Beam/Beam.Temporary.Cli/DownloadBuilder.cs

using aeqw89.DataKeys;
using Beam.Dynamic;
using Beam;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using HtmlAgilityPack;

namespace Beam.Temporary.Cli {
    /// <summary>
    ///     Type‑safe, staged builder that prevents callers from forgetting the mandatory steps
    ///     (source → link selection → transformer) and surfaces operational knobs as first‑class
    ///     methods instead of magic parameters.
    /// </summary>
    public static class DownloadBuilder<RawType, OutType> {
        /* ──────────────────────────── Entry points ─────────────────────────── */

        public static ILinkStage FromMeta(DataKey<TextResource> novelKey, BeamDataDictionary data) =>
            Create(novelKey, data, SourceKind.Meta);

        public static ILinkStage FromText(DataKey<TextResource> novelKey, BeamDataDictionary data) =>
            Create(novelKey, data, SourceKind.Text);

        public static IAlternativeLinkStage FromScratch()
            => new LinkStage(null!, null!, null!, new());

        /* ────────────────────────────── Stages ─────────────────────────────── */

        public interface ILinkStage {
            ITransformStage WithLink();
            ITransformStage WithLinkGenerator();
            ILinkStage WithRange(Range range);
        }

        public interface IAlternativeLinkStage {
            IAlternativeTransformStage WithLinks(IEnumerable<SourceLink> links);
        }

        public interface ITransformStage {
            IContextStage WithTransformer(Func<DataBindings, AsyncTransformer<RawType, OutType>> factory);
        }

        public interface IAlternativeTransformStage {
            IContextStage WithTransformer(AsyncTransformer<RawType, OutType> transformer);
            IContextStage WithTransformer(Func<RawType, OutType> transformer) {
                return WithTransformer(rt => Task.FromResult(transformer(rt)));
            }
        }

        public interface IContextStage {
            IContextStage Configure(Action<DownloadContextBuilder<RawType>> configure);
            IContextStage WithParallelism(int degree);
            IContextStage WithTimeout(TimeSpan timeout);
            IContextStage WithRetryReporter(IProgress<RetryReport> reporter);
            DownloadEnumerable<OutType> Build();
            IContextStage UseFragments();
        }

        /* ────────────────────────── Implementation ────────────────────────── */

        private enum SourceKind { Meta, Text }

        private static ILinkStage Create(DataKey<TextResource> novelKey, BeamDataDictionary data, SourceKind kind) {
            var (source, initial) = Resolve(novelKey, data, kind);
            var ctxBuilder = new DownloadContextBuilder<RawType>().WithLinks(Array.Empty<SourceLink>()); // placeholder, filled later.
            return new LinkStage(source, initial, data, ctxBuilder);
        }

        private static (WebResource Source, State Initial) Resolve(DataKey<TextResource> novelKey, BeamDataDictionary data, SourceKind kind) {
            if (!data.Novels.TryGetValue(novelKey, out var tr))
                throw new KeyNotFoundException($"Novel '{novelKey}' not found in BeamDataDictionary.");

            var textRecord = tr.ToRecord(data);
            WebResource? source;
            State? initial;

            if (kind == SourceKind.Meta) {
                source = textRecord.AssociatedMetaSource ?? throw new InvalidOperationException($"Meta source missing for '{novelKey}'.");
                initial = textRecord.Resource.MetaTemplateInitialData ?? throw new InvalidOperationException("Meta template data missing.");
            } else {
                source = textRecord.AssociatedSource ?? throw new InvalidOperationException($"Text source missing for '{novelKey}'.");
                initial = textRecord.Resource.TemplateInitialData;
            }

            return (source, initial);
        }

        /* ──────────────────────────── Stage types ─────────────────────────── */


        private sealed record LinkStage(
            WebResource Source,
            State Initial,
            BeamDataDictionary Data,
            DownloadContextBuilder<RawType> CtxBuilder) : ILinkStage, IAlternativeLinkStage {

            private State? endState;
            private bool linksFrozen = false;

            public ITransformStage WithLink() {
                var link = Data.Templates[Source.Key].Builder.Build(Initial);
                CtxBuilder.WithLinks(new[] { link });
                return new TransformStage(Source, Data, CtxBuilder);
            }

            public ITransformStage WithLinkGenerator() {
                var template = Data.Templates[Source.Key];
                var generator = SourceLinkEnumerable.FromGenerator(new OrderedSourceLinkGenerator(
                    template.Builder,
                    new NumberedStateChanger(template.Factory.Behavior),
                    Initial, endState));
                CtxBuilder.WithLinks(generator);
                linksFrozen = true;
                return new TransformStage(Source, Data, CtxBuilder);
            }

            public IAlternativeTransformStage WithLinks(IEnumerable<SourceLink> links) {
                CtxBuilder.WithLinks(links);
                return new TransformStage(Source, Data, CtxBuilder);
            }

            public ILinkStage WithRange(Range range) {
                if (linksFrozen)
                    throw new InvalidOperationException($"WithRange must be called before WithLinkGenerator");
                if (range.End.Value < range.Start.Value)
                    throw new ArgumentOutOfRangeException(nameof(range), $" start must be < end");
                var template = Data.Templates[Source.Key];
                var stateChanger = new NumberedStateChanger(template.Factory.Behavior);
                endState = Initial.Copy();
                stateChanger.Apply(Initial, range.Start.Value - 1);
                stateChanger.Apply(endState, range.End.Value - 1);
                return this;
            }
        }

        private sealed record TransformStage(
            WebResource Source,
            BeamDataDictionary Data,
            DownloadContextBuilder<RawType> CtxBuilder) : ITransformStage, IAlternativeTransformStage {
            public IContextStage WithTransformer(Func<DataBindings, AsyncTransformer<RawType, OutType>> factory) {
                var transformer = factory(Data.Bindings[Source.Bindings]);
                return new ContextStage(CtxBuilder, transformer);
            }

            public IContextStage WithTransformer(AsyncTransformer<RawType, OutType> transformer) {
                return new ContextStage(CtxBuilder, transformer);
            }
        }

        private sealed class ContextStage : IContextStage {
            private readonly DownloadContextBuilder<RawType> _ctxBuilder;
            private readonly AsyncTransformer<RawType, OutType> _transformer;
            private int _parallelism = 4;
            private bool useFragments = false;

            public ContextStage(DownloadContextBuilder<RawType> ctxBuilder, AsyncTransformer<RawType, OutType> transformer) {
                _ctxBuilder = ctxBuilder;
                _transformer = transformer;
            }

            public IContextStage Configure(Action<DownloadContextBuilder<RawType>> configure) {
                configure(_ctxBuilder);
                return this;
            }

            public IContextStage WithParallelism(int degree) {
                _parallelism = Math.Max(1, degree);
                return this;
            }

            public IContextStage WithTimeout(TimeSpan timeout) {
                _ctxBuilder.WithTimeOut(timeout);
                return this;
            }

            public IContextStage WithRetryReporter(IProgress<RetryReport> reporter) {
                _ctxBuilder.WithRetryReporter(reporter);
                return this;
            }

            public IContextStage UseFragments() {
                useFragments = true;
                return this;
            }

            private object ConstructUnitDownloader(DownloadContext<RawType> context) {
                return (useFragments, _transformer, context.AsyncFailurePredicates) switch {
                    // ────────────────  fragmented HTML  ────────────────
                    (true, AsyncTransformer<HtmlDocument, OutType> asyncHtmlTransformer,
                    AsyncDownloadFailurePredicate<HtmlDocument>[] documentFailurePredicates)
                        => new UnitFragmentDownloader<OutType>(
                            context.Web,
                            asyncHtmlTransformer,
                            documentFailurePredicates,
                            _parallelism,
                            context.DownloadLogger),
                    // ────────────────  fragmented binary  ────────────────
                    (true, AsyncTransformer<ByteDocument, OutType> asyncBinaryTransformer,
                    AsyncDownloadFailurePredicate<ByteDocument>[] responseFailurePredicates)
                        => new UnitFragmentDownloaderBinary<OutType>(
                            context.Client,
                            asyncBinaryTransformer,
                            responseFailurePredicates,
                            _parallelism,
                            context.DownloadLogger),
                    // ────────────────  single HTML  ────────────────
                    (false, AsyncTransformer<HtmlDocument, OutType> asyncHtmlTransformer,
                    AsyncDownloadFailurePredicate<HtmlDocument>[] documentFailurePredicates)
                        => new UnitDownloader<OutType>(
                            context.Web,
                            asyncHtmlTransformer,
                            documentFailurePredicates),
                    // ────────────────  single binary  ────────────────
                    (false, AsyncTransformer<ByteDocument, OutType> asyncBinaryTransformer,
                    AsyncDownloadFailurePredicate<ByteDocument>[] responseFailurePredicates)
                        => new UnitDownloaderBinary<OutType>(
                            context.Client,
                            asyncBinaryTransformer,
                            responseFailurePredicates),
                    _ => throw new Exception($"Unsupported transformer / failure-predicate combination. Missing pattern: {useFragments} , {_transformer.GetType().AsUniqueName()} , {context.AsyncFailurePredicates?.GetType().AsUniqueName()}"),
                };
            }

            private IAsyncEnumerator<Ordered<OutType>> ConstructDownloader(DownloadContext<RawType> context) {
                var copyOfContext = context.CreateBuilder().Build();
                return useFragments switch {
                    true => new SequentialFragmentDownloader<RawType, OutType>(
                        copyOfContext,
                        ctx => (IUnitDownloader<Fragment<Ordered<OutType>>>)ConstructUnitDownloader(ctx),
                        context.DownloadLogger).UnwrapFragmented(),
                    false => new SequentialDownloader<RawType, OutType>(
                        copyOfContext,
                        ctx => (IUnitDownloader<OutType>)ConstructUnitDownloader(ctx),
                        context.DownloadLogger).WrapOrdered()
                };
            }

            public DownloadEnumerable<OutType> Build() {
                var context = _ctxBuilder.Build();
                var enumerable = new DownloadEnumerable<OutType>(ConstructDownloader(context));
                return enumerable;
            }
        }
    }
}