#!/bin/bash
# git-credential-mosaic — git credential helper. Resolves a Gitea token from the
# Mosaic credential store at runtime so remote URLs never embed secrets.
#
# Install (one-time, per clone or globally):
#   git config credential.helper "$HOME/.config/mosaic/tools/git/git-credential-mosaic"
#
# Per-agent identity (Gate-16 author != reviewer separation):
#   git config mosaic.gitIdentity <agent-id>   # per-worktree, persists on disk
#   # or: export MOSAIC_GIT_IDENTITY=<agent-id>
#
# ── WHY THIS FAILS CLOSED ──────────────────────────────────────────────────────
# This helper used to end by emitting the shared account's token for any request
# it could not resolve to an identity. A seat with no identity, or with an
# identity whose token was never provisioned, therefore received the most
# privileged credential configured on the host — silently, and indistinguishably
# from correct operation. Every record it then created (commit, push, PR, review)
# was attributed to that shared account, so author != reviewer separation was
# unenforceable and the true actor was unrecoverable after the fact.
#
# Under-provisioning must fail loudly, not impersonate. A refused git operation
# is recoverable in one command; a merged pull request attributed to the wrong
# principal is not.
#
# ── CONTRACT ───────────────────────────────────────────────────────────────────
#   identity : MOSAIC_GIT_IDENTITY  >  git config mosaic.gitIdentity  >  the
#              username git supplies on stdin
#   store    : chosen by what the identity IS, with no precedence and no
#              cross-store fallback (see "Credential store selection" below)
#   hit      : emit username + password, exit 0
#   miss     : emit NOTHING, spool a durable escalation record, explain on
#              stderr, exit 1 — git surfaces the failure and nothing is attributed
#   unknown host : exit 0 with no output, no record (passthrough for non-Mosaic
#              remotes handled by another helper)
#
# Backward compatibility is preserved for exactly one case: a host with no fleet
# and no identity requested still gets the shared account, because on such a host
# the shared account is the operator's own and there is no attribution to lose.
# A host that HAS a fleet has agents whose records must be distinguishable, so
# the shared fallback is refused there.
#
# A token is never written to stderr, to the escalation record, or to any log.

[ "$1" = "get" ] || exit 0

host=""; username_in=""
while IFS= read -r line; do
  [ -z "$line" ] && break
  case "$line" in
    host=*)     host=${line#host=};;
    username=*) username_in=${line#username=};;
  esac
done

# Recognized Gitea hosts carry the per-identity token scheme. Anything else is
# declined quietly — another helper owns it, and refusing would break it.
case "$host" in
  git.uscllc.com)      idpfx=gitea-usc;;
  git.mosaicstack.dev) idpfx=gitea-mosaicstack;;
  *) exit 0;;
esac

ident="$MOSAIC_GIT_IDENTITY"; ident_src="MOSAIC_GIT_IDENTITY"
if [ -z "$ident" ]; then
  ident=$(git config --get mosaic.gitIdentity 2>/dev/null)
  ident_src="git config mosaic.gitIdentity"
fi
if [ -z "$ident" ]; then
  ident="$username_in"
  ident_src="the username git supplied"
fi

# ── Credential store selection ────────────────────────────────────────────────
# An identity is a SEAT or it is a SERVICE, and which one it is determines where
# its credential lives. There is no precedence rule between the two stores and no
# fallback from one to the other: a seat whose slot is empty fails closed rather
# than reading a service credential that happens to share its name.
#
#   seat     — <brain>/fleet/agents/<ident>/ exists
#              credential at <brain>/fleet/agents/<ident>/secrets/<idpfx>-<ident>.token
#   service  — it does not
#              credential at ~/.config/mosaic/secrets/gitea-tokens/<idpfx>-<ident>.token
#
# One credential, one location. Two copies of one credential diverge, and the
# stale copy fails in a way that reads as a revoked token rather than as drift.
#
# Brain-home resolution mirrors packages/mosaic/src/fleet/brain-home.ts and
# tools/fleet/start-agent-session.sh: MOSAIC_BRAIN_HOME wins, else ~/.mosaic.
brain_home="${MOSAIC_BRAIN_HOME:-$HOME/.mosaic}"
svc_store="$HOME/.config/mosaic/secrets/gitea-tokens"

idtok=""; ident_kind=""
if [ -n "$ident" ]; then
  if [ -d "$brain_home/fleet/agents/$ident" ]; then
    ident_kind="seat"
    idtok="$brain_home/fleet/agents/$ident/secrets/${idpfx}-${ident}.token"
  else
    ident_kind="service identity"
    idtok="$svc_store/${idpfx}-${ident}.token"
  fi
  if [ -r "$idtok" ]; then
    echo "username=${ident}"
    echo "password=$(cat "$idtok")"
    exit 0
  fi
fi

# ── Shared-account fallback: ONLY on a host with no fleet and no identity ──────
# `fleet/agents` existing is the same signal brain-home.ts uses to decide a brain
# is active. Where there are seats, records must be attributable, so an
# unresolvable request is refused instead of borrowing the shared account.
fleet_present=0
[ -d "$brain_home/fleet/agents" ] && fleet_present=1

if [ -z "$ident" ] && [ "$fleet_present" -eq 0 ]; then
  script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
  # shellcheck source=../_lib/credentials.sh
  source "$script_dir/../_lib/credentials.sh"
  load_credentials "$idpfx" >/dev/null 2>&1 || exit 0
  # GITEA_USER is not populated by load_credentials (it exports GITEA_URL and
  # GITEA_TOKEN only). Gitea's git-over-HTTP auth authenticates from the token in
  # the password field, not from the username string, so any non-empty
  # placeholder works — deliberately NOT a real account name, since framework
  # files stay operator-agnostic (tools/quality/scripts/verify-sanitized.sh).
  echo "username=${GITEA_USER:-git}"
  echo "password=$GITEA_TOKEN"
  exit 0
fi

# ── FAIL CLOSED ───────────────────────────────────────────────────────────────
if [ -z "$ident" ]; then
  reason="no-identity"
else
  reason="no-token-for-identity"
fi

seat="${MOSAIC_AGENT_NAME:-unknown}"
ts=$(date -u +%Y-%m-%dT%H:%M:%SZ)

# The escalation RECORD is durable and unconditional; any notification built on
# top of it is best-effort. Record and alert are deduplicated separately — a cap
# on the alert alone lets the spool grow without bound exactly while the operator
# is being told nothing, so the louder the failure the quieter it gets.
spool="${MOSAIC_CREDENTIAL_SPOOL:-$HOME/.local/state/mosaic-credential-escalations}"
if mkdir -p "$spool" 2>/dev/null; then
  chmod 700 "$spool" 2>/dev/null
  dedupe="$spool/.spooled-${seat}-${ident:-none}-${reason}-$(date -u +%Y%m%d%H%M)"
  if [ ! -e "$dedupe" ]; then
    : > "$dedupe" 2>/dev/null
    spoolfile="$spool/$(date -u +%Y%m%d).jsonl"
    printf '{"ts":"%s","reason":"%s","identity":"%s","identity_source":"%s","kind":"%s","seat":"%s","host":"%s","cwd":"%s"}\n' \
      "$ts" "$reason" "${ident:-<unset>}" "$ident_src" "${ident_kind:-none}" "$seat" "$host" "$PWD" \
      >> "$spoolfile" 2>/dev/null
    chmod 600 "$spoolfile" 2>/dev/null
  fi
  find "$spool" -maxdepth 1 -name '.spooled-*' -mmin +120 -delete 2>/dev/null
fi

cat >&2 <<EOF
git-credential-mosaic: REFUSED (fail-closed).
  host     : ${host}
  identity : ${ident:-<unset>}${ident:+  (from ${ident_src}; resolved as a ${ident_kind})}
  reason   : ${reason}
EOF

if [ -n "$ident" ]; then
  cat >&2 <<EOF
  expected : ${idtok}
EOF
fi

cat >&2 <<EOF

No per-identity credential resolved. This helper does NOT fall back to the shared
account: that fallback makes every record it creates attributable to one
principal, which is unrecoverable once a pull request has merged under it.

Fix (pick one):
  export MOSAIC_GIT_IDENTITY=<agent-id>        # process-scoped
  git config mosaic.gitIdentity <agent-id>     # per-repo/worktree, persists
Then provision that identity's credential at the path named above. An identity
with a directory under \${MOSAIC_BRAIN_HOME:-\$HOME/.mosaic}/fleet/agents/ is a
seat and is read ONLY from its own secrets/ slot; any other identity is read from
~/.config/mosaic/secrets/gitea-tokens/. There is no fallback between the two.

If this identity legitimately needs git access and has none, ask the orchestrator
to provision one.

  record: ${spool}/$(date -u +%Y%m%d).jsonl
EOF
exit 1