const std = @import("std");
const util = @import("util");
const http = @import("../lib.zig");

const Method = http.Method;
const Headers = http.Headers;

const Request = @import("../request.zig").Request;

const request_buf_size = 1 << 16;
const max_path_len = 1 << 10;
const max_body_len = 1 << 12;

fn ParseError(comptime Reader: type) type {
    return error{
        MethodNotImplemented,
    } | Reader.ReadError;
}

const Encoding = enum {
    identity,
    chunked,
};

pub fn parse(alloc: std.mem.Allocator, reader: anytype, address: std.net.Address) !Request {
    const method = try parseMethod(reader);
    const uri = reader.readUntilDelimiterAlloc(alloc, ' ', max_path_len) catch |err| switch (err) {
        error.StreamTooLong => return error.RequestUriTooLong,
        else => return err,
    };
    errdefer alloc.free(uri);

    const proto = try parseProto(reader);

    // discard \r\n
    _ = try reader.readByte();
    _ = try reader.readByte();

    var headers = try parseHeaders(alloc, reader);
    errdefer freeHeaders(alloc, &headers);

    const body = if (method.requestHasBody())
        try readBody(alloc, headers, reader)
    else
        null;
    errdefer if (body) |b| alloc.free(b);

    const eff_addr = if (headers.get("X-Real-IP")) |ip|
        std.net.Address.parseIp(ip, address.getPort()) catch {
            return error.BadRequest;
        }
    else
        address;

    return Request{
        .protocol = proto,
        .source_address = eff_addr,

        .method = method,
        .uri = uri,
        .headers = headers,
        .body = body,
    };
}

fn parseMethod(reader: anytype) !Method {
    var buf: [8]u8 = undefined;
    const str = reader.readUntilDelimiter(&buf, ' ') catch |err| switch (err) {
        error.StreamTooLong => return error.MethodNotImplemented,
        else => return err,
    };

    inline for (@typeInfo(Method).Enum.fields) |method| {
        if (std.mem.eql(u8, method.name, str)) {
            return @intToEnum(Method, method.value);
        }
    }

    return error.MethodNotImplemented;
}

fn parseProto(reader: anytype) !Request.Protocol {
    var buf: [8]u8 = undefined;
    const proto = reader.readUntilDelimiter(&buf, '/') catch |err| switch (err) {
        error.StreamTooLong => return error.UnknownProtocol,
        else => return err,
    };

    if (!std.mem.eql(u8, proto, "HTTP")) {
        return error.UnknownProtocol;
    }

    const count = try reader.read(buf[0..3]);
    if (count != 3 or buf[1] != '.') {
        return error.BadRequest;
    }

    if (buf[0] != '1') return error.HttpVersionNotSupported;
    return switch (buf[2]) {
        '0' => .http_1_0,
        '1' => .http_1_1,
        else => error.HttpVersionNotSupported,
    };
}

fn parseHeaders(allocator: std.mem.Allocator, reader: anytype) !Headers {
    var map = Headers.init(allocator);
    errdefer map.deinit();
    errdefer {
        var iter = map.iterator();
        while (iter.next()) |it| {
            allocator.free(it.key_ptr.*);
            allocator.free(it.value_ptr.*);
        }
    }
    // todo:
    //errdefer {
    //var iter = map.iterator();
    //while (iter.next()) |it| {
    //allocator.free(it.key_ptr);
    //allocator.free(it.value_ptr);
    //}
    //}

    var buf: [1024]u8 = undefined;

    while (true) {
        const line = try reader.readUntilDelimiter(&buf, '\n');
        if (line.len == 0 or (line.len == 1 and line[0] == '\r')) break;

        // TODO: handle multi-line headers
        const name = extractHeaderName(line) orelse continue;
        const value_end = if (line[line.len - 1] == '\r') line.len - 1 else line.len;
        const value = line[name.len + 1 + 1 .. value_end];

        if (name.len == 0 or value.len == 0) return error.BadRequest;

        const name_alloc = try allocator.alloc(u8, name.len);
        errdefer allocator.free(name_alloc);
        const value_alloc = try allocator.alloc(u8, value.len);
        errdefer allocator.free(value_alloc);

        @memcpy(name_alloc.ptr, name.ptr, name.len);
        @memcpy(value_alloc.ptr, value.ptr, value.len);

        try map.put(name_alloc, value_alloc);
    }

    return map;
}

fn extractHeaderName(line: []const u8) ?[]const u8 {
    var index: usize = 0;

    // TODO: handle whitespace
    while (index < line.len) : (index += 1) {
        if (line[index] == ':') {
            if (index == 0) return null;
            return line[0..index];
        }
    }

    return null;
}

fn readBody(alloc: std.mem.Allocator, headers: Headers, reader: anytype) !?[]const u8 {
    const xfer_encoding = try parseEncoding(headers.get("Transfer-Encoding"));
    if (xfer_encoding != .identity) return error.UnsupportedMediaType;
    const content_encoding = try parseEncoding(headers.get("Content-Encoding"));
    if (content_encoding != .identity) return error.UnsupportedMediaType;

    const len_str = headers.get("Content-Length") orelse return null;
    const len = std.fmt.parseInt(usize, len_str, 10) catch return error.BadRequest;
    if (len > max_body_len) return error.RequestEntityTooLarge;
    const body = try alloc.alloc(u8, len);
    errdefer alloc.free(body);

    reader.readNoEof(body) catch return error.BadRequest;

    return body;
}

// TODO: assumes that there's only one encoding, not layered encodings
fn parseEncoding(encoding: ?[]const u8) !Encoding {
    if (encoding == null) return .identity;
    if (std.mem.eql(u8, encoding.?, "identity")) return .identity;
    if (std.mem.eql(u8, encoding.?, "chunked")) return .chunked;
    return error.UnsupportedMediaType;
}

pub fn parseFree(allocator: std.mem.Allocator, request: *Request) void {
    allocator.free(request.uri);
    freeHeaders(allocator, &request.headers);
    if (request.body) |body| allocator.free(body);
}

fn freeHeaders(allocator: std.mem.Allocator, headers: *http.Headers) void {
    var iter = headers.iterator();
    while (iter.next()) |it| {
        allocator.free(it.key_ptr.*);
        allocator.free(it.value_ptr.*);
    }
    headers.deinit();
}

const _test = struct {
    const expectEqual = std.testing.expectEqual;
    const expectEqualStrings = std.testing.expectEqualStrings;

    fn toCrlf(comptime str: []const u8) []const u8 {
        comptime {
            var buf: [str.len * 2]u8 = undefined;

            @setEvalBranchQuota(@intCast(u32, str.len * 2)); // TODO: why does this need to be *2

            var buf_len: usize = 0;
            for (str) |ch| {
                if (ch == '\n') {
                    buf[buf_len] = '\r';
                    buf_len += 1;
                }

                buf[buf_len] = ch;
                buf_len += 1;
            }

            return buf[0..buf_len];
        }
    }

    fn makeHeaders(alloc: std.mem.Allocator, headers: anytype) !Headers {
        var result = Headers.init(alloc);
        inline for (headers) |tup| {
            try result.put(tup[0], tup[1]);
        }
        return result;
    }

    fn areEqualHeaders(lhs: Headers, rhs: Headers) bool {
        if (lhs.count() != rhs.count()) return false;
        var iter = lhs.iterator();
        while (iter.next()) |it| {
            const rhs_val = rhs.get(it.key_ptr.*) orelse return false;
            if (!std.mem.eql(u8, it.value_ptr.*, rhs_val)) return false;
        }
        return true;
    }

    fn printHeaders(headers: Headers) void {
        var iter = headers.iterator();
        while (iter.next()) |it| {
            std.debug.print("{s}: {s}\n", .{ it.key_ptr.*, it.value_ptr.* });
        }
    }

    fn expectEqualHeaders(expected: Headers, actual: Headers) !void {
        if (!areEqualHeaders(expected, actual)) {
            std.debug.print("\nexpected: \n", .{});
            printHeaders(expected);
            std.debug.print("\n\nfound: \n", .{});
            printHeaders(actual);
            std.debug.print("\n\n", .{});
            return error.TestExpectedEqual;
        }
    }

    fn parseTestCase(alloc: std.mem.Allocator, comptime request: []const u8, expected: http.Request) !void {
        var stream = std.io.fixedBufferStream(toCrlf(request));

        const result = try parse(alloc, stream.reader());

        try expectEqual(expected.method, result.method);
        try expectEqualStrings(expected.path, result.path);
        try expectEqualHeaders(expected.headers, result.headers);
        if ((expected.body == null) != (result.body == null)) {
            const null_str: []const u8 = "(null)";
            const exp = expected.body orelse null_str;
            const act = result.body orelse null_str;
            std.debug.print("\nexpected:\n{s}\n\nfound:\n{s}\n\n", .{ exp, act });
            return error.TestExpectedEqual;
        }
        if (expected.body != null) {
            try expectEqualStrings(expected.body.?, result.body.?);
        }
    }
};

// TOOD: failure test cases
test "parse" {
    const testCase = _test.parseTestCase;
    var buf = [_]u8{0} ** (1 << 16);
    var fba = std.heap.FixedBufferAllocator.init(&buf);
    const alloc = fba.allocator();
    try testCase(alloc, (
        \\GET / HTTP/1.1
        \\
        \\
    ), .{
        .method = .GET,
        .headers = try _test.makeHeaders(alloc, .{}),
        .path = "/",
    });

    fba.reset();
    try testCase(alloc, (
        \\POST / HTTP/1.1
        \\
        \\
    ), .{
        .method = .POST,
        .headers = try _test.makeHeaders(alloc, .{}),
        .path = "/",
    });

    fba.reset();
    try testCase(alloc, (
        \\HEAD / HTTP/1.1
        \\Authorization: bearer <token>
        \\
        \\
    ), .{
        .method = .HEAD,
        .headers = try _test.makeHeaders(alloc, .{
            .{ "Authorization", "bearer <token>" },
        }),
        .path = "/",
    });

    fba.reset();
    try testCase(alloc, (
        \\POST /nonsense HTTP/1.1
        \\Authorization: bearer <token>
        \\Content-Length: 5
        \\
        \\12345
    ), .{
        .method = .POST,
        .headers = try _test.makeHeaders(alloc, .{
            .{ "Authorization", "bearer <token>" },
            .{ "Content-Length", "5" },
        }),
        .path = "/nonsense",
        .body = "12345",
    });

    fba.reset();
    try std.testing.expectError(
        error.MethodNotImplemented,
        testCase(alloc, (
            \\FOO /nonsense HTTP/1.1
            \\
            \\
        ), undefined),
    );

    fba.reset();
    try std.testing.expectError(
        error.MethodNotImplemented,
        testCase(alloc, (
            \\FOOBARBAZ /nonsense HTTP/1.1
            \\
            \\
        ), undefined),
    );

    fba.reset();
    try std.testing.expectError(
        error.RequestUriTooLong,
        testCase(alloc, (
            \\GET /
        ++ ("a" ** 2048)), undefined),
    );

    fba.reset();
    try std.testing.expectError(
        error.UnknownProtocol,
        testCase(alloc, (
            \\GET /nonsense SPECIALHTTP/1.1
            \\
            \\
        ), undefined),
    );

    fba.reset();
    try std.testing.expectError(
        error.UnknownProtocol,
        testCase(alloc, (
            \\GET /nonsense JSON/1.1
            \\
            \\
        ), undefined),
    );

    fba.reset();
    try std.testing.expectError(
        error.HttpVersionNotSupported,
        testCase(alloc, (
            \\GET /nonsense HTTP/1.9
            \\
            \\
        ), undefined),
    );

    fba.reset();
    try std.testing.expectError(
        error.HttpVersionNotSupported,
        testCase(alloc, (
            \\GET /nonsense HTTP/8.1
            \\
            \\
        ), undefined),
    );

    fba.reset();
    try std.testing.expectError(
        error.BadRequest,
        testCase(alloc, (
            \\GET /nonsense HTTP/blah blah blah
            \\
            \\
        ), undefined),
    );

    fba.reset();
    try std.testing.expectError(
        error.BadRequest,
        testCase(alloc, (
            \\GET /nonsense HTTP/1/1
            \\
            \\
        ), undefined),
    );

    fba.reset();
    try std.testing.expectError(
        error.BadRequest,
        testCase(alloc, (
            \\GET /nonsense HTTP/1/1
            \\
            \\
        ), undefined),
    );
}