alef_e2e/codegen/

csharp.rs

//! C# e2e test generator using xUnit.
//!
//! Generates `e2e/csharp/E2eTests.csproj` and `tests/{Category}Tests.cs`
//! files from JSON fixtures, driven entirely by `E2eConfig` and `CallConfig`.

use crate::config::E2eConfig;
use crate::escape::{escape_csharp, sanitize_filename};
use crate::field_access::FieldResolver;
use crate::fixture::{Assertion, CallbackAction, Fixture, FixtureGroup};
use alef_core::backend::GeneratedFile;
use alef_core::config::AlefConfig;
use alef_core::hash::{self, CommentStyle};
use alef_core::template_versions as tv;
use anyhow::Result;
use heck::ToUpperCamelCase;
use std::collections::HashMap;
use std::fmt::Write as FmtWrite;
use std::path::PathBuf;

use super::E2eCodegen;

/// C# e2e code generator.
pub struct CSharpCodegen;

impl E2eCodegen for CSharpCodegen {
    fn generate(
        &self,
        groups: &[FixtureGroup],
        e2e_config: &E2eConfig,
        alef_config: &AlefConfig,
    ) -> Result<Vec<GeneratedFile>> {
        let lang = self.language_name();
        let output_base = PathBuf::from(e2e_config.effective_output()).join(lang);

        let mut files = Vec::new();

        // Resolve call config with overrides.
        let call = &e2e_config.call;
        let overrides = call.overrides.get(lang);
        let function_name = overrides
            .and_then(|o| o.function.as_ref())
            .cloned()
            .unwrap_or_else(|| call.function.to_upper_camel_case());
        let class_name = overrides
            .and_then(|o| o.class.as_ref())
            .cloned()
            .unwrap_or_else(|| format!("{}Lib", alef_config.crate_config.name.to_upper_camel_case()));
        // The exception class is always {CrateName}Exception, generated by the C# backend.
        let exception_class = format!("{}Exception", alef_config.crate_config.name.to_upper_camel_case());
        let namespace = overrides.and_then(|o| o.module.as_ref()).cloned().unwrap_or_else(|| {
            if call.module.is_empty() {
                "Kreuzberg".to_string()
            } else {
                call.module.to_upper_camel_case()
            }
        });
        let result_is_simple = overrides.is_some_and(|o| o.result_is_simple);
        let result_var = &call.result_var;
        let is_async = call.r#async;

        // Resolve package config.
        let cs_pkg = e2e_config.resolve_package("csharp");
        let pkg_name = cs_pkg
            .as_ref()
            .and_then(|p| p.name.as_ref())
            .cloned()
            .unwrap_or_else(|| alef_config.crate_config.name.to_upper_camel_case());
        // The project reference path uses the crate name (with hyphens) for the directory
        // and the PascalCase name for the .csproj file.
        let pkg_path = cs_pkg
            .as_ref()
            .and_then(|p| p.path.as_ref())
            .cloned()
            .unwrap_or_else(|| format!("../../packages/csharp/{pkg_name}.csproj"));
        let pkg_version = cs_pkg
            .as_ref()
            .and_then(|p| p.version.as_ref())
            .cloned()
            .unwrap_or_else(|| "0.1.0".to_string());

        // Generate the .csproj using a unique name derived from the package name so
        // it does not conflict with any hand-written project files in the same directory.
        let csproj_name = format!("{pkg_name}.E2eTests.csproj");
        files.push(GeneratedFile {
            path: output_base.join(&csproj_name),
            content: render_csproj(&pkg_name, &pkg_path, &pkg_version, e2e_config.dep_mode),
            generated_header: false,
        });

        // Generate test files per category.
        let tests_base = output_base.join("tests");
        let field_resolver = FieldResolver::new(
            &e2e_config.fields,
            &e2e_config.fields_optional,
            &e2e_config.result_fields,
            &e2e_config.fields_array,
        );

        // Resolve enum_fields from C# override config.
        static EMPTY_ENUM_FIELDS: std::sync::LazyLock<HashMap<String, String>> = std::sync::LazyLock::new(HashMap::new);
        let enum_fields = overrides.map(|o| &o.enum_fields).unwrap_or(&EMPTY_ENUM_FIELDS);

        for group in groups {
            let active: Vec<&Fixture> = group
                .fixtures
                .iter()
                .filter(|f| f.skip.as_ref().is_none_or(|s| !s.should_skip(lang)))
                .collect();

            if active.is_empty() {
                continue;
            }

            let test_class = format!("{}Tests", sanitize_filename(&group.category).to_upper_camel_case());
            let filename = format!("{test_class}.cs");
            let content = render_test_file(
                &group.category,
                &active,
                &namespace,
                &class_name,
                &function_name,
                &exception_class,
                result_var,
                &test_class,
                &e2e_config.call.args,
                &field_resolver,
                result_is_simple,
                is_async,
                e2e_config,
                enum_fields,
            );
            files.push(GeneratedFile {
                path: tests_base.join(filename),
                content,
                generated_header: true,
            });
        }

        Ok(files)
    }

    fn language_name(&self) -> &'static str {
        "csharp"
    }
}

// ---------------------------------------------------------------------------
// Rendering
// ---------------------------------------------------------------------------

fn render_csproj(pkg_name: &str, pkg_path: &str, pkg_version: &str, dep_mode: crate::config::DependencyMode) -> String {
    let pkg_ref = match dep_mode {
        crate::config::DependencyMode::Registry => {
            format!("    <PackageReference Include=\"{pkg_name}\" Version=\"{pkg_version}\" />")
        }
        crate::config::DependencyMode::Local => {
            format!("    <ProjectReference Include=\"{pkg_path}\" />")
        }
    };
    format!(
        r#"<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net10.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <IsPackable>false</IsPackable>
    <IsTestProject>true</IsTestProject>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="{ms_test_sdk}" />
    <PackageReference Include="xunit" Version="{xunit}" />
    <PackageReference Include="xunit.runner.visualstudio" Version="{xunit_runner}" />
  </ItemGroup>

  <ItemGroup>
{pkg_ref}
  </ItemGroup>
</Project>
"#,
        ms_test_sdk = tv::nuget::MICROSOFT_NET_TEST_SDK,
        xunit = tv::nuget::XUNIT,
        xunit_runner = tv::nuget::XUNIT_RUNNER_VISUALSTUDIO,
    )
}

#[allow(clippy::too_many_arguments)]
fn render_test_file(
    category: &str,
    fixtures: &[&Fixture],
    namespace: &str,
    class_name: &str,
    function_name: &str,
    exception_class: &str,
    result_var: &str,
    test_class: &str,
    args: &[crate::config::ArgMapping],
    field_resolver: &FieldResolver,
    result_is_simple: bool,
    is_async: bool,
    e2e_config: &E2eConfig,
    enum_fields: &HashMap<String, String>,
) -> String {
    let mut out = String::new();
    out.push_str(&hash::header(CommentStyle::DoubleSlash));
    // Always import System.Text.Json for the shared JsonOptions field.
    let _ = writeln!(out, "using System.Text.Json;");
    let _ = writeln!(out, "using System.Text.Json.Serialization;");
    let _ = writeln!(out, "using System.Threading.Tasks;");
    let _ = writeln!(out, "using Xunit;");
    let _ = writeln!(out, "using {namespace};");
    let _ = writeln!(out);
    let _ = writeln!(out, "namespace Kreuzberg.E2e;");
    let _ = writeln!(out);
    let _ = writeln!(out, "/// <summary>E2e tests for category: {category}.</summary>");
    let _ = writeln!(out, "public class {test_class}");
    let _ = writeln!(out, "{{");
    // Shared options used when deserializing config JSON in test setup.
    // Mirrors the options used by the library to ensure enum values round-trip correctly.
    let _ = writeln!(
        out,
        "    private static readonly JsonSerializerOptions ConfigOptions = new() {{ Converters = {{ new JsonStringEnumConverter(JsonNamingPolicy.SnakeCaseLower) }}, DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault }};"
    );
    let _ = writeln!(out);

    for (i, fixture) in fixtures.iter().enumerate() {
        render_test_method(
            &mut out,
            fixture,
            class_name,
            function_name,
            exception_class,
            result_var,
            args,
            field_resolver,
            result_is_simple,
            is_async,
            e2e_config,
            enum_fields,
        );
        if i + 1 < fixtures.len() {
            let _ = writeln!(out);
        }
    }

    let _ = writeln!(out, "}}");
    out
}

#[allow(clippy::too_many_arguments)]
fn render_test_method(
    out: &mut String,
    fixture: &Fixture,
    class_name: &str,
    _function_name: &str,
    exception_class: &str,
    _result_var: &str,
    _args: &[crate::config::ArgMapping],
    field_resolver: &FieldResolver,
    result_is_simple: bool,
    _is_async: bool,
    e2e_config: &E2eConfig,
    enum_fields: &HashMap<String, String>,
) {
    let method_name = fixture.id.to_upper_camel_case();
    let description = &fixture.description;
    let expects_error = fixture.assertions.iter().any(|a| a.assertion_type == "error");

    // Resolve call config per-fixture so named calls (e.g. "parse") use the
    // correct function name, result variable, and async flag.
    let call_config = e2e_config.resolve_call(fixture.call.as_deref());
    let lang = "csharp";
    let cs_overrides = call_config.overrides.get(lang);
    let effective_function_name = cs_overrides
        .and_then(|o| o.function.as_ref())
        .cloned()
        .unwrap_or_else(|| call_config.function.to_upper_camel_case());
    let effective_result_var = &call_config.result_var;
    let effective_is_async = call_config.r#async;
    let function_name = effective_function_name.as_str();
    let result_var = effective_result_var.as_str();
    let is_async = effective_is_async;
    let args = call_config.args.as_slice();

    let (mut setup_lines, args_str) =
        build_args_and_setup(&fixture.input, args, class_name, e2e_config, enum_fields, &fixture.id);

    // Build visitor if present and add to setup
    let mut visitor_arg = String::new();
    if let Some(visitor_spec) = &fixture.visitor {
        visitor_arg = build_csharp_visitor(&mut setup_lines, visitor_spec);
    }

    let final_args = if visitor_arg.is_empty() {
        args_str
    } else {
        format!("{args_str}, {visitor_arg}")
    };

    let return_type = if is_async { "async Task" } else { "void" };
    let await_kw = if is_async { "await " } else { "" };

    let _ = writeln!(out, "    [Fact]");
    let _ = writeln!(out, "    public {return_type} Test_{method_name}()");
    let _ = writeln!(out, "    {{");
    let _ = writeln!(out, "        // {description}");

    for line in &setup_lines {
        let _ = writeln!(out, "        {line}");
    }

    if expects_error {
        if is_async {
            let _ = writeln!(
                out,
                "        await Assert.ThrowsAsync<{exception_class}>(() => {class_name}.{function_name}({final_args}));"
            );
        } else {
            let _ = writeln!(
                out,
                "        Assert.Throws<{exception_class}>(() => {class_name}.{function_name}({final_args}));"
            );
        }
        let _ = writeln!(out, "    }}");
        return;
    }

    let _ = writeln!(
        out,
        "        var {result_var} = {await_kw}{class_name}.{function_name}({final_args});"
    );

    for assertion in &fixture.assertions {
        render_assertion(
            out,
            assertion,
            result_var,
            class_name,
            exception_class,
            field_resolver,
            result_is_simple,
        );
    }

    let _ = writeln!(out, "    }}");
}

/// Build setup lines (e.g. handle creation) and the argument list for the function call.
///
/// Returns `(setup_lines, args_string)`.
fn build_args_and_setup(
    input: &serde_json::Value,
    args: &[crate::config::ArgMapping],
    class_name: &str,
    e2e_config: &E2eConfig,
    enum_fields: &HashMap<String, String>,
    fixture_id: &str,
) -> (Vec<String>, String) {
    if args.is_empty() {
        return (Vec::new(), json_to_csharp(input));
    }

    let overrides = e2e_config.call.overrides.get("csharp");
    let options_type = overrides.and_then(|o| o.options_type.as_deref());

    let mut setup_lines: Vec<String> = Vec::new();
    let mut parts: Vec<String> = Vec::new();

    for arg in args {
        if arg.arg_type == "mock_url" {
            setup_lines.push(format!(
                "var {} = Environment.GetEnvironmentVariable(\"MOCK_SERVER_URL\") + \"/fixtures/{fixture_id}\";",
                arg.name,
            ));
            parts.push(arg.name.clone());
            continue;
        }

        if arg.arg_type == "handle" {
            // Generate a CreateEngine (or equivalent) call and pass the variable.
            let constructor_name = format!("Create{}", arg.name.to_upper_camel_case());
            let field = arg.field.strip_prefix("input.").unwrap_or(&arg.field);
            let config_value = input.get(field).unwrap_or(&serde_json::Value::Null);
            if config_value.is_null()
                || config_value.is_object() && config_value.as_object().is_some_and(|o| o.is_empty())
            {
                setup_lines.push(format!("var {} = {class_name}.{constructor_name}(null);", arg.name,));
            } else {
                // Sort discriminator fields ("type") to appear first in nested objects so
                // System.Text.Json [JsonPolymorphic] can find the type discriminator before
                // reading other properties (a requirement as of .NET 8).
                let sorted = sort_discriminator_first(config_value.clone());
                let json_str = serde_json::to_string(&sorted).unwrap_or_default();
                let name = &arg.name;
                setup_lines.push(format!(
                    "var {name}Config = JsonSerializer.Deserialize<CrawlConfig>(\"{}\", ConfigOptions)!;",
                    escape_csharp(&json_str),
                ));
                setup_lines.push(format!(
                    "var {} = {class_name}.{constructor_name}({name}Config);",
                    arg.name,
                    name = name,
                ));
            }
            parts.push(arg.name.clone());
            continue;
        }

        let field = arg.field.strip_prefix("input.").unwrap_or(&arg.field);
        let val = input.get(field);
        match val {
            None | Some(serde_json::Value::Null) if arg.optional => {
                // Optional arg with no fixture value: pass null explicitly since
                // C# nullable parameters still require an argument at the call site.
                parts.push("null".to_string());
                continue;
            }
            None | Some(serde_json::Value::Null) => {
                // Required arg with no fixture value: pass a language-appropriate default.
                let default_val = match arg.arg_type.as_str() {
                    "string" => "\"\"".to_string(),
                    "int" | "integer" => "0".to_string(),
                    "float" | "number" => "0.0d".to_string(),
                    "bool" | "boolean" => "false".to_string(),
                    _ => "null".to_string(),
                };
                parts.push(default_val);
            }
            Some(v) => {
                // For json_object args with options_type, construct a typed C# object.
                if let (Some(opts_type), "json_object") = (options_type, arg.arg_type.as_str()) {
                    if let Some(obj) = v.as_object() {
                        let props: Vec<String> = obj
                            .iter()
                            .map(|(k, vv)| {
                                let pascal_key = k.to_upper_camel_case();
                                // Check if this field maps to an enum type.
                                let cs_val = if let Some(enum_type) = enum_fields.get(k) {
                                    // Map string value to enum constant (PascalCase).
                                    if let Some(s) = vv.as_str() {
                                        let pascal_val = s.to_upper_camel_case();
                                        format!("{enum_type}.{pascal_val}")
                                    } else {
                                        json_to_csharp(vv)
                                    }
                                } else {
                                    json_to_csharp(vv)
                                };
                                format!("{pascal_key} = {cs_val}")
                            })
                            .collect();
                        parts.push(format!("new {opts_type} {{ {} }}", props.join(", ")));
                        continue;
                    }
                }
                parts.push(json_to_csharp(v));
            }
        }
    }

    (setup_lines, parts.join(", "))
}

fn render_assertion(
    out: &mut String,
    assertion: &Assertion,
    result_var: &str,
    class_name: &str,
    exception_class: &str,
    field_resolver: &FieldResolver,
    result_is_simple: bool,
) {
    // Skip assertions on fields that don't exist on the result type.
    if let Some(f) = &assertion.field {
        if !f.is_empty() && !field_resolver.is_valid_for_result(f) {
            let _ = writeln!(out, "        // skipped: field '{f}' not available on result type");
            return;
        }
    }

    let field_expr = if result_is_simple {
        result_var.to_string()
    } else {
        match &assertion.field {
            Some(f) if !f.is_empty() => field_resolver.accessor(f, "csharp", result_var),
            _ => result_var.to_string(),
        }
    };

    // Determine whether the field resolves to an optional (nullable) type in C#.
    let field_is_optional = assertion
        .field
        .as_deref()
        .map(|f| field_resolver.is_optional(field_resolver.resolve(f)))
        .unwrap_or(false);

    match assertion.assertion_type.as_str() {
        "equals" => {
            if let Some(expected) = &assertion.value {
                let cs_val = json_to_csharp(expected);
                // Only call .Trim() on string fields, not numeric or boolean ones.
                if expected.is_string() {
                    let _ = writeln!(out, "        Assert.Equal({cs_val}, {field_expr}.Trim());");
                } else if expected.is_number() && field_is_optional {
                    // Nullable numeric fields require an explicit cast of the expected
                    // literal so that C# can resolve the overload (e.g. ulong?).
                    let _ = writeln!(out, "        Assert.Equal((object?){cs_val}, (object?){field_expr});");
                } else {
                    let _ = writeln!(out, "        Assert.Equal({cs_val}, {field_expr});");
                }
            }
        }
        "contains" => {
            if let Some(expected) = &assertion.value {
                // Lowercase both expected and actual so that enum fields (where .ToString()
                // returns the PascalCase C# member name like "Anchor") correctly match
                // fixture snake_case values like "anchor".  String fields are unaffected
                // because lowercasing both sides preserves substring matches.
                let lower_expected = expected.as_str().map(|s| s.to_lowercase());
                let cs_val = lower_expected
                    .as_deref()
                    .map(|s| format!("\"{}\"", escape_csharp(s)))
                    .unwrap_or_else(|| json_to_csharp(expected));
                let _ = writeln!(
                    out,
                    "        Assert.Contains({cs_val}, {field_expr}.ToString().ToLower());"
                );
            }
        }
        "contains_all" => {
            if let Some(values) = &assertion.values {
                for val in values {
                    let lower_val = val.as_str().map(|s| s.to_lowercase());
                    let cs_val = lower_val
                        .as_deref()
                        .map(|s| format!("\"{}\"", escape_csharp(s)))
                        .unwrap_or_else(|| json_to_csharp(val));
                    let _ = writeln!(
                        out,
                        "        Assert.Contains({cs_val}, {field_expr}.ToString().ToLower());"
                    );
                }
            }
        }
        "not_contains" => {
            if let Some(expected) = &assertion.value {
                let cs_val = json_to_csharp(expected);
                let _ = writeln!(out, "        Assert.DoesNotContain({cs_val}, {field_expr}.ToString());");
            }
        }
        "not_empty" => {
            let _ = writeln!(
                out,
                "        Assert.False(string.IsNullOrEmpty({field_expr}?.ToString()));"
            );
        }
        "is_empty" => {
            let _ = writeln!(
                out,
                "        Assert.True(string.IsNullOrEmpty({field_expr}?.ToString()));"
            );
        }
        "contains_any" => {
            if let Some(values) = &assertion.values {
                let checks: Vec<String> = values
                    .iter()
                    .map(|v| {
                        let cs_val = json_to_csharp(v);
                        format!("{field_expr}.ToString().Contains({cs_val})")
                    })
                    .collect();
                let joined = checks.join(" || ");
                let _ = writeln!(
                    out,
                    "        Assert.True({joined}, \"expected to contain at least one of the specified values\");"
                );
            }
        }
        "greater_than" => {
            if let Some(val) = &assertion.value {
                let cs_val = json_to_csharp(val);
                let _ = writeln!(
                    out,
                    "        Assert.True({field_expr} > {cs_val}, \"expected > {cs_val}\");"
                );
            }
        }
        "less_than" => {
            if let Some(val) = &assertion.value {
                let cs_val = json_to_csharp(val);
                let _ = writeln!(
                    out,
                    "        Assert.True({field_expr} < {cs_val}, \"expected < {cs_val}\");"
                );
            }
        }
        "greater_than_or_equal" => {
            if let Some(val) = &assertion.value {
                let cs_val = json_to_csharp(val);
                let _ = writeln!(
                    out,
                    "        Assert.True({field_expr} >= {cs_val}, \"expected >= {cs_val}\");"
                );
            }
        }
        "less_than_or_equal" => {
            if let Some(val) = &assertion.value {
                let cs_val = json_to_csharp(val);
                let _ = writeln!(
                    out,
                    "        Assert.True({field_expr} <= {cs_val}, \"expected <= {cs_val}\");"
                );
            }
        }
        "starts_with" => {
            if let Some(expected) = &assertion.value {
                let cs_val = json_to_csharp(expected);
                let _ = writeln!(out, "        Assert.StartsWith({cs_val}, {field_expr});");
            }
        }
        "ends_with" => {
            if let Some(expected) = &assertion.value {
                let cs_val = json_to_csharp(expected);
                let _ = writeln!(out, "        Assert.EndsWith({cs_val}, {field_expr});");
            }
        }
        "min_length" => {
            if let Some(val) = &assertion.value {
                if let Some(n) = val.as_u64() {
                    let _ = writeln!(
                        out,
                        "        Assert.True({field_expr}.Length >= {n}, \"expected length >= {n}\");"
                    );
                }
            }
        }
        "max_length" => {
            if let Some(val) = &assertion.value {
                if let Some(n) = val.as_u64() {
                    let _ = writeln!(
                        out,
                        "        Assert.True({field_expr}.Length <= {n}, \"expected length <= {n}\");"
                    );
                }
            }
        }
        "count_min" => {
            if let Some(val) = &assertion.value {
                if let Some(n) = val.as_u64() {
                    let _ = writeln!(
                        out,
                        "        Assert.True({field_expr}.Count >= {n}, \"expected at least {n} elements\");"
                    );
                }
            }
        }
        "count_equals" => {
            if let Some(val) = &assertion.value {
                if let Some(n) = val.as_u64() {
                    let _ = writeln!(out, "        Assert.Equal({n}, {field_expr}.Count);");
                }
            }
        }
        "is_true" => {
            let _ = writeln!(out, "        Assert.True({field_expr});");
        }
        "is_false" => {
            let _ = writeln!(out, "        Assert.False({field_expr});");
        }
        "not_error" => {
            // Already handled by the call succeeding without exception.
        }
        "error" => {
            // Handled at the test method level.
        }
        "method_result" => {
            if let Some(method_name) = &assertion.method {
                let call_expr = build_csharp_method_call(result_var, method_name, assertion.args.as_ref(), class_name);
                let check = assertion.check.as_deref().unwrap_or("is_true");
                match check {
                    "equals" => {
                        if let Some(val) = &assertion.value {
                            if val.as_bool() == Some(true) {
                                let _ = writeln!(out, "        Assert.True({call_expr});");
                            } else if val.as_bool() == Some(false) {
                                let _ = writeln!(out, "        Assert.False({call_expr});");
                            } else {
                                let cs_val = json_to_csharp(val);
                                let _ = writeln!(out, "        Assert.Equal({cs_val}, {call_expr});");
                            }
                        }
                    }
                    "is_true" => {
                        let _ = writeln!(out, "        Assert.True({call_expr});");
                    }
                    "is_false" => {
                        let _ = writeln!(out, "        Assert.False({call_expr});");
                    }
                    "greater_than_or_equal" => {
                        if let Some(val) = &assertion.value {
                            let n = val.as_u64().unwrap_or(0);
                            let _ = writeln!(out, "        Assert.True({call_expr} >= {n}, \"expected >= {n}\");");
                        }
                    }
                    "count_min" => {
                        if let Some(val) = &assertion.value {
                            let n = val.as_u64().unwrap_or(0);
                            let _ = writeln!(
                                out,
                                "        Assert.True({call_expr}.Count >= {n}, \"expected at least {n} elements\");"
                            );
                        }
                    }
                    "is_error" => {
                        let _ = writeln!(
                            out,
                            "        Assert.Throws<{exception_class}>(() => {{ {call_expr}; }});"
                        );
                    }
                    "contains" => {
                        if let Some(val) = &assertion.value {
                            let cs_val = json_to_csharp(val);
                            let _ = writeln!(out, "        Assert.Contains({cs_val}, {call_expr});");
                        }
                    }
                    other_check => {
                        panic!("C# e2e generator: unsupported method_result check type: {other_check}");
                    }
                }
            } else {
                panic!("C# e2e generator: method_result assertion missing 'method' field");
            }
        }
        "matches_regex" => {
            if let Some(expected) = &assertion.value {
                let cs_val = json_to_csharp(expected);
                let _ = writeln!(out, "        Assert.Matches({cs_val}, {field_expr});");
            }
        }
        other => {
            panic!("C# e2e generator: unsupported assertion type: {other}");
        }
    }
}

/// Recursively sort JSON objects so that any key named `"type"` appears first.
///
/// System.Text.Json's `[JsonPolymorphic]` requires the type discriminator to be
/// the first property when deserializing polymorphic types. Fixture config values
/// serialised via serde_json preserve insertion/alphabetical order, which may put
/// `"type"` after other keys (e.g. `"password"` before `"type"` in auth configs).
fn sort_discriminator_first(value: serde_json::Value) -> serde_json::Value {
    match value {
        serde_json::Value::Object(map) => {
            let mut sorted = serde_json::Map::with_capacity(map.len());
            // Insert "type" first if present.
            if let Some(type_val) = map.get("type") {
                sorted.insert("type".to_string(), sort_discriminator_first(type_val.clone()));
            }
            for (k, v) in map {
                if k != "type" {
                    sorted.insert(k, sort_discriminator_first(v));
                }
            }
            serde_json::Value::Object(sorted)
        }
        serde_json::Value::Array(arr) => {
            serde_json::Value::Array(arr.into_iter().map(sort_discriminator_first).collect())
        }
        other => other,
    }
}

/// Convert a `serde_json::Value` to a C# literal string.
fn json_to_csharp(value: &serde_json::Value) -> String {
    match value {
        serde_json::Value::String(s) => format!("\"{}\"", escape_csharp(s)),
        serde_json::Value::Bool(true) => "true".to_string(),
        serde_json::Value::Bool(false) => "false".to_string(),
        serde_json::Value::Number(n) => {
            if n.is_f64() {
                format!("{}d", n)
            } else {
                n.to_string()
            }
        }
        serde_json::Value::Null => "null".to_string(),
        serde_json::Value::Array(arr) => {
            let items: Vec<String> = arr.iter().map(json_to_csharp).collect();
            format!("new[] {{ {} }}", items.join(", "))
        }
        serde_json::Value::Object(_) => {
            let json_str = serde_json::to_string(value).unwrap_or_default();
            format!("\"{}\"", escape_csharp(&json_str))
        }
    }
}

// ---------------------------------------------------------------------------
// Visitor generation
// ---------------------------------------------------------------------------

/// Build a C# visitor class and add setup lines. Returns the visitor variable name.
fn build_csharp_visitor(setup_lines: &mut Vec<String>, visitor_spec: &crate::fixture::VisitorSpec) -> String {
    setup_lines.push("var _testVisitor = new TestVisitor();".to_string());
    setup_lines.push("class TestVisitor : IVisitor".to_string());
    setup_lines.push("{".to_string());
    for (method_name, action) in &visitor_spec.callbacks {
        emit_csharp_visitor_method(setup_lines, method_name, action);
    }
    setup_lines.push("}".to_string());
    "_testVisitor".to_string()
}

/// Emit a C# visitor method for a callback action.
fn emit_csharp_visitor_method(setup_lines: &mut Vec<String>, method_name: &str, action: &CallbackAction) {
    let camel_method = method_to_camel(method_name);
    let params = match method_name {
        "visit_link" => "VisitContext ctx, string href, string text, string title",
        "visit_image" => "VisitContext ctx, string src, string alt, string title",
        "visit_heading" => "VisitContext ctx, int level, string text, string id",
        "visit_code_block" => "VisitContext ctx, string lang, string code",
        "visit_code_inline"
        | "visit_strong"
        | "visit_emphasis"
        | "visit_strikethrough"
        | "visit_underline"
        | "visit_subscript"
        | "visit_superscript"
        | "visit_mark"
        | "visit_button"
        | "visit_summary"
        | "visit_figcaption"
        | "visit_definition_term"
        | "visit_definition_description" => "VisitContext ctx, string text",
        "visit_text" => "VisitContext ctx, string text",
        "visit_list_item" => "VisitContext ctx, bool ordered, string marker, string text",
        "visit_blockquote" => "VisitContext ctx, string content, int depth",
        "visit_table_row" => "VisitContext ctx, IReadOnlyList<string> cells, bool isHeader",
        "visit_custom_element" => "VisitContext ctx, string tagName, string html",
        "visit_form" => "VisitContext ctx, string actionUrl, string method",
        "visit_input" => "VisitContext ctx, string inputType, string name, string value",
        "visit_audio" | "visit_video" | "visit_iframe" => "VisitContext ctx, string src",
        "visit_details" => "VisitContext ctx, bool isOpen",
        "visit_element_end" | "visit_table_end" | "visit_definition_list_end" | "visit_figure_end" => {
            "VisitContext ctx, string output"
        }
        "visit_list_start" => "VisitContext ctx, bool ordered",
        "visit_list_end" => "VisitContext ctx, bool ordered, string output",
        _ => "VisitContext ctx",
    };

    setup_lines.push(format!("    public VisitResult {camel_method}({params})"));
    setup_lines.push("    {".to_string());
    match action {
        CallbackAction::Skip => {
            setup_lines.push("        return VisitResult.Skip();".to_string());
        }
        CallbackAction::Continue => {
            setup_lines.push("        return VisitResult.Continue();".to_string());
        }
        CallbackAction::PreserveHtml => {
            setup_lines.push("        return VisitResult.PreserveHtml();".to_string());
        }
        CallbackAction::Custom { output } => {
            let escaped = escape_csharp(output);
            setup_lines.push(format!("        return VisitResult.Custom(\"{escaped}\");"));
        }
        CallbackAction::CustomTemplate { template } => {
            let escaped = escape_csharp(template);
            setup_lines.push(format!("        return VisitResult.Custom($\"{escaped}\");"));
        }
    }
    setup_lines.push("    }".to_string());
}

/// Convert snake_case method names to C# PascalCase.
fn method_to_camel(snake: &str) -> String {
    use heck::ToUpperCamelCase;
    snake.to_upper_camel_case()
}

/// Build a C# call expression for a `method_result` assertion on a tree-sitter Tree.
///
/// Maps well-known method names to the appropriate C# static helper calls on the
/// generated lib class, falling back to `result_var.PascalCase()` for unknowns.
fn build_csharp_method_call(
    result_var: &str,
    method_name: &str,
    args: Option<&serde_json::Value>,
    class_name: &str,
) -> String {
    match method_name {
        "root_child_count" => format!("{result_var}.RootNode.ChildCount"),
        "root_node_type" => format!("{result_var}.RootNode.Kind"),
        "named_children_count" => format!("{result_var}.RootNode.NamedChildCount"),
        "has_error_nodes" => format!("{class_name}.TreeHasErrorNodes({result_var})"),
        "error_count" | "tree_error_count" => format!("{class_name}.TreeErrorCount({result_var})"),
        "tree_to_sexp" => format!("{class_name}.TreeToSexp({result_var})"),
        "contains_node_type" => {
            let node_type = args
                .and_then(|a| a.get("node_type"))
                .and_then(|v| v.as_str())
                .unwrap_or("");
            format!("{class_name}.TreeContainsNodeType({result_var}, \"{node_type}\")")
        }
        "find_nodes_by_type" => {
            let node_type = args
                .and_then(|a| a.get("node_type"))
                .and_then(|v| v.as_str())
                .unwrap_or("");
            format!("{class_name}.FindNodesByType({result_var}, \"{node_type}\")")
        }
        "run_query" => {
            let query_source = args
                .and_then(|a| a.get("query_source"))
                .and_then(|v| v.as_str())
                .unwrap_or("");
            let language = args
                .and_then(|a| a.get("language"))
                .and_then(|v| v.as_str())
                .unwrap_or("");
            format!("{class_name}.RunQuery({result_var}, \"{language}\", \"{query_source}\", source)")
        }
        _ => {
            use heck::ToUpperCamelCase;
            let pascal = method_name.to_upper_camel_case();
            format!("{result_var}.{pascal}()")
        }
    }
}