# =============================================================================
# Projet : AIR — Accounting Intermediate Representation
# Auteur : Simon-Pierre Boucher
# Contact : contact@spboucher.ai
# Fichier : backend.py
# Description : Generic CSV backend — the first, universal journal export target.
# =============================================================================
"""Generic CSV backend.

Lowers a CompiledJournal to flat CSV rows (one row per journal line) that any
accounting system or spreadsheet can import. Reversal emits contra rows
(sides swapped) — history is never deleted.
"""
from __future__ import annotations

import csv
import io
from pathlib import Path

from backends.base import (
    Backend,
    BackendCapabilities,
    PostingReceipt,
    ReversalReceipt,
    TargetPayload,
)
from core.journal import CompiledJournal, Side

COLUMNS = [
    "entry_id", "date", "description", "account_code", "account_name",
    "account_type", "side", "amount", "currency", "memo",
    "source_event_id", "provenance_id", "policy_set", "policy_version",
    "reverses",
]


class GenericCsvBackend(Backend):
    """Writes journals to CSV files under an output directory."""

    def __init__(self, output_dir: str | Path = "out"):
        self.output_dir = Path(output_dir)

    def capabilities(self) -> BackendCapabilities:
        return BackendCapabilities(
            name="generic_csv",
            posts_remotely=False,
            native_reversal=False,      # reversal = contra rows
            multi_currency=True,
            idempotency="client-side",
            notes="universal flat-file journal export",
        )

    def _rows(self, journal: CompiledJournal, *, reverse: bool = False) -> list[list[str]]:
        rows: list[list[str]] = []
        for entry in journal.entries:
            for line in entry.lines:
                side = line.side
                if reverse:
                    side = Side.CREDIT if side is Side.DEBIT else Side.DEBIT
                rows.append([
                    ("rev_" if reverse else "") + entry.id,
                    entry.date.isoformat(),
                    ("REVERSAL: " if reverse else "") + entry.description,
                    line.account.code,
                    line.account.name,
                    line.account.type.value,
                    side.value,
                    str(line.amount.amount),
                    line.amount.currency,
                    line.memo,
                    entry.source_event_id,
                    line.provenance_id or "",
                    entry.policy_set,
                    entry.policy_version,
                    (entry.id if reverse else entry.reverses or ""),
                ])
        return rows

    def compile(self, journal: CompiledJournal) -> TargetPayload:
        buf = io.StringIO()
        writer = csv.writer(buf)
        writer.writerow(COLUMNS)
        writer.writerows(self._rows(journal))
        return TargetPayload(backend="generic_csv", format="csv", body=buf.getvalue())

    def post(self, payload: TargetPayload, idempotency_key: str) -> PostingReceipt:
        self.output_dir.mkdir(parents=True, exist_ok=True)
        path = self.output_dir / f"journal_{idempotency_key}.csv"
        if not path.exists():             # idempotent: same key never rewrites
            path.write_text(str(payload.body), encoding="utf-8")
        return PostingReceipt(
            backend="generic_csv",
            reference=str(path),
            idempotency_key=idempotency_key,
        )

    def reverse(self, receipt: PostingReceipt) -> ReversalReceipt:
        original = Path(receipt.reference)
        reader = csv.reader(io.StringIO(original.read_text(encoding="utf-8")))
        rows = list(reader)
        header, body = rows[0], rows[1:]
        side_i, entry_i, desc_i, rev_i = (
            header.index("side"), header.index("entry_id"),
            header.index("description"), header.index("reverses"),
        )
        for row in body:
            row[rev_i] = row[entry_i]
            row[entry_i] = "rev_" + row[entry_i]
            row[desc_i] = "REVERSAL: " + row[desc_i]
            row[side_i] = "credit" if row[side_i] == "debit" else "debit"
        buf = io.StringIO()
        writer = csv.writer(buf)
        writer.writerow(header)
        writer.writerows(body)
        path = original.with_name(original.stem + "_reversal.csv")
        path.write_text(buf.getvalue(), encoding="utf-8")
        return ReversalReceipt(
            backend="generic_csv",
            reference=str(path),
            reversed_reference=receipt.reference,
        )