<?php

namespace Scientific;

use InvalidArgumentException;

abstract class Quantity
{
    /*
     * https://en.wikipedia.org/wiki/Metric_prefix
     */
    private const METRIC_PREFIXES = [
        'yotta' => 'Y',
        'zetta' => 'Z',
        'exa'   => 'E',
        'peta'  => 'P',
        'tera'  => 'T',
        'giga'  => 'G',
        'mega'  => 'M',
        'kilo'  => 'k',
        'hecto' => 'h',
        'deca'  => 'da',
        'unit'  => '',
        'deci'  => 'd',
        'centi' => 'c',
        'milli' => 'm',
        'micro' => 'μ',
        'nano'  => 'n',
        'pico'  => 'p',
        'femto' => 'f',
        'atto'  => 'a',
        'zepto' => 'z',
        'yocto' => 'y',
    ];

    abstract protected function getSymbol(): string;

    abstract protected function getName(): string;

    public function __construct(
        private Unit $value
    )
    {
    }

    final public static function fromValue(float $value): static
    {
        return new static(new Unit($value));
    }

    final public function getValue(): Unit
    {
        return $this->value;
    }

    final public function format(string $prefix = 'auto'): string
    {
        if ($prefix === 'auto') {
            $prefix = $this->getAppropriatePrefix();
        } else if (!method_exists($this->value, $prefix)) {
            throw new InvalidArgumentException('Invalid size: ' . $prefix);
        }

        $value = $this->value->{$prefix}();
        $prefix = self::METRIC_PREFIXES[$prefix] ?? '?';
        $symbol = $this->getSymbol();

        return sprintf('%.3g %s%s', $value, $prefix, $symbol);
    }

    private function getAppropriatePrefix(): string
    {
        foreach (array_keys(self::METRIC_PREFIXES) as $prefix) {
            $value = $this->value->{$prefix}();
            if ($value >= 1. && $value < 1000.) {
                return $prefix;
            }
        }
        return 'unit';
    }

    public function __toString(): string
    {
        return $this->format();
    }
}