-- ffi/readline.lua — GNU readline binding.
-- Phase 0: readline + add_history + EOF handling.
-- Phase 1: custom key bindings via rl_bind_keyseq.
-- See docs/PHASE0.md §9 and docs/PHASE1.md §7.

local ffi = require("ffi")

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

typedef int (*rl_command_func_t)(int, int);
int rl_bind_keyseq(const char *keyseq, rl_command_func_t function);
]]

-- 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

-- Bind `seq` (e.g. "\\C-n") to a Lua function that runs when the user types
-- that key sequence at the readline prompt. The Lua fn takes no arguments
-- (readline passes count + key, but Phase 1 consumers don't need them).
-- Callback trampolines are pinned in module-local state so they outlive the
-- M.bind call — readline retains the function pointer indefinitely.
local _bound = {}

function M.bind(seq, fn)
    if _bound[seq] then
        _bound[seq]:free()
    end
    local cb = ffi.cast("rl_command_func_t", function(_count, _key)
        local ok, err = pcall(fn)
        if not ok then
            io.stderr:write("ffi/readline bind handler error: " .. tostring(err) .. "\n")
        end
        return 0
    end)
    _bound[seq] = cb
    return rl.rl_bind_keyseq(seq, cb) == 0
end

return M