const std = @import("std");
const base = @import("aws_http_base.zig");
const auth = @import("aws_authentication.zig");

const log = std.log.scoped(.aws_signing);

// see https://github.com/awslabs/aws-c-auth/blob/ace1311f8ef6ea890b26dd376031bed2721648eb/include/aws/auth/signing_config.h#L186-L207
const ConfigFlags = packed struct {
    // We assume the uri will be encoded once in preparation for transmission.  Certain services
    // do not decode before checking signature, requiring us to actually double-encode the uri in the canonical
    // request in order to pass a signature check.

    use_double_uri_encode: bool = true,

    // Controls whether or not the uri paths should be normalized when building the canonical request
    should_normalize_uri_path: bool = true,

    // Controls whether "X-Amz-Security-Token" is omitted from the canonical request.
    // "X-Amz-Security-Token" is added during signing, as a header or
    // query param, when credentials have a session token.
    // If false (the default), this parameter is included in the canonical request.
    // If true, this parameter is still added, but omitted from the canonical request.
    omit_session_token: bool = true,
};

pub const Config = struct {
    // These two should be all you need to set most of the time
    service: []const u8,
    credentials: auth.Credentials,

    region: []const u8 = "aws-global",
    // https://github.com/awslabs/aws-c-auth/blob/ace1311f8ef6ea890b26dd376031bed2721648eb/include/aws/auth/signing_config.h#L38
    algorithm: enum { v4, v4a } = .v4,
    // https://github.com/awslabs/aws-c-auth/blob/ace1311f8ef6ea890b26dd376031bed2721648eb/include/aws/auth/signing_config.h#L24
    // config_type: ?? // CRT only has one value. We'll ignore for now
    // https://github.com/awslabs/aws-c-auth/blob/ace1311f8ef6ea890b26dd376031bed2721648eb/include/aws/auth/signing_config.h#L49
    signature_type: enum {
        headers, // we only support this
        query_params,
        request_chunk,
        request_event, // not implemented by CRT
        canonical_request_headers,
        canonical_request_query_params,
    } = .headers,
    signing_time: ?i64 = null, // Used for testing. If null, will use current time

    // In the CRT, should_sign_header is a function to allow header filtering.
    // The _ud would be a anyopaque user defined data for the function to use
    //     .should_sign_header = null,
    //     .should_sign_header_ud = null,

    // In the CRT, this is only used if the body has been precalculated. We don't have
    // this use case, and we'll ignore
    //     .signed_body_value = c.aws_byte_cursor_from_c_str(""),
    signed_body_header: SignatureType = .sha256, // https://github.com/awslabs/aws-c-auth/blob/ace1311f8ef6ea890b26dd376031bed2721648eb/include/aws/auth/signing_config.h#L131

    // This is more complex in the CRT. We'll just take the creds. Someone
    // else can use a provider and get them in advance
    // https://github.com/awslabs/aws-c-auth/blob/ace1311f8ef6ea890b26dd376031bed2721648eb/include/aws/auth/signing_config.h#L225-L251
    // If non-zero and the signing transform is query param, then signing will add X-Amz-Expires to the query
    // string, equal to the value specified here.  If this value is zero or if header signing is being used then
    // this parameter has no effect.
    expiration_in_seconds: u64 = 0,

    flags: ConfigFlags = .{},
};

pub const SignatureType = enum { sha256, none };
pub const SigningError = error{
    NotImplemented,
};

pub fn signRequest(allocator: std.mem.Allocator, http_request: base.Request, config: Config) SigningError!void {
    _ = allocator;
    _ = http_request;
    try validateConfig(config);
    log.debug("Signing with access key: {s}", .{config.credentials.access_key});
}

fn validateConfig(config: Config) SigningError!void {
    if (config.signature_type != .headers or
        config.signed_body_header != .sha256 or
        config.expiration_in_seconds != 0 or
        config.algorithm != .v4 or
        !config.flags.omit_session_token or
        !config.flags.should_normalize_uri_path or
        !config.flags.use_double_uri_encode)
        return SigningError.NotImplemented;
}

fn createCanonicalRequest(allocator: std.mem.Allocator, request: base.Request, config: Config) ![]const u8 {
    // CanonicalRequest =
    // HTTPRequestMethod + '\n' +
    // CanonicalURI + '\n' +
    // CanonicalQueryString + '\n' +
    // CanonicalHeaders + '\n' +
    // SignedHeaders + '\n' +
    // HexEncode(Hash(RequestPayload))
    const fmt =
        \\{s}
        \\{s}
        \\{s}
        \\{s}
        \\{s}
        \\{s}
    ;

    // TODO: This is all better as a writer - less allocations/copying
    const canonical_method = canonicalRequestMethod(request.method);
    const canonical_url = try canonicalUri(allocator, request.path, config.flags.use_double_uri_encode);
    defer allocator.free(canonical_url);
    const canonical_query = try canonicalQueryString(allocator, request.path);
    defer allocator.free(canonical_query);
    const canonical_headers = try canonicalHeaders(allocator, request.headers);
    defer allocator.free(canonical_headers.str);
    defer allocator.free(canonical_headers.signed_headers);
    const payload_hash = try hashPayload(allocator, request.body, config.signed_body_header);
    defer allocator.free(payload_hash);
    return try std.fmt.allocPrint(allocator, fmt, .{
        canonical_method,
        canonical_url,
        canonical_query,
        canonical_headers.str,
        canonical_headers.signed_headers,
        payload_hash,
    });
}

fn canonicalRequestMethod(method: []const u8) ![]const u8 {
    return method; // We assume it's good
}

fn canonicalUri(allocator: std.mem.Allocator, path: []const u8, double_encode: bool) ![]const u8 {
    // Add the canonical URI parameter, followed by a newline character. The
    // canonical URI is the URI-encoded version of the absolute path component
    // of the URI, which is everything in the URI from the HTTP host to the
    // question mark character ("?") that begins the query string parameters (if any).
    //
    // Normalize URI paths according to RFC 3986. Remove redundant and relative
    // path components. Each path segment must be URI-encoded twice
    // (except for Amazon S3 which only gets URI-encoded once).
    //
    // Note: In exception to this, you do not normalize URI paths for requests
    // to Amazon S3. For example, if you have a bucket with an object
    // named my-object//example//photo.user, use that path. Normalizing
    // the path to my-object/example/photo.user will cause the request to
    // fail. For more information, see Task 1: Create a Canonical Request in
    // the Amazon Simple Storage Service API Reference.
    //
    // If the absolute path is empty, use a forward slash (/)
    //
    // For now, we will "Remove redundant and relative path components". This
    // doesn't apply to S3 anyway, and we'll make it the callers's problem
    if (!double_encode)
        return error.S3NotImplemented;
    if (path.len == 0 or path[0] == '?' or path[0] == '#')
        return try allocator.dupe(u8, "/");
    const encoded_once = try encodeUri(allocator, path);
    if (!double_encode)
        return encoded_once[0 .. std.mem.lastIndexOf(u8, encoded_once, "?") orelse encoded_once.len];
    defer allocator.free(encoded_once);
    const encoded_twice = try encodeUri(allocator, encoded_once);
    return encoded_twice[0 .. std.mem.lastIndexOf(u8, encoded_twice, "?") orelse encoded_twice.len];
}

fn encodeParamPart(allocator: std.mem.Allocator, path: []const u8) ![]const u8 {
    const unreserved_marks = "-_.!~*'()";
    var encoded = try std.ArrayList(u8).initCapacity(allocator, path.len);
    defer encoded.deinit();
    for (path) |c| {
        var should_encode = true;
        for (unreserved_marks) |r|
            if (r == c) {
                should_encode = false;
                break;
            };
        if (should_encode and std.ascii.isAlNum(c))
            should_encode = false;

        if (!should_encode) {
            try encoded.append(c);
            continue;
        }
        // Whatever remains, encode it
        try encoded.append('%');
        const hex = try std.fmt.allocPrint(allocator, "{s}", .{std.fmt.fmtSliceHexUpper(&[_]u8{c})});
        defer allocator.free(hex);
        try encoded.appendSlice(hex);
    }
    return encoded.toOwnedSlice();
}
fn encodeUri(allocator: std.mem.Allocator, path: []const u8) ![]const u8 {
    const reserved_characters = ";,/?:@&=+$#";
    const unreserved_marks = "-_.!~*'()";
    var encoded = try std.ArrayList(u8).initCapacity(allocator, path.len);
    defer encoded.deinit();
    for (path) |c| {
        var should_encode = true;
        for (reserved_characters) |r|
            if (r == c) {
                should_encode = false;
                break;
            };
        if (should_encode) {
            for (unreserved_marks) |r|
                if (r == c) {
                    should_encode = false;
                    break;
                };
        }
        if (should_encode and std.ascii.isAlNum(c))
            should_encode = false;

        if (!should_encode) {
            try encoded.append(c);
            continue;
        }
        // Whatever remains, encode it
        try encoded.append('%');
        const hex = try std.fmt.allocPrint(allocator, "{s}", .{std.fmt.fmtSliceHexUpper(&[_]u8{c})});
        defer allocator.free(hex);
        try encoded.appendSlice(hex);
    }
    return encoded.toOwnedSlice();
}

fn canonicalQueryString(allocator: std.mem.Allocator, path: []const u8) ![]const u8 {
    //     To construct the canonical query string, complete the following steps:
    //
    //     Sort the parameter names by character code point in ascending order.
    //     Parameters with duplicate names should be sorted by value. For example,
    //     a parameter name that begins with the uppercase letter F precedes a
    //     parameter name that begins with a lowercase letter b.
    //
    //     URI-encode each parameter name and value according to the following rules:
    //
    //         Do not URI-encode any of the unreserved characters that RFC 3986
    //         defines: A-Z, a-z, 0-9, hyphen ( - ), underscore ( _ ), period ( . ), and tilde ( ~ ).
    //
    //         Percent-encode all other characters with %XY, where X and Y are
    //         hexadecimal characters (0-9 and uppercase A-F). For example, the
    //         space character must be encoded as %20 (not using '+', as some
    //         encoding schemes do) and extended UTF-8 characters must be in the
    //         form %XY%ZA%BC.
    //
    //         Double-encode any equals ( = ) characters in parameter values.
    //
    //     Build the canonical query string by starting with the first parameter
    //     name in the sorted list.
    //
    //     For each parameter, append the URI-encoded parameter name, followed by
    //     the equals sign character (=), followed by the URI-encoded parameter
    //     value. Use an empty string for parameters that have no value.
    //
    //     Append the ampersand character (&) after each parameter value, except
    //     for the last value in the list.
    //
    // One option for the query API is to put all request parameters in the query
    // string. For example, you can do this for Amazon S3 to create a presigned
    // URL. In that case, the canonical query string must include not only
    // parameters for the request, but also the parameters used as part of the
    // signing process—the hashing algorithm, credential scope, date, and signed
    // headers parameters.
    //
    // The following example shows a query string that includes authentication
    // information. The example is formatted with line breaks for readability, but
    // the canonical query string must be one continuous line of text in your code.
    const first_question = std.mem.indexOf(u8, path, "?");
    if (first_question == null)
        return try allocator.dupe(u8, "");

    // We have a query string
    const query = path[first_question.? + 1 ..];

    // Split this by component
    var portions = std.mem.split(u8, query, "&");
    var sort_me = std.ArrayList([]const u8).init(allocator);
    defer sort_me.deinit();
    while (portions.next()) |item|
        try sort_me.append(item);
    std.sort.sort([]const u8, sort_me.items, {}, lessThanBinary);

    var normalized = try std.ArrayList(u8).initCapacity(allocator, path.len);
    defer normalized.deinit();
    var first = true;
    for (sort_me.items) |i| {
        if (!first) try normalized.append('&');
        first = false;
        var first_equals = std.mem.indexOf(u8, i, "=");
        if (first_equals == null) {
            // Rare. This is "foo="
            const normed_item = try encodeUri(allocator, i);
            defer allocator.free(normed_item);
            try normalized.appendSlice(i); // This should be encoded
            try normalized.append('=');
            continue;
        }

        // normal key=value stuff
        const key = try encodeParamPart(allocator, i[0..first_equals.?]);
        defer allocator.free(key);

        const value = try encodeParamPart(allocator, i[first_equals.? + 1 ..]);
        defer allocator.free(value);
        // Double-encode any = in the value. But not anything else?
        const weird_equals_in_value_thing = try replace(allocator, value, "%3D", "%253D");
        defer allocator.free(weird_equals_in_value_thing);
        try normalized.appendSlice(key);
        try normalized.append('=');
        try normalized.appendSlice(weird_equals_in_value_thing);
    }

    return normalized.toOwnedSlice();
}

fn replace(allocator: std.mem.Allocator, haystack: []const u8, needle: []const u8, replacement_value: []const u8) ![]const u8 {
    var buffer = try allocator.alloc(u8, std.mem.replacementSize(u8, haystack, needle, replacement_value));
    _ = std.mem.replace(u8, haystack, needle, replacement_value, buffer);
    return buffer;
}

fn lessThanBinary(context: void, lhs: []const u8, rhs: []const u8) bool {
    _ = context;
    return std.mem.lessThan(u8, lhs, rhs);
}
const CanonicalHeaders = struct {
    str: []const u8,
    signed_headers: []const u8,
};
fn canonicalHeaders(allocator: std.mem.Allocator, headers: []base.Header) !CanonicalHeaders {
    //
    // Doc example. Original:
    //
    // Host:iam.amazonaws.com\n
    // Content-Type:application/x-www-form-urlencoded; charset=utf-8\n
    // My-header1:    a   b   c  \n
    // X-Amz-Date:20150830T123600Z\n
    // My-Header2:    "a   b   c"  \n
    //
    // Canonical form:
    // content-type:application/x-www-form-urlencoded; charset=utf-8\n
    // host:iam.amazonaws.com\n
    // my-header1:a b c\n
    // my-header2:"a b c"\n
    // x-amz-date:20150830T123600Z\n
    var dest = try allocator.alloc(base.Header, headers.len);
    defer {
        for (dest) |h| {
            allocator.free(h.name);
            allocator.free(h.value);
        }
        allocator.free(dest);
    }
    var total_len: usize = 0;
    var total_name_len: usize = 0;
    for (headers) |h, i| {
        total_len += (h.name.len + h.value.len + 2);
        total_name_len += (h.name.len + 1);
        const value = try canonicalHeaderValue(allocator, h.value);
        defer allocator.free(value);
        dest[i] = .{
            .name = try std.ascii.allocLowerString(allocator, h.name),
            .value = try std.fmt.allocPrint(allocator, "{s}", .{value}),
        };
    }

    std.sort.sort(base.Header, dest, {}, lessThan);

    var dest_str = try std.ArrayList(u8).initCapacity(allocator, total_len);
    defer dest_str.deinit();
    var signed_headers = try std.ArrayList(u8).initCapacity(allocator, total_name_len);
    defer signed_headers.deinit();
    var first = true;
    for (dest) |h| {
        dest_str.appendSliceAssumeCapacity(h.name);
        dest_str.appendAssumeCapacity(':');
        dest_str.appendSliceAssumeCapacity(h.value);
        dest_str.appendAssumeCapacity('\n');

        if (!first) signed_headers.appendAssumeCapacity(';');
        first = false;
        signed_headers.appendSliceAssumeCapacity(h.name);
    }
    return CanonicalHeaders{
        .str = dest_str.toOwnedSlice(),
        .signed_headers = signed_headers.toOwnedSlice(),
    };
}

fn canonicalHeaderValue(allocator: std.mem.Allocator, value: []const u8) ![]const u8 {
    var started = false;
    var in_quote = false;
    var start: usize = 0;
    const rc = try allocator.alloc(u8, value.len);
    var rc_inx: usize = 0;
    for (value) |c, i| {
        if (!started and !std.ascii.isSpace(c)) {
            started = true;
            start = i;
        }
        if (started) {
            if (!in_quote and i > 0 and std.ascii.isSpace(c) and std.ascii.isSpace(value[i - 1]))
                continue;
            // if (c == '"') in_quote = !in_quote;
            rc[rc_inx] = c;
            rc_inx += 1;
        }
    }
    // Trim end
    while (std.ascii.isSpace(rc[rc_inx - 1]))
        rc_inx -= 1;
    return rc[0..rc_inx];
}
fn lessThan(context: void, lhs: base.Header, rhs: base.Header) bool {
    _ = context;
    return std.ascii.lessThanIgnoreCase(lhs.name, rhs.name);
}

fn hashPayload(allocator: std.mem.Allocator, payload: []const u8, sig_type: SignatureType) ![]const u8 {
    if (sig_type != .sha256)
        return error.NotImplemented;
    const to_hash = blk: {
        if (payload.len > 0) {
            break :blk payload;
        }
        break :blk "";
    };
    var out: [std.crypto.hash.sha2.Sha256.digest_length]u8 = undefined;
    std.crypto.hash.sha2.Sha256.hash(to_hash, &out, .{});
    return try std.fmt.allocPrint(allocator, "{s}", .{std.fmt.fmtSliceHexLower(&out)});
}
// SignedHeaders + '\n' +
// HexEncode(Hash(RequestPayload))
test "canonical method" {
    const actual = try canonicalRequestMethod("GET");
    try std.testing.expectEqualStrings("GET", actual);
}

test "canonical uri" {
    const allocator = std.testing.allocator;
    const path = "/documents and settings/?foo=bar";
    const expected = "/documents%2520and%2520settings/";
    const actual = try canonicalUri(allocator, path, true);
    defer allocator.free(actual);
    try std.testing.expectEqualStrings(expected, actual);

    const slash = try canonicalUri(allocator, "", true);
    defer allocator.free(slash);
    try std.testing.expectEqualStrings("/", slash);
}
test "canonical query" {
    const allocator = std.testing.allocator;
    const path = "blahblahblah?foo=bar&zed=dead&qux&equals=x=y&Action=ListUsers&Version=2010-05-08";

    // {
    //     // TODO: Remove block
    //     std.testing.log_level = .debug;
    //     _ = try std.io.getStdErr().write("\n");
    // }
    const expected = "Action=ListUsers&Version=2010-05-08&equals=x%253Dy&foo=bar&qux=&zed=dead";
    const actual = try canonicalQueryString(allocator, path);
    defer allocator.free(actual);
    try std.testing.expectEqualStrings(expected, actual);
}
test "canonical headers" {
    const allocator = std.testing.allocator;
    var headers = try std.ArrayList(base.Header).initCapacity(allocator, 5);
    defer headers.deinit();
    try headers.append(.{ .name = "Host", .value = "iam.amazonaws.com" });
    try headers.append(.{ .name = "Content-Type", .value = "application/x-www-form-urlencoded; charset=utf-8" });
    try headers.append(.{ .name = "My-header1", .value = "  a  b  c  " });
    try headers.append(.{ .name = "X-Amz-Date", .value = "20150830T123600Z" });
    try headers.append(.{ .name = "My-header2", .value = "  \"a  b  c\"  " });
    const expected =
        \\content-type:application/x-www-form-urlencoded; charset=utf-8
        \\host:iam.amazonaws.com
        \\my-header1:a b c
        \\my-header2:"a b c"
        \\x-amz-date:20150830T123600Z
        \\
    ;
    // {
    //     // TODO: Remove block
    //     std.testing.log_level = .debug;
    //     _ = try std.io.getStdErr().write("\n");
    // }
    const actual = try canonicalHeaders(allocator, headers.items);
    defer allocator.free(actual.str);
    defer allocator.free(actual.signed_headers);
    try std.testing.expectEqualStrings(expected, actual.str);
    try std.testing.expectEqualStrings("content-type;host;my-header1;my-header2;x-amz-date", actual.signed_headers);
}

test "canonical request" {
    const allocator = std.testing.allocator;
    var headers = try std.ArrayList(base.Header).initCapacity(allocator, 5);
    defer headers.deinit();
    try headers.append(.{ .name = "Content-Type", .value = "application/x-www-form-urlencoded" });
    try headers.append(.{ .name = "Content-Length", .value = "43" });
    try headers.append(.{ .name = "User-Agent", .value = "zig-aws 1.0, Powered by the AWS Common Runtime." });
    try headers.append(.{ .name = "Host", .value = "sts.us-west-2.amazonaws.com" });
    try headers.append(.{ .name = "Accept", .value = "application/json" });
    const req = base.Request{
        .path = "/",
        .query = "",
        .body = "Action=GetCallerIdentity&Version=2011-06-15",
        .method = "POST",
        .content_type = "application/json",
        .headers = headers.items,
    };
    {
        // TODO: Remove block
        std.testing.log_level = .debug;
        _ = try std.io.getStdErr().write("\n");
    }
    const request = try createCanonicalRequest(allocator, req, .{
        .region = "us-west-2", // us-east-1
        .service = "sts", // service
        .credentials = .{
            .access_key = "AKIDEXAMPLE",
            .secret_key = "wJalrXUtnFEMI/K7MDENG+bPxRfiCYEXAMPLEKEY",
            .session_token = null,
        },
        .signing_time = 1642187728, // Should be 2015-08-30T12:36:00Z. Does zig stdlib have date parsing?
    });
    defer allocator.free(request);
    std.log.debug("canonical request:\n{s}", .{request});
    try std.testing.expect(request.len > 0); // TODO: improvify this

}
test "can sign" {
    // [debug] (aws): call: prefix sts, sigv4 sts, version 2011-06-15, action GetCallerIdentity
    // [debug] (aws): proto: AwsProtocol.query
    // [debug] (awshttp): host: sts.us-west-2.amazonaws.com, scheme: https, port: 443
    // [debug] (awshttp): Calling endpoint https://sts.us-west-2.amazonaws.com
    // [debug] (awshttp): Path: /
    // [debug] (awshttp): Query:
    // [debug] (awshttp): Method: POST
    // [debug] (awshttp): body length: 43
    // [debug] (awshttp): Body
    // ====
    // Action=GetCallerIdentity&Version=2011-06-15
    // ====
    // [debug] (awshttp): All Request Headers:
    // [debug] (awshttp):      Accept: application/json
    // [debug] (awshttp):      Host: sts.us-west-2.amazonaws.com
    // [debug] (awshttp):      User-Agent: zig-aws 1.0, Powered by the AWS Common Runtime.
    // [debug] (awshttp):      Content-Type: application/x-www-form-urlencoded
    // [debug] (awshttp):      Content-Length: 43

    const allocator = std.testing.allocator;
    var headers = try std.ArrayList(base.Header).initCapacity(allocator, 5);
    defer headers.deinit();
    try headers.append(.{ .name = "Content-Type", .value = "application/x-www-form-urlencoded" });
    try headers.append(.{ .name = "Content-Length", .value = "43" });
    try headers.append(.{ .name = "User-Agent", .value = "zig-aws 1.0, Powered by the AWS Common Runtime." });
    try headers.append(.{ .name = "Host", .value = "sts.us-west-2.amazonaws.com" });
    try headers.append(.{ .name = "Accept", .value = "application/json" });
    const req = base.Request{
        .path = "/",
        .query = "",
        .body = "Action=GetCallerIdentity&Version=2011-06-15",
        .method = "POST",
        .content_type = "application/json",
        .headers = headers.items,
    };
    {
        // TODO: Remove block
        std.testing.log_level = .debug;
        _ = try std.io.getStdErr().write("\n");
    }

    // we could look at sigv4 signing tests at:
    // https://github.com/awslabs/aws-c-auth/blob/ace1311f8ef6ea890b26dd376031bed2721648eb/tests/sigv4_signing_tests.c#L1478
    //
    // for valid signatures. TODO: Get literally anything working first
    try signRequest(allocator, req, .{
        .region = "us-west-2", // us-east-1
        .service = "sts", // service
        .credentials = .{
            .access_key = "AKIDEXAMPLE",
            .secret_key = "wJalrXUtnFEMI/K7MDENG+bPxRfiCYEXAMPLEKEY",
            .session_token = null,
        },
        .signing_time = 1642187728, // Should be 2015-08-30T12:36:00Z. Does zig stdlib have date parsing?
    });
}