const std = @import("std");
const smithy = @import("smithy");
const snake = @import("snake.zig");
const Hasher = @import("Hasher.zig");
const json_zig = @embedFile("json.zig");

var verbose = false;

pub fn main() anyerror!void {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer arena.deinit();
    const allocator = arena.allocator();

    const args = try std.process.argsAlloc(allocator);
    defer std.process.argsFree(allocator, args);
    const stdout = std.io.getStdOut().writer();

    var output_dir = std.fs.cwd();
    defer if (output_dir.fd > 0) output_dir.close();
    var models_dir: ?std.fs.IterableDir = null;
    defer if (models_dir) |*m| m.close();
    for (args, 0..) |arg, i| {
        if (std.mem.eql(u8, "--help", arg) or
            std.mem.eql(u8, "-h", arg))
        {
            try stdout.print("usage: {s} [--verbose] [--models dir] [--output dir] [file...]\n\n", .{args[0]});
            try stdout.print(" --models specifies a directory with all model files (do not specify files if --models is used)\n", .{});
            try stdout.print(" --output specifies an output directory, otherwise the current working directory will be used\n", .{});
            std.process.exit(0);
        }
        if (std.mem.eql(u8, "--output", arg))
            output_dir = try output_dir.makeOpenPath(args[i + 1], .{});
        if (std.mem.eql(u8, "--models", arg))
            models_dir = try std.fs.cwd().openIterableDir(args[i + 1], .{});
    }
    // TODO: Seems like we should remove this in favor of a package
    try output_dir.writeFile("json.zig", json_zig);

    // TODO: We need a different way to handle this file...
    var manifest_file_started = false;
    var manifest_file: std.fs.File = undefined;
    defer if (manifest_file_started) manifest_file.close();
    var manifest: std.fs.File.Writer = undefined;
    var files_processed: usize = 0;
    var skip_next = true;
    for (args) |arg| {
        if (skip_next) {
            skip_next = false;
            continue;
        }
        if (std.mem.eql(u8, "--verbose", arg)) {
            verbose = true;
            continue;
        }

        if (std.mem.eql(u8, "--models", arg) or
            std.mem.eql(u8, "--output", arg))
        {
            skip_next = true;
            continue;
        }
        if (!manifest_file_started) {
            manifest_file = try output_dir.createFile("service_manifest.zig", .{});
            manifest = manifest_file.writer();
        }
        try processFile(arg, stdout, output_dir, manifest);
        files_processed += 1;
    }
    if (files_processed == 0) {
        // no files specified, look for json files in models directory or cwd
        // this is our normal mode of operation and where initial optimizations
        // can be made
        if (models_dir) |m| {
            var cwd = try std.fs.cwd().openDir(".", .{});
            defer cwd.close();
            defer cwd.setAsCwd() catch unreachable;

            try m.dir.setAsCwd();
            try processDirectories(m, output_dir, stdout);
        }
    }

    if (args.len == 0)
        _ = try generateServices(allocator, ";", std.io.getStdIn(), stdout);
}
const OutputManifest = struct {
    model_dir_hash_digest: [Hasher.hex_multihash_len]u8,
    output_dir_hash_digest: [Hasher.hex_multihash_len]u8,
};
fn processDirectories(models_dir: std.fs.IterableDir, output_dir: std.fs.Dir, stdout: anytype) !void {
    // Let's get ready to hash!!
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer arena.deinit();
    const allocator = arena.allocator();
    var thread_pool: std.Thread.Pool = undefined;
    try thread_pool.init(.{ .allocator = allocator });
    defer thread_pool.deinit();
    var calculated_manifest = try calculateDigests(models_dir, output_dir, &thread_pool);
    const output_stored_manifest = output_dir.readFileAlloc(allocator, "output_manifest.json", std.math.maxInt(usize)) catch null;
    if (output_stored_manifest) |o| {
        // we have a stored manifest. Parse it and compare to our calculations
        // we can leak as we're using an arena allocator
        const stored_manifest = try std.json.parseFromSliceLeaky(OutputManifest, allocator, o, .{});
        if (std.mem.eql(u8, &stored_manifest.model_dir_hash_digest, &calculated_manifest.model_dir_hash_digest) and
            std.mem.eql(u8, &stored_manifest.output_dir_hash_digest, &calculated_manifest.output_dir_hash_digest))
        {
            // hashes all match, we can end now
            if (verbose)
                std.log.info("calculated hashes match output_manifest.json. Nothing to do", .{});
            return;
        }
    }
    // Do this in a brain dead fashion from here, no optimization
    const manifest_file = try output_dir.createFile("service_manifest.zig", .{});
    defer manifest_file.close();
    const manifest = manifest_file.writer();
    var mi = models_dir.iterate();
    while (try mi.next()) |e| {
        if ((e.kind == .file or e.kind == .sym_link) and
            std.mem.endsWith(u8, e.name, ".json"))
            try processFile(e.name, stdout, output_dir, manifest);
    }
    // re-calculate so we can store the manifest
    model_digest = calculated_manifest.model_dir_hash_digest;
    calculated_manifest = try calculateDigests(models_dir, output_dir, &thread_pool);
    try output_dir.writeFile("output_manifest.json", try std.json.stringifyAlloc(
        allocator,
        calculated_manifest,
        .{ .whitespace = .indent_2 },
    ));
}

var model_digest: ?[Hasher.hex_multihash_len]u8 = null;
fn calculateDigests(models_dir: std.fs.IterableDir, output_dir: std.fs.Dir, thread_pool: *std.Thread.Pool) !OutputManifest {
    const model_hash = if (model_digest) |m| m[0..Hasher.digest_len].* else try Hasher.computeDirectoryHash(thread_pool, models_dir, @constCast(&Hasher.ComputeDirectoryOptions{
        .isIncluded = struct {
            pub fn include(entry: std.fs.IterableDir.Walker.WalkerEntry) bool {
                return std.mem.endsWith(u8, entry.basename, ".json");
            }
        }.include,
        .isExcluded = struct {
            pub fn exclude(entry: std.fs.IterableDir.Walker.WalkerEntry) bool {
                _ = entry;
                return false;
            }
        }.exclude,
        .needFileHashes = false,
    }));
    if (verbose) std.log.info("Model directory hash: {s}", .{model_digest orelse Hasher.hexDigest(model_hash)});

    const output_hash = try Hasher.computeDirectoryHash(thread_pool, try output_dir.openIterableDir(".", .{}), @constCast(&Hasher.ComputeDirectoryOptions{
        .isIncluded = struct {
            pub fn include(entry: std.fs.IterableDir.Walker.WalkerEntry) bool {
                return std.mem.endsWith(u8, entry.basename, ".zig");
            }
        }.include,
        .isExcluded = struct {
            pub fn exclude(entry: std.fs.IterableDir.Walker.WalkerEntry) bool {
                _ = entry;
                return false;
            }
        }.exclude,
        .needFileHashes = false,
    }));
    if (verbose) std.log.info("Output directory hash: {s}", .{Hasher.hexDigest(output_hash)});
    return .{
        .model_dir_hash_digest = model_digest orelse Hasher.hexDigest(model_hash),
        .output_dir_hash_digest = Hasher.hexDigest(output_hash),
    };
}
fn processFile(file_name: []const u8, stdout: anytype, output_dir: std.fs.Dir, manifest: anytype) !void {
    // It's probably best to create our own allocator here so we can deint at the end and
    // toss all allocations related to the services in this file
    // I can't guarantee we're not leaking something, and at the end of the
    // day I'm not sure we want to track down leaks
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer arena.deinit();
    const allocator = arena.allocator();
    var writer = &stdout;
    var file: std.fs.File = undefined;
    const output_file_name = try std.fmt.allocPrint(allocator, "{s}.zig", .{file_name});
    defer allocator.free(output_file_name);
    file = try output_dir.createFile(output_file_name, .{ .truncate = true });
    errdefer file.close();
    writer = &file.writer();
    _ = try writer.write("const std = @import(\"std\");\n");
    _ = try writer.write("const serializeMap = @import(\"json.zig\").serializeMap;\n");
    _ = try writer.write("const smithy = @import(\"smithy\");\n\n");
    if (verbose) std.log.info("Processing file: {s}", .{file_name});
    const service_names = generateServicesForFilePath(allocator, ";", file_name, writer) catch |err| {
        std.log.err("Error processing file: {s}", .{file_name});
        return err;
    };
    defer {
        for (service_names) |name| allocator.free(name);
        allocator.free(service_names);
    }
    file.close();
    for (service_names) |name| {
        try manifest.print("pub const {s} = @import(\"{s}\");\n", .{ name, std.fs.path.basename(output_file_name) });
    }
}

fn generateServicesForFilePath(
    allocator: std.mem.Allocator,
    comptime terminator: []const u8,
    path: []const u8,
    writer: anytype,
) ![][]const u8 {
    const file = try std.fs.cwd().openFile(path, .{});
    defer file.close();
    return try generateServices(allocator, terminator, file, writer);
}

fn addReference(id: []const u8, map: *std.StringHashMap(u64)) !void {
    const res = try map.getOrPut(id);
    if (res.found_existing) {
        res.value_ptr.* += 1;
    } else {
        res.value_ptr.* = 1;
    }
}
fn countAllReferences(shape_ids: [][]const u8, shapes: std.StringHashMap(smithy.ShapeInfo), shape_references: *std.StringHashMap(u64), stack: *std.ArrayList([]const u8)) anyerror!void {
    for (shape_ids) |id| {
        try countReferences(shapes.get(id).?, shapes, shape_references, stack);
    }
}
fn countTypeMembersReferences(type_members: []smithy.TypeMember, shapes: std.StringHashMap(smithy.ShapeInfo), shape_references: *std.StringHashMap(u64), stack: *std.ArrayList([]const u8)) anyerror!void {
    for (type_members) |m| {
        try countReferences(shapes.get(m.target).?, shapes, shape_references, stack);
    }
}

fn countReferences(shape: smithy.ShapeInfo, shapes: std.StringHashMap(smithy.ShapeInfo), shape_references: *std.StringHashMap(u64), stack: *std.ArrayList([]const u8)) anyerror!void {
    // Add ourselves as a reference, then we will continue down the tree
    try addReference(shape.id, shape_references);
    // Put ourselves on the stack. If we come back to ourselves, we want to end.
    for (stack.items) |i| {
        if (std.mem.eql(u8, shape.id, i))
            return;
    }
    try stack.append(shape.id);
    defer _ = stack.pop();
    // Well, this is a fun read: https://awslabs.github.io/smithy/1.0/spec/core/model.html#recursive-shape-definitions
    // Looks like recursion has special rules in the spec to accomodate Java.
    // This is silly and we will ignore
    switch (shape.shape) {
        // We don't care about these primitives - they don't have children
        .blob,
        .boolean,
        .string,
        .byte,
        .short,
        .integer,
        .long,
        .float,
        .double,
        .bigInteger,
        .bigDecimal,
        .timestamp,
        => {},
        .document, .member, .resource => {}, // less sure about these?
        .list => |i| try countReferences(shapes.get(i.member_target).?, shapes, shape_references, stack),
        .set => |i| try countReferences(shapes.get(i.member_target).?, shapes, shape_references, stack),
        .map => |i| {
            try countReferences(shapes.get(i.key).?, shapes, shape_references, stack);
            try countReferences(shapes.get(i.value).?, shapes, shape_references, stack);
        },
        .structure => |m| try countTypeMembersReferences(m.members, shapes, shape_references, stack),
        .uniontype => |m| try countTypeMembersReferences(m.members, shapes, shape_references, stack),
        .service => |i| try countAllReferences(i.operations, shapes, shape_references, stack),
        .operation => |op| {
            if (op.input) |i| try countReferences(shapes.get(i).?, shapes, shape_references, stack);
            if (op.output) |i| try countReferences(shapes.get(i).?, shapes, shape_references, stack);
            if (op.errors) |i| try countAllReferences(i, shapes, shape_references, stack);
        },
    }
}

fn generateServices(allocator: std.mem.Allocator, comptime _: []const u8, file: std.fs.File, writer: anytype) ![][]const u8 {
    const json = try file.readToEndAlloc(allocator, 1024 * 1024 * 1024);
    defer allocator.free(json);
    const model = try smithy.parse(allocator, json);
    defer model.deinit();
    var shapes = std.StringHashMap(smithy.ShapeInfo).init(allocator);
    defer shapes.deinit();
    var services = std.ArrayList(smithy.ShapeInfo).init(allocator);
    defer services.deinit();
    for (model.shapes) |shape| {
        try shapes.put(shape.id, shape);
        switch (shape.shape) {
            .service => try services.append(shape),
            else => {},
        }
    }
    // At this point we want to generate a graph of shapes, starting
    // services -> operations -> other shapes. This will allow us to get
    // a reference count in case there are recursive data structures
    var shape_references = std.StringHashMap(u64).init(allocator);
    defer shape_references.deinit();
    var stack = std.ArrayList([]const u8).init(allocator);
    defer stack.deinit();
    for (services.items) |service|
        try countReferences(service, shapes, &shape_references, &stack);

    var constant_names = std.ArrayList([]const u8).init(allocator);
    defer constant_names.deinit();
    var unresolved = std.ArrayList(smithy.ShapeInfo).init(allocator);
    defer unresolved.deinit();
    var generated = std.StringHashMap(void).init(allocator);
    defer generated.deinit();

    var state = FileGenerationState{
        .shape_references = shape_references,
        .additional_types_to_generate = &unresolved,
        .additional_types_generated = &generated,
        .shapes = shapes,
    };
    for (services.items) |service| {
        var sdk_id: []const u8 = undefined;
        var version: []const u8 = service.shape.service.version;
        var name: []const u8 = service.name;
        var arn_namespace: []const u8 = undefined;
        var sigv4_name: []const u8 = undefined;
        var endpoint_prefix: []const u8 = undefined;
        var aws_protocol: smithy.AwsProtocol = undefined;
        for (service.shape.service.traits) |trait| {
            // need the info/get the info
            switch (trait) {
                .aws_api_service => {
                    arn_namespace = trait.aws_api_service.arn_namespace;
                    sdk_id = trait.aws_api_service.sdk_id;
                    endpoint_prefix = trait.aws_api_service.endpoint_prefix;
                },
                .aws_auth_sigv4 => sigv4_name = trait.aws_auth_sigv4.name,
                .aws_protocol => aws_protocol = trait.aws_protocol,
                else => {},
            }
        }

        // Service struct
        // name of the field will be snake_case of whatever comes in from
        // sdk_id. Not sure this will simple...
        const constant_name = try constantName(allocator, sdk_id);
        try constant_names.append(constant_name);
        try writer.print("const Self = @This();\n", .{});
        try writer.print("pub const version: []const u8 = \"{s}\";\n", .{version});
        try writer.print("pub const sdk_id: []const u8 = \"{s}\";\n", .{sdk_id});
        try writer.print("pub const arn_namespace: []const u8 = \"{s}\";\n", .{arn_namespace});
        try writer.print("pub const endpoint_prefix: []const u8 = \"{s}\";\n", .{endpoint_prefix});
        try writer.print("pub const sigv4_name: []const u8 = \"{s}\";\n", .{sigv4_name});
        try writer.print("pub const name: []const u8 = \"{s}\";\n", .{name});
        // TODO: This really should just be ".whatevs". We're fully qualifying here, which isn't typical
        try writer.print("pub const aws_protocol: smithy.AwsProtocol = {};\n\n", .{aws_protocol});
        _ = try writer.write("pub const service_metadata: struct {\n");
        try writer.print("    version: []const u8 = \"{s}\",\n", .{version});
        try writer.print("    sdk_id: []const u8 = \"{s}\",\n", .{sdk_id});
        try writer.print("    arn_namespace: []const u8 = \"{s}\",\n", .{arn_namespace});
        try writer.print("    endpoint_prefix: []const u8 = \"{s}\",\n", .{endpoint_prefix});
        try writer.print("    sigv4_name: []const u8 = \"{s}\",\n", .{sigv4_name});
        try writer.print("    name: []const u8 = \"{s}\",\n", .{name});
        // TODO: This really should just be ".whatevs". We're fully qualifying here, which isn't typical
        try writer.print("    aws_protocol: smithy.AwsProtocol = {},\n", .{aws_protocol});
        _ = try writer.write("} = .{};\n");

        // Operations
        for (service.shape.service.operations) |op|
            try generateOperation(allocator, shapes.get(op).?, state, writer);
    }
    try generateAdditionalTypes(allocator, state, writer);
    return constant_names.toOwnedSlice();
}

fn generateAdditionalTypes(allocator: std.mem.Allocator, file_state: FileGenerationState, writer: anytype) !void {
    // More types may be added during processing
    while (file_state.additional_types_to_generate.popOrNull()) |t| {
        if (file_state.additional_types_generated.getEntry(t.name) != null) continue;
        // std.log.info("\t\t{s}", .{t.name});
        var type_stack = std.ArrayList(*const smithy.ShapeInfo).init(allocator);
        defer type_stack.deinit();
        const state = GenerationState{
            .type_stack = &type_stack,
            .file_state = file_state,
            .allocator = allocator,
            .indent_level = 0,
        };
        const type_name = avoidReserved(t.name);
        try writer.print("\npub const {s} = ", .{type_name});
        try file_state.additional_types_generated.putNoClobber(t.name, {});
        _ = try generateTypeFor(t.id, writer, state, true);
        _ = try writer.write(";\n");
    }
}

fn constantName(allocator: std.mem.Allocator, id: []const u8) ![]const u8 {
    // There are some ids that don't follow consistent rules, so we'll
    // look for the exceptions and, if not found, revert to the snake case
    // algorithm

    // This one might be a bug in snake, but it's the only example so HPDL
    if (std.mem.eql(u8, id, "SESv2")) return try std.fmt.allocPrint(allocator, "ses_v2", .{});
    if (std.mem.eql(u8, id, "CloudFront")) return try std.fmt.allocPrint(allocator, "cloudfront", .{});
    // IoT is an acryonym, but snake wouldn't know that. Interestingly not all
    // iot services are capitalizing that way.
    if (std.mem.eql(u8, id, "IoTSiteWise")) return try std.fmt.allocPrint(allocator, "iot_sitewise", .{});
    if (std.mem.eql(u8, id, "IoTFleetHub")) return try std.fmt.allocPrint(allocator, "iot_fleet_hub", .{});
    if (std.mem.eql(u8, id, "IoTSecureTunneling")) return try std.fmt.allocPrint(allocator, "iot_secure_tunneling", .{});
    if (std.mem.eql(u8, id, "IoTThingsGraph")) return try std.fmt.allocPrint(allocator, "iot_things_graph", .{});
    // snake turns this into dev_ops, which is a little weird
    if (std.mem.eql(u8, id, "DevOps Guru")) return try std.fmt.allocPrint(allocator, "devops_guru", .{});
    if (std.mem.eql(u8, id, "FSx")) return try std.fmt.allocPrint(allocator, "fsx", .{});

    // Not a special case - just snake it
    return try snake.fromPascalCase(allocator, id);
}

const FileGenerationState = struct {
    shapes: std.StringHashMap(smithy.ShapeInfo),
    shape_references: std.StringHashMap(u64),
    additional_types_to_generate: *std.ArrayList(smithy.ShapeInfo),
    additional_types_generated: *std.StringHashMap(void),
};
const GenerationState = struct {
    type_stack: *std.ArrayList(*const smithy.ShapeInfo),
    file_state: FileGenerationState,
    // we will need some sort of "type decls needed" for recursive structures
    allocator: std.mem.Allocator,
    indent_level: u64,
};

fn outputIndent(state: GenerationState, writer: anytype) !void {
    const n_chars = 4 * state.indent_level;
    try writer.writeByteNTimes(' ', n_chars);
}
fn generateOperation(allocator: std.mem.Allocator, operation: smithy.ShapeInfo, file_state: FileGenerationState, writer: anytype) !void {
    const snake_case_name = try snake.fromPascalCase(allocator, operation.name);
    defer allocator.free(snake_case_name);

    var type_stack = std.ArrayList(*const smithy.ShapeInfo).init(allocator);
    defer type_stack.deinit();
    const state = GenerationState{
        .type_stack = &type_stack,
        .file_state = file_state,
        .allocator = allocator,
        .indent_level = 1,
    };
    var child_state = state;
    child_state.indent_level += 1;
    // indent should start at 4 spaces here
    const operation_name = avoidReserved(snake_case_name);
    try writer.print("pub const {s}: struct ", .{operation_name});
    _ = try writer.write("{\n");
    for (operation.shape.operation.traits) |trait| {
        if (trait == .http) {
            try outputIndent(state, writer);
            _ = try writer.write("pub const http_config = .{\n");
            try outputIndent(child_state, writer);
            try writer.print(".method = \"{s}\",\n", .{trait.http.method});
            try outputIndent(child_state, writer);
            try writer.print(".uri = \"{s}\",\n", .{trait.http.uri});
            try outputIndent(child_state, writer);
            try writer.print(".success_code = {d},\n", .{trait.http.code});
            try outputIndent(state, writer);
            _ = try writer.write("};\n\n");
        }
    }

    try outputIndent(state, writer);
    try writer.print("action_name: []const u8 = \"{s}\",\n", .{operation.name});
    try outputIndent(state, writer);
    _ = try writer.write("Request: type = ");
    if (operation.shape.operation.input) |member| {
        if (try generateTypeFor(member, writer, state, false)) unreachable; // we expect only structs here
        _ = try writer.write("\n");
        try generateMetadataFunction(operation_name, state, writer);
    } else {
        _ = try writer.write("struct {\n");
        try generateMetadataFunction(operation_name, state, writer);
    }
    _ = try writer.write(",\n");
    try outputIndent(state, writer);
    _ = try writer.write("Response: type = ");
    if (operation.shape.operation.output) |member| {
        if (try generateTypeFor(member, writer, state, true)) unreachable; // we expect only structs here
    } else _ = try writer.write("struct {}"); // we want to maintain consistency with other ops
    _ = try writer.write(",\n");

    if (operation.shape.operation.errors) |errors| {
        try outputIndent(state, writer);
        _ = try writer.write("ServiceError: type = error{\n");
        for (errors) |err| {
            const err_name = getErrorName(file_state.shapes.get(err).?.name); // need to remove "exception"
            try outputIndent(child_state, writer);
            try writer.print("{s},\n", .{err_name});
        }
        try outputIndent(state, writer);
        _ = try writer.write("},\n");
    }
    _ = try writer.write("} = .{};\n");
}

fn generateMetadataFunction(operation_name: []const u8, state: GenerationState, writer: anytype) !void {
    // TODO: Shove these lines in here, and also the else portion
    // pub fn metaInfo(self: @This()) struct { service: @TypeOf(sts), action: @TypeOf(sts.get_caller_identity) } {
    //     return .{ .service = sts, .action = sts.get_caller_identity };
    // }
    // We want to add a short "get my parents" function into the response
    var child_state = state;
    child_state.indent_level += 1;
    try outputIndent(child_state, writer);
    _ = try writer.write("pub fn metaInfo() struct { ");
    try writer.print("service_metadata: @TypeOf(service_metadata), action: @TypeOf({s})", .{operation_name});
    _ = try writer.write(" } {\n");
    child_state.indent_level += 1;
    try outputIndent(child_state, writer);
    _ = try writer.write("return .{ .service_metadata = service_metadata, ");
    try writer.print(".action = {s}", .{operation_name});
    _ = try writer.write(" };\n");
    child_state.indent_level -= 1;
    try outputIndent(child_state, writer);
    _ = try writer.write("}\n");
    try outputIndent(state, writer);
    try writer.writeByte('}');
}
fn getErrorName(err_name: []const u8) []const u8 {
    if (endsWith("Exception", err_name))
        return err_name[0 .. err_name.len - "Exception".len];

    if (endsWith("Fault", err_name))
        return err_name[0 .. err_name.len - "Fault".len];
    return err_name;
}

fn endsWith(item: []const u8, str: []const u8) bool {
    if (str.len < item.len) return false;
    return std.mem.eql(u8, item, str[str.len - item.len ..]);
}

fn reuseCommonType(shape: smithy.ShapeInfo, writer: anytype, state: GenerationState) !bool {
    // We want to return if we're at the top level of the stack. There are three
    // reasons for this:
    // 1. For operations, we have a request that includes a metadata function
    //    to enable aws.zig eventually to find the action based on a request.
    //    This could be considered a hack and maybe we should remove that
    //    caller convenience ability.
    // 2. Given the state of zig compiler tooling, "intellisense" or whatever
    //    we're calling it these days, isn't real mature, so we end up looking
    //    at the models quite a bit. Leaving the top level alone here reduces
    //    the need for users to hop around too much looking at types as they
    //    can at least see the top level.
    // 3. When we come through at the end, we want to make sure we're writing
    //    something or we'll have an infinite loop!
    if (state.type_stack.items.len == 1) return false;
    var rc = false;
    if (state.file_state.shape_references.get(shape.id)) |r| {
        if (r > 1 and (shape.shape == .structure or shape.shape == .uniontype)) {
            rc = true;
            _ = try writer.write(avoidReserved(shape.name)); // This can't possibly be this easy...
            if (state.file_state.additional_types_generated.getEntry(shape.name) == null)
                try state.file_state.additional_types_to_generate.append(shape);
        }
    }
    return rc;
}
/// return type is anyerror!void as this is a recursive function, so the compiler cannot properly infer error types
fn generateTypeFor(shape_id: []const u8, writer: anytype, state: GenerationState, end_structure: bool) anyerror!bool {
    var rc = false;

    // We assume it must exist
    const shape_info = state.file_state.shapes.get(shape_id) orelse {
        std.debug.print("Shape ID not found. This is most likely a bug. Shape ID: {s}\n", .{shape_id});
        return error.InvalidType;
    };
    const shape = shape_info.shape;
    // Check for ourselves up the stack
    var self_occurences: u8 = 0;
    for (state.type_stack.items) |i| {
        // NOTE: shapes.get isn't providing a consistent pointer - is it allocating each time?
        // we will therefore need to compare ids
        if (std.mem.eql(u8, i.*.id, shape_info.id))
            self_occurences = self_occurences + 1;
    }
    // Debugging
    // if (std.mem.eql(u8, shape_info.name, "Expression")) {
    //     std.log.info("  Type stack len: {d}, occurences: {d}\n", .{ type_stack.items.len, self_occurences });
    //     if (type_stack.items.len > 15) {
    //         std.log.info("  Type stack:\n", .{});
    //         for (type_stack.items) |i|
    //             std.log.info("  {s}: {*}", .{ i.*.id, i });
    //         return error.BugDetected;
    //     }
    // }
    // End Debugging
    if (self_occurences > 2) { // TODO: What's the appropriate number here?
        // TODO: Determine if this warrants the creation of another public
        // type to properly reference. Realistically, AWS or the service
        // must be blocking deep recursion somewhere or this would be a great
        // DOS attack
        try generateSimpleTypeFor("nothing", "[]const u8", writer);
        std.log.warn("Type cycle detected, limiting depth. Type: {s}", .{shape_id});
        // if (std.mem.eql(u8, "com.amazonaws.workmail#Timestamp", shape_id)) {
        //     std.log.info("  Type stack:\n", .{});
        //     for (state.type_stack.items) |i|
        //         std.log.info("  {s}", .{i.*.id});
        // }
        return false; // not a map
    }
    try state.type_stack.append(&shape_info);
    defer _ = state.type_stack.pop();
    switch (shape) {
        .structure => {
            if (!try reuseCommonType(shape_info, writer, state)) {
                try generateComplexTypeFor(shape_id, shape.structure.members, "struct", writer, state);
                if (end_structure) {
                    // epilog
                    try outputIndent(state, writer);
                    _ = try writer.write("}");
                }
            }
        },
        .uniontype => {
            if (!try reuseCommonType(shape_info, writer, state)) {
                try generateComplexTypeFor(shape_id, shape.uniontype.members, "union", writer, state);
                // epilog
                try outputIndent(state, writer);
                _ = try writer.write("}");
            }
        },
        .string => |s| try generateSimpleTypeFor(s, "[]const u8", writer),
        .integer => |s| try generateSimpleTypeFor(s, "i64", writer),
        .list => {
            _ = try writer.write("[]");
            // The serializer will have to deal with the idea we might be an array
            return try generateTypeFor(shape.list.member_target, writer, state, true);
        },
        .set => {
            _ = try writer.write("[]");
            // The serializer will have to deal with the idea we might be an array
            return try generateTypeFor(shape.set.member_target, writer, state, true);
        },
        .timestamp => |s| try generateSimpleTypeFor(s, "i64", writer),
        .blob => |s| try generateSimpleTypeFor(s, "[]const u8", writer),
        .boolean => |s| try generateSimpleTypeFor(s, "bool", writer),
        .double => |s| try generateSimpleTypeFor(s, "f64", writer),
        .float => |s| try generateSimpleTypeFor(s, "f32", writer),
        .long => |s| try generateSimpleTypeFor(s, "i64", writer),
        .map => {
            _ = try writer.write("[]struct {\n");
            var child_state = state;
            child_state.indent_level += 1;
            try outputIndent(child_state, writer);
            _ = try writer.write("key: ");
            try writeOptional(shape.map.traits, writer, null);
            var sub_maps = std.ArrayList([]const u8).init(state.allocator);
            defer sub_maps.deinit();
            if (try generateTypeFor(shape.map.key, writer, child_state, true))
                try sub_maps.append("key");
            try writeOptional(shape.map.traits, writer, " = null");
            _ = try writer.write(",\n");
            try outputIndent(child_state, writer);
            _ = try writer.write("value: ");
            try writeOptional(shape.map.traits, writer, null);
            if (try generateTypeFor(shape.map.value, writer, child_state, true))
                try sub_maps.append("value");
            try writeOptional(shape.map.traits, writer, " = null");
            _ = try writer.write(",\n");
            if (sub_maps.items.len > 0) {
                _ = try writer.write("\n");
                try writeStringify(state, sub_maps.items, writer);
            }
            try outputIndent(state, writer);
            _ = try writer.write("}");

            rc = true;
        },
        else => {
            std.log.err("encountered unimplemented shape type {s} for shape_id {s}. Generated code will not compile", .{ @tagName(shape), shape_id });
            // Not sure we want to return here - I think we want an exhaustive list
            // return error{UnimplementedShapeType}.UnimplementedShapeType;
        },
    }
    return rc;
}

fn generateSimpleTypeFor(_: anytype, type_name: []const u8, writer: anytype) !void {
    _ = try writer.write(type_name); // This had required stuff but the problem was elsewhere. Better to leave as function just in case
}
fn generateComplexTypeFor(shape_id: []const u8, members: []smithy.TypeMember, type_type_name: []const u8, writer: anytype, state: GenerationState) anyerror!void {
    _ = shape_id;
    const Mapping = struct { snake: []const u8, original: []const u8 };
    var field_name_mappings = try std.ArrayList(Mapping).initCapacity(state.allocator, members.len);
    defer {
        for (field_name_mappings.items) |mapping|
            state.allocator.free(mapping.snake);
        field_name_mappings.deinit();
    }
    // There is an httpQueryParams trait as well, but nobody is using it. API GW
    // pretends to, but it's an empty map
    //
    // Same with httpPayload
    //
    // httpLabel is interesting - right now we just assume anything can be used - do we need to track this?
    var http_query_mappings = try std.ArrayList(Mapping).initCapacity(state.allocator, members.len);
    defer {
        for (http_query_mappings.items) |mapping|
            state.allocator.free(mapping.snake);
        http_query_mappings.deinit();
    }
    var http_header_mappings = try std.ArrayList(Mapping).initCapacity(state.allocator, members.len);
    defer {
        for (http_header_mappings.items) |mapping|
            state.allocator.free(mapping.snake);
        http_header_mappings.deinit();
    }
    var map_fields = std.ArrayList([]const u8).init(state.allocator);
    defer {
        for (map_fields.items) |f| state.allocator.free(f);
        map_fields.deinit();
    }
    // prolog. We'll rely on caller to get the spacing correct here
    _ = try writer.write(type_type_name);
    _ = try writer.write(" {\n");
    var child_state = state;
    child_state.indent_level += 1;
    var payload: ?[]const u8 = null;
    for (members) |member| {
        // This is our mapping
        const snake_case_member = try snake.fromPascalCase(state.allocator, member.name);
        // So it looks like some services have duplicate names?! Check out "httpMethod"
        // in API Gateway. Not sure what we're supposed to do there. Checking the go
        // sdk, they move this particular duplicate to 'http_method' - not sure yet
        // if this is a hard-coded exception`
        var found_name_trait = false;
        for (member.traits) |trait| {
            switch (trait) {
                .json_name => |n| {
                    found_name_trait = true;
                    field_name_mappings.appendAssumeCapacity(.{ .snake = try state.allocator.dupe(u8, snake_case_member), .original = n });
                },
                .xml_name => |n| {
                    found_name_trait = true;
                    field_name_mappings.appendAssumeCapacity(.{ .snake = try state.allocator.dupe(u8, snake_case_member), .original = n });
                },
                .http_query => |n| http_query_mappings.appendAssumeCapacity(.{ .snake = try state.allocator.dupe(u8, snake_case_member), .original = n }),
                .http_header => http_header_mappings.appendAssumeCapacity(.{ .snake = try state.allocator.dupe(u8, snake_case_member), .original = trait.http_header }),
                .http_payload => {
                    // Don't assert as that will be optimized for Release* builds
                    // We'll continue here and treat the above as a warning
                    if (payload) |first| {
                        std.log.err("Found multiple httpPayloads in violation of smithy spec! Ignoring '{s}' and using '{s}'", .{ first, snake_case_member });
                    }
                    payload = try state.allocator.dupe(u8, snake_case_member);
                },
                else => {},
            }
        }
        if (!found_name_trait)
            field_name_mappings.appendAssumeCapacity(.{ .snake = try state.allocator.dupe(u8, snake_case_member), .original = member.name });
        defer state.allocator.free(snake_case_member);
        try outputIndent(child_state, writer);
        const member_name = avoidReserved(snake_case_member);
        try writer.print("{s}: ", .{member_name});
        try writeOptional(member.traits, writer, null);
        if (try generateTypeFor(member.target, writer, child_state, true))
            try map_fields.append(try std.fmt.allocPrint(state.allocator, "{s}", .{member_name}));

        if (!std.mem.eql(u8, "union", type_type_name))
            try writeOptional(member.traits, writer, " = null");
        _ = try writer.write(",\n");
    }

    // Add in http query metadata (only relevant to REST JSON APIs - do we care?
    // pub const http_query = .{
    //     .master_region = "MasterRegion",
    //     .function_version = "FunctionVersion",
    //     .marker = "Marker",
    //     .max_items = "MaxItems",
    // };
    if (http_query_mappings.items.len > 0) _ = try writer.write("\n");
    try writeMappings(child_state, "pub ", "http_query", http_query_mappings, false, writer);
    if (http_query_mappings.items.len > 0 and http_header_mappings.items.len > 0) _ = try writer.write("\n");
    try writeMappings(child_state, "pub ", "http_header", http_header_mappings, false, writer);

    // Add in json mappings. The function looks like this:
    //
    // pub fn jsonFieldNameFor(_: @This(), comptime field_name: []const u8) []const u8 {
    //     const mappings = .{
    //         .exclusive_start_table_name = "ExclusiveStartTableName",
    //         .limit = "Limit",
    //     };
    //     return @field(mappings, field_name);
    // }
    //
    if (payload) |load| {
        try writer.writeByte('\n');
        try outputIndent(child_state, writer);
        try writer.print("pub const http_payload: []const u8 = \"{s}\";", .{load});
    }

    try writer.writeByte('\n');
    try outputIndent(child_state, writer);
    _ = try writer.write("pub fn fieldNameFor(_: @This(), comptime field_name: []const u8) []const u8 {\n");
    var grandchild_state = child_state;
    grandchild_state.indent_level += 1;
    // We need to force output here becaseu we're referencing the field in the return statement below
    try writeMappings(grandchild_state, "", "mappings", field_name_mappings, true, writer);
    try outputIndent(grandchild_state, writer);
    _ = try writer.write("return @field(mappings, field_name);\n");
    try outputIndent(child_state, writer);
    _ = try writer.write("}\n");
    try writeStringify(child_state, map_fields.items, writer);
}

fn writeStringify(state: GenerationState, fields: [][]const u8, writer: anytype) !void {
    if (fields.len > 0) {
        // pub fn jsonStringifyField(self: @This(), comptime field_name: []const u8, options: anytype, out_stream: anytype) !bool {
        //     if (std.mem.eql(u8, "tags", field_name))
        //         return try serializeMap(self.tags, self.jsonFieldNameFor("tags"), options, out_stream);
        //     return false;
        // }
        var child_state = state;
        child_state.indent_level += 1;
        try writer.writeByte('\n');
        try outputIndent(state, writer);
        _ = try writer.write("pub fn jsonStringifyField(self: @This(), comptime field_name: []const u8, options: anytype, out_stream: anytype) !bool {\n");
        var return_state = child_state;
        return_state.indent_level += 1;
        for (fields) |field| {
            try outputIndent(child_state, writer);
            try writer.print("if (std.mem.eql(u8, \"{s}\", field_name))\n", .{field});
            try outputIndent(return_state, writer);
            try writer.print("return try serializeMap(self.{s}, self.fieldNameFor(\"{s}\"), options, out_stream);\n", .{ field, field });
        }
        try outputIndent(child_state, writer);
        _ = try writer.write("return false;\n");
        try outputIndent(state, writer);
        _ = try writer.write("}\n");
    }
}

fn writeMappings(state: GenerationState, @"pub": []const u8, mapping_name: []const u8, mappings: anytype, force_output: bool, writer: anytype) !void {
    if (mappings.items.len == 0 and !force_output) return;
    try outputIndent(state, writer);
    if (mappings.items.len == 0) {
        try writer.print("{s}const {s} = ", .{ @"pub", mapping_name });
        _ = try writer.write(".{};\n");
        return;
    }
    try writer.print("{s}const {s} = .", .{ @"pub", mapping_name });
    _ = try writer.write("{\n");
    var child_state = state;
    child_state.indent_level += 1;
    for (mappings.items) |mapping| {
        try outputIndent(child_state, writer);
        try writer.print(".{s} = \"{s}\",\n", .{ avoidReserved(mapping.snake), mapping.original });
    }
    try outputIndent(state, writer);
    _ = try writer.write("};\n");
}

fn writeOptional(traits: ?[]smithy.Trait, writer: anytype, value: ?[]const u8) !void {
    if (traits) |ts| {
        for (ts) |t|
            if (t == .required) return;
    }

    // not required
    if (value) |v| {
        _ = try writer.write(v);
    } else _ = try writer.write("?");
}
fn camelCase(allocator: std.mem.Allocator, name: []const u8) ![]const u8 {
    const first_letter = name[0] + ('a' - 'A');
    return try std.fmt.allocPrint(allocator, "{c}{s}", .{ first_letter, name[1..] });
}
fn avoidReserved(snake_name: []const u8) []const u8 {
    if (std.mem.eql(u8, snake_name, "error")) return "@\"error\"";
    if (std.mem.eql(u8, snake_name, "return")) return "@\"return\"";
    if (std.mem.eql(u8, snake_name, "not")) return "@\"not\"";
    if (std.mem.eql(u8, snake_name, "and")) return "@\"and\"";
    if (std.mem.eql(u8, snake_name, "or")) return "@\"or\"";
    if (std.mem.eql(u8, snake_name, "test")) return "@\"test\"";
    if (std.mem.eql(u8, snake_name, "null")) return "@\"null\"";
    return snake_name;
}