variant compilation

// Test 817: Variant Compilation Architecture
//
// Demonstrates the complete pattern for variant compilation using |variant syntax.
// This test proves the architecture WITHOUT modifying compiler_bootstrap.kz!
//
// KEY CONCEPTS (see docs/KORU-BUILD.md):
//
// 1. VARIANTS (|gpu, |js, |zig) - Semantically equivalent implementations
//    - Same algorithm, different execution platform
//    - Permanent, version-controlled
//    - Testably equivalent (property tests)
//    - Compiler selects based on platform/benchmarks
//
// 2. MOCKS (for testing) - Use subflow syntax, NOT variants!
//    - ~event.path = branch { fake_data }
//    - Scoped to individual tests
//    - Applied via compile-time AST substitution
//    - See TESTING-STORY.md
//
// 3. COMPILER PASSES - Transform AST before emission
//    - Walk AST looking for procs with .target field
//    - Invoke ~compile.target event (proc-based compiler pass)
//    - Replace proc.body with generated Zig wrapper
//    - Happens in compiler.coordinate pipeline, NOT in emitter!
//
// This test demonstrates:
// ✅ Coordinator override mechanism (subflow)
// ✅ compile.target event interface
// ✅ Proc-based compiler passes
// ✅ Architecture is sound and composable
//
// Phase 2 (not in this test):
// - Add compiler.passes.compile_variants pass
// - Walk AST, transform procs with .target
// - Insert pass into compiler.coordinate pipeline

const std = @import("std");

// ================================================================
// Compiler Pass Interface (would come from koru-gpu package)
// ================================================================

~pub event compile.target {
    target_name: []const u8,
    body: []const u8,
    path: []const []const u8,
}
| compiled []const u8
| unsupported []const u8

// ================================================================
// Mock Compiler Passes (simplified for testing)
// ================================================================

~proc compile.target|zig {
    const allocator = std.heap.page_allocator;

    // GPU target: Wrap GLSL code in Zig wrapper
    if (std.mem.eql(u8, target_name, "gpu")) {
        // In real implementation, would:
        // - Extract GLSL code
        // - Validate syntax
        // - Generate proper Vulkan wrapper
        // - Return BuildSteps for glslangValidator

        // For this test, just return a simple wrapper
        const wrapper =
            \\// GPU implementation (GLSL shader compiled to SPIR-V)
            \\// Original shader embedded as comment:
            \\//
        ;

        var result = try std.ArrayList(u8).initCapacity(allocator, wrapper.len + body.len + 100);
        try result.appendSlice(wrapper);

        // Comment out the GLSL code
        var i: usize = 0;
        while (i < body.len) : (i += 1) {
            if (i == 0 or body[i-1] == '\n') {
                try result.appendSlice("// ");
            }
            try result.append(body[i]);
        }

        try result.appendSlice("\n//\n// Zig wrapper that loads compiled shader:\nreturn .{ .done = .{} };\n");

        return .{ .compiled = result.items };
    }

    // JavaScript target: Wrap JS code for V8
    if (std.mem.eql(u8, target_name, "js")) {
        const wrapper =
            \\// JavaScript implementation (V8 embedded)
            \\// Original JS embedded as string:
            \\const js_code =
        ;

        var result = try std.ArrayList(u8).initCapacity(allocator, wrapper.len + body.len + 100);
        try result.appendSlice(wrapper);
        try result.appendSlice("\n    \\\\");

        // Embed JS as multiline string
        var i: usize = 0;
        while (i < body.len) : (i += 1) {
            try result.append(body[i]);
            if (body[i] == '\n' and i + 1 < body.len) {
                try result.appendSlice("    \\\\");
            }
        }

        try result.appendSlice("\n;\n// TODO: Call V8 engine with js_code\nreturn .{ .done = .{} };\n");

        return .{ .compiled = result.items };
    }

    // Unsupported target
    const msg = try std.fmt.allocPrint(allocator, "Target '{s}' not supported - only 'gpu' and 'js' available", .{target_name});
    return .{ .unsupported = msg };
}

// ================================================================
// Custom Compiler Coordinator (demonstrates override mechanism)
// ================================================================
// By defining compiler.coordinate as a SUBFLOW, we can completely
// replace the compilation pipeline! Real variant coordinator would:
//
// ~compiler.coordinate =
//     compiler.passes.evaluate_comptime(ast: ast)
//     | evaluated ev |> compiler.check.structure(ast: ev.ast)
//     | valid v |> compiler.passes.compile_variants(ast: v.ast)  ← NEW!
//     | transformed t |> compiler.check.phantom.semantic(ast: t.ast)
//     | valid v2 |> compiler.emit.zig(ast: v2.ast)
//     | emitted em |> coordinated { ... }
//
// The compiler.passes.compile_variants pass would:
// 1. Walk AST for procs with .target field
// 2. For each, invoke ~compile.target event (defined above)
// 3. Replace proc.body with returned wrapper code
// 4. Set proc.target = null (now it's pure Zig!)
//
// For this test, we just delegate to default:

~compiler.coordinate =
    compiler.coordinate.default(ast)
    | coordinated c => c

// ================================================================
// Simple Test Event (verifies basic compilation works)
// ================================================================

~pub event greet { }
| done { }

~proc greet|zig {
    return .{ .done = .{} };
}