using System.Diagnostics.CodeAnalysis;

namespace StellaOps.PolicyDsl;

/// <summary>
/// Represents a precise source location within a policy DSL document.
/// </summary>
public readonly struct SourceLocation : IEquatable<SourceLocation>, IComparable<SourceLocation>
{
    public SourceLocation(int offset, int line, int column)
    {
        if (offset < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(offset));
        }

        if (line < 1)
        {
            throw new ArgumentOutOfRangeException(nameof(line));
        }

        if (column < 1)
        {
            throw new ArgumentOutOfRangeException(nameof(column));
        }

        Offset = offset;
        Line = line;
        Column = column;
    }

    public int Offset { get; }

    public int Line { get; }

    public int Column { get; }

    public override string ToString() => $"(L{Line}, C{Column})";

    public bool Equals(SourceLocation other) =>
        Offset == other.Offset && Line == other.Line && Column == other.Column;

    public override bool Equals([NotNullWhen(true)] object? obj) =>
        obj is SourceLocation other && Equals(other);

    public override int GetHashCode() => HashCode.Combine(Offset, Line, Column);

    public int CompareTo(SourceLocation other) => Offset.CompareTo(other.Offset);

    public static bool operator ==(SourceLocation left, SourceLocation right) => left.Equals(right);

    public static bool operator !=(SourceLocation left, SourceLocation right) => !left.Equals(right);

    public static bool operator <(SourceLocation left, SourceLocation right) => left.CompareTo(right) < 0;

    public static bool operator <=(SourceLocation left, SourceLocation right) => left.CompareTo(right) <= 0;

    public static bool operator >(SourceLocation left, SourceLocation right) => left.CompareTo(right) > 0;

    public static bool operator >=(SourceLocation left, SourceLocation right) => left.CompareTo(right) >= 0;
}

/// <summary>
/// Represents a start/end location pair within a policy DSL source document.
/// </summary>
public readonly struct SourceSpan : IEquatable<SourceSpan>
{
    public SourceSpan(SourceLocation start, SourceLocation end)
    {
        if (start.Offset > end.Offset)
        {
            throw new ArgumentException("Start must not be after end.", nameof(start));
        }

        Start = start;
        End = end;
    }

    public SourceLocation Start { get; }

    public SourceLocation End { get; }

    public override string ToString() => $"{Start}->{End}";

    public bool Equals(SourceSpan other) => Start.Equals(other.Start) && End.Equals(other.End);

    public override bool Equals([NotNullWhen(true)] object? obj) => obj is SourceSpan other && Equals(other);

    public override int GetHashCode() => HashCode.Combine(Start, End);

    public static SourceSpan Combine(SourceSpan first, SourceSpan second)
    {
        var start = first.Start <= second.Start ? first.Start : second.Start;
        var end = first.End >= second.End ? first.End : second.End;
        return new SourceSpan(start, end);
    }
}