const std = @import("std");
const Allocator = std.mem.Allocator;
const patterns = @import("patterns.zig");
const naming = @import("naming.zig");
const resolved_decl = @import("resolved_decl.zig");
const types = @import("types.zig");

const EnumDecl = patterns.EnumDecl;
const FlagDecl = patterns.FlagDecl;
const OpaqueType = patterns.OpaqueType;
const ResolvedDecl = resolved_decl.ResolvedDecl;
const StructDecl = patterns.StructDecl;

const ImportedModule = struct {
    module_name: []const u8,
    import_name: []const u8,
};

const TypeAlias = struct {
    name: []const u8,
    import_name: []const u8,
    target_name: []const u8,
};

pub const CodeGenOptions = struct {
    decls: []const ResolvedDecl,
    module_name: []const u8,
    c_import_path: []const u8 = "c.zig",
    skipped: []const patterns.SkippedDecl = &.{},
};

pub const CodeGen = struct {
    decls: []const ResolvedDecl,
    module_name: []const u8,
    c_import_path: []const u8,
    skipped: []const patterns.SkippedDecl,
    allocator: Allocator,
    output: std.ArrayList(u8),
    opaque_methods: std.StringHashMap(std.ArrayList(patterns.FunctionDecl)),
    import_modules: std.ArrayList(ImportedModule),
    aliases: std.ArrayList(TypeAlias),

    pub fn generate(allocator: Allocator, options: CodeGenOptions) ![]const u8 {
        var gen = CodeGen{
            .decls = options.decls,
            .module_name = options.module_name,
            .c_import_path = options.c_import_path,
            .skipped = options.skipped,
            .allocator = allocator,
            .output = try std.ArrayList(u8).initCapacity(allocator, 4096),
            .opaque_methods = std.StringHashMap(std.ArrayList(patterns.FunctionDecl)).init(allocator),
            .import_modules = .empty,
            .aliases = .empty,
        };
        defer gen.deinit();

        try gen.planDependencies();
        try gen.categorizeDeclarations();
        try gen.writeHeader();
        try gen.writeDeclarations();
        return try gen.output.toOwnedSlice(allocator);
    }

    fn deinit(self: *CodeGen) void {
        var method_it = self.opaque_methods.valueIterator();
        while (method_it.next()) |methods| {
            methods.deinit(self.allocator);
        }
        self.opaque_methods.deinit();

        for (self.import_modules.items) |module| {
            self.allocator.free(module.module_name);
            self.allocator.free(module.import_name);
        }
        self.import_modules.deinit(self.allocator);

        for (self.aliases.items) |alias_decl| {
            self.allocator.free(alias_decl.import_name);
        }
        self.aliases.deinit(self.allocator);

        self.output.deinit(self.allocator);
    }

    fn planDependencies(self: *CodeGen) !void {
        var seen_modules = std.StringHashMap(void).init(self.allocator);
        defer {
            var module_it = seen_modules.keyIterator();
            while (module_it.next()) |key| {
                self.allocator.free(key.*);
            }
            seen_modules.deinit();
        }

        var seen_aliases = std.StringHashMap(void).init(self.allocator);
        defer {
            var alias_it = seen_aliases.keyIterator();
            while (alias_it.next()) |key| {
                self.allocator.free(key.*);
            }
            seen_aliases.deinit();
        }

        for (self.decls) |resolved| {
            const type_name = resolved.typeName() orelse continue;
            const owner_module = try resolved_decl.headerToModuleNameAlloc(self.allocator, resolved.source_header);
            defer self.allocator.free(owner_module);
            if (std.mem.eql(u8, owner_module, self.module_name)) continue;

            if (!seen_modules.contains(owner_module)) {
                const module_name = try self.allocator.dupe(u8, owner_module);
                const import_name = try std.fmt.allocPrint(self.allocator, "{s}_api", .{owner_module});
                try seen_modules.put(try self.allocator.dupe(u8, owner_module), {});
                try self.import_modules.append(self.allocator, .{
                    .module_name = module_name,
                    .import_name = import_name,
                });
            }

            const alias_name = naming.typeNameToZig(type_name);
            if (!seen_aliases.contains(alias_name)) {
                try seen_aliases.put(try self.allocator.dupe(u8, alias_name), {});
                const import_name = try std.fmt.allocPrint(self.allocator, "{s}_api", .{owner_module});
                try self.aliases.append(self.allocator, .{
                    .name = alias_name,
                    .import_name = import_name,
                    .target_name = alias_name,
                });
            }
        }
    }

    fn categorizeDeclarations(self: *CodeGen) !void {
        var opaque_names: std.ArrayList([]const u8) = .empty;
        defer opaque_names.deinit(self.allocator);

        for (self.decls) |resolved| {
            if (!try self.isOwnedDecl(resolved)) continue;
            if (resolved.decl == .opaque_type) {
                const zig_name = naming.typeNameToZig(resolved.decl.opaque_type.name);
                try opaque_names.append(self.allocator, zig_name);
                try self.opaque_methods.put(zig_name, .empty);
            }
        }

        for (self.decls) |resolved| {
            if (!try self.isOwnedDecl(resolved)) continue;
            if (resolved.decl != .function_decl) continue;

            const func = resolved.decl.function_decl;
            if (func.params.len == 0) continue;

            const first_param_type = try types.convertType(func.params[0].type_name, self.allocator);
            defer self.allocator.free(first_param_type);

            for (opaque_names.items) |opaque_name| {
                const opt_ptr = try std.fmt.allocPrint(self.allocator, "?*{s}", .{opaque_name});
                defer self.allocator.free(opt_ptr);
                const ptr = try std.fmt.allocPrint(self.allocator, "*{s}", .{opaque_name});
                defer self.allocator.free(ptr);

                if (std.mem.eql(u8, first_param_type, opt_ptr) or std.mem.eql(u8, first_param_type, ptr)) {
                    var methods = self.opaque_methods.getPtr(opaque_name).?;
                    try methods.append(self.allocator, func);
                    break;
                }
            }
        }
    }

    fn isOwnedDecl(self: *CodeGen, resolved: ResolvedDecl) !bool {
        if (!resolved.is_primary_header_decl and resolved.typeName() == null) return true;

        const owner_module = try resolved_decl.headerToModuleNameAlloc(self.allocator, resolved.source_header);
        defer self.allocator.free(owner_module);
        return std.mem.eql(u8, owner_module, self.module_name);
    }

    fn writeHeader(self: *CodeGen) !void {
        try self.output.writer(self.allocator).print(
            \\const std = @import("std");
            \\pub const c = @import("{s}").c;
            \\
        , .{self.c_import_path});

        for (self.import_modules.items) |module| {
            try self.output.writer(self.allocator).print("const {s} = @import(\"{s}.zig\");\n", .{
                module.import_name,
                module.module_name,
            });
        }
        if (self.import_modules.items.len > 0) {
            try self.output.appendSlice(self.allocator, "\n");
        }

        for (self.aliases.items) |alias_decl| {
            try self.output.writer(self.allocator).print("pub const {s} = {s}.{s};\n", .{
                alias_decl.name,
                alias_decl.import_name,
                alias_decl.target_name,
            });
        }
        if (self.aliases.items.len > 0) {
            try self.output.appendSlice(self.allocator, "\n");
        }

        if (self.skipped.len > 0) {
            try self.output.appendSlice(self.allocator, "pub const unsupported = struct {\n");
            for (self.skipped) |item| {
                try self.output.writer(self.allocator).print("    pub const @\"{s}\" = \"{s}\";\n", .{ item.name, item.reason });
            }
            try self.output.appendSlice(self.allocator, "};\n\n");
        }
    }

    fn writeDeclarations(self: *CodeGen) !void {
        for (self.decls) |resolved| {
            if (!try self.isOwnedDecl(resolved)) continue;

            switch (resolved.decl) {
                .opaque_type => |opaque_decl| try self.writeOpaqueWithMethods(opaque_decl),
                .typedef_decl => |typedef_decl| try self.writeTypedef(typedef_decl),
                .function_pointer_decl => |func_ptr_decl| try self.writeFunctionPointer(func_ptr_decl),
                .c_type_alias => |alias| try self.writeCTypeAlias(alias),
                .enum_decl => |enum_decl| try self.writeEnum(enum_decl),
                .struct_decl => |struct_decl| try self.writeStruct(struct_decl),
                .union_decl => |union_decl| try self.writeUnion(union_decl),
                .flag_decl => |flag_decl| try self.writeFlags(flag_decl),
                .function_decl => |func| {
                    if (try self.isStandaloneFunction(func)) {
                        try self.writeFunction(func);
                    }
                },
            }
        }
    }

    fn isStandaloneFunction(self: *CodeGen, func: patterns.FunctionDecl) !bool {
        if (func.params.len == 0) return true;

        const first_param_type = try types.convertType(func.params[0].type_name, self.allocator);
        defer self.allocator.free(first_param_type);

        var it = self.opaque_methods.keyIterator();
        while (it.next()) |opaque_name| {
            const opt_ptr = try std.fmt.allocPrint(self.allocator, "?*{s}", .{opaque_name.*});
            defer self.allocator.free(opt_ptr);
            const ptr = try std.fmt.allocPrint(self.allocator, "*{s}", .{opaque_name.*});
            defer self.allocator.free(ptr);
            if (std.mem.eql(u8, first_param_type, opt_ptr) or std.mem.eql(u8, first_param_type, ptr)) return false;
        }
        return true;
    }

    fn writeOpaqueWithMethods(self: *CodeGen, opaque_type: OpaqueType) !void {
        const zig_name = naming.typeNameToZig(opaque_type.name);
        if (opaque_type.doc_comment) |doc| try self.writeDocComment(doc);

        if (self.opaque_methods.get(zig_name)) |method_list| {
            if (method_list.items.len > 0) {
                try self.output.writer(self.allocator).print("pub const {s} = opaque {{\n", .{zig_name});
                for (method_list.items) |func| {
                    try self.writeFunctionAsMethod(func, zig_name);
                }
                try self.output.appendSlice(self.allocator, "};\n\n");
                return;
            }
        }

        try self.output.writer(self.allocator).print("pub const {s} = opaque {{}};\n\n", .{zig_name});
    }

    fn writeTypedef(self: *CodeGen, typedef_decl: patterns.TypedefDecl) !void {
        if (typedef_decl.doc_comment) |doc| try self.writeDocComment(doc);
        const zig_name = naming.typeNameToZig(typedef_decl.name);
        const zig_type = try types.convertType(typedef_decl.underlying_type, self.allocator);
        defer self.allocator.free(zig_type);

        try self.output.appendSlice(self.allocator, "pub const ");
        try self.output.appendSlice(self.allocator, zig_name);
        try self.output.appendSlice(self.allocator, " = ");
        try self.output.appendSlice(self.allocator, zig_type);
        try self.output.appendSlice(self.allocator, ";\n\n");
    }

    fn writeFunctionPointer(self: *CodeGen, func_ptr_decl: patterns.FunctionPointerDecl) !void {
        if (func_ptr_decl.doc_comment) |doc| try self.writeDocComment(doc);
        const zig_name = naming.typeNameToZig(func_ptr_decl.name);
        const return_type = try types.convertType(func_ptr_decl.return_type, self.allocator);
        defer self.allocator.free(return_type);

        try self.output.writer(self.allocator).print("pub const {s} = *const fn(", .{zig_name});
        for (func_ptr_decl.params, 0..) |param, i| {
            if (i > 0) try self.output.appendSlice(self.allocator, ", ");
            const param_type = try types.convertType(param.type_name, self.allocator);
            defer self.allocator.free(param_type);
            try self.output.writer(self.allocator).print("{s}: {s}", .{ param.name, param_type });
        }
        try self.output.writer(self.allocator).print(") callconv(.C) {s};\n\n", .{return_type});
    }

    fn writeCTypeAlias(self: *CodeGen, alias: patterns.CTypeAlias) !void {
        if (alias.doc_comment) |doc| try self.writeDocComment(doc);
        const zig_name = naming.typeNameToZig(alias.name);
        try self.output.writer(self.allocator).print("pub const {s} = c.{s};\n\n", .{ zig_name, alias.name });
    }

    fn enumShouldBeFlags(self: *CodeGen, enum_decl: EnumDecl) bool {
        _ = self;
        for (enum_decl.values) |value| {
            if (value.value) |val| {
                if (std.mem.indexOf(u8, val, "|") != null) return true;
            }
        }
        return false;
    }

    fn convertEnumToFlags(self: *CodeGen, enum_decl: EnumDecl) !FlagDecl {
        var flags_list: std.ArrayList(patterns.FlagValue) = .empty;
        errdefer flags_list.deinit(self.allocator);
        var implicit_value: u32 = 0;

        for (enum_decl.values) |value| {
            const current_value: ?u32 = if (value.value) |val| blk: {
                const trimmed = std.mem.trim(u8, val, " \t");
                if (std.mem.indexOf(u8, trimmed, "|") != null) break :blk null;
                const parsed = std.fmt.parseInt(u32, trimmed, 0) catch break :blk null;
                implicit_value = parsed + 1;
                break :blk parsed;
            } else blk: {
                const val = implicit_value;
                implicit_value += 1;
                break :blk val;
            };

            if (current_value) |val| {
                if (val == 0) continue;
                if (val > 0 and (val & (val - 1)) == 0) {
                    try flags_list.append(self.allocator, .{
                        .name = try self.allocator.dupe(u8, value.name),
                        .value = try std.fmt.allocPrint(self.allocator, "(1u << {d})", .{@ctz(val)}),
                        .comment = if (value.comment) |c| try self.allocator.dupe(u8, c) else null,
                    });
                }
            }
        }

        return .{
            .name = try self.allocator.dupe(u8, enum_decl.name),
            .underlying_type = try self.allocator.dupe(u8, "Uint32"),
            .flags = try flags_list.toOwnedSlice(self.allocator),
            .constants = &.{},
            .doc_comment = if (enum_decl.doc_comment) |doc| try self.allocator.dupe(u8, doc) else null,
        };
    }

    fn writeEnum(self: *CodeGen, enum_decl: EnumDecl) !void {
        if (enum_decl.values.len == 0) return;
        if (self.enumShouldBeFlags(enum_decl)) {
            const flag_decl = try self.convertEnumToFlags(enum_decl);
            defer flag_decl.deinit(self.allocator);
            return self.writeFlags(flag_decl);
        }

        const zig_name = naming.typeNameToZig(enum_decl.name);
        if (enum_decl.doc_comment) |doc| try self.writeDocComment(doc);
        try self.output.writer(self.allocator).print("pub const {s} = enum(c_int) {{\n", .{zig_name});

        const value_names = try self.allocator.alloc([]const u8, enum_decl.values.len);
        defer self.allocator.free(value_names);
        for (enum_decl.values, 0..) |value, i| value_names[i] = value.name;
        const prefix = try naming.detectCommonPrefix(value_names, self.allocator);
        defer self.allocator.free(prefix);

        var identifier_to_value = std.StringHashMap([]const u8).init(self.allocator);
        defer identifier_to_value.deinit();
        var value_to_name = std.StringHashMap([]const u8).init(self.allocator);
        defer value_to_name.deinit();

        for (enum_decl.values) |value| {
            if (value.value) |explicit_value| {
                const clean_value = if (std.mem.endsWith(u8, explicit_value, "u")) explicit_value[0 .. explicit_value.len - 1] else explicit_value;
                try identifier_to_value.put(value.name, clean_value);
            }
        }

        const resolved_values = try self.allocator.alloc(?[]const u8, enum_decl.values.len);
        defer self.allocator.free(resolved_values);
        for (enum_decl.values, 0..) |value, i| {
            if (value.value) |explicit_value| {
                const clean_value = if (std.mem.endsWith(u8, explicit_value, "u")) explicit_value[0 .. explicit_value.len - 1] else explicit_value;
                if (clean_value.len > 0 and !std.ascii.isDigit(clean_value[0])) {
                    resolved_values[i] = identifier_to_value.get(clean_value) orelse clean_value;
                } else {
                    resolved_values[i] = clean_value;
                }
            } else {
                resolved_values[i] = null;
            }
        }

        const EnumAlias = struct { name: []const u8, target: []const u8, comment: ?[]const u8 };
        var aliases: std.ArrayList(EnumAlias) = .empty;
        defer aliases.deinit(self.allocator);

        for (enum_decl.values, 0..) |value, i| {
            const zig_value = try naming.enumValueToZig(value.name, prefix, self.allocator);
            defer self.allocator.free(zig_value);

            if (resolved_values[i]) |numeric_value| {
                if (value_to_name.get(numeric_value)) |first_name| {
                    try aliases.append(self.allocator, .{
                        .name = try self.allocator.dupe(u8, zig_value),
                        .target = try naming.enumValueToZig(first_name, prefix, self.allocator),
                        .comment = if (value.comment) |c| try self.allocator.dupe(u8, c) else null,
                    });
                } else {
                    try value_to_name.put(numeric_value, value.name);
                    if (value.comment) |comment| {
                        try self.output.writer(self.allocator).print("    {s} = {s}, //{s}\n", .{ zig_value, numeric_value, comment });
                    } else {
                        try self.output.writer(self.allocator).print("    {s} = {s},\n", .{ zig_value, numeric_value });
                    }
                }
            } else if (value.comment) |comment| {
                try self.output.writer(self.allocator).print("    {s}, //{s}\n", .{ zig_value, comment });
            } else {
                try self.output.writer(self.allocator).print("    {s},\n", .{zig_value});
            }
        }

        if (aliases.items.len > 0) {
            try self.output.appendSlice(self.allocator, "\n");
            for (aliases.items) |alias_decl| {
                if (alias_decl.comment) |comment| {
                    try self.output.writer(self.allocator).print("    pub const {s} = .{s}; //{s}\n", .{ alias_decl.name, alias_decl.target, comment });
                } else {
                    try self.output.writer(self.allocator).print("    pub const {s} = .{s};\n", .{ alias_decl.name, alias_decl.target });
                }
                self.allocator.free(alias_decl.name);
                self.allocator.free(alias_decl.target);
                if (alias_decl.comment) |comment| self.allocator.free(comment);
            }
        }

        try self.output.appendSlice(self.allocator, "};\n\n");
    }

    fn writeStruct(self: *CodeGen, struct_decl: StructDecl) !void {
        const zig_name = naming.typeNameToZig(struct_decl.name);
        if (struct_decl.doc_comment) |doc| try self.writeDocComment(doc);

        if (struct_decl.has_unions) {
            try self.output.writer(self.allocator).print("pub const {s} = opaque {{}};\n\n", .{zig_name});
            return;
        }

        try self.output.writer(self.allocator).print("pub const {s} = extern struct {{\n", .{zig_name});
        for (struct_decl.fields) |field| {
            const zig_type = try self.convertAggregateFieldType(field.type_name);
            defer self.allocator.free(zig_type);
            if (field.comment) |comment| {
                try self.output.writer(self.allocator).print("    {s}: {s}, // {s}\n", .{ field.name, zig_type, comment });
            } else {
                try self.output.writer(self.allocator).print("    {s}: {s},\n", .{ field.name, zig_type });
            }
        }
        try self.output.appendSlice(self.allocator, "};\n\n");
    }

    fn writeUnion(self: *CodeGen, union_decl: patterns.UnionDecl) !void {
        const zig_name = naming.typeNameToZig(union_decl.name);
        if (union_decl.doc_comment) |doc| try self.writeDocComment(doc);
        try self.output.writer(self.allocator).print("pub const {s} = extern union {{\n", .{zig_name});
        for (union_decl.fields) |field| {
            const zig_type = try self.convertAggregateFieldType(field.type_name);
            defer self.allocator.free(zig_type);
            if (field.comment) |comment| {
                try self.output.writer(self.allocator).print("    {s}: {s}, // {s}\n", .{ field.name, zig_type, comment });
            } else {
                try self.output.writer(self.allocator).print("    {s}: {s},\n", .{ field.name, zig_type });
            }
        }
        try self.output.appendSlice(self.allocator, "};\n\n");
    }

    fn writeFlags(self: *CodeGen, flag_decl: FlagDecl) !void {
        const zig_name = naming.typeNameToZig(flag_decl.name);
        if (flag_decl.doc_comment) |doc| try self.writeDocComment(doc);

        const underlying_type = if (std.mem.eql(u8, flag_decl.underlying_type, "Uint8"))
            "u8"
        else if (std.mem.eql(u8, flag_decl.underlying_type, "Uint16"))
            "u16"
        else if (std.mem.eql(u8, flag_decl.underlying_type, "Uint64"))
            "u64"
        else
            "u32";

        const type_bits: u32 = if (std.mem.eql(u8, underlying_type, "u8"))
            8
        else if (std.mem.eql(u8, underlying_type, "u16"))
            16
        else if (std.mem.eql(u8, underlying_type, "u64"))
            64
        else
            32;

        try self.output.writer(self.allocator).print("pub const {s} = packed struct({s}) {{\n", .{ zig_name, underlying_type });

        const flag_names = try self.allocator.alloc([]const u8, flag_decl.flags.len);
        defer self.allocator.free(flag_names);
        for (flag_decl.flags, 0..) |flag, i| flag_names[i] = flag.name;
        const prefix = try naming.detectCommonPrefix(flag_names, self.allocator);
        defer self.allocator.free(prefix);

        var used_bits = std.bit_set.IntegerBitSet(64).initEmpty();
        for (flag_decl.flags) |flag| {
            const zig_flag = try naming.flagNameToZig(flag.name, prefix, self.allocator);
            defer self.allocator.free(zig_flag);
            const bit_pos = self.parseBitPosition(flag.value) catch continue;
            used_bits.set(bit_pos);
            if (flag.comment) |comment| {
                try self.output.writer(self.allocator).print("    {s}: bool = false, // {s}\n", .{ zig_flag, comment });
            } else {
                try self.output.writer(self.allocator).print("    {s}: bool = false,\n", .{zig_flag});
            }
        }

        const padding_bits = type_bits - used_bits.count() - 1;
        if (padding_bits > 0) {
            try self.output.writer(self.allocator).print("    pad0: u{d} = 0,\n", .{padding_bits});
        }
        try self.output.appendSlice(self.allocator, "    rsvd: bool = false,\n\n");
        try self.output.writer(self.allocator).print("    pub const None = {s}{{}};\n", .{zig_name});

        for (flag_decl.constants) |constant| {
            const zig_const_camel = try naming.flagNameToZig(constant.name, prefix, self.allocator);
            defer self.allocator.free(zig_const_camel);
            const zig_const = try self.allocator.dupe(u8, zig_const_camel);
            defer self.allocator.free(zig_const);
            if (zig_const.len > 0) zig_const[0] = std.ascii.toUpper(zig_const[0]);

            if (constant.comment) |comment| {
                try self.output.writer(self.allocator).print("    pub const {s}: {s} = @bitCast(@as({s}, {s})); // {s}\n", .{ zig_const, zig_name, underlying_type, constant.value, comment });
            } else {
                try self.output.writer(self.allocator).print("    pub const {s}: {s} = @bitCast(@as({s}, {s}));\n", .{ zig_const, zig_name, underlying_type, constant.value });
            }
        }

        try self.output.appendSlice(self.allocator, "};\n\n");
    }

    fn writeFunctionAsMethod(self: *CodeGen, func: patterns.FunctionDecl, owner_type: []const u8) !void {
        const zig_name = try naming.functionNameToZig(func.name, self.allocator);
        defer self.allocator.free(zig_name);
        if (func.doc_comment) |doc| try self.writeDocComment(doc);

        const zig_return_type = try types.convertType(func.return_type, self.allocator);
        defer self.allocator.free(zig_return_type);

        try self.output.writer(self.allocator).print("    pub inline fn {s}(", .{zig_name});
        for (func.params, 0..) |param, i| {
            const zig_type = try self.convertFunctionParamType(func, param);
            defer self.allocator.free(zig_type);
            if (i > 0) try self.output.appendSlice(self.allocator, ", ");

            if (i == 0) {
                const lower_name = try std.ascii.allocLowerString(self.allocator, owner_type);
                defer self.allocator.free(lower_name);
                const non_nullable = if (std.mem.startsWith(u8, zig_type, "?*")) zig_type[1..] else zig_type;
                try self.output.writer(self.allocator).print("{s}: {s}", .{ lower_name, non_nullable });
            } else if (param.name.len > 0) {
                try self.output.writer(self.allocator).print("{s}: {s}", .{ param.name, zig_type });
            } else {
                try self.output.writer(self.allocator).print("{s}", .{zig_type});
            }
        }
        try self.output.writer(self.allocator).print(") {s} {{\n", .{zig_return_type});
        try self.output.appendSlice(self.allocator, "        return ");

        const return_cast = if (!std.mem.eql(u8, zig_return_type, "void")) types.getReturnCastType(zig_return_type) else .none;
        if (return_cast != .none) {
            try self.output.writer(self.allocator).print("{s}(", .{castTypeToString(return_cast)});
        }

        try self.output.writer(self.allocator).print("c.{s}(", .{func.name});
        for (func.params, 0..) |param, i| {
            if (i > 0) try self.output.appendSlice(self.allocator, ", ");
            if (param.name.len > 0 or i == 0) {
                const param_name = if (i == 0) blk: {
                    const lower = try std.ascii.allocLowerString(self.allocator, owner_type);
                    defer self.allocator.free(lower);
                    break :blk try self.allocator.dupe(u8, lower);
                } else try self.allocator.dupe(u8, param.name);
                defer self.allocator.free(param_name);

                const zig_param_type = try self.convertFunctionParamType(func, param);
                defer self.allocator.free(zig_param_type);
                const param_cast = self.getFunctionParamCastType(param, zig_param_type);

                if (param_cast == .none) {
                    try self.output.writer(self.allocator).print("{s}", .{param_name});
                } else {
                    try self.output.writer(self.allocator).print("{s}({s})", .{ castTypeToString(param_cast), param_name });
                }
            }
        }

        if (return_cast != .none) {
            try self.output.appendSlice(self.allocator, "));\n");
        } else {
            try self.output.appendSlice(self.allocator, ");\n");
        }
        try self.output.appendSlice(self.allocator, "    }\n\n");
    }

    fn writeFunction(self: *CodeGen, func: patterns.FunctionDecl) !void {
        const zig_name = try naming.functionNameToZig(func.name, self.allocator);
        defer self.allocator.free(zig_name);
        if (func.doc_comment) |doc| try self.writeDocComment(doc);

        const zig_return_type = try types.convertType(func.return_type, self.allocator);
        defer self.allocator.free(zig_return_type);
        try self.output.writer(self.allocator).print("pub inline fn {s}(", .{zig_name});

        for (func.params, 0..) |param, i| {
            const zig_type = try self.convertFunctionParamType(func, param);
            defer self.allocator.free(zig_type);
            if (i > 0) try self.output.appendSlice(self.allocator, ", ");
            if (param.name.len > 0) {
                try self.output.writer(self.allocator).print("{s}: {s}", .{ param.name, zig_type });
            } else {
                try self.output.writer(self.allocator).print("{s}", .{zig_type});
            }
        }
        try self.output.writer(self.allocator).print(") {s} {{\n", .{zig_return_type});
        try self.output.appendSlice(self.allocator, "    return ");

        const return_cast = if (!std.mem.eql(u8, zig_return_type, "void")) types.getReturnCastType(zig_return_type) else .none;
        if (return_cast != .none) {
            try self.output.writer(self.allocator).print("{s}(", .{castTypeToString(return_cast)});
        }

        try self.output.writer(self.allocator).print("c.{s}(", .{func.name});
        for (func.params, 0..) |param, i| {
            if (i > 0) try self.output.appendSlice(self.allocator, ", ");
            if (param.name.len > 0) {
                const zig_param_type = try self.convertFunctionParamType(func, param);
                defer self.allocator.free(zig_param_type);
                const param_cast = self.getFunctionParamCastType(param, zig_param_type);

                if (param_cast == .none) {
                    try self.output.writer(self.allocator).print("{s}", .{param.name});
                } else {
                    try self.output.writer(self.allocator).print("{s}({s})", .{ castTypeToString(param_cast), param.name });
                }
            }
        }

        if (return_cast != .none) {
            try self.output.appendSlice(self.allocator, "));\n");
        } else {
            try self.output.appendSlice(self.allocator, ");\n");
        }
        try self.output.appendSlice(self.allocator, "}\n\n");
    }

    fn convertAggregateFieldType(self: *CodeGen, c_type: []const u8) ![]const u8 {
        if (self.isOpaqueFieldPointerType(c_type)) {
            return try types.convertType(c_type, self.allocator);
        }
        return try types.convertStructFieldType(c_type, self.allocator);
    }

    fn convertFunctionParamType(self: *CodeGen, func: patterns.FunctionDecl, param: patterns.ParamDecl) ![]const u8 {
        const zig_type = try types.convertType(param.type_name, self.allocator);
        errdefer self.allocator.free(zig_type);

        if (std.mem.startsWith(u8, zig_type, "?*") or std.mem.startsWith(u8, zig_type, "[*c]")) {
            return zig_type;
        }

        const should_make_nullable =
            self.paramMayBeNull(func, param.name) or
            (std.mem.startsWith(u8, zig_type, "*") and !std.mem.startsWith(u8, zig_type, "*const "));

        if (should_make_nullable and std.mem.startsWith(u8, zig_type, "*")) {
            const nullable = try std.fmt.allocPrint(self.allocator, "?{s}", .{zig_type});
            self.allocator.free(zig_type);
            return nullable;
        }

        return zig_type;
    }

    fn getFunctionParamCastType(self: *CodeGen, param: patterns.ParamDecl, zig_param_type: []const u8) types.CastType {
        if (self.isSDLPointerArrayParam(param.type_name)) {
            return .ptr_cast;
        }
        return types.getParamCastType(zig_param_type);
    }

    fn paramMayBeNull(self: *CodeGen, func: patterns.FunctionDecl, param_name: []const u8) bool {
        _ = self;
        if (param_name.len == 0) return false;
        const doc = func.doc_comment orelse return false;

        const marker = std.fmt.allocPrint(std.heap.smp_allocator, "\\param {s}", .{param_name}) catch return false;
        defer std.heap.smp_allocator.free(marker);

        const start = std.mem.indexOf(u8, doc, marker) orelse return false;
        const tail = doc[start + marker.len ..];
        const next_param = std.mem.indexOf(u8, tail, "\\param ") orelse tail.len;
        const next_returns = std.mem.indexOf(u8, tail, "\\returns") orelse tail.len;
        const end = @min(next_param, next_returns);
        const param_doc = tail[0..end];

        return std.mem.indexOf(u8, param_doc, "may be NULL") != null or
            std.mem.indexOf(u8, param_doc, "or NULL") != null;
    }

    fn isOpaqueFieldPointerType(self: *CodeGen, c_type: []const u8) bool {
        const trimmed = std.mem.trim(u8, c_type, " \t");
        if (std.mem.indexOf(u8, trimmed, "(SDLCALL *") != null or std.mem.indexOf(u8, trimmed, "(*") != null) {
            return false;
        }
        if (std.mem.indexOfScalar(u8, trimmed, '*') == null) {
            return false;
        }

        var rest = trimmed;
        if (std.mem.startsWith(u8, rest, "const ")) {
            rest = std.mem.trim(u8, rest[6..], " \t");
        }

        const first_star = std.mem.indexOfScalar(u8, rest, '*') orelse return false;
        const base_type = std.mem.trim(u8, rest[0..first_star], " \t");
        if (!std.mem.startsWith(u8, base_type, "SDL_")) {
            return false;
        }

        const zig_name = naming.typeNameToZig(base_type);
        if (self.opaque_methods.contains(zig_name)) {
            return true;
        }

        for (self.decls) |resolved| {
            if (resolved.decl != .opaque_type) continue;
            if (std.mem.eql(u8, resolved.decl.opaque_type.name, base_type)) {
                return true;
            }
            if (std.mem.eql(u8, naming.typeNameToZig(resolved.decl.opaque_type.name), zig_name)) {
                return true;
            }
        }

        return false;
    }

    fn isSDLPointerArrayParam(self: *CodeGen, c_type: []const u8) bool {
        _ = self;
        const trimmed = std.mem.trim(u8, c_type, " \t");
        if (std.mem.indexOf(u8, trimmed, "(SDLCALL *") != null or std.mem.indexOf(u8, trimmed, "(*") != null) {
            return false;
        }
        if (std.mem.count(u8, trimmed, "*") < 2) {
            return false;
        }

        var rest = trimmed;
        if (std.mem.startsWith(u8, rest, "const ")) {
            rest = std.mem.trim(u8, rest[6..], " \t");
        }

        const first_star = std.mem.indexOfScalar(u8, rest, '*') orelse return false;
        const base_type = std.mem.trim(u8, rest[0..first_star], " \t");
        return std.mem.startsWith(u8, base_type, "SDL_");
    }

    fn castTypeToString(cast_type: types.CastType) []const u8 {
        return switch (cast_type) {
            .none => "none",
            .ptr_cast => "@ptrCast",
            .bit_cast => "@bitCast",
            .int_from_enum => "@intFromEnum",
            .enum_from_int => "@enumFromInt",
        };
    }

    fn writeDocComment(self: *CodeGen, comment: []const u8) !void {
        _ = self;
        _ = comment;
    }

    fn parseBitPosition(self: *CodeGen, value: []const u8) !u6 {
        _ = self;
        var trimmed = std.mem.trim(u8, value, " \t()");

        if (std.mem.startsWith(u8, trimmed, "SDL_UINT64_C(")) {
            trimmed = std.mem.trim(u8, trimmed["SDL_UINT64_C(".len..], " \t)");
        }
        if (trimmed.len > 0 and (trimmed[trimmed.len - 1] == 'u' or trimmed[trimmed.len - 1] == 'U')) {
            trimmed = trimmed[0 .. trimmed.len - 1];
        }
        if (std.mem.indexOf(u8, trimmed, "<<")) |shift_pos| {
            const after_shift = std.mem.trim(u8, trimmed[shift_pos + 2 ..], " \t)");
            return try std.fmt.parseInt(u6, after_shift, 10);
        }
        if (std.mem.startsWith(u8, trimmed, "0x")) {
            const val = try std.fmt.parseInt(u64, trimmed[2..], 16);
            var bit: u7 = 0;
            while (bit < 64) : (bit += 1) {
                if (val == (@as(u64, 1) << @as(u6, @intCast(bit)))) return @intCast(bit);
            }
        }
        if (std.fmt.parseInt(u64, trimmed, 10)) |val| {
            if (val == 0) return error.InvalidBitPosition;
            var bit: u7 = 0;
            while (bit < 64) : (bit += 1) {
                if (val == (@as(u64, 1) << @as(u6, @intCast(bit)))) return @intCast(bit);
            }
            return error.InvalidBitPosition;
        } else |_| {}

        return error.InvalidBitPosition;
    }
};

test "generated module aliases foreign shared types" {
    const allocator = std.testing.allocator;

    var decls: std.ArrayList(ResolvedDecl) = .empty;
    defer {
        for (decls.items) |decl| decl.deinit(allocator);
        decls.deinit(allocator);
    }

    const method_params = try allocator.alloc(patterns.ParamDecl, 2);
    method_params[0] = .{ .name = try allocator.dupe(u8, "device"), .type_name = try allocator.dupe(u8, "SDL_GPUDevice *") };
    method_params[1] = .{ .name = try allocator.dupe(u8, "window"), .type_name = try allocator.dupe(u8, "SDL_Window *") };

    try decls.append(allocator, .{
        .decl = .{ .opaque_type = .{ .name = try allocator.dupe(u8, "SDL_GPUDevice"), .doc_comment = null } },
        .source_header = try allocator.dupe(u8, "SDL_gpu.h"),
        .is_primary_header_decl = true,
    });
    try decls.append(allocator, .{
        .decl = .{ .function_decl = .{
            .name = try allocator.dupe(u8, "SDL_WaitForWindow"),
            .return_type = try allocator.dupe(u8, "void"),
            .params = method_params,
            .doc_comment = null,
        } },
        .source_header = try allocator.dupe(u8, "SDL_gpu.h"),
        .is_primary_header_decl = true,
    });
    try decls.append(allocator, .{
        .decl = .{ .opaque_type = .{ .name = try allocator.dupe(u8, "SDL_Window"), .doc_comment = null } },
        .source_header = try allocator.dupe(u8, "SDL_video.h"),
        .is_primary_header_decl = false,
    });

    const output = try CodeGen.generate(allocator, .{
        .decls = decls.items,
        .module_name = "gpu",
        .c_import_path = "../c.zig",
    });
    defer allocator.free(output);

    try std.testing.expect(std.mem.indexOf(u8, output, "const video_api = @import(\"video.zig\");") != null);
    try std.testing.expect(std.mem.indexOf(u8, output, "pub const Window = video_api.Window;") != null);
    try std.testing.expect(std.mem.indexOf(u8, output, "pub const c = @import(\"../c.zig\").c;") != null);
    try std.testing.expect(std.mem.indexOf(u8, output, "pub const Window = opaque") == null);
}

test "primary declarations are emitted without self imports" {
    const allocator = std.testing.allocator;

    var decls: std.ArrayList(ResolvedDecl) = .empty;
    defer {
        for (decls.items) |decl| decl.deinit(allocator);
        decls.deinit(allocator);
    }

    try decls.append(allocator, .{
        .decl = .{ .opaque_type = .{ .name = try allocator.dupe(u8, "SDL_Window"), .doc_comment = null } },
        .source_header = try allocator.dupe(u8, "SDL_video.h"),
        .is_primary_header_decl = true,
    });

    const output = try CodeGen.generate(allocator, .{
        .decls = decls.items,
        .module_name = "video",
    });
    defer allocator.free(output);

    try std.testing.expect(std.mem.indexOf(u8, output, "const video_api = @import(\"video.zig\");") == null);
    try std.testing.expect(std.mem.indexOf(u8, output, "pub const Window = opaque") != null);
}

test "function params make plain out pointers nullable" {
    const allocator = std.testing.allocator;
    var gen = CodeGen{
        .decls = &.{},
        .module_name = "gpu",
        .c_import_path = "c.zig",
        .skipped = &.{},
        .allocator = allocator,
        .output = .empty,
        .opaque_methods = std.StringHashMap(std.ArrayList(patterns.FunctionDecl)).init(allocator),
        .import_modules = .empty,
        .aliases = .empty,
    };
    defer gen.deinit();

    var params = [_]patterns.ParamDecl{
        .{ .name = "swapchain_texture_width", .type_name = "Uint32 *" },
    };
    const func = patterns.FunctionDecl{
        .name = "SDL_WaitAndAcquireGPUSwapchainTexture",
        .return_type = "bool",
        .params = params[0..],
        .doc_comment = null,
    };

    const zig_type = try gen.convertFunctionParamType(func, params[0]);
    defer allocator.free(zig_type);
    try std.testing.expectEqualStrings("?*u32", zig_type);
}

test "opaque methods cast enum params to C ABI" {
    const allocator = std.testing.allocator;

    var decls: std.ArrayList(ResolvedDecl) = .empty;
    defer {
        for (decls.items) |decl| decl.deinit(allocator);
        decls.deinit(allocator);
    }

    try decls.append(allocator, .{
        .decl = .{ .opaque_type = .{ .name = try allocator.dupe(u8, "SDL_GPURenderPass"), .doc_comment = null } },
        .source_header = try allocator.dupe(u8, "SDL_gpu.h"),
        .is_primary_header_decl = true,
    });
    try decls.append(allocator, .{
        .decl = .{ .struct_decl = .{
            .name = try allocator.dupe(u8, "SDL_GPUBufferBinding"),
            .fields = &.{},
            .doc_comment = null,
            .has_unions = false,
        } },
        .source_header = try allocator.dupe(u8, "SDL_gpu.h"),
        .is_primary_header_decl = true,
    });
    const enum_values = try allocator.alloc(patterns.EnumValue, 1);
    enum_values[0] = .{ .name = try allocator.dupe(u8, "SDL_GPU_INDEXELEMENTSIZE_16BIT"), .value = null, .comment = null };
    try decls.append(allocator, .{
        .decl = .{ .enum_decl = .{
            .name = try allocator.dupe(u8, "SDL_GPUIndexElementSize"),
            .values = enum_values,
            .doc_comment = null,
        } },
        .source_header = try allocator.dupe(u8, "SDL_gpu.h"),
        .is_primary_header_decl = true,
    });
    const func_params = try allocator.alloc(patterns.ParamDecl, 3);
    func_params[0] = .{ .name = try allocator.dupe(u8, "render_pass"), .type_name = try allocator.dupe(u8, "SDL_GPURenderPass *") };
    func_params[1] = .{ .name = try allocator.dupe(u8, "binding"), .type_name = try allocator.dupe(u8, "const SDL_GPUBufferBinding *") };
    func_params[2] = .{ .name = try allocator.dupe(u8, "index_element_size"), .type_name = try allocator.dupe(u8, "SDL_GPUIndexElementSize") };
    try decls.append(allocator, .{
        .decl = .{ .function_decl = .{
            .name = try allocator.dupe(u8, "SDL_BindGPUIndexBuffer"),
            .return_type = try allocator.dupe(u8, "void"),
            .params = func_params,
            .doc_comment = null,
        } },
        .source_header = try allocator.dupe(u8, "SDL_gpu.h"),
        .is_primary_header_decl = true,
    });

    const output = try CodeGen.generate(allocator, .{
        .decls = decls.items,
        .module_name = "gpu",
        .c_import_path = "../c.zig",
    });
    defer allocator.free(output);

    try std.testing.expect(std.mem.indexOf(u8, output, "@intFromEnum(index_element_size)") != null);
}