#!/usr/bin/env bash
# (c) GPL nai https://git.monade.li/nai/dotfiles
# templum - a bash template engine
# edited by neeasade to assume {{value}} -> {{$value}}

delim_expression=('{{' '}}')
delim_block=('{{{' '}}}')

while getopts :s:o: o; do
    case $o in
        s) source "$OPTARG" || exit 1;;
        o) exec > "$OPTARG" || exit 1;;
        *) echo "usage: ${0##*/} [-s <source>]... [-o <output>] [<input>]" >&2; exit 1;;
    esac
done
shift "$(( OPTIND - 1 ))"

if (( $# )); then
    exec < "$1" || exit 1
fi

while IFS= read -r line; do
    while
        type=
        if [[ $line == !(*"${delim_expression[0]}"*)"${delim_block[0]}"* ]]; then
            type=block
        elif [[ $line == *"${delim_expression[0]}"* ]]; then
            type=expression
        fi
        [[ $type ]]
    do
        declare -n delim=delim_$type
        printf '%s' "${line%%"${delim[0]}"*}"
        code=
        code_line=${line#*"${delim[0]}"}
        while [[ $code_line != *"${delim[1]}"* ]]; do
            code+=$code_line$'\n'
            IFS= read -r code_line || exit
        done
        code+=${code_line%%"${delim[1]}"*}
        line=${code_line#*"${delim[1]}"}
        if [[ $type == block ]]; then
            eval "$code"
        else
            eval "printf '%s' \"\$$code\""
        fi
    done
    printf '%s\n' "$line"
done