#!/usr/bin/env bash
#
# synology-prompt.sh
#
# Universal Powerline-style SysAdmin prompt for Synology DSM.
#
# Features:
#   - No external prompt framework required
#   - Nerd Font / Powerline icons
#   - User and hostname
#   - Current working directory
#   - Git branch and repository state
#   - Current filesystem usage
#   - Indonesian date
#   - Clock
#   - Previous command exit status
#   - Automatic root warning palette
#
# Requirements:
#   - Bash
#   - Standard DSM utilities: date, df, awk
#
# Optional:
#   - Git
#
# Nerd Font only needs to be installed on the SSH client/terminal.
#
# This file is intended to be installed as:
#
#   /etc/synology-prompt.sh
#
# and sourced from the user's interactive Bash environment.
#


# ==============================================================================
# GUARD
# ==============================================================================

# Interactive shell only.
case "$-" in
    *i*) ;;
      *) return 0 2>/dev/null || exit 0 ;;
esac

# Bash is required.
if [ -z "${BASH_VERSION:-}" ]; then
    return 0 2>/dev/null || exit 0
fi

# Prevent loading more than once in the same shell.
if [ "${SYNO_PROMPT_LOADED:-0}" = "1" ]; then
    return 0
fi

SYNO_PROMPT_LOADED=1


# ==============================================================================
# CONFIGURATION
# ==============================================================================

# Maximum displayed PWD length.
SYNO_MAX_PWD_LENGTH=35

# Show filesystem usage segment.
SYNO_SHOW_DISK=1

# Show Git segment when inside a Git repository.
SYNO_SHOW_GIT=1

# Show previous command exit code when non-zero.
SYNO_SHOW_EXIT_CODE=1


# ==============================================================================
# NERD FONT ICONS
#
# Fonts are rendered by the SSH client.
# Nothing needs to be installed on DSM.
# ==============================================================================

SYNO_ICON_USER=$'\uf007'       # 
SYNO_ICON_HOST=$'\uf233'       # 
SYNO_ICON_FOLDER=$'\uf07b'     # 
SYNO_ICON_GIT=$'\ue725'        # 
SYNO_ICON_DISK=$'\uf0a0'       # 
SYNO_ICON_CALENDAR=$'\uf073'   # 
SYNO_ICON_CLOCK=$'\uf017'      # 

SYNO_SEPARATOR=$'\ue0b0'       # 


# ==============================================================================
# INDONESIAN DATE
#
# Deliberately does not depend on id_ID locale being installed on DSM.
# ==============================================================================

_syno_day()
{
    case "$(date +%u)" in
        1) printf 'Senin' ;;
        2) printf 'Selasa' ;;
        3) printf 'Rabu' ;;
        4) printf 'Kamis' ;;
        5) printf 'Jumat' ;;
        6) printf 'Sabtu' ;;
        7) printf 'Minggu' ;;
    esac
}


_syno_month()
{
    case "$(date +%m)" in
        01) printf 'Januari' ;;
        02) printf 'Februari' ;;
        03) printf 'Maret' ;;
        04) printf 'April' ;;
        05) printf 'Mei' ;;
        06) printf 'Juni' ;;
        07) printf 'Juli' ;;
        08) printf 'Agustus' ;;
        09) printf 'September' ;;
        10) printf 'Oktober' ;;
        11) printf 'November' ;;
        12) printf 'Desember' ;;
    esac
}


_syno_date()
{
    printf '%s, %s %s %s' \
        "$(_syno_day)" \
        "$(date +%d)" \
        "$(_syno_month)" \
        "$(date +%Y)"
}


# ==============================================================================
# WORKING DIRECTORY
# ==============================================================================

_syno_pwd()
{
    local p="$PWD"

    # Replace the current user's home directory with ~.
    case "$p" in
        "$HOME")
            p="~"
            ;;
        "$HOME"/*)
            p="~${p#$HOME}"
            ;;
    esac

    # Shorten very long paths.
    if [ "${#p}" -gt "$SYNO_MAX_PWD_LENGTH" ]; then
        p="…${p: -$((SYNO_MAX_PWD_LENGTH - 1))}"
    fi

    printf '%s' "$p"
}


# ==============================================================================
# GIT STATUS
#
# Symbols:
#
#   clean                 no symbol
#   dirty                 ◔
#   ahead                 ▲
#   behind                ▼
#   diverged              ◆
#   dirty + ahead         ◔ △
#   dirty + behind        ◔ ▽
#   dirty + diverged      ◔ ◇
#   stash                 N🗎
#
# The segment automatically disappears outside a Git repository.
# ==============================================================================

_syno_git()
{
    [ "$SYNO_SHOW_GIT" = "1" ] || return

    command -v git >/dev/null 2>&1 || return

    git rev-parse --is-inside-work-tree >/dev/null 2>&1 || return

    local branch
    local status
    local first_line

    local dirty=0
    local ahead=0
    local behind=0
    local stash=0

    local symbol=""

    branch="$(git symbolic-ref --quiet --short HEAD 2>/dev/null)"

    # Detached HEAD fallback.
    if [ -z "$branch" ]; then
        branch="$(git rev-parse --short HEAD 2>/dev/null)"
    fi

    [ -n "$branch" ] || return

    status="$(git status --porcelain -b 2>/dev/null)"
    first_line="$(printf '%s\n' "$status" | head -n 1)"

    # Lines after the ## branch line indicate working-tree/index changes.
    if printf '%s\n' "$status" | tail -n +2 | grep -q .; then
        dirty=1
    fi

    case "$first_line" in
        *ahead*)
            ahead=1
            ;;
    esac

    case "$first_line" in
        *behind*)
            behind=1
            ;;
    esac

    if [ "$dirty" -eq 1 ] &&
       [ "$ahead" -eq 1 ] &&
       [ "$behind" -eq 1 ]; then

        symbol=" ◔ ◇"

    elif [ "$dirty" -eq 1 ] &&
         [ "$ahead" -eq 1 ]; then

        symbol=" ◔ △"

    elif [ "$dirty" -eq 1 ] &&
         [ "$behind" -eq 1 ]; then

        symbol=" ◔ ▽"

    elif [ "$dirty" -eq 1 ]; then

        symbol=" ◔"

    elif [ "$ahead" -eq 1 ] &&
         [ "$behind" -eq 1 ]; then

        symbol=" ◆"

    elif [ "$ahead" -eq 1 ]; then

        symbol=" ▲"

    elif [ "$behind" -eq 1 ]; then

        symbol=" ▼"
    fi

    stash="$(git stash list 2>/dev/null | wc -l | tr -d ' ')"

    printf '%s %s%s' \
        "$SYNO_ICON_GIT" \
        "$branch" \
        "$symbol"

    if [ "${stash:-0}" -gt 0 ] 2>/dev/null; then
        printf ' %s🗎' "$stash"
    fi
}


# ==============================================================================
# FILESYSTEM USAGE
#
# Displays usage of the filesystem containing the current working directory.
#
# Example:
#
#   /volume1/docker/...  -> volume1 usage
#   /tmp/...             -> filesystem containing /tmp
#   /root                -> root filesystem usage
# ==============================================================================

_syno_disk_percent()
{
    [ "$SYNO_SHOW_DISK" = "1" ] || return

    local usage

    usage="$(
        df -P "$PWD" 2>/dev/null |
        awk 'NR==2 {gsub(/%/, "", $5); print $5}'
    )"

    [ -n "$usage" ] || return

    printf '%s' "$usage"
}


# ==============================================================================
# POWERLINE SEGMENT RENDERER
#
# Escape sequences are stored directly in PS1.
#
# \[ and \] tell Bash that ANSI escape sequences consume zero terminal columns.
# This keeps cursor positioning and line editing correct.
# ==============================================================================

_syno_add_segment()
{
    local text="$1"
    local fg="$2"
    local bg="$3"
    local next_bg="$4"

    PS1+="\[\e[1;38;5;${fg};48;5;${bg}m\]"
    PS1+=" ${text} "

    # Arrow:
    # foreground = current background
    # background = next segment background
    PS1+="\[\e[0;38;5;${bg};48;5;${next_bg}m\]"
    PS1+="${SYNO_SEPARATOR}"
}


_syno_add_last_segment()
{
    local text="$1"
    local fg="$2"
    local bg="$3"

    PS1+="\[\e[1;38;5;${fg};48;5;${bg}m\]"
    PS1+=" ${text} "

    # Final arrow into terminal default background.
    PS1+="\[\e[0;38;5;${bg};49m\]"
    PS1+="${SYNO_SEPARATOR}"

    PS1+="\[\e[0m\]"
}


# ==============================================================================
# PROMPT BUILDER
# ==============================================================================

_syno_prompt()
{
    # IMPORTANT:
    # This must be the first command so $? still contains the exit status
    # of the user's previous command.
    local exit_code=$?

    local user_text
    local host_text
    local pwd_text
    local git_text=""
    local disk_text=""
    local disk_percent=""
    local date_text
    local clock_text

    user_text="${SYNO_ICON_USER} ${USER:-$(id -un)}"
    host_text="${SYNO_ICON_HOST} ${HOSTNAME:-$(hostname)}"
    pwd_text="${SYNO_ICON_FOLDER} $(_syno_pwd)"

    git_text="$(_syno_git)"

    disk_percent="$(_syno_disk_percent)"

    if [ -n "$disk_percent" ]; then
        disk_text="${SYNO_ICON_DISK} ${disk_percent}%"
    fi

    date_text="${SYNO_ICON_CALENDAR} $(_syno_date)"
    clock_text="${SYNO_ICON_CLOCK} $(date +%H:%M:%S)"


    # ==========================================================================
    # NORMAL USER PALETTE
    # ==========================================================================

    local user_fg=16
    local user_bg=46

    local host_fg=231
    local host_bg=33

    local pwd_fg=238
    local pwd_bg=255

    local git_fg=250
    local git_bg=238

    local disk_fg=231
    local disk_bg=31

    local date_fg=231
    local date_bg=135

    local clock_fg=231
    local clock_bg=16

    local input_fg=45


    # ==========================================================================
    # ROOT WARNING PALETTE
    #
    # Root is deliberately visually obvious.
    # ==========================================================================

    if [ "$(id -u)" -eq 0 ]; then

        user_fg=231
        user_bg=196

        host_fg=231
        host_bg=203

        pwd_fg=16
        pwd_bg=226

        git_fg=231
        git_bg=196

        disk_fg=16
        disk_bg=214

        date_fg=231
        date_bg=203

        clock_fg=231
        clock_bg=196

        input_fg=203
    fi


    # ==========================================================================
    # BUILD FIRST LINE
    # ==========================================================================

    PS1="\n╭"

    _syno_add_segment \
        "$user_text" \
        "$user_fg" \
        "$user_bg" \
        "$host_bg"

    _syno_add_segment \
        "$host_text" \
        "$host_fg" \
        "$host_bg" \
        "$pwd_bg"


    # --------------------------------------------------------------------------
    # PWD -> optional Git -> optional Disk -> Date -> Clock
    #
    # We need to determine the background of the segment following PWD.
    # --------------------------------------------------------------------------

    if [ -n "$git_text" ]; then

        _syno_add_segment \
            "$pwd_text" \
            "$pwd_fg" \
            "$pwd_bg" \
            "$git_bg"

        if [ -n "$disk_text" ]; then

            _syno_add_segment \
                "$git_text" \
                "$git_fg" \
                "$git_bg" \
                "$disk_bg"

        else

            _syno_add_segment \
                "$git_text" \
                "$git_fg" \
                "$git_bg" \
                "$date_bg"
        fi

    else

        if [ -n "$disk_text" ]; then

            _syno_add_segment \
                "$pwd_text" \
                "$pwd_fg" \
                "$pwd_bg" \
                "$disk_bg"

        else

            _syno_add_segment \
                "$pwd_text" \
                "$pwd_fg" \
                "$pwd_bg" \
                "$date_bg"
        fi
    fi


    if [ -n "$disk_text" ]; then

        _syno_add_segment \
            "$disk_text" \
            "$disk_fg" \
            "$disk_bg" \
            "$date_bg"
    fi


    _syno_add_segment \
        "$date_text" \
        "$date_fg" \
        "$date_bg" \
        "$clock_bg"


    _syno_add_last_segment \
        "$clock_text" \
        "$clock_fg" \
        "$clock_bg"


    # ==========================================================================
    # BUILD SECOND LINE
    # ==========================================================================

    local symbol='$'

    if [ "$(id -u)" -eq 0 ]; then
        symbol='#'
    fi

    PS1+="\n╰> "


    # Previous command failed.
    if [ "$SYNO_SHOW_EXIT_CODE" = "1" ] &&
       [ "$exit_code" -ne 0 ]; then

        PS1+="\[\e[1;38;5;196m\]"
        PS1+="✘ ${exit_code} "
        PS1+="\[\e[0m\]"
    fi


    PS1+="\[\e[1;38;5;${input_fg}m\]"
    PS1+="${symbol} "
    PS1+="\[\e[0m\]"
}


# ==============================================================================
# ACTIVATE PROMPT
# ==============================================================================

PROMPT_COMMAND=_syno_prompt


# ==============================================================================
# OPTIONAL CONVENIENCE ALIASES
#
# Only simple commands known to work on DSM are used.
# ==============================================================================

alias ll='ls -lah'
alias la='ls -A'
alias l='ls -CF'

alias dfh='df -h'
alias duh='du -h'

if command -v git >/dev/null 2>&1; then
    alias gs='git status'
    alias gl='git log --oneline --decorate --graph -15'
fi


# ==============================================================================
# CLEAN TERMINAL FORMATTING ON EXIT
# ==============================================================================

trap 'printf "\033[0m"' EXIT