//! An HTTP view of the upstream 9P tree under `/fs/<path>`, served through the
//! shared `Mux` at the fid level. It is file operations, not verbs: HTTP
//! methods map onto the tree.
//!
//!   GET  /fs/<file>              bytes (Content-Type sniffed; Range honored)
//!   GET  /fs/<file>?follow=1     server-sent events, one per blocking read
//!   GET  /fs/<dir>               JSON array of entries (HTML with Accept: text/html)
//!   HEAD /fs/<path>              stat as headers
//!   PUT  /fs/<file>             write (create if missing; truncate unless ?append=1)
//!   PUT  /fs/<dir>/             create a directory
//!   DELETE /fs/<path>           remove
//!
//! A 9P Rerror becomes 404/403/409/500 with the ename in the body. Two
//! caller-owned scratch buffers are used: `big` (>= msize) for read/dir/body
//! data, `small` (>= a few KiB) for control replies and response framing.
const std = @import("std");
const c9 = @import("cloud9");
const wire = c9.wire;
const Server = std.http.Server;
const Status = std.http.Status;
const Request = c9.Client.Request;

const max_components = 64;
const name_bytes = 8192;

pub fn handle(m: anytype, request: *Server.Request, path: []const u8, big: []u8, small: []u8) void {
    const M = @TypeOf(m.*);
    var fs: FS(M) = .{ .m = m, .request = request, .big = big, .small = small };
    fs.serve(path) catch |err| switch (err) {
        error.Handled => {},
        error.NotFound => fs.fail(.not_found, "No such file or directory\n"),
        error.BadPath => fs.fail(.bad_request, "Invalid path\n"),
        error.Upstream, error.Disconnected => fs.fail(.bad_gateway, "9P upstream unavailable\n"),
        else => fs.fail(.internal_server_error, "Internal error\n"),
    };
    fs.cleanup();
}

fn FS(comptime M: type) type {
    return struct {
        const Self = @This();

        m: *M,
        request: *Server.Request,
        big: []u8,
        small: []u8,
        root_fid: ?u32 = null,
        leaf_fid: ?u32 = null,
        responded: bool = false,

        fn rpcSmall(self: *Self, req: Request) !wire.Decoded {
            var r: M.Rpc = .{ .buf = self.small };
            return self.m.rpc(req, &r);
        }

        fn fail(self: *Self, status: Status, text: []const u8) void {
            if (self.responded) return;
            self.responded = true;
            self.request.respond(text, .{ .status = status, .keep_alive = false, .extra_headers = &.{
                .{ .name = "content-type", .value = "text/plain; charset=utf-8" },
                .{ .name = "cache-control", .value = "no-store" },
                .{ .name = "x-content-type-options", .value = "nosniff" },
            } }) catch {};
        }

        /// A 9P Rerror: map to a status and answer, then stop the request.
        fn rerr(self: *Self, ename: []const u8) anyerror {
            var buf: [160]u8 = undefined;
            const body = std.fmt.bufPrint(&buf, "{s}\n", .{ename[0..@min(ename.len, 128)]}) catch "error\n";
            self.fail(mapError(ename), body);
            return error.Handled;
        }

        fn cleanup(self: *Self) void {
            if (self.leaf_fid) |f| {
                _ = self.rpcSmall(.{ .clunk = .{ .fid = f } }) catch {};
                self.leaf_fid = null;
            }
            if (self.root_fid) |f| {
                _ = self.rpcSmall(.{ .clunk = .{ .fid = f } }) catch {};
                self.root_fid = null;
            }
        }

        // -- session helpers ----------------------------------------------

        fn attach(self: *Self) !void {
            if (self.root_fid != null) return;
            const fid = self.m.takeFid() orelse return error.Upstream;
            const got = try self.rpcSmall(.{ .attach = .{ .fid = fid, .uname = self.m.user, .aname = self.m.tree } });
            if (got.msg == .rerror) {
                self.m.dropFid(fid);
                return self.rerr(got.msg.rerror.ename);
            }
            if (got.msg != .rattach) {
                self.m.dropFid(fid);
                return error.Upstream;
            }
            self.root_fid = fid;
        }

        /// Walks from the root to `names`, leaving `leaf_fid` on the target and
        /// returning its stat. A missing component is `error.NotFound`.
        fn walkTo(self: *Self, names: [][]const u8) !wire.Stat {
            try self.attach();
            if (self.leaf_fid) |old| {
                _ = self.rpcSmall(.{ .clunk = .{ .fid = old } }) catch {};
                self.leaf_fid = null;
            }
            const leaf = self.m.takeFid() orelse return error.Upstream;
            var start: usize = 0;
            var src = self.root_fid.?;
            var first = true;
            while (first or start < names.len) {
                const batch = names[start..@min(start + 16, names.len)];
                const got = try self.rpcSmall(.{ .walk = .{ .fid = src, .newfid = leaf, .names = batch } });
                if (got.msg == .rerror) {
                    self.m.dropFid(leaf);
                    return self.rerr(got.msg.rerror.ename);
                }
                if (got.msg != .rwalk or got.msg.rwalk.nwqid != batch.len) {
                    self.m.dropFid(leaf); // short walk: newfid was not bound
                    return error.NotFound;
                }
                self.leaf_fid = leaf;
                src = leaf;
                start += batch.len;
                first = false;
                if (batch.len == 0) break;
            }
            const st = try self.rpcSmall(.{ .stat = .{ .fid = leaf } });
            if (st.msg == .rerror) return self.rerr(st.msg.rerror.ename);
            if (st.msg != .rstat) return error.Upstream;
            return st.msg.rstat.stat;
        }

        // -- dispatch ------------------------------------------------------

        fn serve(self: *Self, path: []const u8) !void {
            const rel = path[3..]; // after "/fs"
            const trailing = rel.len != 0 and rel[rel.len - 1] == '/';
            var storage: [name_bytes]u8 = undefined;
            var names: [max_components][]const u8 = undefined;
            const count = try decodePath(rel, &storage, &names);
            const comps = names[0..count];

            switch (self.request.head.method) {
                .GET => try self.get(comps),
                .HEAD => try self.head(comps),
                .PUT => if (trailing) try self.mkdir(comps) else try self.put(comps),
                .DELETE => try self.delete(comps),
                else => self.fail(.method_not_allowed, "Method not allowed\n"),
            }
        }

        fn head(self: *Self, comps: [][]const u8) !void {
            const st = try self.walkTo(comps);
            const dir = st.qid.type & c9.qtdir != 0;
            var len_buf: [24]u8 = undefined;
            const clen = std.fmt.bufPrint(&len_buf, "{d}", .{st.length}) catch "0";
            var qid_buf: [48]u8 = undefined;
            const qid = std.fmt.bufPrint(&qid_buf, "{d}.{d}.{d}", .{ st.qid.type, st.qid.version, st.qid.path }) catch "";
            var mode_buf: [16]u8 = undefined;
            const mode = std.fmt.bufPrint(&mode_buf, "{o}", .{st.mode}) catch "";
            var mtime_buf: [16]u8 = undefined;
            const mtime = std.fmt.bufPrint(&mtime_buf, "{d}", .{st.mtime}) catch "";
            self.responded = true;
            self.request.respond("", .{ .status = .ok, .keep_alive = false, .transfer_encoding = .none, .extra_headers = &.{
                .{ .name = "content-type", .value = if (dir) "application/json" else "application/octet-stream" },
                .{ .name = "content-length", .value = clen },
                .{ .name = "x-9p-qid", .value = qid },
                .{ .name = "x-9p-mode", .value = mode },
                .{ .name = "x-9p-mtime", .value = mtime },
                .{ .name = "accept-ranges", .value = "bytes" },
                .{ .name = "cache-control", .value = "no-store" },
            } }) catch {};
        }

        fn get(self: *Self, comps: [][]const u8) !void {
            const follow = self.wantsFollow();
            const st = try self.walkTo(comps);
            if (st.qid.type & c9.qtdir != 0) return self.listDir(st);
            if (follow) return self.followFile();
            return self.getFile(st);
        }

        // -- files ---------------------------------------------------------

        fn getFile(self: *Self, st: wire.Stat) !void {
            const leaf = self.leaf_fid.?;
            const opened = try self.rpcSmall(.{ .open = .{ .fid = leaf, .mode = c9.oread } });
            if (opened.msg == .rerror) return self.rerr(opened.msg.rerror.ename);
            if (opened.msg != .ropen) return error.Upstream;

            const range = self.parseRange(st.length);
            const status: Status = if (range.partial) .partial_content else .ok;

            var offset: u64 = range.start;
            const first = try self.readAt(leaf, offset, self.chunk());
            if (first.msg == .rerror) return self.rerr(first.msg.rerror.ename);
            if (first.msg != .rread) return error.Upstream;
            const ctype = sniff(first.msg.rread.data);

            var cr_buf: [64]u8 = undefined;
            var headers: [4]std.http.Header = undefined;
            var nh: usize = 0;
            headers[nh] = .{ .name = "content-type", .value = ctype };
            nh += 1;
            headers[nh] = .{ .name = "accept-ranges", .value = "bytes" };
            nh += 1;
            headers[nh] = .{ .name = "cache-control", .value = "no-store" };
            nh += 1;
            if (range.partial) {
                headers[nh] = .{ .name = "content-range", .value = std.fmt.bufPrint(&cr_buf, "bytes {d}-{d}/{d}", .{ range.start, range.end - 1, st.length }) catch return error.Upstream };
                nh += 1;
            }

            self.responded = true;
            var bw = try self.request.respondStreaming(self.small, .{
                .respond_options = .{ .status = status, .keep_alive = false, .extra_headers = headers[0..nh] },
            });
            // A synthetic/control file reports length 0 but streams content, so
            // clamp to the length only for an explicit Range.
            const limit: u64 = if (range.partial) range.end - range.start else std.math.maxInt(u64);
            var sent: u64 = 0;
            var data = first.msg.rread.data;
            while (true) {
                const take = @min(@as(u64, data.len), limit - sent);
                try bw.writer.writeAll(data[0..@intCast(take)]);
                sent += take;
                if (sent >= limit or data.len == 0) break;
                offset += data.len;
                const r = try self.readAt(leaf, offset, self.chunk());
                if (r.msg != .rread) break;
                data = r.msg.rread.data;
                if (data.len == 0) break;
            }
            try bw.end();
        }

        fn followFile(self: *Self) !void {
            const leaf = self.leaf_fid.?;
            const opened = try self.rpcSmall(.{ .open = .{ .fid = leaf, .mode = c9.oread } });
            if (opened.msg == .rerror) return self.rerr(opened.msg.rerror.ename);
            if (opened.msg != .ropen) return error.Upstream;

            self.responded = true;
            var bw = try self.request.respondStreaming(self.small, .{
                .respond_options = .{ .status = .ok, .keep_alive = false, .extra_headers = &.{
                    .{ .name = "content-type", .value = "text/event-stream; charset=utf-8" },
                    .{ .name = "cache-control", .value = "no-store" },
                    .{ .name = "x-content-type-options", .value = "nosniff" },
                } },
            });
            bw.writer.writeAll(": follow\n\n") catch return;
            flushBody(&bw) catch return;
            var offset: u64 = 0;
            while (true) {
                var r: M.Rpc = .{ .buf = self.big };
                // On client disconnect / deadline this rpc is cancelled; the
                // mux Tflushes the parked upstream read before returning.
                const got = self.m.rpc(.{ .read = .{ .fid = leaf, .offset = offset, .count = self.chunk() } }, &r) catch return;
                if (got.msg != .rread) return;
                const data = got.msg.rread.data;
                if (data.len == 0) {
                    bw.writer.writeAll("event: eof\ndata:\n\n") catch return;
                    flushBody(&bw) catch return;
                    return;
                }
                offset += data.len;
                self.writeSse(&bw, data) catch return;
                flushBody(&bw) catch return;
            }
        }

        /// Drains the body writer's buffer as a chunk, then flushes to the peer.
        fn flushBody(bw: anytype) !void {
            try bw.writer.flush();
            try bw.flush();
        }

        fn writeSse(self: *Self, bw: anytype, data: []const u8) !void {
            _ = self;
            var it = std.mem.splitScalar(u8, std.mem.trimEnd(u8, data, "\n"), '\n');
            while (it.next()) |line| {
                try bw.writer.writeAll("data: ");
                try bw.writer.writeAll(line);
                try bw.writer.writeByte('\n');
            }
            try bw.writer.writeByte('\n');
        }

        // -- directories ---------------------------------------------------

        fn listDir(self: *Self, st: wire.Stat) !void {
            const html = self.wantsHtml();
            const leaf = self.leaf_fid.?;
            const opened = try self.rpcSmall(.{ .open = .{ .fid = leaf, .mode = c9.oread } });
            if (opened.msg == .rerror) return self.rerr(opened.msg.rerror.ename);
            if (opened.msg != .ropen) return error.Upstream;

            // JSON/HTML is built into `big`; directory data is read into `small`.
            var w: std.Io.Writer = .fixed(self.big);
            if (html) {
                w.writeAll("<!doctype html><meta charset=utf-8><title>") catch return error.Upstream;
                writeHtml(&w, st.name);
                w.writeAll("</title><ul>") catch return error.Upstream;
            } else {
                w.writeByte('[') catch return error.Upstream;
            }
            var offset: u64 = 0;
            var first = true;
            while (true) {
                var r: M.Rpc = .{ .buf = self.small };
                const got = try self.m.rpc(.{ .read = .{ .fid = leaf, .offset = offset, .count = self.chunk() } }, &r);
                if (got.msg != .rread) break;
                const data = got.msg.rread.data;
                if (data.len == 0) break;
                offset += data.len;
                var rest: []const u8 = data;
                while (rest.len >= 2) {
                    const size: usize = @as(usize, std.mem.readInt(u16, rest[0..2], .little)) + 2;
                    if (size > rest.len) break;
                    const entry = c9.Stat.decode(rest[0..size]) catch break;
                    rest = rest[size..];
                    if (html) {
                        w.writeAll("<li>") catch return error.Upstream;
                        writeHtml(&w, entry.name);
                        if (entry.qid.type & c9.qtdir != 0) w.writeByte('/') catch {};
                        w.writeAll("</li>") catch return error.Upstream;
                    } else {
                        if (!first) w.writeByte(',') catch return error.Upstream;
                        first = false;
                        writeEntryJson(&w, entry) catch return error.Upstream;
                    }
                }
            }
            if (html) w.writeAll("</ul>") catch return error.Upstream else w.writeByte(']') catch return error.Upstream;
            self.responded = true;
            self.request.respond(w.buffered(), .{ .status = .ok, .keep_alive = false, .extra_headers = &.{
                .{ .name = "content-type", .value = if (html) "text/html; charset=utf-8" else "application/json" },
                .{ .name = "cache-control", .value = "no-store" },
                .{ .name = "x-content-type-options", .value = "nosniff" },
            } }) catch {};
        }

        // -- writes --------------------------------------------------------

        fn put(self: *Self, comps: [][]const u8) !void {
            if (comps.len == 0) return error.BadPath;
            const append = self.wantsAppend();
            const existed = self.tryWalk(comps) catch |err| switch (err) {
                error.NotFound => false,
                else => return err,
            };
            var write_off: u64 = 0;
            if (existed) {
                const leaf = self.leaf_fid.?;
                if (append) {
                    const st = try self.rpcSmall(.{ .stat = .{ .fid = leaf } });
                    if (st.msg == .rstat) write_off = st.msg.rstat.stat.length;
                    const o = try self.rpcSmall(.{ .open = .{ .fid = leaf, .mode = c9.owrite } });
                    if (o.msg == .rerror) return self.rerr(o.msg.rerror.ename);
                    if (o.msg != .ropen) return error.Upstream;
                } else {
                    const o = try self.rpcSmall(.{ .open = .{ .fid = leaf, .mode = c9.owrite | c9.otrunc } });
                    if (o.msg == .rerror) return self.rerr(o.msg.rerror.ename);
                    if (o.msg != .ropen) return error.Upstream;
                }
            } else {
                _ = try self.walkTo(comps[0 .. comps.len - 1]);
                const parent = self.leaf_fid.?;
                const cr = try self.rpcSmall(.{ .create = .{ .fid = parent, .name = comps[comps.len - 1], .perm = 0o644, .mode = c9.owrite } });
                if (cr.msg == .rerror) return self.rerr(cr.msg.rerror.ename);
                if (cr.msg != .rcreate) return error.Upstream;
            }
            const written = try self.streamBody(self.leaf_fid.?, write_off);
            var buf: [48]u8 = undefined;
            const body = std.fmt.bufPrint(&buf, "{{\"written\":{d}}}\n", .{written}) catch "{}\n";
            self.responded = true;
            self.request.respond(body, .{ .status = if (existed) .ok else .created, .keep_alive = false, .extra_headers = &.{
                .{ .name = "content-type", .value = "application/json" },
                .{ .name = "cache-control", .value = "no-store" },
            } }) catch {};
        }

        fn mkdir(self: *Self, comps: [][]const u8) !void {
            if (comps.len == 0) return error.BadPath;
            _ = try self.walkTo(comps[0 .. comps.len - 1]);
            const parent = self.leaf_fid.?;
            const cr = try self.rpcSmall(.{ .create = .{ .fid = parent, .name = comps[comps.len - 1], .perm = c9.dmdir | 0o755, .mode = c9.oread } });
            if (cr.msg == .rerror) return self.rerr(cr.msg.rerror.ename);
            if (cr.msg != .rcreate) return error.Upstream;
            self.fail(.created, "created\n");
        }

        fn delete(self: *Self, comps: [][]const u8) !void {
            if (comps.len == 0) return error.BadPath;
            _ = try self.walkTo(comps);
            const leaf = self.leaf_fid.?;
            const rm = try self.rpcSmall(.{ .remove = .{ .fid = leaf } });
            self.m.dropFid(leaf); // Tremove clunks the fid upstream regardless
            self.leaf_fid = null;
            if (rm.msg == .rerror) return self.rerr(rm.msg.rerror.ename);
            self.fail(.no_content, "");
        }

        /// walkTo that reports missing as `false` rather than an HTTP error.
        fn tryWalk(self: *Self, comps: [][]const u8) !bool {
            _ = self.walkTo(comps) catch |err| switch (err) {
                error.NotFound => return false,
                else => return err,
            };
            return true;
        }

        fn streamBody(self: *Self, fid: u32, start: u64) !u64 {
            const body_buf = self.big[0..16384];
            const cbuf = self.big[16384..];
            const br = self.request.readerExpectContinue(body_buf) catch return error.Upstream;
            const maxw = @min(self.m.negotiatedMsize() -| 23, cbuf.len);
            var offset: u64 = start;
            var total: u64 = 0;
            while (true) {
                const n = br.readSliceShort(cbuf[0..maxw]) catch return error.Upstream;
                if (n == 0) break;
                var done: usize = 0;
                while (done < n) {
                    const w = try self.rpcSmall(.{ .write = .{ .fid = fid, .offset = offset + done, .data = cbuf[done..n] } });
                    if (w.msg == .rerror) return self.rerr(w.msg.rerror.ename);
                    if (w.msg != .rwrite or w.msg.rwrite.count == 0) return error.Upstream;
                    done += w.msg.rwrite.count;
                }
                offset += n;
                total += n;
            }
            return total;
        }

        // -- small helpers -------------------------------------------------

        fn readAt(self: *Self, fid: u32, offset: u64, count: u32) !wire.Decoded {
            var r: M.Rpc = .{ .buf = self.big };
            return self.m.rpc(.{ .read = .{ .fid = fid, .offset = offset, .count = count } }, &r);
        }

        fn chunk(self: *Self) u32 {
            const ms = self.m.negotiatedMsize();
            return if (ms > 11) ms - 11 else 0;
        }

        const Range = struct { start: u64, end: u64, partial: bool };
        fn parseRange(self: *Self, length: u64) Range {
            var it = self.request.iterateHeaders();
            while (it.next()) |h| {
                if (!std.ascii.eqlIgnoreCase(h.name, "range")) continue;
                if (!std.mem.startsWith(u8, h.value, "bytes=")) break;
                const spec = h.value[6..];
                const dash = std.mem.indexOfScalar(u8, spec, '-') orelse break;
                const start = std.fmt.parseInt(u64, spec[0..dash], 10) catch break;
                var end: u64 = length;
                if (dash + 1 < spec.len) {
                    const e = std.fmt.parseInt(u64, spec[dash + 1 ..], 10) catch break;
                    end = @min(e + 1, length);
                }
                if (start >= length or start >= end) break;
                return .{ .start = start, .end = end, .partial = true };
            }
            return .{ .start = 0, .end = length, .partial = false };
        }

        fn wantsFollow(self: *Self) bool {
            if (std.mem.indexOf(u8, self.request.head.target, "follow=1") != null) return true;
            return self.acceptHas("text/event-stream");
        }
        fn wantsHtml(self: *Self) bool {
            return self.acceptHas("text/html");
        }
        fn wantsAppend(self: *Self) bool {
            return std.mem.indexOf(u8, self.request.head.target, "append=1") != null;
        }
        fn acceptHas(self: *Self, what: []const u8) bool {
            var it = self.request.iterateHeaders();
            while (it.next()) |h| {
                if (std.ascii.eqlIgnoreCase(h.name, "accept") and std.mem.indexOf(u8, h.value, what) != null) return true;
            }
            return false;
        }
    };
}

fn mapError(ename: []const u8) Status {
    if (contains(ename, "No such file") or contains(ename, "does not exist") or contains(ename, "not found") or contains(ename, "unknown")) return .not_found;
    if (contains(ename, "permission") or contains(ename, "not permitted") or contains(ename, "denied")) return .forbidden;
    if (contains(ename, "exists")) return .conflict;
    if (contains(ename, "not empty") or contains(ename, "in use") or contains(ename, "Is a directory") or contains(ename, "Not a directory")) return .conflict;
    return .internal_server_error;
}

fn contains(haystack: []const u8, needle: []const u8) bool {
    return std.mem.indexOf(u8, haystack, needle) != null;
}

fn sniff(data: []const u8) []const u8 {
    const n = @min(data.len, 1024);
    for (data[0..n]) |b| if (b == 0) return "application/octet-stream";
    return "text/plain; charset=utf-8";
}

/// Decodes a `/fs`-relative path into non-empty, percent-decoded components.
fn decodePath(rel: []const u8, storage: []u8, names: *[max_components][]const u8) !usize {
    var out: usize = 0;
    var count: usize = 0;
    var it = std.mem.splitScalar(u8, rel, '/');
    while (it.next()) |raw| {
        if (raw.len == 0) continue;
        var i: usize = 0;
        const begin = out;
        while (i < raw.len) {
            const ch = raw[i];
            if (ch == '%') {
                if (i + 2 >= raw.len) return error.BadPath;
                const hi = hex(raw[i + 1]) orelse return error.BadPath;
                const lo = hex(raw[i + 2]) orelse return error.BadPath;
                const byte = (hi << 4) | lo;
                if (byte == 0 or byte == '/') return error.BadPath;
                if (out >= storage.len) return error.BadPath;
                storage[out] = byte;
                out += 1;
                i += 3;
            } else {
                if (out >= storage.len) return error.BadPath;
                storage[out] = ch;
                out += 1;
                i += 1;
            }
        }
        const comp = storage[begin..out];
        if (std.mem.eql(u8, comp, ".")) {
            out = begin;
            continue;
        }
        if (std.mem.eql(u8, comp, "..")) return error.BadPath;
        if (count >= max_components) return error.BadPath;
        names[count] = comp;
        count += 1;
    }
    return count;
}

fn hex(c: u8) ?u8 {
    return switch (c) {
        '0'...'9' => c - '0',
        'a'...'f' => c - 'a' + 10,
        'A'...'F' => c - 'A' + 10,
        else => null,
    };
}

fn writeHtml(w: *std.Io.Writer, text: []const u8) void {
    for (text) |c| switch (c) {
        '<' => w.writeAll("&lt;") catch {},
        '>' => w.writeAll("&gt;") catch {},
        '&' => w.writeAll("&amp;") catch {},
        '"' => w.writeAll("&quot;") catch {},
        else => w.writeByte(c) catch {},
    };
}

fn writeEntryJson(w: *std.Io.Writer, e: wire.Stat) !void {
    const dir = e.qid.type & c9.qtdir != 0;
    try w.writeAll("{\"name\":");
    try std.json.Stringify.value(e.name, .{}, w);
    try w.print(",\"dir\":{s},\"length\":{d},\"mode\":{d},\"mtime\":{d},\"qid\":{{\"type\":{d},\"version\":{d},\"path\":{d}}}}}", .{
        if (dir) "true" else "false",
        e.length,
        e.mode,
        e.mtime,
        e.qid.type,
        e.qid.version,
        e.qid.path,
    });
}