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

package model

import (
	"fmt"
	"strings"

	"git.labunix.xyz/krino/internal/config"
	"git.labunix.xyz/krino/internal/sexp"
)

// FormKind is what an editable form is.
type FormKind int

const (
	RuleForm FormKind = iota
	ExcludeForm
)

// Form is one editable form of a directory's file, as the list on the left
// of the Rules tab shows it (GUI design §5.1).
type Form struct {
	Kind    FormKind
	Label   string // the rule's name, or the exclude as written
	Pos     sexp.Pos
	End     sexp.Pos
	Rule    *config.Rule    // RuleForm
	Exclude *config.Exclude // ExcludeForm
}

// Forms parses the text in the editor and lists what can be edited, in file
// order: the excludes and rules of this directory. Text that does not parse
// has no forms - the Text tab keeps it until it is fixed (GUI design §5.2).
func (r *Rules) Forms() ([]Form, error) {
	over := map[string][]byte{r.File: []byte(r.Text)}
	cfg, diags := config.LoadWith(r.e.MainFile, over, r.Name)
	if len(diags) > 0 {
		return nil, fmt.Errorf("%s", diags[0])
	}
	var d *config.Dir
	for _, cd := range cfg.Dirs {
		if cd.Name == r.Name {
			d = cd
			break
		}
	}
	if d == nil {
		return nil, fmt.Errorf("model: %s is not in the configuration", r.Name)
	}
	var out []Form
	for _, x := range d.Excludes {
		out = append(out, Form{Kind: ExcludeForm, Label: x.Text, Pos: x.Pos, End: x.End, Exclude: x})
	}
	for _, rule := range d.Rules {
		out = append(out, Form{Kind: RuleForm, Label: rule.Name, Pos: rule.Pos, End: rule.End, Rule: rule})
	}
	sortByPosition(out)
	return out, nil
}

// sortByPosition puts forms in the order they are written, since excludes
// and rules are parsed into separate lists.
func sortByPosition(forms []Form) {
	for i := 1; i < len(forms); i++ {
		for j := i; j > 0 && forms[j].Pos.Offset < forms[j-1].Pos.Offset; j-- {
			forms[j], forms[j-1] = forms[j-1], forms[j]
		}
	}
}

// ReplaceForm swaps form i's text for text - what config.PrintRule or
// PrintExclude wrote for the edited form - leaving every other byte of the
// file, comments and layout included, exactly as it was (GUI design §5.1).
func (r *Rules) ReplaceForm(i int, text string) error {
	f, err := r.form(i)
	if err != nil {
		return err
	}
	out, err := config.Splice([]byte(r.Text), f.Pos, f.End, strings.TrimRight(text, "\n"))
	if err != nil {
		return err
	}
	r.Text = string(out)
	return nil
}

// DeleteForm removes form i and the comment lines directly above it - its
// block (GUI design §5.1). A comment separated from the form by a blank
// line belongs to the file, not to the form, and stays.
func (r *Rules) DeleteForm(i int) error {
	f, err := r.form(i)
	if err != nil {
		return err
	}
	start, end := r.block(f)
	r.Text = join(r.Text[:start], r.Text[end:])
	return nil
}

// MoveForm moves form i one place up (delta -1) or down (delta 1), with its
// comments. Moving past either end does nothing.
func (r *Rules) MoveForm(i, delta int) error {
	forms, err := r.Forms()
	if err != nil {
		return err
	}
	j := i + delta
	if i < 0 || i >= len(forms) || j < 0 || j >= len(forms) {
		return nil
	}
	a, b := forms[i], forms[j]
	if a.Pos.Offset > b.Pos.Offset {
		a, b = b, a
	}
	as, ae := r.block(a)
	bs, be := r.block(b)
	if ae > bs {
		return fmt.Errorf("model: the two forms share lines")
	}
	r.Text = r.Text[:as] + r.Text[bs:be] + r.Text[ae:bs] + r.Text[as:ae] + r.Text[be:]
	return nil
}

// AddRuleAfter inserts a new rule after form i - after every form when i is
// out of range - and returns its place in the new list. The rule it writes
// is the smallest one that loads, for the form editor to fill in.
func (r *Rules) AddRuleAfter(i int, name string) (int, error) {
	forms, err := r.Forms()
	if err != nil {
		return 0, err
	}
	text := config.PrintRule(&config.Rule{
		Name:    name,
		Actions: []config.Action{{Kind: config.Move, Arg: "TODO"}},
	})
	at := len(r.Text)
	if i >= 0 && i < len(forms) {
		_, at = r.block(forms[i])
	}
	r.Text = join(r.Text[:at], "\n"+text+r.Text[at:])
	after, err := r.Forms()
	if err != nil {
		return 0, err
	}
	for n, f := range after {
		if f.Kind == RuleForm && f.Label == name && !was(forms, f) {
			return n, nil
		}
	}
	return 0, fmt.Errorf("model: the new rule is not in the file")
}

// was reports whether a form of the same kind and label was already there
// at the same offset, so AddRuleAfter can tell its new rule from a rule of
// the same name that existed before.
func was(before []Form, f Form) bool {
	for _, b := range before {
		if b.Kind == f.Kind && b.Label == f.Label && b.Pos.Offset == f.Pos.Offset {
			return true
		}
	}
	return false
}

// FormHasComments reports whether form i holds a comment inside it. A form
// editor writes the form back from what was parsed, and the parser drops
// comments, so the caller warns before replacing one (GUI design §5.1).
func (r *Rules) FormHasComments(i int) (bool, error) {
	f, err := r.form(i)
	if err != nil {
		return false, err
	}
	return hasComment(r.Text[f.Pos.Offset:f.End.Offset]), nil
}

// hasComment reports whether s holds a ";" that starts a comment: one
// outside a string, since a name pattern may well contain a semicolon.
func hasComment(s string) bool {
	inString, escaped := false, false
	for _, c := range s {
		switch {
		case escaped:
			escaped = false
		case c == '\\' && inString:
			escaped = true
		case c == '"':
			inString = !inString
		case c == ';' && !inString:
			return true
		}
	}
	return false
}

// form is form i of the current text.
func (r *Rules) form(i int) (Form, error) {
	forms, err := r.Forms()
	if err != nil {
		return Form{}, err
	}
	if i < 0 || i >= len(forms) {
		return Form{}, fmt.Errorf("model: no form %d", i)
	}
	return forms[i], nil
}

// block is the span a form moves and is deleted with: from the start of the
// first comment line that touches it, to the end of the line its closing
// paren is on.
func (r *Rules) block(f Form) (start, end int) {
	start = lineStart(r.Text, f.Pos.Offset)
	for start > 0 {
		prev := lineStart(r.Text, start-1)
		line := strings.TrimSpace(r.Text[prev : start-1])
		if !strings.HasPrefix(line, ";") {
			break
		}
		start = prev
	}
	end = lineEnd(r.Text, f.End.Offset)
	return start, end
}

// lineStart is the offset just after the newline before at.
func lineStart(s string, at int) int {
	if at > len(s) {
		at = len(s)
	}
	if i := strings.LastIndexByte(s[:at], '\n'); i >= 0 {
		return i + 1
	}
	return 0
}

// lineEnd is the offset just past the newline that ends at's line.
func lineEnd(s string, at int) int {
	if at >= len(s) {
		return len(s)
	}
	if i := strings.IndexByte(s[at:], '\n'); i >= 0 {
		return at + i + 1
	}
	return len(s)
}

// join puts two pieces of a file back together without leaving a run of
// blank lines where something was taken out or put in.
func join(before, after string) string {
	for strings.HasSuffix(before, "\n\n") && strings.HasPrefix(after, "\n") {
		after = after[1:]
	}
	return before + after
}