Map channels with an approved dictionary

The rules

These rules decide what a correct result is. Your answer is checked on this dataset and on hidden datasets that follow the same rules.

Input
  tickets(id, channel) — text. id is unique. channel may be missing.

Rules
  channel: remove ASCII whitespace (space, tab, CR, LF) at both ends, then lowercase; an empty result is missing.
  Map channel with this approved dictionary (left → right) and nothing else:
    email → email      e-mail → email
    phone → phone      telephone → phone
    chat → chat        web chat → chat      webchat → chat
  Quarantine to exceptions with reason:
    missing_channel    channel is missing
    unmapped_channel   channel is present but not in the dictionary (never guess a mapping)

Outputs (row order does not matter)
  clean(id text, channel text)
  exceptions(id text, reason text)