// This is a mkfile parser. It executes assignments and includes as it goes, and
// collects a set of rules, which are returned as a ruleSet object.

package main

import (
	"fmt"
	"os"
)

type parser struct {
	l        *lexer   // underlying lexer
	name     string   // name of the file being parsed
	tokenbuf []token  // tokens consumed on the current statement
	rules    *ruleSet // current ruleSet
}

// Pretty errors.
func (p *parser) parseError(context string, expected string, found token) {
	fmt.Fprintf(os.Stderr, "%s:%d: syntax error: ", p.name, found.line)
	fmt.Fprintf(os.Stderr, "while %s, expected %s but found \"%s\".\n",
		context, expected, found.String())
	os.Exit(1)
}

// More basic errors.
func (p *parser) basicErrorAtToken(what string, found token) {
	p.basicErrorAtLine(what, found.line)
}

func (p *parser) basicErrorAtLine(what string, line int) {
	fmt.Fprintf(os.Stderr, "%s:%d: syntax error: %s\n",
		p.name, line, what)
	os.Exit(1)
}

// Accept a token for use in the current statement being parsed.
func (p *parser) push(t token) {
	p.tokenbuf = append(p.tokenbuf, t)
}

// Clear all the accepted tokens. Called when a statement is finished.
func (p *parser) clear() {
	p.tokenbuf = p.tokenbuf[:0]
}

// A parser state function takes a parser and the next token and returns a new
// state function, or nil if there was a parse error.
type parserStateFun func(*parser, token) parserStateFun

// Parse a mkfile, returning a new ruleSet.
func parse(input string, name string) *ruleSet {
	rules := &ruleSet{make(map[string][]string), make([]rule, 0)}
	parseInto(input, name, rules)
	return rules
}

// Parse a mkfile inserting rules and variables into a given ruleSet.
func parseInto(input string, name string, rules *ruleSet) {
	l, tokens := lex(input)
	p := &parser{l, name, []token{}, rules}
	state := parseTopLevel
	for t := range tokens {
		if t.typ == tokenError {
			// TODO: fancier error messages
			fmt.Fprintf(os.Stderr, "Error: %s", l.errmsg)
			break
		}

		state = state(p, t)
	}

	// insert a dummy newline to allow parsing of any assignments or recipeless
	// rules to finish.
	state = state(p, token{tokenNewline, "\n", l.line})

	// TODO: Error when state != parseTopLevel
}

// We are at the top level of a mkfile, expecting rules, assignments, or
// includes.
func parseTopLevel(p *parser, t token) parserStateFun {
	switch t.typ {
	case tokenNewline:
		return parseTopLevel
	case tokenPipeInclude:
		return parsePipeInclude
	case tokenRedirInclude:
		return parseRedirInclude
	case tokenWord:
		return parseAssignmentOrTarget(p, t)
	default:
		p.parseError("parsing mkfile",
			"a rule, include, or assignment", t)
	}

	return parseTopLevel
}

// Consumed a '<|'
func parsePipeInclude(p *parser, t token) parserStateFun {
	switch t.typ {
	case tokenNewline:
		if len(p.tokenbuf) == 0 {
			p.basicErrorAtToken("empty pipe include", t)
		}

		args := make([]string, len(p.tokenbuf)-1)
		for i := 1; i < len(p.tokenbuf); i++ {
			args[i-1] = p.tokenbuf[i].val
		}

		output := executeRecipe("sh", args, "", false, false, true)
		parseInto(output, fmt.Sprintf("%s:sh", p.name), p.rules)

		p.clear()
		return parseTopLevel

	// Almost anything goes. Let the shell sort it out.
	case tokenPipeInclude:
		fallthrough
	case tokenRedirInclude:
		fallthrough
	case tokenColon:
		fallthrough
	case tokenAssign:
		fallthrough
	case tokenWord:
		p.tokenbuf = append(p.tokenbuf, t)

	default:
		// TODO: Complain about unexpected tokens.
	}

	return parsePipeInclude
}

// Consumed a '<'
func parseRedirInclude(p *parser, t token) parserStateFun {
	switch t.typ {
	case tokenNewline:
		// TODO:
		// Open the file, read its context, call parseInto recursively.
		// Clear out p.tokenbuf

	case tokenWord:
		// TODO:

	default:
		// TODO: Complain about unexpected tokens.
	}

	return parseRedirInclude
}

// Encountered a bare string at the beginning of the line.
func parseAssignmentOrTarget(p *parser, t token) parserStateFun {
	fmt.Println("assignment or target")
	p.push(t)
	return parseEqualsOrTarget
}

// Consumed one bare string ot the beginning of the line.
func parseEqualsOrTarget(p *parser, t token) parserStateFun {
	fmt.Println("equals or target")
	switch t.typ {
	case tokenAssign:
		return parseAssignment

	case tokenWord:
		p.push(t)
		return parseTargets

	case tokenColon:
		p.push(t)
		return parseAttributesOrPrereqs

	default:
		p.parseError("reading a a target or assignment",
			"'=', ':', or another target", t)
	}

	return parseTopLevel // unreachable
}

// Consumed 'foo='. Everything else is a value being assigned to foo.
func parseAssignment(p *parser, t token) parserStateFun {
	switch t.typ {
	case tokenNewline:
		err := p.rules.executeAssignment(p.tokenbuf)
		if err != nil {
			p.basicErrorAtToken(err.what, err.where)
		}
		p.clear()
		return parseTopLevel

	default:
		p.push(t)
	}

	return parseAssignment
}

// Everything up to ':' must be a target.
func parseTargets(p *parser, t token) parserStateFun {
	switch t.typ {
	case tokenWord:
		p.push(t)
	case tokenColon:
		p.push(t)
		return parseAttributesOrPrereqs

	default:
		p.parseError("reading a rule's targets",
			"filename or pattern", t)
	}

	return parseTargets
}

// Consumed one or more strings followed by a first ':'.
func parseAttributesOrPrereqs(p *parser, t token) parserStateFun {
	fmt.Println("attributes or prereqs")
	switch t.typ {
	case tokenNewline:
		return parseRecipe
	case tokenColon:
		p.push(t)
		return parsePrereqs
	case tokenWord:
		p.push(t)
	default:
		p.parseError("reading a rule's attributes or prerequisites",
			"an attribute, pattern, or filename", t)
	}

	return parseAttributesOrPrereqs
}

// Targets and attributes and the second ':' have been consumed.
func parsePrereqs(p *parser, t token) parserStateFun {
	fmt.Println("prereqs")
	switch t.typ {
	case tokenNewline:
		return parseRecipe
	case tokenWord:
		p.push(t)

	default:
		p.parseError("reading a rule's prerequisites",
			"filename or pattern", t)
	}

	return parsePrereqs
}

// An entire rule has been consumed.
func parseRecipe(p *parser, t token) parserStateFun {
	fmt.Println("recipe")

	// Assemble the rule!
	r := rule{}

	// find one or two colons
	i := 0
	for ; i < len(p.tokenbuf) && p.tokenbuf[i].typ != tokenColon; i++ {
	}
	j := i + 1
	for ; j < len(p.tokenbuf) && p.tokenbuf[j].typ != tokenColon; j++ {
	}

	// targets
	r.targets = make([]string, i)
	for k := 0; k < i; k++ {
		r.targets[k] = p.rules.expand(p.tokenbuf[k].val, true)
	}

	// rule has attributes
    // TODO: should we be expanding the attribute strings?
	if j < len(p.tokenbuf) {
		attribs := make([]string, j-i-1)
		for k := i + 1; k < j; k++ {
			attribs[k-i-1] = p.tokenbuf[k].val
		}
		err := r.parseAttribs(attribs)
		if err != nil {
			msg := fmt.Sprintf("while reading a rule's attributes expected an attribute but found \"%c\".", err.found)
			p.basicErrorAtToken(msg, p.tokenbuf[i+1])
		}
	} else {
		j = i
	}

	// prereqs
	r.prereqs = make([]string, len(p.tokenbuf)-j-1)
	for k := j + 1; k < len(p.tokenbuf); k++ {
		r.prereqs[k-j-1] = p.rules.expand(p.tokenbuf[k].val, true)
	}

	if t.typ == tokenRecipe {
		r.recipe = p.rules.expand(t.val, false)
	}

	p.rules.push(r)
	p.clear()

	// the current token doesn't belong to this rule
	if t.typ != tokenRecipe {
		return parseTopLevel(p, t)
	}

	return parseTopLevel
}