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,
    EmitError,
    TypeError,
};

/// Does not account for custom types e.g structs, better type resolution
/// should be found
fn basicTypeToLLVM(ret_type: []const u8) !llvm.LLVMTypeRef {
    if (std.mem.eql(u8, ret_type, "i32")) {
        return llvm.LLVMInt32Type();
    } else if (std.mem.eql(u8, ret_type, "bool")) {
        return llvm.LLVMInt1Type();
    } else {
        std.debug.warn("Invalid return type: {}\n", ret_type);
        return CompileError.TypeError;
    }
}

fn mkLLVMBool(val: bool) llvm.LLVMValueRef {
    if (val) {
        return llvm.LLVMConstInt(llvm.LLVMInt1Type(), 1, 1);
    } else {
        return llvm.LLVMConstInt(llvm.LLVMInt1Type(), 0, 1);
    }
}

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

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

    fn emitExpr(self: *Codegen, builder: var, expr: *const ast.Expr) anyerror!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
        return switch (expr.*) {

            // TODO handle all literals, construct llvm values for them
            .Literal => |literal| blk: {
                break :blk switch (literal) {
                    // TODO other literals
                    .Integer => |val| blk2: {
                        var val_cstr = try std.cstr.addNullByte(self.allocator, val);
                        break :blk2 llvm.LLVMConstIntOfString(llvm.LLVMInt32Type(), val_cstr.ptr, 10);
                    },
                    .Float => |val| blk2: {
                        var val_cstr = try std.cstr.addNullByte(self.allocator, val);
                        break :blk2 llvm.LLVMConstRealOfString(llvm.LLVMDoubleType(), val_cstr.ptr);
                    },
                    .Bool => |val| blk2: {
                        break :blk2 mkLLVMBool(val);
                    },
                    else => unreachable,
                };
            },

            .Binary => |binary| {
                var left = try self.emitExpr(builder, binary.left);
                var right = try self.emitExpr(builder, binary.right);

                return switch (binary.op) {
                    .Add => llvm.LLVMBuildAdd(builder, left, right, c"addtmp"),
                    .Sub => llvm.LLVMBuildSub(builder, left, right, c"subtmp"),
                    .Mul => llvm.LLVMBuildMul(builder, left, right, c"multmp"),

                    //.Div => llvm.LLVMBuildDiv(builder, left, right, c"divtmp"),
                    .And => llvm.LLVMBuildAnd(builder, left, right, c"andtmp"),
                    .Or => llvm.LLVMBuildOr(builder, left, right, c"ortmp"),

                    else => {
                        std.debug.warn("Unexpected binary operator: '{}'\n", binary.op);
                        return CompileError.EmitError;
                    },
                };
            },

            // TODO codegen errors
            else => {
                std.debug.warn("Got unexpected expr {}\n", expr.*);
                return CompileError.EmitError;
            },
        };
    }

    fn emitStmt(self: *Codegen, builder: var, stmt: *const ast.Stmt) !void {
        switch (stmt.*) {
            .Expr => |expr| _ = try self.emitExpr(builder, expr),

            .Return => |ret| {
                var ret_expr = try self.emitExpr(builder, ret.value);
                _ = llvm.LLVMBuildRet(builder, ret_expr);
            },

            .If => |ifstmt| {
                var cond = try self.emitExpr(builder, ifstmt.condition);
                var zero = mkLLVMBool(false);
                var icmp = llvm.LLVMBuildICmp(builder, llvm.LLVMIntPredicate.LLVMIntNE, cond, zero, c"ifcond");
            },

            else => {
                std.debug.warn("Got unexpected statement {}\n", stmt.*);
                return CompileError.EmitError;
            },
        }
    }

    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 fn_ret_type = decl.return_type.lexeme;

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

                for (decl.params.toSlice()) |param| {
                    // TODO better type resolution
                    try param_types.append(try basicTypeToLLVM(param.typ.lexeme));
                }

                var llvm_ret_type = llvm.LLVMFunctionType(
                    try basicTypeToLLVM(fn_ret_type),
                    param_types.toSlice().ptr,
                    @intCast(c_uint, param_types.len),
                    0,
                );

                var func = llvm.LLVMAddFunction(mod, name_cstr.ptr, llvm_ret_type);

                var buf = try self.allocator.alloc(u8, 512);
                var entry_lbl = try std.fmt.bufPrint(buf, "fn_{}_entry", name);
                var entry_lbl_cstr = try std.cstr.addNullByte(self.allocator, entry_lbl);
                var entry = llvm.LLVMAppendBasicBlock(func, entry_lbl_cstr.ptr);

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

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

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

                std.debug.warn("cgen: generated function '{}'\n", name);
            },
            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_cstr = try std.cstr.addNullByte(self.allocator, "outpath.o");

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

        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;
        }
    }
};