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 VALUE_TOKEN = { IDENTIFIER = true }
for k in pairs(CONSTANT_VALUE_TOKEN) do  VALUE_TOKEN[k] = true  end

local COMPARE_BINOP = {
    EQ  = true,
    NEQ = true,
    LEQ = true,
    GEQ = true,
    LE  = true,
    GT  = true,
}

local function get_value_token (token)
    if CONSTANT_VALUE_TOKEN[token.token]then
        return { exp = token.token, value = CONSTANT_VALUE_TOKEN[token.token](token.text) }
    elseif token.token == 'IDENTIFIER' then
        return { exp = 'LVALUE', token.text }
    end
    assert(false)
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
    local 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 function parse (tokens)
    -- TODO: Make a more general parser
    assert(type(tokens) == 'table')
    --

    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.exp == 'LVALUE' then
            node.value = get_value_from_lvalue(node, info)
        end
    end)
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
            local filehandle = io.open(call_info.short_src, 'r')
            filetext = filehandle:read '*all'
            filehandle:close()
        elseif call_info.short_src:find '^%[string' then
            filetext = call_info.source
        else
            error 'Not implemented yet!'
        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.
        return table.concat(lines_after, '\n'):match('assert%s*(%b())'):sub(2, -2)
    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 (lvalue, var_scope)
    assert(type(lvalue) == 'table' and lvalue.exp == 'LVALUE')
    --
    local base_var = tostring(lvalue[1])
    if var_scope then
        base_var = ('%s \'%s\''):format(var_scope, lvalue[1])
    end
    --
    if     #lvalue == 1 then  return base_var
    elseif #lvalue == 2 then  return string.format('key %s in %s', fmt_val(lvalue[2].value), base_var)
    else  error 'Not implemented yet!'
    end

end

local function get_variable_and_prefix (lvalue, call_info)
    assert(type(lvalue) == 'table' and lvalue.exp == 'LVALUE')
    --
    local value, var_scope, in_func = get_value_from_lvalue(lvalue, call_info)
    --
    local func_name = in_func and (' to '..get_function_name(call_info)) or ''
    return value, ('bad %s%s'):format(fmt_lvalue(lvalue, var_scope), func_name)
end


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

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

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
    -- 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)

    -- 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)

    -- 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 node.exp == 'LVALUE' then
                l[#l+1] = fmt_lvalue(node) ..' was ' .. fmt_val_with_type(node.value)
            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 == 'COMPARE' and ast.binop == 'EQ' and ast[1].exp == 'CALL' and ast[1][1].exp == 'LVALUE' and ast[1][1][1] == 'type' then
        local gotten_val, prefix  =  var_prefix(ast[1][2])
        msg[1], msg[2] = prefix, ('%s expected, but got %s'):format(ast[2].value, fmt_val_with_type(gotten_val))

    elseif ast.exp == 'COMPARE' and ast.binop == 'EQ' then
        local gotten_value, prefix  = var_prefix(ast[1])
        local expected_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 == 'COMPARE' and ast.binop == 'NEQ' then
        local gotten_val, prefix  = var_prefix(ast[1])
        local expected_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 gotten_val, prefix  =  var_prefix(ast)
        msg[1], msg[2] = prefix, ('truthy expected, but got %s'):format(fmt_val(gotten_val))

    elseif CONSTANT_VALUE_TOKEN[ast.exp] 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)
    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
    --
    assert(#msg_container <= 2 and type(msg_container[1]) == 'string')
    local l = {'assertion failed! ', msg_container[1]}
    if msg_container[2] then
        assert(type(msg_container[2]) == 'string')
        l[3] = ' ('
        l[4] = msg_container[2]
        l[5] = ')'
    end
    error(table.concat(l, ''), 2)
end