#!/usr/bin/env bash
# lib/forge.sh — one forge abstraction, two backends (issue #188).
#
# Sourced, never executed: no set -e/-u here — the sourcing script owns its
# own shell options, exactly as lib/version.sh does. This file is the
# selector only; the backends live beside it in lib/forge-github.sh and
# lib/forge-forgejo.sh, and nothing here talks to a network.
#
# WHY THIS FILE EXISTS, stated once. Until #188 the reconcilers were `gh`
# all the way down — 61 runtime call sites, no indirection, no forge check.
# Pointed at a Forgejo instance (heavy-duty/rig, which moved here and runs
# its CI on a Forgejo Actions runner) they did not fail usefully. Measured
# against forgejo.heavyduty.builders on 2026-08-02, at ceremony 84bb1a4:
#
#   labels-scope         exit 0  "no .github/labeler.yml at main — nothing
#                                 to derive"   — the file exists (HTTP 200)
#   labels-reconcile     exit 0  "reconciled."  — having enumerated ZERO PRs
#   issueflow-reconcile  exit 1  "unexpected end of JSON input"
#
# Two of the three reported SUCCESS having read nothing. labels-reconcile's
# own blind-sweep warning (#96) could not fire, because it counts unreadable
# PRs against a list `gh pr list` never produced — and a process
# substitution's failure does not trip set -e, so `total` stayed 0 and the
# sweep called itself reconciled. rig run 979 is the log.
#
# The tempting fix — install gh on the runner — makes it WORSE. gh speaks
# GitHub's /api/v3 against api.github.com; Forgejo serves /api/v1 and no
# GraphQL at all. With gh present and GH_HOST set to the Forgejo host, the
# one loud failure goes quiet (`gh pr list` hits /api/graphql -> HTTP 405,
# prints nothing, exits into the same empty loop) and all three actions go
# green while reading nothing. That is this repo's own doctrine — an
# unreadable rollup reads as "nothing is failing" — being violated by the
# repo that wrote it.
#
# So: the forge is decided ONCE, before any sweep, and a client that cannot
# speak it refuses loudly. Never "probably github".

# forge_detect — print "github" or "forgejo"; exit 1 loudly when it cannot
# tell. Order matters and every signal below was measured, not read from
# docs: a real forgejo-runner v6.3.1 job on forgejo.heavyduty.builders
# (probe task 278, 2026-08-02) dumped its environment, and a GitHub-hosted
# runner's is the control.
#
# The trap that makes this non-obvious: **the Forgejo runner populates the
# whole GITHUB_* namespace.** GITHUB_ACTIONS=true, GITHUB_REPOSITORY,
# GITHUB_SHA, GITHUB_TOKEN — all set, all correct-looking. Detecting on
# "GITHUB_ACTIONS is set" would answer "github" on both forges, which is
# precisely the bug. What actually differs:
#
#   signal              GitHub                      Forgejo (measured)
#   GITHUB_API_URL      https://api.github.com      https://<host>/api/v1
#   GITHUB_GRAPHQL_URL  https://api.github.com/…    (empty)
#   GITEA_ACTIONS       (unset)                     true
#
# GITHUB_GRAPHQL_URL being empty on Forgejo is not a curiosity — it is the
# forge telling us the two `gh api graphql` sites #188 retired can never
# work here. It is deliberately NOT a detection signal, though: an empty
# variable is also what a hand-rolled harness leaves behind, and a signal
# that fires on absence is a signal that fires by accident.
forge_detect() {
  # 1. The explicit override outranks every probe — the escape hatch for a
  #    forge this file has not met, and the handle the tests drive. A typo
  #    in it is fatal on purpose: the operator said something and it was
  #    wrong, and falling through to a probe that guesses right by accident
  #    would hide that until the guess was wrong too.
  if [ -n "${CEREMONY_FORGE:-}" ]; then
    case "$CEREMONY_FORGE" in
      github | forgejo) printf '%s\n' "$CEREMONY_FORGE"; return 0 ;;
      *)
        echo "forge_detect: unknown forge: CEREMONY_FORGE=$CEREMONY_FORGE (expected github or forgejo)" >&2
        return 1
        ;;
    esac
  fi

  # 2. Forgejo's and Gitea's own positive marker. Unambiguous where a
  #    hand-set GITHUB_API_URL might not be, so it is read first.
  if [ "${GITEA_ACTIONS:-}" = true ] || [ "${FORGEJO_ACTIONS:-}" = true ]; then
    printf 'forgejo\n'
    return 0
  fi

  # 3. The API URL's shape. /api/v3 is GitHub's (github.com and GitHub
  #    Enterprise Server alike — GHES is a github backend on a non-github.com
  #    host, and routing it to the forgejo backend would regress term 5's
  #    "GitHub consumers are unchanged"). /api/v1 is the Gitea shape Forgejo
  #    serves.
  case "${GITHUB_API_URL:-}" in
    https://api.github.com | https://api.github.com/*) printf 'github\n'; return 0 ;;
    */api/v3 | */api/v3/*) printf 'github\n'; return 0 ;;
    */api/v1 | */api/v1/*) printf 'forgejo\n'; return 0 ;;
  esac

  # 4. Last resort, the server host. Only github.com itself is conclusive
  #    here: a bare hostname says nothing about which API it serves.
  case "${GITHUB_SERVER_URL:-}" in
    https://github.com | https://github.com/*) printf 'github\n'; return 0 ;;
  esac

  # 5. Refuse. "Nothing to read" is not "probably github" — guessing here
  #    reinstates the exact blind sweep this file exists to end. Name what
  #    was inspected and the escape hatch, so the log answers "why" without
  #    a second run (#101 D5, one layer up: report, do not diagnose).
  cat >&2 <<EOF
forge_detect: cannot determine which forge this is — refusing to guess (#188).
  GITHUB_API_URL='${GITHUB_API_URL:-}'
  GITHUB_SERVER_URL='${GITHUB_SERVER_URL:-}'
  GITEA_ACTIONS='${GITEA_ACTIONS:-}'
Set CEREMONY_FORGE=github or CEREMONY_FORGE=forgejo to say so explicitly.
EOF
  return 1
}

# Where the backends live. Captured at source time, not call time: a
# function that resolves BASH_SOURCE later would resolve its own file, not
# this one.
FORGE_LIB_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

# forge_select [forge] — source the backend for this forge, so the forge_*
# verbs exist. Exactly one backend is ever loaded; both define the same
# names, which is what keeps the branching out of the 61 call sites (term 1)
# and the single-forge assumption from growing back.
#
# Idempotent, because the actions call it once and the tests call it per
# case. Pass a forge explicitly to load a specific backend; omit it and the
# environment decides via forge_detect.
forge_select() {
  local forge="${1:-}"
  # One default for every consumer: the forgejo backend addresses the repo
  # through REPO, the github backend reads GITHUB_REPOSITORY. Defaulting
  # here means no call site — workflow step or script — can forget it and
  # get a repo-less path (#191). The reconcilers still assert their own.
  REPO="${REPO:-${GITHUB_REPOSITORY:-}}"
  export REPO
  if [ -z "$forge" ]; then
    forge="$(forge_detect)" || return 1
  fi
  case "$forge" in
    github | forgejo) ;;
    *)
      echo "forge_select: unknown forge: $forge (expected github or forgejo)" >&2
      return 1
      ;;
  esac
  # shellcheck source=/dev/null
  . "$FORGE_LIB_DIR/forge-$forge.sh" || return 1
  # Read by callers and tests to assert which backend is loaded, so the
  # choice is inspectable rather than implied by which functions exist.
  # shellcheck disable=SC2034 # consumed by sourcing scripts, not this file
  FORGE="$forge"
}

# forge_client <forge> — print the client that backend requires.
#
#   github  -> gh    the current call set, extracted 1:1 (term 5)
#   forgejo -> rest  /api/v1 over curl+jq
#
# forgejo is "rest" by MEASUREMENT, not preference. The image the Forgejo
# instance actually runs jobs in (ghcr.io/catthehacker/ubuntu:act-22.04,
# probe task 278) carries curl, jq and node — and has neither `gh` NOR
# `stoke` on PATH. That second absence is what retired option A from the
# ruling: porting the call sites to the stoke CLI would have put a binary
# on the critical path that the runner does not have and that would need
# installing before every job.
forge_client() {
  case "${1:?forge_client: forge required}" in
    github) printf 'gh\n' ;;
    forgejo) printf 'rest\n' ;;
    *)
      echo "forge_client: unknown forge: $1 (expected github or forgejo)" >&2
      return 1
      ;;
  esac
}

# forge_preflight — the gate. Run it BEFORE any sweep: it decides the forge
# and proves the client can speak it, or exits non-zero with a named reason.
#
# CEREMONY_FORGE_CLIENT declares the client the caller will actually use —
# how a call site that still hard-codes `gh` announces itself honestly while
# the backends are being ported. Two checks run, in order:
#
#   1. the declaration, when made, must match what this forge needs;
#   2. that client's binaries must actually be on PATH — checked whether or
#      not a declaration was made, because a call site that declares the
#      right client on a runner that lacks it is still a blind sweep waiting
#      to happen.
forge_preflight() {
  local forge want
  forge="$(forge_detect)" || return 1
  want="$(forge_client "$forge")" || return 1

  if [ -n "${CEREMONY_FORGE_CLIENT:-}" ] && [ "$CEREMONY_FORGE_CLIENT" != "$want" ]; then
    cat >&2 <<EOF
forge_preflight: this is a '$forge' forge and the '$CEREMONY_FORGE_CLIENT' client cannot speak it (#188).
  gh speaks GitHub's /api/v3 against api.github.com; Forgejo serves /api/v1
  and has no GraphQL surface at all. Pointing one at the other does not
  fail usefully — it reads nothing and reports success.
  This forge needs the '$want' client.
EOF
    return 1
  fi

  # Then prove the tools are actually here — declared or not. A missing
  # binary is the rig failure verbatim, "line 692: gh: command not found",
  # and it must be a refusal before the sweep, not a 127 halfway through
  # one. Checked on BOTH paths deliberately: a call site that declares the
  # right client on a runner that lacks it is still a blind sweep waiting
  # to happen.
  local missing_bins=() bin
  case "$want" in
    gh) command -v gh >/dev/null 2>&1 || missing_bins+=(gh) ;;
    rest) for bin in curl jq; do command -v "$bin" >/dev/null 2>&1 || missing_bins+=("$bin"); done ;;
  esac
  if [ "${#missing_bins[@]}" -gt 0 ]; then
    cat >&2 <<EOF
forge_preflight: this is a '$forge' forge, which needs the '$want' client, and ${missing_bins[*]} is not installed (#188).
  Refusing before the sweep: a reconciler that cannot read the board must
  not report that it reconciled one.
EOF
    return 1
  fi
  return 0
}