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


class CobolBinaryReader:
    def read(self, path: str, tree: FieldTree) -> list[dict]:
        d = Path(path).read_bytes()
        rs = self._record_size(tree)
        if rs == 0 or len(d) == 0:
            return []
        return [self._parse(d[o:o + rs], tree) for o in range(0, len(d), rs) if len(d[o:o + rs]) >= rs]

    def _record_size(self, tree):
        return max((f.offset + f.length for f in tree.fields), default=0)

    def _parse(self, r, tree):
        out = {}
        for n, f in tree.flatten().items():
            if f.length == 0 or f.offset + f.length > len(r):
                continue
            raw = r[f.offset:f.offset + f.length]
            if f.usage == "COMP-3":
                out[n] = self._comp3(raw, f.signed, f.decimal)
            elif f.usage in ("COMP", "COMP-5"):
                out[n] = int.from_bytes(raw, "big", signed=f.signed)
            else:
                out[n] = raw.decode("ascii", errors="replace").strip()
        return out

    def _comp3(self, raw, signed, dec):
        if not raw:
            return "0"
        nib = []
        for b in raw:
            nib.append((b >> 4) & 0xF)
            nib.append(b & 0xF)
        s = nib.pop()
        v = sum(n * (10 ** (len(nib) - i)) for i, n in zip(range(len(nib)), nib))
        if signed and s in (0xD, 0xB):
            v = -v
        d = 10 ** dec
        return f"{float(v) / d:.{dec}f}" if dec else str(v)