local M = {}

---Collect formatter names from a single `formatters_by_ft` entry.
---
---A conform filetype formatter can be any of:
---  * a list of formatter names, optionally followed by string-keyed format
---    options (e.g. `{ "stylua", lsp_format = "fallback" }`)
---  * a function `fun(bufnr): string[]`, used by the "run the first available
---    formatter" recipe
---  * the legacy nested list `{ { "prettierd", "prettier" } }`
---
---Only the array part of the table is traversed, so format options such as
---`lsp_format` and `stop_after_first` are ignored.
---@param value any
---@param out table<string, boolean>
local function collect_entry(value, out)
    local list = value
    if type(list) == "function" then
        -- A function may depend on a buffer and/or on run-time availability.
        -- We don't have a buffer to pass here, so evaluate it best-effort and
        -- silently skip it when it cannot be called without one.
        local ok, result = pcall(list)
        if not ok or type(result) ~= "table" then
            return
        end
        list = result
    end

    if type(list) ~= "table" then
        return
    end

    for _, formatter in ipairs(list) do
        if type(formatter) == "table" then
            -- Legacy "run the first available formatter" syntax.
            collect_entry(formatter, out)
        elseif type(formatter) == "string" then
            out[formatter] = true
        end
    end
end

---List every formatter configured in conform's `formatters_by_ft`.
---
---Understands all `formatters_by_ft` shapes supported by conform, including
---functions returning a list and the legacy nested "run the first available"
---syntax.
---@return string[] names Sorted, de-duplicated formatter names.
function M.configured()
    local out = {}
    for _, entry in pairs(require("conform").formatters_by_ft or {}) do
        collect_entry(entry, out)
    end

    local names = {}
    for name in pairs(out) do
        names[#names + 1] = name
    end
    table.sort(names)
    return names
end

return M