local PageTitleSimilar = { suite  = "PageTitleSimilar",
                           serial = "2025-02-11",
                           item   = 0 }
--[==[
Check whether similar page name is existing
]==]
local Failsafe = PageTitleSimilar
local THIS     = { }



local fault = function ( alert )
    -- Format error message
    -- Precondition:
    --     alert   -- string, with message
    -- Postcondition:
    --     Returns string
    local e = mw.html.create( "span" )
                :addClass( "error" )
                :wikitext( string.format( "%s * %s",
                                          PageTitleSimilar.suite,
                                          alert ) )
    return tostring( e )
end -- fault()



local find = function ( ask )
    -- Check whether page title exists in this namespace
    -- Precondition:
    --     ask   -- string, with page title
    -- Postcondition:
    --     Returns true, if existing
    --     THIS.title is the title of an existing page
    local t = mw.title.new( ask, THIS.ns )
    local r
    if t then
        r = t.exists
        if r then
            THIS.title = t
        end
    end
    return r
end -- find()



local found = function ( apply )
    -- Communicate match by transclusion
    -- Precondition:
    --     apply   -- string, with message type
    --                        -- Typogr
    --                        -- URL
    --     THIS.title has been defined
    -- Postcondition:
    --     Returns string
    local source = "source" .. apply
    local shift  = THIS.JSON[ source ]
    local r
    if type( shift ) == "string" then
        local t = mw.title.new( shift )
        if t and t.exists then
            local params = { ["1"] = THIS.title.prefixedText }
            r = THIS.frame:expandTemplate{ title = t,
                                           args  = params }
        end
    end
    if not r then
        r = fault( "missing transclusion for " .. source )
    end
    return r
end -- found()



local fraction = function ()
    -- Try URL completion when common special chars were truncated
    -- Postcondition:
    --     Returns string, or not
    local s = THIS.self
    local r
    if s:find( "(", 1, true ) then
        find( s .. ")" )
    end
    if not THIS.title then
        local shift = s .. "."
        if not find( shift ) then
            shift = s .. "?"
            find( shift )
        end
    end
    if THIS.title then
        r = found( "URL" )
    end
    return r
end -- fraction()



local further = function ()
    -- Try improvements by typographical chars
    -- Postcondition:
    --     Returns string, or not
    local rep = THIS.JSON.replace
    local r
    if type( rep ) == "table" then
        local s = THIS.self
        local shift
        for k, v in pairs( rep ) do
            if type( v[ 1 ] ) == "string"  and
               type( v[ 2 ] ) == "string" then
                shift = mw.ustring.gsub( s, v[ 1 ], v[ 2 ] )
                if shift ~= s then
                    if find( shift ) then
                        r = found( "Typogr" )
                        break -- for k, v
                    else
                        s = shift
                    end
                end
            else
                r = fault( string.format( "replace[%s]", k ) )
                break -- for k, v
            end
        end -- for k, v
    end
    return r
end -- further()



Failsafe.failsafe = function ( atleast )
    -- Retrieve versioning and check for compliance
    -- Precondition:
    --     atleast  -- string, with required version
    --                         or wikidata|item|~|@ or false
    -- Postcondition:
    --     Returns  string  -- with queried version/item, also if problem
    --              false   -- if appropriate
    -- 2024-03-01
    local since  = atleast
    local last   = ( since == "~" )
    local linked = ( since == "@" )
    local link   = ( since == "item" )
    local r
    if last  or  link  or  linked  or  since == "wikidata" then
        local item = Failsafe.item
        since = false
        if type( item ) == "number"  and  item > 0 then
            local suited = string.format( "Q%d", item )
            if link then
                r = suited
            else
                local entity = mw.wikibase.getEntity( suited )
                if type( entity ) == "table" then
                    local seek = Failsafe.serialProperty or "P348"
                    local vsn  = entity:formatPropertyValues( seek )
                    if type( vsn ) == "table"  and
                       type( vsn.value ) == "string"  and
                       vsn.value ~= "" then
                        if last  and  vsn.value == Failsafe.serial then
                            r = false
                        elseif linked then
                            if mw.title.getCurrentTitle().prefixedText
                               ==  mw.wikibase.getSitelink( suited ) then
                                r = false
                            else
                                r = suited
                            end
                        else
                            r = vsn.value
                        end
                    end
                end
            end
        elseif link then
            r = false
        end
    end
    if type( r ) == "nil" then
        if not since  or  since <= Failsafe.serial then
            r = Failsafe.serial
        else
            r = false
        end
    end
    return r
end -- Failsafe.failsafe()



-- Export
local p = { }

p.f = function ( frame )
    local source = frame.args[ 1 ]
    local r, scream
    if source then
        local lucky
        lucky, THIS.JSON = pcall( mw.loadJsonData, source )
        if lucky then
            local t = mw.title.getCurrentTitle()
            THIS.frame = frame
            THIS.ns    = t.ns
            THIS.self  = t.prefixedText
            if frame.args.URL == "1" then
                r = fraction()
            end
            if not r then
                r = further()
            end
        else
            scream = "no valid JSON found: " .. mw.text.nowiki( source )
        end
    else
        scream = "invoked without JSON"
    end
    if scream then
        r = fault( scream )
    end
    return r or ""
end    -- p.f



p.failsafe = function ( frame )
    -- Versioning interface
    local s = type( frame )
    local since
    if s == "table" then
        since = frame.args[ 1 ]
    elseif s == "string" then
        since = frame
    end
    if since then
        since = mw.text.trim( since )
        if since == "" then
            since = false
        end
    end
    return Failsafe.failsafe( since )  or  ""
end -- p.failsafe

return p