module.exports = class Indentation

    rule:
        name: 'indentation'
        value : 2
        level : 'error'
        message : 'Line contains inconsistent indentation'
        description: """
            This rule imposes a standard number of spaces to be used for
            indentation. Since whitespace is significant in CoffeeScript, it's
            critical that a project chooses a standard indentation format and
            stays consistent. Other roads lead to darkness. <pre> <code>#
            Enabling this option will prevent this ugly
            # but otherwise valid CoffeeScript.
            twoSpaces = () ->
              fourSpaces = () ->
                  eightSpaces = () ->
                        'this is valid CoffeeScript'

            </code>
            </pre>
            Two space indentation is enabled by default.
            """

    tokens: ['INDENT', '[', ']', '.']

    constructor: ->
        @arrayTokens = []   # A stack tracking the array token pairs.

    # Return an error if the given indentation token is not correct.
    lintToken: (token, tokenApi) ->
        [type, numIndents, { first_line: lineNumber }] = token
        { lines, lineNumber } = tokenApi

        expected = tokenApi.config[@rule.name].value

        # See: 'Indented chained invocations with bad indents'
        # This actually checks the chained call to see if its properly indented
        if type is '.'
            # Keep this if statement separately, since we still need to let
            # the linting pass if the '.' token is not at the beginning of
            # the line

            currentLine = lines[lineNumber]

            if currentLine.match(/\S/i)?[0] is '.'
                return @handleChain(tokenApi, expected)
            return undefined

        if type in ['[', ']']
            @lintArray(token)
            return undefined

        return null if token.generated?

        # HACK: CoffeeScript's lexer insert indentation in string
        # interpolations that start with spaces e.g. "#{ 123 }"
        # so ignore such cases. Are there other times an indentation
        # could possibly follow a '+'?
        previous = tokenApi.peek(-2)
        isInterpIndent = previous and previous[0] is '+'

        # Ignore the indentation inside of an array, so that
        # we can allow things like:
        #   x = ["foo",
        #             "bar"]
        previous = tokenApi.peek(-1)
        isArrayIndent = @inArray() and previous?.newLine

        # Ignore indents used to for formatting on multi-line expressions, so
        # we can allow things like:
        #   a = b =
        #     c = d
        previousSymbol = tokenApi.peek(-1)?[0]
        isMultiline = previousSymbol in ['=', ',']

        # Summarize the indentation conditions we'd like to ignore
        ignoreIndent = isInterpIndent or isArrayIndent or isMultiline

        # Correct CoffeeScript's incorrect INDENT token value when functions
        # get chained. See https://github.com/jashkenas/coffeescript/issues/3137
        # Also see CoffeeLint Issues: #4, #88, #128, and many more.
        numIndents = @getCorrectIndent(tokenApi)

        # Now check the indentation.
        if not ignoreIndent and numIndents isnt expected
            return { context: "Expected #{expected} got #{numIndents}" }

    # Return true if the current token is inside of an array.
    inArray: () ->
        return @arrayTokens.length > 0

    # Lint the given array token.
    lintArray: (token) ->
        # Track the array token pairs
        if token[0] is '['
            @arrayTokens.push(token)
        else if token[0] is ']'
            @arrayTokens.pop()
        # Return null, since we're not really linting
        # anything here.
        null

    handleChain: (tokenApi, expected) ->
        lastCheck = 1
        callStart = 1
        prevNum = 1

        { lineNumber, lines } = tokenApi
        currentLine = lines[lineNumber]

        # Traverse up the token list until we see a CALL_START token.
        # Don't scan above this line
        findCallStart = tokenApi.peek(-callStart)
        while (findCallStart and findCallStart[0] isnt 'TERMINATOR')
            { first_line: lastCheck } = findCallStart[2]
            callStart += 1
            findCallStart = tokenApi.peek(-callStart)

        # Keep going back until we are not at a comment or a blank lines
        # and set a new "previousLine"
        while (lineNumber - prevNum > lastCheck) and
                not /^\s*\./.test(lines[lineNumber - prevNum])
            prevNum += 1

        checkNum = lineNumber - prevNum
        if checkNum >= 0
            prevLine = lines[checkNum]

            # If this is just a one-chain function, or the "corrected"
            # previous line begins with a '.', check for correct
            # indentation
            if prevLine.match(/\S/i)[0] is '.' or checkNum is lastCheck
                currentSpaces = currentLine.match(/\S/i)?.index
                prevSpaces = prevLine.match(/\S/i)?.index
                numIndents = currentSpaces - prevSpaces

                # If both prev and current lines have uneven spacing,
                # assume the current line could be lined by default
                # indent spacing, and set numIndents to current
                # number of spaces
                prevIsIndent = prevSpaces % expected isnt 0
                currIsIndent = currentSpaces % expected isnt 0

                if prevIsIndent and currIsIndent
                    numIndents = currentSpaces

                if numIndents % expected isnt 0
                    return { context: "Expected #{expected} got #{numIndents}" }

    # Returns a corrected INDENT value if the current line is part of
    # a chained call. Otherwise returns original INDENT value.
    getCorrectIndent: (tokenApi) ->
        { lineNumber, lines, tokens, i } = tokenApi

        curIndent = lines[lineNumber].match(/\S/)?.index

        prevNum = 1
        prevNum += 1 while (/^\s*(#|$)/.test(lines[lineNumber - prevNum]))

        prevLine = lines[lineNumber - prevNum]
        prevIndent = prevLine.match(/^(\s*)\./)?[1].length

        if prevIndent > 0
            return curIndent - prevLine.match(/\S/)?.index
        else
            return tokens[i][1]