-- broker.lua — llama.cpp HTTP client.
-- Phase 0: blocking POST via ffi/curl + vendored dkjson; the response is read
-- to completion and returned as a Lua string. SSE streaming wired in Phase 1.
-- See docs/PHASE0.md §6.

local curl = require("ffi.curl")
local json = require("dkjson")

local M = {}

local function build_headers(model_cfg)
    local h = { "Content-Type: application/json" }
    if model_cfg.key_env then
        local key = os.getenv(model_cfg.key_env)
        if key and key ~= "" then
            h[#h + 1] = "Authorization: Bearer " .. key
        end
    end
    return h
end

-- Send a /v1/chat/completions request.
--   model_cfg : entry from config.models — { endpoint, model, temperature,
--               [key_env], [timeout_ms] }
--   messages  : ordered list of { role = ..., content = ... }, system
--               prompt already prepended (context:to_messages handles that).
-- Returns:
--   assistant_content_string         on success
--   nil, errmsg                       on transport / decode / API failure
function M.chat(model_cfg, messages)
    if not (model_cfg and model_cfg.endpoint and model_cfg.model) then
        return nil, "broker.chat: model_cfg.endpoint and .model are required"
    end

    local url = model_cfg.endpoint:gsub("/+$", "") .. "/v1/chat/completions"
    local body = json.encode({
        model       = model_cfg.model,
        messages    = messages,
        stream      = false,
        temperature = model_cfg.temperature or 0.2,
    })
    local headers    = build_headers(model_cfg)
    local timeout_ms = model_cfg.timeout_ms or 60000

    local resp, err = curl.post(url, body, headers, timeout_ms)
    if not resp then return nil, "transport: " .. tostring(err) end

    local doc, _, derr = json.decode(resp)
    if not doc then
        return nil, "decode: " .. tostring(derr) .. " (raw: " .. resp:sub(1, 200) .. ")"
    end

    -- OpenAI-style error envelope: { error: { message, type, ... } }
    if doc.error then
        local m = (type(doc.error) == "table" and doc.error.message) or tostring(doc.error)
        return nil, "api: " .. m
    end

    local choice  = doc.choices and doc.choices[1]
    local msg     = choice and choice.message
    local content = msg and msg.content
    if type(content) ~= "string" then
        return nil, "broker.chat: no choices[1].message.content in response"
    end

    return content
end

return M