unit Myc.Ast.RTL.Series;

interface

uses
    System.SysUtils,
    System.Generics.Collections,
    Myc.Data.Scalar,
    Myc.Data.Value,
    Myc.Data.Series,
    Myc.Ast.Attributes;

type
    TRtlSeriesFunctions = record
    public
        // --- Functional / Series ---

        [TRtlExport('memoize', Pure)]
        [AstDoc('Creates a memoized version of a function for performance.')]
        [AstSignature('((any) -> any) -> ((any) -> any)')]
        class function Memoize(const Args: TArray<TDataValue>): TDataValue; static;

        [TRtlExport('map', Pure)]
        [AstDoc('Applies a function to every element of a series.')]
        [AstSignature('(series, (any) -> any) -> series')]
        class function Map(const Args: TArray<TDataValue>): TDataValue; static;

        [TRtlExport('reduce', Pure)]
        [AstDoc('Collapses a series into a single value using a reducer function.')]
        [AstSignature('(series, any, (any, any) -> any) -> any')]
        class function Reduce(const Args: TArray<TDataValue>): TDataValue; static;

        [TRtlExport('where', Pure)]
        [AstDoc('Filters a series based on a predicate function.')]
        [AstSignature('(series, (any) -> boolean) -> series')]
        class function Where(const Args: TArray<TDataValue>): TDataValue; static;

        [TRtlExport('any', Pure)]
        [AstDoc('Returns true if at least one element satisfies the predicate.')]
        [AstSignature('(series, (any) -> boolean) -> boolean')]
        class function Any(const Args: TArray<TDataValue>): TDataValue; static;

        [TRtlExport('count', Pure)]
        [AstDoc('Returns the current number of elements in a series.')]
        [AstSignature('(series) -> number')]
        [AstScriptExample('(count prices)')]
        class function Count(const Args: TArray<TDataValue>): TDataValue; static;
    end;

implementation

{ TRtlSeriesFunctions }

class function TRtlSeriesFunctions.Memoize(const Args: TArray<TDataValue>): TDataValue;
var
    funcToMemoize: TDataValue.TFunc;
    memoizedFunc: TDataValue.TFunc;
begin
    if Length(Args) <> 1 then
        raise EArgumentException.Create('Memoize requires exactly one argument.');
    if Args[0].Kind <> vkMethod then
        raise EArgumentException.Create('The argument to Memoize must be a function.');

    // We store the dictionary inside a TObjVal wrapped in a TDataValue to keep it alive
    // as part of the closure's captured state (or rather, accessible via the closure).
    // Note: In a pure closure implementation, capturing a local variable would be enough,
    // but here we ensure explicit lifetime management via the TDataValue ownership mechanism if needed.
    var cCache: TDataValue;
    cCache.FromObj(TDictionary<Int64, TDataValue>.Create);

    funcToMemoize := Args[0].AsMethod();

    memoizedFunc :=
        function(const AArgs: TArray<TDataValue>): TDataValue
        var
            argScalar: TScalar;
            key: Int64;
        begin
            if (Length(AArgs) <> 1) or (AArgs[0].Kind <> vkScalar) then
                raise EArgumentException.Create('This memoized function can only be called with a single scalar argument.');

            argScalar := AArgs[0].AsScalar;
            if argScalar.Kind <> TScalar.TKind.Ordinal then
                raise EArgumentException.Create('This memoized function expects an ordinal argument for caching.');

            key := argScalar.Value.AsInt64;

            // Unsafe cast is safe here because we created it above
            var cache := TDictionary<Int64, TDataValue>(cCache.AsObject);

            if cache.TryGetValue(key, Result) then
                exit;

            Result := funcToMemoize(AArgs);
            cache.Add(key, Result);
        end;

    Result := TDataValue(memoizedFunc);
end;

class function TRtlSeriesFunctions.Map(const Args: TArray<TDataValue>): TDataValue;
var
    sourceArg: TDataValue;
begin
    if Length(Args) <> 2 then
        raise EArgumentException.Create('Map requires exactly two arguments: a series and a function.');

    sourceArg := Args[0];
    if not (sourceArg.Kind in [vkSeries]) then
        raise EArgumentException.Create('The first argument to Map must be a series.');

    if Args[1].Kind <> vkMethod then
        raise EArgumentException.Create('The second argument to Map must be a function.');

    Result := TDataValue.Map(sourceArg.AsSeries, Args[1].AsMethod());
end;

class function TRtlSeriesFunctions.Reduce(const Args: TArray<TDataValue>): TDataValue;
var
    sourceArg: TDataValue;
    sourceSeries: ISeries;
    accumulator: TDataValue;
    reducerFunc: TDataValue.TFunc;
    i: Integer;
    currentItem: TScalar;
    reducerArgs: TArray<TDataValue>;
begin
    if Length(Args) <> 3 then
        raise EArgumentException.Create('Reduce requires exactly three arguments: a series, an initial value, and a reducer function.');

    sourceArg := Args[0];
    if sourceArg.Kind <> vkSeries then
        raise EArgumentException.Create('The first argument to Reduce must be a series.');

    if Args[2].Kind <> vkMethod then
        raise EArgumentException.Create('The third argument to Reduce must be a function.');

    sourceSeries := sourceArg.AsSeries;
    accumulator := Args[1];
    reducerFunc := Args[2].AsMethod();

    // Reduce typically iterates from oldest to newest (index count-1 downto 0 in standard array,
    // but TSeries logic might define 0 as newest. Assuming standard iteration order here).
    // Note: Based on previous TSeries implementation, Index 0 is newest.
    // Usually Reduce goes chronologically: Oldest (High) -> Newest (0).
    for i := sourceSeries.Count - 1 downto 0 do
    begin
        currentItem := sourceSeries.Items[i];
        reducerArgs := [accumulator, TDataValue(currentItem)];
        accumulator := reducerFunc(reducerArgs);
    end;

    Result := accumulator;
end;

class function TRtlSeriesFunctions.Where(const Args: TArray<TDataValue>): TDataValue;
var
    sourceArg: TDataValue;
    sourceSeries: ISeries;
    predicateFunc: TDataValue.TFunc;
    matchingIndices: TList<Integer>;
    i: Integer;
    item: TScalar;
    predicateResult: TDataValue;
    indexSeries: ISeries;
    mapperFunc: TDataValue.TFunc;
begin
    if Length(Args) <> 2 then
        raise EArgumentException.Create('Where requires exactly two arguments: a series and a predicate function.');

    sourceArg := Args[0];
    if sourceArg.Kind <> vkSeries then
        raise EArgumentException.Create('The first argument to Where must be a series.');

    if Args[1].Kind <> vkMethod then
        raise EArgumentException.Create('The second argument to Where must be a function.');

    sourceSeries := sourceArg.AsSeries;
    predicateFunc := Args[1].AsMethod();

    matchingIndices := TList<Integer>.Create;
    try
        // We scan all items. Order doesn't strictly matter for building the index list
        // if we just want to filter, but keeping order is good.
        // Iterating 0 to Count-1 (Newest to Oldest) or vice versa depends on desired output series order.
        // TIndexSeries usually expects indices.
        for i := 0 to sourceSeries.Count - 1 do
        begin
            item := sourceSeries.Items[i];
            // Perf warning: Allocation of array for every call
            predicateResult := predicateFunc([TDataValue(item)]);

            if (predicateResult.Kind = vkScalar) and (Boolean(predicateResult.AsScalar)) then
                matchingIndices.Add(i);
        end;

        indexSeries := TIndexSeries.Create(matchingIndices.ToArray);
    finally
        matchingIndices.Free;
    end;

    // Create a lazy mapper that looks up the original value based on the index
    mapperFunc :=
        function(const AArgs: TArray<TDataValue>): TDataValue
        var
            idx: Integer;
        begin
            idx := AArgs[0].AsScalar.Value.AsInt64;
            Result := TDataValue(sourceSeries.Items[idx]);
        end;

    // Result is a new series containing only the filtered items
    Result := TDataValue.Map(indexSeries, mapperFunc);
end;

class function TRtlSeriesFunctions.Any(const Args: TArray<TDataValue>): TDataValue;
var
    sourceArg: TDataValue;
    sourceSeries: ISeries;
    predicateFunc: TDataValue.TFunc;
    i: Integer;
    item: TScalar;
    predicateResult: TDataValue;
begin
    if Length(Args) <> 2 then
        raise EArgumentException.Create('Any requires exactly two arguments: a series and a predicate function.');

    sourceArg := Args[0];
    if sourceArg.Kind <> vkSeries then
        raise EArgumentException.Create('The first argument to Any must be a series.');

    if Args[1].Kind <> vkMethod then
        raise EArgumentException.Create('The second argument to Any must be a function.');

    sourceSeries := sourceArg.AsSeries;
    predicateFunc := Args[1].AsMethod();

    for i := 0 to sourceSeries.Count - 1 do
    begin
        item := sourceSeries.Items[i];
        predicateResult := predicateFunc([TDataValue(item)]);

        if (predicateResult.Kind = vkScalar) and (Boolean(predicateResult.AsScalar)) then
        begin
            Result := TScalar.FromBoolean(True);
            exit;
        end;
    end;

    Result := TScalar.FromBoolean(False);
end;

class function TRtlSeriesFunctions.Count(const Args: TArray<TDataValue>): TDataValue;
begin
    if Length(Args) <> 1 then
        raise EArgumentException.Create('Count requires one argument: a series.');

    var sourceArg := Args[0];

    case sourceArg.Kind of
        vkSeries: Result := sourceArg.AsSeries.Count;
        vkRecordSeries: Result := sourceArg.AsRecordSeries.Count;
    else
        raise EArgumentException.Create('The argument to Count must be a series.');
    end;
end;

end.