Module:Sandbox/extract database report

--- Extract values from Database report footers.
---
--- Reads saved page wikitext and matches
--- "{{Database report/footer|...}}" directly.
--- Supports "count", "last_updated", and
--- "query_runtime".
---
--- Arg 1 is the page title. Arg 2 is the
--- optional footer index. Default is 1.
--- Negative values count from the end.

require("strict")

local getArgs = require("Module:Arguments").getArgs
local p = {}

---@alias IndexInput integer|string|nil

---@param value unknown
---@return string
local function trim(value)
    if type(value) ~= "string" then
        return ""
    end
    return mw.text.trim(value)
end

---@param message string
---@return string
local function format_error(message)
    return string.format(
        '<strong class="error">Database report extract: %s</strong>',
        message
    )
end

---@param raw IndexInput
---@return integer
local function parse_index(raw)
    local parsed = tonumber(trim(raw))
    if parsed == nil then
        return 1
    end

    parsed = math.floor(parsed)

    if parsed == 0 then
        return 1
    end

    return parsed
end

---@param requested integer
---@param total integer
---@return integer|nil
local function resolve_index(requested, total)
    if total < 1 then
        return nil
    end

    if requested < 0 then
        requested = total + requested + 1
    end

    if requested < 1 or requested > total then
        return nil
    end

    return requested
end

---@param title_text string
---@return string|nil, string|nil
local function get_page_text(title_text)
    local title = mw.title.new(title_text)

    if title == nil then
        return nil, "invalid page title"
    end

    local content = title:getContent()
    if content == nil then
        return nil, "page does not exist or has no readable content"
    end

    return content, nil
end

---@param page_text string
---@return string[]
local function find_footers(page_text)
    local footers = {}

    for footer in page_text:gmatch(
        "{{Database report/footer|[^{}]-}}"
    ) do
        table.insert(footers, footer)
    end

    return footers
end

---@param footer string
---@param key string
---@return string|nil
local function extract_param(footer, key)
    local pattern = "|" .. key .. "=([^|}]-)[|}]"
    local value = footer:match(pattern)

    if value == nil or value == "" then
        return nil
    end

    return value
end

---@param key string
---@param args table
---@return string
local function get_value(key, args)
    local title_text = trim(args[1])
    if title_text == "" then
        return format_error("missing page title")
    end

    local requested_index = parse_index(args[2])
    local page_text, read_error = get_page_text(title_text)

    if page_text == nil then
        return format_error(read_error or "unable to read page")
    end

    local footers = find_footers(page_text)
    if #footers == 0 then
        return format_error("no Database report/footer found")
    end

    local resolved_index = resolve_index(requested_index, #footers)
    if resolved_index == nil then
        return format_error(string.format(
            "report index %d is out of range; found %d footer(s)",
            requested_index,
            #footers
        ))
    end

    local value = extract_param(footers[resolved_index], key)
    if value == nil then
        return format_error(string.format(
            "footer %d has no %s parameter",
            resolved_index,
            key
        ))
    end

    return value
end

---@param frame table
---@return string
function p.count(frame)
    local args = getArgs(frame)
    return get_value("count", args)
end

---@param frame table
---@return string
function p.last_updated(frame)
    local args = getArgs(frame)
    return get_value("last_updated", args)
end

---@param frame table
---@return string
function p.query_runtime(frame)
    local args = getArgs(frame)
    return get_value("query_runtime", args)
end

return p