# Author: Sandeep Belgavi
"""Offline approval state machine; reviewer identity is injected by trusted code."""
import hashlib
import json
import sqlite3
import tempfile
from pathlib import Path


def digest(action):
    return hashlib.sha256(json.dumps(action, sort_keys=True, separators=(',', ':')).encode()).hexdigest()


class ApprovalStore:
    def __init__(self, path):
        self.db = sqlite3.connect(path)
        self.db.execute('CREATE TABLE IF NOT EXISTS approvals(id TEXT PRIMARY KEY, fingerprint TEXT, revision TEXT, reviewer TEXT, expires INTEGER, state TEXT)')

    def request(self, key, action, revision, reviewer, expires):
        if not all(isinstance(v, str) and v for v in (key, revision, reviewer)) or type(expires) is not int:
            raise ValueError('approval contract')
        with self.db:
            self.db.execute('INSERT INTO approvals VALUES (?,?,?,?,?,?)', (key, digest(action), revision, reviewer, expires, 'pending'))

    def decide(self, key, principal, action, revision, now, approve=True):
        if type(approve) is not bool:
            raise ValueError('decision must be boolean')
        with self.db:
            self.db.execute('BEGIN IMMEDIATE')
            row = self.db.execute('SELECT fingerprint,revision,reviewer,expires,state FROM approvals WHERE id=?', (key,)).fetchone()
            if row is None: raise KeyError(key)
            fp, rev, reviewer, expires, state = row
            if principal != reviewer: raise PermissionError('wrong reviewer')
            if digest(action) != fp or revision != rev: raise ValueError('stale or changed proposal')
            if now >= expires: raise ValueError('approval expired')
            if state != 'pending': raise ValueError('already decided')
            state = 'approved' if approve else 'rejected'
            self.db.execute('UPDATE approvals SET state=? WHERE id=?', (state, key))
        return state

    def consume(self, key, action, revision, now):
        # Returns a local dispatch marker; does not perform an external action.
        with self.db:
            changed = self.db.execute("UPDATE approvals SET state='consumed' WHERE id=? AND fingerprint=? AND revision=? AND expires>? AND state='approved'", (key, digest(action), revision, now)).rowcount
            if changed != 1: raise PermissionError('no current unconsumed approval')
        return {'approval': key, 'dispatch': 'local-marker'}

    def close(self): self.db.close()


class ProposalAdapter:
    """Deterministic proposal seam; it has no approval authority."""
    def propose(self): return {'incident': 'inc-42', 'action': 'restart-worker', 'target': 'worker-7'}


def demo():
    with tempfile.TemporaryDirectory() as folder:
        store = ApprovalStore(Path(folder) / 'approval.db')
        action = ProposalAdapter().propose()
        store.request('approval-1', action, 'v1', 'reviewer-7', 200)
        decision = store.decide('approval-1', 'reviewer-7', action, 'v1', 100)
        receipt = store.consume('approval-1', action, 'v1', 101)
        store.close()
        return {'decision': decision, **receipt}


if __name__ == '__main__': print(json.dumps(demo(), sort_keys=True))