#!/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
# * that the following conditions are met:
# *
# *   Redistributions of source code must retain the above
# *   copyright notice, this list of conditions and the
# *   following disclaimer.
# *
# *   Redistributions in binary form must reproduce the above
# *   copyright notice, this list of conditions and the following
# *   disclaimer in the documentation and/or other materials
# *   provided with the distribution.
# *
# *   Neither the name of the copyright holder nor the names
# *   of any other contributors may be used to endorse or
# *   promote products derived from this software without
# *   specific prior written permission.
# *
# * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
# * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
# * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
# * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
# * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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# * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
# * OF SUCH DAMAGE.
# ------------------------------------------------------------------------------

# Private helpers of profile.d/rain.sh, loaded by the module itself.

# Fill RAIN_ENGINE_COLORS with the escape sequences of the drop colours (head to
# tail) of the colour theme $1: a 20-step 24-bit gradient when the terminal
# supports truecolor, a short 256-colour palette otherwise.
# Usage: _rain_build_colors <colour_name>
_rain_build_colors()
{
    # Case-insensitive: the configuration documents capitalised names (Green)
    local base_color="${1,,}"
    local i
    RAIN_ENGINE_COLORS=()

    case "$base_color" in
        green|blue|red|yellow|cyan|white) ;;
        *)
            disp E "Unknown color: ${1} (supported: green, blue, red, yellow, cyan, white)."
            return 1
            ;;
    esac

    local use_truecolor=0
    # term_set() already sets TERM=*-direct when truecolor is available;
    # honour COLORTERM as a belt-and-suspenders fallback.
    [[ "$TERM" == *direct* || "${COLORTERM:-}" == "truecolor" || "${COLORTERM:-}" == "24bit" ]] && use_truecolor=1

    if (( use_truecolor )); then
        # 24-bit gradient from a near-black shade to a vivid hue.
        # 20 steps provide smooth depth variation across simultaneous drops.
        local steps=20
        local r1 g1 b1 r2 g2 b2
        case "${base_color}" in
            green)  r1=0;  g1=12;  b1=2;   r2=50;  g2=255; b2=90  ;;
            blue)   r1=0;  g1=5;   b1=25;  r2=60;  g2=140; b2=255 ;;
            red)    r1=15; g1=0;   b1=0;   r2=255; g2=40;  b2=40  ;;
            yellow) r1=25; g1=18;  b1=0;   r2=255; g2=240; b2=50  ;;
            cyan)   r1=0;  g1=18;  b1=18;  r2=50;  g2=255; b2=240 ;;
            *)      r1=40; g1=40;  b1=45;  r2=220; g2=220; b2=255 ;;
        esac

        local r g b
        for ((i = 0; i < steps; i++)); do
            r=$(( r1 + (r2 - r1) * i / (steps - 1) ))
            g=$(( g1 + (g2 - g1) * i / (steps - 1) ))
            b=$(( b1 + (b2 - b1) * i / (steps - 1) ))
            RAIN_ENGINE_COLORS+=("\e[38;2;${r};${g};${b}m")
        done
    else
        # Fallback: 256-colour palettes.
        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
    fi
}

# Fill RAIN_ENGINE_CHARS with the characters a drop may be made of, according to
# the animation ($1: rain or matrix) and the matrix charset name ($2).
# Usage: _rain_build_chars <mode> <charset>
_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
}

# Validate a speed and print it as a delay in seconds for read -t / sleep:
# values >= 1 are centiseconds (5 -> 0.050), values < 1 are raw seconds.
# Return 1 for a non-numeric or null value.
# Usage: _rain_normalize_speed <speed>
_rain_normalize_speed()
{
    local raw_speed="$1"

    # Accept integer/floating values. UI scale is centiseconds by default:
    # 5 -> 0.05s, 2.5 -> 0.025s. Values < 1 are treated as direct seconds
    # for backward compatibility (e.g. 0.03).
    if [[ ! "$raw_speed" =~ ^[0-9]+([.][0-9]+)?$ ]]; then
        return 1
    fi

    # A null delay is refused: "read -t 0" does not wait, the animation loop
    # would spin and use a whole CPU.
    if LC_ALL=C awk -v s="$raw_speed" 'BEGIN { exit !(s == 0) }'; then
        return 1
    fi

    if LC_ALL=C awk -v s="$raw_speed" 'BEGIN { exit !(s < 1) }'; then
        printf "%s" "$raw_speed"
    else
        LC_ALL=C awk -v s="$raw_speed" 'BEGIN { printf "%.3f", s / 100 }'
    fi
}

# Validate a density (maximum number of simultaneous drops, an integer >= 1)
# and print it; return 1 otherwise.
# Usage: _rain_normalize_density <density>
_rain_normalize_density()
{
    local raw_density="$1"

    if [[ ! "$raw_density" =~ ^[0-9]+$ || "$raw_density" -lt 1 ]]; then
        return 1
    fi

    printf "%s" "$raw_density"
}

# Fill RAINBOW_BG_PALETTE with <width> background colour escapes sweeping the
# hue wheel: 6 bands of 256 steps in 24-bit colour, or 12 fixed ANSI colours
# spread over the width otherwise.
# Usage: _rainbow_build_palette <width> <use_truecolor (0|1)>
_rainbow_build_palette()
{
    local palette_width="$1"
    local use_truecolor="$2"
    local x=0 wheel_pos=0 band=0 blend=0
    local red=0 green=0 blue=0

    RAINBOW_BG_PALETTE=()

    if (( palette_width < 1 )); then
        RAINBOW_BG_PALETTE+=("\e[41m")
        return 0
    fi

    if (( use_truecolor )); then
        for ((x = 0; x < palette_width; x++)); do
            wheel_pos=$((x * 1536 / palette_width))
            band=$((wheel_pos / 256))
            blend=$((wheel_pos % 256))

            case "$band" in
                0)
                    red=255; green=$blend; blue=0
                    ;;
                1)
                    red=$((255 - blend)); green=255; blue=0
                    ;;
                2)
                    red=0; green=255; blue=$blend
                    ;;
                3)
                    red=0; green=$((255 - blend)); blue=255
                    ;;
                4)
                    red=$blend; green=0; blue=255
                    ;;
                *)
                    red=255; green=0; blue=$((255 - blend))
                    ;;
            esac

            RAINBOW_BG_PALETTE+=("\e[48;2;${red};${green};${blue}m")
        done
    else
        local ansi_palette=(41 101 43 103 42 102 46 106 44 104 45 105)
        local ansi_count=${#ansi_palette[@]}

        for ((x = 0; x < palette_width; x++)); do
            RAINBOW_BG_PALETTE+=("\e[${ansi_palette[x * ansi_count / palette_width]}m")
        done
    fi
}

# Stop request of the animation loops: sets exit_st, a local of the running
# animation (dynamic scoping). Installed as the TERM/INT trap.
_rain_stop()
{
    exit_st=1
}

# The animations read a key from the terminal and draw on it, and need tput.
# Usage: _rain_need_tty <command-name>
_rain_need_tty()
{
    if [[ ! -t 0 || ! -t 1 ]]; then
        disp E "$1: a terminal is required (standard input and output must be a terminal)."
        return 1
    fi
    command -v tput >/dev/null 2>&1 || {
        disp E "The program 'tput' is required but not installed."
        return 1
    }
}

# Prepare the terminal for an animation: save its settings and the TERM, INT
# and WINCH traps of the caller, install the animation traps, disable echo,
# hide the cursor and clear the screen.
# saved_stty and saved_traps are locals of the calling animation.
# Usage: _rain_enter <winch_handler_function>
_rain_enter()
{
    saved_stty=$(stty -g 2>/dev/null)
    saved_traps=$(trap -p TERM INT WINCH)
    trap _rain_stop TERM INT
    trap "$1" WINCH
    stty -echo
    printf '\e[?25l\e[2J'
}

# Undo _rain_enter: reset the colours (the last drawn drop colour would
# otherwise stay active), show the cursor, clear the screen, then restore the
# terminal settings and the caller's traps.
_rain_leave()
{
    printf '\e[0m\e[?25h\e[2J\e[H'
    [[ -n "$saved_stty" ]] && stty "$saved_stty"
    trap - TERM INT WINCH
    _trap_restore "$saved_traps"
    return 0
}

# Shared engine of the rain and matrix animations: draws the falling drops until
# a key is pressed, a signal is received, or the terminal is resized (the
# state is rebuilt). The terminal state is always restored on exit.
# Usage: _rain_engine <delay_seconds> <colour> <rain|matrix> <charset> <density>
_rain_engine()
{
    local step_duration="$1"
    local base_color="$2"
    local mode="$3"
    local charset="$4"
    local density_override="$5"

    _rain_need_tty "$mode" || return 1

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

    local rain_colors=("${RAIN_ENGINE_COLORS[@]}")
    local rain_chars=("${RAIN_ENGINE_CHARS[@]}")
    unset RAIN_ENGINE_COLORS RAIN_ENGINE_CHARS
    local rain_color_tab=${#rain_colors[@]}
    local rain_tab=${#rain_chars[@]}
    local matrix_head_color=$'\e[1;97m'

    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
    local term_area=0
    local frame_sleep="$step_duration"
    local saved_stty="" saved_traps=""

    # The drops: 5 consecutive entries each (X, Y of the top, character, colour,
    # length).
    local rains=()
    local num_rains=0
    local ch=""

    # WINCH handler (and initial sizing). Called with the animation running, it
    # sees its locals through dynamic scoping.
    _rain_sigwinch()
    {
        term_width=$(tput cols)
        term_height=$(tput lines)
        term_area=$(( term_width * term_height ))

        case "$mode" in
            matrix)
                max_rain_width=$(( term_area / 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

                # Adapt cadence and density to terminal size for smoother rendering.
                if ((term_area < 1200)); then
                    max_rain_width=$(( term_area / 4 ))
                    frame_sleep=$(LC_ALL=C awk -v s="$step_duration" 'BEGIN { printf "%.3f", s * 1.15 }')
                elif ((term_area > 5000)); then
                    max_rain_width=$(( term_area / 2 ))
                    frame_sleep=$(LC_ALL=C awk -v s="$step_duration" 'BEGIN { printf "%.3f", s * 0.85 }')
                else
                    frame_sleep="$step_duration"
                fi
                ;;
            *)
                max_rain_width=$(( term_area / 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=$(( falling_odd * 90 / 100 ))
                frame_sleep="$step_duration"
                ;;
        esac

        if [[ -n "$density_override" ]]; then
            max_rain_width="$density_override"
        fi

        # The drops were placed for the previous size and the screen content
        # does not fit the new one: start again from an empty screen.
        rains=()
        num_rains=0
        printf '\e[2J'
    }

    # Draw one frame. The whole frame (erasing the previous drop positions,
    # then the new ones) is built in a string and written with one printf: a
    # write per character made the animation slow and flickering.
    _rain_render()
    {
        local idx=0 y=0 drop_color="" current_char="" render_color="" out=""
        local esc=$'\e'

        for ((idx = 0; idx < num_rains * num_rain_metadata; idx += num_rain_metadata)); do
            X=${rains[idx]}
            Y=${rains[idx + 1]}
            drop_length=${rains[idx + 4]}
            for ((y = Y; y < Y + drop_length; y++)); do
                ((y < 1 || y > term_height)) && continue
                out+="${esc}[${y};${X}H "
            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
                    # The drop left the screen: remove it. The next drop moves
                    # into this slot, which must be processed again (the loop
                    # increment would skip it, and it would vanish for a frame).
                    rains=("${rains[@]:0:idx}" "${rains[@]:idx+num_rain_metadata}")
                    num_rains=$(( num_rains - 1 ))
                    idx=$(( idx - num_rain_metadata ))
                    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
                if [[ "$mode" == "matrix" ]]; then
                    current_char="${rain_chars[rain_tab * RANDOM / 32768]}"
                    if ((y == Y + drop_length - 1)); then
                        render_color="$matrix_head_color"
                    else
                        render_color="$drop_color"
                    fi
                else
                    current_char="$rain_drop"
                    render_color="$drop_color"
                fi
                # render_color holds a literal \e[...m: hence %b below
                out+="${esc}[${y};${X}H${render_color}${current_char}"
            done
        done

        [[ -n "$out" ]] && printf '%b' "$out"
        return 0
    }

    _rain_enter _rain_sigwinch
    _rain_sigwinch
    while ((exit_st <= 0)); do
        ch=""
        # A timeout makes read fail (status > 128): expected, not an error
        read -r -n 1 -t "$frame_sleep" ch || true
        case "$ch" in
            q|Q)
                _rain_stop
                ;;
        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]}"
            if [[ "$mode" == "matrix" ]]; then
                drop_length=$((max_rain_height * RANDOM / 32768 + 2))
            else
                drop_length=$((max_rain_height * RANDOM / 32768 + 1))
            fi
            X=$((term_width * RANDOM / 32768 + 1))
            Y=$((1 - drop_length))
            rains+=("$X" "$Y" "$rain_drop" "$drop_color" "$drop_length")
            num_rains=$(( num_rains + 1 ))
        fi

        _rain_render
    done

    _rain_leave
    unset -f _rain_sigwinch _rain_render
    return 0
}