#!/usr/bin/env bash
# session-handoff PostToolUse hook (POSIX). See commit-detector.ps1 for prose.
set -euo pipefail

raw=$(cat)
[[ -z "$raw" ]] && exit 0

# Helper: extract a JSON path via python3
jget() {
    python3 -c "
import sys, json
try:
    d = json.loads(sys.argv[1])
    out = d
    for k in sys.argv[2].split('.'):
        if isinstance(out, dict):
            out = out.get(k)
        else:
            out = None
            break
    print('' if out is None else out)
" "$raw" "$1" 2>/dev/null || echo ''
}

cmd=$(jget tool_input.command)
[[ -z "$cmd" ]] && exit 0

# Only `git commit`, not `--amend`
if ! echo "$cmd" | grep -qE '(^|[^[:alnum:]_-])git[[:space:]]+commit($|[^[:alnum:]_-])'; then exit 0; fi
if echo "$cmd" | grep -qE '(^|[^[:alnum:]_-])git[[:space:]]+commit\b.*--amend'; then exit 0; fi

# Only on successful commit (if exit_code present and non-zero, skip)
exit_code=$(jget tool_response.exit_code)
if [[ -n "$exit_code" && "$exit_code" != "0" ]]; then exit 0; fi

cwd=$(jget cwd)
[[ -z "$cwd" ]] && cwd=$(pwd)

# Require git work-tree
git -C "$cwd" rev-parse --is-inside-work-tree >/dev/null 2>&1 || exit 0

subject=$(git -C "$cwd" log -1 --format='%s')
body=$(git -C "$cwd" log -1 --format='%b')
files=$(git -C "$cwd" diff-tree --no-commit-id --name-only -r HEAD | wc -l | tr -d ' ')

# Trivial-prefix check
prefix=$(echo "$subject" | sed -E 's/^([a-z]+)(\([^)]+\))?:.*$/\1/')
case "$prefix" in
    meta|docs|style|chore) exit 0 ;;
esac
echo "$subject" | grep -qE 'fix[[:space:]]+typo' && exit 0

# Threshold
body_len=${#body}
if [[ "$body_len" -le 200 && "$files" -le 3 ]]; then exit 0; fi

# Substantive — emit JSON via python3 to handle quoting safely
python3 -c "
import json, sys
msg = (
    'Substantive commit detected on $cwd: \`' + '''$subject''' + '\` '
    + '($files files changed, body $body_len chars). '
    + 'Consider invoking session-handoff write-mode to update .tasks/NEXT_SESSION.md.'
)
print(json.dumps({
    'hookSpecificOutput': {
        'hookEventName': 'PostToolUse',
        'additionalContext': msg,
    },
    'systemMessage': 'session-handoff: substantive commit detected',
    'suppressOutput': False,
}))
"