"""Flat file I/O — write fixed-length records from COBOL FD definitions"""
import struct, re
from pathlib import Path
from typing import Any

def analyze_fd_layout(source_text: str) -> dict[str, dict]:
    """From preprocessed COBOL source, extract FD file layouts.

    Returns: {assign_to_filename: {
        "fd_name": str,
        "records": [{record_name, record_length, fields: [{name, offset, length, type, pic}]}],
        "direction": "INPUT"|"OUTPUT"|"I-O"
    }}
    """
    from .read import parse_file_control, parse_file_section, parse_data_division, extract_data_division, scan_open_statements

    fc = parse_file_control(source_text) if source_text else {}
    fs = parse_file_section(source_text) if source_text else {}
    ops = scan_open_statements(source_text) if source_text else {}
    dd = extract_data_division(source_text)
    all_fields = parse_data_division(dd) if dd else []

    layouts = {}
    for fd_name, rec_names in fs.items():
        records = []
        for rec_name in rec_names:
            children = []
            found = False
            rec_level = None
            offset = 0
            for f in all_fields:
                if f.name == rec_name:
                    found = True
                    rec_level = f.level
                    continue
                if found:
                    if f.level is not None and f.level <= rec_level:
                        break
                    if f.is_88 or f.is_filler:
                        continue
                    pi = f.pic_info
                    if pi:
                        length = (pi.digits + pi.decimal) if pi.type == "numeric" else (pi.length or 0)
                    else:
                        length = 0
                    ftype = pi.type if pi else "unknown"
                    children.append({
                        "name": f.name, "pic": str(f.pic or ""),
                        "type": ftype, "length": length, "offset": offset,
                    })
                    offset += length

            records.append({"record_name": rec_name, "fields": children, "record_length": offset})

        assign_to = fc.get(fd_name, {}).get("assign_to", fd_name)
        layouts[assign_to] = {
            "fd_name": fd_name, "records": records,
            "direction": ops.get(fd_name, "INPUT"),
        }
    return layouts


def _format_value(value: Any, field: dict) -> bytes:
    """Format a value for COBOL fixed-length storage."""
    ftype = field["type"]
    length = field["length"]
    val = str(value) if value is not None else ""

    if ftype == "numeric":
        # COBOL numeric DISPLAY format: right-justified, zero-padded
        try:
            num = int(float(val)) if val else 0
        except (ValueError, TypeError):
            num = 0
        num = abs(num)
        s = str(num).zfill(length)
        if len(s) > length:
            s = s[-length:]
        return s.encode("ascii")
    else:
        # Alphanumeric: left-justified, space-padded
        s = val.ljust(length)[:length]
        return s.encode("ascii", errors="replace")


def _format_comp3(value: Any, field: dict) -> bytes:
    """Format as COMP-3 (packed decimal)."""
    length = field["length"]
    val = str(value) if value else "0"
    try:
        num_str = val.replace(".", "").lstrip("0") or "0"
        if num_str.startswith("-"):
            sign_nibble = 0x0D
            num_str = num_str[1:]
        else:
            sign_nibble = 0x0C
        if len(num_str) % 2 == 1:
            num_str = "0" + num_str
        result = []
        for i in range(0, len(num_str), 2):
            result.append(int(num_str[i:i+2], 16))
        result[-1] = (result[-1] & 0xF0) | sign_nibble
        return bytes(result)
    except (ValueError, TypeError):
        return bytes([0x00] * (length // 2 + 1 if length % 2 else length // 2))


def write_flat_file(records: list[dict], layout: dict, outpath: Path):
    """Write generated records as a COBOL-compatible fixed-length flat file.

    Args:
        records: list of dicts with field_name: value
        layout: file layout from analyze_fd_layout()
        outpath: output file path
    """
    if not layout or not layout.get("records"):
        return

    rec = layout["records"][0]  # Use first record format
    rec_len = rec["record_length"]
    if rec_len == 0:
        return

    with open(outpath, "wb") as f:
        for row in records:
            buf = bytearray(rec_len)
            for field in rec["fields"]:
                val = row.get(field["name"], "")
                formatted = _format_value(val, field)
                end = min(field["offset"] + len(formatted), rec_len)
                buf[field["offset"]:end] = formatted[:end - field["offset"]]
            f.write(buf)


def write_all_files(records: list[dict], source_text: str, outdir: Path, prefix: str = ""):
    """Analyze source, write flat files for all FDs that have data."""
    layouts = analyze_fd_layout(source_text)
    written = []
    for filename, layout in layouts.items():
        if layout["direction"] == "OUTPUT":
            continue  # Don't write output files (COBOL will create them)
        outpath = outdir / (prefix + filename)
        write_flat_file(records, layout, outpath)
        written.append((filename, outpath))
    return written