Connected.Framework/Connected.Expressions/Mappings/EntityMapping.cs

using Connected.Collections;
using Connected.Entities.Annotations;
using Connected.Expressions.Expressions;
using Connected.Expressions.Reflection;
using Connected.Expressions.Translation;
using Connected.Expressions.Translation.Projections;
using Connected.Interop;
using System.Collections.Immutable;
using System.Linq.Expressions;
using System.Reflection;
using Binder = Connected.Expressions.Translation.Binder;

namespace Connected.Expressions.Mappings;
internal sealed class EntityMapping
{
    private List<MemberMapping> _members;
    public EntityMapping(Type entityType)
    {
        EntityType = entityType;
        _members = new();

        InitializeSchema();
        InitializeMembers();
    }

    public string Id => $"{Schema}.{Name}";
    public string Name { get; private set; } = default!;
    public string Schema { get; private set; } = default!;
    private Type EntityType { get; }
    public ImmutableList<MemberMapping> Members => _members.ToImmutableList();

    private void InitializeSchema()
    {
        var att = EntityType.ResolveTableAttribute();

        if (string.IsNullOrWhiteSpace(att.Name))
            Name = EntityType.Name;
        else
            Name = att.Name;

        if (string.IsNullOrWhiteSpace(att.Schema))
            Schema = SchemaAttribute.DefaultSchema;
        else
            Schema = att.Schema;
    }

    private void InitializeMembers()
    {
        var properties = Properties.GetImplementedProperties(EntityType);

        foreach (var property in properties)
        {
            var member = new MemberMapping(property);

            if (member.IsValid)
                _members.Add(member);
        }

        _members.SortByOrdinal();
    }

    public Expression CreateExpression(ExpressionCompilationContext context)
    {
        var tableAlias = Alias.New();
        var selectAlias = Alias.New();
        var table = new TableExpression(tableAlias, EntityType, Schema, Name);
        var projector = CreateEntityExpression(context, table);
        var pc = ColumnProjector.ProjectColumns(context.Language, projector, null, selectAlias, tableAlias);

        return new ProjectionExpression(new SelectExpression(selectAlias, pc.Columns, table, null), pc.Projector);
    }

    private EntityExpression CreateEntityExpression(ExpressionCompilationContext context, Expression root)
    {
        var assignments = new List<EntityAssignment>();

        foreach (var member in Members)
        {
            if (CreateMemberExpression(context, root, member) is Expression memberExpression)
                assignments.Add(new EntityAssignment(member, memberExpression));
        }

        return new EntityExpression(EntityType, CreateEntityExpression(assignments));
    }

    private Expression CreateMemberExpression(ExpressionCompilationContext context, Expression root, MemberMapping member)
    {
        if (root is AliasedExpression aliasedRoot)
        {
            return new ColumnExpression(Interop.Members.GetMemberType(member.MemberInfo), context.Language.TypeSystem.ResolveColumnType(member.Type),
                aliasedRoot.Alias, member.Name);
        }

        return Binder.Bind(root, member.MemberInfo);
    }

    private Expression CreateEntityExpression(IList<EntityAssignment> assignments)
    {
        NewExpression newExpression;
        var readonlyMembers = assignments.Where(f => f.Mapping.IsReadOnly).ToArray();
        var cons = EntityType.GetTypeInfo().DeclaredConstructors.Where(c => c.IsPublic && !c.IsStatic).ToArray();
        var hasNoArgConstructor = cons.Any(c => c.GetParameters().Length == 0);

        if (readonlyMembers.Any() || !hasNoArgConstructor)
        {
            var consThatApply = cons.Select(c => BindConstructor(c, readonlyMembers)).Where(cbr => cbr is not null && !cbr.Remaining.Any()).ToList();

            if (!consThatApply.Any())
                throw new InvalidOperationException($"Cannot construct type '{EntityType}' with all mapped and included members.");

            if (readonlyMembers.Length == assignments.Count)
                return consThatApply[0].Expression;

            var r = BindConstructor(consThatApply[0].Expression.Constructor, assignments);

            newExpression = r.Expression;
            assignments = r.Remaining;
        }
        else
            newExpression = Expression.New(EntityType);

        Expression result;

        if (assignments.Any())
        {
            if (EntityType.GetTypeInfo().IsInterface)
                assignments = RemapAssignments(assignments, EntityType).ToList();

            result = Expression.MemberInit(newExpression, assignments.Select(a => Expression.Bind(a.Mapping.MemberInfo, a.Expression)).ToArray());
        }
        else
            result = newExpression;

        return result;
    }

    private ConstructorBindResult BindConstructor(ConstructorInfo cons, IList<EntityAssignment> assignments)
    {
        var ps = cons.GetParameters();
        var args = new Expression[ps.Length];
        var mis = new MemberInfo[ps.Length];
        var members = new HashSet<EntityAssignment>(assignments);
        var used = new HashSet<EntityAssignment>();

        for (var i = 0; i < ps.Length; i++)
        {
            var p = ps[i];
            var assignment = members.FirstOrDefault(a => string.Equals(p.Name, a.Mapping.Name, StringComparison.OrdinalIgnoreCase) && p.ParameterType.IsAssignableFrom(a.Expression.Type));

            if (assignment is null)
                assignment = members.FirstOrDefault(a => string.Equals(p.Name, a.Mapping.Name, StringComparison.OrdinalIgnoreCase) && p.ParameterType.IsAssignableFrom(a.Expression.Type));

            if (assignment is not null)
            {
                args[i] = assignment.Expression;

                if (mis is not null)
                    mis[i] = assignment.Mapping.MemberInfo;

                used.Add(assignment);
            }
            else
            {
                var mem = Members.Where(m => string.Equals(m.Name, p.Name, StringComparison.OrdinalIgnoreCase)).FirstOrDefault();

                if (mem is not null)
                {
                    args[i] = Expression.Constant(Types.GetDefault(p.ParameterType), p.ParameterType);
                    mis[i] = mem.MemberInfo;
                }
                else
                    return null;
            }
        }

        members.ExceptWith(used);

        return new ConstructorBindResult(Expression.New(cons, args, mis), members);
    }

    private IEnumerable<EntityAssignment> RemapAssignments(IEnumerable<EntityAssignment> assignments, Type entityType)
    {
        foreach (var assign in assignments)
        {
            var member = Members.FirstOrDefault(f => string.Equals(f.Name, assign.Mapping.Name, StringComparison.Ordinal));

            if (member is not null)
                yield return new EntityAssignment(member, assign.Expression);
            else
                yield return assign;
        }
    }
}