"""cobol-reconcile-two-files.py - compute the report cobol-reconcile-two-files.cob should write.

Reads the same two files the COBOL program reads, checks their layout and their sort order, runs
the same balance-line match (HIGH-VALUES as the end-of-file key), and prints recon.txt line by
line with the same edited pictures:

  ZZZ,ZZZ,ZZ9.99 BLANK WHEN ZERO       bank and book amounts on a detail line
  -,---,---,--9.99 BLANK WHEN ZERO     the difference on a detail line (floating minus)
  ZZ,ZZ9                               the four counts
  -,---,---,---,--9.99                 the three money totals (floating minus)

Lines are printed without trailing blanks. Standard library only; Python 3.8 or later.
Run from the site folder:  python code/cobol-reconcile-two-files.py
"""
from decimal import Decimal
import sys

BANK = "datasets/cobol-reconcile-two-files-bank.dat"
BOOK = "datasets/cobol-reconcile-two-files.dat"
HIGH = "￿" * 8          # stands in for HIGH-VALUES: sorts above every digit string


def load(path):
    recs, prev = [], ""
    for n, line in enumerate(open(path, encoding="ascii").read().split("\n"), 1):
        if not line:
            continue
        assert len(line) == 47, f"{path} line {n}: {len(line)} bytes, expected 47"
        ref, date, amt, desc = line[0:8], line[8:16], line[16:27], line[27:47]
        assert ref.isdigit() and date.isdigit() and amt.isdigit(), f"{path} line {n}: non-digit in a numeric field"
        if ref <= prev:
            sys.exit(f"SEQUENCE ERROR IN {path} AT {ref}  (the COBOL program would stop with return code 16)")
        prev = ref
        recs.append((ref, int(amt), date, desc.rstrip()))
    return recs


def z_amount(cents):                      # ZZZ,ZZZ,ZZ9.99 BLANK WHEN ZERO, 14 characters
    return " " * 14 if cents == 0 else f"{Decimal(cents) / 100:,.2f}".rjust(14)


def floating_minus(cents, width):         # the sign lands immediately left of the first digit
    s = f"{Decimal(abs(cents)) / 100:,.2f}"
    return (("-" + s) if cents < 0 else s).rjust(width)


def z_diff(cents):                        # -,---,---,--9.99 BLANK WHEN ZERO, 16 characters
    return " " * 16 if cents == 0 else floating_minus(cents, 16)


def z_count(n):                           # ZZ,ZZ9, 6 characters
    return f"{n:,}".rjust(6)


def z_money(cents):                       # -,---,---,---,--9.99, 20 characters
    return floating_minus(cents, 20)


def detail(status, ref, bank, book, diff):
    return status.ljust(14) + "  " + ref + "  " + z_amount(bank) + "  " + z_amount(book) + "  " + z_diff(diff)


bank, book = load(BANK), load(BOOK)
out = ["RECONCILIATION: BANK FILE AGAINST BOOK FILE",
       "STATUS".ljust(16) + "REFERENCE".ljust(10) + "   BANK AMOUNT" + "  " + "   BOOK AMOUNT" + "  " + "      DIFFERENCE"]
counts = dict(matched=0, differs=0, bank_only=0, book_only=0)
diffs = []
i = j = 0
bkey = bank[0][0] if bank else HIGH
kkey = book[0][0] if book else HIGH
while not (bkey == HIGH and kkey == HIGH):
    if bkey == kkey:
        d = bank[i][1] - book[j][1]
        status = "MATCHED" if d == 0 else "AMOUNT DIFFERS"
        counts["matched" if d == 0 else "differs"] += 1
        out.append(detail(status, bkey, bank[i][1], book[j][1], d))
        diffs.append(d)
        i += 1
        j += 1
    elif bkey < kkey:
        d = bank[i][1]
        counts["bank_only"] += 1
        out.append(detail("BANK ONLY", bkey, bank[i][1], 0, d))
        diffs.append(d)
        i += 1
    else:
        d = -book[j][1]
        counts["book_only"] += 1
        out.append(detail("BOOK ONLY", kkey, 0, book[j][1], d))
        diffs.append(d)
        j += 1
    bkey = bank[i][0] if i < len(bank) else HIGH
    kkey = book[j][0] if j < len(book) else HIGH

bank_total = sum(r[1] for r in bank)
book_total = sum(r[1] for r in book)
out.append("")
for label, key in (("MATCHED", "matched"), ("AMOUNT DIFFERS", "differs"), ("BANK ONLY", "bank_only"), ("BOOK ONLY", "book_only")):
    out.append(label.ljust(24) + z_count(counts[key]))
out.append("BANK FILE TOTAL".ljust(24) + z_money(bank_total))
out.append("BOOK FILE TOTAL".ljust(24) + z_money(book_total))
out.append("NET DIFFERENCE".ljust(24) + z_money(bank_total - book_total))
for line in out:
    print(line.rstrip())

# The control-total identity the report rests on: every reference is counted once, and the net
# difference of the two file totals is exactly the sum of the per-reference differences.
assert sum(counts.values()) == len({r[0] for r in bank} | {r[0] for r in book})
assert bank_total - book_total == sum(diffs)
print(f"\nstdout: MATCHED {counts['matched']:05d} DIFFERS {counts['differs']:05d} "
      f"BANK ONLY {counts['bank_only']:05d} BOOK ONLY {counts['book_only']:05d}")