#!/usr/bin/env bash
# ------------------------------------------------------------------------------
# Copyright (c) 2013-2026 Geoffray Levasseur <fatalerrors@geoffray-levasseur.org>
# Protected by the BSD3 license. Please read bellow for details.
#
# * Redistribution and use in source and binary forms,
# * with or without modification, are permitted provided
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# *
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# *   following disclaimer.
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# * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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# * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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# * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
# * OF SUCH DAMAGE.
# ------------------------------------------------------------------------------

# ------------------------------------------------------------------------------
# Generic rain-like engine and presets

_rain_build_colors()
{
    local base_color="$1"
    RAIN_ENGINE_COLORS=()

    case $base_color in
        green)
            for i in {22..28} {34..40} {46..48}; do RAIN_ENGINE_COLORS+=("\e[38;5;${i}m"); done ;;
        blue)
            for i in {17..21} {27..33} {39..45}; do RAIN_ENGINE_COLORS+=("\e[38;5;${i}m"); done ;;
        red)
            for i in {52..52} {88..88} {124..124} {160..160} {196..201}; do RAIN_ENGINE_COLORS+=("\e[38;5;${i}m"); done ;;
        yellow)
            for i in {58..58} {100..100} {142..142} {184..184} {226..229}; do RAIN_ENGINE_COLORS+=("\e[38;5;${i}m"); done ;;
        cyan)
            for i in {30..31} {37..38} {44..45} {50..51}; do RAIN_ENGINE_COLORS+=("\e[38;5;${i}m"); done ;;
        *)
            RAIN_ENGINE_COLORS=("\e[37m" "\e[37;1m")
            for i in {244..255}; do RAIN_ENGINE_COLORS+=("\e[38;5;${i}m"); done ;;
    esac
}

_rain_build_chars()
{
    local mode="$1"
    local charset="$2"
    RAIN_ENGINE_CHARS=()

    case "$mode" in
        matrix)
            case "$charset" in
                ""|binary)
                    RAIN_ENGINE_CHARS=("0" "1")
                    ;;
                kana|kanji)
                    # Half-width katakana set, generally rendered as single-cell glyphs.
                    RAIN_ENGINE_CHARS=("ｱ" "ｲ" "ｳ" "ｴ" "ｵ" "ｶ" "ｷ" "ｸ" "ｹ" "ｺ" "ｻ" "ｼ" "ｽ" "ｾ" "ｿ" "ﾀ" "ﾁ" "ﾂ" "ﾃ" "ﾄ" "ﾅ" "ﾆ" "ﾇ" "ﾈ" "ﾉ" "ﾊ" "ﾋ" "ﾌ" "ﾍ" "ﾎ" "ﾏ" "ﾐ" "ﾑ" "ﾒ" "ﾓ" "ﾔ" "ﾕ" "ﾖ" "ﾗ" "ﾘ" "ﾙ" "ﾚ" "ﾛ" "ﾜ" "ﾝ")
                    ;;
                ascii)
                    RAIN_ENGINE_CHARS=("0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "A" "B" "C" "D" "E" "F")
                    ;;
                *)
                    disp E "Unknown charset: ${charset} (supported: binary, kana, ascii)."
                    return 1
                    ;;
            esac
            ;;
        *)
            RAIN_ENGINE_CHARS=("|" "│" "┃" "┆" "┇" "┊" "┋" "╽" "╿")
            ;;
    esac

    return 0
}

_rain_engine()
{
    local step_duration="$1"
    local base_color="$2"
    local mode="$3"
    local charset="$4"

    command -v tput >/dev/null 2>&1 || {
        disp E "The program 'tput' is required but not installed."
        return 1
    }

    _rain_build_colors "$base_color"
    _rain_build_chars "$mode" "$charset" || return 1

    local rain_colors=("${RAIN_ENGINE_COLORS[@]}")
    local rain_chars=("${RAIN_ENGINE_CHARS[@]}")
    local rain_color_tab=${#rain_colors[@]}
    local rain_tab=${#rain_chars[@]}

    local exit_st=0
    local num_rain_metadata=5
    local term_height=0 term_width=0
    local X=0 Y=0 drop_length=0 rain_drop=0
    local max_rain_width=0 max_rain_height=0
    local new_rain_odd=0 falling_odd=0

    sigwinch()
    {
        term_width=$(tput cols)
        term_height=$(tput lines)

        case "$mode" in
            matrix)
                ((max_rain_width = term_width * term_height / 3))
                ((max_rain_height = term_height < 8 ? 1 : term_height / 6))
                ((new_rain_odd = term_height > 50 ? 100 : term_height * 2))
                ((new_rain_odd = new_rain_odd * 85 / 100))
                ((falling_odd = 100))
                ;;
            *)
                ((max_rain_width = term_width * term_height / 4))
                ((max_rain_height = term_height < 10 ? 1 : term_height / 10))
                ((new_rain_odd = term_height > 50 ? 100 : term_height * 2))
                ((new_rain_odd = new_rain_odd * 75 / 100))
                ((falling_odd = term_height > 25 ? 100 : term_height * 4))
                ((falling_odd = falling_odd * 90 / 100))
                ;;
        esac
    }

    do_exit()
    {
        exit_st=1
    }

    do_render()
    {
        local idx=0 y=0 drop_color=""

        for ((idx = 0; idx < num_rains * num_rain_metadata; idx += num_rain_metadata)); do
            X=${rains[idx]}
            Y=${rains[idx + 1]}
            drop_length=${rains[idx + 4]}
            for ((y = Y; y < Y + drop_length; y++)); do
                ((y < 1 || y > term_height)) && continue
                printf "\e[%d;%dH " "$y" "$X"
            done
        done

        for ((idx = 0; idx < num_rains * num_rain_metadata; idx += num_rain_metadata)); do
            if ((100 * RANDOM / 32768 < falling_odd)); then
                if ((++rains[idx + 1] > term_height)); then
                    rains=("${rains[@]:0:idx}" "${rains[@]:idx+num_rain_metadata:num_rains*num_rain_metadata}")
                    ((num_rains--))
                    continue
                fi
            fi

            X=${rains[idx]}
            Y=${rains[idx + 1]}
            rain_drop=${rains[idx + 2]}
            drop_color=${rains[idx + 3]}
            drop_length=${rains[idx + 4]}

            for ((y = Y; y < Y + drop_length; y++)); do
                ((y < 1 || y > term_height)) && continue
                printf "\e[%d;%dH%s%s" "$y" "$X" "$drop_color" "$rain_drop"
            done
        done
    }

    trap do_exit TERM INT
    trap sigwinch WINCH
    stty -echo
    printf "\e[?25l"
    printf "\e[2J"

    local rains=()
    local num_rains=0
    local ch=""

    sigwinch
    while ((exit_st <= 0)); do
        read -r -n 1 -t "$step_duration" ch
        case "$ch" in
            q|Q)
                do_exit
                ;;
        esac

        if ((num_rains < max_rain_width)) && ((100 * RANDOM / 32768 < new_rain_odd)); then
            rain_drop="${rain_chars[rain_tab * RANDOM / 32768]}"
            drop_color="${rain_colors[rain_color_tab * RANDOM / 32768]}"
            drop_length=$((max_rain_height * RANDOM / 32768 + 1))
            X=$((term_width * RANDOM / 32768 + 1))
            Y=$((1 - drop_length))
            rains=("${rains[@]}" "$X" "$Y" "$rain_drop" "$drop_color" "$drop_length")
            ((num_rains++))
        fi

        do_render
    done

    printf "\e[%d;1H\e[0K" "$term_height"
    printf "\e[?25h"
    stty echo
    trap - TERM INT
    trap - WINCH
}

# ------------------------------------------------------------------------------
# Let the rain fall (current style)
# Usage: rain [OPTIONS]
rain()
{
    _rain_show_usage()
    {
        printf "Usage: rain [OPTIONS]\n"
        printf "Options:\n"
        printf "\t-s, --speed NUM    Set the drop delay in seconds (default: 0.050).\n"
        printf "\t                   Lower values = faster rain.\n"
        printf "\t-c, --color COLOR  Set the color theme (default: white).\n"
        printf "\t-h, --help         Display this help message and exit.\n\n"
        printf "Available Colors:\n"
        printf "\t\e[32mgreen\e[0m\t: Matrix-like green shades\n"
        printf "\t\e[34mblue\e[0m\t: Deep ocean blue gradients\n"
        printf "\t\e[31mred\e[0m\t: Crimson/Blood rain\n"
        printf "\t\e[33myellow\e[0m\t: Amber and gold tones\n"
        printf "\t\e[36mcyan\e[0m\t: Electric cyan/turquoise\n"
        printf "\twhite\t: Greyscale and white (original style)\n\n"
        printf "Example: rain --color green --speed 0.03\n"
    }

    local step_duration=0.050
    local base_color="white"

    while [[ "$#" -gt 0 ]]; do
        case $1 in
            -s|--speed)
                if [[ -n "$2" && ! "$2" =~ ^- ]]; then
                    step_duration="$2"
                    shift
                else
                    disp E "--speed requires a numeric value."
                    _rain_show_usage
                    return 1
                fi
                ;;
            -c|--color)
                if [[ -n "$2" && ! "$2" =~ ^- ]]; then
                    base_color="$2"
                    shift
                else
                    disp E "--color requires a color name."
                    _rain_show_usage
                    return 1
                fi
                ;;
            -h|--help)
                _rain_show_usage
                return 0
                ;;
            --)
                shift
                break
                ;;
            *)
                disp E "Unknown option: $1"
                _rain_show_usage
                return 1
                ;;
        esac
        shift
    done

    _rain_engine "$step_duration" "$base_color" "rain" ""
}
export -f rain

# ------------------------------------------------------------------------------
# Matrix style digital rain
# Usage: matrix [OPTIONS]
matrix()
{
    _matrix_show_usage()
    {
        printf "Usage: matrix [OPTIONS]\n"
        printf "Options:\n"
        printf "\t-s, --speed NUM    Set the drop delay in seconds (default: 0.035).\n"
        printf "\t                   Lower values = faster stream.\n"
        printf "\t-c, --color COLOR  Set color theme (default: green).\n"
        printf "\t-t, --charset SET  Character set: binary, kana, ascii (default: binary).\n"
        printf "\t-h, --help         Display this help message and exit.\n\n"
        printf "Example: matrix --charset kana --speed 0.02\n"
    }

    local step_duration=0.035
    local base_color="green"
    local charset="binary"

    while [[ "$#" -gt 0 ]]; do
        case $1 in
            -s|--speed)
                if [[ -n "$2" && ! "$2" =~ ^- ]]; then
                    step_duration="$2"
                    shift
                else
                    disp E "--speed requires a numeric value."
                    _matrix_show_usage
                    return 1
                fi
                ;;
            -c|--color)
                if [[ -n "$2" && ! "$2" =~ ^- ]]; then
                    base_color="$2"
                    shift
                else
                    disp E "--color requires a color name."
                    _matrix_show_usage
                    return 1
                fi
                ;;
            -t|--charset)
                if [[ -n "$2" && ! "$2" =~ ^- ]]; then
                    charset="${2,,}"
                    shift
                else
                    disp E "--charset requires a value."
                    _matrix_show_usage
                    return 1
                fi
                ;;
            -h|--help)
                _matrix_show_usage
                return 0
                ;;
            --)
                shift
                break
                ;;
            *)
                disp E "Unknown option: $1"
                _matrix_show_usage
                return 1
                ;;
        esac
        shift
    done

    _rain_engine "$step_duration" "$base_color" "matrix" "$charset"
}
export -f matrix

# ------------------------------------------------------------------------------
# EOF