import struct
from pathlib import Path
from data.field_tree import FieldTree


class CobolBinaryReader:
    def read(self, binary_path: str, tree: FieldTree) -> list[dict]:
        data = Path(binary_path).read_bytes()
        record_size = self._compute_record_size(tree)
        if record_size == 0 or len(data) == 0:
            return []
        records = []
        for offset in range(0, len(data), record_size):
            record = data[offset:offset + record_size]
            if len(record) >= record_size:
                records.append(self._parse_record(record, tree))
        return records

    def _compute_record_size(self, tree: FieldTree) -> int:
        max_end = 0
        for f in tree.fields:
            end = f.offset + f.length
            if end > max_end:
                max_end = end
        return max_end

    def _parse_record(self, record: bytes, tree: FieldTree) -> dict:
        result = {}
        for name, field in tree.flatten().items():
            if field.length == 0 or field.offset + field.length > len(record):
                continue
            raw = record[field.offset:field.offset + field.length]
            if field.usage == "COMP-3":
                result[name] = self._parse_comp3(raw, field.signed, field.decimal)
            elif field.usage == "COMP" or field.usage == "COMP-5":
                result[name] = int.from_bytes(raw, "big", signed=field.signed)
            else:
                result[name] = raw.decode("ascii", errors="replace").strip()
        return result

    def _parse_comp3(self, raw: bytes, signed: bool, decimal: int) -> str:
        if not raw:
            return "0"
        nibbles = []
        for b in raw:
            nibbles.append((b >> 4) & 0x0F)
            nibbles.append(b & 0x0F)
        sign = nibbles.pop()
        value = 0
        for n in nibbles:
            value = value * 10 + n
        if signed and sign in (0x0D, 0x0B):
            value = -value
        divisor = 10 ** decimal
        result = float(value) / divisor
        return f"{result:.{decimal}f}" if decimal else str(value)