//! End-to-end test: load example module, compile to binary, run it.
//!
//! This test guards the most important property of the entire pipeline:
//! AST → typecheck → LLVM IR → clang → binary → correct stdout.

use std::path::Path;
use std::process::Command;

fn ail_bin() -> &'static str {
    env!("CARGO_BIN_EXE_ail")
}

fn build_and_run(example: &str) -> String {
    // Workspace root is two levels above the crate manifest.
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let src = workspace.join("examples").join(example);
    let tmp = std::env::temp_dir().join(format!(
        "ailang_e2e_{}_{}",
        example.replace('.', "_"),
        std::process::id()
    ));
    std::fs::create_dir_all(&tmp).unwrap();
    let out = tmp.join("bin");
    let status = Command::new(ail_bin())
        .args(["build", src.to_str().unwrap(), "-o"])
        .arg(&out)
        .status()
        .expect("ail build failed to run");
    assert!(status.success(), "ail build failed for {example}");
    let output = Command::new(&out).output().expect("execute binary");
    assert!(
        output.status.success(),
        "binary {} exited non-zero",
        out.display()
    );
    String::from_utf8(output.stdout).expect("stdout utf8")
}

#[test]
fn sum_1_to_10_is_55() {
    let stdout = build_and_run("sum.ail.json");
    assert_eq!(stdout.trim(), "55");
}

/// Guards block tracking in codegen: max3 has nested `if`s, and wrong
/// phi block tracking would produce a wrong result here.
#[test]
fn max3_picks_largest() {
    let stdout = build_and_run("max3.ail.json");
    assert_eq!(stdout.trim(), "17");
}

#[test]
fn hello_world_str_lit() {
    let stdout = build_and_run("hello.ail.json");
    assert_eq!(stdout.trim(), "Hello, AILang.");
}

/// Guards ADT codegen + match: recursive list, sum_list via match on Cons/Nil.
#[test]
fn list_sum_via_match() {
    let stdout = build_and_run("list.ail.json");
    assert_eq!(stdout.trim(), "42");
}

/// Iter 7: first-class function references — `apply(inc, 41)` must
/// produce 42, exercising fn-typed parameters and indirect call.
#[test]
fn higher_order_apply_inc() {
    let stdout = build_and_run("hof.ail.json");
    assert_eq!(stdout.trim(), "42");
}

/// Iter 8b: lambdas with capture. `let n = 3 in apply(\x. x + n, 39)`
/// must print 42 — the lambda captures `n` from the enclosing `let`,
/// the env struct is malloc'd, the closure pair is passed to `apply`,
/// and apply's indirect call unpacks both halves.
#[test]
fn closure_captures_let_n() {
    let stdout = build_and_run("closure.ail.json");
    assert_eq!(stdout.trim(), "42");
}

/// Iter 9 dogfood: a non-trivial program that combines ADTs, recursion,
/// closure-without-capture, fn-typed parameters, IO effects, and `let`-
/// sequencing of effectful sub-expressions in a pattern-match arm.
/// `map (\x. x * 2)` over `[1, 2, 3]` then print each element.
#[test]
fn list_map_doubles_then_prints() {
    let stdout = build_and_run("list_map.ail.json");
    let lines: Vec<&str> = stdout.lines().collect();
    assert_eq!(lines, vec!["2", "4", "6"]);
}

/// Iter 14a: end-to-end exercise of parameterised ADTs through a
/// polymorphic higher-order fn. `data List a` plus
/// `map : forall a b. ((a) -> b, List<a>) -> List<b>` recursive,
/// instantiated at `(Int, Int)`. Guards: forall with two type vars +
/// recursive call inside its own body + ctor construction with
/// substituted field types + match-arm bindings flowing into an
/// effectful tail call.
#[test]
fn list_map_poly_inc_then_prints() {
    let stdout = build_and_run("list_map_poly.ail.json");
    let lines: Vec<&str> = stdout.lines().collect();
    assert_eq!(lines, vec!["2", "3", "4"]);
}

/// Iter 14e: `tail: true` annotation on `print_list`'s recursive
/// call must reach LLVM as a `musttail call`. Asserted by emitting IR
/// for list_map_poly and grepping for the exact instruction. This is
/// the only direct evidence that the type-system marker actually
/// influences codegen — the e2e test above only checks observed
/// stdout, which `musttail` does not change.
#[test]
fn iter14e_print_list_recursion_emits_musttail() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let src = workspace.join("examples").join("list_map_poly.ail.json");
    let tmp = std::env::temp_dir().join(format!(
        "ailang_iter14e_musttail_{}",
        std::process::id()
    ));
    std::fs::create_dir_all(&tmp).unwrap();
    let out_ll = tmp.join("list_map_poly.ll");
    let status = Command::new(ail_bin())
        .args(["emit-ir", src.to_str().unwrap(), "-o"])
        .arg(&out_ll)
        .status()
        .expect("ail emit-ir failed to run");
    assert!(status.success(), "ail emit-ir failed");
    let ir = std::fs::read_to_string(&out_ll).expect("read emitted IR");

    // Find the musttail call to print_list inside the print_list body.
    // The exact line shape:
    //   %vN = musttail call i8 @ail_list_map_poly_print_list(ptr %vM)
    let has_musttail = ir.lines().any(|l| {
        l.contains("musttail call")
            && l.contains("@ail_list_map_poly_print_list(")
    });
    assert!(
        has_musttail,
        "expected `musttail call ... @ail_list_map_poly_print_list(...)` \
         in emitted IR; not found.\nIR:\n{ir}"
    );
    // Defence-in-depth: the musttail call must be immediately followed
    // by a `ret i8 %v...`. We assert the next non-empty line is a ret.
    let mut lines = ir.lines();
    while let Some(line) = lines.next() {
        if line.contains("musttail call")
            && line.contains("@ail_list_map_poly_print_list(")
        {
            let next = lines.next().unwrap_or("").trim();
            assert!(
                next.starts_with("ret i8 "),
                "musttail call must be immediately followed by `ret i8 ...`; \
                 got: `{next}`"
            );
            return;
        }
    }
    panic!("musttail call line not found (sanity check)");
}

/// Iter 11 dogfood: insertion sort over an 11-element IntList.
/// Exercises `<=`, `if`, mutual-leaf recursion (`insert` and `sort`),
/// nested ctor construction, and the Iter 10 seq operator inside
/// print_list. Validates that the language handles deeper ADT
/// recursion + branching without surprises.
#[test]
fn insertion_sort_orders_list() {
    let stdout = build_and_run("sort.ail.json");
    let lines: Vec<&str> = stdout.lines().collect();
    assert_eq!(
        lines,
        vec!["1", "1", "2", "3", "3", "4", "5", "5", "5", "6", "9"],
    );
}

/// Iter 12b: polymorphism end-to-end. `id : forall a. (a) -> a`
/// gets called with `42` (Int) and `true` (Bool); each instantiation
/// triggers a separate specialised LLVM fn. Output: 42, then "true".
#[test]
fn polymorphic_id_at_int_and_bool() {
    let stdout = build_and_run("poly_id.ail.json");
    let lines: Vec<&str> = stdout.lines().collect();
    assert_eq!(lines, vec!["42", "true"]);
}

/// Iter 12b: polymorphism with a function-typed parameter.
/// `apply : forall a b. ((a) -> b, a) -> b` invoked as
/// `apply(succ, 41) == 42`. Exercises the closure-pair ABI inside a
/// monomorphised body (a fn-typed param survives substitution).
#[test]
fn polymorphic_apply_with_fn_param() {
    let stdout = build_and_run("poly_apply.ail.json");
    assert_eq!(stdout.trim(), "42");
}

/// Iter 13b: round-trip a primitive through a parameterised ADT and a
/// polymorphic-fn boundary. `type Box[a] = MkBox(a)` plus
/// `unbox : forall a. (Box<a>) -> a` plus `print_int(unbox(MkBox(42)))`.
/// Guards: ctor lower with substituted LLVM field types,
/// match-arm field bindings carrying the substituted AILang type
/// down into a polymorphic fn body.
#[test]
fn parameterised_box_round_trip() {
    let stdout = build_and_run("box.ail.json");
    assert_eq!(stdout.trim(), "42");
}

/// Iter 13b: pattern-match on `Maybe<Int>`. `or_else(Some(7), 99) == 7`
/// then `or_else(None, 99) == 99`. Guards: match-arm field
/// substitution at a parameterised ctor (the `Some(x)` arm must bind
/// `x : Int`, not `x : a`).
#[test]
fn parameterised_maybe_match() {
    let stdout = build_and_run("maybe_int.ail.json");
    let lines: Vec<&str> = stdout.lines().collect();
    assert_eq!(lines, vec!["7", "99"]);
}

/// Guards `ail diff`: a modified body changes the hash of `sum`, while
/// `main` stays unchanged. Expects exit code 1, `changed` contains exactly
/// `sum`, `unchanged` contains `main`, `added`/`removed` empty.
#[test]
fn diff_detects_changed_def() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let src_a = workspace.join("examples").join("sum.ail.json");

    // Variant: load sum.ail.json, mutate the true-arm body of the
    // top-level `match` in `sum` (literal 0 → literal 1). `main` stays
    // bit-identical. After Iter 14d the body is `Match` (not `If`); the
    // first arm is the `(lit-bool true)` arm, formerly the `then`
    // branch.
    let raw = std::fs::read(&src_a).expect("read sum.ail.json");
    let mut module: serde_json::Value = serde_json::from_slice(&raw).expect("parse sum.ail.json");
    {
        let defs = module
            .get_mut("defs")
            .and_then(|d| d.as_array_mut())
            .expect("defs array");
        for def in defs.iter_mut() {
            if def.get("name").and_then(|n| n.as_str()) == Some("sum") {
                let new_body = serde_json::json!({
                    "t": "lit",
                    "lit": { "kind": "int", "value": 1 }
                });
                def["body"]["arms"][0]["body"] = new_body;
            }
        }
    }

    let tmp = std::env::temp_dir().join(format!(
        "ailang_diff_changed_{}",
        std::process::id()
    ));
    std::fs::create_dir_all(&tmp).unwrap();
    let path_b = tmp.join("sum_v2.ail.json");
    std::fs::write(&path_b, serde_json::to_vec_pretty(&module).unwrap())
        .expect("write sum_v2.ail.json");

    let output = Command::new(ail_bin())
        .args([
            "diff",
            src_a.to_str().unwrap(),
            path_b.to_str().unwrap(),
            "--json",
        ])
        .output()
        .expect("ail diff failed to run");

    let code = output.status.code().expect("process terminated by signal");
    assert_eq!(
        code,
        1,
        "expected exit code 1 for differing modules; stderr: {}",
        String::from_utf8_lossy(&output.stderr)
    );

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let v: serde_json::Value =
        serde_json::from_str(stdout.trim()).expect("stdout must be valid JSON");

    let added = v["added"].as_array().expect("added array");
    let removed = v["removed"].as_array().expect("removed array");
    let changed = v["changed"].as_array().expect("changed array");
    let unchanged = v["unchanged"].as_array().expect("unchanged array");

    assert!(added.is_empty(), "expected added empty: {added:?}");
    assert!(removed.is_empty(), "expected removed empty: {removed:?}");
    assert_eq!(changed.len(), 1, "expected one changed entry: {changed:?}");
    assert_eq!(
        changed[0].get("name").and_then(|n| n.as_str()),
        Some("sum")
    );
    assert_ne!(
        changed[0].get("hash_a").and_then(|n| n.as_str()),
        changed[0].get("hash_b").and_then(|n| n.as_str()),
        "hash_a and hash_b must differ for a changed def"
    );

    assert!(
        unchanged.iter().any(|e| e.get("name").and_then(|n| n.as_str()) == Some("main")),
        "expected `main` in unchanged: {unchanged:?}"
    );
}

/// Diff of a module with itself: exit 0, all lists except `unchanged` empty.
#[test]
fn diff_no_changes_exit_zero() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let src = workspace.join("examples").join("sum.ail.json");

    let output = Command::new(ail_bin())
        .args([
            "diff",
            src.to_str().unwrap(),
            src.to_str().unwrap(),
            "--json",
        ])
        .output()
        .expect("ail diff failed to run");

    let code = output.status.code().expect("process terminated by signal");
    assert_eq!(
        code,
        0,
        "expected exit code 0 for identical modules; stderr: {}",
        String::from_utf8_lossy(&output.stderr)
    );

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let v: serde_json::Value =
        serde_json::from_str(stdout.trim()).expect("stdout must be valid JSON");

    assert!(v["added"].as_array().unwrap().is_empty());
    assert!(v["removed"].as_array().unwrap().is_empty());
    assert!(v["changed"].as_array().unwrap().is_empty());
    assert!(
        !v["unchanged"].as_array().unwrap().is_empty(),
        "self-diff should report unchanged defs"
    );
}

/// Guards the workspace loader (Iter 5a): the entry module `ws_main`
/// imports `ws_lib`; both must be found by the loader, loaded, and listed
/// in the JSON output. Cross-module typecheck/codegen is explicitly not
/// part of this test — it only verifies the loader pipeline.
#[test]
fn workspace_lists_imported_modules() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let entry = workspace.join("examples").join("ws_main.ail.json");

    let output = Command::new(ail_bin())
        .args(["workspace", entry.to_str().unwrap(), "--json"])
        .output()
        .expect("ail workspace failed to run");

    assert!(
        output.status.success(),
        "ail workspace exited non-zero; stderr: {}",
        String::from_utf8_lossy(&output.stderr)
    );

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let v: serde_json::Value =
        serde_json::from_str(stdout.trim()).expect("stdout must be valid JSON");

    assert_eq!(
        v.get("entry").and_then(|n| n.as_str()),
        Some("ws_main"),
        "entry must be ws_main: {stdout}"
    );

    let modules = v["modules"].as_array().expect("modules must be array");
    assert_eq!(modules.len(), 2, "expected 2 modules: {stdout}");

    let names: Vec<&str> = modules
        .iter()
        .filter_map(|m| m.get("name").and_then(|n| n.as_str()))
        .collect();
    assert!(names.contains(&"ws_main"), "ws_main missing: {names:?}");
    assert!(names.contains(&"ws_lib"), "ws_lib missing: {names:?}");
}

/// Guards Iter 5b: `ail check examples/ws_main.ail.json --json` must
/// resolve the cross-module call `ws_lib.add`. Expected: exit 0,
/// stdout exactly `[]` (empty diagnostic array).
#[test]
fn check_workspace_resolves_import() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let entry = workspace.join("examples").join("ws_main.ail.json");

    let output = Command::new(ail_bin())
        .args(["check", entry.to_str().unwrap(), "--json"])
        .output()
        .expect("ail check --json failed to run");

    let code = output.status.code().expect("process terminated by signal");
    assert_eq!(
        code,
        0,
        "expected exit 0; stderr: {}; stdout: {}",
        String::from_utf8_lossy(&output.stderr),
        String::from_utf8_lossy(&output.stdout),
    );

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    assert_eq!(stdout.trim(), "[]", "expected empty diagnostic array");
}

/// Guards Iter 5c (cross-module codegen): `ail build` over
/// `examples/ws_main.ail.json` must lower the workspace incl. `ws_lib`;
/// `@ail_ws_main_main` must call `@ail_ws_lib_add(2,3)` and print `5`.
#[test]
fn workspace_build_runs_imported_fn() {
    let stdout = build_and_run("ws_main.ail.json");
    assert_eq!(stdout.trim(), "5", "ws_lib.add(2,3) should print 5");
}

/// Guards Iter 5d: `ail manifest --workspace --json` lists defs from all
/// modules of the workspace — visible via a `module` field per entry.
#[test]
fn manifest_workspace_lists_all_defs() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let entry = workspace.join("examples").join("ws_main.ail.json");

    let output = Command::new(ail_bin())
        .args([
            "manifest",
            entry.to_str().unwrap(),
            "--workspace",
            "--json",
        ])
        .output()
        .expect("ail manifest --workspace failed to run");

    assert!(
        output.status.success(),
        "ail manifest --workspace exited non-zero; stderr: {}",
        String::from_utf8_lossy(&output.stderr)
    );

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let v: serde_json::Value =
        serde_json::from_str(stdout.trim()).expect("stdout must be valid JSON");

    let symbols = v["symbols"].as_array().expect("symbols must be array");
    let modules: Vec<&str> = symbols
        .iter()
        .filter_map(|s| s.get("module").and_then(|m| m.as_str()))
        .collect();
    assert!(
        modules.contains(&"ws_main"),
        "expected at least one symbol with module=ws_main; got {modules:?}"
    );
    assert!(
        modules.contains(&"ws_lib"),
        "expected at least one symbol with module=ws_lib; got {modules:?}"
    );
}

/// Guards Iter 5d: `ail describe --workspace ws_lib.add` resolves the
/// qualified dot notation to the actually imported module.
#[test]
fn describe_workspace_resolves_qualified_name() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let entry = workspace.join("examples").join("ws_main.ail.json");

    let output = Command::new(ail_bin())
        .args([
            "describe",
            entry.to_str().unwrap(),
            "ws_lib.add",
            "--workspace",
            "--json",
        ])
        .output()
        .expect("ail describe --workspace failed to run");

    assert!(
        output.status.success(),
        "ail describe --workspace exited non-zero; stderr: {}",
        String::from_utf8_lossy(&output.stderr)
    );

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let v: serde_json::Value =
        serde_json::from_str(stdout.trim()).expect("stdout must be valid JSON");

    assert_eq!(
        v.get("module").and_then(|m| m.as_str()),
        Some("ws_lib"),
        "module field must be ws_lib; got {stdout}"
    );
    assert_eq!(
        v.get("name").and_then(|n| n.as_str()),
        Some("add"),
        "def name must be add; got {stdout}"
    );
}

/// Guards Iter 6: `ail deps` no longer surfaces built-ins, params, or
/// let-bindings as edges. The single-module `sum` def in `sum.ail.json`
/// uses `+`, `-`, `==`, the param `n`, and the recursive call `sum`.
/// Only the recursive call must remain.
#[test]
fn deps_filters_builtins_params_locals() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let src = workspace.join("examples").join("sum.ail.json");

    let output = Command::new(ail_bin())
        .args(["deps", src.to_str().unwrap(), "--of", "sum", "--json"])
        .output()
        .expect("ail deps failed to run");
    assert!(
        output.status.success(),
        "ail deps exited non-zero; stderr: {}",
        String::from_utf8_lossy(&output.stderr)
    );

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let v: serde_json::Value = serde_json::from_str(stdout.trim()).expect("valid JSON");
    let arr = v.as_array().expect("array of {name, refs}");
    let entry = arr
        .iter()
        .find(|e| e["name"].as_str() == Some("sum"))
        .expect("sum entry present");
    let refs: Vec<&str> = entry["refs"]
        .as_array()
        .expect("refs array")
        .iter()
        .filter_map(|x| x.as_str())
        .collect();
    assert_eq!(
        refs,
        vec!["sum"],
        "expected only the recursive call `sum`; got {refs:?}"
    );
}

/// Guards Iter 6 in workspace mode: edges into built-ins (`ws_lib.+`)
/// and into the params (`ws_lib.a`, `ws_lib.b`) of `ws_lib.add` must be
/// gone after the deps refactor.
#[test]
fn deps_workspace_filters_builtins_and_params() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let entry = workspace.join("examples").join("ws_main.ail.json");

    let output = Command::new(ail_bin())
        .args(["deps", entry.to_str().unwrap(), "--workspace", "--json"])
        .output()
        .expect("ail deps --workspace failed to run");
    assert!(output.status.success());

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let v: serde_json::Value = serde_json::from_str(stdout.trim()).expect("valid JSON");
    let edges = v["edges"].as_array().expect("edges array");

    for e in edges {
        let to_def = e.get("to_def").and_then(|x| x.as_str()).unwrap_or("");
        assert_ne!(to_def, "+", "built-in `+` must not appear: {e}");
        assert_ne!(to_def, "a", "param `a` must not appear: {e}");
        assert_ne!(to_def, "b", "param `b` must not appear: {e}");
    }
}

/// Guards Iter 5d: `ail deps --workspace` contains a cross-module edge
/// `ws_main.main -> ws_lib.add`, because `ws_main` calls `ws_lib.add(2,3)`.
#[test]
fn deps_workspace_includes_cross_module() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let entry = workspace.join("examples").join("ws_main.ail.json");

    let output = Command::new(ail_bin())
        .args(["deps", entry.to_str().unwrap(), "--workspace", "--json"])
        .output()
        .expect("ail deps --workspace failed to run");

    assert!(
        output.status.success(),
        "ail deps --workspace exited non-zero; stderr: {}",
        String::from_utf8_lossy(&output.stderr)
    );

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let v: serde_json::Value =
        serde_json::from_str(stdout.trim()).expect("stdout must be valid JSON");
    let edges = v["edges"].as_array().expect("edges must be array");

    let has_cross_edge = edges.iter().any(|e| {
        e.get("from_module").and_then(|s| s.as_str()) == Some("ws_main")
            && e.get("from_def").and_then(|s| s.as_str()) == Some("main")
            && e.get("to_module").and_then(|s| s.as_str()) == Some("ws_lib")
            && e.get("to_def").and_then(|s| s.as_str()) == Some("add")
    });
    assert!(
        has_cross_edge,
        "expected cross-module edge ws_main.main -> ws_lib.add; got {stdout}"
    );
}

/// Guards Iter 5d: `ail diff --workspace` detects an additional module
/// in the B workspace as an `added_modules` entry and exits with code 1.
#[test]
fn diff_workspace_added_module() {
    use std::fs;

    fn write_module(dir: &Path, name: &str, body: serde_json::Value) {
        let p = dir.join(format!("{name}.ail.json"));
        fs::write(&p, serde_json::to_vec_pretty(&body).unwrap()).unwrap();
    }

    let dir_a = std::env::temp_dir().join(format!(
        "ailang_diff_ws_a_{}",
        std::process::id()
    ));
    let dir_b = std::env::temp_dir().join(format!(
        "ailang_diff_ws_b_{}",
        std::process::id()
    ));
    let _ = fs::remove_dir_all(&dir_a);
    let _ = fs::remove_dir_all(&dir_b);
    fs::create_dir_all(&dir_a).unwrap();
    fs::create_dir_all(&dir_b).unwrap();

    // Both workspaces have an empty module `root`. B additionally
    // imports `extra`. Loader convention: `<root_dir>/<name>.ail.json`,
    // module name must match the file name.
    let empty_root = serde_json::json!({
        "schema": "ailang/v0",
        "name": "root",
        "imports": [],
        "defs": [],
    });
    let root_with_import = serde_json::json!({
        "schema": "ailang/v0",
        "name": "root",
        "imports": [{ "module": "extra" }],
        "defs": [],
    });
    let extra = serde_json::json!({
        "schema": "ailang/v0",
        "name": "extra",
        "imports": [],
        "defs": [],
    });

    write_module(&dir_a, "root", empty_root);
    write_module(&dir_b, "root", root_with_import);
    write_module(&dir_b, "extra", extra);

    let entry_a = dir_a.join("root.ail.json");
    let entry_b = dir_b.join("root.ail.json");

    let output = Command::new(ail_bin())
        .args([
            "diff",
            entry_a.to_str().unwrap(),
            entry_b.to_str().unwrap(),
            "--workspace",
            "--json",
        ])
        .output()
        .expect("ail diff --workspace failed to run");

    let code = output.status.code().expect("process terminated by signal");
    assert_eq!(
        code,
        1,
        "expected exit 1 when workspaces differ; stderr: {}",
        String::from_utf8_lossy(&output.stderr)
    );

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let v: serde_json::Value =
        serde_json::from_str(stdout.trim()).expect("stdout must be valid JSON");

    let added = v["added_modules"]
        .as_array()
        .expect("added_modules must be array");
    assert!(
        added.iter().any(|e| e.get("name").and_then(|n| n.as_str()) == Some("extra")),
        "expected `extra` in added_modules; got {stdout}"
    );
    let removed = v["removed_modules"]
        .as_array()
        .expect("removed_modules must be array");
    assert!(
        removed.is_empty(),
        "expected removed_modules empty; got {stdout}"
    );
}

/// Guards the `--json` diagnostic format for tooling consumers.
/// `broken_unbound.ail.json` references a non-existent variable;
/// exit code 1 is expected, plus at least one diagnostic with
/// `severity == "error"` and `code == "unbound-var"`.
#[test]
fn check_json_unbound_var() {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let src = workspace.join("examples").join("broken_unbound.ail.json");

    let output = Command::new(ail_bin())
        .args(["check", src.to_str().unwrap(), "--json"])
        .output()
        .expect("ail check --json failed to run");

    let code = output.status.code().expect("process terminated by signal");
    assert_eq!(code, 1, "expected exit code 1, stderr: {}", String::from_utf8_lossy(&output.stderr));

    let stdout = String::from_utf8(output.stdout).expect("stdout utf8");
    let diags: serde_json::Value =
        serde_json::from_str(stdout.trim()).expect("stdout must be valid JSON");
    let arr = diags.as_array().expect("diagnostics must be a JSON array");
    assert!(
        arr.iter().any(|d| {
            d.get("severity").and_then(|v| v.as_str()) == Some("error")
                && d.get("code").and_then(|v| v.as_str()) == Some("unbound-var")
        }),
        "expected at least one error diagnostic with code unbound-var; got: {stdout}"
    );
}