package main

import (
	"math"

	"github.com/shopspring/decimal"
)

var unitRegistry = make(map[string]UnitInfo)

func d(f float64) decimal.Decimal {
	return decimal.NewFromFloat(f)
}

// initUnits populates the unitRegistry with supported units.
func initUnits() {
	// Length (Pivot: meter)
	unitRegistry["M"] = UnitInfo{d(1.0), DimLength, "m"}
	unitRegistry["DM"] = UnitInfo{d(0.1), DimLength, "dm"}
	unitRegistry["CM"] = UnitInfo{d(0.01), DimLength, "cm"}
	unitRegistry["MM"] = UnitInfo{d(0.001), DimLength, "mm"}
	unitRegistry["UM"] = UnitInfo{d(1e-6), DimLength, "um"}
	unitRegistry["NM"] = UnitInfo{d(1e-9), DimLength, "nm"}
	unitRegistry["KM"] = UnitInfo{d(1000.0), DimLength, "km"}
	unitRegistry["IN"] = UnitInfo{d(0.0254), DimLength, "in"}
	unitRegistry["FT"] = UnitInfo{d(0.3048), DimLength, "ft"}
	unitRegistry["YD"] = UnitInfo{d(0.9144), DimLength, "yd"}
	unitRegistry["MI"] = UnitInfo{d(1609.344), DimLength, "mi"}
	unitRegistry["NMI"] = UnitInfo{d(1852.0), DimLength, "nmi"}

	// Mass (Pivot: gram)
	unitRegistry["G"] = UnitInfo{d(1.0), DimMass, "g"}
	unitRegistry["MG"] = UnitInfo{d(0.001), DimMass, "mg"}
	unitRegistry["KG"] = UnitInfo{d(1000.0), DimMass, "kg"}
	unitRegistry["T"] = UnitInfo{d(1e6), DimMass, "t"}
	unitRegistry["CT"] = UnitInfo{d(0.2), DimMass, "ct"}
	unitRegistry["LB"] = UnitInfo{d(453.592), DimMass, "lb"}
	unitRegistry["OZ"] = UnitInfo{d(28.3495), DimMass, "oz"}

	// Time (Pivot: second)
	unitRegistry["S"] = UnitInfo{d(1.0), DimTime, "s"}
	unitRegistry["MS"] = UnitInfo{d(0.001), DimTime, "ms"}
	unitRegistry["US"] = UnitInfo{d(1e-6), DimTime, "us"}
	unitRegistry["NS"] = UnitInfo{d(1e-9), DimTime, "ns"}
	unitRegistry["MIN"] = UnitInfo{d(60.0), DimTime, "min"}
	unitRegistry["H"] = UnitInfo{d(3600.0), DimTime, "h"}
	unitRegistry["D"] = UnitInfo{d(86400.0), DimTime, "d"}
	unitRegistry["WK"] = UnitInfo{d(604800.0), DimTime, "wk"}
	unitRegistry["YR"] = UnitInfo{d(31536000.0), DimTime, "yr"}

	// Digital (Pivot: byte)
	unitRegistry["B"] = UnitInfo{d(1.0), DimDigital, "B"}
	unitRegistry["KB"] = UnitInfo{d(1024.0), DimDigital, "KB"}
	unitRegistry["MB"] = UnitInfo{d(1024.0 * 1024.0), DimDigital, "MB"}
	unitRegistry["GB"] = UnitInfo{d(1024.0 * 1024.0 * 1024.0), DimDigital, "GB"}
	unitRegistry["TB"] = UnitInfo{d(1024.0 * 1024.0 * 1024.0 * 1024.0), DimDigital, "TB"}
	unitRegistry["PB"] = UnitInfo{d(1024.0 * 1024.0 * 1024.0 * 1024.0 * 1024.0), DimDigital, "PB"}
	unitRegistry["EB"] = UnitInfo{d(1024.0 * 1024.0 * 1024.0 * 1024.0 * 1024.0 * 1024.0), DimDigital, "EB"}

	// Area (Pivot: square meter)
	unitRegistry["M2"] = UnitInfo{d(1.0), DimArea, "m²"}
	unitRegistry["CM2"] = UnitInfo{d(1e-4), DimArea, "cm²"}
	unitRegistry["MM2"] = UnitInfo{d(1e-6), DimArea, "mm²"}
	unitRegistry["KM2"] = UnitInfo{d(1e6), DimArea, "km²"}
	unitRegistry["HA"] = UnitInfo{d(10000.0), DimArea, "ha"}
	unitRegistry["ACRE"] = UnitInfo{d(4046.8564), DimArea, "acre"}

	// Temperature (Pivot: Kelvin)
	unitRegistry["K"] = UnitInfo{d(1.0), DimTemp, "K"}
	unitRegistry["C"] = UnitInfo{d(1.0), DimTemp, "°C"}
	unitRegistry["F"] = UnitInfo{d(1.0), DimTemp, "°F"}
	unitRegistry["KELVIN"] = UnitInfo{d(1.0), DimTemp, "K"}
	unitRegistry["CELSIUS"] = UnitInfo{d(1.0), DimTemp, "°C"}
	unitRegistry["FAHRENHEIT"] = UnitInfo{d(1.0), DimTemp, "°F"}

	// Angle (Pivot: Radian)
	unitRegistry["RAD"] = UnitInfo{d(1.0), DimAngle, "rad"}
	unitRegistry["DEG"] = UnitInfo{d(math.Pi / 180.0), DimAngle, "deg"}
	unitRegistry["GRAD"] = UnitInfo{d(math.Pi / 200.0), DimAngle, "grad"}
	unitRegistry["RADIAN"] = UnitInfo{d(1.0), DimAngle, "rad"}
	unitRegistry["DEGREE"] = UnitInfo{d(math.Pi / 180.0), DimAngle, "deg"}
	unitRegistry["DEGREES"] = UnitInfo{d(math.Pi / 180.0), DimAngle, "deg"}
	unitRegistry["GRADIAN"] = UnitInfo{d(math.Pi / 200.0), DimAngle, "grad"}
}

// getDimName returns a human-readable string for a dimension.
func getDimName(d Dimension) string {
	switch d {
	case DimCurrency:
		return "Currency"
	case DimLength:
		return "Length"
	case DimMass:
		return "Mass"
	case DimTime:
		return "Time"
	case DimDigital:
		return "Digital Storage"
	case DimArea:
		return "Area"
	case DimTemp:
		return "Temperature"
	case DimAngle:
		return "Angle"
	default:
		return "Number"
	}
}