#!/bin/bash

# Terminal Progress Bar Library
#
# Description:
#   Provides a reusable progress bar that occupies the last terminal row
#   while allowing normal command output to continue scrolling above it.
#
# Usage:
#   Source this file from another Bash script:
#
#       source ./progress_bar.sh
#
#   Then:
#
#       enable_trapping
#       setup_scroll_area
#
#       draw_progress_bar 10
#       draw_progress_bar 40
#
#       # Indicates that user interaction/action is required.
#       block_progress_bar 45
#
#       draw_progress_bar 90
#       destroy_scroll_area
#
# Functions:
#   enable_trapping
#       Enable Ctrl-C cleanup for the progress bar.
#
#   setup_scroll_area
#       Create the terminal scrolling area and display an empty progress bar.
#
#   draw_progress_bar <percentage>
#       Draw a normal green progress bar.
#
#   block_progress_bar <percentage>
#       Draw a yellow progress bar to indicate that user action is required.
#
#   clear_progress_bar
#       Clear the progress bar without destroying the scroll area.
#
#   destroy_scroll_area
#       Restore the terminal scrolling region and remove the progress bar.
#
# Notes:
#   - Bash is required.
#   - Requires `tput` and a terminal supporting ANSI escape sequences.
#   - This script is intended to be sourced, not executed directly.
#

# ---------------------------------------------------------------------------
# Terminal escape sequences
# ---------------------------------------------------------------------------

readonly CODE_SAVE_CURSOR=$'\033[s'
readonly CODE_RESTORE_CURSOR=$'\033[u'
readonly CODE_CURSOR_IN_SCROLL_AREA=$'\033[1A'

readonly COLOR_FG=$'\e[30m'
readonly COLOR_BG=$'\e[42m'
readonly COLOR_BG_BLOCKED=$'\e[43m'
readonly RESTORE_FG=$'\e[39m'
readonly RESTORE_BG=$'\e[49m'

# ---------------------------------------------------------------------------
# State
# ---------------------------------------------------------------------------

PROGRESS_BLOCKED=false
TRAPPING_ENABLED=false
TRAP_SET=false


# ---------------------------------------------------------------------------
# Internal helpers
# ---------------------------------------------------------------------------

_terminal_rows() {
    tput lines
}

_terminal_columns() {
    tput cols
}

_move_to_progress_row() {
    local rows
    rows=$(_terminal_rows)

    printf '%s' "${CODE_SAVE_CURSOR}"
    printf '\033[%d;0f' "$rows"
    tput el
}

_restore_cursor() {
    printf '%s' "${CODE_RESTORE_CURSOR}"
}

_validate_percentage() {
    local percentage=$1

    if ! [[ "$percentage" =~ ^[0-9]+$ ]]; then
        percentage=0
    elif (( percentage > 100 )); then
        percentage=100
    fi

    printf '%d' "$percentage"
}

_print_repeated() {
    local character=$1
    local count=$2

    (( count <= 0 )) && return

    printf '%*s' "$count" '' | tr ' ' "$character"
}

_print_bar() {
    local percentage
    local columns
    local bar_size
    local complete_size
    local remainder_size
    local background

    percentage=$(_validate_percentage "$1")
    columns=$(_terminal_columns)

    # 17 characters are reserved for:
    # " Progress XXX% []"
    bar_size=$((columns - 17))

    # Prevent negative printf field widths on very small terminals.
    (( bar_size < 1 )) && bar_size=1

    complete_size=$((bar_size * percentage / 100))
    remainder_size=$((bar_size - complete_size))

    if [[ "$PROGRESS_BLOCKED" == true ]]; then
        background=$COLOR_BG_BLOCKED
    else
        background=$COLOR_BG
    fi

    printf ' Progress %3d%% [' "$percentage"
    printf '%s%s' "$COLOR_FG" "$background"
    _print_repeated '#' "$complete_size"
    printf '%s%s' "$RESTORE_FG" "$RESTORE_BG"
    _print_repeated '.' "$remainder_size"
    printf ']'
}


# ---------------------------------------------------------------------------
# Public API
# ---------------------------------------------------------------------------

setup_scroll_area() {
    if [[ "$TRAPPING_ENABLED" == true ]]; then
        trap_on_interrupt
    fi

    local rows
    rows=$(_terminal_rows)
    (( rows > 1 )) || return 1

    # Create a line for the progress bar and avoid terminal resize glitches.
    printf '\n'

    # Reserve the final terminal row for the progress bar.
    printf '%s' "$CODE_SAVE_CURSOR"
    printf '\033[0;%dr' "$((rows - 1))"

    # Restore the cursor inside the scrolling region.
    printf '%s%s' "$CODE_RESTORE_CURSOR" "$CODE_CURSOR_IN_SCROLL_AREA"

    draw_progress_bar 0
}

destroy_scroll_area() {
    local rows
    rows=$(_terminal_rows)

    # Restore the full terminal scrolling region.
    printf '%s' "$CODE_SAVE_CURSOR"
    printf '\033[0;%dr' "$rows"
    printf '%s%s' "$CODE_RESTORE_CURSOR" "$CODE_CURSOR_IN_SCROLL_AREA"

    clear_progress_bar

    # Allow the terminal to resume normal scrolling.
    printf '\n\n'

    if [[ "$TRAP_SET" == true ]]; then
        trap - INT
        TRAP_SET=false
    fi
}

draw_progress_bar() {
    PROGRESS_BLOCKED=false

    _move_to_progress_row
    _print_bar "$1"
    _restore_cursor
}

block_progress_bar() {
    PROGRESS_BLOCKED=true

    _move_to_progress_row
    _print_bar "$1"
    _restore_cursor
}

clear_progress_bar() {
    _move_to_progress_row
    _restore_cursor
}

enable_trapping() {
    TRAPPING_ENABLED=true
}

trap_on_interrupt() {
    TRAP_SET=true
    trap cleanup_on_interrupt INT
}

cleanup_on_interrupt() {
    destroy_scroll_area
    exit 130
}