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

package config

import (
	"fmt"
	"path/filepath"
	"strings"

	"krino/internal/sexp"
	"krino/internal/xdg"
)

// Dir is one directory's config, dirs/<name>.conf.
type Dir struct {
	Name     string
	File     string
	Path     string // absolute and cleaned
	PathText string // as written in the file
	Settings Settings
	Ignore   []string // gitignore patterns, in order
	Excludes []*Exclude
	Rules    []*Rule
}

// Exclude is one (exclude COND...) form: a file for which every condition
// holds is set aside before any rule runs. Forms may repeat, so a file is
// excluded when any one form matches it.
type Exclude struct {
	Pos  sexp.Pos
	Text string       // the form as written, whitespace collapsed, for check and explain
	When []*sexp.Node // the conditions, all of which must hold
}

// parseExclude reads an (exclude COND...) form from src; nil when it has no
// usable condition.
func parseExclude(n *sexp.Node, src []byte, d *diags) *Exclude {
	conds := n.Args()
	if len(conds) == 0 {
		d.at(n, "(exclude) needs a condition, like (exclude (type iso))")
		return nil
	}
	bad := false
	for _, c := range conds {
		if c.Kind != sexp.List {
			d.at(c, "exclude: a condition is a form like (type pdf), not %s", c)
			bad = true
		}
	}
	if bad {
		return nil
	}
	text := strings.Join(strings.Fields(string(src[n.Pos.Offset:n.End.Offset])), " ")
	return &Exclude{Pos: n.Pos, Text: text, When: conds}
}

// Rule is a named condition with the actions it performs.
type Rule struct {
	Name     string
	Pos      sexp.Pos
	When     []*sexp.Node // the conditions, all of which must hold
	HasWhen  bool         // false: the rule matches every file
	Settings Settings     // only case, fold and on-conflict
	Actions  []Action     // in the order written
	Stop     bool
}

// ActionKind is what an action does.
type ActionKind int

const (
	Copy ActionKind = iota
	Move
	Rename
	Delete          // to the Trash
	DeletePermanent // unlink
)

func (k ActionKind) String() string {
	switch k {
	case Copy:
		return "copy"
	case Move:
		return "move"
	case Rename:
		return "rename"
	case Delete:
		return "delete"
	case DeletePermanent:
		return "delete permanent"
	}
	return fmt.Sprintf("ActionKind(%d)", int(k))
}

// Action is one step of a rule.
type Action struct {
	Kind ActionKind
	Arg  string // the directory of copy and move, the new name of rename
	Pos  sexp.Pos
}

// ParseDir reads the text of dirs/<name>.conf.
func ParseDir(name, file string, src []byte) (*Dir, []*Diag) {
	dir := &Dir{Name: name, File: file}
	nodes, err := sexp.Parse(file, src)
	if err != nil {
		return dir, []*Diag{fromSyntax(err)}
	}
	d := &diags{file: file}
	var pathNode *sexp.Node
	seen := map[string]*sexp.Node{}
	rules := map[string]*Rule{}
	for _, n := range nodes {
		switch head := n.Head(); {
		case head == "":
			d.at(n, "expected a form like (rule ...), got %s", n)
		case head == "path":
			if pathNode != nil {
				d.at(n, "path given twice (first at line %d)", pathNode.Pos.Line)
				continue
			}
			pathNode = n
			dir.parsePath(n, d)
		case head == "ignore":
			for _, a := range n.Args() {
				if a.Kind != sexp.String {
					d.at(a, `ignore takes patterns in quotes, like "*.part"; got %s`, a)
					continue
				}
				dir.Ignore = append(dir.Ignore, a.Text)
			}
		case head == "exclude":
			if x := parseExclude(n, src, d); x != nil {
				dir.Excludes = append(dir.Excludes, x)
			}
		case head == "rule":
			r := parseRule(n, d)
			if r == nil {
				continue
			}
			if first, ok := rules[r.Name]; ok {
				d.at(n, "rule %q defined twice (first at line %d)", r.Name, first.Pos.Line)
				continue
			}
			rules[r.Name] = r
			dir.Rules = append(dir.Rules, r)
		case isSetting(head):
			dir.Settings.parse(n, d, seen)
		default:
			d.at(n, "unknown form (%s ...); a directory file has path, ignore, exclude, rule and settings like (recursive yes)", head)
		}
	}
	if pathNode == nil {
		d.at(nil, "no (path ...): say which directory this file sorts")
	}
	return dir, d.list
}

func (dir *Dir) parsePath(n *sexp.Node, d *diags) {
	args := n.Args()
	if len(args) == 1 && args[0].Kind == sexp.Symbol {
		d.at(args[0], "path must be a string: write (path %s)", sexp.Quote(args[0].Text))
		return
	}
	if len(args) != 1 || args[0].Kind != sexp.String {
		d.at(n, `path takes one directory in quotes, like (path "~/downloads")`)
		return
	}
	p := xdg.Expand(args[0].Text)
	if !filepath.IsAbs(p) {
		d.at(args[0], "path must be absolute or start with ~, not %s", sexp.Quote(args[0].Text))
		return
	}
	dir.Path = filepath.Clean(p)
	dir.PathText = args[0].Text
}

var actionHeads = map[string]bool{"copy": true, "move": true, "rename": true, "delete": true}

// parseRule reads (rule "NAME" ITEM...); nil if it has no usable name.
func parseRule(n *sexp.Node, d *diags) *Rule {
	args := n.Args()
	if len(args) == 0 || args[0].Kind != sexp.String || args[0].Text == "" {
		d.at(n, `rule needs a name in quotes first, like (rule "invoices" ...)`)
		return nil
	}
	if strings.HasPrefix(args[0].Text, "(") {
		d.at(n, `rule names cannot start with "(": (review) marks choices made in review`)
		return nil
	}
	r := &Rule{Name: args[0].Text, Pos: n.Pos}
	seen := map[string]*sexp.Node{}
	var whenNode *sexp.Node
	triedAction, deleted := false, false
	errorCount := len(d.list)
	for _, item := range args[1:] {
		switch head := item.Head(); {
		case head == "":
			d.at(item, "rule %q: expected a form like (when ...) or (move ...), got %s", r.Name, item)
		case head == "when":
			if whenNode != nil {
				d.at(item, "rule %q: when given twice (first at line %d)", r.Name, whenNode.Pos.Line)
				continue
			}
			whenNode = item
			r.HasWhen = true
			r.When = item.Args()
			if len(r.When) == 0 {
				d.at(item, "rule %q: (when) needs a condition; leave it out to match every file", r.Name)
			}
			for _, c := range r.When {
				if c.Kind != sexp.List {
					d.at(c, "rule %q: a condition is a form like (type pdf), not %s", r.Name, c)
				}
			}
		case head == "stop":
			if len(item.Args()) != 0 {
				d.at(item, "rule %q: stop takes nothing: write (stop)", r.Name)
				continue
			}
			r.Stop = true
		case isSetting(head):
			if !ruleSettings[head] {
				d.at(item, "rule %q: %s cannot be set in a rule, only case, fold and on-conflict", r.Name, head)
				continue
			}
			r.Settings.parse(item, d, seen)
		case actionHeads[head]:
			triedAction = true
			a, ok := parseAction(r.Name, item, d)
			if !ok {
				continue
			}
			if deleted {
				d.at(item, "rule %q: %s after delete would never run", r.Name, item)
				continue
			}
			deleted = a.Kind == Delete || a.Kind == DeletePermanent
			r.Actions = append(r.Actions, a)
		default:
			d.at(item, "rule %q: unknown form (%s ...); a rule has when, copy, move, rename, delete, stop, case, fold and on-conflict", r.Name, head)
			triedAction = true
		}
	}
	if !triedAction && !r.Stop && len(d.list) == errorCount {
		d.at(n, `rule %q does nothing: give it an action like (move "Somewhere") or (stop)`, r.Name)
	}
	return r
}

// parseAction reads one of copy, move, rename or delete.
func parseAction(rule string, n *sexp.Node, d *diags) (Action, bool) {
	head, args := n.Head(), n.Args()
	a := Action{Pos: n.Pos}
	if head == "delete" {
		switch {
		case len(args) == 0:
			a.Kind = Delete
		case len(args) == 1 && args[0].Kind == sexp.Symbol && args[0].Text == "permanent":
			a.Kind = DeletePermanent
		default:
			d.at(n, "rule %q: write (delete) for the Trash or (delete permanent)", rule)
			return a, false
		}
		return a, true
	}
	if len(args) == 1 && args[0].Kind == sexp.Symbol {
		d.at(args[0], "rule %q: %s takes a string: write (%s %s)", rule, head, head, sexp.Quote(args[0].Text))
		return a, false
	}
	what := map[string]string{"copy": "directory", "move": "directory", "rename": "new name"}[head]
	if len(args) != 1 || args[0].Kind != sexp.String || args[0].Text == "" {
		d.at(n, "rule %q: %s takes one %s in quotes", rule, head, what)
		return a, false
	}
	a.Kind = map[string]ActionKind{"copy": Copy, "move": Move, "rename": Rename}[head]
	a.Arg = args[0].Text
	if a.Kind == Rename && strings.Contains(a.Arg, "/") {
		d.at(args[0], "rule %q: rename gives a new name, not a path; use move to change directory", rule)
		return a, false
	}
	return a, true
}