-- modules/json.lua - High-performance JSON module

local json = {}

function json.encode(value)
	local buffer = {}
	local pos = 1

	local function encode_string(s)
		buffer[pos] = '"'
		pos = pos + 1

		local start = 1
		for i = 1, #s do
			local c = s:byte(i)
			if c == 34 then -- "
				if i > start then
					buffer[pos] = s:sub(start, i - 1)
					pos = pos + 1
				end
				buffer[pos] = '\\"'
				pos = pos + 1
				start = i + 1
			elseif c == 92 then -- \
				if i > start then
					buffer[pos] = s:sub(start, i - 1)
					pos = pos + 1
				end
				buffer[pos] = '\\\\'
				pos = pos + 1
				start = i + 1
			elseif c < 32 then
				if i > start then
					buffer[pos] = s:sub(start, i - 1)
					pos = pos + 1
				end
				if c == 8 then
					buffer[pos] = '\\b'
				elseif c == 9 then
					buffer[pos] = '\\t'
				elseif c == 10 then
					buffer[pos] = '\\n'
				elseif c == 12 then
					buffer[pos] = '\\f'
				elseif c == 13 then
					buffer[pos] = '\\r'
				else
					buffer[pos] = ('\\u%04x'):format(c)
				end
				pos = pos + 1
				start = i + 1
			end
		end

		if start <= #s then
			buffer[pos] = s:sub(start)
			pos = pos + 1
		end

		buffer[pos] = '"'
		pos = pos + 1
	end

	local function encode_value(v, depth)
		local t = type(v)

		if t == 'string' then
			encode_string(v)
		elseif t == 'number' then
			if v ~= v then -- NaN
				buffer[pos] = 'null'
			elseif v == 1/0 or v == -1/0 then -- Infinity
				buffer[pos] = 'null'
			else
				buffer[pos] = tostring(v)
			end
			pos = pos + 1
		elseif t == 'boolean' then
			buffer[pos] = v and 'true' or 'false'
			pos = pos + 1
		elseif t == 'table' then
			if depth > 100 then error('circular reference') end

			local is_array = true
			local max_index = 0
			local count = 0

			for k, _ in pairs(v) do
				count = count + 1
				if type(k) ~= 'number' or k <= 0 or k % 1 ~= 0 then
					is_array = false
					break
				end
				if k > max_index then max_index = k end
			end

			if is_array and count == max_index then
				buffer[pos] = '['
				pos = pos + 1

				for i = 1, max_index do
					if i > 1 then
						buffer[pos] = ','
						pos = pos + 1
					end
					encode_value(v[i], depth + 1)
				end

				buffer[pos] = ']'
				pos = pos + 1
			else
				buffer[pos] = '{'
				pos = pos + 1

				local first = true
				for k, val in pairs(v) do
					if not first then
						buffer[pos] = ','
						pos = pos + 1
					end
					first = false

					encode_string(tostring(k))
					buffer[pos] = ':'
					pos = pos + 1
					encode_value(val, depth + 1)
				end

				buffer[pos] = '}'
				pos = pos + 1
			end
		else
			buffer[pos] = 'null'
			pos = pos + 1
		end
	end

	encode_value(value, 0)
	return table.concat(buffer)
end

function json.decode(str)
	local pos = 1
	local len = #str

	local function skip_whitespace()
		while pos <= len do
			local c = str:byte(pos)
			if c ~= 32 and c ~= 9 and c ~= 10 and c ~= 13 then break end
			pos = pos + 1
		end
	end

	local function decode_string()
		local start = pos + 1
		pos = pos + 1

		while pos <= len do
			local c = str:byte(pos)
			if c == 34 then -- "
				local result = str:sub(start, pos - 1)
				pos = pos + 1

				if result:find('\\') then
					result = result:gsub('\\(.)', {
						['"'] = '"',
						['\\'] = '\\',
						['/'] = '/',
						['b'] = '\b',
						['f'] = '\f',
						['n'] = '\n',
						['r'] = '\r',
						['t'] = '\t'
					})
					result = result:gsub('\\u(%x%x%x%x)', function(hex)
						return string.char(tonumber(hex, 16))
					end)
				end

				return result
			elseif c == 92 then -- \
				pos = pos + 2
			else
				pos = pos + 1
			end
		end

		error('unterminated string')
	end

	local function decode_number()
		local start = pos
		local c = str:byte(pos)

		if c == 45 then pos = pos + 1 end -- -

		c = str:byte(pos)
		if not c or c < 48 or c > 57 then error('invalid number') end

		if c == 48 then
			pos = pos + 1
		else
			while pos <= len do
				c = str:byte(pos)
				if c < 48 or c > 57 then break end
				pos = pos + 1
			end
		end

		if pos <= len and str:byte(pos) == 46 then -- .
			pos = pos + 1
			local found_digit = false
			while pos <= len do
				c = str:byte(pos)
				if c < 48 or c > 57 then break end
				found_digit = true
				pos = pos + 1
			end
			if not found_digit then error('invalid number') end
		end

		if pos <= len then
			c = str:byte(pos)
			if c == 101 or c == 69 then -- e or E
				pos = pos + 1
				if pos <= len then
					c = str:byte(pos)
					if c == 43 or c == 45 then pos = pos + 1 end -- + or -
				end
				local found_digit = false
				while pos <= len do
					c = str:byte(pos)
					if c < 48 or c > 57 then break end
					found_digit = true
					pos = pos + 1
				end
				if not found_digit then error('invalid number') end
			end
		end

		return tonumber(str:sub(start, pos - 1))
	end

	local function decode_value()
		skip_whitespace()
		if pos > len then error('unexpected end') end

		local c = str:byte(pos)

		if c == 34 then -- "
			return decode_string()
		elseif c == 123 then -- {
			local result = {}
			pos = pos + 1
			skip_whitespace()

			if pos <= len and str:byte(pos) == 125 then -- }
				pos = pos + 1
				return result
			end

			while true do
				skip_whitespace()
				if pos > len or str:byte(pos) ~= 34 then error('expected string key') end

				local key = decode_string()
				skip_whitespace()

				if pos > len or str:byte(pos) ~= 58 then error('expected :') end
				pos = pos + 1

				result[key] = decode_value()
				skip_whitespace()

				if pos > len then error('unexpected end') end
				c = str:byte(pos)

				if c == 125 then -- }
					pos = pos + 1
					return result
				elseif c == 44 then -- ,
					pos = pos + 1
				else
					error('expected , or }')
				end
			end

		elseif c == 91 then -- [
			local result = {}
			local index = 1
			pos = pos + 1
			skip_whitespace()

			if pos <= len and str:byte(pos) == 93 then -- ]
				pos = pos + 1
				return result
			end

			while true do
				result[index] = decode_value()
				index = index + 1
				skip_whitespace()

				if pos > len then error('unexpected end') end
				c = str:byte(pos)

				if c == 93 then -- ]
					pos = pos + 1
					return result
				elseif c == 44 then -- ,
					pos = pos + 1
				else
					error('expected , or ]')
				end
			end

		elseif c == 116 then -- true
			if str:sub(pos, pos + 3) == 'true' then
				pos = pos + 4
				return true
			end
			error('invalid literal')

		elseif c == 102 then -- false
			if str:sub(pos, pos + 4) == 'false' then
				pos = pos + 5
				return false
			end
			error('invalid literal')

		elseif c == 110 then -- null
			if str:sub(pos, pos + 3) == 'null' then
				pos = pos + 4
				return nil
			end
			error('invalid literal')

		elseif (c >= 48 and c <= 57) or c == 45 then -- 0-9 or -
			return decode_number()

		else
			error('unexpected character')
		end
	end

	local result = decode_value()
	skip_whitespace()
	if pos <= len then error('unexpected content after JSON') end
	return result
end

function json.load_file(filename)
	local file = io.open(filename, "r")
	if not file then
		error("Cannot open file: " .. filename)
	end

	local content = file:read("*all")
	file:close()

	return json.decode(content)
end

function json.save_file(filename, data)
	local file = io.open(filename, "w")
	if not file then
		error("Cannot write to file: " .. filename)
	end

	file:write(json.encode(data))
	file:close()
end

function json.merge(...)
	local result = {}
	local n = select("#", ...)
	for i = 1, n do
		local obj = select(i, ...)
		if type(obj) == "table" then
			for k, v in pairs(obj) do
				result[k] = v
			end
		end
	end
	return result
end

function json.extract(data, path)
	local current = data
	local start = 1
	local len = #path

	while start <= len do
		local dot_pos = path:find(".", start, true)
		local part = dot_pos and path:sub(start, dot_pos - 1) or path:sub(start)

		if type(current) ~= "table" then
			return nil
		end

		local bracket_start, bracket_end = part:find("^%[(%d+)%]$")
		if bracket_start then
			local index = tonumber(part:sub(2, -2)) + 1
			current = current[index]
		else
			current = current[part]
		end

		if current == nil then
			return nil
		end

		start = dot_pos and dot_pos + 1 or len + 1
	end

	return current
end

function json.pretty(value, indent)
	local buffer = {}
	local pos = 1
	indent = indent or "  "

	local function encode_string(s)
		buffer[pos] = '"'
		pos = pos + 1

		local start = 1
		for i = 1, #s do
			local c = s:byte(i)
			if c == 34 then -- "
				if i > start then
					buffer[pos] = s:sub(start, i - 1)
					pos = pos + 1
				end
				buffer[pos] = '\\"'
				pos = pos + 1
				start = i + 1
			elseif c == 92 then -- \
				if i > start then
					buffer[pos] = s:sub(start, i - 1)
					pos = pos + 1
				end
				buffer[pos] = '\\\\'
				pos = pos + 1
				start = i + 1
			elseif c < 32 then
				if i > start then
					buffer[pos] = s:sub(start, i - 1)
					pos = pos + 1
				end
				if c == 8 then
					buffer[pos] = '\\b'
				elseif c == 9 then
					buffer[pos] = '\\t'
				elseif c == 10 then
					buffer[pos] = '\\n'
				elseif c == 12 then
					buffer[pos] = '\\f'
				elseif c == 13 then
					buffer[pos] = '\\r'
				else
					buffer[pos] = ('\\u%04x'):format(c)
				end
				pos = pos + 1
				start = i + 1
			end
		end

		if start <= #s then
			buffer[pos] = s:sub(start)
			pos = pos + 1
		end

		buffer[pos] = '"'
		pos = pos + 1
	end

	local function encode_value(v, depth)
		local t = type(v)
		local current_indent = string.rep(indent, depth)
		local next_indent = string.rep(indent, depth + 1)

		if t == 'string' then
			encode_string(v)
		elseif t == 'number' then
			if v ~= v then -- NaN
				buffer[pos] = 'null'
			elseif v == 1/0 or v == -1/0 then -- Infinity
				buffer[pos] = 'null'
			else
				buffer[pos] = tostring(v)
			end
			pos = pos + 1
		elseif t == 'boolean' then
			buffer[pos] = v and 'true' or 'false'
			pos = pos + 1
		elseif t == 'table' then
			if depth > 100 then error('circular reference') end

			local is_array = true
			local max_index = 0
			local count = 0

			for k, _ in pairs(v) do
				count = count + 1
				if type(k) ~= 'number' or k <= 0 or k % 1 ~= 0 then
					is_array = false
					break
				end
				if k > max_index then max_index = k end
			end

			if is_array and count == max_index then
				buffer[pos] = '[\n'
				pos = pos + 1

				for i = 1, max_index do
					buffer[pos] = next_indent
					pos = pos + 1
					encode_value(v[i], depth + 1)
					if i < max_index then
						buffer[pos] = ','
						pos = pos + 1
					end
					buffer[pos] = '\n'
					pos = pos + 1
				end

				buffer[pos] = current_indent .. ']'
				pos = pos + 1
			else
				buffer[pos] = '{\n'
				pos = pos + 1

				local keys = {}
				for k in pairs(v) do
					keys[#keys + 1] = k
				end

				for i, k in ipairs(keys) do
					buffer[pos] = next_indent
					pos = pos + 1
					encode_string(tostring(k))
					buffer[pos] = ': '
					pos = pos + 1
					encode_value(v[k], depth + 1)
					if i < #keys then
						buffer[pos] = ','
						pos = pos + 1
					end
					buffer[pos] = '\n'
					pos = pos + 1
				end

				buffer[pos] = current_indent .. '}'
				pos = pos + 1
			end
		else
			buffer[pos] = 'null'
			pos = pos + 1
		end
	end

	encode_value(value, 0)
	return table.concat(buffer)
end

function json.validate(data, schema)
	local function validate_value(value, schema_value)
		local value_type = type(value)
		local schema_type = schema_value.type

		if schema_type and value_type ~= schema_type then
			return false, "Expected " .. schema_type .. ", got " .. value_type
		end

		if schema_type == "table" and schema_value.properties then
			local required = schema_value.required
			for prop, prop_schema in pairs(schema_value.properties) do
				local prop_value = value[prop]

				if required and required[prop] and prop_value == nil then
					return false, "Missing required property: " .. prop
				end

				if prop_value ~= nil then
					local valid, err = validate_value(prop_value, prop_schema)
					if not valid then
						return false, "Property " .. prop .. ": " .. err
					end
				end
			end
		end

		return true
	end

	return validate_value(data, schema)
end

return json