// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.

// NOTE: the code in this file is a drop-in replacement runtime for Parsing.fs from the FsLexYacc repository

namespace Internal.Utilities.Text.Parsing

open Internal.Utilities.Text.Lexing

open System
open System.Buffers

exception RecoverableParseError
exception Accept of obj

[<Sealed>]
type internal IParseState
    (
        ruleStartPoss: Position[],
        ruleEndPoss: Position[],
        lhsPos: Position[],
        ruleValues: obj[],
        lexbuf: LexBuffer<char>
    ) =
    member _.LexBuffer = lexbuf

    member _.InputRange index =
        ruleStartPoss[index - 1], ruleEndPoss[index - 1]

    member _.InputStartPosition index = ruleStartPoss[index - 1]

    member _.InputEndPosition index = ruleEndPoss[index - 1]

    member _.ResultStartPosition = lhsPos[0]

    member _.ResultEndPosition = lhsPos[1]

    member _.GetInput index = ruleValues[index - 1]

    member _.ResultRange = (lhsPos[0], lhsPos[1])

    // Side note: this definition coincidentally tests the fairly complex logic associated with an object expression implementing a generic abstract method.
    member _.RaiseError() = raise RecoverableParseError

/// This context is passed to the error reporter when a syntax error occurs
[<Sealed>]
type internal ParseErrorContext<'Token>
    (
        stateStack: int list,
        parseState: IParseState,
        reduceTokens: int list,
        currentToken: 'Token option,
        reducibleProductions: int list list,
        shiftableTokens: int list,
        message: string
    ) =

    //member _.LexBuffer = lexbuf

    member _.StateStack = stateStack

    member _.ReduceTokens = reduceTokens

    member _.CurrentToken = currentToken

    member _.ParseState = parseState

    member _.ReducibleProductions = reducibleProductions

    member _.ShiftTokens = shiftableTokens

    member _.Message = message

//-------------------------------------------------------------------------
// This is the data structure emitted as code by FSYACC.

type internal Tables<'Token> =
    {
        reductions: (IParseState -> obj)[]
        endOfInputTag: int
        tagOfToken: 'Token -> int
        dataOfToken: 'Token -> obj
        actionTableElements: uint16[]
        actionTableRowOffsets: uint16[]
        reductionSymbolCounts: uint16[]
        immediateActions: uint16[]
        gotos: uint16[]
        sparseGotoTableRowOffsets: uint16[]
        stateToProdIdxsTableElements: uint16[]
        stateToProdIdxsTableRowOffsets: uint16[]
        productionToNonTerminalTable: uint16[]

        /// For fsyacc.exe, this entry is filled in by context from the generated parser file. If no 'parse_error' function
        /// is defined by the user then ParseHelpers.parse_error is used by default (ParseHelpers is opened
        /// at the top of the generated parser file)
        parseError: ParseErrorContext<'Token> -> unit
        numTerminals: int
        tagOfErrorTerminal: int
    }

//-------------------------------------------------------------------------
// An implementation of stacks.

// This type is in <c>System.dll</c> so for the moment we can't use it in <c>FSharp.Core.dll</c>
// type Stack<'a> = System.Collections.Generic.Stack<'a>

type Stack<'a>(n) =
    let mutable contents = Array.zeroCreate<'a> (n)
    let mutable count = 0

    member buf.Ensure newSize =
        let oldSize = contents.Length

        if newSize > oldSize then
            let old = contents
            contents <- Array.zeroCreate (max newSize (oldSize * 2))
            Array.blit old 0 contents 0 count

    member buf.Count = count
    member buf.Pop() = count <- count - 1
    member buf.Peep() = contents[count - 1]

    member buf.Top(n) =
        [ for x in contents[max 0 (count - n) .. count - 1] -> x ] |> List.rev

    member buf.Push(x) =
        buf.Ensure(count + 1)
        contents[count] <- x
        count <- count + 1

    member buf.IsEmpty = (count = 0)

    member buf.PrintStack() =
        for i = 0 to (count - 1) do
            Console.Write("{0}{1}", contents[i], (if i = count - 1 then ":" else "-"))

module Flags =
#if DEBUG
    let mutable debug = false
#else
    // Debugging tracing for parsing always off for release code
    let debug = false
#endif

module internal Implementation =

    // Definitions shared with fsyacc
    let anyMarker = 0xffff
    let shiftFlag = 0x0000
    let reduceFlag = 0x4000
    let errorFlag = 0x8000
    let acceptFlag = 0xc000
    let actionMask = 0xc000

    let actionValue action = action &&& (~~~actionMask)
    let actionKind action = action &&& actionMask

    //-------------------------------------------------------------------------
    // Read the tables written by FSYACC.

    type AssocTable(elemTab: uint16[], offsetTab: uint16[], cache: int[], cacheSize: int) =

        member t.ReadAssoc(minElemNum, maxElemNum, defaultValueOfAssoc, keyToFind) =
            // do a binary chop on the table
            let elemNumber: int = (minElemNum + maxElemNum) / 2

            if elemNumber = maxElemNum then
                defaultValueOfAssoc
            else
                let x = int elemTab[elemNumber * 2]

                if keyToFind = x then
                    int elemTab[elemNumber * 2 + 1]
                elif keyToFind < x then
                    t.ReadAssoc(minElemNum, elemNumber, defaultValueOfAssoc, keyToFind)
                else
                    t.ReadAssoc(elemNumber + 1, maxElemNum, defaultValueOfAssoc, keyToFind)

        member t.Read(rowNumber, keyToFind) =

            // First check the sparse lookaside table
            // Performance note: without this lookaside table the binary chop in ReadAssoc
            // takes up around 10% of of parsing time
            // for parsing intensive samples such as the bootstrapped F# compiler.
            //
            // NOTE: using a .NET Dictionary for this int -> int table looks like it could be sub-optimal.
            // Some other better sparse lookup table may be better.
            assert (rowNumber < 0x10000)
            assert (keyToFind < 0x10000)
            let cacheKey = (rowNumber <<< 16) ||| keyToFind
            let cacheIdx = (int32 (uint32 cacheKey % uint32 cacheSize)) * 2
            let cacheKey2 = cache[cacheIdx]
            let v = cache[cacheIdx + 1]

            if cacheKey = cacheKey2 then
                v
            else
                let headOfTable = int offsetTab[rowNumber]
                let firstElemNumber = headOfTable + 1
                let numberOfElementsInAssoc = int elemTab[headOfTable * 2]
                let defaultValueOfAssoc = int elemTab[headOfTable * 2 + 1]

                let res =
                    t.ReadAssoc(firstElemNumber, firstElemNumber + numberOfElementsInAssoc, defaultValueOfAssoc, keyToFind)

                cache[cacheIdx] <- cacheKey
                cache[cacheIdx + 1] <- res
                res

        // Read all entries in the association table
        // Used during error recovery to find all valid entries in the table
        member _.ReadAll(n) =
            let headOfTable = int offsetTab[n]
            let firstElemNumber = headOfTable + 1
            let numberOfElementsInAssoc = int32 elemTab[headOfTable * 2]
            let defaultValueOfAssoc = int elemTab[headOfTable * 2 + 1]

            [
                for i in firstElemNumber .. (firstElemNumber + numberOfElementsInAssoc - 1) -> (int elemTab[i * 2], int elemTab[i * 2 + 1])
            ],
            defaultValueOfAssoc

    type IdxToIdxListTable(elemTab: uint16[], offsetTab: uint16[]) =

        // Read all entries in a row of the table
        member _.ReadAll(n) =
            let headOfTable = int offsetTab[n]
            let firstElemNumber = headOfTable + 1
            let numberOfElements = int32 elemTab[headOfTable]

            [
                for i in firstElemNumber .. (firstElemNumber + numberOfElements - 1) -> int elemTab[i]
            ]

    //-------------------------------------------------------------------------
    // interpret the tables emitted by FSYACC.

    [<NoEquality; NoComparison>]
    [<Struct>]
    type ValueInfo =
        val value: obj
        val startPos: Position
        val endPos: Position

        new(value, startPos, endPos) =
            {
                value = value
                startPos = startPos
                endPos = endPos
            }

    let interpret (tables: Tables<'Token>) lexer (lexbuf: LexBuffer<_>) initialState =
        if Flags.debug then
            Console.WriteLine("\nParser: interpret tables")

        let stateStack: Stack<int> = Stack<_>(100)
        stateStack.Push(initialState)
        let valueStack = Stack<ValueInfo>(100)
        let mutable haveLookahead = false
        let mutable lookaheadToken = Unchecked.defaultof<'Token>
        let mutable lookaheadEndPos = Unchecked.defaultof<Position>
        let mutable lookaheadStartPos = Unchecked.defaultof<Position>
        let mutable finished = false
        // After an error occurs, we suppress errors until we've shifted three tokens in a row.
        let mutable errorSuppressionCountDown = 0

        // When we hit the end-of-file we don't fail straight away but rather keep permitting shift
        // and reduce against the last token in the token stream 20 times or until we've accepted
        // or exhausted the stack. This allows error recovery rules of the form
        //      input : realInput EOF | realInput error EOF | error EOF
        // where consuming one EOF to trigger an error doesn't result in overall parse failure
        // catastrophe and the loss of intermediate results.
        //
        let mutable inEofCountDown = false
        let mutable eofCountDown = 20 // Number of EOFs to supply at the end for error recovery
        // The 100 here means a maximum of 100 elements for each rule
        let ruleStartPoss = (Array.zeroCreate 100: Position[])
        let ruleEndPoss = (Array.zeroCreate 100: Position[])
        let ruleValues = (Array.zeroCreate 100: obj[])
        let lhsPos = (Array.zeroCreate 2: Position[])
        let reductions = tables.reductions
        let cacheSize = 7919 // the 1000'th prime
        // Use a simpler hash table with faster lookup, but only one
        // hash bucket per key.
        let actionTableCache = ArrayPool<int>.Shared.Rent (cacheSize * 2)
        let gotoTableCache = ArrayPool<int>.Shared.Rent (cacheSize * 2)
        // Clear the arrays since ArrayPool does not
        Array.Clear(actionTableCache, 0, actionTableCache.Length)
        Array.Clear(gotoTableCache, 0, gotoTableCache.Length)

        use _cacheDisposal =
            { new IDisposable with
                member _.Dispose() =
                    ArrayPool<int>.Shared.Return actionTableCache
                    ArrayPool<int>.Shared.Return gotoTableCache
            }

        let actionTable =
            AssocTable(tables.actionTableElements, tables.actionTableRowOffsets, actionTableCache, cacheSize)

        let gotoTable =
            AssocTable(tables.gotos, tables.sparseGotoTableRowOffsets, gotoTableCache, cacheSize)

        let stateToProdIdxsTable =
            IdxToIdxListTable(tables.stateToProdIdxsTableElements, tables.stateToProdIdxsTableRowOffsets)

        let parseState = IParseState(ruleStartPoss, ruleEndPoss, lhsPos, ruleValues, lexbuf)

        let report haveLookahead lookaheadToken =
            if haveLookahead then
                sprintf "%+A" lookaheadToken
            else
                "[TBC]"

        // Pop the stack until we can shift the 'error' token. If 'tokenOpt' is given
        // then keep popping until we can shift both the 'error' token and the token in 'tokenOpt'.
        // This is used at end-of-file to make sure we can shift both the 'error' token and the 'EOF' token.
        let rec popStackUntilErrorShifted tokenOpt =
            // Keep popping the stack until the "error" terminal is shifted
            if Flags.debug then
                Console.WriteLine("popStackUntilErrorShifted")

            if stateStack.IsEmpty then
                if Flags.debug then
                    Console.WriteLine("state stack empty during error recovery - generating parse error")

                failwith "parse error"

            let currState = stateStack.Peep()

            if Flags.debug then
                Console.WriteLine("In state {0} during error recovery", currState)

            let action = actionTable.Read(currState, tables.tagOfErrorTerminal)

            if
                actionKind action = shiftFlag
                && (match tokenOpt with
                    | None -> true
                    | Some (token) ->
                        let nextState = actionValue action
                        actionKind (actionTable.Read(nextState, tables.tagOfToken (token))) = shiftFlag)
            then

                if Flags.debug then
                    Console.WriteLine("shifting error, continuing with error recovery")

                let nextState = actionValue action
                // The "error" non terminal needs position information, though it tends to be unreliable.
                // Use the StartPos/EndPos from the lex buffer.
                valueStack.Push(ValueInfo(box (), lexbuf.StartPos, lexbuf.EndPos))
                stateStack.Push(nextState)
            else
                if valueStack.IsEmpty then
                    failwith "parse error"

                if Flags.debug then
                    Console.WriteLine("popping stack during error recovery")

                valueStack.Pop()
                stateStack.Pop()
                popStackUntilErrorShifted (tokenOpt)

        while not finished do
            if stateStack.IsEmpty then
                finished <- true
            else
                let state = stateStack.Peep()

                if Flags.debug then
                    (Console.Write("{0} value(state), state ", valueStack.Count)
                     stateStack.PrintStack())

                let action =
                    let immediateAction = int tables.immediateActions[state]

                    if not (immediateAction = anyMarker) then
                        // Action has been pre-determined, no need to lookahead
                        // Expecting it to be a Reduce action on a non-fakeStartNonTerminal ?
                        immediateAction
                    else
                        // Lookahead required to determine action
                        if not haveLookahead then
                            if lexbuf.IsPastEndOfStream then
                                // When the input runs out, keep supplying the last token for eofCountDown times
                                if eofCountDown > 0 then
                                    haveLookahead <- true
                                    eofCountDown <- eofCountDown - 1
                                    inEofCountDown <- true
                                else
                                    haveLookahead <- false
                            else
                                lookaheadToken <- lexer lexbuf
                                lookaheadStartPos <- lexbuf.StartPos
                                lookaheadEndPos <- lexbuf.EndPos
                                haveLookahead <- true

                        let tag =
                            if haveLookahead then
                                tables.tagOfToken lookaheadToken
                            else
                                tables.endOfInputTag

                        // printf "state %d\n" state
                        actionTable.Read(state, tag)

                let kind = actionKind action

                if kind = shiftFlag then
                    (if errorSuppressionCountDown > 0 then
                         errorSuppressionCountDown <- errorSuppressionCountDown - 1

                         if Flags.debug then
                             Console.WriteLine("shifting, reduced errorRecoveryLevel to {0}\n", errorSuppressionCountDown)

                     let nextState = actionValue action

                     if not haveLookahead then
                         failwith "shift on end of input!"

                     let data = tables.dataOfToken lookaheadToken
                     valueStack.Push(ValueInfo(data, lookaheadStartPos, lookaheadEndPos))
                     stateStack.Push(nextState)

                     if Flags.debug then
                         Console.WriteLine("shift/consume input {0}, shift to state {1}", report haveLookahead lookaheadToken, nextState)

                     haveLookahead <- false

                    )
                elif kind = reduceFlag then
                    let prod = actionValue action
                    let reduction = reductions[prod]
                    let n = int tables.reductionSymbolCounts[prod]
                    // pop the symbols, populate the values and populate the locations
                    if Flags.debug then
                        Console.Write("reduce popping {0} values/states, lookahead {1}", n, report haveLookahead lookaheadToken)
                    // For every range to reduce merge it
                    for i = 0 to n - 1 do
                        if valueStack.IsEmpty then
                            failwith "empty symbol stack"

                        let topVal = valueStack.Peep() // Grab topVal
                        valueStack.Pop()
                        stateStack.Pop()

                        let ruleIndex = (n - i) - 1
                        ruleValues[ruleIndex] <- topVal.value
                        ruleStartPoss[ruleIndex] <- topVal.startPos
                        ruleEndPoss[ruleIndex] <- topVal.endPos

                        if i = 0 then
                            // Initial range
                            lhsPos[0] <- topVal.startPos
                            lhsPos[1] <- topVal.endPos
                        elif
                            topVal.startPos.FileIndex = lhsPos[1].FileIndex
                            && topVal.startPos.Line <= lhsPos[1].Line
                        then
                            // Reduce range if same file as the initial end point
                            lhsPos[0] <- topVal.startPos

                    // Use the lookahead token to populate the locations if the rhs is empty
                    if n = 0 then
                        if haveLookahead then
                            lhsPos[0] <- lookaheadStartPos
                            lhsPos[1] <- lookaheadEndPos
                        else
                            lhsPos[0] <- lexbuf.StartPos
                            lhsPos[1] <- lexbuf.EndPos

                    try
                        // printf "reduce %d\n" prod
                        let redResult = reduction parseState
                        let valueInfo = ValueInfo(redResult, lhsPos[0], lhsPos[1])
                        valueStack.Push(valueInfo)
                        let currState = stateStack.Peep()

                        let newGotoState =
                            gotoTable.Read(int tables.productionToNonTerminalTable[prod], currState)

                        stateStack.Push(newGotoState)

                        if Flags.debug then
                            Console.WriteLine(" goto state {0}", newGotoState)
                    with
                    | Accept res ->
                        finished <- true
                        valueStack.Push(ValueInfo(res, lhsPos[0], lhsPos[1]))
                    | RecoverableParseError ->
                        if Flags.debug then
                            Console.WriteLine("RecoverableParseErrorException...\n")

                        popStackUntilErrorShifted (None)
                        // User code raised a Parse_error. Don't report errors again until three tokens have been shifted
                        errorSuppressionCountDown <- 3
                elif kind = errorFlag then
                    (if Flags.debug then
                         Console.Write("ErrorFlag... ")
                     // Silently discard inputs and don't report errors
                     // until three tokens in a row have been shifted
                     if Flags.debug then
                         printfn "error on token '%s' " (report haveLookahead lookaheadToken)

                     if errorSuppressionCountDown > 0 then
                         // If we're in the end-of-file count down then we're very keen to 'Accept'.
                         // We can only do this by repeatedly popping the stack until we can shift both an 'error' token
                         // and an EOF token.
                         if inEofCountDown && eofCountDown < 10 then
                             if Flags.debug then
                                 printfn "popping stack, looking to shift both 'error' and that token, during end-of-file error recovery"

                             popStackUntilErrorShifted (if haveLookahead then Some(lookaheadToken) else None)

                         // If we don't haveLookahead then the end-of-file count down is over and we have no further options.
                         if not haveLookahead then
                             failwith "parse error: unexpected end of file"

                         if Flags.debug then
                             printfn "discarding token '%s' during error suppression" (report haveLookahead lookaheadToken)
                         // Discard the token
                         haveLookahead <- false
                         // Try again to shift three tokens
                         errorSuppressionCountDown <- 3
                     else
                         (

                          let currentToken = if haveLookahead then Some(lookaheadToken) else None
                          let actions, defaultAction = actionTable.ReadAll(state)
                          let explicit = Set.ofList [ for tag, _action in actions -> tag ]

                          let shiftableTokens =
                              [
                                  for tag, action in actions do
                                      if (actionKind action) = shiftFlag then
                                          yield tag
                                  if actionKind defaultAction = shiftFlag then
                                      for tag in 0 .. tables.numTerminals - 1 do
                                          if not (explicit.Contains(tag)) then
                                              yield tag
                              ]

                          let stateStack = stateStack.Top(12)

                          let reducibleProductions =
                              [
                                  for state in stateStack do
                                      yield stateToProdIdxsTable.ReadAll(state)
                              ]

                          let reduceTokens =
                              [
                                  for tag, action in actions do
                                      if actionKind (action) = reduceFlag then
                                          yield tag
                                  if actionKind (defaultAction) = reduceFlag then
                                      for tag in 0 .. tables.numTerminals - 1 do
                                          if not (explicit.Contains(tag)) then
                                              yield tag
                              ]
                          //let activeRules = stateStack |> List.iter (fun state ->
                          let errorContext =
                              new ParseErrorContext<'Token>(
                                  stateStack,
                                  parseState,
                                  reduceTokens,
                                  currentToken,
                                  reducibleProductions,
                                  shiftableTokens,
                                  "syntax error"
                              )

                          tables.parseError (errorContext)
                          popStackUntilErrorShifted (None)
                          errorSuppressionCountDown <- 3

                          if Flags.debug then
                              Console.WriteLine("generated syntax error and shifted error token, haveLookahead = {0}\n", haveLookahead)))
                elif kind = acceptFlag then
                    finished <- true
                else if Flags.debug then
                    Console.WriteLine("ALARM!!! drop through case in parser")
        // OK, we're done - read off the overall generated value
        valueStack.Peep().value

type internal Tables<'Token> with

    member tables.Interpret(lexer, lexbuf, initialState) =
        Implementation.interpret tables lexer lexbuf initialState

module internal ParseHelpers =

    let parse_error (_s: string) = ()

    let parse_error_rich = (None: (ParseErrorContext<_> -> unit) option)
