using System.Collections.Generic;
using System.IO;
using System.Linq;
using Microsoft.Extensions.Logging;

namespace Migrato.Core;

/// <summary>
///     Loads and orders the migrations found in a directory
/// </summary>
public static class MigrationLoader
{
    /// <summary>
    ///     Parses every "*.sql" file in <paramref name="directory"/> and returns them ordered by version
    /// </summary>
    /// <exception cref="DirectoryNotFoundException"><paramref name="directory"/> does not exist</exception>
    /// <exception cref="MigrationFormatException">A file is malformed, or two files share the same version</exception>
    public static IReadOnlyList<Migration> LoadFromDirectory(string directory)
    {
        if (!Directory.Exists(directory))
        {
            throw new DirectoryNotFoundException($"Migrations directory '{directory}' does not exist");
        }

        var migrations = Directory.EnumerateFiles(directory, "*.sql")
            .Select(MigrationParser.Parse)
            .OrderBy(m => m.Version)
            .ToList();

        var duplicate = migrations
            .GroupBy(m => m.Version)
            .FirstOrDefault(g => g.Count() > 1);

        return duplicate is not null ? 
            throw new MigrationFormatException($"Multiple migration files share version {duplicate.Key}")
            : migrations;
    }
}