const std = @import("std");
const ast = @import("ast.zig");
const llvm = @import("llvm.zig");

fn sliceify(non_slice: ?[*]const u8) []const u8 {
    if (non_slice == null) return "";
    return non_slice.?[0..std.mem.len(u8, non_slice.?)];
}

pub const Codegen = struct {
    allocator: *std.mem.Allocator,

    pub fn init(allocator: *std.mem.Allocator) Codegen {
        return Codegen{ .allocator = allocator };
    }

    fn genNode(
        self: *Codegen,
        mod: llvm.LLVMModuleRef,
        node: *const ast.Node,
    ) !void {
        switch (node.*) {
            .Root => @panic("Should not have gotten Root"),
            .FnDecl => |decl| {
                const name = decl.func_name.lexeme;
                const name_cstr = try std.cstr.addNullByte(self.allocator, name);
                errdefer self.allocator.free(name_cstr);

                //const ret_type = decl.return_type.lexeme;

                var param_types = llvm.LLVMTypeList.init(self.allocator);
                errdefer param_types.deinit();

                for (decl.params.toSlice()) |param| {
                    try param_types.append(llvm.LLVMInt32Type());
                }

                var ret_type = llvm.LLVMFunctionType(
                    llvm.LLVMInt32Type(),
                    param_types.toSlice().ptr,
                    @intCast(c_uint, param_types.len),
                    0,
                );

                var func = llvm.LLVMAddFunction(mod, name_cstr.ptr, ret_type);
                var entry = llvm.LLVMAppendBasicBlock(func, c"entry");

                var builder = llvm.LLVMCreateBuilder();
                llvm.LLVMPositionBuilderAtEnd(builder, entry);

                // TODO codegen decl.body
                var tmp = llvm.LLVMBuildAdd(
                    builder,
                    llvm.LLVMGetParam(func, 0),
                    llvm.LLVMGetParam(func, 1),
                    c"tmp",
                );

                _ = llvm.LLVMBuildRet(builder, tmp);
                std.debug.warn("cgen: fn decl done\n");
            },
            else => {
                std.debug.warn("got unhandled Node {}\n", node.*);
                unreachable;
            },
        }
    }

    pub fn gen(self: *Codegen, root: *ast.Node) !void {
        std.debug.warn("cgen: start gen\n");
        _ = llvm.LLVMInitializeNativeTarget();

        var mod = llvm.LLVMModuleCreateWithName(c"awoo").?;
        defer llvm.LLVMDisposeModule(mod);

        for (root.Root.toSlice()) |child| {
            std.debug.warn("cgen: gen child {}\n", child);
            try self.genNode(mod, &child);
        }

        var err: ?[*]u8 = null;
        defer llvm.LLVMDisposeMessage(err);

        _ = llvm.LLVMVerifyModule(
            mod,
            llvm.LLVMVerifierFailureAction.LLVMAbortProcessAction,
            &err,
        );

        if (llvm.LLVMWriteBitcodeToFile(mod, c"awoo.bc") != 0) {
            std.debug.warn("error writing bitcode to file: {}\n", sliceify(err));

            // TODO return error value
            @panic("compile error");
        }

        //llvm.InitializeAllTargetInfos();
        //llvm.InitializeAllTargets();
        //llvm.InitializeAllTargetMCs();
        //llvm.InitializeAllAsmParsers();
        //llvm.InitializeAllAsmPrinters();

        var engine: llvm.LLVMExecutionEngineRef = undefined;
        if (llvm.LLVMCreateExecutionEngineForModule(&engine, mod, &err) != 0) {
            std.debug.warn("failed to create execution engine: {}\n", sliceify(err));

            // TODO return error value
            @panic("compile error");
        }

        var machine = llvm.LLVMGetExecutionEngineTargetMachine(engine);
        defer llvm.LLVMDisposeTargetMachine(machine);

        var target = llvm.LLVMGetTargetMachineTarget(machine);
        var target_data = llvm.LLVMCreateTargetDataLayout(machine);
        var data_layout = llvm.LLVMCopyStringRepOfTargetData(target_data);
        llvm.LLVMSetDataLayout(mod, data_layout);

        var outpath = try std.mem.dupe(self.allocator, u8, "output.o");
        var outpath_cstr = try std.cstr.addNullByte(self.allocator, outpath);

        var desc = llvm.LLVMGetTargetDescription(target);
        var features = llvm.LLVMGetTargetMachineFeatureString(machine);
        var triple = llvm.LLVMGetTargetMachineTriple(machine);

        std.debug.warn("target: {}\n", sliceify(desc));
        std.debug.warn("triple: {}\n", sliceify(triple));
        std.debug.warn("features: {}\n", sliceify(features));

        if (llvm.LLVMTargetMachineEmitToFile(
            machine,
            mod,
            outpath_cstr.ptr,
            llvm.LLVMCodeGenFileType.LLVMObjectFile,
            &err,
        ) != 0) {
            std.debug.warn("failed to emit to file: {}\n", sliceify(err));

            // TODO return error value
            @panic("compile error");
        }
    }
};