static def evalVar(vars, String var) {
    if (var.number) {
        return var as int
    } else {
        return vars[var]
    }
}

import java.util.regex.Pattern

static def evalExpr(vars, String expr) {
    def matcher = Pattern.compile(/(.+)(<=|>=|<|>)(.+)/).matcher(expr)
    if (matcher.matches()) {
        def lhs = evalVar(vars, matcher.group(1))
        def rhs = evalVar(vars, matcher.group(3))
        switch (matcher.group(2)) {
            case '>=': return lhs >= rhs
            case '<=': return lhs <= rhs
            case '>': return lhs > rhs
            case '<': return lhs < rhs
        }
    }
}

static def getIndent(String str) {
    return str.takeWhile {it == ' '}.length()
}

class ParserException extends RuntimeException {
    ParserException(String str) {
        super(str)
    }
}

static def convertSource(Map<String, String> kws, Map<String, Integer> vars, List<String> lines, String fileName) {
    def ifStack = []
    List<Integer> indentStack = []
    def active = true
    def n = 0
    lines = lines.collect { line ->
        n++
        def trimmed = line.trim()
        if (trimmed.startsWith(kws.if)) {
            def result = evalExpr(vars, trimmed.substring(kws.if.length()))
            ifStack.push(result)
            if (result != null) {
                indentStack.push(getIndent(line))
                active &= result
            }
        } else if (trimmed.startsWith(kws.else)) {
            if (ifStack.isEmpty()) {
                throw new ParserException("Unexpected else in line $n of $fileName")
            }
            def head = ifStack.pop()
            if (head != null) {
                head = !head
                indentStack.pop()
                indentStack.push(getIndent(line))
            }
            ifStack.push(head)
            active = true;
            ifStack.each {
                if (it != null) {
                    active &= it
                }
            }
        } else if (trimmed.startsWith(kws.ifdef)) {
            def result = vars.containsKey(trimmed.substring(kws.ifdef.length()))
            ifStack.push(result)
            indentStack.push(getIndent(line))
            active &= result
        } else if (trimmed.startsWith(kws.endif)) {
            if (ifStack.isEmpty()) {
                throw new ParserException("Unexpected endif in line $n of $fileName")
            }
            def head = ifStack.pop()
            if (head != null) {
                indentStack.pop()
                active = true;
                ifStack.each {
                    if (it != null) {
                        active &= it
                    }
                }
            }
        } else {
            if (active) {
                if (trimmed.startsWith(kws.eval)) {
                    line = line.replaceFirst(Pattern.quote(kws.eval) + ' ?', '')
                    if (line.trim().isEmpty()) {
                        line = ''
                    }
                }
            } else {
                def currIndent = indentStack.last()
                if (trimmed.isEmpty()) {
                    line = ' ' * currIndent + kws.eval
                } else if (!trimmed.startsWith(kws.eval)) {
                    def actualIndent = getIndent(line)
                    if (currIndent <= actualIndent) {
                        line = ' ' * currIndent + kws.eval + ' ' + line.substring(currIndent)
                    }
                }
            }
        }
        line
    }
    if (!ifStack.isEmpty()) {
        throw new ParserException("Missing endif in $fileName")
    }
    return lines
}

import java.nio.charset.StandardCharsets

static def convertFile(Map<String, String> kws, Map<String, Integer> vars, File inFile, File outFile) {
    def string = new String(inFile.readBytes(), StandardCharsets.UTF_8)
    def lines = string.readLines()
    try {
        lines = convertSource(kws, vars, lines, inFile.path)
    } catch (e) {
        if (e instanceof ParserException) {
            throw e
        }
        throw new RuntimeException("Failed to convert file " + inFile, e)
    }
    outFile.parentFile.mkdirs()
    if (string.endsWith('\n')) {
        outFile.write(lines.collect { it + '\n' }.join(''))
    } else {
        outFile.write(lines.join('\n'))
    }
}

project.ext.convertTree = { Map<String, Integer> vars, String inName, String outName=inName ->
    def defaultKws = [if: '//#if ', ifdef: '//#ifdef ', else: '//#else', endif: '//#endif', eval: '//$$']
    def cfgKws = [if: '##if ', ifdef: '##ifdef ', else: '##else', endif: '##endif', eval: '#$$']
    def extensions = ['.java': defaultKws, '.gradle': defaultKws, '.json': defaultKws, '.cfg': cfgKws]
    def inPath = project.file(inName).toPath()
    def outPath = project.file(outName).toPath()
    def inPlace = inPath.toAbsolutePath().equals(outPath.toAbsolutePath())
    project.fileTree(inName).forEach { file ->
        def outFile = outPath.resolve(inPath.relativize(file.toPath())).toFile()
        def kws = extensions.find { ext, _ -> file.name.endsWith(ext) }
        if (kws) {
            convertFile(kws.value, vars, file, outFile)
        } else if (!inPlace) {
            copy {
                from file
                into outFile.parentFile
            }
        }
    }
}