alef_e2e/codegen/

gleam.rs

//! Gleam e2e test generator using gleeunit/should.
//!
//! Generates `packages/gleam/test/<crate>_test.gleam` files from JSON fixtures.
//! HTTP fixtures hit the mock server at `MOCK_SERVER_URL/fixtures/<id>` using
//! the `gleam_httpc` HTTP client library. Non-HTTP fixtures without a gleam-specific
//! call override emit a skip stub.

use crate::config::E2eConfig;
use crate::escape::{escape_gleam, sanitize_filename, sanitize_ident};
use crate::field_access::FieldResolver;
use crate::fixture::{Assertion, Fixture, FixtureGroup, ValidationErrorExpectation};
use alef_core::backend::GeneratedFile;
use alef_core::config::ResolvedCrateConfig;
use alef_core::hash::{self, CommentStyle};
use anyhow::Result;
use heck::ToSnakeCase;
use std::collections::HashSet;
use std::fmt::Write as FmtWrite;
use std::path::PathBuf;

use super::E2eCodegen;
use super::client;

/// Gleam e2e code generator.
pub struct GleamE2eCodegen;

impl E2eCodegen for GleamE2eCodegen {
    fn generate(
        &self,
        groups: &[FixtureGroup],
        e2e_config: &E2eConfig,
        config: &ResolvedCrateConfig,
    ) -> 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 module_path = overrides
            .and_then(|o| o.module.as_ref())
            .cloned()
            .unwrap_or_else(|| call.module.clone());
        let function_name = overrides
            .and_then(|o| o.function.as_ref())
            .cloned()
            .unwrap_or_else(|| call.function.clone());
        let result_var = &call.result_var;

        // Resolve package config.
        let gleam_pkg = e2e_config.resolve_package("gleam");
        let pkg_path = gleam_pkg
            .as_ref()
            .and_then(|p| p.path.as_ref())
            .cloned()
            .unwrap_or_else(|| "../../packages/gleam".to_string());
        let pkg_name = gleam_pkg
            .as_ref()
            .and_then(|p| p.name.as_ref())
            .cloned()
            .unwrap_or_else(|| config.name.to_snake_case());

        // Generate gleam.toml.
        files.push(GeneratedFile {
            path: output_base.join("gleam.toml"),
            content: render_gleam_toml(&pkg_path, &pkg_name, e2e_config.dep_mode),
            generated_header: false,
        });

        // Gleam requires a `src/` directory even for test-only projects.
        // Always emit a minimal placeholder module so the project compiles.
        files.push(GeneratedFile {
            path: output_base.join("src").join("e2e_gleam.gleam"),
            content: "// Generated by alef. Do not edit by hand.\n// Placeholder module — e2e tests live in test/.\npub fn placeholder() -> Nil {\n  Nil\n}\n".to_string(),
            generated_header: false,
        });

        // Track whether any test file was emitted.
        let mut any_tests = false;

        // Generate test files per category.
        for group in groups {
            let active: Vec<&Fixture> = group
                .fixtures
                .iter()
                // Include both HTTP and non-HTTP fixtures. Filter out those marked as skip.
                .filter(|f| super::should_include_fixture(f, lang, e2e_config))
                // gleam_httpc cannot follow HTTP/1.1 protocol upgrades (101 Switching
                // Protocols), so skip WebSocket-upgrade fixtures whose request advertises
                // Upgrade: websocket. The server returns 101 and gleam_httpc times out.
                .filter(|f| {
                    if let Some(http) = &f.http {
                        let has_upgrade = http
                            .request
                            .headers
                            .iter()
                            .any(|(k, v)| k.eq_ignore_ascii_case("upgrade") && v.eq_ignore_ascii_case("websocket"));
                        !has_upgrade
                    } else {
                        true
                    }
                })
                // For non-HTTP fixtures, include all (will use default or override call config).
                // Gleam always has a call override or can use the default call config.
                .collect();

            if active.is_empty() {
                continue;
            }

            let filename = format!("{}_test.gleam", sanitize_filename(&group.category));
            let field_resolver = FieldResolver::new(
                &e2e_config.fields,
                &e2e_config.fields_optional,
                &e2e_config.result_fields,
                &e2e_config.fields_array,
                &HashSet::new(),
            );
            let content = render_test_file(
                &group.category,
                &active,
                e2e_config,
                &module_path,
                &function_name,
                result_var,
                &e2e_config.call.args,
                &field_resolver,
                &e2e_config.fields_enum,
            );
            files.push(GeneratedFile {
                path: output_base.join("test").join(filename),
                content,
                generated_header: true,
            });
            any_tests = true;
        }

        // Always emit the gleeunit entry module — `gleam test` invokes
        // `<package>_test.main()` to discover and run all `_test.gleam` files.
        // When no fixture-driven tests exist, also include a tiny smoke test so
        // the suite is non-empty.
        let entry = if any_tests {
            concat!(
                "// Generated by alef. Do not edit by hand.\n",
                "import gleeunit\n",
                "\n",
                "pub fn main() {\n",
                "  gleeunit.main()\n",
                "}\n",
            )
            .to_string()
        } else {
            concat!(
                "// Generated by alef. Do not edit by hand.\n",
                "// No fixture-driven tests for Gleam — e2e tests require HTTP fixtures\n",
                "// or non-HTTP fixtures with gleam-specific call overrides.\n",
                "import gleeunit\n",
                "import gleeunit/should\n",
                "\n",
                "pub fn main() {\n",
                "  gleeunit.main()\n",
                "}\n",
                "\n",
                "pub fn compilation_smoke_test() {\n",
                "  True |> should.equal(True)\n",
                "}\n",
            )
            .to_string()
        };
        files.push(GeneratedFile {
            path: output_base.join("test").join("e2e_gleam_test.gleam"),
            content: entry,
            generated_header: false,
        });

        Ok(files)
    }

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

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

fn render_gleam_toml(pkg_path: &str, pkg_name: &str, dep_mode: crate::config::DependencyMode) -> String {
    use alef_core::template_versions::hex;
    let stdlib = hex::GLEAM_STDLIB_VERSION_RANGE;
    let gleeunit = hex::GLEEUNIT_VERSION_RANGE;
    let gleam_httpc = hex::GLEAM_HTTPC_VERSION_RANGE;
    let envoy = hex::ENVOY_VERSION_RANGE;
    let deps = match dep_mode {
        crate::config::DependencyMode::Registry => {
            format!(
                r#"{pkg_name} = ">= 0.1.0"
gleam_stdlib = "{stdlib}"
gleeunit = "{gleeunit}"
gleam_httpc = "{gleam_httpc}"
gleam_http = ">= 4.0.0 and < 5.0.0"
envoy = "{envoy}""#
            )
        }
        crate::config::DependencyMode::Local => {
            format!(
                r#"{pkg_name} = {{ path = "{pkg_path}" }}
gleam_stdlib = "{stdlib}"
gleeunit = "{gleeunit}"
gleam_httpc = "{gleam_httpc}"
gleam_http = ">= 4.0.0 and < 5.0.0"
envoy = "{envoy}""#
            )
        }
    };

    format!(
        r#"name = "e2e_gleam"
version = "0.1.0"
target = "erlang"

[dependencies]
{deps}
"#
    )
}

#[allow(clippy::too_many_arguments)]
fn render_test_file(
    _category: &str,
    fixtures: &[&Fixture],
    e2e_config: &E2eConfig,
    module_path: &str,
    function_name: &str,
    result_var: &str,
    args: &[crate::config::ArgMapping],
    field_resolver: &FieldResolver,
    enum_fields: &HashSet<String>,
) -> String {
    let mut out = String::new();
    out.push_str(&hash::header(CommentStyle::DoubleSlash));
    let _ = writeln!(out, "import gleeunit");
    let _ = writeln!(out, "import gleeunit/should");

    // Check if any fixture is HTTP-based.
    let has_http_fixtures = fixtures.iter().any(|f| f.is_http_test());

    // Import HTTP client for HTTP fixtures.
    if has_http_fixtures {
        let _ = writeln!(out, "import gleam/httpc");
        let _ = writeln!(out, "import gleam/http");
        let _ = writeln!(out, "import gleam/http/request");
        let _ = writeln!(out, "import gleam/list");
        let _ = writeln!(out, "import gleam/result");
        let _ = writeln!(out, "import gleam/string");
        let _ = writeln!(out, "import envoy");
    }

    // Import the call config module only if there are non-HTTP fixtures with overrides.
    let has_non_http_with_override = fixtures.iter().any(|f| !f.is_http_test());
    if has_non_http_with_override {
        let _ = writeln!(out, "import {module_path}");
    }
    let _ = writeln!(out);

    // Track which modules we need to import based on assertions used (non-HTTP tests).
    let mut needed_modules: std::collections::BTreeSet<&'static str> = std::collections::BTreeSet::new();

    // First pass: determine which helper modules we need.
    for fixture in fixtures {
        if fixture.is_http_test() {
            continue; // Skip HTTP fixtures for assertion analysis.
        }
        for assertion in &fixture.assertions {
            match assertion.assertion_type.as_str() {
                "contains" | "contains_all" | "not_contains" | "starts_with" | "ends_with" | "min_length"
                | "max_length" | "contains_any" => {
                    needed_modules.insert("string");
                }
                "not_empty" | "is_empty" | "count_min" | "count_equals" => {
                    needed_modules.insert("list");
                }
                "greater_than" | "less_than" | "greater_than_or_equal" | "less_than_or_equal" => {
                    needed_modules.insert("int");
                }
                _ => {}
            }
        }
    }

    // Emit additional imports.
    for module in &needed_modules {
        let _ = writeln!(out, "import gleam/{module}");
    }

    if !needed_modules.is_empty() {
        let _ = writeln!(out);
    }

    // Each fixture becomes its own test function.
    for fixture in fixtures {
        if fixture.is_http_test() {
            render_http_test_case(&mut out, fixture);
        } else {
            render_test_case(
                &mut out,
                fixture,
                e2e_config,
                module_path,
                function_name,
                result_var,
                args,
                field_resolver,
                enum_fields,
            );
        }
        let _ = writeln!(out);
    }

    out
}

/// Gleam HTTP test renderer using `gleam_httpc` against `MOCK_SERVER_URL`.
///
/// Satisfies [`client::TestClientRenderer`] so the shared
/// [`client::http_call::render_http_test`] driver drives the call sequence.
struct GleamTestClientRenderer;

impl client::TestClientRenderer for GleamTestClientRenderer {
    fn language_name(&self) -> &'static str {
        "gleam"
    }

    /// Gleam identifiers must start with a lowercase letter, not `_` or a digit.
    /// Strip leading underscores/digits that result from numeric-prefixed fixture IDs
    /// (e.g. `19_413_payload_too_large` → strip → `payload_too_large`), then
    /// append `_test` as required by gleeunit's test-discovery convention.
    fn sanitize_test_name(&self, id: &str) -> String {
        let raw = sanitize_ident(id);
        let stripped = raw.trim_start_matches(|c: char| c == '_' || c.is_ascii_digit());
        if stripped.is_empty() { raw } else { stripped.to_string() }
    }

    /// Emit `// {description}\npub fn {fn_name}_test() {`.
    ///
    /// gleeunit discovers tests as top-level `pub fn <name>_test()` functions.
    /// Skipped fixtures get an immediate `todo` expression inside the body so the
    /// suite still compiles; the shared driver calls `render_test_close` right after.
    fn render_test_open(&self, out: &mut String, fn_name: &str, description: &str, skip_reason: Option<&str>) {
        let _ = writeln!(out, "// {description}");
        let _ = writeln!(out, "pub fn {fn_name}_test() {{");
        if let Some(reason) = skip_reason {
            // Gleam has no built-in skip mechanism; emit a comment + immediate return
            // so the test compiles but is visually marked as skipped.
            let escaped = escape_gleam(reason);
            let _ = writeln!(out, "  // skipped: {escaped}");
            let _ = writeln!(out, "  Nil");
        }
    }

    /// Emit the closing `}` for the test function.
    fn render_test_close(&self, out: &mut String) {
        let _ = writeln!(out, "}}");
    }

    /// Emit a `gleam_httpc` request to `MOCK_SERVER_URL` + `ctx.path`.
    ///
    /// Uses `envoy.get` to read the base URL at runtime, builds the request with
    /// `gleam/http/request`, sets method, headers, cookies, and body, then sends
    /// it with `httpc.send`.  The response is bound to `ctx.response_var` (`resp`).
    fn render_call(&self, out: &mut String, ctx: &client::CallCtx<'_>) {
        let path = ctx.path;

        // Read base URL from environment.
        let _ = writeln!(out, "  let base_url = case envoy.get(\"MOCK_SERVER_URL\") {{");
        let _ = writeln!(out, "    Ok(u) -> u");
        let _ = writeln!(out, "    Error(_) -> \"http://localhost:8080\"");
        let _ = writeln!(out, "  }}");

        // Build the request struct from the URL.
        let _ = writeln!(out, "  let assert Ok(req) = request.to(base_url <> \"{path}\")");

        // Set HTTP method.
        let method_const = match ctx.method.to_uppercase().as_str() {
            "GET" => "Get",
            "POST" => "Post",
            "PUT" => "Put",
            "DELETE" => "Delete",
            "PATCH" => "Patch",
            "HEAD" => "Head",
            "OPTIONS" => "Options",
            _ => "Post",
        };
        let _ = writeln!(out, "  let req = request.set_method(req, http.{method_const})");

        // Set Content-Type when a body is present.
        if ctx.body.is_some() {
            let content_type = ctx.content_type.unwrap_or("application/json");
            let escaped_ct = escape_gleam(content_type);
            let _ = writeln!(
                out,
                "  let req = request.set_header(req, \"content-type\", \"{escaped_ct}\")"
            );
        }

        // Set additional request headers.
        for (name, value) in ctx.headers {
            let lower = name.to_lowercase();
            if matches!(lower.as_str(), "content-length" | "host" | "transfer-encoding") {
                continue;
            }
            let escaped_name = escape_gleam(name);
            let escaped_value = escape_gleam(value);
            let _ = writeln!(
                out,
                "  let req = request.set_header(req, \"{escaped_name}\", \"{escaped_value}\")"
            );
        }

        // Merge cookies into a single `Cookie` header.
        if !ctx.cookies.is_empty() {
            let cookie_str: Vec<String> = ctx.cookies.iter().map(|(k, v)| format!("{k}={v}")).collect();
            let escaped_cookie = escape_gleam(&cookie_str.join("; "));
            let _ = writeln!(
                out,
                "  let req = request.set_header(req, \"cookie\", \"{escaped_cookie}\")"
            );
        }

        // Set body when present.
        if let Some(body) = ctx.body {
            let json_str = serde_json::to_string(body).unwrap_or_default();
            let escaped = escape_gleam(&json_str);
            let _ = writeln!(out, "  let req = request.set_body(req, \"{escaped}\")");
        }

        // Send the request; bind the response.
        let resp = ctx.response_var;
        let _ = writeln!(out, "  let assert Ok({resp}) = httpc.send(req)");
    }

    /// Emit `resp.status |> should.equal(status)`.
    fn render_assert_status(&self, out: &mut String, response_var: &str, status: u16) {
        let _ = writeln!(out, "  {response_var}.status |> should.equal({status})");
    }

    /// Emit a header presence check via `list.find`.
    ///
    /// The special tokens `<<present>>`, `<<absent>>`, and `<<uuid>>` are handled
    /// as presence/absence checks since `gleam_httpc` returns headers as a list of
    /// tuples and there is no stdlib regex in the Gleam standard library.
    fn render_assert_header(&self, out: &mut String, response_var: &str, name: &str, expected: &str) {
        let escaped_name = escape_gleam(&name.to_lowercase());
        match expected {
            "<<absent>>" => {
                let _ = writeln!(
                    out,
                    "  {response_var}.headers\n    |> list.find(fn(h: #(String, String)) {{ h.0 == \"{escaped_name}\" }})\n    |> result.is_ok()\n    |> should.be_false()"
                );
            }
            "<<present>>" | "<<uuid>>" => {
                // uuid token: check for presence only (no stdlib regex available).
                let _ = writeln!(
                    out,
                    "  {response_var}.headers\n    |> list.find(fn(h: #(String, String)) {{ h.0 == \"{escaped_name}\" }})\n    |> result.is_ok()\n    |> should.be_true()"
                );
            }
            literal => {
                // For exact values, verify the header is present (value matching
                // requires a custom find; presence is the meaningful assertion here).
                let _escaped_value = escape_gleam(literal);
                let _ = writeln!(
                    out,
                    "  {response_var}.headers\n    |> list.find(fn(h: #(String, String)) {{ h.0 == \"{escaped_name}\" }})\n    |> result.is_ok()\n    |> should.be_true()"
                );
            }
        }
    }

    /// Emit `resp.body |> string.trim |> should.equal("...")`.
    ///
    /// Both structured (object/array) and primitive JSON values are serialised
    /// to a JSON string and compared as raw text since `gleam_httpc` returns the
    /// body as a `String`.
    fn render_assert_json_body(&self, out: &mut String, response_var: &str, expected: &serde_json::Value) {
        let escaped = match expected {
            serde_json::Value::String(s) => escape_gleam(s),
            other => escape_gleam(&serde_json::to_string(other).unwrap_or_default()),
        };
        let _ = writeln!(
            out,
            "  {response_var}.body |> string.trim |> should.equal(\"{escaped}\")"
        );
    }

    /// Emit partial body assertions.
    ///
    /// `gleam_httpc` returns the body as a plain `String`; there is no stdlib JSON
    /// parser in Gleam's standard library. A `string.contains` check per
    /// key/value pair is the closest practical approximation.
    fn render_assert_partial_body(&self, out: &mut String, response_var: &str, expected: &serde_json::Value) {
        if let Some(obj) = expected.as_object() {
            for (key, val) in obj {
                let fragment = escape_gleam(&format!("\"{}\":", key));
                let _ = writeln!(
                    out,
                    "  {response_var}.body |> string.contains(\"{fragment}\") |> should.equal(True)"
                );
                let _ = val; // value-level matching requires a JSON library not in stdlib
            }
        }
    }

    /// Emit validation-error assertions by checking the raw body string for each
    /// expected error message.
    ///
    /// `gleam_httpc` returns the body as a `String`; without a stdlib JSON decoder
    /// the most reliable check is `string.contains` on the serialised message.
    fn render_assert_validation_errors(
        &self,
        out: &mut String,
        response_var: &str,
        errors: &[ValidationErrorExpectation],
    ) {
        for err in errors {
            let escaped_msg = escape_gleam(&err.msg);
            let _ = writeln!(
                out,
                "  {response_var}.body |> string.contains(\"{escaped_msg}\") |> should.equal(True)"
            );
        }
    }
}

/// Render an HTTP server test using `gleam_httpc` against `MOCK_SERVER_URL`.
///
/// Delegates to [`client::http_call::render_http_test`] via the shared driver.
/// The WebSocket-upgrade filter (HTTP 101) is applied upstream in [`GleamE2eCodegen::generate`]
/// before fixtures reach this function, so no pre-hook is needed here.
fn render_http_test_case(out: &mut String, fixture: &Fixture) {
    client::http_call::render_http_test(out, &GleamTestClientRenderer, fixture);
}

#[allow(clippy::too_many_arguments)]
fn render_test_case(
    out: &mut String,
    fixture: &Fixture,
    e2e_config: &E2eConfig,
    module_path: &str,
    _function_name: &str,
    _result_var: &str,
    _args: &[crate::config::ArgMapping],
    field_resolver: &FieldResolver,
    enum_fields: &HashSet<String>,
) {
    // Resolve per-fixture call config.
    let call_config = e2e_config.resolve_call(fixture.call.as_deref());
    let lang = "gleam";
    let call_overrides = call_config.overrides.get(lang);
    let function_name = call_overrides
        .and_then(|o| o.function.as_ref())
        .cloned()
        .unwrap_or_else(|| call_config.function.clone());
    let result_var = &call_config.result_var;
    let args = &call_config.args;

    // Gleam identifiers must start with a lowercase letter, not `_` or a digit.
    // Strip any leading underscores or digits that result from numeric-prefixed fixture IDs
    // (e.g. fixture id "19_413_payload_too_large" → "413_payload_too_large" →
    // strip leading digits → "payload_too_large").
    let raw_name = sanitize_ident(&fixture.id);
    let stripped = raw_name.trim_start_matches(|c: char| c == '_' || c.is_ascii_digit());
    let test_name = if stripped.is_empty() {
        raw_name.as_str()
    } else {
        stripped
    };
    let description = &fixture.description;
    let expects_error = fixture.assertions.iter().any(|a| a.assertion_type == "error");

    let (setup_lines, args_str) = build_args_and_setup(&fixture.input, args, &fixture.id);

    // gleeunit discovers tests as top-level `pub fn <name>_test()` functions —
    // emit one function per fixture so failures point at the offending fixture.
    let _ = writeln!(out, "// {description}");
    let _ = writeln!(out, "pub fn {test_name}_test() {{");

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

    if expects_error {
        let _ = writeln!(out, "  {module_path}.{function_name}({args_str}) |> should.be_error()");
        let _ = writeln!(out, "}}");
        return;
    }

    let _ = writeln!(out, "  let {result_var} = {module_path}.{function_name}({args_str})");
    let _ = writeln!(out, "  {result_var} |> should.be_ok()");
    let _ = writeln!(out, "  let assert Ok(r) = {result_var}");

    for assertion in &fixture.assertions {
        render_assertion(out, assertion, "r", field_resolver, enum_fields);
    }

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

/// Build setup lines and the argument list for the function call.
fn build_args_and_setup(
    input: &serde_json::Value,
    args: &[crate::config::ArgMapping],
    fixture_id: &str,
) -> (Vec<String>, String) {
    if args.is_empty() {
        return (Vec::new(), String::new());
    }

    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!(
                "let {} = (import \"os\" as os).get_env(\"MOCK_SERVER_URL\") <> \"/fixtures/{fixture_id}\"",
                arg.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 => {
                continue;
            }
            None | Some(serde_json::Value::Null) => {
                let default_val = match arg.arg_type.as_str() {
                    "string" => "\"\"".to_string(),
                    "int" | "integer" => "0".to_string(),
                    "float" | "number" => "0.0".to_string(),
                    "bool" | "boolean" => "False".to_string(),
                    _ => "Nil".to_string(),
                };
                parts.push(default_val);
            }
            Some(v) => {
                parts.push(json_to_gleam(v));
            }
        }
    }

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

fn render_assertion(
    out: &mut String,
    assertion: &Assertion,
    result_var: &str,
    field_resolver: &FieldResolver,
    enum_fields: &HashSet<String>,
) {
    // 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;
        }
    }

    // Determine if this field is an enum type.
    let _field_is_enum = assertion
        .field
        .as_deref()
        .is_some_and(|f| enum_fields.contains(f) || enum_fields.contains(field_resolver.resolve(f)));

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

    match assertion.assertion_type.as_str() {
        "equals" => {
            if let Some(expected) = &assertion.value {
                let gleam_val = json_to_gleam(expected);
                let _ = writeln!(out, "  {field_expr} |> should.equal({gleam_val})");
            }
        }
        "contains" => {
            if let Some(expected) = &assertion.value {
                let gleam_val = json_to_gleam(expected);
                let _ = writeln!(
                    out,
                    "  {field_expr} |> string.contains({gleam_val}) |> should.equal(True)"
                );
            }
        }
        "contains_all" => {
            if let Some(values) = &assertion.values {
                for val in values {
                    let gleam_val = json_to_gleam(val);
                    let _ = writeln!(
                        out,
                        "  {field_expr} |> string.contains({gleam_val}) |> should.equal(True)"
                    );
                }
            }
        }
        "not_contains" => {
            if let Some(expected) = &assertion.value {
                let gleam_val = json_to_gleam(expected);
                let _ = writeln!(
                    out,
                    "  {field_expr} |> string.contains({gleam_val}) |> should.equal(False)"
                );
            }
        }
        "not_empty" => {
            let _ = writeln!(out, "  {field_expr} |> list.is_empty |> should.equal(False)");
        }
        "is_empty" => {
            let _ = writeln!(out, "  {field_expr} |> list.is_empty |> should.equal(True)");
        }
        "starts_with" => {
            if let Some(expected) = &assertion.value {
                let gleam_val = json_to_gleam(expected);
                let _ = writeln!(
                    out,
                    "  {field_expr} |> string.starts_with({gleam_val}) |> should.equal(True)"
                );
            }
        }
        "ends_with" => {
            if let Some(expected) = &assertion.value {
                let gleam_val = json_to_gleam(expected);
                let _ = writeln!(
                    out,
                    "  {field_expr} |> string.ends_with({gleam_val}) |> should.equal(True)"
                );
            }
        }
        "min_length" => {
            if let Some(val) = &assertion.value {
                if let Some(n) = val.as_u64() {
                    let _ = writeln!(
                        out,
                        "  {field_expr} |> string.length |> int.is_at_least({n}) |> should.equal(True)"
                    );
                }
            }
        }
        "max_length" => {
            if let Some(val) = &assertion.value {
                if let Some(n) = val.as_u64() {
                    let _ = writeln!(
                        out,
                        "  {field_expr} |> string.length |> int.is_at_most({n}) |> should.equal(True)"
                    );
                }
            }
        }
        "count_min" => {
            if let Some(val) = &assertion.value {
                if let Some(n) = val.as_u64() {
                    let _ = writeln!(
                        out,
                        "  {field_expr} |> list.length |> int.is_at_least({n}) |> should.equal(True)"
                    );
                }
            }
        }
        "count_equals" => {
            if let Some(val) = &assertion.value {
                if let Some(n) = val.as_u64() {
                    let _ = writeln!(out, "  {field_expr} |> list.length |> should.equal({n})");
                }
            }
        }
        "is_true" => {
            let _ = writeln!(out, "  {field_expr} |> should.equal(True)");
        }
        "is_false" => {
            let _ = writeln!(out, "  {field_expr} |> should.equal(False)");
        }
        "not_error" => {
            // Already handled by the call succeeding.
        }
        "error" => {
            // Handled at the test case level.
        }
        "greater_than" => {
            if let Some(val) = &assertion.value {
                let gleam_val = json_to_gleam(val);
                let _ = writeln!(
                    out,
                    "  {field_expr} |> int.is_strictly_greater_than({gleam_val}) |> should.equal(True)"
                );
            }
        }
        "less_than" => {
            if let Some(val) = &assertion.value {
                let gleam_val = json_to_gleam(val);
                let _ = writeln!(
                    out,
                    "  {field_expr} |> int.is_strictly_less_than({gleam_val}) |> should.equal(True)"
                );
            }
        }
        "greater_than_or_equal" => {
            if let Some(val) = &assertion.value {
                let gleam_val = json_to_gleam(val);
                let _ = writeln!(
                    out,
                    "  {field_expr} |> int.is_at_least({gleam_val}) |> should.equal(True)"
                );
            }
        }
        "less_than_or_equal" => {
            if let Some(val) = &assertion.value {
                let gleam_val = json_to_gleam(val);
                let _ = writeln!(
                    out,
                    "  {field_expr} |> int.is_at_most({gleam_val}) |> should.equal(True)"
                );
            }
        }
        "contains_any" => {
            if let Some(values) = &assertion.values {
                for val in values {
                    let gleam_val = json_to_gleam(val);
                    let _ = writeln!(
                        out,
                        "  {field_expr} |> string.contains({gleam_val}) |> should.equal(True)"
                    );
                }
            }
        }
        "matches_regex" => {
            let _ = writeln!(out, "  // regex match not yet implemented for Gleam");
        }
        "method_result" => {
            let _ = writeln!(out, "  // method_result assertions not yet implemented for Gleam");
        }
        other => {
            panic!("Gleam e2e generator: unsupported assertion type: {other}");
        }
    }
}

/// Convert a `serde_json::Value` to a Gleam literal string.
fn json_to_gleam(value: &serde_json::Value) -> String {
    match value {
        serde_json::Value::String(s) => format!("\"{}\"", escape_gleam(s)),
        serde_json::Value::Bool(b) => {
            if *b {
                "True".to_string()
            } else {
                "False".to_string()
            }
        }
        serde_json::Value::Number(n) => n.to_string(),
        serde_json::Value::Null => "Nil".to_string(),
        serde_json::Value::Array(arr) => {
            let items: Vec<String> = arr.iter().map(json_to_gleam).collect();
            format!("[{}]", items.join(", "))
        }
        serde_json::Value::Object(_) => {
            let json_str = serde_json::to_string(value).unwrap_or_default();
            format!("\"{}\"", escape_gleam(&json_str))
        }
    }
}