overload

#!/usr/bin/env bash

LIB_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"


overload:call()
{
    name=$1
    shift


    overloads="overloads_$name"
    eval 'local offset=${#'"$overloads"'[@]}'
    while true
    do
        ((offset--))
        eval 'local callable=${'"$overloads"'[$offset]}'
        if (( $offset == 0 ))
        then
            break
        fi

        ((offset--))
        eval 'local argc=${'"$overloads"'[$offset]}'
        
        if (( $argc > 0 ))
        then
            ((offset-=$argc))
            eval 'local argv=( "${'"$overloads"'[@]:$offset:$argc}" )'
            for arg in `seq 1 $argc`
            do
                val=${argv[$(( $arg - 1 ))]}
                if [[ "$val" != "${!arg}" ]] && [[ "$val" != "*" ]]
                then
                    callable=
                    break
                fi
            done
        fi

        if [ -n "$callable" ]
        then
            break
        fi
    done

    if [ -n "$callable" ]
    then
        eval 'parent() { _'"$name"' "$@"; }'
        eval 'call() { '"$callable"'; }'
        call "$@"
        unset -f parent
    else
        eval '_'"$name"' "$@"'
    fi


    eval 'extensions=("${extensions_'"$name"'[@]}")'
    for extension in "${extensions[@]}"
    do
        eval 'call() { '"$extension"'; }'
        call "$@"
    done
}

overload:init()
{
    name="$1"

    name_source="$(type $name)"
    name_source_lines="$(echo "$name_source" | wc -l)"
    name_source="$(echo "$name_source" | head -n $(($name_source_lines - 1)))"
    name_source="$(echo "$name_source" | tail -n $(($name_source_lines - 4)))"
    eval "_$name() { $name_source; }"
    eval "$name() { overload:call $name \"\$@\"; }"
    eval 'overloads_'"$name"'=("")'
    eval 'extensions_'"$name"'=()'
}

overload:add()
{
    if [[ "$1" == '-e' ]]
    then
        shift

        extending=true
    else
        extending=false
    fi

    name="$1"
    shift

    if $extending
    then
        callable="$1"
        eval 'extensions_'"$name"'+=( "$callable" )'
    else
        # The 'filter' arguments need to be saved in reverse
        argv=()
        while (( $# > 1 ))
        do
            argv=( "${argv[@]}" "$1" )
            shift
        done

        callable="$1"
        eval 'overloads_'"$name"'+=( "${argv[@]}" ${#argv[@]} "$callable" )'
    fi
}

##Overload
#
# Usage:
# overload name [val [val [...]]] callable
#   name
#     Name of function to be overloaded.
#   val
#     Values that have to match the arguments of the call
#     in order for callable to be called.
#   callable
#     A callable expression string that will be expanded
#     upon call.
#
# Example:
#   key_pressed(){echo "key:  $1";}
#   overload key_pressed "h" 'echo "before"; parent "$@"; echo "after"'
#   overload key_pressed "q" exit
#   key_pressed a
#   > key: a
#   key_pressed h
#   > before
#   > key: h
#   > after
#   key_pressed q
overload()
{
    if [[ "$1" == '-e' ]]
    then
        shift

        local extending=true
    else
        local extending=false
    fi

    name="$1"

    if (( $# <= 1 ))
    then
        overload:list "$name"
    else
        count="$(eval 'printf %i ${#overloads_'"$name"'[@]}')"
        if (( $count == 0 ))
        then
            overload:init $name
        fi
        
        if $extending
        then
            overload:add -e "$@"
        else
            overload:add "$@"
        fi
    fi
}