/* ========================================================================
 * Copyright (c) 2005-2026 The OPC Foundation, Inc. All rights reserved.
 *
 * OPC Foundation MIT License 1.00
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * The complete license agreement can be found here:
 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using Opc.Ua.Schema.Model;

namespace Opc.Ua.SourceGeneration
{
    /// <summary>
    /// Emits strongly-typed identifier classes for every concrete
    /// <c>FiniteStateMachineType</c> subtype in a model. For each FSM
    /// type the generator emits a nested static class containing
    /// <c>StateIds</c> / <c>StateNumbers</c> / <c>TransitionIds</c> /
    /// <c>TransitionNumbers</c> constants so application code can
    /// reference Part-16 state identifiers symbolically rather than by
    /// magic numeric NodeId.
    /// </summary>
    /// <remarks>
    /// <para>
    /// Example output (excerpt) for <c>InstallationStateMachineType</c>
    /// in the DI model:
    /// </para>
    /// <code language="csharp">
    /// public static partial class InstallationStateMachineIds
    /// {
    ///     public static partial class StateIds
    ///     {
    ///         public const uint Idle      = Objects.InstallationStateMachineType_Idle;
    ///         public const uint Installing = Objects.InstallationStateMachineType_Installing;
    ///         public const uint Error      = Objects.InstallationStateMachineType_Error;
    ///     }
    ///     public static partial class StateNumbers
    ///     {
    ///         public const uint Idle = 1u; public const uint Installing = 2u; public const uint Error = 3u;
    ///     }
    ///     // ... TransitionIds, TransitionNumbers
    /// }
    /// </code>
    /// <para>
    /// The generator runs by default for every model that defines at
    /// least one FSM subtype; consumers can suppress it with
    /// <see cref="GeneratorOptions.OmitStateMachineIds"/>.
    /// </para>
    /// </remarks>
    internal sealed class StateMachineIdsGenerator : IGenerator
    {
        private const string kFiniteStateMachineTypeName = "FiniteStateMachineType";
        private const string kStateType = "StateType";
        private const string kInitialStateType = "InitialStateType";
        private const string kTransitionType = "TransitionType";
        private const string kStateNumberProperty = "StateNumber";
        private const string kTransitionNumberProperty = "TransitionNumber";
        private const string kStandardUaNamespaceUri = "http://opcfoundation.org/UA/";

        private readonly IGeneratorContext m_context;
        private Dictionary<string, string> m_nonNumericIdentifiedNodes = [];

        public StateMachineIdsGenerator(IGeneratorContext context)
        {
            m_context = context ?? throw new ArgumentNullException(nameof(context));
        }

        /// <inheritdoc/>
        public IEnumerable<Resource> Emit()
        {
            List<FsmTypeInfo> machines = CollectFiniteStateMachineTypes();
            if (machines.Count == 0)
            {
                return [];
            }
            string namespacePrefix = m_context.ModelDesign.TargetNamespace.Prefix;
            string fileName = Path.Combine(m_context.OutputFolder,
                CoreUtils.Format("{0}.StateMachineIds.g.cs", namespacePrefix));

            using TextWriter writer = m_context.FileSystem.CreateTextWriter(fileName);
            using var templateWriter = new TemplateWriter(writer);
            var template = new Template(templateWriter, StateMachineIdsTemplates.File);

            template.AddReplacement(Tokens.Namespace, namespacePrefix);
            template.AddReplacement(
                Tokens.ListOfTypes,
                StateMachineIdsTemplates.IdsClass,
                machines,
                WriteTemplate_Machine);

            template.Render();

            return [fileName.AsTextFileResource()];
        }

        private bool WriteTemplate_Machine(IWriteContext context)
        {
            if (context.Target is not FsmTypeInfo machine)
            {
                return false;
            }
            string namespacePrefix = m_context.ModelDesign.TargetNamespace.Prefix;

            context.Template.AddReplacement(Tokens.TypeName, machine.TypeName);
            context.Template.AddReplacement(
                Tokens.ClassName, CoreUtils.Format("{0}Ids", machine.TypeName));

            AddEntrySection(
                context.Template,
                Tokens.ListOfIdentifiers,
                machine.States,
                isId: true,
                namespacePrefix);
            AddEntrySection(
                context.Template,
                Tokens.ListOfValues,
                machine.States,
                isId: false,
                namespacePrefix);
            AddEntrySection(
                context.Template,
                Tokens.ListOfChildren,
                machine.Transitions,
                isId: true,
                namespacePrefix);
            AddEntrySection(
                context.Template,
                Tokens.ListOfFields,
                machine.Transitions,
                isId: false,
                namespacePrefix);

            return context.Template.Render();
        }

        private static void AddEntrySection(
            Template parent,
            string token,
            List<FsmEntry> entries,
            bool isId,
            string namespacePrefix)
        {
            if (entries.Count == 0)
            {
                // Render a single placeholder comment in the section.
                parent.AddReplacement(
                    token,
                    StateMachineIdsTemplates.EmptySectionComment,
                    [EmptyMarker.Instance],
                    null,
                    static ctx => ctx.Template.Render());
                return;
            }

            if (isId)
            {
                parent.AddReplacement(
                    token,
                    StateMachineIdsTemplates.IdEntry,
                    entries,
                    null,
                    ctx => RenderIdEntry(ctx, namespacePrefix));
            }
            else
            {
                parent.AddReplacement(
                    token,
                    StateMachineIdsTemplates.NumberEntry,
                    entries,
                    LoadNumberTemplate,
                    RenderNumberEntry);
            }
        }

        private static bool RenderIdEntry(IWriteContext context, string namespacePrefix)
        {
            if (context.Target is not FsmEntry entry)
            {
                return false;
            }
            context.Template.AddReplacement(Tokens.Name, entry.Name);
            context.Template.AddReplacement(Tokens.NamespacePrefix, namespacePrefix);
            context.Template.AddReplacement(Tokens.Identifier, entry.ObjectsConstantName);
            context.Template.AddReplacement(Tokens.IdType, entry.IdType);
            context.Template.AddReplacement(Tokens.IdModifier, entry.IdModifier);
            return context.Template.Render();
        }

        private static bool RenderNumberEntry(IWriteContext context)
        {
            if (context.Target is not FsmEntry entry)
            {
                return false;
            }
            context.Template.AddReplacement(Tokens.Name, entry.Name);
            if (entry.Number.HasValue)
            {
                context.Template.AddReplacement(
                    Tokens.NumericIdValue,
                    entry.Number.Value.ToString(CultureInfo.InvariantCulture));
            }
            return context.Template.Render();
        }

        /// <summary>
        /// onLoad callback that picks NumberEntry or NumberMissingComment
        /// template per-item based on whether the entry has a value.
        /// </summary>
        /// <param name="context"></param>
        /// <returns></returns>
        private static TemplateString LoadNumberTemplate(ILoadContext context)
        {
            if (context.Target is FsmEntry entry && !entry.Number.HasValue)
            {
                return StateMachineIdsTemplates.NumberMissingComment;
            }
            return context.TemplateString;
        }

        /// <summary>
        /// Sentinel marker used as the single 'target' in empty
        /// sections so the EmptySectionComment template gets rendered
        /// exactly once.
        /// </summary>
        private sealed class EmptyMarker
        {
            public static readonly EmptyMarker Instance = new();

            private EmptyMarker()
            {
            }
        }

        private List<FsmTypeInfo> CollectFiniteStateMachineTypes()
        {
            // The Objects constants this generator aliases are emitted by
            // NodeIdGenerator from the flattened node list, keyed by symbolic id
            // name, and typed uint or string depending on the node's identifier.
            // The declaration children walked below carry no identifier of their
            // own, so the constant type has to come from the flattened node.
            //
            // NodeIdGenerator reads the top-level nodes *and* each node's
            // instance hierarchy (GetIdentifiers), and a state or transition of
            // a FiniteStateMachineType only ever exists as a hierarchy entry -
            // never as a top-level item. Indexing just the top-level list left
            // the lookup permanently empty, so every alias fell back to "uint"
            // and the CS0029 this was meant to fix survived.
            m_nonNumericIdentifiedNodes = [];
            foreach (NodeDesign node in m_context.ModelDesign.GetNodeDesigns())
            {
                AddIfNotNumericallyIdentified(node);

                if (node.Hierarchy?.Nodes == null)
                {
                    continue;
                }

                foreach (KeyValuePair<string, HierarchyNode> entry in node.Hierarchy.Nodes)
                {
                    AddIfNotNumericallyIdentified((entry.Value?.Instance)!);
                }
            }

            var result = new List<FsmTypeInfo>();
            foreach (NodeDesign node in m_context.ModelDesign.GetNodeDesigns())
            {
                if (node is not ObjectTypeDesign objectType ||
                    m_context.ModelDesign.IsExcluded(objectType) ||
                    !IsFiniteStateMachineSubtype(objectType))
                {
                    continue;
                }
                FsmTypeInfo? info = BuildMachineInfo(objectType);
                if (info != null)
                {
                    result.Add(info);
                }
            }
            result.Sort(static (a, b) => string.CompareOrdinal(a.TypeName, b.TypeName));
            return result;
        }

        private static bool IsFiniteStateMachineSubtype(ObjectTypeDesign type)
        {
            TypeDesign? current = type;
            while (current != null)
            {
                if (string.Equals(current.SymbolicName?.Name, kFiniteStateMachineTypeName,
                        StringComparison.Ordinal) &&
                    string.Equals(current.SymbolicName?.Namespace, kStandardUaNamespaceUri,
                        StringComparison.Ordinal))
                {
                    return true;
                }
                current = current.BaseTypeNode;
            }
            return false;
        }

        private FsmTypeInfo? BuildMachineInfo(ObjectTypeDesign objectType)
        {
            // FiniteStateMachineType itself is abstract / has no child
            // state objects — skip it; only concrete subtypes get IDs.
            if (string.Equals(objectType.SymbolicName?.Namespace, kStandardUaNamespaceUri,
                    StringComparison.Ordinal) &&
                string.Equals(objectType.SymbolicName?.Name, kFiniteStateMachineTypeName,
                    StringComparison.Ordinal))
            {
                return null;
            }

            InstanceDesign[]? children = objectType.Children?.Items;
            if (children == null || children.Length == 0)
            {
                return null;
            }
            var info = new FsmTypeInfo(objectType.SymbolicName?.Name);

            foreach (InstanceDesign child in children)
            {
                if (child is not ObjectDesign childObject ||
                    childObject.TypeDefinition == null)
                {
                    continue;
                }
                string typeDefName = childObject.TypeDefinition.Name;
                string typeDefNs = childObject.TypeDefinition.Namespace;
                if (!string.Equals(typeDefNs, kStandardUaNamespaceUri, StringComparison.Ordinal))
                {
                    continue;
                }
                if (string.Equals(typeDefName, kStateType, StringComparison.Ordinal) ||
                    string.Equals(typeDefName, kInitialStateType, StringComparison.Ordinal))
                {
                    info.States.Add(BuildStateEntry(objectType.SymbolicName?.Name, childObject,
                        kStateNumberProperty));
                }
                else if (string.Equals(typeDefName, kTransitionType, StringComparison.Ordinal))
                {
                    info.Transitions.Add(BuildStateEntry(objectType.SymbolicName?.Name, childObject,
                        kTransitionNumberProperty));
                }
            }

            if (info.States.Count == 0 && info.Transitions.Count == 0)

            {
                return null;
            }
            info.States.Sort(static (a, b) => string.CompareOrdinal(a.Name, b.Name));
            info.Transitions.Sort(static (a, b) => string.CompareOrdinal(a.Name, b.Name));
            return info;
        }

        /// <summary>
        /// Records the C# type of a node whose <c>Objects</c> constant
        /// NodeIdGenerator does not emit as a <c>uint</c> - that is, one without
        /// a numeric identifier. Guid and Opaque identified nodes are emitted as
        /// their identifier type, everything else as a <c>string</c>.
        /// </summary>
        private void AddIfNotNumericallyIdentified(NodeDesign node)
        {
            if (node is ObjectDesign &&
                !node.NumericIdSpecified &&
                node.SymbolicId?.Name != null)
            {
                if (node.HasNonConstantIdentifier())
                {
                    ModelDesignExtensions.GetIdentifierAsCode(
                        node.GetIdentifier()!,
                        out string? idType);
                    m_nonNumericIdentifiedNodes[node.SymbolicId.Name] = idType!;
                    return;
                }
                m_nonNumericIdentifiedNodes[node.SymbolicId.Name] = "string";
            }
        }

        private FsmEntry BuildStateEntry(
            string? parentTypeName, ObjectDesign child, string numberPropertyName)
        {
            string name = child.SymbolicName?.Name ?? string.Empty;
            uint? number = ExtractNumberProperty(child, numberPropertyName);
            string objectsConstantName = string.IsNullOrEmpty(parentTypeName)
                ? name
                : CoreUtils.Format("{0}_{1}", parentTypeName, name);
            // The Objects constant this entry aliases is emitted by NodeIdGenerator as a
            // uint only when the node carries a numeric identifier; string, Guid and
            // Opaque identified nodes get a constant of their own type, so the alias
            // has to follow the same type.
            if (!m_nonNumericIdentifiedNodes.TryGetValue(objectsConstantName, out string? idType))
            {
                idType = "uint";
            }
            return new FsmEntry(name, number, objectsConstantName, idType);
        }

        private static uint? ExtractNumberProperty(
            ObjectDesign parent, string propertyName)
        {
            InstanceDesign[]? grandchildren = parent.Children?.Items;
            if (grandchildren == null)
            {
                return null;
            }
            foreach (InstanceDesign grandchild in grandchildren)
            {
                if (grandchild is not VariableDesign property ||
                    !string.Equals(property.SymbolicName?.Name, propertyName,
                        StringComparison.Ordinal))
                {
                    continue;
                }
                if (TryReadNumber(property, out uint value))
                {
                    return value;
                }
            }
            return null;
        }

        private static bool TryReadNumber(VariableDesign property, out uint value)
        {
            if (property.DecodedValue != null &&
                uint.TryParse(
                    Convert.ToString(property.DecodedValue, CultureInfo.InvariantCulture),
                    NumberStyles.Integer,
                    CultureInfo.InvariantCulture,
                    out value))
            {
                return true;
            }

            System.Xml.XmlElement element = property.DefaultValue;
            if (element != null &&
                !string.IsNullOrWhiteSpace(element.InnerText) &&
                uint.TryParse(element.InnerText.Trim(), NumberStyles.Integer,
                    CultureInfo.InvariantCulture, out value))
            {
                return true;
            }

            value = 0;
            return false;
        }

        private sealed class FsmTypeInfo
        {
            public FsmTypeInfo(string? typeName)
            {
                TypeName = typeName ?? string.Empty;
            }

            public string TypeName { get; }
            public List<FsmEntry> States { get; } = [];
            public List<FsmEntry> Transitions { get; } = [];
        }

        private sealed class FsmEntry
        {
            public FsmEntry(string name, uint? number, string objectsConstantName, string idType)
            {
                Name = name ?? string.Empty;
                Number = number;
                ObjectsConstantName = objectsConstantName ?? string.Empty;
                IdType = idType ?? "uint";
            }

            public string Name { get; }
            public uint? Number { get; }
            public string ObjectsConstantName { get; }
            public string IdType { get; }

            /// <summary>
            /// Guid and Opaque identifiers have no C# constant form, so the
            /// alias of such an identifier is a static readonly field.
            /// </summary>
            public string IdModifier => IdType is "uint" or "string"
                ? "const"
                : "static readonly";
        }
    }
}