-- ffi/curl.lua — libcurl easy interface binding.
-- Phase 0: blocking POST with header list and response capture into Lua string.
-- Phase 1: M.post_sse for incremental Server-Sent-Events streaming. Reuses the
-- same WRITEFUNCTION hook; parses `data: ...\n\n` events out of the chunk
-- stream and invokes the caller's on_event(data) per event. JSON decode and
-- OpenAI-shape interpretation stay in broker.lua (this module is HTTP-only).
-- See docs/PHASE0.md §6 and docs/PHASE1.md §4.

local ffi = require("ffi")

ffi.cdef[[
typedef void CURL;

struct curl_slist {
    char *data;
    struct curl_slist *next;
};

CURL *curl_easy_init(void);
void  curl_easy_cleanup(CURL *handle);
int   curl_easy_perform(CURL *handle);
const char *curl_easy_strerror(int code);

struct curl_slist *curl_slist_append(struct curl_slist *list, const char *string);
void               curl_slist_free_all(struct curl_slist *list);

int   curl_easy_setopt(CURL *handle, int option, ...);
int   curl_easy_getinfo(CURL *handle, int info, ...);
]]

-- libcurl-dev's unversioned `libcurl.so` symlink isn't assumed; fall back to
-- versioned sonames so a runtime-only host (Debian without -dev) just works.
local function load_curl()
    local errs = {}
    for _, name in ipairs({"curl", "curl.so.4", "curl-gnutls.so.4"}) do
        local ok, lib = pcall(ffi.load, name)
        if ok then return lib end
        errs[#errs+1] = name .. ": " .. tostring(lib)
    end
    error("libcurl not loadable: " .. table.concat(errs, "; "))
end

local C = load_curl()

-- CURLoption codes from curl/curl.h. The bases are:
--   CURLOPTTYPE_LONG          = 0
--   CURLOPTTYPE_OBJECTPOINT   = 10000
--   CURLOPTTYPE_FUNCTIONPOINT = 20000
local OPT = {
    URL            = 10002,
    POST           = 47,
    POSTFIELDS     = 10015,
    HTTPHEADER     = 10023,
    WRITEFUNCTION  = 20011,
    NOSIGNAL       = 99,
    TIMEOUT_MS     = 155,
    USERAGENT      = 10018,
    FAILONERROR    = 45,
}

-- Variadic FFI calls demand explicit per-argument types. Pre-cast setopt to
-- the three concrete signatures Phase 0 needs; bypasses libffi-flavoured
-- variadic dispatch entirely.
local setopt_str  = ffi.cast("int(*)(void*, int, const char*)", C.curl_easy_setopt)
local setopt_long = ffi.cast("int(*)(void*, int, long)",        C.curl_easy_setopt)
local setopt_ptr  = ffi.cast("int(*)(void*, int, void*)",       C.curl_easy_setopt)

-- curl_easy_getinfo is variadic too. The Phase 2 caller only needs the
-- CURLINFO_LONG family (HTTP response code); pre-cast to that signature.
-- CURLINFO_RESPONSE_CODE = CURLINFO_LONG (0x200000) + 2 = 2097154.
local getinfo_long = ffi.cast("int(*)(void*, int, long*)", C.curl_easy_getinfo)
local INFO_RESPONSE_CODE = 2097154

local function get_response_code(handle)
    local out = ffi.new("long[1]")
    if getinfo_long(handle, INFO_RESPONSE_CODE, out) == 0 then
        return tonumber(out[0])
    end
    return 0  -- 0 = no response (e.g. couldn't connect)
end

local M = {}

-- POST `body` to `url` with `headers` (list of "Name: value" strings) and an
-- optional `timeout_ms`.
-- Returns:
--   body, status_code   on transport success — body is the raw response
--                       string (may be empty); status_code is the HTTP
--                       response code (2xx success, 4xx/5xx surface as
--                       transport-level failure for callers that care,
--                       e.g. mcp.lua treating 401 as auth failure).
--                       FAILONERROR is intentionally NOT set so the body
--                       is observable on non-2xx (lmcp's 401 returns a
--                       non-JSON-RPC body that callers need to recognise).
--   nil, errmsg         on libcurl-level failure (non-zero CURLcode)
-- Phase 1 callers reading only the first slot stay correct: success
-- returns truthy body, failure returns nil — same disjunction as before.
function M.post(url, body, headers, timeout_ms)
    local handle = C.curl_easy_init()
    if handle == nil then return nil, "curl_easy_init returned NULL" end

    local chunks = {}
    local write_cb = ffi.cast(
        "size_t(*)(char*, size_t, size_t, void*)",
        function(ptr, size, nmemb, _)
            local n = tonumber(size) * tonumber(nmemb)
            chunks[#chunks+1] = ffi.string(ptr, n)
            return n
        end)

    local slist = nil
    for _, h in ipairs(headers or {}) do
        slist = C.curl_slist_append(slist, h)
    end

    setopt_str (handle, OPT.URL,            url)
    setopt_long(handle, OPT.POST,           1)
    setopt_str (handle, OPT.POSTFIELDS,     body)
    setopt_ptr (handle, OPT.HTTPHEADER,     slist)
    setopt_ptr (handle, OPT.WRITEFUNCTION,  write_cb)
    setopt_long(handle, OPT.NOSIGNAL,       1)
    setopt_str (handle, OPT.USERAGENT,      "aish/0.0 (luajit-ffi)")
    if timeout_ms then
        setopt_long(handle, OPT.TIMEOUT_MS, timeout_ms)
    end

    local rc = C.curl_easy_perform(handle)
    local result, status, err
    if rc == 0 then
        result = table.concat(chunks)
        status = get_response_code(handle)
    else
        err = ffi.string(C.curl_easy_strerror(rc))
    end

    C.curl_easy_cleanup(handle)
    if slist ~= nil then C.curl_slist_free_all(slist) end
    write_cb:free()

    if rc == 0 then return result, status end
    return nil, err
end

-- POST `body` to `url` with `headers`, streaming Server-Sent-Events back.
-- For each complete `data: ...\n\n` event, `on_event(data_string)` is invoked
-- synchronously from within the WRITEFUNCTION callback. The caller decides
-- what to do with the payload (broker.lua decodes JSON, extracts the OpenAI
-- delta.content). `[DONE]` sentinels and `:` comment lines are passed
-- through as-is to on_event (broker filters them).
-- Returns:
--   true             stream completed successfully (HTTP 2xx, perform OK)
--   nil, errmsg      libcurl failure (non-zero CURLcode); FAILONERROR is set
--                    so non-2xx surfaces as a transport error rather than a
--                    silent garbage-into-the-parser scenario.
function M.post_sse(url, body, headers, on_event, timeout_ms)
    local handle = C.curl_easy_init()
    if handle == nil then return nil, "curl_easy_init returned NULL" end

    -- SSE parse state: buffer holds incomplete tail between callback deliveries.
    local buffer = ""
    local cb_error = nil

    local write_cb = ffi.cast(
        "size_t(*)(char*, size_t, size_t, void*)",
        function(ptr, size, nmemb, _)
            local n = tonumber(size) * tonumber(nmemb)
            -- pcall-wrap so a Lua error in on_event (or in the parse loop)
            -- doesn't propagate across the FFI callback boundary — LuaJIT
            -- documents that as process-fatal. Surface via cb_error and let
            -- curl keep draining (return n) so we can report after perform.
            local ok, err = pcall(function()
                buffer = buffer .. ffi.string(ptr, n)
                while true do
                    local b = buffer:find("\n\n", 1, true)
                    if not b then break end
                    local event = buffer:sub(1, b - 1)
                    buffer = buffer:sub(b + 2)

                    local data_parts = {}
                    for line in (event .. "\n"):gmatch("([^\n]*)\n") do
                        if line:sub(1, 1) == ":" then
                            -- SSE keepalive comment; ignore.
                        elseif line:sub(1, 6) == "data: " then
                            data_parts[#data_parts + 1] = line:sub(7)
                        elseif line:sub(1, 5) == "data:" then
                            data_parts[#data_parts + 1] = line:sub(6)
                        end
                    end
                    if #data_parts > 0 then
                        on_event(table.concat(data_parts, "\n"))
                    end
                end
            end)
            if not ok and not cb_error then cb_error = err end
            return n
        end)

    local slist = nil
    for _, h in ipairs(headers or {}) do
        slist = C.curl_slist_append(slist, h)
    end

    setopt_str (handle, OPT.URL,            url)
    setopt_long(handle, OPT.POST,           1)
    setopt_str (handle, OPT.POSTFIELDS,     body)
    setopt_ptr (handle, OPT.HTTPHEADER,     slist)
    setopt_ptr (handle, OPT.WRITEFUNCTION,  write_cb)
    setopt_long(handle, OPT.NOSIGNAL,       1)
    setopt_long(handle, OPT.FAILONERROR,    1)
    setopt_str (handle, OPT.USERAGENT,      "aish/0.0 (luajit-ffi)")
    if timeout_ms then
        setopt_long(handle, OPT.TIMEOUT_MS, timeout_ms)
    end

    local rc = C.curl_easy_perform(handle)
    local err
    if rc ~= 0 then err = ffi.string(C.curl_easy_strerror(rc)) end

    -- End-of-stream flush: the final event may lack a trailing \n\n if the
    -- server closed the connection right after writing the last data: line
    -- (some llama.cpp builds, and any plain HTTP/1.0 close-on-EOF feed).
    -- Parse any remaining buffer content as one last event. Same pcall shield.
    if rc == 0 and #buffer > 0 then
        local ok, perr = pcall(function()
            local data_parts = {}
            for line in (buffer .. "\n"):gmatch("([^\n]*)\n") do
                if line:sub(1, 6) == "data: " then
                    data_parts[#data_parts + 1] = line:sub(7)
                elseif line:sub(1, 5) == "data:" then
                    data_parts[#data_parts + 1] = line:sub(6)
                end
            end
            if #data_parts > 0 then on_event(table.concat(data_parts, "\n")) end
        end)
        if not ok and not cb_error then cb_error = perr end
    end

    C.curl_easy_cleanup(handle)
    if slist ~= nil then C.curl_slist_free_all(slist) end
    write_cb:free()

    if cb_error then return nil, "callback: " .. tostring(cb_error) end
    if rc == 0   then return true end
    return nil, err
end

return M