fediglam/src/http/middleware.zig

const std = @import("std");
const root = @import("root");
const builtin = @import("builtin");
const http = @import("./lib.zig");
const util = @import("util");
//const query_utils = @import("./query.zig");
//const json_utils = @import("./json.zig");
const json_utils = util;
const query_utils = util;

fn AddFields(comptime lhs: type, comptime rhs: type) type {
    const Ctx = @Type(.{ .Struct = .{
        .layout = .Auto,
        .fields = std.meta.fields(lhs) ++ std.meta.fields(rhs),
        .decls = &.{},
        .is_tuple = false,
    } });
    return Ctx;
}

fn addFields(lhs: anytype, rhs: anytype) AddFields(@TypeOf(lhs), @TypeOf(rhs)) {
    var result: AddFields(@TypeOf(lhs), @TypeOf(rhs)) = undefined;
    inline for (comptime std.meta.fieldNames(@TypeOf(lhs))) |f| @field(result, f) = @field(lhs, f);
    inline for (comptime std.meta.fieldNames(@TypeOf(rhs))) |f| @field(result, f) = @field(rhs, f);
    return result;
}

test {
    // apply is a plumbing function that applies a tuple of middlewares in order
    const base = apply(.{
        split_uri,
        mount("/abc"),
    });

    const request = .{ .uri = "/abc/defg/hijkl?some_query=true#section" };
    const response = .{};
    const initial_context = .{};
    try base.handle(request, response, initial_context, {});
}

fn ApplyInternal(comptime fields: []const std.builtin.Type.StructField) type {
    if (fields.len == 0) return void;

    return NextHandler(
        fields[0].field_type,
        ApplyInternal(fields[1..]),
    );
}

fn applyInternal(middlewares: anytype, comptime fields: []const std.builtin.Type.StructField) ApplyInternal(fields) {
    if (fields.len == 0) return {};
    return .{
        .first = @field(middlewares, fields[0].name),
        .next = applyInternal(middlewares, fields[1..]),
    };
}

pub fn apply(middlewares: anytype) ApplyInternal(std.meta.fields(@TypeOf(middlewares))) {
    return applyInternal(middlewares, std.meta.fields(@TypeOf(middlewares)));
}

pub fn AddContext(comptime Rhs: type) type {
    return struct {
        values: Rhs,
        pub fn handle(self: @This(), req: anytype, res: anytype, ctx: anytype, next: anytype) !void {
            return next.handle(req, res, addFields(ctx, self.values), {});
        }
    };
}

pub fn NextHandler(comptime First: type, comptime Next: type) type {
    return struct {
        first: First,
        next: Next,

        pub fn handle(
            self: @This(),
            req: anytype,
            res: anytype,
            ctx: anytype,
            next: void,
        ) !void {
            _ = next;
            return self.first.handle(req, res, ctx, self.next);
        }
    };
}

pub fn CatchErrors(comptime ErrorHandler: type) type {
    return struct {
        error_handler: ErrorHandler,
        pub fn handle(self: @This(), req: anytype, res: anytype, ctx: anytype, next: anytype) !void {
            return next.handle(req, res, ctx, {}) catch |err| {
                return self.error_handler.handle(
                    req,
                    res,
                    addFields(ctx, .{ .err = err }),
                    next,
                );
            };
        }
    };
}
pub fn catchErrors(error_handler: anytype) CatchErrors(@TypeOf(error_handler)) {
    return .{ .error_handler = error_handler };
}

pub const default_error_handler = struct {
    fn handle(_: @This(), req: anytype, res: anytype, ctx: anytype, next: anytype) !void {
        _ = next;
        std.log.err("Error {} on uri {s}", .{ ctx.err, req.uri });
        if (!res.was_opened) {
            if (res.open(.internal_server_error)) |stream| {
                defer stream.close();
                stream.finish() catch {};
            }
        }

        // Tell the server to close the connection after this request
        res.should_close = true;
    }
}{};

pub const split_uri = struct {
    pub fn handle(_: @This(), req: anytype, res: anytype, ctx: anytype, next: anytype) !void {
        var frag_split = std.mem.split(u8, req.uri, "#");
        const without_fragment = frag_split.first();
        const fragment = frag_split.rest();

        var query_split = std.mem.split(u8, without_fragment, "?");
        const path = query_split.first();
        const query = query_split.rest();

        const added_ctx = .{
            .path = path,
            .query_string = query,
            .fragment_string = fragment,
        };

        return next.handle(
            req,
            res,
            addFields(ctx, added_ctx),
            {},
        );
    }
}{};

// helper function for doing route analysis
fn routeApplies(comptime R: type, req: anytype) bool {
    if (R.method != req.method) return false;

    var path_iter = util.PathIter.from(req.path);
    comptime var route_iter = util.PathIter.from(R.path);
    inline while (comptime route_iter.next()) |route_segment| {
        const path_segment = path_iter.next() orelse return false;
        if (route_segment.len > 0 and route_segment[0] == ':') {
            // Route Argument
        } else {
            if (!std.ascii.eqlIgnoreCase(route_segment, path_segment)) return false;
        }
    }
    if (path_iter.next() != null) return false;

    return true;
}

// routes a request to the correct handler based on declared HTTP method and path
pub fn Router(comptime Routes: []const type) type {
    return struct {
        routes: std.meta.Tuple(Routes),

        pub fn handle(self: @This(), req: anytype, res: anytype, ctx: anytype, next: void) !void {
            _ = next;

            inline for (self.routes) |r| if (routeApplies(@TypeOf(r), req, ctx)) {
                if (r.handle(req, res, ctx, {})) |_| {
                    // success!
                    return;
                } else |err| switch (err) {
                    error.RouteMismatch => {},
                    else => return err,
                }
            };

            return error.RouteMismatch;
        }
    };
}

pub fn Mount(comptime route: []const u8) type {
    return struct {
        pub fn handle(_: @This(), req: anytype, res: anytype, ctx: anytype, next: anytype) !void {
            var path_iter = util.PathIter.from(ctx.path);
            comptime var route_iter = util.PathIter.from(route);
            var path_unused = ctx.path;

            inline while (comptime route_iter.next()) |route_segment| {
                if (comptime route_segment.len == 0) continue;
                const path_segment = path_iter.next() orelse return error.RouteMismatch;
                path_unused = path_iter.rest();
                if (comptime route_segment[0] == ':') {
                    @compileLog("Argument segments cannot be mounted");
                    // Route Argument
                } else {
                    if (!std.ascii.eqlIgnoreCase(route_segment, path_segment)) return error.RouteMismatch;
                }
            }

            var new_ctx = ctx;
            new_ctx.path = path_unused;
            return next.handle(req, res, new_ctx, {});
        }
    };
}
pub fn mount(comptime route: []const u8) Mount(route) {
    return .{};
}

pub fn HandleNotFound(comptime NotFoundHandler: type) type {
    return struct {
        not_found: NotFoundHandler,

        pub fn handler(self: @This(), req: anytype, res: anytype, ctx: anytype, next: anytype) !void {
            return next.handler(req, res, ctx, {}) catch |err| switch (err) {
                error.RouteMismatch => return self.not_found.handler(req, res, ctx, {}),
                else => return err,
            };
        }
    };
}

fn parsePathArgs(comptime route: []const u8, comptime Args: type, path: []const u8) !Args {
    var args: Args = undefined;
    var path_iter = util.PathIter.from(path);
    comptime var route_iter = util.PathIter.from(route);
    inline while (comptime route_iter.next()) |route_segment| {
        const path_segment = path_iter.next() orelse return error.RouteMismatch;
        if (route_segment.len > 0 and route_segment[0] == ':') {
            // route segment is an argument segment
            const A = @TypeOf(@field(args, route_segment[1..]));
            @field(args, route_segment[1..]) = try parsePathArg(A, path_segment);
        } else {
            if (!std.ascii.eqlIgnoreCase(route_segment, path_segment)) return error.RouteMismatch;
        }
    }

    if (path_iter.next() != null) return error.RouteMismatch;

    return args;
}

fn parsePathArg(comptime T: type, segment: []const u8) !T {
    if (T == []const u8) return segment;
    if (comptime std.meta.trait.isContainer(T) and std.meta.trait.hasFn("parse")(T)) return T.parse(segment);

    @compileError("Unsupported Type " ++ @typeName(T));
}

pub fn ParsePathArgs(comptime route: []const u8, comptime Args: type) type {
    return struct {
        pub fn handle(_: @This(), req: anytype, res: anytype, ctx: anytype, next: anytype) !void {
            return next.handle(
                req,
                res,
                addFields(ctx, .{ .args = parsePathArgs(route, Args, req.path) }),
                {},
            );
        }
    };
}

const BaseContentType = enum {
    json,
    url_encoded,
    octet_stream,

    other,
};

fn parseBody(comptime T: type, content_type: BaseContentType, reader: anytype, alloc: std.mem.Allocator) !T {
    const buf = try reader.readAllAlloc(alloc, 1 << 16);
    defer alloc.free(buf);

    switch (content_type) {
        .octet_stream, .json => {
            const body = try json_utils.parse(T, buf, alloc);
            defer json_utils.parseFree(body, alloc);

            return try util.deepClone(alloc, body);
        },
        .url_encoded => return query_utils.parseQuery(alloc, T, buf) catch |err| switch (err) {
            error.NoQuery => error.NoBody,
            else => err,
        },
        else => return error.UnsupportedMediaType,
    }
}

fn matchContentType(hdr: ?[]const u8) ?BaseContentType {
    if (hdr) |h| {
        if (std.ascii.eqlIgnoreCase(h, "application/x-www-form-urlencoded")) return .url_encoded;
        if (std.ascii.eqlIgnoreCase(h, "application/json")) return .json;
        if (std.ascii.eqlIgnoreCase(h, "application/octet-stream")) return .octet_stream;

        return .other;
    }

    return null;
}

pub fn ParseBody(comptime Body: type) type {
    return struct {
        pub fn handle(_: @This(), req: anytype, res: anytype, ctx: anytype, next: anytype) !void {
            const base_content_type = matchContentType(req.headers.get("Content-Type"));

            var stream = req.body orelse return error.NoBody;
            const body = try parseBody(Body, base_content_type orelse .json, stream.reader(), ctx.allocator);
            defer ctx.allocator.free(body);

            return next.handler(
                req,
                res,
                addFields(ctx, .{ .body = body }),
            );
        }
    };
}

pub fn ParseQueryParams(comptime Next: type, comptime QueryParams: type) type {
    return struct {
        next: Next,

        pub fn handler(self: @This(), req: anytype, res: anytype, ctx: anytype) !void {
            const query = try query_utils.parseQuery(ctx.allocator, QueryParams, ctx.query_string);
            defer ctx.allocator.free(query);

            return self.next.handler(
                req,
                res,
                addFields(ctx, .{ .query = query }),
            );
        }
    };
}