-- executor.lua — command execution.
-- Phase 0: io.popen with stderr merged. PTY (forkpty) lands in Phase 1.
-- `cd` is intercepted before popen and routed through libc.chdir so the
-- working directory persists across calls (popen forks; cd inside it would
-- otherwise be discarded). See docs/PHASE0.md §6, §7.

local libc = require("ffi.libc")

local M = {}

-- LuaJIT 2.1's io.popen():close() returns only `true` (Lua 5.1 ABI) — it
-- does not surface the child exit status. Recover it via a sentinel echo
-- appended after the command. Phase 1's PTY work will wire waitpid via FFI
-- and replace this hack.
local EXIT_SENTINEL = "__AISH_EXIT_4F8E91__"

-- Execute a shell command.
-- Returns: (output_string, exit_code).
-- exit_code == 0 on success; non-zero on failure; -1 on no-output / sentinel-
-- parse failure (popen failed, empty cmd, shell parse error, sentinel collision).
function M.exec(cmd)
    if not cmd or cmd:match("^%s*$") then
        return "(empty command)", -1
    end
    local wrapped = string.format("(%s) 2>&1; echo %s$?", cmd, EXIT_SENTINEL)
    local handle, err = io.popen(wrapped, "r")
    if not handle then return ("popen failed: " .. tostring(err)), -1 end
    local output = handle:read("*a") or ""
    handle:close()

    local body, code = output:match("^(.-)" .. EXIT_SENTINEL .. "(%-?%d+)%s*$")
    if code then return body, tonumber(code) end
    if output == "" then
        return "(no output — possible shell parse error)", -1
    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