using System;
using System.IO;
using System.Text.RegularExpressions;

namespace Migrato.Core;

/// <summary>
///     Parses a "-- +migrato Up" / "-- +migrato Down" annotated SQL file into a <see cref="Migration"/>
/// </summary>
public static partial class MigrationParser
{
    private const string UpMarker = "-- +migrato Up";
    private const string DownMarker = "-- +migrato Down";

    /// <summary>
    ///     Parses the migration file at <paramref name="path"/>
    /// </summary>
    /// <exception cref="MigrationFormatException">The file name or contents do not follow Migrato's conventions</exception>
    public static Migration Parse(string path)
    {
        var fileName = Path.GetFileName(path);
        var match = FileNameRegex().Match(fileName);
        if (!match.Success)
        {
            throw new MigrationFormatException(
                $"'{fileName}' is not a valid migration file name; expected '<14-digit version>_<name>.sql'");
        }

        var version = long.Parse(match.Groups["version"].Value);
        var name = match.Groups["name"].Value;

        var content = File.ReadAllText(path);
        var (upSql, downSql) = ParseSections(content, fileName);

        return new Migration(version)
        {
            Source = path,
            Name = name,
            UpSql = upSql,
            DownSql = downSql,
        };
    }

    private static (string UpSql, string DownSql) ParseSections(string content, string fileName)
    {
        var lines = content.Replace("\r\n", "\n").Split('\n');

        var upIndex = -1;
        var downIndex = -1;

        for (var i = 0; i < lines.Length; i++)
        {
            var trimmed = lines[i].Trim();

            if (trimmed.Equals(UpMarker, StringComparison.OrdinalIgnoreCase))
            {
                if (upIndex != -1)
                {
                    throw new MigrationFormatException($"'{fileName}' has more than one '{UpMarker}' marker");
                }

                upIndex = i;
            }
            else if (trimmed.Equals(DownMarker, StringComparison.OrdinalIgnoreCase))
            {
                if (downIndex != -1)
                {
                    throw new MigrationFormatException($"'{fileName}' has more than one '{DownMarker}' marker");
                }

                downIndex = i;
            }
        }

        if (upIndex == -1)
        {
            throw new MigrationFormatException($"'{fileName}' is missing a '{UpMarker}' marker");
        }

        if (downIndex == -1)
        {
            throw new MigrationFormatException($"'{fileName}' is missing a '{DownMarker}' marker");
        }

        if (downIndex < upIndex)
        {
            throw new MigrationFormatException($"'{fileName}' has '{DownMarker}' before '{UpMarker}'");
        }

        var upSql = string.Join('\n', lines[(upIndex + 1)..downIndex]).Trim();
        var downSql = string.Join('\n', lines[(downIndex + 1)..]).Trim();

        return (upSql, downSql);
    }

    [GeneratedRegex(@"^(?<version>\d{14})_(?<name>.+)\.sql$")]
    private static partial Regex FileNameRegex();
}