/*
Copyright The Helm Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package ignore

import (
	"bufio"
	"bytes"
	"errors"
	"io"
	"log/slog"
	"os"
	"path/filepath"
	"strings"
)

// HelmIgnore default name of an ignorefile.
const HelmIgnore = ".helmignore"

// Rules is a collection of path matching rules.
//
// Parse() and ParseFile() will construct and populate new Rules.
// Empty() will create an immutable empty ruleset.
type Rules struct {
	patterns []*pattern
}

// Empty builds an empty ruleset.
func Empty() *Rules {
	return &Rules{patterns: []*pattern{}}
}

// AddDefaults adds default ignore patterns.
//
// Ignore all dotfiles in "templates/"
func (r *Rules) AddDefaults() {
	r.parseRule(`templates/.?*`)
}

// ParseFile parses a helmignore file and returns the *Rules.
func ParseFile(file string) (*Rules, error) {
	f, err := os.Open(file)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	return Parse(f)
}

// Parse parses a rules file
func Parse(file io.Reader) (*Rules, error) {
	r := &Rules{patterns: []*pattern{}}

	s := bufio.NewScanner(file)
	currentLine := 0
	utf8bom := []byte{0xEF, 0xBB, 0xBF}
	for s.Scan() {
		scannedBytes := s.Bytes()
		// We trim UTF8 BOM
		if currentLine == 0 {
			scannedBytes = bytes.TrimPrefix(scannedBytes, utf8bom)
		}
		line := string(scannedBytes)
		currentLine++

		if err := r.parseRule(line); err != nil {
			return r, err
		}
	}
	return r, s.Err()
}

// Ignore evaluates the file at the given path, and returns true if it should be ignored.
//
// Ignore evaluates path against all rules in order. Later rules can override earlier ones,
// following gitignore semantics where negation patterns (starting with !) can re-include
// previously excluded files.
func (r *Rules) Ignore(path string, fi os.FileInfo) bool {
	// Don't match on empty dirs.
	if path == "" {
		return false
	}

	// Disallow ignoring the current working directory.
	// See issue:
	// 1776 (New York City) Hamilton: "Pardon me, are you Aaron Burr, sir?"
	if path == "." || path == "./" {
		return false
	}

	// Track whether the file should be ignored. Start with false (not ignored),
	// and let each matching rule update this value. The last matching rule wins.
	ignored := false

	for _, p := range r.patterns {
		if p.match == nil {
			slog.Info("this will be ignored no matcher supplied", "patterns", p.raw)
			return false
		}

		// If the rule is looking for directories, and this is not a directory,
		// skip it.
		if p.mustDir && !fi.IsDir() {
			continue
		}

		if p.match(path, fi) {
			// For negation rules, matching means "don't ignore this file"
			// For regular rules, matching means "ignore this file"
			ignored = !p.negate
		}
	}
	return ignored
}

// parseRule parses a rule string and creates a pattern, which is then stored in the Rules object.
func (r *Rules) parseRule(rule string) error {
	rule = strings.TrimSpace(rule)

	// Ignore blank lines
	if rule == "" {
		return nil
	}
	// Comment
	if strings.HasPrefix(rule, "#") {
		return nil
	}

	// Fail any rules that contain **
	if strings.Contains(rule, "**") {
		return errors.New("double-star (**) syntax is not supported")
	}

	// Fail any patterns that can't compile. A non-empty string must be
	// given to Match() to avoid optimization that skips rule evaluation.
	if _, err := filepath.Match(rule, "abc"); err != nil {
		return err
	}

	p := &pattern{raw: rule}

	// Negation is handled at a higher level, so strip the leading ! from the
	// string.
	if strings.HasPrefix(rule, "!") {
		p.negate = true
		rule = rule[1:]
	}

	// Directory verification is handled by a higher level, so the trailing /
	// is removed from the rule. That way, a directory named "foo" matches,
	// even if the supplied string does not contain a literal slash character.
	if strings.HasSuffix(rule, "/") {
		p.mustDir = true
		rule = strings.TrimSuffix(rule, "/")
	}

	if after, ok := strings.CutPrefix(rule, "/"); ok {
		// Require path matches the root path.
		p.match = func(n string, _ os.FileInfo) bool {
			rule = after
			ok, err := filepath.Match(rule, n)
			if err != nil {
				slog.Error("failed to compile", slog.String("rule", rule), slog.Any("error", err))
				return false
			}
			return ok
		}
	} else if strings.Contains(rule, "/") {
		// require structural match.
		p.match = func(n string, _ os.FileInfo) bool {
			ok, err := filepath.Match(rule, n)
			if err != nil {
				slog.Error(
					"failed to compile",
					slog.String("rule", rule),
					slog.Any("error", err),
				)
				return false
			}
			return ok
		}
	} else {
		p.match = func(n string, _ os.FileInfo) bool {
			// When there is no slash in the pattern, we evaluate ONLY the
			// filename.
			n = filepath.Base(n)
			ok, err := filepath.Match(rule, n)
			if err != nil {
				slog.Error("failed to compile", slog.String("rule", rule), slog.Any("error", err))
				return false
			}
			return ok
		}
	}

	r.patterns = append(r.patterns, p)
	return nil
}

// matcher is a function capable of computing a match.
//
// It returns true if the rule matches.
type matcher func(name string, fi os.FileInfo) bool

// pattern describes a pattern to be matched in a rule set.
type pattern struct {
	// raw is the unparsed string, with nothing stripped.
	raw string
	// match is the matcher function.
	match matcher
	// negate indicates that the rule's outcome should be negated.
	negate bool
	// mustDir indicates that the matched file must be a directory.
	mustDir bool
}