using System.Text.RegularExpressions;
using w4c_workflows.Services;
using Xunit;

namespace w4c_workflows.Tests;

public class MermaidGeneratorServiceTests
{
    private const string Tenant = "t1";
    private const string Path = "workflows/main-task.yaml";

    /// <summary>Diagram names accepted by <see cref="MermaidGeneratorService.Generate"/>.
    /// Centralising them removes magic strings and keeps tests in sync with the service.</summary>
    private static class Diagram
    {
        public const string Flowchart = "flowchart";
        public const string Sequence = "sequence";
        public const string State = "state";
        public const string Class = "class";
    }

    /// <summary><see cref="MermaidGeneratorService"/> is stateless (its methods are all static), so a
    /// single instance is shared instead of allocating one per <see cref="Render(string)"/> call.</summary>
    private static readonly MermaidGeneratorService Generator = new();

    private static readonly string ExampleYaml = """
        name: main-task
        mode: handler
        language: typescript
        trigger:
          type: queue
          stream: orders
        entry: { file: index.ts, function: handler }
        tasks:
          - id: validate
            parent: root
            next: enrich
            onError: compensate
            language: python
            entry: { file: validate.py }
          - id: enrich
            parent: root
            next: persist
            language: csharp
            entry: { file: Enrich.cs }
          - id: persist
            parent: root
            language: shell
            entry: { file: persist.sh }
          - id: compensate
            parent: root
            language: python
            entry: { file: compensate.py }
        """;

    private static CompiledWorkflow Compile()
        => new WorkflowCompiler(new WorkflowValidator(new LanguageRegistry()))
            .Compile(ExampleYaml, Path, Tenant).Workflow!;

    private static string Render(string type) => Render(Compile(), type);

    private static string Render(CompiledWorkflow compiled, string type)
        => Generator.Generate(type, compiled.Workflow, compiled.Tasks);

    [Fact]
    public void Flowchart_renders_next_solid_and_onError_dashed()
    {
        var source = Render(Diagram.Flowchart);

        Assert.Contains("flowchart TD", source);
        Assert.Contains("root --> validate", source);
        Assert.Contains("validate --> enrich", source);
        Assert.Contains("validate -.->|error| compensate", source);
        Assert.Contains("class root root", source);
    }

    [Fact]
    public void Sequence_renders_happy_path_and_alt_error_block()
    {
        var source = Render(Diagram.Sequence);

        Assert.Contains("sequenceDiagram", source);
        Assert.Contains("root->>validate", source);
        Assert.Contains("validate->>enrich", source);
        Assert.Contains("alt on error", source);
        Assert.Contains("validate->>compensate", source);
    }

    [Fact]
    public void State_renders_entry_terminal_and_error_transitions()
    {
        var compiled = Compile();
        var source = Render(compiled, Diagram.State);
        var (aliasOf, edges) = ParseStateDiagram(source);

        Assert.StartsWith("stateDiagram-v2", source.TrimStart(), StringComparison.Ordinal);

        // Every task (including the synthesized "root") is declared exactly once as a
        // labelled state. We must not assert literal transition text such as
        // "[*] --> root": State() aliases every key to a reserved-word-safe id (s0,
        // s1, ...) and prints the human key only inside the quoted label. Comparing
        // the declared labels against the compiled keys is order- and index-agnostic.
        Assert.Equal(
            compiled.Tasks.Select(t => t.Key).OrderBy(k => k, StringComparer.Ordinal),
            aliasOf.Keys.OrderBy(k => k, StringComparer.Ordinal));

        // Entry: exactly one initial transition, and it starts at "root".
        var entryEdges = edges.Where(e => e.From == "[*]").ToList();
        Assert.Single(entryEdges);
        Assert.Equal(aliasOf["root"], entryEdges[0].To);

        // Terminal: each task with no success/error successor ends at "[*]"
        // (persist and compensate in this fixture), so no other task is terminal.
        Assert.Equal(
            compiled.Tasks.Where(t => t.NextId == null && t.OnErrorId == null)
                .Select(t => aliasOf[t.Key]).OrderBy(a => a, StringComparer.Ordinal),
            edges.Where(e => e.To == "[*]").Select(e => e.From).OrderBy(a => a, StringComparer.Ordinal));

        // Error path: validate's onError: compensate is rendered as a labelled edge.
        var errorEdge = Assert.Single(edges.Where(e => e.Label == "error"));
        Assert.Equal(aliasOf["validate"], errorEdge.From);
        Assert.Equal(aliasOf["compensate"], errorEdge.To);

        // Structural integrity: no edge may reference an undeclared state, which would
        // render as a raw id instead of a labelled node.
        var declared = aliasOf.Values.Append("[*]").ToHashSet(StringComparer.Ordinal);
        foreach (var edge in edges)
        {
            Assert.Contains(edge.From, declared);
            Assert.Contains(edge.To, declared);
        }
    }

    [Fact]
    public void Class_renders_language_not_runtime()
    {
        var source = Render(Diagram.Class);

        Assert.Contains("classDiagram", source);
        Assert.Contains("<<typescript>>", source);   // root language
        Assert.Contains("<<python>>", source);        // validate language
        Assert.Contains("entry: index.ts", source);
        Assert.DoesNotContain("runtime", source);
    }

    [Fact]
    public void Unknown_type_throws()
    {
        var compiled = Compile();
        Assert.Throws<ArgumentException>(() => Render(compiled, "pie"));
    }

    // ------------------------------------------------------------------ state helpers
    // State() is the only generator that aliases task keys to generated ids, so its output
    // is verified structurally (labelled declarations + edges) rather than by exact
    // substrings, which would silently couple the test to the alias numbering.

    private sealed record StateEdge(string From, string To, string? Label);

    private static readonly Regex StateDeclRegex = new(
        @"^state ""(?<label>.+?)""\s+as\s+(?<alias>\w+)$", RegexOptions.Compiled);

    private static readonly Regex StateEdgeRegex = new(
        @"^(?<from>\[\*\]|\w+) --> (?<to>\[\*\]|\w+)(?:\s*:\s*(?<label>.+))?$", RegexOptions.Compiled);

    private static (Dictionary<string, string> AliasOf, IReadOnlyList<StateEdge> Edges)
        ParseStateDiagram(string source)
    {
        var aliasOf = new Dictionary<string, string>(StringComparer.Ordinal);
        var edges = new List<StateEdge>();

        foreach (var rawLine in source.Split('\n'))
        {
            var line = rawLine.Trim();
            if (line.Length == 0)
                continue;

            var declaration = StateDeclRegex.Match(line); // state "key" as sN
            if (declaration.Success)
            {
                aliasOf.TryAdd(declaration.Groups["label"].Value, declaration.Groups["alias"].Value);
                continue;
            }

            var edge = StateEdgeRegex.Match(line);        // from --> to[: label]
            if (edge.Success)
            {
                edges.Add(new StateEdge(
                    edge.Groups["from"].Value,
                    edge.Groups["to"].Value,
                    edge.Groups["label"].Success ? edge.Groups["label"].Value : null));
            }
            // Other lines (the "stateDiagram-v2" header) are intentionally ignored.
        }

        return (aliasOf, edges);
    }
}