"""Task loading and prefix substitution."""
import json
import os


_B36 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"


def _b36(n, width):
    out = ""
    while n:
        n, r = divmod(n, 36)
        out = _B36[r] + out
    return out.rjust(width, "0")[-width:]


def prefix_for(run_no, task_id):
    """Z + run (4 chars base36) + task (3 chars base36) + '_'.

    Run numbers below 36**3 keep a digit at position 2; the proxy uses this to tell
    harness objects from other Z objects. Old prefixes (Z201001_) match the same pattern.
    """
    task_no = int("".join(ch for ch in task_id if ch.isdigit()) or 0)
    return f"Z{_b36(int(run_no), 4)}{_b36(task_no, 3)}_"


class Task:
    def __init__(self, task_dir, prefix):
        self.dir = task_dir
        self.prefix = prefix
        self.meta = json.loads(self._read("task.json"))
        self.id = self.meta["id"]

    def _read(self, rel):
        with open(os.path.join(self.dir, rel)) as f:
            return f.read()

    def sub(self, text):
        return text.replace("{{P}}", self.prefix).replace("{{p}}", self.prefix.lower())

    def text(self, rel):
        return self.sub(self._read(rel))

    def objects(self, key):
        """List of dicts with substituted names and loaded source (if 'file')."""
        out = []
        for o in self.meta.get(key, []):
            o = {k: self.sub(v) if isinstance(v, str) else v for k, v in o.items()}
            if "file" in o:
                o["source"] = self.text(o["file"])
            if "testclasses_file" in o:
                o["testclasses_source"] = self.text(o["testclasses_file"])
            out.append(o)
        return out

    @property
    def spec(self):
        return self.text("spec.md")

    @property
    def out_of_scope(self):
        return [self.sub(n) for n in self.meta.get("out_of_scope", [])]