open Internal.Utilities

open FSharp.Compiler.AbstractIL.Internal.Library

open System.Collections

open System.Collections.Generic

let maxSuggestions = 5

let minThresholdForSuggestions = 0.7

let highConfidenceThreshold = 0.85

let minStringLengthForSuggestion = 3

let IsInEditDistanceProximity idText suggestion =

let editDistance = EditDistance.CalcEditDistance(idText, suggestion)

let threshold =

match idText.Length with

| x when x < 5 -> 1

| x when x < 7 -> 2

| x -> x / 4 + 1

editDistance <= threshold

let DemangleOperator (nm: string) =

if nm.StartsWithOrdinal("( ") && nm.EndsWithOrdinal(" )") then

nm.[2..nm.Length - 3]

else

nm

type SuggestionBufferEnumerator(tail: int, data: KeyValuePair<float,string> []) =

let mutable current = data.Length

interface IEnumerator<string> with

member __.Current

with get () =

let kvpr = &data.[current]

kvpr.Value

interface System.Collections.IEnumerator with

member __.Current with get () = box data.[current].Value

member __.MoveNext() =

current <- current - 1

current > tail || (current = tail && data.[current] <> Unchecked.defaultof<_>)

member __.Reset () = current <- data.Length

interface System.IDisposable with

member __.Dispose () = ()

type SuggestionBuffer(idText: string) =

let data = Array.zeroCreate<KeyValuePair<float,string>>(maxSuggestions)

let mutable tail = maxSuggestions - 1

let uppercaseText = idText.ToUpperInvariant()

let dotIdText = "." + idText

let mutable disableSuggestions = idText.Length < minStringLengthForSuggestion

let insert (k,v) =

let mutable pos = tail

while pos < maxSuggestions && (let kv = &data.[pos] in kv.Key < k) do

pos <- pos + 1

if pos > 0 then

if pos >= maxSuggestions || (let kv = &data.[pos] in k <> kv.Key || v <> kv.Value) then

if tail < pos - 1 then

for i = tail to pos - 2 do

data.[i] <- data.[i + 1]

data.[pos - 1] <- KeyValuePair(k,v)

if tail > 0 then tail <- tail - 1

member __.Add (suggestion: string) =

if not disableSuggestions then

if suggestion = idText then // some other parse error happened

disableSuggestions <- true

// Because beginning a name with _ is used both to indicate an unused

// value as well as to formally squelch the associated compiler

// error/warning (FS1182), we remove such names from the suggestions,

// both to prevent accidental usages as well as to encourage good taste

if suggestion.Length >= minStringLengthForSuggestion && not (suggestion.StartsWithOrdinal "_") then

let suggestion:string = DemangleOperator suggestion

let suggestedText = suggestion.ToUpperInvariant()

let similarity = EditDistance.JaroWinklerDistance uppercaseText suggestedText

if similarity >= highConfidenceThreshold ||

suggestion.EndsWithOrdinal dotIdText ||

(similarity >= minThresholdForSuggestions && IsInEditDistanceProximity uppercaseText suggestedText)

then

insert(similarity, suggestion) |> ignore

member __.Disabled with get () = disableSuggestions

member __.IsEmpty with get () = disableSuggestions || (tail = maxSuggestions - 1)

interface IEnumerable<string> with

member this.GetEnumerator () =

if this.IsEmpty then

Seq.empty.GetEnumerator()

else

new SuggestionBufferEnumerator(tail, data) :> IEnumerator<string>

interface IEnumerable with

member this.GetEnumerator () =

if this.IsEmpty then

Seq.empty.GetEnumerator() :> IEnumerator

else

new SuggestionBufferEnumerator(tail, data) :> IEnumerator