-- executor.lua — command execution.
-- Phase 1: forkpty via ffi/pty. Replaces Phase 0's io.popen + sentinel-echo
-- exit-code workaround; vim/less/htop now work because the child runs on a
-- real PTY. `cd` interception is unchanged (still libc.chdir per §3, §7).
-- See docs/PHASE0.md §7 and docs/PHASE1.md §5.

local libc = require("ffi.libc")
local pty  = require("ffi.pty")

local M = {}

-- Execute a shell command.
-- Returns: (output_string, exit_code).
--   0       success
--   1..255  child exited with that status
--   128+N   child killed by signal N (bash convention)
--   -1      forkpty / spawn / wait failure
function M.exec(cmd)
    if not cmd or cmd:match("^%s*$") then
        return "(empty command)", -1
    end

    local sess, err = pty.spawn(cmd)
    if not sess then
        return "(pty.spawn failed: " .. tostring(err) .. ")", -1
    end

    -- Drain until the child closes its end. PTY combines stdout+stderr
    -- on the master fd (no 2>&1 needed); CR LF gets normalized below.
    local chunks = {}
    while true do
        local data, n = sess:read()
        if not data then break end
        if n == 0 then break end
        chunks[#chunks + 1] = data
    end

    local kind, code = sess:wait()
    sess:close()

    -- PTY line discipline emits \r\n for every \n the child writes; collapse
    -- back to \n so the Phase 0 caller contract ("output uses \n separators")
    -- still holds.
    local output = table.concat(chunks):gsub("\r\n", "\n")

    if kind == "exit"   then return output, code         end
    if kind == "signal" then return output, 128 + code   end
    return output, -1
end

-- Intercept and apply `cd <path>` (or bare `cd` -> $HOME) without forking.
-- Returns:
--   nil          : the command is not a `cd` (caller falls through to exec)
--   true         : it was a cd, libc.chdir succeeded
--   false, err   : it was a cd, libc.chdir failed with errmsg
function M.maybe_chdir(cmd)
    local rest = cmd:match("^%s*cd%s*$") and ""
              or cmd:match("^%s*cd%s+(.+)$")
    if not rest then return nil end

    local target = rest:match("^%s*(.-)%s*$") or ""

    -- Phase 0: no $OLDPWD support, so `cd -` is not handled.
    if target == ""  then target = os.getenv("HOME") or "/" end
    if target == "~" then target = os.getenv("HOME") or "/" end
    if target:sub(1, 2) == "~/" then
        target = (os.getenv("HOME") or "") .. target:sub(2)
    end

    return libc.chdir(target)
end

-- Extract `CMD: ` lines from an assistant response per the §6 broker contract.
-- The "CMD: " prefix is a §3 substrate invariant: exact prefix, single space,
-- start-of-line only. Leading whitespace before CMD: does NOT match.
function M.extract_cmd_lines(text)
    local cmds = {}
    for line in (text or ""):gmatch("[^\n]+") do
        local cmd = line:match("^CMD: (.*)$")
        -- Skip whitespace-only / empty bodies; "CMD: " alone is degenerate.
        if cmd and cmd:match("%S") then cmds[#cmds + 1] = cmd end
    end
    return cmds
end

return M