image-density-fixer

#!/usr/bin/env bash
# Program to fix image density via user input of real image demensions
# 林博仁 © 2018

## Makes debuggers' life easier - Unofficial Bash Strict Mode
## BASHDOC: Shell Builtin Commands - Modifying Shell Behavior - The Set Builtin
set \
    -o errexit \
    -o errtrace \
    -o nounset \
    -o pipefail

## Runtime Dependencies Checking
declare\
    runtime_dependency_checking_result=still-pass\
    required_software

for required_command in \
    basename \
    bc \
    dirname \
    identify \
    mogrify \
    realpath \
    sed; do
    if ! command -v "${required_command}" &>/dev/null; then
        runtime_dependency_checking_result=fail

        case "${required_command}" in
            basename \
            |dirname \
            |realpath)
                required_software='GNU Coreutils'
                ;;
            bc)
                required_software='GNU bc'
                ;;
            identify \
            |mogrify)
                required_software='ImageMagick'
                ;;
            sed)
                required_software='GNU Sed'
                ;;
            *)
                required_software="${required_command}"
                ;;
        esac

        printf -- \
            'Error: This program requires "%s" to be installed and its executables in the executable searching paths.\n' \
            "${required_software}" \
            1>&2
        unset required_software
    fi
done; unset required_command required_software

if [ "${runtime_dependency_checking_result}" = fail ]; then
    printf -- \
        'Error: Runtime dependency checking fail, the progrom cannot continue.\n' \
        1>&2
    exit 1
fi; unset runtime_dependency_checking_result

## Non-overridable Primitive Variables
## BASHDOC: Shell Variables » Bash Variables
## BASHDOC: Basic Shell Features » Shell Parameters » Special Parameters
if [ -v 'BASH_SOURCE[0]' ]; then
    RUNTIME_EXECUTABLE_PATH="$(realpath --strip "${BASH_SOURCE[0]}")"
    RUNTIME_EXECUTABLE_FILENAME="$(basename "${RUNTIME_EXECUTABLE_PATH}")"
    RUNTIME_EXECUTABLE_NAME="${RUNTIME_EXECUTABLE_FILENAME%.*}"
    RUNTIME_EXECUTABLE_DIRECTORY="$(dirname "${RUNTIME_EXECUTABLE_PATH}")"
    RUNTIME_COMMANDLINE_BASECOMMAND="${0}"
    # We intentionally leaves these variables for script developers
    # shellcheck disable=SC2034
    declare -r \
        RUNTIME_EXECUTABLE_PATH \
        RUNTIME_EXECUTABLE_FILENAME \
        RUNTIME_EXECUTABLE_NAME \
        RUNTIME_EXECUTABLE_DIRECTORY \
        RUNTIME_COMMANDLINE_BASECOMMAND
fi
declare -ar RUNTIME_COMMANDLINE_ARGUMENTS=("${@}")

## init function: entrypoint of main program
## This function is called near the end of the file,
## with the script's command-line parameters as arguments
init(){
    local -i \
        width_in_px \
        height_in_px

    local \
        width_in_cm \
        height_in_cm \
        width_in_inch \
        height_in_inch \
        horizontal_dpi \
        vertical_dpi \
        is_dry_run=false

    local \
        image_file

    if ! \
        process_commandline_arguments \
            width_in_cm \
            height_in_cm \
            image_file \
            is_dry_run; then
        printf -- \
            'Error: Invalid command-line parameters.\n' \
            1>&2

        printf '\n' # separate error message and help message
        print_help
        exit 1
    fi

    width_in_px="$(
        identify \
            -format %w \
            "${image_file}"
    )"
    height_in_px="$(
        identify \
            -format %h \
            "${image_file}"
    )"

    # 1 inch = 2.54 centimeters
    # https://en.wikipedia.org/wiki/Inch
    width_in_inch="$(
        printf --\
            "%s / 2.54\\n" \
            "${width_in_cm}" \
            | bc --mathlib
    )"
    height_in_inch="$(
        printf --\
            "%s / 2.54\\n" \
            "${height_in_cm}" \
            | bc --mathlib
    )"

    horizontal_dpi="$(
        printf --\
            "%s / %s\\n" \
            "${width_in_px}" \
            "${width_in_inch}" \
            | bc --mathlib \
            | sed 's/\..*$//' # Remove fraction part of decimal
    )"
    vertical_dpi="$(
        printf --\
            "%s / %s\\n" \
            "${height_in_px}" \
            "${height_in_inch}" \
            | bc --mathlib \
            | sed 's/\..*$//' # Remove fraction part of decimal
    )"

    if test "${is_dry_run}" != false; then
        printf -- \
            'The resulting horizontal dpi: %s\n' \
            "${horizontal_dpi}"
        printf -- \
            'The resulting vertical dpi: %s\n' \
            "${vertical_dpi}"
        printf -- \
            'The resulting mogrify command:\n    '
        echo mogrify \
            -density "${horizontal_dpi}"x"${vertical_dpi}" \
            "${image_file}"
    else
        mogrify \
            -density "${horizontal_dpi}"x"${vertical_dpi}" \
            "${image_file}"
    fi

    exit 0
}; declare -fr init

print_help(){
    # Backticks in help message is Markdown's <code> markup
    # shellcheck disable=SC2016
    {
        printf '# Help Information for %s #\n' \
            "${RUNTIME_COMMANDLINE_BASECOMMAND}"
        printf '## SYNOPSIS ##\n'
        printf '* `"%s" _command-line_options_ _real_width_in_centimeters_ _real_height_in_centimeters_ _image_file_`\n\n' \
            "${RUNTIME_COMMANDLINE_BASECOMMAND}"

        printf '## COMMAND-LINE OPTIONS ##\n'
        printf '### `-d` / `--debug` ###\n'
        printf 'Enable script debugging\n\n'

        printf '### `--dry-run` ###\n'
        printf "Don't actually apply modification to the image, just print what we gonna do.\\n\\n"

        printf '### `-h` / `--help` ###\n'
        printf 'Print this message\n\n'

        printf '### `-u` / `--usage` ###\n'
        printf 'Print simple usage information\n\n'
    }
    return 0
}; declare -fr print_help;

print_usage(){
    printf -- \
        'Usage: image-density-fixer _command-line_options_ _real_width_in_centimeters_ _real_height_in_centimeters_ _image_file_\n'
}

process_commandline_arguments() {
    local -n \
        width_in_cm_ref \
        height_in_cm_ref \
        image_file_ref \
        is_dry_run_ref

    width_in_cm_ref="${1}"; shift 1
    height_in_cm_ref="${1}"; shift 1
    image_file_ref="${1}"; shift 1
    is_dry_run_ref="${1}"; shift 1

    if [ "${#RUNTIME_COMMANDLINE_ARGUMENTS[@]}" -eq 0 ]; then
        print_help
        exit 0
    fi

    # Modifyable parameters for parsing by consuming
    local -a parameters=("${RUNTIME_COMMANDLINE_ARGUMENTS[@]}")

    # Normally we won't want debug traces to appear during parameter parsing, so we add this flag and defer its activation till returning
    local enable_debug=false

    while true; do
        if [ "${#parameters[@]}" -eq 0 ]; then
            break
        else
            case "${parameters[0]}" in
                --debug \
                |-d)
                    enable_debug=true
                    ;;
                --dry-run)
                    # Whitelist usage of namerefs indirection
                    # shellcheck disable=SC2034
                    is_dry_run_ref=true
                    ;;
                --help \
                |-h)
                    print_help
                    exit 0
                    ;;
                --usage \
                |-u)
                    print_usage
                    exit 0
                    ;;
                *)
                    if [ "${#parameters[@]}" -ne 3 ]; then
                        printf -- \
                            '%s: Error: Invalid command-line argument count!\n' \
                            "${FUNCNAME[0]}" \
                            >&2
                        return 1
                    else
                        # Whitelist usage of namerefs indirections
                        # shellcheck disable=SC2034
                        {
                            width_in_cm_ref="${parameters[0]}"
                            height_in_cm_ref="${parameters[1]}"
                            image_file_ref="${parameters[2]}"
                        }
                        unset \
                            'parameters[0]' \
                            'parameters[1]' \
                            'parameters[2]'
                        if [ "${#parameters[@]}" -ne 0 ]; then
                            parameters=("${parameters[@]}")
                        fi
                    fi
                    ;;
            esac
            # shift array by 1 = unset 1st then repack
            unset 'parameters[0]'
            if [ "${#parameters[@]}" -ne 0 ]; then
                parameters=("${parameters[@]}")
            fi
        fi
    done

    if ! test -v width_in_cm_ref \
        || ! test -v height_in_cm_ref \
        || ! test -v image_file_ref; then
        print_help
        exit 0
    fi

    if [ "${enable_debug}" = true ]; then
        trap 'trap_return "${FUNCNAME[0]}"' RETURN
        set -o xtrace
    fi
    return 0
}; declare -fr process_commandline_arguments

## Traps: Functions that are triggered when certain condition occurred
## Shell Builtin Commands » Bourne Shell Builtins » trap
trap_errexit(){
    printf \
        'An error occurred and the script is prematurely aborted\n' \
        1>&2
    return 0
}; declare -fr trap_errexit; trap trap_errexit ERR

trap_exit(){
    return 0
}; declare -fr trap_exit; trap trap_exit EXIT

trap_return(){
    local returning_function="${1}"

    printf \
        'DEBUG: %s: returning from %s\n' \
        "${FUNCNAME[0]}" \
        "${returning_function}" \
        1>&2
}; declare -fr trap_return

trap_interrupt(){
    printf '\n' # Separate previous output
    printf \
        'Recieved SIGINT, script is interrupted.' \
        1>&2
    return 1
}; declare -fr trap_interrupt; trap trap_interrupt INT

init "${@}"

## This script is based on the GNU Bash Shell Script Template project
## https://github.com/Lin-Buo-Ren/GNU-Bash-Shell-Script-Template
## and is based on the following version:
## GNU_BASH_SHELL_SCRIPT_TEMPLATE_VERSION="v3.2.0-1-g26c6eba"
## You may rebase your script to incorporate new features and fixes from the template