// ll1 is a tool to parse LL1 grammar definitions and to use those then 
// to generate code or reports using Go templates. 
// Inside the ll1 templates, the following template functions are available:
// - Most functions from the strings package (see go doc strings).
// - CompileRegexp compiles a regexp package regexp which can be used as such.
// - ToString to convert anything anything that isn't a string to a string.
// - NewMap creates a map based it's argumens wich have string keys and interface{} values
//  This is handly to pass multiple aruments to a sub-template
// - NewList creates a list from the given arguments.
package main

import "flag"
import "os"
import "strings"
import "text/template"
import "fmt"
import "path"
import "sort"

func showUsage() {    
    fmt.Fprintf(flag.CommandLine.Output(), 
                "%s: %s [options] input_file.ll1 [template_file.ext*]\n",
                os.Args[0], os.Args[0])
    
    fmt.Fprintf(flag.CommandLine.Output(), 
                "\n  [options] may be one of the following:\n\n")
	flag.PrintDefaults()
    fmt.Fprintf(flag.CommandLine.Output(), "\n")
}

const helpText = `
ll1 is a tool to parse and check LL(1) specifications, and to generate 
code or reports using Go templates based on these specifications. 
ll1 specifications must contain a definition for an ll1 grammar, and 
may optionally also specify a lexer for that grammar.

Usage: 
    ll1 [options] input_file.ll1 [template_file.ext*]

The [options] are:

    -a file
        Name of output file to append. Takes precedence over -out.
    -d definition
    	Add a definition for the template, in the form of key:value or 
        []key:value. Keys that start with a [] are arrays and can be 
        concatenated to by specifying the same definition key again.
        Non array keys will be overwoitten if they are specified again. 
    -help -h
        Shows the help page.
    -l format
        Inject line directives with the given format before template expansion.
    -o file
        Name of output file to overwrite. 
    -t file
    	Template file to expand. This may be repeated to make use 
        of several templates to generate one output file.
    -v
    	Be more verbose. Shows the scanned tokens as well.

The names of template files may be given with the -t option, or after the 
ll1 input file.

The syntax of an LL1 grammar itself is: 
    
    Specification -> Grammar OptLexer.
    Grammar -> Rules.
    Rules -> Rule OptRules .
    OptRules -> dot Rules | epsilon.
    Rule -> Name arrow Definition Template.
    Name -> ruleName .
    Template -> rawString | epsilon .
    // Alternates consist of sequences.
    Definition -> Alternates . 
    Alternates -> Sequence OptSequences .
    OptSequences -> or Alternates | epsilon.
    Sequence -> Element OptElements . 
    OptElements -> Element OptElements | epsilon .
    Element -> Parenthesis .
    Element -> Name .
    Element -> literal .
    Parenthesis -> '(' Definition ')' .
    OptLexer -> LexerTerminal OptLexerTerminals | epsilon .
    LexerTerminal -> terminalName arrow LexerDefinition Template .
    LexerDefinition -> LexerAlternates . 
    LexerAlternates -> LexerPattern OptLexerMatches .
    OptLexerMatches -> or LexerPattern | epsilon.
    LexerPattern -> literal .
    OptElements -> Element OptElements | epsilon .
    Element -> Parenthesis .
    Element -> Name .
    Element -> literal /*| Rule */.
    // Lexer specification starts here:
    dot          -> '.'
    or           -> '|'
    literal      -> characterLiteral | stringLiteral
    ruleName     -> "re:[[:isUpper:]][[:isAlNum]]"
    terminalName -> "re:[[:isLower:]][[:isAlNum]]"
    epsilon      -> "epsilon" | 'ε'
    arrow        -> "->" | '→'

The syntax of an ll1 grammar has the following elements:  
  - //comment : Line comments start with //, /*block comments*/ are C-like
  - RuleName  : names that start with an upper case letter are 
                rule names or nonterminals defined by the grammar.
  - terminal  : names that start with a lower case letter are names of 
                teminals that the lexer produces.
  - 'l'       : single quoted strings are rune literals that the lexer produces.
  - "literal" : double quoted strings are rune literals that the lexer produces.
  - arrow     : a literal -> → as a separator.
  - epsion    : a literal "epsilon" or 'ε', which indicates the empty rule.
                this is used in conjunction with alternates to make a rule 
                optional.

If no templates are given, ll1 simply checks the grammar and outputs a 
simple text report to the output file.

If a template is given, it will be expanded and output to the output file. 

Inside the template the following variables are available: 
  - .Grammar: contains the .Rules of the grammar.
  - .InName: contains the name of the ll1 input file.
  - .OutName: contains the name of the output file specified with -a or -o.
  - .Templates: contains the names of the templates read.
  - .Definitions: contains the keys of the available definitions.
  - All other variables defined with -d
    
Inside the ll1 templates, the following template functions are available:
  - Most functions from the strings package (see go doc strings).
  - CompileRegexp compiles a regexp package regexp which can be used as such.
  - ToString to convert anything anything that isn't a string to a string.
  - NewMap creates a map based it's argumens wich have string keys and interface{} values
    This is handly to pass multiple aruments to a sub-template
  - NewList creates a list from the given arguments.
`

func showHelp() {    
    fmt.Fprintf(flag.CommandLine.Output(), "\n%s\n", helpText)
}

type arrayFlags []string

func (i *arrayFlags) String() string {
	return "my string representation"
}

func (i *arrayFlags) Set(value string) error {
	*i = append(*i, value)
	return nil
}

// The prefix for array definitions
const definitionArrayPrefix = "[]"

type definitionMap map[string]interface{}

func (i *definitionMap) Set(in string) error {
	parts := strings.SplitN(in, ":", 2)
	if len(parts) < 2 {
		return fmt.Errorf("Could not split definition on ':' for %s ", in)
	}
	key := parts[0]
	value := parts[1]

	if strings.HasPrefix(key, definitionArrayPrefix) {
		key = strings.TrimPrefix(key, definitionArrayPrefix)
		existing, exists := (*i)[key]
		if !exists {
			slice := make([]string, 0)
			slice = append(slice, value)
			(*i)[key] = slice
		} else {
			slice, isSlice := existing.([]string)
			if isSlice {
				slice = append(slice, value)
				(*i)[key] = slice
			} else {
				return fmt.Errorf("Cannot mix array and non array definitions: %s -> %s:\n", key, value)
			}
		}
	} else {
		(*i)[key] = value
	}
	return nil
}

func (i *definitionMap) String() string {
	s := "{"
	for k, v := range *i {
        switch vv := v.(type) {
            case string:  s = s + fmt.Sprintf("%s:%s;", k, vv)            
            case []string: s = s + fmt.Sprintf("%s:%v;", k, vv)
            default: s = s + fmt.Sprintf("%s:<omitted>;", k)
        }
	}
    s = s + "}"
	return s
}

func (i *definitionMap) Keys() []string {
    res := []string{}
	for k, _ := range *i {
           res = append(res, k) 
	}
    sort.Strings(res)
	return res
}


// LL1 contains the options and variables of the ll1 program.
type Ll1 struct { 
    definitions definitionMap
    templateNames arrayFlags
    outName string
    usedName string
    appendName string
    help bool
    verbose bool
    debug bool
    lineFormat string
    fout *os.File
    parser *Parser
    grammar *Grammar
    tmpl *template.Template
}

func main() {
    var err error
    flag.Usage = showUsage
    ll1 := Ll1{}
    
	// Set up a few default definitions
    ll1.definitions = make(definitionMap)
    ll1.definitions["Package"] = "main"
    ll1.definitions["Prefix"] = "Ll1"
    
	flag.BoolVar(&ll1.verbose,      "v", false, "Be more verbose. ")
    flag.BoolVar(&ll1.debug,        "D", false, "Show debug info. Shows the scanned tokens as well.")
	flag.Var(&ll1.templateNames,    "t", "Template `file` to expand.")
	flag.StringVar(&ll1.outName,    "o", "", "Name of output `file` to overwrite.")
	flag.StringVar(&ll1.appendName, "a", "", "Name of output `file` to append.")
    flag.StringVar(&ll1.lineFormat, "l", "", "Inject line directives before template epansion.")
	flag.Var(&ll1.definitions,      "d", "Add a `definition` for the template, in the form of key:value or []key:value.")
    flag.BoolVar(&ll1.help,         "h", false, "Shows the help page.")
    flag.BoolVar(&ll1.help,         "help", false, "Shows the help page.")
	flag.Parse()
    
    if ll1.help {
        showUsage()
        showHelp()
        os.Exit(1)
    }
    
    if (len(flag.Args()) < 1) {
        showUsage()
        os.Exit(1)
        return 
    }
    
    ll1Name := flag.Arg(0)
    
    // other file names after the first are templates.
    for i := 1 ; i <  len(flag.Args()) ; i ++ {
        ll1.templateNames.Set(flag.Arg(i))
    }
    
    
    // Parse grammar
    ll1.parser, ll1.grammar, err = ParseFile(ll1Name, ll1.debug)
    if err != nil {        
        fmt.Fprintf(os.Stderr, "%v\n", err)
        for _, e := range ll1.parser.Errors {
            fmt.Fprintf(os.Stderr, "%v\n", e)
        }
        os.Exit(2)
    }
    
    // Check grammar and report errors
    errs := ll1.grammar.Check()
    if len(errs) > 0 { 
        for _, err := range errs {
            fmt.Fprintf(os.Stderr, "%v\n", err)
        }
        os.Exit(5)
    }
    
    // If not templates given, output just a grammar report
    if len(ll1.templateNames) < 1 {
        fmt.Fprintf(ll1.fout, "Grammar:\n%v\n", ll1.grammar)
        os.Exit(0)
    }
 
    // parse the templates
	if len(ll1.templateNames) > 0 {
        name := path.Base(ll1.templateNames[0])
        if ll1.verbose {
            fmt.Printf("Parsing templates: %s\n", name)
        }
                
        ll1.tmpl, err = template.New(name).Funcs(templateFunctionMap).ParseFiles([]string(ll1.templateNames)...)
        if err != nil {
            fmt.Printf("%s: %s: template parsing error\n", err, name)
            os.Exit(7)
        }
    }

    // Determine output file
	ll1.usedName = ll1.outName
	
	if ll1.appendName != "" {
		ll1.fout, err = os.OpenFile(ll1.appendName, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0600)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Could not append to output file %s: %s\n", ll1.appendName, err)
            os.Exit(9)
		} else {
			ll1.usedName = ll1.appendName
		}
        defer ll1.fout.Close()
	} else if ll1.outName == "" {
		ll1.fout = os.Stdout
	} else {
		ll1.fout, err = os.Create(ll1.outName)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Could not open output file %s: %s\n", ll1.outName, err)
		}
        defer ll1.fout.Close()
	}
    
    // Set up the template definitions
    ll1.definitions["InName"] = ll1Name
	ll1.definitions["OutName"] = ll1.usedName
	ll1.definitions["Templates"] = strings.Join(ll1.templateNames, "\n")
    ll1.definitions["Grammar"] = ll1.grammar
    ll1.definitions["Parser"] = ll1.parser
    ll1.definitions["Definitions"] = ll1.definitions.Keys()

    // And execute the template, generating output
	err = ll1.tmpl.Execute(ll1.fout, ll1.definitions)
	if err != nil {
		fmt.Fprintf(os.Stderr, "%s: template execution error", err)
        if ll1.usedName != "" {
            os.Remove(ll1.usedName)
        }
        os.Exit(10)
	}
}