using MeterVault.App;

namespace MeterVault.Integration.Tests;

/// <summary>
/// The manual-reading keypad buffer: the pure part of entering a reading by hand at the meter.
/// No database — these are the rules that decide what number gets stored, so they are pinned here
/// rather than left to a render test.
/// </summary>
public sealed class ReadingEntryTests
{
    [Theory]
    // The keypad's own output, and what a German keyboard produces.
    [InlineData("12345,6", 12345.6)]
    [InlineData("12345,", 12345)]
    // An English keyboard: a lone dot is decimal, because nobody groups thousands on a register.
    [InlineData("12345.6", 12345.6)]
    [InlineData("1.234", 1.234)]
    // Both separators present: the last one is decimal, whichever dialect it came from.
    [InlineData("1.234,5", 1234.5)]
    [InlineData("1,234.5", 1234.5)]
    [InlineData("1.234.567,89", 1234567.89)]
    [InlineData("0", 0)]
    [InlineData("-12,5", -12.5)]
    public void Parses_either_dialect_taking_the_last_separator_as_decimal(string text, double expected)
    {
        Assert.True(ReadingEntry.TryParse(text, out var value));
        Assert.Equal(expected, value, 9);
    }

    [Theory]
    [InlineData("")]
    [InlineData("   ")]
    [InlineData(",")]
    [InlineData("-")]
    [InlineData("12 345")]
    [InlineData("abc")]
    public void Rejects_input_that_is_not_a_number(string text) =>
        Assert.False(ReadingEntry.TryParse(text, out _));

    [Fact]
    public void Prefill_shows_the_last_reading_in_the_dialect_the_keypad_types()
    {
        var entry = new ReadingEntry();
        entry.Prefill(12345.6);

        Assert.Equal("12345,6", entry.Text);
        Assert.True(entry.IsPristine);
        Assert.Equal(12345.6, entry.Value!.Value, 9);
    }

    [Fact]
    public void Prefill_does_not_invent_precision_the_meter_never_reported()
    {
        var entry = new ReadingEntry();
        entry.Prefill(2287);

        Assert.Equal("2287", entry.Text);
    }

    [Fact]
    public void First_digit_after_a_prefill_starts_a_fresh_value()
    {
        // Reading a completely different register: typing must not append to the prefill.
        var entry = new ReadingEntry();
        entry.Prefill(12345.6);

        entry.AppendDigit('9');

        Assert.Equal("9", entry.Text);
        Assert.False(entry.IsPristine);
    }

    [Fact]
    public void Backspace_after_a_prefill_edits_it_in_place()
    {
        // The walk-up case: only the last digits of a register have moved, so backspace keeps the
        // leading digits instead of clearing them the way a digit key does.
        var entry = new ReadingEntry();
        entry.Prefill(12345.6);

        entry.Backspace();  // "12345,"
        entry.Backspace();  // "12345"
        entry.AppendDigit('8');
        entry.AppendSeparator();
        entry.AppendDigit('9');

        Assert.Equal("123458,9", entry.Text);
        Assert.Equal(123458.9, entry.Value!.Value, 9);
    }

    [Fact]
    public void Accepts_at_most_one_separator()
    {
        var entry = new ReadingEntry();
        entry.AppendDigit('1');
        entry.AppendSeparator();
        entry.AppendSeparator();
        entry.AppendDigit('5');

        Assert.Equal("1,5", entry.Text);
    }

    [Fact]
    public void A_leading_separator_becomes_a_leading_zero()
    {
        var entry = new ReadingEntry();
        entry.AppendSeparator();
        entry.AppendDigit('5');

        Assert.Equal("0,5", entry.Text);
        Assert.Equal(0.5, entry.Value!.Value, 9);
    }

    [Fact]
    public void A_leading_zero_is_replaced_rather_than_kept()
    {
        var entry = new ReadingEntry();
        entry.AppendDigit('0');
        entry.AppendDigit('7');

        Assert.Equal("7", entry.Text);
    }

    [Fact]
    public void Clear_empties_the_buffer_and_leaves_no_value()
    {
        var entry = new ReadingEntry();
        entry.Prefill(500);
        entry.Clear();

        Assert.Equal(string.Empty, entry.Text);
        Assert.False(entry.IsPristine);
        Assert.Null(entry.Value);
    }

    [Fact]
    public void Backspace_on_an_empty_buffer_is_a_no_op()
    {
        var entry = new ReadingEntry();
        entry.Backspace();

        Assert.Equal(string.Empty, entry.Text);
        Assert.Null(entry.Value);
    }

    [Fact]
    public void Typed_text_keeps_only_what_can_form_a_number()
    {
        var entry = new ReadingEntry();
        entry.Prefill(1);
        entry.SetText("1 234,5 kWh");

        Assert.Equal("1234,5", entry.Text);
        Assert.False(entry.IsPristine);
        Assert.Equal(1234.5, entry.Value!.Value, 9);
    }

    [Fact]
    public void A_stuck_key_cannot_grow_the_buffer_without_bound()
    {
        var entry = new ReadingEntry();
        for (var i = 0; i < ReadingEntry.MaxLength + 10; i++)
        {
            entry.AppendDigit('9');
        }

        Assert.Equal(ReadingEntry.MaxLength, entry.Text.Length);
    }
}