use units::si

### Temperature conversion functions K <-> °C and K <-> °F

let _offset_celsius = 273.15

@description("Converts from degree Celsius (°C) to Kelvin.")
@example("from_celsius(300)", "300 °C in Kelvin.")
@url("https://en.wikipedia.org/wiki/Conversion_of_scales_of_temperature")
fn from_celsius(t_celsius: Scalar) -> Temperature = (t_celsius + _offset_celsius) kelvin

@description("Converts from Kelvin to degree Celcius (°C). This can be used on the right hand side of a conversion operator: `200 K -> celsius`.")
@example("300K -> celsius", "300 K in degree Celsius.")
@url("https://en.wikipedia.org/wiki/Conversion_of_scales_of_temperature")
fn celsius(t_kelvin: Temperature) -> Scalar = t_kelvin / kelvin - _offset_celsius

let _offset_fahrenheit = 459.67
let _scale_fahrenheit = 5 / 9

@description("Converts from degree Fahrenheit (°F) to Kelvin.")
@example("from_fahrenheit(300)", "300 °F in Kelvin.")
@url("https://en.wikipedia.org/wiki/Conversion_of_scales_of_temperature")
fn from_fahrenheit(t_fahrenheit: Scalar) -> Temperature = ((t_fahrenheit + _offset_fahrenheit) × _scale_fahrenheit) kelvin

@description("Converts from Kelvin to degree Fahrenheit (°F). This can be used on the right hand side of a conversion operator: `200 K -> fahrenheit`.")
@example("300K -> fahrenheit", "300 K in degree Fahrenheit.")
@url("https://en.wikipedia.org/wiki/Conversion_of_scales_of_temperature")
fn fahrenheit(t_kelvin: Temperature) -> Scalar = (t_kelvin / kelvin) / _scale_fahrenheit - _offset_fahrenheit