#!/usr/bin/env bash
# Enforce commit message layout and line length (pure bash; no helper scripts).
# Enable with: git config core.hooksPath .githooks
#
# Required shape (merge commits skip all checks while .git/MERGE_HEAD exists):
#   1) subject (non-empty, <=80 chars)
#   2) blank line
#   3) one or more summary lines (no "- " bullet prefix), <=80 chars each
#   4) blank line
#   5) one or more body lines, each a "- ..." bullet, <=80 chars each
#
# Merge templates from Git can exceed 80 columns; skip checks then.

set -euo pipefail

msg_file=${1:?commit-msg hook requires path to message file}

if [[ -f .git/MERGE_HEAD ]]; then
    exit 0
fi

lines=()
lineno=0
while IFS= read -r line || [[ -n "${line}" ]]; do
    lineno=$((lineno + 1))
    len=${#line}
    if ((len > 80)); then
        echo "❌ COMMIT MESSAGE: line ${lineno} is ${len} chars (max 80)"
        echo ""
        echo "Required: subject, blank, summary, blank, then \"- ...\" bullets."
        echo "See .github/prompts/commit.prompt.md"
        echo ""
        echo "Offending line (truncated for display):"
        printf '%s\n' "${line}" | cut -c1-120
        exit 1
    fi
    lines+=("$line")
done <"${msg_file}"

# Drop trailing empty lines so optional final newline does not confuse counts.
while ((${#lines[@]} > 0)); do
    last=$(( ${#lines[@]} - 1 ))
    if [[ -z "${lines[last]}" ]]; then
        unset "lines[last]"
    else
        break
    fi
done

n=${#lines[@]}
if ((n < 5)); then
    echo "❌ COMMIT MESSAGE: need subject, blank, summary, blank, bullets"
    echo "(five or more lines). See .github/prompts/commit.prompt.md"
    exit 1
fi

if [[ -z "${lines[0]}" ]]; then
    echo "❌ COMMIT MESSAGE: first line (subject) must not be empty"
    exit 1
fi

if [[ -n "${lines[1]}" ]]; then
    echo "❌ COMMIT MESSAGE: line 2 must be blank (separator after subject)"
    exit 1
fi

bullet_idx=-1
for ((i = 2; i < n; i++)); do
    line=${lines[i]}
    if [[ "${line}" =~ ^[[:space:]]*-[[:space:]] ]]; then
        bullet_idx=$i
        break
    fi
done

if ((bullet_idx < 0)); then
    echo "❌ COMMIT MESSAGE: no bullet list found (lines starting with \"- \")"
    echo "After the summary paragraph and its trailing blank line, add details"
    echo "as \"- ...\" bullets. See .github/prompts/commit.prompt.md"
    exit 1
fi

if ((bullet_idx < 3)); then
    echo "❌ COMMIT MESSAGE: add a summary line after the subject blank line"
    echo "before the blank that precedes bullets."
    exit 1
fi

if [[ -n "${lines[bullet_idx - 1]}" ]]; then
    echo "❌ COMMIT MESSAGE: blank line required between summary and bullet list"
    echo "(line $((bullet_idx)) should be empty)."
    exit 1
fi

has_summary=0
for ((i = 2; i < bullet_idx - 1; i++)); do
    line=${lines[i]}
    if [[ -n "${line}" ]] && [[ "${line}" =~ ^[[:space:]]*-[[:space:]] ]]; then
        echo "❌ COMMIT MESSAGE: summary line $((i + 1)) starts like a bullet"
        echo "Use prose first, one blank line, then hyphen bullets."
        exit 1
    fi
    if [[ -n "${line}" ]]; then
        has_summary=1
    fi
done

if ((has_summary == 0)); then
    echo "❌ COMMIT MESSAGE: summary paragraph is empty before the bullet list"
    echo "Add one to three sentences, then a blank line, then bullets."
    exit 1
fi

for ((i = bullet_idx; i < n; i++)); do
    line=${lines[i]}
    if [[ -z "${line}" ]]; then
        echo "❌ COMMIT MESSAGE: empty line $((i + 1)) inside bullet block"
        echo "Remove blanks between bullets or end after the last bullet."
        exit 1
    fi
    if ! [[ "${line}" =~ ^[[:space:]]*-[[:space:]] ]]; then
        echo "❌ COMMIT MESSAGE: line $((i + 1)) is not a hyphen bullet"
        echo "Each bullet line must start with dash then space after summary."
        exit 1
    fi
done

exit 0