#!/usr/bin/env lua
-- lmcp hub — fleet-wide MCP broker.
--
-- One MCP endpoint that fans out to every lmcp-backed host, with an SSH
-- fallback for hosts whose lmcp is temporarily down (or not installed).
-- Exposes a small set of "remote_*" tools that all take a `host` arg
-- naming the target in the backend registry.
--
-- Registry file (default /opt/herding/etc/hub-backends.conf):
--   # name  ssh_host            lmcp_url                               token
--   boltzmann boltzmann.fritz.box http://boltzmann.fritz.box:8080/mcp   <bearer>
--   tesla     tesla               http://tesla.fritz.box:8080/mcp       -
--   broglie   -                   http://broglie.fritz.box:8080/mcp     -
-- Use `-` for "not applicable". Lines starting with # are comments.
-- Missing `ssh_host`: no ssh fallback available. Missing `lmcp_url`: ssh-only.
--
-- SPDX-License-Identifier: MIT

local dir = arg[0]:match('(.*/)') or './'
package.path = package.path .. ';' .. dir .. '?.lua'
local lmcp = require('lmcp')
local json = require('json')
local socket = require('socket')

-- ---- Backend registry ---------------------------------------------------

local CONF_PATH = os.getenv("LMCP_HUB_BACKENDS") or "/opt/herding/etc/hub-backends.conf"
local PROBE_TTL_UP = tonumber(os.getenv("LMCP_HUB_PROBE_TTL_UP") or "30")
local PROBE_TTL_DOWN_MIN = tonumber(os.getenv("LMCP_HUB_PROBE_TTL_DOWN_MIN") or "60")
local PROBE_TTL_DOWN_MAX = tonumber(os.getenv("LMCP_HUB_PROBE_TTL_DOWN_MAX") or "900")
local PROBE_BUDGET = tonumber(os.getenv("LMCP_HUB_PROBE_BUDGET") or "3")
local LMCP_TIMEOUT = tonumber(os.getenv("LMCP_HUB_LMCP_TIMEOUT") or "6")
local SSH_TIMEOUT = tonumber(os.getenv("LMCP_HUB_SSH_TIMEOUT") or "10")
local SSH_HARD_TIMEOUT = tonumber(os.getenv("LMCP_HUB_SSH_HARD_TIMEOUT") or "30")
local LOG_REQUESTS = (os.getenv("LMCP_HUB_LOG") or "1") ~= "0"

local function logreq(fmt, ...)
    if not LOG_REQUESTS then return end
    io.stderr:write(string.format("[hub %s] " .. fmt .. "\n",
        os.date("%H:%M:%S"), ...))
    io.stderr:flush()
end

local function monotonic()
    local ok, s = pcall(socket.gettime)
    return ok and s or os.time()
end

local backends = {}  -- name -> { name, ssh_host, lmcp_url, token }
local status = {}    -- name -> { up=bool, via="lmcp"|"ssh"|nil, checked=t, err=... }

local function load_registry()
    local f = io.open(CONF_PATH, "r")
    if not f then
        io.stderr:write("hub: no backend registry at " .. CONF_PATH .. "\n")
        return
    end
    backends = {}
    for line in f:lines() do
        line = line:gsub("^%s+", ""):gsub("%s+$", "")
        if line ~= "" and not line:match("^#") then
            local parts = {}
            for p in line:gmatch("%S+") do parts[#parts+1] = p end
            if #parts >= 2 then
                local name = parts[1]
                local ssh_host = (parts[2] ~= "-" and parts[2]) or nil
                local lmcp_url = (parts[3] ~= "-" and parts[3]) or nil
                local token = (parts[4] ~= "-" and parts[4]) or nil
                backends[name] = {
                    name = name,
                    ssh_host = ssh_host,
                    lmcp_url = lmcp_url,
                    token = token,
                }
            end
        end
    end
    f:close()
end

-- ---- Outbound HTTP client (plain, no TLS) ------------------------------

local function parse_url(url)
    local scheme, host, port, path = url:match("^(%w+)://([^:/]+):?(%d*)(/?.*)$")
    if not scheme then return nil, "bad url" end
    port = tonumber(port) or (scheme == "https" and 443 or 80)
    if path == "" then path = "/" end
    return { scheme = scheme, host = host, port = port, path = path }
end

local function http_post_json(url, body, token, timeout)
    local u, err = parse_url(url)
    if not u then return nil, err end
    if u.scheme ~= "http" then return nil, "hub only speaks http to backends" end

    local sock = socket.tcp()
    sock:settimeout(timeout or 6)
    local ok, e = sock:connect(u.host, u.port)
    if not ok then sock:close(); return nil, "connect: " .. e end

    local headers = {
        "POST " .. u.path .. " HTTP/1.1",
        "Host: " .. u.host .. ":" .. u.port,
        "Content-Type: application/json",
        "Content-Length: " .. tostring(#body),
        "Connection: close",
    }
    if token then
        headers[#headers+1] = "Authorization: Bearer " .. token
    end
    local req = table.concat(headers, "\r\n") .. "\r\n\r\n" .. body
    local _, se = sock:send(req)
    if se then sock:close(); return nil, "send: " .. se end

    local chunks = {}
    while true do
        local data, rerr, partial = sock:receive(4096)
        if data then chunks[#chunks+1] = data
        elseif partial and #partial > 0 then chunks[#chunks+1] = partial
        end
        if not data then
            if rerr == "timeout" then sock:close(); return nil, "timeout" end
            break
        end
    end
    sock:close()

    local resp = table.concat(chunks)
    local hend = resp:find("\r\n\r\n", 1, true)
    if not hend then return nil, "no body separator" end
    local status_line = resp:sub(1, resp:find("\r\n", 1, true) - 1)
    local status_code = tonumber(status_line:match("HTTP/[%d%.]+%s+(%d+)"))
    local body_str = resp:sub(hend + 4)
    if status_code ~= 200 then
        return nil, "http " .. tostring(status_code) .. ": " .. body_str:sub(1, 200)
    end
    local ok2, parsed = pcall(json.decode, body_str)
    if not ok2 then return nil, "bad json: " .. body_str:sub(1, 200) end
    return parsed
end

local function jsonrpc_call(url, token, method, params)
    local body = json.encode({
        jsonrpc = "2.0",
        id = os.time() * 1000 + math.random(1000, 9999),
        method = method,
        params = params or {},
    })
    local resp, err = http_post_json(url, body, token, LMCP_TIMEOUT)
    if not resp then return nil, err end
    if resp.error then
        return nil, "rpc: " .. (resp.error.message or "unknown")
    end
    return resp.result
end

-- ---- SSH exec (shell-escape-free via bash -s on stdin) -----------------

local function shell_quote(s)
    -- Single-quote wrap, replace embedded single quotes with '\''
    return "'" .. tostring(s):gsub("'", "'\\''") .. "'"
end

local function tmpwrite(content)
    local path = os.tmpname()
    local f = io.open(path, "w")
    if not f then return nil, "tmpfile create failed" end
    f:write(content)
    f:close()
    return path
end

local function ssh_run_script(ssh_host, script)
    -- Write the script body locally, then ssh with stdin redirected from it.
    -- bash -s reads the script from stdin. Nothing inside `script` is subject
    -- to another shell round of expansion — this is the escape-free path.
    local spath, perr = tmpwrite(script)
    if not spath then return nil, perr, -1 end
    local outpath = spath .. ".out"
    -- Hard-cap wall time with GNU `timeout` — ssh's ConnectTimeout only
    -- bounds TCP connect, not the session. Without this, a half-dead sshd
    -- (auth stall, remote bash-s hang) locks the hub event loop indefinitely.
    local cmd = string.format(
        "timeout --kill-after=2 %d ssh -o ConnectTimeout=%d -o ServerAliveInterval=5 -o ServerAliveCountMax=2 -o BatchMode=yes -o StrictHostKeyChecking=accept-new %s 'bash -s' < %s > %s 2>&1; echo $? > %s.rc",
        SSH_HARD_TIMEOUT, SSH_TIMEOUT, shell_quote(ssh_host), shell_quote(spath),
        shell_quote(outpath), shell_quote(spath)
    )
    local t0 = monotonic()
    os.execute(cmd)
    local dt = monotonic() - t0
    local rc_f = io.open(spath .. ".rc", "r")
    local rc = -1
    if rc_f then
        local s = rc_f:read("*a") or ""
        s = s:match("^(%S+)") or ""
        rc = tonumber(s) or -1
        rc_f:close()
    end
    local out_f = io.open(outpath, "r")
    local output = out_f and out_f:read("*a") or ""
    if out_f then out_f:close() end
    os.remove(spath); os.remove(outpath); os.remove(spath .. ".rc")
    -- timeout(1) exits 124 on wall-clock expiry, 137 on SIGKILL. Surface it.
    if rc == 124 or rc == 137 then
        logreq("ssh HARD-TIMEOUT host=%s after=%.2fs rc=%d", ssh_host, dt, rc)
        return nil, string.format("ssh hard-timeout after %ds", SSH_HARD_TIMEOUT), rc
    end
    logreq("ssh host=%s elapsed=%.2fs rc=%d bytes=%d", ssh_host, dt, rc, #output)
    return output, nil, rc
end

-- ---- Health probe ------------------------------------------------------
--
-- Design notes:
--   - Probe is lmcp-only. SSH is NOT checked here: it's expensive (3-6s per
--     offline host) and the hub exists specifically to absorb lots of
--     offline hosts. Hosts with lmcp down but ssh up show as DOWN in the
--     health list, but actual remote_* calls still fall through to ssh
--     fallback correctly.
--   - Sticky DOWN cache with exponential backoff: a DOWN host is re-probed
--     at intervals that grow from PROBE_TTL_DOWN_MIN (default 60s) up to
--     PROBE_TTL_DOWN_MAX (default 900s). Prevents a sleeping fleet from
--     burning probe budget every health check.
--   - `remote_list_hosts` uses a parallel curl fan-out for all hosts at
--     once so wall-clock is bounded by PROBE_BUDGET (default 3s), not the
--     sum of per-host timeouts.

local function cache_fresh(s, now)
    if not s then return false end
    local ttl
    if s.up then
        ttl = PROBE_TTL_UP
    else
        ttl = math.min(PROBE_TTL_DOWN_MAX, PROBE_TTL_DOWN_MIN * (2 ^ (s.down_streak or 0)))
    end
    return (now - s.checked) < ttl
end

local function apply_probe_result(name, up, err, via, tool_count)
    local prev = status[name]
    local new_s = {
        checked = os.time(),
        up = up,
        via = up and (via or "lmcp") or nil,
        err = err,
        tool_count = tool_count,
        down_streak = up and 0 or ((prev and prev.down_streak or 0) + 1),
    }
    status[name] = new_s
    return new_s
end

-- Fallback single-host probe used only when a caller explicitly needs a
-- status refresh outside the parallel path (currently only
-- remote_list_hosts when a single host is looked up). lmcp-only.
local function probe(name, force)
    local b = backends[name]
    if not b then return { up = false, err = "unknown host" } end
    local s = status[name]
    if not force and cache_fresh(s, os.time()) then return s end
    if not b.lmcp_url then
        return apply_probe_result(name, false, "no lmcp url", nil, nil)
    end
    local result, err = jsonrpc_call(b.lmcp_url, b.token, "tools/list", {})
    if result and result.tools then
        return apply_probe_result(name, true, nil, "lmcp", #result.tools)
    end
    return apply_probe_result(name, false, "lmcp: " .. tostring(err), nil, nil)
end

-- Parallel lmcp probe for every backend with an lmcp_url, via a single
-- bash fan-out of curl calls. Total wall clock ≈ PROBE_BUDGET.
local function probe_all_parallel(force)
    local now = os.time()
    local need = {}
    for name, b in pairs(backends) do
        if b.lmcp_url and (force or not cache_fresh(status[name], now)) then
            need[#need+1] = b
        end
    end
    if #need == 0 then return end

    local script_parts = {}
    for _, b in ipairs(need) do
        local auth = b.token and (" -H 'Authorization: Bearer " .. b.token .. "'") or ""
        local url = b.lmcp_url:gsub("'", "'\\''")
        script_parts[#script_parts+1] = string.format(
            "(curl --max-time %d -s -o /dev/null -w '%s %%{http_code} %%{time_total}\\n' -X POST%s -H 'Content-Type: application/json' -d '{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"tools/list\",\"params\":{}}' '%s' || echo '%s ERR 0') &",
            PROBE_BUDGET, b.name, auth, url, b.name
        )
    end
    script_parts[#script_parts+1] = "wait"

    local t0 = monotonic()
    local p = io.popen(table.concat(script_parts, "\n"))
    local out = p and p:read("*a") or ""
    if p then p:close() end
    local dt = monotonic() - t0

    local seen = {}
    for line in out:gmatch("[^\n]+") do
        local name, code, t = line:match("^(%S+)%s+(%S+)%s+([%d%.]+)")
        if name then
            seen[name] = true
            local is_up = (code == "200")
            if is_up then
                apply_probe_result(name, true, nil, "lmcp", nil)
            else
                apply_probe_result(name, false, "lmcp code=" .. code, nil, nil)
            end
        end
    end
    -- Hosts with no output (fan-out error): mark DOWN
    for _, b in ipairs(need) do
        if not seen[b.name] then
            apply_probe_result(b.name, false, "probe fan-out missing", nil, nil)
        end
    end
    logreq("probe_all_parallel n=%d elapsed=%.2fs", #need, dt)
end

-- ---- Call-tool dispatcher ----------------------------------------------

-- `allow_ssh`: whether the tool has an SSH fallback path
-- `ssh_impl`: function(backend, args) -> output string, or nil + error
local function call_remote(tool, args, allow_ssh, ssh_impl)
    local t_start = monotonic()
    local host = args.host
    if type(host) ~= "string" or host == "" then
        logreq("tool=%s ERR missing-host", tool)
        return "Error: missing `host` parameter"
    end
    local b = backends[host]
    if not b then
        logreq("tool=%s host=%s ERR unknown-host", tool, host)
        return string.format("Error: unknown host %q (registry: %s)", host, CONF_PATH)
    end

    local errs = {}
    local via = nil

    -- Try lmcp first
    if b.lmcp_url then
        local args_pass = {}
        for k, v in pairs(args) do if k ~= "host" then args_pass[k] = v end end
        local result, err = jsonrpc_call(b.lmcp_url, b.token, "tools/call",
            { name = tool, arguments = args_pass })
        if result then
            via = "lmcp"
            logreq("tool=%s host=%s via=lmcp elapsed=%.2fs", tool, host, monotonic() - t_start)
            -- Propagate backend's content, extract first text block
            if type(result.content) == "table" and result.content[1] and result.content[1].text then
                local prefix = result.isError and "[lmcp isError] " or ""
                return prefix .. result.content[1].text
            end
            return json.encode(result)
        end
        errs[#errs+1] = "lmcp: " .. tostring(err)
    else
        errs[#errs+1] = "lmcp: no url configured"
    end

    -- Fallback to ssh
    if allow_ssh and ssh_impl and b.ssh_host then
        local out, serr = ssh_impl(b, args)
        if out ~= nil then
            logreq("tool=%s host=%s via=ssh elapsed=%.2fs", tool, host, monotonic() - t_start)
            return "[via ssh fallback]\n" .. out
        end
        errs[#errs+1] = "ssh: " .. tostring(serr)
    elseif allow_ssh and not b.ssh_host then
        errs[#errs+1] = "ssh: no host configured"
    end

    logreq("tool=%s host=%s FAIL elapsed=%.2fs err=%s", tool, host, monotonic() - t_start, table.concat(errs, " | "):sub(1, 200))
    return "Error: " .. table.concat(errs, " | ")
end

-- ---- SSH implementations for each fallback-capable tool ----------------

local function ssh_shell(b, a)
    if type(a.command) ~= "string" then return nil, "command required" end
    local cwd_prefix = ""
    if a.cwd and a.cwd ~= "" then
        cwd_prefix = "cd " .. shell_quote(a.cwd) .. " && "
    end
    local script = cwd_prefix .. a.command .. "\n"
    local out, err, rc = ssh_run_script(b.ssh_host, script)
    if err then return nil, err end
    -- ssh exits 255 when it couldn't connect/authenticate. Treat that as
    -- fallback-failed so the caller sees the combined lmcp+ssh errors.
    if rc == 255 then
        local line1 = (out:match("^([^\n]+)") or ""):gsub("%s+$", "")
        return nil, "ssh connect failed: " .. line1
    end
    return string.format("[rc=%d]\n%s", rc, out)
end

local function ssh_read_file(b, a)
    if type(a.path) ~= "string" then return nil, "path required" end
    local script = "cat -- " .. shell_quote(a.path) .. "\n"
    local out, err, rc = ssh_run_script(b.ssh_host, script)
    if err then return nil, err end
    if rc ~= 0 then return nil, "cat exit " .. rc .. ": " .. out:sub(1, 200) end
    return out
end

local function ssh_write_file(b, a)
    if type(a.path) ~= "string" or type(a.content) ~= "string" then
        return nil, "path and content required"
    end
    -- Emit a script that decodes content from base64, so no shell
    -- interpretation of the payload is possible. Lua stdlib has no base64;
    -- implement a minimal encoder inline.
    local b64_alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
    local function b64enc(data)
        local out = {}
        local pad = (3 - (#data % 3)) % 3
        local padded = data .. ("\0"):rep(pad)
        for i = 1, #padded, 3 do
            local a1, a2, a3 = padded:byte(i), padded:byte(i+1), padded:byte(i+2)
            local n = a1 * 65536 + a2 * 256 + a3
            out[#out+1] = b64_alphabet:sub(((n >> 18) & 63) + 1, ((n >> 18) & 63) + 1)
            out[#out+1] = b64_alphabet:sub(((n >> 12) & 63) + 1, ((n >> 12) & 63) + 1)
            out[#out+1] = b64_alphabet:sub(((n >>  6) & 63) + 1, ((n >>  6) & 63) + 1)
            out[#out+1] = b64_alphabet:sub(((n      ) & 63) + 1, ((n      ) & 63) + 1)
        end
        local s = table.concat(out)
        if pad > 0 then s = s:sub(1, -pad - 1) .. ("="):rep(pad) end
        return s
    end
    local payload = b64enc(a.content)
    local script = string.format(
        "base64 -d > %s <<'EOF_B64_PAYLOAD'\n%s\nEOF_B64_PAYLOAD\n",
        shell_quote(a.path), payload
    )
    local out, err, rc = ssh_run_script(b.ssh_host, script)
    if err then return nil, err end
    if rc ~= 0 then return nil, "write exit " .. rc .. ": " .. out:sub(1, 200) end
    return string.format("Written %d bytes to %s (via ssh)", #a.content, a.path)
end

local function ssh_list_dir(b, a)
    local path = (a and type(a.path) == "string" and a.path) or "."
    local script = "ls -1 -- " .. shell_quote(path) .. "\n"
    local out, err, rc = ssh_run_script(b.ssh_host, script)
    if err then return nil, err end
    if rc ~= 0 then return nil, "ls exit " .. rc .. ": " .. out:sub(1, 200) end
    return out
end

local function ssh_search_files(b, a)
    if type(a.pattern) ~= "string" then return nil, "pattern required" end
    local path = (a.path and a.path ~= "") and a.path or "/"
    local script = string.format(
        "find %s -name %s 2>/dev/null | head -200\n",
        shell_quote(path), shell_quote(a.pattern)
    )
    local out, err, rc = ssh_run_script(b.ssh_host, script)
    if err then return nil, err end
    return out
end

-- ---- Server setup ------------------------------------------------------

load_registry()
math.randomseed(os.time())

local server = lmcp.new(os.getenv("LMCP_NAME") or "hub-tools", {
    port = tonumber(os.getenv("LMCP_PORT") or arg[1]) or 8090,
    version = "0.5.4",
    conf = os.getenv("LMCP_HUB_CONF") or "/opt/herding/etc/lmcp-hub.conf",
})

local HOST_ARG = {
    type = "string",
    description = "Name of the backend host (see remote_list_hosts)",
}

server:tool("remote_list_hosts",
    "List all registered fleet hosts and their live status (lmcp vs ssh vs down).",
    { type = "object", properties = {
        force = { type = "boolean", description = "Force re-probe (bypass cache)", default = false },
    } },
    function(a)
        local force = a and a.force or false
        probe_all_parallel(force)
        local lines = {}
        local names = {}
        for n in pairs(backends) do names[#names+1] = n end
        table.sort(names)
        for _, n in ipairs(names) do
            local b = backends[n]
            local s = status[n] or { up = false, err = "no probe result" }
            local paths = {}
            if b.lmcp_url then paths[#paths+1] = "lmcp" end
            if b.ssh_host then paths[#paths+1] = "ssh" end
            lines[#lines+1] = string.format(
                "%-14s  %-6s  via=%-4s  paths=%s  %s",
                n,
                s.up and "UP" or "DOWN",
                tostring(s.via or "-"),
                table.concat(paths, ","),
                s.err and ("[" .. s.err .. "]") or ""
            )
        end
        return table.concat(lines, "\n")
    end
)

server:tool("remote_shell", "Run a shell command on a fleet host. lmcp-primary with ssh fallback.",
    { type = "object", properties = {
        host = HOST_ARG,
        command = { type = "string", description = "Shell command" },
        cwd = { type = "string", description = "Working directory" },
        timeout = { type = "integer", description = "Timeout (seconds)", default = 120 },
    }, required = { "host", "command" } },
    function(a) return call_remote("shell", a, true, ssh_shell) end
)

server:tool("remote_read_file", "Read a file from a fleet host.",
    { type = "object", properties = {
        host = HOST_ARG,
        path = { type = "string", description = "File path" },
    }, required = { "host", "path" } },
    function(a) return call_remote("read_file", a, true, ssh_read_file) end
)

server:tool("remote_write_file", "Write content to a file on a fleet host.",
    { type = "object", properties = {
        host = HOST_ARG,
        path = { type = "string" },
        content = { type = "string" },
    }, required = { "host", "path", "content" } },
    function(a) return call_remote("write_file", a, true, ssh_write_file) end
)

server:tool("remote_edit_file",
    "Literal-match edit on a fleet host. **Requires backend lmcp up** — no ssh fallback.",
    { type = "object", properties = {
        host = HOST_ARG,
        path = { type = "string" },
        old_string = { type = "string" },
        new_string = { type = "string" },
        replace_all = { type = "boolean", default = false },
    }, required = { "host", "path", "old_string", "new_string" } },
    function(a) return call_remote("edit_file", a, false, nil) end
)

server:tool("remote_shell_bg",
    "Launch a detached background command on a fleet host (Linux). Returns PID + log path immediately. Requires backend lmcp v0.5.2+.",
    { type = "object", properties = {
        host = HOST_ARG,
        command = { type = "string", description = "Shell command" },
        cwd = { type = "string" },
        log = { type = "string", description = "Log file path" },
    }, required = { "host", "command" } },
    function(a) return call_remote("shell_bg", a, false, nil) end
)

server:tool("remote_list_dir", "List directory entries on a fleet host.",
    { type = "object", properties = {
        host = HOST_ARG,
        path = { type = "string", default = "." },
    }, required = { "host" } },
    function(a) return call_remote("list_dir", a, true, ssh_list_dir) end
)

server:tool("remote_search_files", "find-by-pattern on a fleet host.",
    { type = "object", properties = {
        host = HOST_ARG,
        pattern = { type = "string" },
        path = { type = "string", default = "/" },
    }, required = { "host", "pattern" } },
    function(a) return call_remote("search_files", a, true, ssh_search_files) end
)

io.stderr:write(string.format("lmcp-hub starting on port %d with %d backends from %s\n",
    server.port, (function() local n = 0; for _ in pairs(backends) do n = n + 1 end; return n end)(), CONF_PATH))
server:run()
