// SPDX-License-Identifier: GPL-3.0-or-later

// Package engine is what every krino front end calls: it loads and compiles
// the configuration, matches files against rules, and plans and applies
// actions. It returns data; front ends only render it.
package engine

import (
	"fmt"
	"os"
	"sort"
	"strings"
	"time"

	"git.labunix.xyz/krino/internal/cond"
	"git.labunix.xyz/krino/internal/config"
	"git.labunix.xyz/krino/internal/extract"
	"git.labunix.xyz/krino/internal/ignore"
	"git.labunix.xyz/krino/internal/plan"
)

// Engine holds a loaded, compiled configuration: everything a front end
// needs to check, match and act.
type Engine struct {
	Config   *config.Config
	Dirs     []*Dir
	Extract  *extract.Extractor
	Now      func() time.Time // time.Now; tests replace it
	MainFile string

	// CacheDir holds each directory's keyword cache (spec §6.1), as
	// NAME.cache; "" means no cache is read or written. Load leaves it
	// empty: the command line sets it.
	CacheDir string
}

// Dir is one configured directory, with its ignore matcher and rules
// compiled.
type Dir struct {
	Name     string
	Root     string // absolute
	Conf     *config.Dir
	Settings config.Resolved // built-in, then defaults, then the directory
	Ignore   *ignore.Matcher
	Rules    []*Rule

	// ContentKeywords is every content keyword the directory's excludes
	// and rules test, once each, sorted by Key. When a file's text is
	// extracted, every one of them is answered at once, so one extraction
	// serves every content test and fills the keyword cache.
	ContentKeywords []cond.Keyword

	// Excludes are the (exclude ...) forms that apply here, compiled with the
	// directory's settings: krino.conf's first, then the directory's own. A
	// file any of them matches is set aside before any rule runs.
	Excludes []*Exclude

	// DupScopes is every distinct directory list the duplicate tests of
	// Rules use, in first-seen order, the plain (duplicate) as an empty
	// list. Spec §5.5 rule 2 looks a file up under each of them before any
	// rule may delete it.
	DupScopes [][]string
}

// Exclude is one compiled (exclude ...) form.
type Exclude struct {
	Text string // the form as written, for check, explain and the plan
	Cond *cond.Cond
}

// Rule is one directory's rule, with its condition compiled.
type Rule struct {
	Name     string
	Conf     *config.Rule
	Settings config.Resolved // the rule's own settings over its directory's
	Cond     *cond.Cond
}

// Load reads and compiles everything. Any problem anywhere returns a nil
// Engine and every diagnostic: krino never acts on a configuration it only
// partly understood. Duplicate names are ignored after their first use.
func Load(mainFile string, names ...string) (*Engine, []*config.Diag) {
	return LoadWith(mainFile, nil, names...)
}

// LoadWith is Load with some configuration files' text supplied by the
// caller (config.LoadWith): the GUI checks unsaved editor text with it,
// compiled exactly as a run would compile it (GUI design §1.3).
func LoadWith(mainFile string, overrides map[string][]byte, names ...string) (*Engine, []*config.Diag) {
	cfg, errs := config.LoadWith(mainFile, overrides, dedupeNames(names)...)
	if cfg == nil {
		return nil, errs
	}

	var dirs []*Dir
	// A mistake inside a krino.conf exclude is compiled once per directory,
	// but reported once.
	reported := map[string]bool{}
	if len(cfg.Dirs) == 0 {
		// With no directory to compile them for, krino.conf's excludes are
		// still checked, so a mistake is reported before one is included.
		// Compiled with the defaults' case and fold, as a directory without
		// settings of its own would compile them.
		def := cfg.Main.Defaults.Over(config.Builtin())
		opt := cond.Options{IgnoreCase: def.Case == config.CaseIgnore, Fold: def.Fold}
		for _, x := range cfg.Main.Excludes {
			_, cerrs := cond.Compile(cfg.Main.File, x.When, opt)
			errs = append(errs, cerrs...)
		}
	}
	for _, d := range cfg.Dirs {
		dir := &Dir{
			Name:     d.Name,
			Root:     d.Path,
			Conf:     d,
			Settings: cfg.Resolved(d),
		}
		if m, err := ignore.New(d.Ignore); err != nil {
			errs = append(errs, &config.Diag{File: d.File, Msg: err.Error()})
		} else {
			dir.Ignore = m
		}
		for _, r := range d.Rules {
			rs := r.Settings.Over(dir.Settings)
			c, cerrs := cond.Compile(d.File, r.When, cond.Options{
				IgnoreCase: rs.Case == config.CaseIgnore,
				Fold:       rs.Fold,
			})
			if len(cerrs) > 0 {
				errs = append(errs, cerrs...)
				continue
			}
			if diag := checkCaptures(d.File, r, c); diag != nil {
				errs = append(errs, diag)
				continue
			}
			if diag := checkDuplicateDelete(d.File, r, c); diag != nil {
				errs = append(errs, diag)
				continue
			}
			dir.Rules = append(dir.Rules, &Rule{Name: r.Name, Conf: r, Settings: rs, Cond: c})
		}
		dirOpt := cond.Options{IgnoreCase: dir.Settings.Case == config.CaseIgnore, Fold: dir.Settings.Fold}
		for _, src := range []struct {
			file     string
			excludes []*config.Exclude
		}{{cfg.Main.File, cfg.Main.Excludes}, {d.File, d.Excludes}} {
			for _, x := range src.excludes {
				c, cerrs := cond.Compile(src.file, x.When, dirOpt)
				for _, ce := range cerrs {
					if key := ce.Error(); !reported[key] {
						reported[key] = true
						errs = append(errs, ce)
					}
				}
				if len(cerrs) == 0 {
					dir.Excludes = append(dir.Excludes, &Exclude{Text: x.Text, Cond: c})
				}
			}
		}
		dir.ContentKeywords = contentKeywords(dir.Rules, dir.Excludes)
		dir.DupScopes = dupScopes(dir.Rules, dir.Excludes)
		dirs = append(dirs, dir)
	}

	if len(errs) > 0 {
		return nil, errs
	}
	return &Engine{
		Config:   cfg,
		Dirs:     dirs,
		Extract:  extract.New(),
		Now:      time.Now,
		MainFile: mainFile,
	}, nil
}

// checkCaptures validates a compiled rule's actions against the capture
// groups its own name tests can supply (spec 7.3): a rule using {N} needs a
// name test at all, and every name test in it needs at least N groups. It
// reports only the first offending action, so one config mistake yields one
// diagnostic.
func checkCaptures(file string, r *config.Rule, c *cond.Cond) *config.Diag {
	groups := c.NameGroups()
	for _, a := range r.Actions {
		if err := plan.CheckTemplate(a.Arg); err != nil {
			// A placeholder that could never expand is a config error, not a
			// step skipped at plan time.
			return &config.Diag{File: file, Pos: a.Pos, Msg: fmt.Sprintf("rule %q: %v", r.Name, err)}
		}
		n, err := plan.MaxIndex(a.Arg)
		if err != nil || n == 0 {
			continue
		}
		if len(groups) == 0 {
			return &config.Diag{File: file, Pos: a.Pos, Msg: fmt.Sprintf("rule %q: {%d} needs a name test to capture from", r.Name, n)}
		}
		for _, g := range groups {
			if g < n {
				return &config.Diag{File: file, Pos: a.Pos, Msg: fmt.Sprintf("rule %q: {%d} but a name test has only %s", r.Name, n, captureGroups(g))}
			}
		}
	}
	return nil
}

// checkDuplicateDelete refuses a rule that combines a duplicate test with a
// delete action (spec §4.5, §5.5): duplicates are found, never deleted.
// Cond.DupDirs records every duplicate test compiled, inside or and not
// too, so a test anywhere in the condition counts. It reports only the
// first delete action, so one config mistake yields one diagnostic.
func checkDuplicateDelete(file string, r *config.Rule, c *cond.Cond) *config.Diag {
	if len(c.DupDirs) == 0 {
		return nil
	}
	for _, a := range r.Actions {
		if a.Kind == config.Delete || a.Kind == config.DeletePermanent {
			return &config.Diag{File: file, Pos: a.Pos, Msg: fmt.Sprintf("rule %q: (duplicate) cannot be combined with (%s): duplicates are never deleted, move them aside instead", r.Name, a.Kind)}
		}
	}
	return nil
}

// captureGroups renders a capture-group count with correct singular/plural.
func captureGroups(n int) string {
	if n == 1 {
		return "1 capture group"
	}
	return fmt.Sprintf("%d capture groups", n)
}

// dedupeNames returns names with every repeat after its first occurrence
// removed, order preserved.
func dedupeNames(names []string) []string {
	var out []string
	seen := map[string]bool{}
	for _, n := range names {
		if seen[n] {
			continue
		}
		seen[n] = true
		out = append(out, n)
	}
	return out
}

// contentKeywords returns every content keyword excludes and rules test,
// each once, sorted by Key: Dir.ContentKeywords.
func contentKeywords(rules []*Rule, excludes []*Exclude) []cond.Keyword {
	seen := map[string]bool{}
	var out []cond.Keyword
	add := func(c *cond.Cond) {
		for _, k := range c.Keywords {
			if !seen[k.Key()] {
				seen[k.Key()] = true
				out = append(out, k)
			}
		}
	}
	for _, x := range excludes {
		add(x.Cond)
	}
	for _, r := range rules {
		add(r.Cond)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Key() < out[j].Key() })
	return out
}

// dupScopes returns the distinct Cond.DupDirs lists a directory uses, in
// first-seen order, from its rules and its excludes alike. Lists are
// compared as written, with their length in the key so (duplicate) and
// (duplicate "") stay apart; two spellings of one directory stay two
// entries, which costs a second lookup but never a wrong answer, since
// facts.Duplicate resolves and shares the index itself.
//
// The excludes count because the protection these scopes drive - no rule
// deletes a file krino has found to be a duplicate - is about what krino
// knows, not about which form taught it. A directory whose only duplicate
// test sat in an (exclude ...) had no scopes at all, so a later rule could
// permanently delete every copy of a file krino had just called a
// duplicate.
func dupScopes(rules []*Rule, excludes []*Exclude) [][]string {
	var out [][]string
	seen := map[string]bool{}
	add := func(lists [][]string) {
		for _, dirs := range lists {
			key := fmt.Sprintf("%d\x00%s", len(dirs), strings.Join(dirs, "\x00"))
			if seen[key] {
				continue
			}
			seen[key] = true
			out = append(out, dirs)
		}
	}
	for _, r := range rules {
		add(r.Cond.DupDirs)
	}
	for _, x := range excludes {
		add(x.Cond.DupDirs)
	}
	return out
}

// Report is what Check reports: the files involved and each directory's
// state.
type Report struct {
	MainFile string
	LogFile  string
	Dirs     []DirReport
	Tools    []extract.Tool
}

// DirReport is one directory's state in a Report.
type DirReport struct {
	Dir     *Dir
	Missing bool // the root is not a directory right now
}

// Check reports the engine's configuration files, each directory's current
// state and the external tools found for content extraction.
func (e *Engine) Check() Report {
	r := Report{
		MainFile: e.MainFile,
		LogFile:  e.Config.LogFile(),
		Tools:    e.Extract.Tools(),
	}
	for _, d := range e.Dirs {
		fi, err := os.Stat(d.Root)
		r.Dirs = append(r.Dirs, DirReport{Dir: d, Missing: err != nil || !fi.IsDir()})
	}
	return r
}