//TODO: multimodal, add interface, test somehow, track performance, refactor sampleSet, refactor ASTEvaluator.res.
type t = DistributionTypes.genericDist
type error = DistributionTypes.error
type toPointSetFn = t => result<PointSetTypes.pointSetDist, error>
type toSampleSetFn = t => result<SampleSetDist.t, error>
type scaleMultiplyFn = (t, float) => result<t, error>
type pointwiseAddFn = (t, t) => result<t, error>

let isPointSet = (t: t) =>
  switch t {
  | PointSet(_) => true
  | _ => false
  }

let isSampleSetSet = (t: t) =>
  switch t {
  | SampleSet(_) => true
  | _ => false
  }

let isSymbolic = (t: t) =>
  switch t {
  | Symbolic(_) => true
  | _ => false
  }

let sampleN = (t: t, n) =>
  switch t {
  | PointSet(r) => PointSetDist.sampleNRendered(n, r)
  | Symbolic(r) => SymbolicDist.T.sampleN(n, r)
  | SampleSet(r) => SampleSetDist.sampleN(r, n)
  }

let toSampleSetDist = (t: t, n) =>
  SampleSetDist.make(sampleN(t, n))->E.R2.errMap(DistributionTypes.Error.sampleErrorToDistErr)

let fromFloat = (f: float): t => Symbolic(SymbolicDist.Float.make(f))

let toString = (t: t) =>
  switch t {
  | PointSet(_) => "Point Set Distribution"
  | Symbolic(r) => SymbolicDist.T.toString(r)
  | SampleSet(_) => "Sample Set Distribution"
  }

let normalize = (t: t): t =>
  switch t {
  | PointSet(r) => PointSet(PointSetDist.T.normalize(r))
  | Symbolic(_) => t
  | SampleSet(_) => t
  }

let integralEndY = (t: t): float =>
  switch t {
  | PointSet(r) => PointSetDist.T.integralEndY(r)
  | Symbolic(_) => 1.0
  | SampleSet(_) => 1.0
  }

let isNormalized = (t: t): bool => Js.Math.abs_float(integralEndY(t) -. 1.0) < 1e-7

module Score = {
  let klDivergence = (prediction, answer, ~toPointSetFn: toPointSetFn): result<float, error> => {
    let pointSets = E.R.merge(toPointSetFn(prediction), toPointSetFn(answer))
    pointSets |> E.R2.bind(((predi, ans)) =>
      PointSetDist.T.klDivergence(predi, ans)->E.R2.errMap(x => DistributionTypes.OperationError(x))
    )
  }

  let logScoreWithPointResolution = (
    prior,
    prediction,
    answer,
    ~toPointSetFn: toPointSetFn,
  ): result<float, error> => {
    switch prior {
    | Some(prior') =>
      E.R.merge(toPointSetFn(prior'), toPointSetFn(prediction))->E.R.bind(((a, b)) =>
        PointSetDist.T.logScoreWithPointResolution(
          a->Some,
          b,
          answer,
        )->E.R2.errMap(x => DistributionTypes.OperationError(x))
      )
    | None =>
      prediction
      ->toPointSetFn
      ->E.R.bind(x =>
        PointSetDist.T.logScoreWithPointResolution(
          None,
          x,
          answer,
        )->E.R2.errMap(x => DistributionTypes.OperationError(x))
      )
    }
  }
}

let toFloatOperation = (
  t,
  ~toPointSetFn: toPointSetFn,
  ~distToFloatOperation: DistributionTypes.DistributionOperation.toFloat,
) => {
  switch distToFloatOperation {
  | #IntegralSum => Ok(integralEndY(t))
  | (#Pdf(_) | #Cdf(_) | #Inv(_) | #Mean | #Sample) as op => {
      let trySymbolicSolution = switch (t: t) {
      | Symbolic(r) => SymbolicDist.T.operate(op, r)->E.R.toOption
      | _ => None
      }

      let trySampleSetSolution = switch ((t: t), distToFloatOperation) {
      | (SampleSet(sampleSet), #Mean) => SampleSetDist.mean(sampleSet)->Some
      | (SampleSet(sampleSet), #Sample) => SampleSetDist.sample(sampleSet)->Some
      | (SampleSet(sampleSet), #Inv(r)) => SampleSetDist.percentile(sampleSet, r)->Some
      | _ => None
      }

      switch trySymbolicSolution {
      | Some(r) => Ok(r)
      | None =>
        switch trySampleSetSolution {
        | Some(r) => Ok(r)
        | None => toPointSetFn(t)->E.R2.fmap(PointSetDist.operate(op))
        }
      }
    }
  }
}

//Todo: If it's a pointSet, but the xyPointLength is different from what it has, it should change.
// This is tricky because the case of discrete distributions.
// Also, change the outputXYPoints/pointSetDistLength details
let toPointSet = (
  t,
  ~xyPointLength,
  ~sampleCount,
  ~xSelection: DistributionTypes.DistributionOperation.pointsetXSelection=#ByWeight,
  (),
): result<PointSetTypes.pointSetDist, error> => {
  switch (t: t) {
  | PointSet(pointSet) => Ok(pointSet)
  | Symbolic(r) => Ok(SymbolicDist.T.toPointSetDist(~xSelection, xyPointLength, r))
  | SampleSet(r) =>
    SampleSetDist.toPointSetDist(
      ~samples=r,
      ~samplingInputs={
        sampleCount: sampleCount,
        outputXYPoints: xyPointLength,
        pointSetDistLength: xyPointLength,
        kernelWidth: None,
      },
    )->E.R2.errMap(x => DistributionTypes.PointSetConversionError(x))
  }
}

/*
  PointSetDist.toSparkline calls "downsampleEquallyOverX", which downsamples it to n=bucketCount.
  It first needs a pointSetDist, so we convert to a pointSetDist. In this process we want the 
  xyPointLength to be a bit longer than the eventual toSparkline downsampling. I chose 3 
  fairly arbitrarily.
 */
let toSparkline = (t: t, ~sampleCount: int, ~bucketCount: int=20, ()): result<string, error> =>
  t
  ->toPointSet(~xSelection=#Linear, ~xyPointLength=bucketCount * 3, ~sampleCount, ())
  ->E.R.bind(r =>
    r->PointSetDist.toSparkline(bucketCount)->E.R2.errMap(x => DistributionTypes.SparklineError(x))
  )

module Truncate = {
  let trySymbolicSimplification = (
    leftCutoff: option<float>,
    rightCutoff: option<float>,
    t: t,
  ): option<t> =>
    switch (leftCutoff, rightCutoff, t) {
    | (None, None, _) => None
    | (Some(lc), Some(rc), Symbolic(#Uniform(u))) if lc < rc =>
      Some(Symbolic(#Uniform(SymbolicDist.Uniform.truncate(Some(lc), Some(rc), u))))
    | (lc, rc, Symbolic(#Uniform(u))) =>
      Some(Symbolic(#Uniform(SymbolicDist.Uniform.truncate(lc, rc, u))))
    | _ => None
    }

  let run = (
    t: t,
    ~toPointSetFn: toPointSetFn,
    ~leftCutoff=None: option<float>,
    ~rightCutoff=None: option<float>,
    (),
  ): result<t, error> => {
    let doesNotNeedCutoff = E.O.isNone(leftCutoff) && E.O.isNone(rightCutoff)
    if doesNotNeedCutoff {
      Ok(t)
    } else {
      switch trySymbolicSimplification(leftCutoff, rightCutoff, t) {
      | Some(r) => Ok(r)
      | None =>
        toPointSetFn(t)->E.R2.fmap(t => {
          DistributionTypes.PointSet(PointSetDist.T.truncate(leftCutoff, rightCutoff, t))
        })
      }
    }
  }
}

let truncate = Truncate.run

/* Given two random variables A and B, this returns the distribution
   of a new variable that is the result of the operation on A and B.
   For instance, normal(0, 1) + normal(1, 1) -> normal(1, 2).
   In general, this is implemented via convolution.
*/
module AlgebraicCombination = {
  module InputValidator = {
    /*
     It would be good to also do a check to make sure that probability mass for the second
     operand, at value 1.0, is 0 (or approximately 0). However, we'd ideally want to check 
     that both the probability mass and the probability density are greater than zero.
     Right now we don't yet have a way of getting probability mass, so I'll leave this for later.
 */
    let getLogarithmInputError = (t1: t, t2: t, ~toPointSetFn: toPointSetFn): option<error> => {
      let firstOperandIsGreaterThanZero =
        toFloatOperation(
          t1,
          ~toPointSetFn,
          ~distToFloatOperation=#Cdf(MagicNumbers.Epsilon.ten),
        ) |> E.R.fmap(r => r > 0.)
      let secondOperandIsGreaterThanZero =
        toFloatOperation(
          t2,
          ~toPointSetFn,
          ~distToFloatOperation=#Cdf(MagicNumbers.Epsilon.ten),
        ) |> E.R.fmap(r => r > 0.)
      let items = E.A.R.firstErrorOrOpen([
        firstOperandIsGreaterThanZero,
        secondOperandIsGreaterThanZero,
      ])
      switch items {
      | Error(r) => Some(r)
      | Ok([true, _]) =>
        Some(LogarithmOfDistributionError("First input must be completely greater than 0"))
      | Ok([false, true]) =>
        Some(LogarithmOfDistributionError("Second input must be completely greater than 0"))
      | Ok([false, false]) => None
      | Ok(_) => Some(Unreachable)
      }
    }

    let run = (t1: t, t2: t, ~toPointSetFn: toPointSetFn, ~arithmeticOperation): option<error> => {
      if arithmeticOperation == #Logarithm {
        getLogarithmInputError(t1, t2, ~toPointSetFn)
      } else {
        None
      }
    }
  }

  module StrategyCallOnValidatedInputs = {
    let convolution = (
      toPointSet: toPointSetFn,
      arithmeticOperation: Operation.convolutionOperation,
      t1: t,
      t2: t,
    ): result<t, error> =>
      E.R.merge(toPointSet(t1), toPointSet(t2))
      ->E.R2.fmap(((a, b)) => PointSetDist.combineAlgebraically(arithmeticOperation, a, b))
      ->E.R2.fmap(r => DistributionTypes.PointSet(r))

    let monteCarlo = (
      toSampleSet: toSampleSetFn,
      arithmeticOperation: Operation.algebraicOperation,
      t1: t,
      t2: t,
    ): result<t, error> => {
      let fn = Operation.Algebraic.toFn(arithmeticOperation)
      E.R.merge(toSampleSet(t1), toSampleSet(t2))
      ->E.R.bind(((t1, t2)) => {
        SampleSetDist.map2(~fn, ~t1, ~t2)->E.R2.errMap(x => DistributionTypes.OperationError(x))
      })
      ->E.R2.fmap(r => DistributionTypes.SampleSet(r))
    }

    let symbolic = (
      arithmeticOperation: Operation.algebraicOperation,
      t1: t,
      t2: t,
    ): SymbolicDistTypes.analyticalSimplificationResult => {
      switch (t1, t2) {
      | (DistributionTypes.Symbolic(d1), DistributionTypes.Symbolic(d2)) =>
        SymbolicDist.T.tryAnalyticalSimplification(d1, d2, arithmeticOperation)
      | _ => #NoSolution
      }
    }
  }

  module StrategyChooser = {
    type specificStrategy = [#AsSymbolic | #AsMonteCarlo | #AsConvolution]

    //I'm (Ozzie) really just guessing here, very little idea what's best
    let expectedConvolutionCost: t => int = x =>
      switch x {
      | Symbolic(#Float(_)) => MagicNumbers.OpCost.floatCost
      | Symbolic(_) => MagicNumbers.OpCost.symbolicCost
      | PointSet(Discrete(m)) => m.xyShape->XYShape.T.length
      | PointSet(Mixed(_)) => MagicNumbers.OpCost.mixedCost
      | PointSet(Continuous(_)) => MagicNumbers.OpCost.continuousCost
      | _ => MagicNumbers.OpCost.wildcardCost
      }

    let hasSampleSetDist = (t1: t, t2: t): bool => isSampleSetSet(t1) || isSampleSetSet(t2)

    let convolutionIsFasterThanMonteCarlo = (t1: t, t2: t): bool =>
      expectedConvolutionCost(t1) * expectedConvolutionCost(t2) < MagicNumbers.OpCost.monteCarloCost

    let preferConvolutionToMonteCarlo = (t1, t2, arithmeticOperation) => {
      !hasSampleSetDist(t1, t2) &&
      Operation.Convolution.canDoAlgebraicOperation(arithmeticOperation) &&
      convolutionIsFasterThanMonteCarlo(t1, t2)
    }

    let run = (~t1: t, ~t2: t, ~arithmeticOperation): specificStrategy => {
      switch StrategyCallOnValidatedInputs.symbolic(arithmeticOperation, t1, t2) {
      | #AnalyticalSolution(_)
      | #Error(_) =>
        #AsSymbolic
      | #NoSolution =>
        preferConvolutionToMonteCarlo(t1, t2, arithmeticOperation) ? #AsConvolution : #AsMonteCarlo
      }
    }
  }

  let runStrategyOnValidatedInputs = (
    ~t1: t,
    ~t2: t,
    ~arithmeticOperation,
    ~strategy: StrategyChooser.specificStrategy,
    ~toPointSetFn: toPointSetFn,
    ~toSampleSetFn: toSampleSetFn,
  ): result<t, error> => {
    switch strategy {
    | #AsMonteCarlo =>
      StrategyCallOnValidatedInputs.monteCarlo(toSampleSetFn, arithmeticOperation, t1, t2)
    | #AsSymbolic =>
      switch StrategyCallOnValidatedInputs.symbolic(arithmeticOperation, t1, t2) {
      | #AnalyticalSolution(symbolicDist) => Ok(Symbolic(symbolicDist))
      | #Error(e) => Error(OperationError(e))
      | #NoSolution => Error(Unreachable)
      }
    | #AsConvolution =>
      switch Operation.Convolution.fromAlgebraicOperation(arithmeticOperation) {
      | Some(convOp) => StrategyCallOnValidatedInputs.convolution(toPointSetFn, convOp, t1, t2)
      | None => Error(Unreachable)
      }
    }
  }

  let run = (
    ~strategy: DistributionTypes.asAlgebraicCombinationStrategy,
    t1: t,
    ~toPointSetFn: toPointSetFn,
    ~toSampleSetFn: toSampleSetFn,
    ~arithmeticOperation: Operation.algebraicOperation,
    ~t2: t,
  ): result<t, error> => {
    let invalidOperationError = InputValidator.run(t1, t2, ~arithmeticOperation, ~toPointSetFn)
    switch (invalidOperationError, strategy) {
    | (Some(e), _) => Error(e)
    | (None, AsDefault) => {
        let chooseStrategy = StrategyChooser.run(~arithmeticOperation, ~t1, ~t2)
        runStrategyOnValidatedInputs(
          ~t1,
          ~t2,
          ~strategy=chooseStrategy,
          ~arithmeticOperation,
          ~toPointSetFn,
          ~toSampleSetFn,
        )
      }
    | (None, AsMonteCarlo) =>
      StrategyCallOnValidatedInputs.monteCarlo(toSampleSetFn, arithmeticOperation, t1, t2)
    | (None, AsSymbolic) =>
      switch StrategyCallOnValidatedInputs.symbolic(arithmeticOperation, t1, t2) {
      | #AnalyticalSolution(symbolicDist) => Ok(Symbolic(symbolicDist))
      | #NoSolution => Error(RequestedStrategyInvalidError(`No analytic solution for inputs`))
      | #Error(err) => Error(OperationError(err))
      }
    | (None, AsConvolution) =>
      switch Operation.Convolution.fromAlgebraicOperation(arithmeticOperation) {
      | None => {
          let errString = `Convolution not supported for ${Operation.Algebraic.toString(
              arithmeticOperation,
            )}`
          Error(RequestedStrategyInvalidError(errString))
        }
      | Some(convOp) => StrategyCallOnValidatedInputs.convolution(toPointSetFn, convOp, t1, t2)
      }
    }
  }
}

let algebraicCombination = AlgebraicCombination.run

//TODO: Add faster pointwiseCombine fn
let pointwiseCombination = (
  t1: t,
  ~toPointSetFn: toPointSetFn,
  ~algebraicCombination: Operation.algebraicOperation,
  ~t2: t,
): result<t, error> => {
  E.R.merge(toPointSetFn(t1), toPointSetFn(t2))->E.R.bind(((t1, t2)) =>
    PointSetDist.combinePointwise(Operation.Algebraic.toFn(algebraicCombination), t1, t2)
    ->E.R2.fmap(r => DistributionTypes.PointSet(r))
    ->E.R2.errMap(err => DistributionTypes.OperationError(err))
  )
}

let pointwiseCombinationFloat = (
  t: t,
  ~toPointSetFn: toPointSetFn,
  ~algebraicCombination: Operation.algebraicOperation,
  ~f: float,
): result<t, error> => {
  let executeCombination = arithOp =>
    toPointSetFn(t)->E.R.bind(t => {
      //TODO: Move to PointSet codebase
      let fn = (secondary, main) => Operation.Scale.toFn(arithOp, main, secondary)
      let integralSumCacheFn = Operation.Scale.toIntegralSumCacheFn(arithOp)
      let integralCacheFn = Operation.Scale.toIntegralCacheFn(arithOp)
      PointSetDist.T.mapYResult(
        ~integralSumCacheFn=integralSumCacheFn(f),
        ~integralCacheFn=integralCacheFn(f),
        ~fn=fn(f),
        t,
      )->E.R2.errMap(x => DistributionTypes.OperationError(x))
    })
  let m = switch algebraicCombination {
  | #Add | #Subtract => Error(DistributionTypes.DistributionVerticalShiftIsInvalid)
  | (#Multiply | #Divide | #Power | #Logarithm) as arithmeticOperation =>
    executeCombination(arithmeticOperation)
  | #LogarithmWithThreshold(eps) => executeCombination(#LogarithmWithThreshold(eps))
  }
  m->E.R2.fmap(r => DistributionTypes.PointSet(r))
}

//Note: The result should always cumulatively sum to 1. This would be good to test.
//Note: If the inputs are not normalized, this will return poor results. The weights probably refer to the post-normalized forms. It would be good to apply a catch to this.
let mixture = (
  values: array<(t, float)>,
  ~scaleMultiplyFn: scaleMultiplyFn,
  ~pointwiseAddFn: pointwiseAddFn,
) => {
  if E.A.length(values) == 0 {
    Error(DistributionTypes.OtherError("Mixture error: mixture must have at least 1 element"))
  } else {
    let totalWeight = values->E.A2.fmap(E.Tuple2.second)->E.A.Floats.sum
    let properlyWeightedValues =
      values
      ->E.A2.fmap(((dist, weight)) => scaleMultiplyFn(dist, weight /. totalWeight))
      ->E.A.R.firstErrorOrOpen
    properlyWeightedValues->E.R.bind(values => {
      values
      |> Js.Array.sliceFrom(1)
      |> E.A.fold_left(
        (acc, x) => E.R.bind(acc, acc => pointwiseAddFn(acc, x)),
        Ok(E.A.unsafe_get(values, 0)),
      )
    })
  }
}