local lexer = assert(require((... and select('1', ...):match('.+%.') or '')..'lua_lang'), '[assert-gooder]: Could not load vital library: lua_lang')

--------------------------------------------------------------------------------

local EXPECTED_GLOBAL = { -- TODO: Expand with other functions.
    ['type']     = 'function',
    ['tonumber'] = 'function',
    ['math']     = 'table',
}

--------------------------------------------------------------------------------

local function get_value_of_string (string_str)
    if string_str:sub(1, 1) == '"' or string_str:sub(1, 1) == '\'' then
        return string_str:sub(2, -2)
    end
    assert(false)
end

local CONSTANT_VALUE_TOKEN = {
    NUMBER  = tonumber,
    STRING  = get_value_of_string,
    TRUE    = function() return true    end,
    FALSE   = function() return false   end,
    NIL     = function() return nil     end
}

local function get_variable (var_name, info)
    --
    assert(type(var_name) == 'string')
    assert(type(info)     == 'table')

    -- Local
    if info.locals[var_name] then
        local var_info = info.locals[var_name]
        return var_info[1], var_info[2] and ('argument #'..var_info[3]) or 'local', info.name or var_info[2] and ''
    end

    -- Up-value
    local index = 0
    repeat
        index = index + 1
        local name, val  =  debug.getupvalue(info.func, index)
        if name == var_name then  return val, 'upvalue'  end
    until not name

    -- Global
    local env = getfenv(info.func)[var_name]
    return env, 'global'
end

--[[
local function get_value_from_lvalue (lvalue, info)
    assert(type(lvalue) == 'table')
    assert(type(info)   == 'table')

    -- Base value
    ilocal value, var_scope, in_func  =  get_variable(lvalue[1], info)
    -- Sub value
    for i = 2, #lvalue do  value = value[lvalue[i].value]  end
    --
    return value, var_scope, in_func
end
--]]

--------------------------------------------------------------------------------
-- Parsing

local shunting_yard = require 'Parser'

local NO_PARSE_TOKENS = {
    FUNCTION   =  true,
    SEMICOLON  =  true,
    BREAK      =  true,
    DO         =  true,
    ELSE       =  true,
    ELSEIF     =  true,
    END        =  true,
    FOR        =  true,
    IF         =  true,
    IN         =  true,
    LOCAL      =  true,
    REPEAT     =  true,
    RETURN     =  true,
    THEN       =  true,
    UNTIL      =  true,
    WHILE      =  true,
    ASSIGN     =  true,

    -- TODO: These below should not be NO-PARSE-TOKENS:
    VARARG  =  true,
    LBRACE  =  true,
    RBRACE  =  true,
}


local LUA_BINOP = {
    ['OR']  = { precedence = 1 },
    ['AND'] = { precedence = 2 },
    ['LE']  = { precedence = 3 },
    ['LEQ'] = { precedence = 3 },
    ['EQ']  = { precedence = 3 },
    ['NEQ'] = { precedence = 3 },
    ['GEQ'] = { precedence = 3 },
    ['GT']      = { precedence = 3 },
    ['CONCAT']  = { precedence = 4, associativity = 'right' },
    ['PLUS']    = { precedence = 5 },
    ['MINUS']   = { precedence = 5 },
    ['TIMES']   = { precedence = 6 },
    ['DIVIDE']  = { precedence = 6 },
    ['MODULO']  = { precedence = 6 },
    ['CARET']   = { precedence = 8, associativity = 'right' },

    ['DOT']     = { precedence = 10 },
    ['COLON']   = { precedence = 10 },
}

local LUA_PREOP = {
    ['MINUS']     = { precedence = 7, val = 'UMINUS' },
    ['NOT']       = { precedence = 7 },
    ['HASHTAG']   = { precedence = 7 },
}

for keyword, binop in pairs (LUA_BINOP) do
    binop.type   = 'op'
    binop.arity  = 2
    binop.val    = binop.val or keyword
    binop.associativity = binop.associativity or 'left'
end

for keyword, unop in pairs (LUA_PREOP) do
    unop.type   = 'op'
    unop.arity  = 1
    unop.val    = unop.val or keyword
    unop.associativity = 'right'
end

local LUA_OP_ARITY = {}

for _, op in pairs(LUA_BINOP) do  LUA_OP_ARITY[op.val] = op.arity  end
for _, op in pairs(LUA_PREOP) do  LUA_OP_ARITY[op.val] = op.arity  end

local function lua_expression_lang (token, prev_token_info)
    local ttype = token.token
    local binary_disallowed   =  prev_token_info == nil or prev_token_info.type == 'bracket' and prev_token_info.open == prev_token_info.val or prev_token_info.type == 'op'

    if LUA_PREOP[ttype] and binary_disallowed then
        -- TODO: Unary minus?
        local op_info = LUA_PREOP[ttype]
        return { type  = 'op', arity = op_info.arity, associativity = op_info.associativity, precedence = op_info.precedence, val = token }
    elseif LUA_BINOP[ttype] and not binary_disallowed then
        local op_info = LUA_BINOP[ttype]
        return { type  = 'op', arity = op_info.arity, associativity = op_info.associativity, precedence = op_info.precedence, val = token }
    elseif LUA_BINOP[ttype] or LUA_PREOP[ttype] then
        error('Cannot use the operation '..ttype..' here')

    elseif ttype == 'LBRACK' or ttype == 'RBRACK' then
        return { type = 'bracket', val = ttype, open = 'LBRACK', close = 'RBRACK', precedence = 10, on_end_call_op = { type = 'op', val = '?', call_op = true } }
    elseif ttype == 'LPAR' or ttype == 'RPAR' then
        return { type = 'bracket', val = ttype, open = 'LPAR', close = 'RPAR', precedence =  9, on_end_call_op = { type = 'op', val = '$', call_op = true } }
    elseif ttype == 'COMMA' then
        return { type = 'arg-sep', val = 'COMMA', open = 'LPAR' }

    elseif type (ttype) == 'number' or type (ttype) == 'string' then
        return { type = 'imm', val = token }
    end
end

local function NUM_ARITY (num)
    assert(type(num) == 'number')
    return { type = 'imm', val = num }
end

local function parse (tokens)
    assert(type(tokens) == 'table')

    --
    for i = 2, #tokens do
        if tokens[i].token == 'IDENTIFIER' and tokens[i-1].token == 'DOT' then
            tokens[i].token = 'STRING'
            tokens[i].text  = '\''..tokens[i].text..'\''
        end
    end

    -- Postfix the tokens
    local postfix_tokens  =  shunting_yard(tokens, lua_expression_lang, NUM_ARITY)
    assert(type(postfix_tokens) == 'table')
    print(require'pretty'(postfix_tokens))

    -- Create AST from postfix tokens
    local ast_stack = {}
    for _, token in ipairs(postfix_tokens) do
        if type(token) == 'table' and LUA_OP_ARITY[token.token] then
            -- Operation
            local node = { exp = 'OP', binop = token.token }
            local start_left, end_right  = math.huge, -math.huge
            --
            for arg_index = LUA_OP_ARITY[token.token], 1, -1 do
                local arg = table.remove(ast_stack)
                assert(type(arg) == 'table')
                start_left, end_right = math.min(start_left, arg.left), math.max(end_right, arg.right)
                node[arg_index] = arg
            end
            --
            node.left, node.right = start_left, end_right
            ast_stack[#ast_stack+1] = node

        elseif token == '$' then
            -- Operation
            local node = { exp = 'CALL' }
            local start_left, end_right  = math.huge, -math.huge
            --
            local num_args = table.remove(ast_stack)
            assert(type(num_args) == 'number')
            --
            for arg_index = num_args + 1, 1, -1 do
                local arg = table.remove(ast_stack)
                assert(type(arg) == 'table')
                start_left, end_right = math.min(start_left, arg.left), math.max(end_right, arg.right)
                node[arg_index] = arg
            end
            --
            node.left, node.right = start_left, end_right
            ast_stack[#ast_stack+1] = node

        elseif token == '?' then
            -- Indexing
            local node = { exp = 'OP', binop = 'DOT' }
            local start_left, end_right  = math.huge, -math.huge
            --
            local num_args = table.remove(ast_stack)
            assert(type(num_args) == 'number' and num_args == 1)
            --
            for arg_index = num_args + 1, 1, -1 do
                local arg = table.remove(ast_stack)
                assert(type(arg) == 'table')
                start_left, end_right = math.min(start_left, arg.left), math.max(end_right, arg.right)
                node[arg_index] = arg
            end
            --
            node.left, node.right = start_left, end_right
            ast_stack[#ast_stack+1] = node

        else
            -- Immediate
            ast_stack[#ast_stack+1] = token

        end
    end
    assert(#ast_stack == 1)

    return ast_stack[1]

    --[[

    if #tokens == 6 and tokens[1].text == 'type' and tokens[2].token == 'LPAR' and tokens[3].token == 'IDENTIFIER' and tokens[4].token == 'RPAR'and tokens[5].token == 'EQ'and tokens[6].token == 'STRING' then
        return {
            exp   = 'COMPARE',
            binop = 'EQ',
            [1]   = { exp = 'CALL', get_value_token(tokens[1]), get_value_token(tokens[3]) },
            [2]   = get_value_token(tokens[6]),
        }
    elseif #tokens == 3 and VALUE_TOKEN[tokens[1].token] and COMPARE_BINOP[tokens[2].token] and VALUE_TOKEN[tokens[3].token] then
        return {
            exp     = 'COMPARE',
            binop   = tokens[2].token,
            [1]     = get_value_token(tokens[1]),
            [2]     = get_value_token(tokens[3])
        }
    elseif #tokens == 4 and tokens[1].token == 'HASHTAG' and VALUE_TOKEN[tokens[2].token] and COMPARE_BINOP[tokens[3].token] and VALUE_TOKEN[tokens[4].token] then
        return {
            exp     = 'COMPARE',
            binop   = tokens[3].token,
            [1]     = { exp = 'UNOP', get_value_token(tokens[2]) } ,
            [2]     = get_value_token(tokens[4])
        }
    elseif #tokens == 3 and tokens[1].token == 'IDENTIFIER' and tokens[2].token == 'DOT' and tokens[3].token == 'IDENTIFIER' then
        return { exp = 'LVALUE', tokens[1].text, { exp = 'STRING', value = tokens[3].text } }
    elseif #tokens == 4 and tokens[1].token == 'IDENTIFIER' and tokens[2].token == 'LBRACK' and VALUE_TOKEN[tokens[3].token] and tokens[4].token == 'RBRACK' then
        return { exp = 'LVALUE', tokens[1].text, get_value_token(tokens[3]) }
    elseif #tokens == 1 then
        return get_value_token(tokens[1])
    else
        io.stderr:write '[assert-gooder/internal]: Unknown AST structure!\n'
    end
    --]]
end

local function for_each_node_in_ast (ast, func)
    assert(type(ast) == 'table')
    assert(type(func)   == 'function')
    --
    for _, node in ipairs(ast) do
        if type(node) == 'table' then
            for_each_node_in_ast(node, func)
        end
    end
    --
    return func(ast)
end

local function populate_ast_with_semantics (ast, info)
    assert(type(ast) == 'table')
    assert(type(info) == 'table')
    return for_each_node_in_ast(ast, function(node)
        if node.token == 'IDENTIFIER' then
            -- TODO: Variable scope, and is it in a function?
            node.value, node.scope, node.function_local  =  get_variable(node.text, info)
        elseif CONSTANT_VALUE_TOKEN[node.token] then
            node.value = CONSTANT_VALUE_TOKEN[node.token](node.text)
        elseif node.exp == 'OP' and node.binop == 'DOT' then
            assert(node[1].value and node[2].value)
            node.value =  node[1].value[ node[2].value ] --TODO
        end
    end)
end

--------------------------------------------------------------------------------

local function get_module_filetext (module_filepath)
    assert(type(module_filepath) == 'string')

    -- Just attempt standard file open
    local filehandle = io.open(module_filepath, 'r')
    if filehandle then
        local filetext = filehandle:read '*all'
        filehandle:close()
        return filetext
    end

    -- What about LÖVE?
    local filetext = love and love.filesystem and love.filesystem.read(module_filepath) or nil
    if filetext then  return filetext  end

    -- I give up...
    return nil
end

local function seperate_by_toplevel_commas (text)
    assert(type(text) == 'string')
    local section_start, index, sections = 1, 1, {}
    while index < #text do
        local next_comma = text:find(',', index)
        local next_par_start, next_par_end = text:find('%b()', index)
        if not next_comma then
            break
        elseif not next_par_start or next_comma < next_par_start then
            sections[#sections+1] = text:sub(section_start, next_comma - 1)
            index = next_comma + 1
            section_start = index
        else
            index = next_par_end + 1
        end
    end
    sections[#sections+1] = text:sub(section_start)
    return sections
end

local function get_assert_body_text (call_info)
    if call_info.what == 'Lua' or call_info.what == 'main' then
        -- Find filetext
        local filetext = nil
        if call_info.source:find '^@' then
            filetext = get_module_filetext(call_info.short_src)
        elseif call_info.short_src:find '^%[string' then
            filetext = call_info.source
        else
            error 'Not implemented yet!'
        end
        -- If cannot find
        if not filetext then  return nil  end
        -- Get lines
        local filetext = filetext .. '\n'
        local lines_after, line_i  =  {}, 0
        for line in filetext:gmatch '([^\r\n]*)[\r\n]' do
            line_i = line_i + 1
            if call_info.currentline == line_i then
                lines_after[#lines_after+1] = line
            end
        end
        -- Find body exclusively.
        local assert_arguments_text = table.concat(lines_after, '\n'):match('assert%s*(%b())'):sub(2, -2)
        local assert_arguments = seperate_by_toplevel_commas(assert_arguments_text)
        return assert_arguments[1]
    end

    error 'Not implemented yet!'
end


local function get_function_name (call_info)
    --
    if call_info.name then  return  string.format('\'%s\'', call_info.name)  end
    --
    local where = nil
    if call_info.source:find '^@' then
        where = 'at '..call_info.short_src..':'..call_info.linedefined
    elseif call_info.short_src:find '^%[string' then
        where = 'from loaded string'
    else
        error 'not yet implemented'
    end
    --
    return string.format('the anonymous function %s', where)
end

local function fmt_val (val)
    if type(val) == 'string' then
        return string.format('%q', val)
    else
        return tostring(val)
    end
end

local function fmt_lvalue (node, with_scope)
    assert(type(node) == 'table')

    if node.token == 'IDENTIFIER' then
        local base = node.text
        if with_scope then  base = ('%s \'%s\''):format(node.scope, base)  end
        return base, node.function_local

    elseif node.exp == 'OP' and node.binop == 'DOT' then
        local base, function_local = fmt_lvalue(node[1], with_scope)
        return ('key %s in %s'):format(fmt_val(node[2].value), base), function_local
    end

    error 'Not implemented yet!'
end

--[[
local function ast_to_formal_lvalue (ast)
    if ast.token == 'IDENTIFIER' then
        return { ast.text, exp = 'LVALUE' }
    elseif ast.exp == 'OP' and ast.binop == 'DOT' then
        local  prev = ast_to_formal_lvalue(ast[1])
               prev[#prev+1] = get_value_token(ast[2]).value
        return prev
    end
    assert(false)
end
--]]

local function fmt_prefix (ast, call_info)
    assert(type(ast) == 'table')
    --
    local name, is_function_local  =  fmt_lvalue(ast, true)
    local func_name = is_function_local and (' to '..get_function_name(call_info)) or ''
    return ('bad %s%s'):format(name, func_name)
end


local PRIMITIVE_VALUES = {
    ['nil']     = true,
    ['boolean'] = true,
}

local COMPLEX_TYPES = {
    ['table']       = true,
    ['userdata']    = true,
    ['cdata']       = true,
    ['function']    = true,
}

local function fmt_table_with_type (val)
    assert(type(val) == 'table')

    local subtype = 'table'

    -- Find "last key"
    do
        local last_key, num_visited = nil, 0
        repeat last_key, num_visited = next(val, last_key), num_visited + 1
        until last_key == nil or type(last_key) ~= 'number' or last_key <= 0 or last_key > #val

        -- Conclude:
        if last_key == nil then
            subtype = (num_visited == 1) and 'empty table' or 'sequence'
        end
    end

    local addr  =  tostring(val):match '^table: (.*)$'
    local attr  =  debug.getmetatable(val) ~= nil and ' with metatable' or ''

    return ('%s%s: %s'):format(subtype, attr, addr)
end

local function fmt_val_with_type (val)

    -- Primitive values ARE their type, and don't need the annotation.
    if PRIMITIVE_VALUES[type(val)] then  return tostring(val)  end

    -- Tables can be of many different styles
    if type(val) == 'table' then
        return fmt_table_with_type(val)
    end

    -- Complex types are already formatted with some type information.
    if COMPLEX_TYPES[type(val)] then  return tostring(val)  end

    -- Numbers and string should have their types with them.
    return type(val) .. ' ' .. fmt_val(val)
end

--------------------------------------------------------------------------------

local function get_assert_body (call_info)
    return lexer:lex(text), text
end


local function determine_error_message (call_info, msg, condition)
    -- Error checking.
    assert(type(call_info) == 'table')
    assert(type(msg)       == 'table' and type(msg[1]) == 'string')
    assert(not condition)

    -- Get assert body.
    local body_text = get_assert_body_text(call_info)

    -- If we couldn't find the body text, we give up.
    if not body_text then  return  end

    -- Simplest formatting.
    -- No analysis of the assert-body, just report that it failed,
    -- along with it's body.
    msg[1] = ('expression `%s` evaluated to %s'):format(body_text, condition)

    -- Lex text.
    local tokens = lexer:lex(body_text)
    assert(type(tokens) == 'table')

    -- Find identifiers and provide simple explanations of their
    -- values.
    do
        local l, seen_variables = {}, {}
        for i, token in ipairs(tokens) do
            local variable_name = token.text
            if token.token == 'IDENTIFIER' and (i == 1 or tokens[i-1].token ~= 'COLON' and tokens[i-1].token ~= 'DOT') and not seen_variables[variable_name] then
                seen_variables[variable_name] = true
                local value = get_variable(variable_name, call_info)
                if EXPECTED_GLOBAL[variable_name] == nil then
                    l[#l+1] = ('%s was %s'):format(token.text, fmt_val_with_type(value))
                elseif EXPECTED_GLOBAL[variable_name] ~= type(value) then
                    l[#l+1] = ('standard-%s %s was %s'):format(EXPECTED_GLOBAL[variable_name], token.text, fmt_val_with_type(value))
                end
            end
        end
        msg[2] = #l > 0 and table.concat(l,', ') or nil
    end


    local ast = parse(tokens)
    if not ast then  return  end
    assert(type(ast) == 'table')
    populate_ast_with_semantics(ast, call_info)

    local function is_l_value (ast)
        print(ast.exp, ast.binop, ast.exp == 'OP' and ast.binop == 'DOT' )
        if ast.exp == 'OP' and ast.binop == 'DOT' then
            print 'Derp?'
            return true
        elseif ast.token == 'IDENTIFIER' then
            return true
        end
        return false
    end

    -- Alternative more detailed formatting.
    -- Identical to last message, but now with values of each involved
    -- identifier.
    do
        local l = {}
        for_each_node_in_ast(ast, function(node)
            if is_l_value(node) then
                local name = fmt_lvalue(node)
                if not l[name] then
                    l[#l+1] = name..' was ' .. fmt_val_with_type(node.value)
                    l[name] = true
                end
            end
        end)
        msg[2] = #l > 0 and table.concat(l,', ') or nil
    end

    -- More specific types
    local var_prefix = function(token)
        return get_variable_and_prefix(token, call_info)
    end

    if not ast then  return nil
    elseif ast.exp == 'OP' and ast.binop == 'EQ' and ast[1].exp == 'CALL' and ast[1][1].value == type then
        local prefix = fmt_prefix(ast[1][2], call_info)
        msg[1], msg[2] = prefix, ('%s expected, but got %s'):format(ast[2].value, fmt_val_with_type(ast[1][2].value))

    elseif ast.exp == 'OP' and ast.binop == 'EQ' then
        local prefix = fmt_prefix(ast[1], call_info)
        local gotten_value, expected_value  =  ast[1].value, ast[2].value
        local fmt_gotten = (type(expected_value) == type(gotten_value)) and fmt_val or fmt_val_with_type
        msg[1], msg[2] = prefix, ('%s expected, but got %s'):format(fmt_val_with_type(expected_value), fmt_gotten(gotten_value))

    elseif ast.exp == 'OP' and ast.binop == 'NEQ' then
        local prefix = fmt_prefix(ast[1], call_info)
        local gotten_value, expected_value  =  ast[1].value, ast[2].value
        msg[1], msg[2] = prefix, ('expected anything other than %s, but got %s'):format(fmt_val_with_type(expected_value), fmt_val(gotten_val))

    elseif ast.exp == 'LVALUE' then
        local prefix = fmt_prefix(ast[1], call_info)
        local gotten_value  =  ast[1].value
        msg[1], msg[2] = prefix, ('truthy expected, but got %s'):format(fmt_val(gotten_val))

    elseif CONSTANT_VALUE_TOKEN[ast.token] then
        local func_name  =  get_function_name(call_info)
        msg[1] = ('this assert will always fail, as it\'s body is `%s`. assumingly this should be an unreachable part of %s'):format(body_text, func_name)

    else
        error(('[assert-gooder/internal]: Unknown expression type %s'):format(ast.exp))
    end
end

return function (condition, format, ...)
    if condition then  return  condition  end
    --
    local level     = 2
    local call_info = debug.getinfo(level)
    call_info.locals = {}
    for i = 1, math.huge do
        local name, value = debug.getlocal(level, i)
        if not name then break end
        call_info.locals[name] = { value, i <= call_info.nparams, i }
    end
    --
    local msg_container = {''}
    local success, internal_error_msg = pcall(determine_error_message, call_info, msg_container, condition)
    -- Handle internal errors
    if not success then
        io.stderr:write(('[assert-gooder/internal]: Internal error occured while determining error message for calling assert:\n    %s\n'):format(internal_error_msg))
    end

    -- Format error message:
    assert(#msg_container <= 2 and type(msg_container[1]) == 'string')
    local l = {}
    if format ~= nil then
        l[#l+1] = (type(format) == 'string') and format:format(...) or tostring(format)
        l[#l+1] = ':'
    else
        l[#l+1] = 'assertion failed!'
    end
    l[#l+1] = ' '
    l[#l+1] = msg_container[1]
    if msg_container[2] then
        assert(type(msg_container[2]) == 'string')
        l[#l+1] = ' ('
        l[#l+1] = msg_container[2]
        l[#l+1] = ')'
    end

    -- Throw error message
    error(table.concat(l, ''), 2)
end