"""Read a task statement and verify its published record bindings."""
import hashlib
import json
from pathlib import Path
import re

from common import ROOT, contained

_cached_index = None


def _signature(path):
    stat = path.stat()
    return stat.st_dev, stat.st_ino, stat.st_size, stat.st_mtime_ns, stat.st_ctime_ns


def _index(root):
    global _cached_index
    root = Path(root).resolve()
    names = ['data/crossswe-bench.jsonl', 'data/task-bindings.jsonl']
    paths = [root / name for name in names]
    checks = root / 'CHECKSUMS.sha256'
    signature = tuple(_signature(path) for path in [*paths, checks])
    expected = {}
    for line in checks.read_text().splitlines():
        digest, name = line.split('  ', 1)
        if name in names:
            if name in expected:
                raise ValueError('Duplicate dataset checksum entry')
            expected[name] = digest
    if set(expected) != set(names):
        raise ValueError('Missing dataset checksum entry')
    payloads = [path.read_bytes() for path in paths]
    digests = [hashlib.sha256(raw).hexdigest() for raw in payloads]
    for name, digest in zip(names, digests):
        if digest != expected[name]:
            raise ValueError('Dataset checksum does not match')
    if signature != tuple(_signature(path) for path in [*paths, checks]):
        raise ValueError('Dataset files changed while reading')
    key = root, *digests
    if _cached_index is not None and _cached_index[0] == key:
        return _cached_index[1]
    bindings = {}
    for line in payloads[1].decode('utf-8').splitlines():
        item = json.loads(line)
        iid = item['instance_id']
        if iid in bindings:
            raise ValueError('Duplicate task binding')
        for field in ['task_sha256', 'source_task_sha256']:
            if not isinstance(item[field], str) or not re.fullmatch('[0-9a-f]{64}', item[field]):
                raise ValueError('Invalid task binding checksum')
        bindings[iid] = item
    index = {}
    for line in payloads[0].decode('utf-8').splitlines():
        row = json.loads(line)
        iid = row['instance_id']
        text = row['problem_statement']
        if not isinstance(iid, str) or not iid or iid in index:
            raise ValueError('Invalid or duplicate dataset instance ID')
        contained(root / 'instances', iid)
        if not isinstance(text, str) or not text.strip():
            raise ValueError('Missing problem statement')
        if iid not in bindings or bindings[iid]['source_task_sha256'] != row['original_task_sha256']:
            raise ValueError('Source task binding does not match')
        index[iid] = text, bindings[iid]['task_sha256'], 'statements/' + iid + '.md'
    if set(index) != set(bindings):
        raise ValueError('Dataset and task-binding IDs differ')
    _cached_index = key, index
    return index


def read_problem_statement(task, root=ROOT):
    root = Path(root).resolve()
    iid = task['instance_id']
    task_path = contained(root / 'instances', iid) / 'task.json'
    try:
        text, expected, statement_path = _index(root)[iid]
    except KeyError as error:
        raise ValueError('Task is absent from the dataset') from error
    raw = task_path.read_bytes()
    if hashlib.sha256(raw).hexdigest() != expected or json.loads(raw) != task:
        raise ValueError('Published task checksum does not match')
    if contained(root, statement_path).read_text(encoding='utf-8') != text:
        raise ValueError('Statement file does not match the dataset')
    return text