cycle_to_value(&bacs_processing_dates(args[0].as_str(), args[1].as_bool()))
}

Install

fune build

With that line in your source, in a Rust project (language rust in fune.project), fune build resolves it and its 3 dependencies, pins them in fune.lock, downloads only the Rust package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. A crate’s build.rs runs it before every compile. Or pin a range in fune.project and build in one step:

fune add banking.bacs-processing-date

The manifest, vectors and README with only the Rust implementation. Install it without the registry with fune add ./banking.bacs-processing-date-1.0.0-rust.fune, or fetch it from a terminal with fune pull banking.bacs-processing-date@1.0.0:rust.

The whole function, every language, is one file too: banking.bacs-processing-date-1.0.0.fune, 16,519 bytes, sha256 d6c142dfcdfc0352df592c4b9d80d19c87383647f6a4e1a3df99f140b852d8cf. It installs into a project of any language.

// fune: before banking.bacs-processing-date

// fune: after banking.bacs-processing-date

// fune: replace dates.add-business-days in banking.bacs-processing-date
// fune: replace dates.bank-holidays in banking.bacs-processing-date
// fune: replace dates.day-of-week in banking.bacs-processing-date

// fune: step banking.bacs-processing-date after <n|label>

More from the author

Bacs describes the cycle for Direct Credit as: "Input day is the latest day a business user/bureau may submit a payment file to Bacs for a processing cycle. Payment files must be transmitted to Bacs between 07.00 and 22.30"; on day 2 files are delivered to the receiving banks; on day 3 "payments are simultaneously credited to the recipients' accounts and debited from your account". Source: Bacs, "Bacs Direct Credit", https://www.bacs.co.uk/bacs-schemes/getting-started/bacs-direct-credit/ (read 2026-09-23).

The days are Bacs processing days: Monday to Friday, excluding bank holidays in England and Wales, which Bacs uses as its non-processing days for the whole of the UK (Scotland's and Northern Ireland's extra holidays do not stop Bacs). The published Bacs processing calendar is the authority; the bank holidays here come from `dates.bank-holidays` (gov.uk data, region `england-and-wales`), and the working-day steps from `dates.add-business-days`.

So:

- input day = the submission date if it is a processing day and the file was sent by 22:30 (`afterCutoff` false); otherwise the next processing day. A file sent at a weekend or on a bank holiday joins the next processing day whatever the time; - processing day = the next processing day after the input day; - entry day = the processing day after that.

## Why `afterCutoff` is a flag

The time of day is the caller's to read (this capability never reads a clock), and comparing a timestamp with 22:30 is simpler at the call site than passing a time zone in. The 22:30 deadline is the one Bacs publishes (quoted above); a bureau or bank may set an earlier internal deadline, in which case pass `afterCutoff` against that.

## Limits

The bank holiday data covers the years gov.uk publishes (2019 to 2028 in `dates.bank-holidays@1.0.0`). A cycle that needs a year outside it fails with that capability's error rather than treating an unknown Christmas as a working day. Next year's calendar is only consulted when the cycle actually runs into next year, so a December cycle in the last published year still works.

This gives the cycle for a submission. It does not work backwards from a required arrival date; for that, step back two processing days from the entry day with `dates.add-business-days` and the same holiday list.

Files