-- Copyright (C) 2021 Kim Alvefur

--

-- This project is MIT/X11 licensed. Please see the

-- COPYING file in the source package for more information.

--

-- Based on

-- https://json-schema.org/draft/2020-12/json-schema-core.html

-- https://json-schema.org/draft/2020-12/json-schema-validation.html

--

local json = require"util.json"

local null = json.null;

local pointer = require "util.jsonpointer"

local type json_type_name = json.json_type_name

-- json_type_name here is non-standard

local type schema_t = boolean | json_type_name | json_schema_object

local record json_schema_object

	type json_type_name = json.json_type_name

	type schema_object = json_schema_object

	type : json_type_name

	enum : { any }

	const : any

	allOf : { schema_t }

	anyOf : { schema_t }

	oneOf : { schema_t }

	["not"] : schema_t

	["if"] : schema_t

	["then"] : schema_t

	["else"] : schema_t

	["$ref"] : string

	-- numbers

	multipleOf : number

	maximum : number

	exclusiveMaximum : number

	minimum : number

	exclusiveMinimum : number

	-- strings

	maxLength : integer

	minLength : integer

	pattern : string

	format : string

	-- arrays

	prefixItems : { schema_t }

	items : schema_t

	contains : schema_t

	maxItems : integer

	minItems : integer

	uniqueItems : boolean

	maxContains : integer

	minContains : integer

	-- objects

	properties : { string : schema_t }

	maxProperties : integer

	minProperties : integer

	required : { string }

	dependentRequired : { string : { string } }

	additionalProperties: schema_t

	patternProperties: schema_t

	propertyNames : schema_t

	-- xml

	record xml_t

		name : string

		namespace : string

		prefix : string

		attribute : boolean

		wrapped : boolean

		-- nonstantard, maybe in the future

		text : boolean

		x_name_is_value : boolean

		x_single_attribute : string

	end

	xml : xml_t

	-- descriptive

	title : string

	description : string

	deprecated : boolean

	readOnly : boolean

	writeOnly : boolean

	-- methods

	validate : function ( schema_t, any, json_schema_object ) : boolean

end

-- TODO validator function per schema property

local type_validators : { json_type_name : function (schema_t, any, json_schema_object) : boolean } = {}

local function simple_validate(schema : json_type_name, data : any) : boolean

	if schema == "object" and data is table then

		return type(data) == "table" and (next(data)==nil or type((next(data, nil))) == "string")

	elseif schema == "array" and data is table then

		return type(data) == "table" and (next(data)==nil or type((next(data, nil))) == "number")

	elseif schema == "integer" then

		return math.type(data) == schema

	elseif schema == "null" then

		return data == null

	else

		return type(data) == schema

	end

end

type_validators.string = function (schema : json_schema_object, data : any) : boolean

	-- XXX this is measured in byte, while JSON measures in ... bork

	-- TODO use utf8.len?

	if data is string then

		if schema.maxLength and #data > schema.maxLength then

			return false

		end

		if schema.minLength and #data < schema.minLength then

			return false

		end

		return true

	end

	return false

end

type_validators.number = function (schema : json_schema_object, data : number) : boolean

	if schema.multipleOf and data % schema.multipleOf ~= 0 then

		return false

	end

	if schema.maximum and not ( data <= schema.maximum ) then

		return false

	end

	if schema.exclusiveMaximum and not ( data < schema.exclusiveMaximum ) then

		return false

	end

	if schema.minimum and not ( data >= schema.minimum ) then

		return false

	end

	if schema.exclusiveMinimum and not ( data > schema.exclusiveMinimum ) then

		return false

	end

	return true

end

type_validators.integer = type_validators.number

local function validate(schema : schema_t, data : any, root : json_schema_object) : boolean

	if schema is boolean then

		return schema

	end

	if schema is json_type_name then

		return simple_validate(schema, data)

	end

	if schema is json_schema_object then

		if root == nil then

			root = schema

		end

		if schema["$ref"] and schema["$ref"]:sub(1,1) == "#" then

			local referenced = pointer.resolve(root as table, schema["$ref"]:sub(2)) as schema_t

			if referenced ~= nil then

				return validate(referenced, data, root);

			end

		end

		if schema.allOf then

			for _, sub in ipairs(schema.allOf) do

				if not validate(sub, data, root) then

					return false

				end

			end

			return true

		end

		if schema.oneOf then

			local valid = 0

			for _, sub in ipairs(schema.oneOf) do

				if validate(sub, data, root) then

					valid = valid + 1

				end

			end

			return valid == 1

		end

		if schema.anyOf then

			for _, sub in ipairs(schema.anyOf) do

				if validate(sub, data, root) then

					return true

				end

			end

			return false

		end

		if schema["not"] then

			if validate(schema["not"], data, root) then

				return false

			end

		end

		if schema["if"] then

			if validate(schema["if"], data, root) then

				if schema["then"] then

					return validate(schema["then"], data, root)

				end

			else

				if schema["else"] then

					return validate(schema["else"], data, root)

				end

			end

		end

		if schema.const ~= nil and schema.const ~= data then

			return false

		end

		if schema["enum"] ~= nil then

			for _, v in ipairs(schema["enum"]) do

				if v == data then

					return true

				end

			end

			return false

		end

		if schema.type then

			if not simple_validate(schema.type, data) then

				return false

			end

			local validator = type_validators[schema.type]

			if validator then

				return validator(schema, data, root)

			end

		end

		return true

	end

end

type_validators.table = function (schema : json_schema_object, data : any, root : json_schema_object) : boolean

	if data is table then

		if schema.maxItems and #data > schema.maxItems then

			return false

		end

		if schema.minItems and #data < schema.minItems then

			return false

		end

		if schema.required then

			for _, k in ipairs(schema.required) do

				if data[k] == nil then

					return false

				end

			end

		end

		if schema.properties then

			local additional : schema_t = schema.additionalProperties or true

			for k, v in pairs(data) do

				if schema.propertyNames and not validate(schema.propertyNames, k, root) then

					return false

				end

				local s = schema.properties[k as string] or additional

				if not validate(s, v, root) then

					return false

				end

			end

		elseif schema.additionalProperties then

			for k, v in pairs(data) do

				if schema.propertyNames and not validate(schema.propertyNames, k, root) then

					return false

				end

				if not validate(schema.additionalProperties, v, root) then

					return false

				end

			end

		end

		if schema.uniqueItems then

			-- only works for scalars, would need to deep-compare for objects/arrays/tables

			local values : { any : boolean } = {}

			for _, v in pairs(data) do

				if values[v] then

					return false

				end

				values[v] = true

			end

		end

		local p = 0

		if schema.prefixItems then

			for i, s in ipairs(schema.prefixItems) do

				if validate(s, data[i], root) then

					p = i

				else

					return false

				end

			end

		end

		if schema.items then

			for i = p+1, #data do

				if not validate(schema.items, data[i], root) then

					return false

				end

			end

		end

		if schema.contains then

			local found = false

			for i = 1, #data do

				if validate(schema.contains, data[i], root) then

					found = true

					break

				end

			end

			if not found then

				return false

			end

		end

		return true

	end

	return false

end

type_validators.object = function (schema : schema_t, data : any, root : json_schema_object) : boolean

	if data is table then

		for k in pairs(data) do

			if not k is string then

				return false

			end

		end

		return type_validators.table(schema, data, root)

	end

	return false

end

type_validators.array = function (schema : schema_t, data : any, root : json_schema_object) : boolean

	if data is table then

		-- just check that there the keys are all numbers

		for i in pairs(data) do

			if not i is number then

				return false

			end

		end

		return type_validators.table(schema, data, root)

	end

	return false

end

json_schema_object.validate = validate;

return json_schema_object;