-- pandoc-aware object dumper

-- helper function to return a sensible typename
-- XXX is there a better way of doing this? using metatables?
local function getTypename(value)
    local typ = type(value)
    if typ == 'table' and value.tag and value.t then
        return value.tag
    elseif typ == 'userdata' then
        if value.tag and value.t then
            return value.tag
        else
            -- e.g., Attributes is userdata but doesn't have tag and t
            return typ
        end
    else
        return typ
    end
end

-- helper function
-- note: don't use anything from the pandoc module (so can test standalone)
-- XXX should detect repetition/recursion
-- XXX would like maxlen logic to apply at all levels? but not trivial
local function helper(prefix, value, maxlen, level, add)
    local buffer = {}
    if prefix == nil then prefix = '' end
    if level == nil then level = 0 end
    if add == nil then add = function(item) table.insert(buffer, item) end end
    local indent = maxlen and '' or ('  '):rep(level)
    local typename = getTypename(value)
    local typ = (({boolean=1, number=1, string=1, table=1, userdata=1})
                 [typename] and '' or typename)
    if ({table=1, userdata=1})[type(value)] then
        local numKeys, lastKey = 0, nil
        for key, val in pairs(value) do
            -- pandoc >= 2.15 includes 'tag', nil values and functions
            if key ~= 'tag' and val and type(val) ~= 'function' then
                numKeys = numKeys + 1
                lastKey = key
            end
        end
        if numKeys == 0 then
            -- XXX this wouldn't be needed with proper maxlen handling
            value = '{}'
        elseif numKeys == 1 and lastKey == 'content' then
            typ = string.format('content: %s', typ)
            value = value.content
        elseif numKeys == 1 and lastKey == 'text' and typename == 'Str' then
            typename = 'string'
            typ = 'Str text:'
            value = value.text
        end
    end
    local presep = #prefix > 0 and ' ' or ''
    local typsep = #typ > 0 and ' ' or ''
    local valtyp = type(value)
    if ({boolean=1, number=1, string=1})[valtyp] then
        local fmt = typename == 'string' and '%q' or '%s'
        add(string.format('%s%s%s%s%s' .. fmt, indent, prefix, presep,
                          typ, typsep, value))
    elseif ({table=1, userdata=1})[valtyp] then
        add(string.format('%s%s%s%s%s{', indent, prefix, presep, typ, typsep))
        -- Attr and Attr.attributes have both numeric and string keys, so
        -- ignore the numeric ones (no longer the case for pandoc >= 2.15?)
        if prefix ~= 'attributes:' and typ ~= 'Attr' then
            for i, val in ipairs(value) do
                local pre = maxlen and i > 1 and ', ' or ''
                local text = helper(string.format('%s[%s]', pre, i), val,
                                    maxlen, level + 1, add)
            end
        end
        local first = true
        for key, val in pairs(value) do
            -- pandoc >= 2.15 includes 'tag'
            if not tonumber(key) and key ~= 'tag' then
                local pre = maxlen and not first and ', ' or ''
                local text = helper(string.format('%s%s:', pre, key), val,
                                    maxlen, level + 1, add)
            end
            first = false
        end
        add(string.format('%s}', indent))
    end
    return table.concat(buffer, maxlen and '' or '\n')
end

local function dump(value, maxlen)
    if maxlen == nil then maxlen = 70 end
    local text = helper(nil, value, maxlen)
    if #text > maxlen then
        text = helper(nil, value, nil)
    end
    return text
end

return dump