git-lg

#!/bin/bash -e

# Git script for printing beautiful logs.

if echo "$*" | grep -Eq -- '--help\b|-h\b'; then
    echo "usage: ${0##*/} [-h|--help] [ARGS]" 1>&2
    echo "Forwards any additional ARGS to the git log command." 1>&2
    exit 1
fi

HASH='%C(red)%h%C(reset)'
DATE='%C(green)(%cr)%C(reset)'
AUTHOR='%C(bold blue)<%an>%C(reset)'
REFS='%C(yellow)%d%C(reset)'
MESSAGE='%s'

# Unit separator: can't appear in a hash, date, author name, ref name or subject,
# so it never collides with the content it delimits.
DELIM=$'\037'

# tput fails when stdout isn't a tty, which -e would turn into an early exit.
TERM_WIDTH="$(tput cols 2>/dev/null || echo 80)"
MAX_HASH_WIDTH="$((TERM_WIDTH / 4))"

make_log() {
    git log \
        --date=relative \
        --graph \
        --pretty="tformat:$HASH$DELIM$DATE$DELIM$AUTHOR$DELIM$REFS $MESSAGE" \
        "$@"
}

# Align the leading columns, padding to the widest value in each one.
#
# This replaces column(1), which on macOS refuses any line longer than 2048
# bytes ("line too long") and then mangles the rest of the table along with it.
# A single commit carrying a lot of tags is enough to blow past that.
#
# Widths are measured with the ANSI escapes stripped, so columns line up by what
# is actually on screen rather than by escape-sequence bytes.
#
# If the first column comes out wider than MAX_HASH_WIDTH -- a deep --graph
# prefix, say -- fall back to single-space separation rather than aligning.
columnize() {
    awk -v delim="$DELIM" -v max_width="$MAX_HASH_WIDTH" '
        function visible_width(s) {
            gsub(/\033\[[0-9;]*m/, "", s)
            return length(s)
        }

        # Split on at most the first FIELDS-1 delimiters, so that a delimiter in
        # the trailing field is left alone rather than becoming a new column.
        function split_fields(s, out,    n, p) {
            n = 0
            while (n < FIELDS - 1) {
                p = index(s, delim)
                if (p == 0) break
                out[++n] = substr(s, 1, p - 1)
                s = substr(s, p + length(delim))
            }
            out[++n] = s
            return n
        }

        BEGIN {
            FIELDS = 4  # hash, date, author, then refs and subject together
            GAP = 2
            BLANKS = sprintf("%256s", "")
        }

        {
            lines[NR] = $0
            n = split_fields($0, field)
            # The trailing field is never padded, so it needs no width.
            for (i = 1; i < n; i++) {
                w = visible_width(field[i])
                if (w > width[i]) width[i] = w
            }
        }

        END {
            aligned = (width[1] <= max_width)
            for (r = 1; r <= NR; r++) {
                n = split_fields(lines[r], field)
                line = field[1]
                for (i = 2; i <= n; i++) {
                    pad = aligned ? width[i - 1] - visible_width(field[i - 1]) + GAP : 1
                    line = line substr(BLANKS, 1, pad) field[i]
                }
                print line
            }
        }
    '
}

git_pretty_log() {
    # 1. Replace (2 years, 5 months) with (2 years)
    # 2. Replace (2 years ago) with (2 years)
    # 3. Color merge commits specially
    # 4. Align the columns
    # 5. Page only if we're asked to (GIT_NO_PAGER)
    # 6. Page only if needed
    make_log "$@" |
        sed -Ee 's/([[:digit:]]+ [[:alpha:]]+), [[:digit:]]+ months? ago/\1/' |
        sed -Ee 's/([[:digit:]]+ [[:alpha:]]+) ago/\1/' |
        sed -Ee "s/(Merge (branch|remote-tracking branch|pull request) .*$)/$(printf '\033[31m')\\1$(printf '\033[0m')/" |
        columnize |
        if [ -n "$GIT_NO_PAGER" ]; then
            cat
        else
            less --quit-if-one-screen --no-init --RAW-CONTROL-CHARS --chop-long-lines
        fi
}

git_pretty_log "$@"