using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

using C4IT.FASD.Base;

namespace C4IT.F4SD
{
    internal sealed class TicketFilterResolution
    {
        public bool Success { get; set; }
        public string Error { get; set; }
        public List<Guid> RoleIds { get; set; } = new List<Guid>();
    }

    internal sealed class TicketFilterCompilationResult
    {
        public bool Success { get; set; }
        public string Clause { get; set; }
        public string Error { get; set; }
    }

    internal static class TicketFilterCompiler
    {
        internal const string ProviderName = "Matrix42";
        internal const string AssignmentGroupField = "AssignmentGroup";
        internal const string QueueField = "Queue";
        internal const string WorkspaceField = "Workspace";

        internal static async Task<TicketFilterCompilationResult> CompileAsync(
            cTicketFilterPolicy policy,
            Func<cTicketFilter, Task<TicketFilterResolution>> workspaceResolver)
        {
            var clauses = new List<string>();
            foreach (var filter in policy?.Filters ?? new List<cTicketFilter>())
            {
                if (filter == null || !filter.Enabled)
                    continue;

                var providerSpecific = !string.IsNullOrWhiteSpace(filter.Provider);
                if (providerSpecific && !string.Equals(filter.Provider, ProviderName, StringComparison.OrdinalIgnoreCase))
                    return Fail($"Unsupported ticket filter provider '{filter.Provider}'.");

                var field = filter.Field?.Trim();
                string emptyClause;
                string valueClause;

                if (!providerSpecific && string.Equals(field, AssignmentGroupField, StringComparison.OrdinalIgnoreCase))
                {
                    emptyClause = "RecipientRole IS NULL";
                    valueClause = BuildValueClause("RecipientRole.T(SPSSecurityClassRole).ID", "RecipientRole.T(SPSSecurityClassRole).Name", filter.Values);
                }
                else if (providerSpecific && string.Equals(field, QueueField, StringComparison.OrdinalIgnoreCase))
                {
                    emptyClause = "Queue IS NULL";
                    valueClause = BuildValueClause("Queue.ID", "Queue.Name", filter.Values);
                }
                else if (providerSpecific && string.Equals(field, WorkspaceField, StringComparison.OrdinalIgnoreCase))
                {
                    if (workspaceResolver == null)
                        return Fail("The Matrix42 Workspace filter is not supported by this product version.");

                    var resolution = await workspaceResolver(filter);
                    if (resolution?.Success != true)
                        return Fail(resolution?.Error ?? "The Matrix42 Workspace filter could not be resolved.");

                    emptyClause = "RecipientRole IS NULL";
                    valueClause = BuildGuidClause("RecipientRole.T(SPSSecurityClassRole).ID", resolution.RoleIds);
                }
                else
                {
                    return Fail($"Unsupported ticket filter field '{filter.Provider}:{field}'.");
                }

                if (filter.EmptyHandling == enumTicketFilterEmptyHandling.only)
                {
                    clauses.Add($"({emptyClause})");
                    continue;
                }

                if (string.IsNullOrWhiteSpace(valueClause))
                    return Fail($"Ticket filter '{filter.Provider}:{field}' has no valid values.");

                var matchClause = filter.Match == enumTicketFilterMatch.exclude
                    ? $"NOT ({valueClause})"
                    : $"({valueClause})";

                clauses.Add(filter.EmptyHandling == enumTicketFilterEmptyHandling.include
                    ? $"(({emptyClause}) OR ({matchClause}))"
                    : $"((NOT ({emptyClause})) AND ({matchClause}))");
            }

            return new TicketFilterCompilationResult
            {
                Success = true,
                Clause = string.Join(" AND ", clauses)
            };
        }

        private static string BuildValueClause(string idField, string nameField, IEnumerable<cTicketFilterValue> values)
        {
            var items = (values ?? Enumerable.Empty<cTicketFilterValue>())
                .Where(value => value != null)
                .ToList();
            var ids = items
                .Select(value => value.ID?.Trim())
                .Where(value => !string.IsNullOrWhiteSpace(value))
                .Distinct(StringComparer.OrdinalIgnoreCase)
                .Select(Quote)
                .ToList();
            var names = items
                .Select(value => value.Name?.Trim())
                .Where(value => !string.IsNullOrWhiteSpace(value))
                .Distinct(StringComparer.OrdinalIgnoreCase)
                .Select(Quote)
                .ToList();

            var clauses = new List<string>();
            if (ids.Count > 0)
                clauses.Add($"{idField} IN ({string.Join(", ", ids)})");
            if (names.Count > 0)
                clauses.Add($"{nameField} IN ({string.Join(", ", names)})");
            return string.Join(" OR ", clauses);
        }

        private static string BuildGuidClause(string field, IEnumerable<Guid> values)
        {
            var ids = (values ?? Enumerable.Empty<Guid>())
                .Where(value => value != Guid.Empty)
                .Distinct()
                .Select(value => Quote(value.ToString("D")))
                .ToList();
            return ids.Count == 0 ? null : $"{field} IN ({string.Join(", ", ids)})";
        }

        private static string Quote(string value)
        {
            return $"'{(value ?? string.Empty).Replace("'", "''")}'";
        }

        private static TicketFilterCompilationResult Fail(string error)
        {
            return new TicketFilterCompilationResult
            {
                Success = false,
                Error = error
            };
        }
    }
}