#!/usr/bin/env sh
#
# by Siddharth Dushantha
#

VERSION="1.0.0"

# Everything related to 'tmpsms' will be stored in this directory. Once the
# computer get restarted, this directory gets deleted.
TMPSMS_DIR="/tmp/tmpsms"

# The phone number that the user has selected gets stored in this file so that
# the do not have reselect at ever run.
TMPSMS_PHONE_NUMBER="$TMPSMS_DIR/phonenumber.txt"

# 'fzf' is used to allow the user to select a phone number. This variable
# stores extra arguments which the user might to provide, so that 'fzf'
# behaves to their liking.
FZF_ARGUMENTS=""

# The temporary SMS service is provided by Upmasked
API="https://upmasked.com"

usage(){
    # Using 'cat << EOF' we can easily output a multiline text. This is much
    # better than using 'echo' for each line or using '\n' to create a new line.
    cat <<EOF
tmpsms [--count <count>]
tmpsms init [--fzf <arguments>]
tmpsms -h | --version

When called with no options or commands, tmpsms lists
the 3 newest messages.

Options
-h, --help     Show this help message
-c, --count    Only show the <count> newest messages
--version      Show version

Commands
init           Initialize a new phone number by selecting one
               from the available ones using 'fzf'
  --fzf        Extra arguments to use for 'fzf'
EOF
}

print_error(){
    # Print error message
    #
    # The first argument provided to this function will be the error message.
    # Script will exit after printing the error message.
    printf "%s\n" "Error: $1" >&2
    exit 1
}


select_phone_number(){
    # There are 2 ways which this function is called in this script.
    # [1] The user wants to initilize a new phone number by running 'tmpsms init'
    # [2] The user runs 'tmpsms' to check for new messages, but $TMPSMS_PHONE_NUMBER
    #     does't exist. Therefore they have to select phone number before we can 
    #     show them the messages.
    #
    # When the function 'select_phone_number()' is called with the argument 'true'
    # that means this function was called becaues the user ran 'tmpsms init'
    #
    # We need this variable so we can know whether or not we need to show the user
    # the phone number they have selected. If they ran 'tmpsms init', then we will
    # show them the phone number they selected. This is so that they can easily
    # copy and paste it to whatever site that needs the phone number.
    EXTERNALLY=${1:-false}
    
    # Fetch the available phone numbers
    DATA=$(curl -s "$API/api/sms/numbers")

    # Using 'jq' we are able to get the length of the JSON data retreived from
    # API. The length indicates the the total number of phone numbers available.
    DATA_LENGTH=$(printf %s "$DATA" | jq length)

    # This is where we store the phone numbers which then gets shown to the user
    # through 'fzf' so that they can select one.
    PHONE_NUMBERS=""

    index=1
    while [ $index -le "$DATA_LENGTH" ]; do
        # Since arrays in JSON data start at 0, we must subtract
        # the value of $index by 1 so that we dont miss one of the
        # phone numbers in the array
        PHONE_NUMBER_INFO=$(printf %s "$DATA" | jq -r ".[$index-1]")
        PHONE_NUMBER=$(printf %s "$PHONE_NUMBER_INFO" | jq -r ".number")
        COUNTRY_CODE=$(printf %s "$PHONE_NUMBER_INFO" | jq -r ".country")

        PHONE_NUMBERS="$PHONE_NUMBERS$COUNTRY_CODE +$PHONE_NUMBER\n"
        index=$((index+1))
    done
    
    # By default we use 'fzf' without any arguments in order to display the
    # phone numbers they can use. If the '--fzf' argument is passed along with
    # 'fzf' arguments, 'tmpsms' will make sure to use them.
    FZF_COMMAND="fzf"
    [ -n "$FZF_ARGUMENTS" ] && FZF_COMMAND="fzf $FZF_ARGUMENTS"

    # If the user did not select a phone number then quit 'tmpsms' as the
    # user might have just wanted to check if there were any new number
    # that they could use.
    SELECTION=$(printf %b "$PHONE_NUMBERS" | $FZF_COMMAND)
    [ -z "$SELECTION" ] && print_error "Phone number was not selected"

    # Store the selected phone number in $TMPSMS_PHONE_NUMBER for later use 
    printf %s "$SELECTION" > "$TMPSMS_PHONE_NUMBER"

    # If the user ran 'tmpsms init', then show them their selection
    [ "$EXTERNALLY" = true ] && printf "%s\n" "$SELECTION"
}

list_messages(){
    # By default, the 3 newest messages are shown. But if the user would like
    # to see more of the messages, they can provide how many they want to see
    # by using the '--count' option.
    COUNT="${1:-3}"

    # The provided value to '--count' must be an interger. We can verify that it is
    # an integer by checking if $COUNT matches the regex.
    REGEX='^[0-9]+$'
    if ! printf %s "$COUNT" | grep -Eq "$REGEX";then
        print_error "'$COUNT' is not an integer"
    fi

    # If /tmp/tmpsms/phonenumber.txt does not exist or is empty that means that
    # the user has not initialized a phone number yet.
    [ ! -s "$TMPSMS_PHONE_NUMBER" ] && print_error "A phone number must be initilzied in order to view the messages"

    # The country code is needed because it gets displayed to the user. It may
    # be useful for the user to know which country the phone number is from
    # so that they dont have to guess by looking at the area code.
    COUNTRY_CODE=$(awk -F" " '{print $1}' < $TMPSMS_PHONE_NUMBER)
    PHONE_NUMBER=$(awk -F"+" '{print $2}' < $TMPSMS_PHONE_NUMBER)
    DATA=$(curl -s "$API/api/sms/messages/$PHONE_NUMBER")

    # Even though we are using the phone numbers that are available on
    # upmasked.com, there is a chance that they might remove one of the numbers.
    # The checking needs to be done in case the phone number that is stored in
    # $TMPSMS_PHONE_NUMBER has been removed.
    if printf %s "$DATA" | grep -Eq "Not Found"; then
        print_error "Looks like the phone number '+$PHONE_NUMBER' no longer exists. Initialize a new one and try again."
    fi

    DATA_LENGTH=$(printf %s "$DATA" | jq length)

    # If the number of messages the user wants to view is greater than the
    # number of messages that are available, then make sure to show
    # all the messages that are available.
    [ "$COUNT" -gt "$DATA_LENGTH" ] && COUNT="$DATA_LENGTH"

    # Show a nice little header before showing the messages
    printf "%s\n\n" "[ Messages for +$PHONE_NUMBER ($COUNTRY_CODE) ]"

    # All the messages get stored in here
    MESSAGES=""

    index=1
    while [ $index -le "$COUNT" ]; do
        # Since arrays in JSON data start at 0, we must subtract
        # the value of $index by 1 so that we dont miss one of the
        # messages in the array
        MESSAGE_DATA=$(printf %s "$DATA" | jq -r ".[$index-1]")
        BODY=$(printf %s "$MESSAGE_DATA" | jq -r ".body" | tr "\n" " ")
        SENDER=$(printf %s "$MESSAGE_DATA" | jq -r ".originator")
        
        # The '||' is used as a divider for 'column'. 'column' will use this
        # divider as a point of reference to create the division. By default
        # 'column' uses a blank space but that would not work in our case as the
        # message could have multiple white spaces and 'column' would
        # split the words that are seperated by white space, in different columns.
        MESSAGES="$MESSAGES$SENDER ||$BODY\n"

        index=$((index+1))
    done

    # Show the messages cleanly
    printf "%b" "$MESSAGES" | column -t -s "||"
}

main(){
    # Iterate the array of dependencies and check if the user has them installed.
    for dependency in jq curl fzf; do
        if ! command -v "$dependency" >/dev/null 2>&1; then
            print_error "Could not find '$dependency', is it installed?"
        fi
    done

    # Create the $TMPSMS_DIR directory and dont throw any errors
    # if it already exists
    mkdir -p "$TMPSMS_DIR"

    # If no arguments are provided just show the messages 
    [ $# -eq 0 ] && list_messages && exit 0

    while [ "$1" ]; do
        case "$1" in
            init)
                case "$2" in
                    --fzf) FZF_ARGUMENTS="$3" && select_phone_number true ;;
                    "") select_phone_number true ;;
                esac ;;
            --help | -h) usage && exit ;;
            --count | -c) list_messages "$2" && shift 2;;
            --version) printf %s "$VERSION" && exit ;;
            -*) print_error "option '$1' does not exist" ;;
            *) print_error "command '$1' does not exist" ;;
        esac
        shift
    done
}

main "$@"