# Emacs?  -*- shell-script -*- please.

# Environment variables:
#
# PS1_SHOWHOSTNAME
#       'auto' (default):       Only show hostname over SSH
#       'yes':                  Always show hostname
#       anything else:          Never show hostname


__show-hostname ()
{
    case ${PS1_SHOWHOSTNAME} in
        (''|auto)
            test "${SSH_CONNECTION}";;
        (yes)
            true;;
        (*)
            false;;
    esac
}

__have-gitprompt ()
{
    test -f /usr/lib/git-core/git-sh-prompt
}

__set-title ()
{
    local title=${USER}
    __show-hostname && title+=@${HOSTNAME}
    title+=:
    title+=${PWD/~/\~}

    # Cf. console_codes(4):
    #
    #   ESC ] 2 ; txt ST        Set window title to txt.
    #
    # ST is a "string terminator", either "ESC \" or "BEL".

    printf $'\E]2;%s\a' "${title}"
}

# Bash relies on \[ \] to distinguish non-printing characters in prompts.
__start-nonprinting ()
{
    test ${BUILDING_PS} && printf '\['
}

__end-nonprinting ()
{
    test ${BUILDING_PS} && printf '\]'
}

__fontify ()
{
    local -r text=$1
    shift

    local -Ar codes=(
        [bold]=1
        [dim]=2
        [reverse]=7
        [red]=31
        [green]=32
        [blue]=34
    )

    local -a params=()
    local c
    for c
    do
        params+=(${codes[${c}]})
    done

    local params_seq
    IFS=';' eval 'params_seq="${params[*]}"'

    __start-nonprinting
    printf $'\E[%sm' "${params_seq}"
    __end-nonprinting

    printf %s "${text}"

    __start-nonprinting
    printf $'\E[0m'
    __end-nonprinting
}

__current-column ()
{
    # Cf. console_codes(4) § ECMA-48 Status Report Commands.

    local position
    read -sdR -p$'\E[6n' position

    local -r pattern='\[[0-9]+;([0-9]+)'

    [[ ${position} =~ ${pattern} ]] || {
        echo 0
        return
    }
    echo ${BASH_REMATCH[1]}
}

__signal-no-newline ()
{
    __fontify ∅ bold red
    echo
}

__draw-rule ()
{
    local -ir pos=$(__current-column)
    local -ir rule_len=$((COLUMNS-pos))

    local rule
    # Hey Future Me 👋 Breaking this down:
    # -v rule       "put this in LINE, do not write to stdout"
    # "%…s"         "pad string…"
    #  -            " … with spaces…"
    #  *            " … with length given by next argument"
    # ${rule_len}   (padding length)
    # ∅             (psych! no arg for %s, default to null string)
    printf -v rule '%-*s' ${rule_len}
    rule=${rule// /─}

    # Flush line to avoid future text being shoved offscreen when autowrap
    # is off.
    rule+=$'\n'

    __fontify "${rule}" "$@"
}

__write-context ()
{
    __fontify '\u' green

    __show-hostname && {
        __fontify @ dim
        __fontify '\H' bold green
    }

    printf ' '
    __fontify '\w' bold blue

    test "${PS1_SHOWGITSTATUS}" && {
        printf ' '
        __fontify "$(__git_ps1 '(%s)')" red
    }
}

__smart-term/set-ps1 ()
{
    BUILDING_PS=t

    PS1="$(__write-context)\n$(__fontify '\$' dim) "

    unset BUILDING_PS
}

__smart-term/refresh ()
{
    local -ir rc=$?

    __set-title

    local -ir pos=$(__current-column)
    ((pos != 1)) && __signal-no-newline

    if ((rc))
    then
        __fontify "${rc} " bold red
        __draw-rule dim red
    else
        __draw-rule dim
    fi

    __smart-term/set-ps1
}

__smart-term/init ()
{
    # Prompts.

    __have-gitprompt && {
        . /usr/lib/git-core/git-sh-prompt
        GIT_PS1_SHOWDIRTYSTATE=t
        GIT_PS1_SHOWUPSTREAM=auto

        PS1_SHOWGITSTATUS=t
    }

    PROMPT_COMMAND=__smart-term/refresh

    PS2=$(
        BUILDING_PS=t
        __fontify '… ' dim
    )

    # Bindings.

    bind -f ~/.bash_inputrc

    # Unset the TTY's "stop" char, so that readline receives C-s.
    tty -s && stty stop ''
}

__dumb-term/set-ps1 ()
{
    local -ir rc=$?

    BUILDING_PS=t

    PS1=''
    ((rc)) && PS1+=$(__fontify "${rc} " bold red)
    PS1+='\W\$ '

    unset BUILDING_PS
}

__dumb-term/init ()
{
    PROMPT_COMMAND=__dumb-term/set-ps1
}


case "${TERM}"
in
    dumb)   __dumb-term/init ;;
    *)      __smart-term/init ;;
esac