using System.Globalization;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Routing;
using Microsoft.Extensions.DependencyInjection;
using ScadaLink.Commons.Entities.Audit;
using ScadaLink.Commons.Interfaces.Repositories;
using ScadaLink.Commons.Messages.Management;
using ScadaLink.Commons.Types.Audit;
using ScadaLink.Commons.Types.Enums;
using ScadaLink.Security;

namespace ScadaLink.ManagementService;

/// <summary>
/// Minimal-API endpoints exposing the central Audit Log (#23) over HTTP for the
/// ScadaLink CLI (M8). Two routes:
/// <list type="bullet">
///   <item><c>GET /api/audit/query</c> — keyset-paged JSON page, gated on the
///   <see cref="AuthorizationPolicies.OperationalAudit"/> permission.</item>
///   <item><c>GET /api/audit/export</c> — streamed bulk export (csv / jsonl;
///   parquet returns HTTP 501), gated on the
///   <see cref="AuthorizationPolicies.AuditExport"/> permission.</item>
/// </list>
///
/// <para>
/// <b>Auth mechanism.</b> ManagementService ships NO ASP.NET authorization-policy
/// pipeline — the existing <c>/management</c> endpoint
/// (<see cref="ManagementEndpoints"/>) authenticates each request by hand:
/// decode HTTP Basic Auth, bind against LDAP via <see cref="LdapAuthService"/>,
/// then map LDAP groups to roles via <see cref="RoleMapper"/>. These audit
/// endpoints follow that exact mechanism rather than <c>.RequireAuthorization()</c>
/// so the CLI authenticates the same way it does for every other management
/// call (HTTP Basic). Permission gating is then a role-set membership check
/// against <see cref="AuthorizationPolicies.OperationalAuditRoles"/> /
/// <see cref="AuthorizationPolicies.AuditExportRoles"/> — the very role sets the
/// CentralUI's <see cref="AuthorizationPolicies"/> enforces, so the two surfaces
/// stay in lockstep.
/// </para>
///
/// <para>
/// <b>Parquet.</b> No Parquet library is referenced by the solution and
/// <c>Component-AuditLog.md</c> explicitly defers Parquet archival to v1.x, so
/// <c>format=parquet</c> returns <c>501 Not Implemented</c> with a guidance
/// message rather than a half-built binary stream. csv + jsonl are fully
/// implemented.
/// </para>
/// </summary>
public static class AuditEndpoints
{
    /// <summary>Default rows per page for <c>/api/audit/query</c>.</summary>
    public const int DefaultPageSize = 100;

    /// <summary>Hard ceiling on a single query page — keeps one page bounded in memory.</summary>
    public const int MaxPageSize = 1000;

    /// <summary>Repository round-trip size used while streaming an export.</summary>
    public const int ExportPageSize = 1000;

    /// <summary>
    /// Serializer for individual <see cref="AuditEvent"/> rows (query results +
    /// jsonl export lines). Drops null columns so a sparse audit row stays
    /// compact on the wire.
    /// </summary>
    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
        Converters = { new JsonStringEnumConverter() },
    };

    /// <summary>
    /// Serializer for the <c>/api/audit/query</c> response envelope. Unlike
    /// <see cref="JsonOptions"/> it does NOT ignore nulls — the contract
    /// requires <c>nextCursor</c> to be present as an explicit <c>null</c> when
    /// there is no further page, so the CLI can rely on the key always existing.
    /// </summary>
    private static readonly JsonSerializerOptions EnvelopeJsonOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        Converters = { new JsonStringEnumConverter() },
    };

    public static IEndpointRouteBuilder MapAuditAPI(this IEndpointRouteBuilder endpoints)
    {
        endpoints.MapGet("/api/audit/query", (Delegate)HandleQuery);
        endpoints.MapGet("/api/audit/export", (Delegate)HandleExport);
        return endpoints;
    }

    // ─────────────────────────────────────────────────────────────────────
    // GET /api/audit/query
    // ─────────────────────────────────────────────────────────────────────

    internal static async Task<IResult> HandleQuery(HttpContext context)
    {
        var auth = await AuthenticateAsync(context);
        if (auth.Failure is not null)
        {
            return auth.Failure;
        }

        if (!HasAnyRole(auth.User!, AuthorizationPolicies.OperationalAuditRoles))
        {
            return Forbidden("OperationalAudit");
        }

        var filter = ParseFilter(context.Request.Query);
        var paging = ParsePaging(context.Request.Query);

        var repo = context.RequestServices.GetRequiredService<IAuditLogRepository>();
        var events = await repo.QueryAsync(filter, paging, context.RequestAborted);

        // The cursor for the next page is the last row of this page — but only
        // when the page came back FULL. A short page means there is no next
        // page, so nextCursor is null and the CLI stops paging.
        object? nextCursor = null;
        if (events.Count == paging.PageSize && events.Count > 0)
        {
            var last = events[^1];
            nextCursor = new
            {
                afterOccurredAtUtc = last.OccurredAtUtc,
                afterEventId = last.EventId,
            };
        }

        var payload = new { events, nextCursor };
        // EnvelopeJsonOptions keeps an explicit null nextCursor on the wire so
        // the CLI can always read the key. AuditEvent rows render with their
        // full (null-inclusive) shape — a stable schema for the consumer.
        return Results.Text(
            JsonSerializer.Serialize(payload, EnvelopeJsonOptions), "application/json", statusCode: 200);
    }

    // ─────────────────────────────────────────────────────────────────────
    // GET /api/audit/export
    // ─────────────────────────────────────────────────────────────────────

    internal static async Task<IResult> HandleExport(HttpContext context)
    {
        var auth = await AuthenticateAsync(context);
        if (auth.Failure is not null)
        {
            return auth.Failure;
        }

        if (!HasAnyRole(auth.User!, AuthorizationPolicies.AuditExportRoles))
        {
            return Forbidden("AuditExport");
        }

        var format = (context.Request.Query["format"].ToString() ?? string.Empty).Trim().ToLowerInvariant();
        if (string.IsNullOrEmpty(format))
        {
            format = "csv";
        }

        if (format == "parquet")
        {
            // Deferred to v1.x (Component-AuditLog.md §"Deferred"): no Parquet
            // library is in the solution. Return a 501 with actionable guidance
            // rather than a partial binary stream.
            return Results.Json(
                new { error = "Parquet export deferred to v1.x; use csv or jsonl.", code = "NOT_IMPLEMENTED" },
                statusCode: 501);
        }

        if (format != "csv" && format != "jsonl")
        {
            return Results.Json(
                new { error = $"Unsupported export format '{format}'. Use csv, jsonl, or parquet.", code = "BAD_REQUEST" },
                statusCode: 400);
        }

        var filter = ParseFilter(context.Request.Query);
        var repo = context.RequestServices.GetRequiredService<IAuditLogRepository>();

        var contentType = format == "csv" ? "text/csv; charset=utf-8" : "application/x-ndjson";
        var extension = format == "csv" ? "csv" : "jsonl";
        var fileName = $"audit-log-{DateTime.UtcNow:yyyyMMdd-HHmmss}.{extension}";

        context.Response.ContentType = contentType;
        context.Response.Headers["Content-Disposition"] = $"attachment; filename=\"{fileName}\"";
        // Defeat intermediate proxy buffering so rows stream as each page flushes.
        context.Response.Headers["Cache-Control"] = "no-store";

        if (format == "csv")
        {
            await StreamCsvAsync(repo, filter, context.Response.Body, context.RequestAborted);
        }
        else
        {
            await StreamJsonlAsync(repo, filter, context.Response.Body, context.RequestAborted);
        }

        return Results.Empty;
    }

    /// <summary>
    /// Streams every matching row as RFC 4180 CSV, paging the repository with its
    /// keyset cursor and flushing after each page so a large export starts
    /// arriving immediately. Column order matches <see cref="AuditEvent"/>.
    /// </summary>
    private static async Task StreamCsvAsync(
        IAuditLogRepository repo, AuditLogQueryFilter filter, Stream output, CancellationToken ct)
    {
        await using var writer = new StreamWriter(
            output,
            new UTF8Encoding(encoderShouldEmitUTF8Identifier: false),
            bufferSize: 4096,
            leaveOpen: true)
        {
            NewLine = "\r\n",
        };

        await writer.WriteLineAsync(CsvHeader);

        await foreach (var page in PageAsync(repo, filter, ct))
        {
            foreach (var evt in page)
            {
                await writer.WriteLineAsync(FormatCsvRow(evt));
            }
            await writer.FlushAsync(ct);
            await output.FlushAsync(ct);
        }
    }

    /// <summary>
    /// Streams every matching row as newline-delimited JSON (one compact object
    /// per line), flushing after each page.
    /// </summary>
    private static async Task StreamJsonlAsync(
        IAuditLogRepository repo, AuditLogQueryFilter filter, Stream output, CancellationToken ct)
    {
        await using var writer = new StreamWriter(
            output,
            new UTF8Encoding(encoderShouldEmitUTF8Identifier: false),
            bufferSize: 4096,
            leaveOpen: true)
        {
            NewLine = "\n",
        };

        await foreach (var page in PageAsync(repo, filter, ct))
        {
            foreach (var evt in page)
            {
                await writer.WriteLineAsync(JsonSerializer.Serialize(evt, JsonOptions));
            }
            await writer.FlushAsync(ct);
            await output.FlushAsync(ct);
        }
    }

    /// <summary>
    /// Lazily yields full repository pages, advancing the keyset cursor until a
    /// short page signals the end. Shared by the csv + jsonl streamers.
    /// </summary>
    private static async IAsyncEnumerable<IReadOnlyList<AuditEvent>> PageAsync(
        IAuditLogRepository repo,
        AuditLogQueryFilter filter,
        [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken ct)
    {
        var cursor = new AuditLogPaging(ExportPageSize);
        while (true)
        {
            ct.ThrowIfCancellationRequested();
            var page = await repo.QueryAsync(filter, cursor, ct);
            if (page.Count == 0)
            {
                yield break;
            }

            yield return page;

            if (page.Count < cursor.PageSize)
            {
                yield break;
            }

            var last = page[^1];
            cursor = new AuditLogPaging(ExportPageSize, last.OccurredAtUtc, last.EventId);
        }
    }

    // ─────────────────────────────────────────────────────────────────────
    // Authentication — Basic Auth → LDAP → roles (mirrors ManagementEndpoints)
    // ─────────────────────────────────────────────────────────────────────

    /// <summary>Outcome of <see cref="AuthenticateAsync"/>: exactly one of the two fields is set.</summary>
    private readonly record struct AuthOutcome(AuthenticatedUser? User, IResult? Failure);

    /// <summary>
    /// Decodes HTTP Basic Auth, binds against LDAP, and resolves roles — the same
    /// flow <see cref="ManagementEndpoints"/> uses. Returns a populated
    /// <see cref="AuthenticatedUser"/> on success, or an <see cref="IResult"/>
    /// carrying the 401 response on any failure.
    /// </summary>
    private static async Task<AuthOutcome> AuthenticateAsync(HttpContext context)
    {
        var authHeader = context.Request.Headers.Authorization.ToString();
        if (string.IsNullOrEmpty(authHeader) || !authHeader.StartsWith("Basic ", StringComparison.OrdinalIgnoreCase))
        {
            return new AuthOutcome(null, Results.Json(
                new { error = "Authorization header required (Basic scheme).", code = "AUTH_FAILED" }, statusCode: 401));
        }

        string username, password;
        try
        {
            var decoded = Encoding.UTF8.GetString(Convert.FromBase64String(authHeader["Basic ".Length..]));
            var colon = decoded.IndexOf(':');
            if (colon < 0) throw new FormatException();
            username = decoded[..colon];
            password = decoded[(colon + 1)..];
        }
        catch
        {
            return new AuthOutcome(null, Results.Json(
                new { error = "Malformed Basic Auth header.", code = "AUTH_FAILED" }, statusCode: 401));
        }

        if (string.IsNullOrWhiteSpace(username) || string.IsNullOrWhiteSpace(password))
        {
            return new AuthOutcome(null, Results.Json(
                new { error = "Username and password are required.", code = "AUTH_FAILED" }, statusCode: 401));
        }

        var ldapAuth = context.RequestServices.GetRequiredService<LdapAuthService>();
        var authResult = await ldapAuth.AuthenticateAsync(username, password);
        if (!authResult.Success)
        {
            return new AuthOutcome(null, Results.Json(
                new { error = authResult.ErrorMessage ?? "Authentication failed.", code = "AUTH_FAILED" }, statusCode: 401));
        }

        var roleMapper = context.RequestServices.GetRequiredService<RoleMapper>();
        var mappingResult = await roleMapper.MapGroupsToRolesAsync(
            authResult.Groups ?? (IReadOnlyList<string>)Array.Empty<string>());

        var permittedSiteIds = mappingResult.IsSystemWideDeployment
            ? Array.Empty<string>()
            : mappingResult.PermittedSiteIds.ToArray();

        var user = new AuthenticatedUser(
            authResult.Username!,
            authResult.DisplayName!,
            mappingResult.Roles.ToArray(),
            permittedSiteIds);

        return new AuthOutcome(user, null);
    }

    private static bool HasAnyRole(AuthenticatedUser user, string[] allowed) =>
        user.Roles.Any(r => allowed.Contains(r, StringComparer.OrdinalIgnoreCase));

    private static IResult Forbidden(string permission) => Results.Json(
        new { error = $"Permission '{permission}' required.", code = "UNAUTHORIZED" }, statusCode: 403);

    // ─────────────────────────────────────────────────────────────────────
    // Query-string parsing
    // ─────────────────────────────────────────────────────────────────────

    /// <summary>
    /// Parses the query-string into an <see cref="AuditLogQueryFilter"/>. The
    /// <c>channel</c>/<c>kind</c>/<c>status</c>/<c>sourceSiteId</c> dimensions are
    /// multi-value: a repeated query param (<c>channel=A&amp;channel=B</c>) yields
    /// a multi-element filter list, while a single param yields a one-element
    /// list. Unknown enum names / un-parseable Guids / dates are silently dropped
    /// (no 400) — the same lax contract the CentralUI export endpoint uses; an
    /// unparseable value within a repeated set is dropped, not the whole set.
    /// </summary>
    /// <remarks>
    /// This endpoint reads the source-site filter from the <c>sourceSiteId</c>
    /// query key, whereas the CentralUI export endpoint reads it as <c>site</c>.
    /// The divergence is deliberate — each endpoint matches its own CLI / UI URL
    /// builder — so do NOT "fix" the two to a single key name.
    /// </remarks>
    public static AuditLogQueryFilter ParseFilter(IQueryCollection query)
    {
        var channels = AuditQueryParamParsers.ParseEnumList<AuditChannel>(query["channel"]);
        var kinds = AuditQueryParamParsers.ParseEnumList<AuditKind>(query["kind"]);
        var statuses = AuditQueryParamParsers.ParseEnumList<AuditStatus>(query["status"]);
        var sourceSiteIds = AuditQueryParamParsers.ParseStringList(query["sourceSiteId"]);

        Guid? correlationId = null;
        if (query.TryGetValue("correlationId", out var corrValues)
            && Guid.TryParse(corrValues.ToString(), out var parsedCorr))
        {
            correlationId = parsedCorr;
        }

        return new AuditLogQueryFilter(
            Channels: channels,
            Kinds: kinds,
            Statuses: statuses,
            SourceSiteIds: sourceSiteIds,
            Target: TrimToNullable(query, "target"),
            Actor: TrimToNullable(query, "actor"),
            CorrelationId: correlationId,
            FromUtc: ParseUtcDate(query, "fromUtc"),
            ToUtc: ParseUtcDate(query, "toUtc"));
    }

    /// <summary>
    /// Parses the keyset-paging query parameters into an
    /// <see cref="AuditLogPaging"/>. <c>pageSize</c> is clamped to
    /// <c>[1, <see cref="MaxPageSize"/>]</c>; a missing / junk value falls back
    /// to <see cref="DefaultPageSize"/>. <c>afterOccurredAtUtc</c> +
    /// <c>afterEventId</c> are honoured only when BOTH parse (the repository's
    /// keyset cursor requires the pair together).
    /// </summary>
    public static AuditLogPaging ParsePaging(IQueryCollection query)
    {
        int pageSize = DefaultPageSize;
        if (query.TryGetValue("pageSize", out var pageSizeRaw)
            && int.TryParse(pageSizeRaw.ToString(), NumberStyles.Integer, CultureInfo.InvariantCulture, out var parsedSize)
            && parsedSize > 0)
        {
            pageSize = Math.Min(parsedSize, MaxPageSize);
        }

        DateTime? afterOccurredAt = ParseUtcDate(query, "afterOccurredAtUtc");

        Guid? afterEventId = null;
        if (query.TryGetValue("afterEventId", out var eventIdRaw)
            && Guid.TryParse(eventIdRaw.ToString(), out var parsedEventId))
        {
            afterEventId = parsedEventId;
        }

        // The cursor pair must be all-or-nothing — a half-supplied cursor would
        // produce an invalid keyset predicate. Drop both unless both are present.
        if (afterOccurredAt is null || afterEventId is null)
        {
            return new AuditLogPaging(pageSize);
        }

        return new AuditLogPaging(pageSize, afterOccurredAt, afterEventId);
    }

    private static string? TrimToNullable(IQueryCollection query, string key)
    {
        if (!query.TryGetValue(key, out var values))
        {
            return null;
        }
        var v = values.ToString();
        return string.IsNullOrWhiteSpace(v) ? null : v.Trim();
    }

    private static DateTime? ParseUtcDate(IQueryCollection query, string key)
    {
        if (!query.TryGetValue(key, out var values))
        {
            return null;
        }
        if (DateTime.TryParse(
            values.ToString(),
            CultureInfo.InvariantCulture,
            DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal,
            out var parsed))
        {
            return DateTime.SpecifyKind(parsed, DateTimeKind.Utc);
        }
        return null;
    }

    // ─────────────────────────────────────────────────────────────────────
    // CSV helpers — 21 columns in AuditEvent declaration order
    // ─────────────────────────────────────────────────────────────────────

    public const string CsvHeader =
        "EventId,OccurredAtUtc,IngestedAtUtc,Channel,Kind,CorrelationId," +
        "SourceSiteId,SourceInstanceId,SourceScript,Actor,Target,Status," +
        "HttpStatus,DurationMs,ErrorMessage,ErrorDetail,RequestSummary," +
        "ResponseSummary,PayloadTruncated,Extra,ForwardState";

    public static string FormatCsvRow(AuditEvent evt)
    {
        var sb = new StringBuilder(256);
        AppendField(sb, evt.EventId.ToString(), first: true);
        AppendField(sb, FormatDate(evt.OccurredAtUtc));
        AppendField(sb, FormatDate(evt.IngestedAtUtc));
        AppendField(sb, evt.Channel.ToString());
        AppendField(sb, evt.Kind.ToString());
        AppendField(sb, evt.CorrelationId?.ToString());
        AppendField(sb, evt.SourceSiteId);
        AppendField(sb, evt.SourceInstanceId);
        AppendField(sb, evt.SourceScript);
        AppendField(sb, evt.Actor);
        AppendField(sb, evt.Target);
        AppendField(sb, evt.Status.ToString());
        AppendField(sb, evt.HttpStatus?.ToString(CultureInfo.InvariantCulture));
        AppendField(sb, evt.DurationMs?.ToString(CultureInfo.InvariantCulture));
        AppendField(sb, evt.ErrorMessage);
        AppendField(sb, evt.ErrorDetail);
        AppendField(sb, evt.RequestSummary);
        AppendField(sb, evt.ResponseSummary);
        AppendField(sb, evt.PayloadTruncated.ToString());
        AppendField(sb, evt.Extra);
        AppendField(sb, evt.ForwardState?.ToString());
        return sb.ToString();
    }

    private static string? FormatDate(DateTime? value) =>
        value?.ToString("O", CultureInfo.InvariantCulture);

    private static string FormatDate(DateTime value) =>
        value.ToString("O", CultureInfo.InvariantCulture);

    private static void AppendField(StringBuilder sb, string? value, bool first = false)
    {
        if (!first) sb.Append(',');
        if (string.IsNullOrEmpty(value))
        {
            return;
        }

        // RFC 4180: quote on comma / quote / CR / LF; double-up embedded quotes.
        if (value.IndexOfAny(s_quoteTriggers) < 0)
        {
            sb.Append(value);
            return;
        }

        sb.Append('"');
        foreach (var ch in value)
        {
            if (ch == '"')
            {
                sb.Append('"').Append('"');
            }
            else
            {
                sb.Append(ch);
            }
        }
        sb.Append('"');
    }

    private static readonly char[] s_quoteTriggers = { ',', '"', '\r', '\n' };
}