package chroma

import (
	"fmt"
	"os"
	"regexp"
	"strings"
	"sync"
	"time"
	"unicode/utf8"

	"github.com/dlclark/regexp2"
)

// A Rule is the fundamental matching unit of the Regex lexer state machine.
type Rule struct {
	Pattern string
	Type    Emitter
	Mutator Mutator
}

// An Emitter takes group matches and returns tokens.
type Emitter interface {
	// Emit tokens for the given regex groups.
	Emit(groups []string, lexer Lexer) Iterator
}

// EmitterFunc is a function that is an Emitter.
type EmitterFunc func(groups []string, lexer Lexer) Iterator

// Emit tokens for groups.
func (e EmitterFunc) Emit(groups []string, lexer Lexer) Iterator { return e(groups, lexer) }

// ByGroups emits a token for each matching group in the rule's regex.
func ByGroups(emitters ...Emitter) Emitter {
	return EmitterFunc(func(groups []string, lexer Lexer) Iterator {
		iterators := make([]Iterator, 0, len(groups)-1)
		if len(emitters) != len(groups)-1 {
			iterators = append(iterators, Error.Emit(groups, lexer))
			// panic(errors.Errorf("number of groups %q does not match number of emitters %v", groups, emitters))
		} else {
			for i, group := range groups[1:] {
				iterators = append(iterators, emitters[i].Emit([]string{group}, lexer))
			}
		}
		return Concaterator(iterators...)
	})
}

// UsingByGroup emits tokens for the matched groups in the regex using a
// "sublexer". Used when lexing code blocks where the name of a sublexer is
// contained within the block, for example on a Markdown text block or SQL
// language block.
//
// The sublexer will be retrieved using sublexerGetFunc (typically
// internal.Get), using the captured value from the matched sublexerNameGroup.
//
// If sublexerGetFunc returns a non-nil lexer for the captured sublexerNameGroup,
// then tokens for the matched codeGroup will be emitted using the retrieved
// lexer. Otherwise, if the sublexer is nil, then tokens will be emitted from
// the passed emitter.
//
// Example:
//
// 	var Markdown = internal.Register(MustNewLexer(
// 		&Config{
// 			Name:      "markdown",
// 			Aliases:   []string{"md", "mkd"},
// 			Filenames: []string{"*.md", "*.mkd", "*.markdown"},
// 			MimeTypes: []string{"text/x-markdown"},
// 		},
// 		Rules{
// 			"root": {
// 				{"^(```)(\\w+)(\\n)([\\w\\W]*?)(^```$)",
// 					UsingByGroup(
// 						internal.Get,
// 						2, 4,
// 						String, String, String, Text, String,
// 					),
// 					nil,
// 				},
// 			},
// 		},
// 	))
//
// See the lexers/m/markdown.go for the complete example.
//
// Note: panic's if the number emitters does not equal the number of matched
// groups in the regex.
func UsingByGroup(sublexerGetFunc func(string) Lexer, sublexerNameGroup, codeGroup int, emitters ...Emitter) Emitter {
	return EmitterFunc(func(groups []string, lexer Lexer) Iterator {
		// bounds check
		if len(emitters) != len(groups)-1 {
			panic("UsingByGroup expects number of emitters to be the same as len(groups)-1")
		}

		// grab sublexer
		sublexer := sublexerGetFunc(groups[sublexerNameGroup])

		// build iterators
		iterators := make([]Iterator, len(groups)-1)
		for i, group := range groups[1:] {
			if i == codeGroup-1 && sublexer != nil {
				var err error
				iterators[i], err = sublexer.Tokenise(nil, groups[codeGroup])
				if err != nil {
					panic(err)
				}
			} else {
				iterators[i] = emitters[i].Emit([]string{group}, lexer)
			}
		}

		return Concaterator(iterators...)
	})
}

// Using returns an Emitter that uses a given Lexer for parsing and emitting.
func Using(lexer Lexer) Emitter {
	return EmitterFunc(func(groups []string, _ Lexer) Iterator {
		it, err := lexer.Tokenise(&TokeniseOptions{State: "root", Nested: true}, groups[0])
		if err != nil {
			panic(err)
		}
		return it
	})
}

// UsingSelf is like Using, but uses the current Lexer.
func UsingSelf(state string) Emitter {
	return EmitterFunc(func(groups []string, lexer Lexer) Iterator {
		it, err := lexer.Tokenise(&TokeniseOptions{State: state, Nested: true}, groups[0])
		if err != nil {
			panic(err)
		}
		return it
	})
}

// Words creates a regex that matches any of the given literal words.
func Words(prefix, suffix string, words ...string) string {
	for i, word := range words {
		words[i] = regexp.QuoteMeta(word)
	}
	return prefix + `(` + strings.Join(words, `|`) + `)` + suffix
}

// Tokenise text using lexer, returning tokens as a slice.
func Tokenise(lexer Lexer, options *TokeniseOptions, text string) ([]Token, error) {
	var out []Token
	it, err := lexer.Tokenise(options, text)
	if err != nil {
		return nil, err
	}
	for t := it(); t != EOF; t = it() {
		out = append(out, t)
	}
	return out, nil
}

// Rules maps from state to a sequence of Rules.
type Rules map[string][]Rule

// Rename clones rules then a rule.
func (r Rules) Rename(old, new string) Rules {
	r = r.Clone()
	r[new] = r[old]
	delete(r, old)
	return r
}

// Clone returns a clone of the Rules.
func (r Rules) Clone() Rules {
	out := map[string][]Rule{}
	for key, rules := range r {
		out[key] = make([]Rule, len(rules))
		copy(out[key], rules)
	}
	return out
}

// Merge creates a clone of "r" then merges "rules" into the clone.
func (r Rules) Merge(rules Rules) Rules {
	out := r.Clone()
	for k, v := range rules.Clone() {
		out[k] = v
	}
	return out
}

// MustNewLexer creates a new Lexer or panics.
func MustNewLexer(config *Config, rules Rules) *RegexLexer {
	lexer, err := NewLexer(config, rules)
	if err != nil {
		panic(err)
	}
	return lexer
}

// NewLexer creates a new regex-based Lexer.
//
// "rules" is a state machine transitition map. Each key is a state. Values are sets of rules
// that match input, optionally modify lexer state, and output tokens.
func NewLexer(config *Config, rules Rules) (*RegexLexer, error) {
	if config == nil {
		config = &Config{}
	}
	if _, ok := rules["root"]; !ok {
		return nil, fmt.Errorf("no \"root\" state")
	}
	compiledRules := map[string][]*CompiledRule{}
	for state, rules := range rules {
		compiledRules[state] = nil
		for _, rule := range rules {
			flags := ""
			if !config.NotMultiline {
				flags += "m"
			}
			if config.CaseInsensitive {
				flags += "i"
			}
			if config.DotAll {
				flags += "s"
			}
			compiledRules[state] = append(compiledRules[state], &CompiledRule{Rule: rule, flags: flags})
		}
	}
	return &RegexLexer{
		config: config,
		rules:  compiledRules,
	}, nil
}

// Trace enables debug tracing.
func (r *RegexLexer) Trace(trace bool) *RegexLexer {
	r.trace = trace
	return r
}

// A CompiledRule is a Rule with a pre-compiled regex.
//
// Note that regular expressions are lazily compiled on first use of the lexer.
type CompiledRule struct {
	Rule
	Regexp *regexp2.Regexp
	flags  string
}

// CompiledRules is a map of rule name to sequence of compiled rules in that rule.
type CompiledRules map[string][]*CompiledRule

// LexerState contains the state for a single lex.
type LexerState struct {
	Lexer *RegexLexer
	Text  []rune
	Pos   int
	Rules CompiledRules
	Stack []string
	State string
	Rule  int
	// Group matches.
	Groups []string
	// Custum context for mutators.
	MutatorContext map[interface{}]interface{}
	iteratorStack  []Iterator
	options        *TokeniseOptions
}

// Set mutator context.
func (l *LexerState) Set(key interface{}, value interface{}) {
	l.MutatorContext[key] = value
}

// Get mutator context.
func (l *LexerState) Get(key interface{}) interface{} {
	return l.MutatorContext[key]
}

// Iterator returns the next Token from the lexer.
func (l *LexerState) Iterator() Token { // nolint: gocognit
	for l.Pos < len(l.Text) && len(l.Stack) > 0 {
		// Exhaust the iterator stack, if any.
		for len(l.iteratorStack) > 0 {
			n := len(l.iteratorStack) - 1
			t := l.iteratorStack[n]()
			if t == EOF {
				l.iteratorStack = l.iteratorStack[:n]
				continue
			}
			return t
		}

		l.State = l.Stack[len(l.Stack)-1]
		if l.Lexer.trace {
			fmt.Fprintf(os.Stderr, "%s: pos=%d, text=%q\n", l.State, l.Pos, string(l.Text[l.Pos:]))
		}
		selectedRule, ok := l.Rules[l.State]
		if !ok {
			panic("unknown state " + l.State)
		}
		ruleIndex, rule, groups := matchRules(l.Text, l.Pos, selectedRule)
		// No match.
		if groups == nil {
			// From Pygments :\
			//
			// If the RegexLexer encounters a newline that is flagged as an error token, the stack is
			// emptied and the lexer continues scanning in the 'root' state. This can help producing
			// error-tolerant highlighting for erroneous input, e.g. when a single-line string is not
			// closed.
			if l.Text[l.Pos] == '\n' && l.State != l.options.State {
				l.Stack = []string{l.options.State}
				continue
			}
			l.Pos++
			return Token{Error, string(l.Text[l.Pos-1 : l.Pos])}
		}
		l.Rule = ruleIndex
		l.Groups = groups
		l.Pos += utf8.RuneCountInString(groups[0])
		if rule.Mutator != nil {
			if err := rule.Mutator.Mutate(l); err != nil {
				panic(err)
			}
		}
		if rule.Type != nil {
			l.iteratorStack = append(l.iteratorStack, rule.Type.Emit(l.Groups, l.Lexer))
		}
	}
	// Exhaust the IteratorStack, if any.
	// Duplicate code, but eh.
	for len(l.iteratorStack) > 0 {
		n := len(l.iteratorStack) - 1
		t := l.iteratorStack[n]()
		if t == EOF {
			l.iteratorStack = l.iteratorStack[:n]
			continue
		}
		return t
	}

	// If we get to here and we still have text, return it as an error.
	if l.Pos != len(l.Text) && len(l.Stack) == 0 {
		value := string(l.Text[l.Pos:])
		l.Pos = len(l.Text)
		return Token{Type: Error, Value: value}
	}
	return EOF
}

// RegexLexer is the default lexer implementation used in Chroma.
type RegexLexer struct {
	config   *Config
	analyser func(text string) float32
	trace    bool

	mu       sync.Mutex
	compiled bool
	rules    map[string][]*CompiledRule
}

// SetAnalyser sets the analyser function used to perform content inspection.
func (r *RegexLexer) SetAnalyser(analyser func(text string) float32) *RegexLexer {
	r.analyser = analyser
	return r
}

func (r *RegexLexer) AnalyseText(text string) float32 { // nolint
	if r.analyser != nil {
		return r.analyser(text)
	}
	return 0.0
}

func (r *RegexLexer) Config() *Config { // nolint
	return r.config
}

// Regex compilation is deferred until the lexer is used. This is to avoid significant init() time costs.
func (r *RegexLexer) maybeCompile() (err error) {
	r.mu.Lock()
	defer r.mu.Unlock()
	if r.compiled {
		return nil
	}
	for state, rules := range r.rules {
		for i, rule := range rules {
			if rule.Regexp == nil {
				pattern := "(?:" + rule.Pattern + ")"
				if rule.flags != "" {
					pattern = "(?" + rule.flags + ")" + pattern
				}
				pattern = `\G` + pattern
				rule.Regexp, err = regexp2.Compile(pattern, 0)
				if err != nil {
					return fmt.Errorf("failed to compile rule %s.%d: %s", state, i, err)
				}
				rule.Regexp.MatchTimeout = time.Millisecond * 250
			}
		}
	}
restart:
	seen := map[LexerMutator]bool{}
	for state := range r.rules {
		for i := 0; i < len(r.rules[state]); i++ {
			rule := r.rules[state][i]
			if compile, ok := rule.Mutator.(LexerMutator); ok {
				if seen[compile] {
					return fmt.Errorf("saw mutator %T twice; this should not happen", compile)
				}
				seen[compile] = true
				if err := compile.MutateLexer(r.rules, state, i); err != nil {
					return err
				}
				// Process the rules again in case the mutator added/removed rules.
				//
				// This sounds bad, but shouldn't be significant in practice.
				goto restart
			}
		}
	}
	r.compiled = true
	return nil
}

func (r *RegexLexer) Tokenise(options *TokeniseOptions, text string) (Iterator, error) { // nolint
	if err := r.maybeCompile(); err != nil {
		return nil, err
	}
	if options == nil {
		options = defaultOptions
	}
	if options.EnsureLF {
		text = ensureLF(text)
	}
	if !options.Nested && r.config.EnsureNL && !strings.HasSuffix(text, "\n") {
		text += "\n"
	}
	state := &LexerState{
		options:        options,
		Lexer:          r,
		Text:           []rune(text),
		Stack:          []string{options.State},
		Rules:          r.rules,
		MutatorContext: map[interface{}]interface{}{},
	}
	return state.Iterator, nil
}

func matchRules(text []rune, pos int, rules []*CompiledRule) (int, *CompiledRule, []string) {
	for i, rule := range rules {
		match, err := rule.Regexp.FindRunesMatchStartingAt(text, pos)
		if match != nil && err == nil && match.Index == pos {
			groups := []string{}
			for _, g := range match.Groups() {
				groups = append(groups, g.String())
			}
			return i, rule, groups
		}
	}
	return 0, &CompiledRule{}, nil
}

// replace \r and \r\n with \n
// same as strings.ReplaceAll but more efficient
func ensureLF(text string) string {
	buf := make([]byte, len(text))
	var j int
	for i := 0; i < len(text); i++ {
		c := text[i]
		if c == '\r' {
			if i < len(text)-1 && text[i+1] == '\n' {
				continue
			}
			c = '\n'
		}
		buf[j] = c
		j++
	}
	return string(buf[:j])
}