/**
 * Utilities for working with the Int8 type.
 * @example from "int8" include Int8
 *
 * @example 1s
 * @example -1s
 *
 * @since v0.6.0
 */
module Int8

from "runtime/unsafe/wasmi32" include WasmI32
use WasmI32.{
  (+),
  (-),
  (*),
  (/),
  (&),
  (|),
  (^),
  (<<),
  (>>),
  (>>),
  (==),
  (!=),
  (<),
  (<=),
  (>),
  (>=),
}
from "runtime/exception" include Exception
from "runtime/numbers" include Numbers
use Numbers.{ coerceNumberToInt8 as fromNumber, coerceInt8ToNumber as toNumber }
from "runtime/dataStructures" include DataStructures
use DataStructures.{ tagInt8, untagInt8 }

@unsafe
let _TAG_BYTE = 0b1010n
@unsafe
let _DATA_MASK = 0xffffff00n

provide { fromNumber, toNumber }

// Trick: can simply use WasmI32.extendS16 to sign-extend 8-bit ints rather
// than having to shift right, extendS8, and retag

/**
 * Converts a Uint8 to an Int8.
 *
 * @param number: The value to convert
 * @returns The Uint8 represented as an Int8
 *
 * @example Int8.fromUint8(1us) == 1s
 *
 * @since v0.6.0
 */
@unsafe
provide let fromUint8 = (number: Uint8) => {
  let x = WasmI32.fromGrain(number)
  // Trick: convert from Uint8 tag 11010 to Int8 tag 1010
  let result = x ^ 0b10000n
  WasmI32.toGrain(WasmI32.extendS16(result)): Int8
}

/**
 * Increments the value by one.
 *
 * @param value: The value to increment
 * @returns The incremented value
 *
 * @example Int8.incr(1s) == 2s
 * @example Int8.incr(-2s) == -1s
 *
 * @since v0.6.0
 */
@unsafe
provide let incr = (value: Int8) => {
  let value = WasmI32.fromGrain(value)
  // Trick: since the data is at offset 8, can just add 1 << 8 == 0x100
  let result = value + 0x100n
  WasmI32.toGrain(WasmI32.extendS16(result)): Int8
}

/**
 * Decrements the value by one.
 *
 * @param value: The value to decrement
 * @returns The decremented value
 *
 * @example Int8.decr(2s) == 1s
 * @example Int8.decr(0s) == -1s
 *
 * @since v0.6.0
 */
@unsafe
provide let decr = (value: Int8) => {
  let value = WasmI32.fromGrain(value)
  // Trick: since the data is at offset 8, can just subtract 1 << 8 == 0x100
  let result = value - 0x100n
  WasmI32.toGrain(WasmI32.extendS16(result)): Int8
}

/**
 * Computes the sum of its operands.
 *
 * @param x: The first operand
 * @param y: The second operand
 * @returns The sum of the two operands
 *
 * @example
 * use Int8.{ (+) }
 * assert 1s + 1s == 2s
 *
 * @since v0.6.0
 */
@unsafe
provide let (+) = (x: Int8, y: Int8) => {
  // Trick: add the values as-is without shifting right 8; this will cause
  // the data to be added correctly but the trailing tag bits will be corrupted:
  // 1010 + 1010 = 10100; xor with 11110 to correct to 1010
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  let val = x + y
  let tagged = val ^ 0b11110n
  WasmI32.toGrain(WasmI32.extendS16(tagged)): Int8
}

/**
 * Computes the difference of its operands.
 *
 * @param x: The first operand
 * @param y: The second operand
 * @returns The difference of the two operands
 *
 * @example
 * use Int8.{ (-) }
 * assert 2s - 1s == 1s
 *
 * @since v0.6.0
 */
@unsafe
provide let (-) = (x: Int8, y: Int8) => {
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  let val = x - y
  let tagged = val | _TAG_BYTE
  WasmI32.toGrain(WasmI32.extendS16(tagged)): Int8
}

/**
 * Computes the product of its operands.
 *
 * @param x: The first operand
 * @param y: The second operand
 * @returns The product of the two operands
 *
 * @example
 * use Int8.{ (*) }
 * assert 2s * 2s == 4s
 *
 * @since v0.6.0
 */
@unsafe
provide let (*) = (x: Int8, y: Int8) => {
  let x = untagInt8(x)
  let y = untagInt8(y)
  let val = WasmI32.extendS8(x * y)
  tagInt8(val)
}

/**
 * Computes the quotient of its operands using signed division.
 *
 * @param x: The first operand
 * @param y: The second operand
 * @returns The quotient of its operands
 *
 * @example
 * use Int8.{ (/) }
 * assert 8s / 2s == 4s
 *
 * @since v0.6.0
 */
@unsafe
provide let (/) = (x: Int8, y: Int8) => {
  let x = untagInt8(x)
  let y = untagInt8(y)
  // No need to re-sign-extend
  let val = x / y
  tagInt8(val)
}

/**
 * Computes the remainder of the division of its operands using signed division.
 *
 * @param x: The first operand
 * @param y: The second operand
 * @returns The remainder of its operands
 *
 * @example Int8.rem(8s, 3s) == 2s
 *
 * @since v0.6.0
 */
@unsafe
provide let rem = (x: Int8, y: Int8) => {
  let x = untagInt8(x)
  let y = untagInt8(y)
  // No need to re-sign-extend
  let val = WasmI32.remS(x, y)
  tagInt8(val)
}

@unsafe
let abs = n => {
  use WasmI32.{ (-) }
  let mask = n >> 31n
  (n ^ mask) - mask
}

/**
 * Computes the remainder of the division of the first operand by the second.
 * The result will have the sign of the second operand.
 *
 * @param x: The first operand
 * @param y: The second operand
 * @returns The modulus of its operands
 *
 * @throws ModuloByZero: When `y` is zero
 *
 * @example
 * use Int8.{ (%) }
 * assert -5s % 3s == 1s
 *
 * @since v0.6.0
 */
@unsafe
provide let (%) = (x: Int8, y: Int8) => {
  use WasmI32.{ (-) }
  let xval = untagInt8(x)
  let yval = untagInt8(y)

  if (WasmI32.eqz(yval)) {
    throw Exception.ModuloByZero
  }

  let val = if ((xval ^ yval) < 0n) {
    let xabs = abs(xval)
    let yabs = abs(yval)
    let mval = WasmI32.remS(xabs, yabs)
    let mres = yabs - mval
    if (mval != 0n) (if (yval < 0n) 0n - mres else mres) else 0n
  } else {
    WasmI32.remS(xval, yval)
  }
  tagInt8(val)
}

/**
 * Shifts the bits of the value left by the given number of bits.
 *
 * @param value: The value to shift
 * @param amount: The number of bits to shift by
 * @returns The shifted value
 *
 * @example
 * use Int8.{ (<<) }
 * assert (5s << 1s) == 10s
 *
 * @since v0.6.0
 */
@unsafe
provide let (<<) = (value: Int8, amount: Int8) => {
  // Trick: do not shift `value` right, just correct tag afterwards
  let x = WasmI32.fromGrain(value) & _DATA_MASK
  let y = untagInt8(amount)
  let val = x << y
  let tagged = val | _TAG_BYTE
  WasmI32.toGrain(WasmI32.extendS16(tagged)): Int8
}

/**
 * Shifts the bits of the value right by the given number of bits, preserving the sign bit.
 *
 * @param value: The value to shift
 * @param amount: The amount to shift by
 * @returns The shifted value
 *
 * @example
 * use Int8.{ (>>) }
 * assert (5s >> 1s) == 2s
 *
 * @since v0.6.0
 */
@unsafe
provide let (>>) = (value: Int8, amount: Int8) => {
  // Trick: do not shift `value` right, just correct tag afterwards
  let x = WasmI32.fromGrain(value)
  let y = untagInt8(amount)
  let val = x >> y
  let tagged = val & _DATA_MASK | _TAG_BYTE
  WasmI32.toGrain(tagged): Int8
}

/**
 * Checks if the first value is equal to the second value.
 *
 * @param x: The first value
 * @param y: The second value
 * @returns `true` if the first value is equal to the second value or `false` otherwise
 *
 * @example
 * use Int8.{ (==) }
 * assert 1s == 1s
 *
 * @since v0.6.0
 */
@unsafe
provide let (==) = (x: Int8, y: Int8) => {
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  x == y
}

/**
 * Checks if the first value is not equal to the second value.
 *
 * @param x: The first value
 * @param y: The second value
 * @returns `true` if the first value is not equal to the second value or `false` otherwise
 *
 * @example
 * use Int8.{ (!=) }
 * assert 1s != 2s
 *
 * @since v0.6.0
 */
@unsafe
provide let (!=) = (x: Int8, y: Int8) => {
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  x != y
}

/**
 * Checks if the first value is less than the second value.
 *
 * @param x: The first value
 * @param y: The second value
 * @returns `true` if the first value is less than the second value or `false` otherwise
 *
 * @example
 * use Int8.{ (<) }
 * assert 1s < 2s
 *
 * @since v0.6.0
 */
@unsafe
provide let (<) = (x: Int8, y: Int8) => {
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  x < y
}

/**
 * Checks if the first value is greater than the second value.
 *
 * @param x: The first value
 * @param y: The second value
 * @returns `true` if the first value is greater than the second value or `false` otherwise
 *
 * @example
 * use Int8.{ (>) }
 * assert 2s > 1s
 *
 * @since v0.6.0
 */
@unsafe
provide let (>) = (x: Int8, y: Int8) => {
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  x > y
}

/**
 * Checks if the first value is less than or equal to the second value.
 *
 * @param x: The first value
 * @param y: The second value
 * @returns `true` if the first value is less than or equal to the second value or `false` otherwise
 *
 * @example
 * use Int8.{ (<=) }
 * assert 1s <= 2s
 * @example
 * use Int8.{ (<=) }
 * assert 1s <= 1s
 *
 * @since v0.6.0
 */
@unsafe
provide let (<=) = (x: Int8, y: Int8) => {
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  x <= y
}

/**
 * Checks if the first value is greater than or equal to the second value.
 *
 * @param x: The first value
 * @param y: The second value
 * @returns `true` if the first value is greater than or equal to the second value or `false` otherwise
 *
 * @example
 * use Int8.{ (>=) }
 * assert 2s >= 1s
 * @example
 * use Int8.{ (>=) }
 * assert 1s >= 1s
 *
 * @since v0.6.0
 */
@unsafe
provide let (>=) = (x: Int8, y: Int8) => {
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  x >= y
}

/**
 * Computes the bitwise NOT of the given value.
 *
 * @param value: The given value
 * @returns Containing the inverted bits of the given value
 *
 * @example Int8.lnot(-5s) == 4s
 *
 * @since v0.6.0
 */
@unsafe
provide let lnot = (value: Int8) => {
  let x = WasmI32.fromGrain(value)
  WasmI32.toGrain(x ^ _DATA_MASK): Int8
}

/**
 * Computes the bitwise AND (`&`) on the given operands.
 *
 * @param x: The first operand
 * @param y: The second operand
 * @returns Containing a `1` in each bit position for which the corresponding bits of both operands are `1`
 *
 * @example
 * use Int8.{ (&) }
 * assert (3s & 4s) == 0s
 *
 * @since v0.6.0
 */
@unsafe
provide let (&) = (x: Int8, y: Int8) => {
  // Tags getting `and`ed together is not a problem
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  let val = x & y
  WasmI32.toGrain(val): Int8
}

/**
 * Computes the bitwise OR (`|`) on the given operands.
 *
 * @param x: The first operand
 * @param y: The second operand
 * @returns Containing a `1` in each bit position for which the corresponding bits of either or both operands are `1`
 *
 * @example
 * use Int8.{ (|) }
 * assert (3s | 4s) == 7s
 *
 * @since v0.6.0
 */
@unsafe
provide let (|) = (x: Int8, y: Int8) => {
  // Tags getting `or`ed together is not a problem
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  let val = x | y
  WasmI32.toGrain(val): Int8
}

/**
 * Computes the bitwise XOR (`^`) on the given operands.
 *
 * @param x: The first operand
 * @param y: The second operand
 * @returns Containing a `1` in each bit position for which the corresponding bits of either but not both operands are `1`
 *
 * @example
 * use Int8.{ (^) }
 * assert (3s ^ 5s) == 6s
 *
 * @since v0.6.0
 */
@unsafe
provide let (^) = (x: Int8, y: Int8) => {
  use WasmI32.{ (|) }
  // Tags getting `xor`ed together will cancel each other out; add back tag with or
  let x = WasmI32.fromGrain(x)
  let y = WasmI32.fromGrain(y)
  let val = x ^ y
  WasmI32.toGrain(val | _TAG_BYTE): Int8
}