-- ffi/readline.lua — GNU readline binding.
-- Phase 0: readline + add_history + EOF handling. Phase 1: custom key bindings.
-- See docs/PHASE0.md §9.

local ffi = require("ffi")

ffi.cdef[[
char *readline(const char *prompt);
void  add_history(const char *line);
void  free(void *ptr);
]]

-- libreadline-dev (which ships the unversioned `libreadline.so` symlink) is
-- not assumed to be installed on the runtime host; fall back to versioned
-- sonames so a base Debian/Arch with just libreadline runtime works.
local function load_readline()
    local errs = {}
    for _, name in ipairs({"readline", "readline.so.8", "readline.so.7"}) do
        local ok, lib = pcall(ffi.load, name)
        if ok then return lib end
        errs[#errs+1] = name .. ": " .. tostring(lib)
    end
    error("libreadline not loadable: " .. table.concat(errs, "; "))
end

local rl = load_readline()
local C  = ffi.C

local M = {}

-- Read one line of input.
-- Returns:
--   string : the line (no trailing newline)
--   nil    : EOF (Ctrl-D on empty line)
function M.readline(prompt)
    local cstr = rl.readline(prompt)
    if cstr == nil then return nil end
    local s = ffi.string(cstr)
    C.free(cstr)
    return s
end

-- Append a non-empty line to readline's in-memory history.
function M.add_history(line)
    if line and #line > 0 then
        rl.add_history(line)
    end
end

return M