"""Author: Sandeep Belgavi. Local transactional actions; no external tools."""
import json
import sqlite3


class ActionStore:
    """One SQLite transaction covers this local effect and its receipt only."""
    def __init__(self, path=':memory:'):
        self.db = sqlite3.connect(path)
        self.db.executescript('''
        CREATE TABLE IF NOT EXISTS actions(
          tenant TEXT, op TEXT, intent TEXT, state TEXT,
          PRIMARY KEY(tenant, op));
        CREATE TABLE IF NOT EXISTS holds(
          tenant TEXT, op TEXT, service TEXT,
          PRIMARY KEY(tenant, op));
        ''')

    def reserve(self, tenant, op, service, authorized=True, fail=False):
        if not authorized:
            raise PermissionError('Action scope required')
        if not all(isinstance(x, str) and x.strip() for x in (tenant, op, service)):
            raise ValueError('Nonempty identifiers required')
        with self.db:
            self.db.execute('BEGIN IMMEDIATE')
            row = self.db.execute('SELECT intent,state FROM actions WHERE tenant=? AND op=?', (tenant, op)).fetchone()
            if row:
                if row[0] != service:
                    raise ValueError('Idempotency key conflicts with prior intent')
                return row[1]
            self.db.execute('INSERT INTO holds VALUES(?,?,?)', (tenant, op, service))
            if fail:
                raise RuntimeError('Injected interruption before receipt')
            self.db.execute('INSERT INTO actions VALUES(?,?,?,?)', (tenant, op, service, 'reserved'))
        return 'reserved'

    def compensate(self, tenant, op, authorized=True):
        if not authorized:
            raise PermissionError('Compensation scope required')
        with self.db:
            self.db.execute('BEGIN IMMEDIATE')
            row = self.db.execute('SELECT state FROM actions WHERE tenant=? AND op=?', (tenant, op)).fetchone()
            if row is None:
                raise KeyError(op)
            self.db.execute('DELETE FROM holds WHERE tenant=? AND op=?', (tenant, op))
            self.db.execute('UPDATE actions SET state=? WHERE tenant=? AND op=?', ('compensated', tenant, op))
        return 'compensated'

    def active(self):
        return self.db.execute('SELECT count(*) FROM holds').fetchone()[0]

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


def main():
    store = ActionStore()
    first = store.reserve('acme', 'incident-42-hold', 'api')
    retry = store.reserve('acme', 'incident-42-hold', 'api')
    compensated = store.compensate('acme', 'incident-42-hold')
    print(json.dumps(dict(first=first, retry=retry, compensated=compensated, active=store.active()), sort_keys=True))
    store.close()


if __name__ == '__main__':
    main()