using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Globalization;
using System.Text;
using System.Text.Json;

namespace StellaOps.Scanner.Surface.Secrets;

public sealed record RegistryAccessSecret(
    IReadOnlyList<RegistryCredential> Entries,
    string? DefaultRegistry);

public sealed record RegistryCredential(
    string Registry,
    string? Username,
    string? Password,
    string? IdentityToken,
    string? RegistryToken,
    string? RefreshToken,
    DateTimeOffset? ExpiresAt,
    IReadOnlyCollection<string> Scopes,
    bool? AllowInsecureTls,
    IReadOnlyDictionary<string, string> Headers,
    string? Email);

public static partial class SurfaceSecretParser
{
    public static RegistryAccessSecret ParseRegistryAccessSecret(SurfaceSecretHandle handle)
    {
        ArgumentNullException.ThrowIfNull(handle);

        var entries = new List<RegistryCredential>();
        string? defaultRegistry = null;

        var payload = handle.AsBytes();
        if (!payload.IsEmpty)
        {
            var jsonText = DecodeUtf8(payload);
            using var document = JsonDocument.Parse(jsonText);
            var root = document.RootElement;

            defaultRegistry = GetString(root, "defaultRegistry") ?? GetMetadataValue(handle.Metadata, "defaultRegistry");

            if (TryParseRegistryEntries(root, handle.Metadata, entries) ||
                TryParseAuthsObject(root, handle.Metadata, entries))
            {
                // entries already populated
            }
            else if (root.ValueKind == JsonValueKind.Object && root.GetRawText().Length > 2) // not empty object
            {
                entries.Add(ParseRegistryEntry(root, handle.Metadata, fallbackRegistry: null));
            }
        }

        if (entries.Count == 0 && TryCreateRegistryEntryFromMetadata(handle.Metadata, out var metadataEntry))
        {
            entries.Add(metadataEntry);
        }

        if (entries.Count == 0)
        {
            throw new InvalidOperationException("Registry secret payload does not contain credentials.");
        }

        defaultRegistry ??= GetMetadataValue(handle.Metadata, "defaultRegistry")
            ?? entries[0].Registry;

        return new RegistryAccessSecret(
            new ReadOnlyCollection<RegistryCredential>(entries),
            string.IsNullOrWhiteSpace(defaultRegistry) ? entries[0].Registry : defaultRegistry.Trim());
    }

    private static bool TryParseRegistryEntries(
        JsonElement root,
        IReadOnlyDictionary<string, string> metadata,
        ICollection<RegistryCredential> entries)
    {
        if (!TryGetPropertyIgnoreCase(root, "entries", out var entriesElement) ||
            entriesElement.ValueKind != JsonValueKind.Array)
        {
            return false;
        }

        foreach (var entryElement in entriesElement.EnumerateArray())
        {
            if (entryElement.ValueKind != JsonValueKind.Object)
            {
                continue;
            }

            entries.Add(ParseRegistryEntry(entryElement, metadata, fallbackRegistry: null));
        }

        return entries.Count > 0;
    }

    private static bool TryParseAuthsObject(
        JsonElement root,
        IReadOnlyDictionary<string, string> metadata,
        ICollection<RegistryCredential> entries)
    {
        if (!TryGetPropertyIgnoreCase(root, "auths", out var authsElement) ||
            authsElement.ValueKind != JsonValueKind.Object)
        {
            return false;
        }

        foreach (var property in authsElement.EnumerateObject())
        {
            if (property.Value.ValueKind != JsonValueKind.Object)
            {
                continue;
            }

            entries.Add(ParseRegistryEntry(property.Value, metadata, property.Name));
        }

        return entries.Count > 0;
    }

    private static RegistryCredential ParseRegistryEntry(
        JsonElement element,
        IReadOnlyDictionary<string, string> metadata,
        string? fallbackRegistry)
    {
        var registry = GetString(element, "registry")
            ?? GetString(element, "server")
            ?? fallbackRegistry
            ?? GetMetadataValue(metadata, "registry")
            ?? throw new InvalidOperationException("Registry credential is missing a registry identifier.");

        registry = registry.Trim();

        var username = GetString(element, "username") ?? GetString(element, "user");
        var password = GetString(element, "password") ?? GetString(element, "pass");
        var token = GetString(element, "token") ?? GetString(element, "registryToken");
        var identityToken = GetString(element, "identityToken") ?? GetString(element, "identitytoken");
        var refreshToken = GetString(element, "refreshToken");
        var email = GetString(element, "email");
        var allowInsecure = GetBoolean(element, "allowInsecureTls");

        var headers = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        PopulateHeaders(element, headers);
        PopulateMetadataHeaders(metadata, headers);

        var scopes = new List<string>();
        PopulateScopes(element, scopes);
        PopulateMetadataScopes(metadata, scopes);

        var expiresAt = ParseDateTime(element, "expiresAt");

        var auth = GetString(element, "auth");
        if (!string.IsNullOrWhiteSpace(auth))
        {
            TryApplyBasicAuth(auth, ref username, ref password);
        }

        username ??= GetMetadataValue(metadata, "username");
        password ??= GetMetadataValue(metadata, "password");
        token ??= GetMetadataValue(metadata, "token") ?? GetMetadataValue(metadata, "registryToken");
        identityToken ??= GetMetadataValue(metadata, "identityToken");
        refreshToken ??= GetMetadataValue(metadata, "refreshToken");
        email ??= GetMetadataValue(metadata, "email");

        return new RegistryCredential(
            registry,
            username?.Trim(),
            password,
            identityToken,
            token,
            refreshToken,
            expiresAt,
            scopes.Count == 0 ? Array.Empty<string>() : new ReadOnlyCollection<string>(scopes),
            allowInsecure,
            new ReadOnlyDictionary<string, string>(headers),
            email);
    }

    private static bool TryCreateRegistryEntryFromMetadata(
        IReadOnlyDictionary<string, string> metadata,
        out RegistryCredential entry)
    {
        var registry = GetMetadataValue(metadata, "registry");
        var username = GetMetadataValue(metadata, "username");
        var password = GetMetadataValue(metadata, "password");
        var identityToken = GetMetadataValue(metadata, "identityToken");
        var token = GetMetadataValue(metadata, "token") ?? GetMetadataValue(metadata, "registryToken");

        if (string.IsNullOrWhiteSpace(registry) &&
            string.IsNullOrWhiteSpace(username) &&
            string.IsNullOrWhiteSpace(password) &&
            string.IsNullOrWhiteSpace(identityToken) &&
            string.IsNullOrWhiteSpace(token))
        {
            entry = null!;
            return false;
        }

        var headers = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        PopulateMetadataHeaders(metadata, headers);

        var scopes = new List<string>();
        PopulateMetadataScopes(metadata, scopes);

        entry = new RegistryCredential(
            registry?.Trim() ?? "registry.local",
            username?.Trim(),
            password,
            identityToken,
            token,
            GetMetadataValue(metadata, "refreshToken"),
            ParseDateTime(metadata, "expiresAt"),
            scopes.Count == 0 ? Array.Empty<string>() : new ReadOnlyCollection<string>(scopes),
            ParseBoolean(metadata, "allowInsecureTls"),
            new ReadOnlyDictionary<string, string>(headers),
            GetMetadataValue(metadata, "email"));
        return true;
    }

    private static void PopulateScopes(JsonElement element, ICollection<string> scopes)
    {
        if (!TryGetPropertyIgnoreCase(element, "scopes", out var scopesElement))
        {
            return;
        }

        switch (scopesElement.ValueKind)
        {
            case JsonValueKind.Array:
                foreach (var scope in scopesElement.EnumerateArray())
                {
                    if (scope.ValueKind == JsonValueKind.String)
                    {
                        var value = scope.GetString();
                        if (!string.IsNullOrWhiteSpace(value))
                        {
                            scopes.Add(value.Trim());
                        }
                    }
                }

                break;
            case JsonValueKind.String:
                var text = scopesElement.GetString();
                if (!string.IsNullOrWhiteSpace(text))
                {
                    foreach (var part in text.Split(new[] { ',', ' ' }, StringSplitOptions.RemoveEmptyEntries))
                    {
                        scopes.Add(part.Trim());
                    }
                }

                break;
        }
    }

    private static void PopulateMetadataScopes(IReadOnlyDictionary<string, string> metadata, ICollection<string> scopes)
    {
        foreach (var (key, value) in metadata)
        {
            if (!key.StartsWith("scope", StringComparison.OrdinalIgnoreCase))
            {
                continue;
            }

            if (string.IsNullOrWhiteSpace(value))
            {
                continue;
            }

            scopes.Add(value.Trim());
        }
    }

    private static void TryApplyBasicAuth(string auth, ref string? username, ref string? password)
    {
        try
        {
            var decoded = Encoding.UTF8.GetString(Convert.FromBase64String(auth));
            var separator = decoded.IndexOf(':');
            if (separator >= 0)
            {
                username ??= decoded[..separator];
                password ??= decoded[(separator + 1)..];
            }
        }
        catch (FormatException)
        {
            // ignore malformed auth; caller may still have explicit username/password fields
        }
    }

    private static DateTimeOffset? ParseDateTime(JsonElement element, string propertyName)
    {
        if (!TryGetPropertyIgnoreCase(element, propertyName, out var value) ||
            value.ValueKind != JsonValueKind.String)
        {
            return null;
        }

        var text = value.GetString();
        if (string.IsNullOrWhiteSpace(text))
        {
            return null;
        }

        if (DateTimeOffset.TryParse(text, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out var parsed))
        {
            return parsed;
        }

        return null;
    }

    private static DateTimeOffset? ParseDateTime(IReadOnlyDictionary<string, string> metadata, string key)
    {
        var value = GetMetadataValue(metadata, key);
        if (string.IsNullOrWhiteSpace(value))
        {
            return null;
        }

        if (DateTimeOffset.TryParse(value, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out var parsed))
        {
            return parsed;
        }

        return null;
    }

    private static bool? ParseBoolean(IReadOnlyDictionary<string, string> metadata, string key)
    {
        var value = GetMetadataValue(metadata, key);
        if (string.IsNullOrWhiteSpace(value))
        {
            return null;
        }

        if (bool.TryParse(value, out var parsed))
        {
            return parsed;
        }

        return null;
    }
}