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 CompileError = error{LLVMError};

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

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

    fn genExpr(self: *Codegen, builder: var, expr: *const ast.Expr) !llvm.LLVMValueRef {
        // TODO if expr is Variable, we should do a variable lookup
        // in a symbol table, going up in scope, etc.

        // TODO VarDecl add things to the symbol table
        // TODO Assign modify symbol table

        // TODO Calls fetch symbol table, check arity of it at codegen level
        switch (expr.*) {

            // TODO handle all literals, construct llvm values for them
            .Literal => |literal| {},
            .Binary => |binary| {
                var left = try self.genExpr(builder, binary.left);
                var right = try self.genExpr(builder, binary.right);

                return switch (binary.op.lexeme[0]) {
                    // TODO other operators
                    '+' => llvm.LLVMBuildAdd(builder, left, right, c"addtmp"),

                    // TODO codegen errors
                    else => @panic("invalid binary operator"),
                };
            },

            // TODO codegen errors
            else => @panic("invalid expr"),
        }
    }

    fn genFuncStmt(self: *Codegen, builder: var, stmt: *const ast.Stmt) !void {
        switch (stmt.*) {
            .Expr => |expr| try self.genExpr(builder, expr),
            else => unreachable,
        }
    }

    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);

                for (decl.body.toSlice()) |stmt| {
                    // TODO custom function context for us
                    try self.genFuncStmt(builder, stmt);
                }

                // 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));
            return CompileError.LLVMError;
        }

        llvm.LLVMInitializeAllTargetInfos();
        llvm.LLVMInitializeAllTargets();
        llvm.LLVMInitializeAllTargetMCs();
        llvm.LLVMInitializeAllAsmParsers();
        llvm.LLVMInitializeAllAsmPrinters();

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

        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 asmpath = try std.mem.dupe(self.allocator, u8, "output.S");
        //var asmpath_cstr = try std.cstr.addNullByte(self.allocator, asmpath);

        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,
        //    asmpath_cstr.ptr,
        //    llvm.LLVMCodeGenFileType.LLVMAssemblyFile,
        //    &err,
        //) != 0) {
        //    std.debug.warn("failed to emit to assembly file: {}\n", sliceify(err));
        //    return CompileError.LLVMError;
        //}

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