#!/usr/bin/env dash
# compat: +ash +bash +dash -hush -ksh -mksh -oksh -osh -posh +yash +zsh
# NOTE: many shells work, but some of them fail to restore tty settings.
# fuck termcap, all my homies hate termcap.

glug() ( # note the subshell syntax. this allows us to abuse globals like crazy.
    [ $# = 0 ] || { printf '%s does not take arguments.\n' glug >&2; return 2; }

    _here="$PWD"
    repo="$PWD"
    i=0
    while ! [ -d .git ] 2>/dev/null; do
        # no one has git repositories with directories deeper than 10 levels, right?
        [ $((i+=1)) -lt 10 ] || { printf '%s: failed to find a .git directory\n' glug >&2; return 2; }
        cd ..
        repo="$PWD"
    done
    cd "$_here"

    detect_size() {
        # globals: $COLUMNS, $LINES
        _size="$(stty size)"
        COLUMNS="${_size#* }"
        LINES="${_size%% *}"
        if [ "$COLUMNS" -gt 0 ] 2>/dev/null && [ "$LINES" -gt 0 ] 2>/dev/null; then
            : # pass
        else
            printf '%s: failed to determine terminal size\n' glug >&2
            return 2
        fi
        unset _size
    }

    [ -n "$ZSH_VERSION" ] || detect_size

    if [ -n "$ZSH_VERSION" ] || [ -n "$BASH_VERSION" ]; then
        esc=$'\e'
        nl=$'\n'
        cr=$'\r'
    else
        esc="$(printf '\033')"
        # shells strip trailing newlines from captures, so work around that:
        nl="$(printf '\nx')"; nl="${nl%x}"
        cr="$(printf '\rx')"; cr="${cr%x}"
    fi

    limit=200 # maximum number of git commits to look back on
    choices=0
    selection=1

    alt=0
    ret=0
    err=

    alt_on() {
        # globals: $alt
        printf '\033[?1049h' # alt screen on (smcup)
        alt=1
        printf '\033[?1h\033=' # no idea but less does it so it must be important (smkx)
        printf '\r' # move cursor to start of line (carriage return)
        printf '\033[H' # move cursor to first line
    }

    alt_off() {
        # globals: $alt
        printf '\r' # move cursor to start of line (carriage return)
        #printf '\033[K' # erase everything after the cursor (el)
        printf '\033[?1l\033>' # no idea but less does it so it must be important (rmkx)
        printf '\033[?1049l' # alt screen off (rmcup)
        alt=0
    }

    glug_enter() {
        # globals: $alt
        [ $alt = 1 ] || alt_on
    }

    glug_exit() {
        # globals: $alt, $err, $ret
        [ $alt = 0 ] || alt_off
        [ -z "$err" ] || printf '%s\n' "$err" >&2
        exit $ret
    }

    die() {
        # globals: $ret, $err
        ret=$?
        err="$@"
        [ $? = 0 ] && exit 1 || exit $?
    }

    read_byte() {
        # NOTE: run this function in a subshell, else everything will blow up.
        old="$(stty -g)"
        trap 'stty "$old"' INT EXIT
        stty -icanon -echo
        dd ibs=1 count=1 2>/dev/null || exit
        echo _ # append an underscore so that newlines are preserved in captures
    } </dev/tty # ensure this interacts with a terminal instead of a pipe

    escape_message() {
        # arguments: $message
        _msg=
        while _seg="${message%%\'*}"; [ "$_seg" != "$message" ]; do
            _msg="$_msg$_seg'\''"
            message="${message#*\'}"
        done
        message="$_msg$message"
        unset _msg _seg
    }

    parse_logs() {
        # arguments: $logs (clobbered)
        # globals: $choices
        logs="$logs$nl" # otherwise the last entry is dropped
        while _next="${logs#*$nl}"; [ "$logs" != "$_next" ]; do
            _line="${logs%%$nl*}"
            #_line="${logs%$cr}" # TODO: handle this more robustly.
            logs="$_next"

            commit="${_line%% *}"
            [ -z "${commit##[a-f0-9]*}" ] || die "invalid commit: $commit"
            message="${_line#* }"
            escape_message

            #printf '~%s~\n' "$_line"
            #printf 'COMMIT="%s"; MESSAGE="%s";\n' "$commit" "$message"

            : $((choices+=1))
            eval "choice_$choices=$commit"
            eval "commit_$commit='$message'"
        done
        unset _line _next
    }

    colorize_pathy() {
        # arguments: $pathy (clobbered)
        printf '%s' "$pathy" # TODO
    }

    colorize_diffy() {
        # arguments: $diffy (clobbered)
        while [ -n "$diffy" ]; do
            if [ "${diffy#[!0-9+-]}" != "$diffy" ]; then
                _seg="${diffy%%[0-9+-]*}"
                printf '\033[m ' # NOTE: this replaces *all* unexpected characters.
            elif [ "${diffy#[0-9]}" != "$diffy" ]; then
                _seg="${diffy%%[!0-9]*}"
                printf '\033[97m%4s' "$_seg"
            elif [ "${diffy#+}" != "$diffy" ]; then
                _seg="${diffy%%[!+]*}"
                printf '\033[92m%s' "$_seg"
            elif [ "${diffy#-}" != "$diffy" ]; then
                _seg="${diffy%%[!-]*}"
                printf '\033[91m%s' "$_seg"
            else
                break # unreachable
            fi
            diffy="${diffy#$_seg}"
        done
        unset _seg
    }

    colorize_summary() {
        # arguments: $gds (clobbered)
        _color=33
        [ "${gds%insertion*}" = "$gds" ]; _ins=$? # _ins=1 when insertion is found
        while [ -n "$gds" ]; do
            if [ "${gds#[!(),0-9+-]}" != "$gds" ]; then
                _seg="${gds%%[(),0-9+-]*}"
                printf '\033[%sm%s' "$_color" "$_seg"
            elif [ "${gds#[()+-]}" != "$gds" ]; then
                _seg="${gds%%[!()+-]*}"
                case "$_seg" in
                ('(+)') printf '\033[m(\033[92m+\033[m)';;
                ('(-)') printf '\033[m(\033[91m-\033[m)';;
                (*) printf '%s' "$_seg";;
                esac
            elif [ "${gds#,}" != "$gds" ]; then
                _seg="${gds%%[!,]*}"
                printf '\033[%sm%s' "$_color" "$_seg"
                : $((_color-=1)) # how convenient that the color codes line up!
                [ $_ins = 1 ] || : $((_color-=1)) # no insertions; skip to red
            elif [ "${gds#[0-9]}" != "$gds" ]; then
                _seg="${gds%%[!0-9]*}"
                printf '\033[97m%s' "$_seg"
            else
                break # unreachable
            fi
            gds="${gds#$_seg}"
        done
        unset _color _ins _seg
    }

    format_stats() {
        # arguments: $gds (clobbered)
        # globals: $linesleft
        [ $linesleft -gt 1 ] || return
        while _line="${gds%%$nl*}"; [ "$_line" != "$gds" ]; do
            gds="${gds#*$nl}"
            [ $linesleft -gt 1 ] || continue
            # NOTE: assumes no filepaths contain a '|' character.
            pathy="${_line%|*}"
            diffy="${_line#*|}"
            colorize_pathy
            printf '\033[m|'
            colorize_diffy
            unset pathy diffy
            printf '\033[m\n'
            : $((linesleft-=1))
        done
        colorize_summary
        printf '\n'
        : $((linesleft-=1))
        unset _line
    }

    present_choices() {
        # arguments: $selection
        # globally influential: $choices
        linesleft=$LINES
        i=$((selection-2))
        while [ $((i+=1)) -le $choices ]; do
            if [ $i -eq 0 ]; then
                printf '%s\n' 'welcome to glug!' # TODO: make this pretty. print cwd?
                : $((linesleft-=1))
                continue
            elif [ $i -lt 0 ]; then
                printf '\n'
                : $((linesleft-=1))
                continue
            fi

            eval "commit=\$choice_$i"
            eval "message=\$commit_$commit"

            if [ $i = $selection ]; then
                #printf ' \033[95m >\033[m \033[33m%s\033[m ' "$commit"
                printf ' \0337 \033[7m>\033[m \033[33m%s\033[m ' "$commit"
            else
                printf '    \033[90m%s\033[m ' "$commit"
            fi

            # TODO: truncate message as necessary.
            printf '%s\n' "$message"
            : $((linesleft-=1))

            if [ $i = $selection ]; then
                gds="$(git diff --stat "$commit~" "$commit" --)"
                if [ $? = 0 ]; then
                    : $((linesleft-=2)) # reserve two lines for present_choices
                    format_stats
                    : $((linesleft+=2)) # ...
                else
                    printf '  \033[91merror:\033[31m failed to run `git diff --stat`\n'
                    : $((linesleft-=1))
                fi
            fi

            [ $linesleft -ge 2 ] || break
        done
        if [ $linesleft -ge 1 ]; then
            printf '\033[%s;0H' $LINES
            linesleft=1
            printf ' \033[33m(\033[97m%s\033[33m/\033[97m%s\033[33m)\033[m ' "$selection" "$choices"
            : $((linesleft-=1))
        fi
        eval "commit=\$choice_$selection" # set $commit to something useful
    }

    handle_input() {
        # globals: $dirty
        # TODO: handle escape codes (especially arrow keys, page up/down)
        # TODO: reset button that checks LINES and COLUMNS again.
        printf '\0338' # restore cursor to prompt position (rc)
        input="$(read_byte)" || return
        if [ "${input%_}" = "$input" ]; then
            # no magic underscore, something went wrong.
            return 1
        else
            input="${input%_}"
        fi
        while [ -n "$input" ]; do
            # replace newlines with spaces for my own sanity.
            # of course, this makes spaces act the same as newlines.
            if [ "${input#$nl}" != "$input" ]; then
                input=" ${input#$nl}"
            fi

            if [ "${input#[! gGjkq]}" != "$input" ]; then
                _seg="${input%%[ gGjkq]*}"
            elif [ "${input# }" != "$input" ]; then
                _seg=' '
                alt_off
                git diff "$commit~" "$commit" -- || exit
                alt_on
                dirty=1
            elif [ "${input#g}" != "$input" ]; then
                _seg=g
                [ $selection = 1 ] || dirty=1
                selection=1
            elif [ "${input#G}" != "$input" ]; then
                _seg=G
                [ $selection = $choices ] || dirty=1
                selection=$choices
            elif [ "${input#j}" != "$input" ]; then
                _seg=j
                [ $selection = $choices ] || dirty=1
                [ $((selection+=1)) -le $choices ] || selection=$choices
            elif [ "${input#k}" != "$input" ]; then
                _seg=k
                [ $selection = 1 ] || dirty=1
                [ $((selection-=1)) -ge 1 ] || selection=1
            elif [ "${input#q}" != "$input" ]; then
                _seg=q
                dirty=0 # stop redrawing and just get outta here
                return 1
            else
                break # unreachable
            fi
            input="${input#$_seg}"
        done
        unset _seg
    }

    trap glug_exit INT EXIT && glug_enter

    # TODO: invoke git with --no-config or whatever?
    # TODO: --decorate=full, and color it.
    logs="$(git log --oneline --first-parent -n $limit 2>&1)" || die "$logs"

    parse_logs
    [ $choices -gt 0 ] || { printf '%s: no commits\n' >&2; return 2; }

    present_choices
    dirty=0
    while handle_input; do
        if [ $dirty = 1 ]; then
            printf '\r' # move cursor to start of line (carriage return)
            printf '\033[H' # move cursor to first line
            printf '\033[J' # clear the rest of the screen
            present_choices
            dirty=0
        fi
    done

) 1<>/dev/tty <&1 # ensure this interacts with a terminal instead of a pipe

[ -n "${preload+-}" ] || glug "$@"