using System.Globalization;

namespace Campaign_Tracker.Server.LegacyData.Schema;

/// <summary>
/// Parses the Access schema text dump shipped at
/// <c>Initial Documents/Access_Schema.txt</c> into a strongly-typed
/// <see cref="LegacySchemaBaseline"/> for compatibility checking.
///
/// File format (one table per block):
/// <code>
/// Table: Contacts
/// ---------------
///   Column: ID            Type: 3      Size:        Nullable: False
///   Column: EMAIL         Type: 130    Size: 255    Nullable: True
/// </code>
/// </summary>
public static class LegacySchemaBaselineParser
{
    public static LegacySchemaBaseline ParseFile(string filePath, DateTimeOffset capturedAt)
    {
        if (!File.Exists(filePath))
        {
            throw new FileNotFoundException(
                $"Legacy schema baseline file not found: {filePath}", filePath);
        }

        var text = File.ReadAllText(filePath);
        return Parse(text, filePath, capturedAt);
    }

    public static LegacySchemaBaseline Parse(string text, string source, DateTimeOffset capturedAt)
    {
        var tables = new List<LegacyTableDefinition>();
        string? currentTable = null;
        var currentColumns = new List<LegacyColumnDefinition>();

        foreach (var rawLine in text.Split('\n'))
        {
            var line = rawLine.TrimEnd('\r').TrimEnd();
            if (line.Length == 0) continue;
            if (line.All(c => c == '-')) continue;

            if (line.StartsWith("Table:", StringComparison.Ordinal))
            {
                FlushTable(tables, currentTable, currentColumns);
                currentTable = line["Table:".Length..].Trim();
                currentColumns = new List<LegacyColumnDefinition>();
                continue;
            }

            var trimmed = line.TrimStart();
            if (!trimmed.StartsWith("Column:", StringComparison.Ordinal))
            {
                throw new FormatException($"Unrecognized legacy schema line: {line}");
            }

            currentColumns.Add(ParseColumn(trimmed));
        }

        FlushTable(tables, currentTable, currentColumns);
        if (tables.Count == 0)
        {
            throw new FormatException("Legacy schema baseline did not contain any table definitions.");
        }

        return new LegacySchemaBaseline(tables, source, capturedAt);
    }

    private static void FlushTable(
        List<LegacyTableDefinition> sink,
        string? tableName,
        List<LegacyColumnDefinition> columns)
    {
        if (string.IsNullOrWhiteSpace(tableName) || columns.Count == 0) return;
        sink.Add(new LegacyTableDefinition(tableName, columns.ToArray()));
    }

    private static LegacyColumnDefinition ParseColumn(string line)
    {
        // "Column: NAME    Type: 130    Size: 255    Nullable: True"
        var name = ReadField(line, "Column:", ["Type:"]);
        var typeRaw = ReadField(line, "Type:", ["Size:", "Nullable:", "Constraints:"]);
        var sizeRaw = ReadField(line, "Size:", ["Nullable:", "Constraints:"]);
        var nullableRaw = ReadField(line, "Nullable:", ["Constraints:"]);
        var constraintsRaw = ReadField(line, "Constraints:", []);

        if (!int.TryParse(typeRaw, NumberStyles.Integer, CultureInfo.InvariantCulture, out var typeCode))
        {
            throw new FormatException($"Invalid Type code in column line: {line}");
        }

        int? size = null;
        if (!string.IsNullOrWhiteSpace(sizeRaw))
        {
            if (!int.TryParse(sizeRaw, NumberStyles.Integer, CultureInfo.InvariantCulture, out var parsedSize))
            {
                throw new FormatException($"Invalid Size value in column line: {line}");
            }

            size = parsedSize;
        }

        if (!bool.TryParse(nullableRaw, out var nullable))
        {
            throw new FormatException($"Invalid Nullable value in column line: {line}");
        }

        return new LegacyColumnDefinition(name, typeCode, size, nullable)
        {
            Constraints = ParseConstraints(constraintsRaw),
        };
    }

    private static string ReadField(string line, string label, string[] terminators)
    {
        var start = line.IndexOf(label, StringComparison.Ordinal);
        if (start < 0) return string.Empty;
        start += label.Length;

        var end = line.Length;
        foreach (var terminator in terminators)
        {
            var t = line.IndexOf(terminator, start, StringComparison.Ordinal);
            if (t >= 0 && t < end) end = t;
        }

        return line[start..end].Trim();
    }

    private static IReadOnlyList<string> ParseConstraints(string value)
    {
        if (string.IsNullOrWhiteSpace(value))
        {
            return [];
        }

        return value
            .Split(',', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries)
            .ToArray();
    }
}