#!/usr/bin/env bash
# Resolve a PR's exact head (spec §10.1) and record its metadata + CI status.
#
# Usage: resolve-pr-head.sh <side: frontend|backend> <repo owner/name> <pr-number>
# Reads:  GH_TOKEN (read-only App installation token)
# Writes: $ARTIFACTS_DIR/<side>-pr.json  (metadata consumed by evidence + agent)
#         <side>_sha / <side>_short_sha to $GITHUB_OUTPUT when present.

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
# shellcheck source=lib.sh
source "$SCRIPT_DIR/lib.sh"

side="${1:?side required}"
repo="${2:?repo required}"
pr="${3:?pr number required}"
require_env GH_TOKEN

pr_json="$(gh api "repos/$repo/pulls/$pr")" || die "failed to fetch $repo PR #$pr"

state="$(jq -r '.state' <<<"$pr_json")"
head_sha="$(jq -r '.head.sha // empty' <<<"$pr_json")"
head_repo="$(jq -r '.head.repo.full_name // empty' <<<"$pr_json")"

[ -n "$head_sha" ] || die "$repo PR #$pr has an empty head"
[ "$state" = "open" ] || log "WARNING: $repo PR #$pr state is '$state', not open"
[ "$head_repo" = "$repo" ] || die "$repo PR #$pr head lives in '$head_repo' (fork heads are not supported)"

short_sha="${head_sha:0:7}"

# CI status on the exact head: green / red / pending / missing / unknown.
#
# A failed API call must NEVER be reported as "missing": that would state as a
# fact ("this PR has no CI") what is actually an unread signal, which is the
# exact failure mode this runner exists to prevent. Reading check-runs needs the
# App's `checks: read` permission; without it the call 403s and the honest
# answer is "unknown".
checks_err="$ARTIFACTS_DIR/$side-checks-error.txt"
if checks_json="$(gh api "repos/$repo/commits/$head_sha/check-runs" \
     --jq '{total: .total_count, runs: [.check_runs[] | {name, status, conclusion}]}' 2>"$checks_err")"; then
  ci_status="$(jq -r '
    if .total == 0 then "missing"
    elif ([.runs[] | select(.status != "completed")] | length) > 0 then "pending"
    elif ([.runs[] | select(.conclusion != "success" and .conclusion != "neutral" and .conclusion != "skipped")] | length) > 0 then "red"
    else "green" end' <<<"$checks_json")"
  rm -f "$checks_err"
else
  reason="$(tr -d '\000-\037' <"$checks_err" | cut -c1-160)"
  log "WARNING: could not read check-runs for $repo@$short_sha: $reason"
  ci_status="unknown (check-runs unreadable; the review App likely lacks 'checks: read')"
  checks_json='{"total":0,"runs":[],"unreadable":true}'
fi

jq -n \
  --arg side "$side" --arg repo "$repo" --argjson pr "$pr" \
  --arg title "$(jq -r '.title' <<<"$pr_json")" \
  --arg head_ref "$(jq -r '.head.ref' <<<"$pr_json")" \
  --arg base_ref "$(jq -r '.base.ref' <<<"$pr_json")" \
  --arg head_sha "$head_sha" --arg short_sha "$short_sha" \
  --arg state "$state" --arg ci_status "$ci_status" \
  --argjson mergeable "$(jq '.mergeable' <<<"$pr_json")" \
  --argjson checks "$checks_json" \
  '{side: $side, repo: $repo, pr: $pr, title: $title, head_ref: $head_ref,
    base_ref: $base_ref, head_sha: $head_sha, short_sha: $short_sha,
    state: $state, mergeable: $mergeable, ci_status: $ci_status, checks: $checks}' \
  >"$ARTIFACTS_DIR/$side-pr.json"

out="${GITHUB_OUTPUT:-/dev/stdout}"
{
  printf '%s_sha=%s\n' "$side" "$head_sha"
  printf '%s_short_sha=%s\n' "$side" "$short_sha"
} >>"$out"

log "$side: $repo#$pr head=$short_sha base=$(jq -r '.base.ref' <<<"$pr_json") ci=$ci_status"