-- router.lua — task classifier: meta / shell / AI.
-- See docs/PHASE0.md §5.
--
-- Pure function. Takes (line, config). Returns (kind, payload).
--   kind   : "meta" | "shell" | "ai"
--   payload: the (possibly stripped) line that the dispatcher should act on.
--
-- Empty / whitespace-only lines are returned as ("ai", ""); the repl loop
-- skips them before dispatching.

local M = {}

local function trim(s)
    return (s:gsub("^%s+", ""):gsub("%s+$", ""))
end

local function first_word(s)
    return s:match("^(%S+)") or ""
end

local function known_commands_set(config)
    local set = {}
    local list = config and config.shell and config.shell.known_commands or {}
    for _, c in ipairs(list) do set[c] = true end
    return set
end

-- §5.1 path-like: ./foo, ../foo, /usr/bin/foo, ~/foo, bare ~. Quoted /
-- escaped paths are intentionally out of scope in Phase 0. ~ is included
-- for symmetry with executor.maybe_chdir, which expands ~ on `cd ~/foo`.
local function path_like(token)
    return token            == "~"
        or token:sub(1, 1)  == "/"
        or token:sub(1, 2)  == "./"
        or token:sub(1, 2)  == "~/"
        or token:sub(1, 3)  == "../"
end

function M.classify(line, config)
    line = trim(line or "")
    if line == "" then return "ai", "" end

    -- meta: ":" prefix
    if line:sub(1, 1) == ":" then
        return "meta", line:sub(2)
    end

    -- shell explicit override: "$" prefix
    if line:sub(1, 1) == "$" then
        return "shell", trim(line:sub(2))
    end

    local first = first_word(line)
    local known = known_commands_set(config)

    -- known-command allowlist
    if known[first] then return "shell", line end

    -- path-like first token
    if path_like(first) then return "shell", line end

    -- everything else -> AI
    return "ai", line
end

return M