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

package model

import (
	"bytes"
	"context"
	"crypto/sha256"
	"errors"
	"fmt"
	"os"
	"strings"

	"git.labunix.xyz/krino/internal/cond"
	"git.labunix.xyz/krino/internal/config"
	"git.labunix.xyz/krino/internal/engine"
	"git.labunix.xyz/krino/internal/xdg"
)

// ErrChangedOnDisk is Save's refusal when the file was edited elsewhere
// since the editor read it: saving would throw that edit away, so the
// caller is asked what to do (GUI design §5.3).
var ErrChangedOnDisk = errors.New("the file changed on disk since it was opened")

// Rules is one directory's own configuration file, open for editing. Only
// dirs/NAME.conf is edited; krino.conf is not, in version 1 (GUI design §5).
type Rules struct {
	Name  string // the directory
	File  string // its file, absolute
	Text  string // what the editor holds, saved or not
	Diags []*config.Diag

	e     *engine.Engine
	saved string   // the text as last read from or written to disk
	stamp [32]byte // what was on disk then, to catch another editor
}

// RuleFiles is every included directory that has a file of its own, in the
// order krino.conf includes them.
func RuleFiles(e *engine.Engine) []string {
	var out []string
	for _, d := range e.Dirs {
		if _, err := os.Stat(config.DirFile(e.MainFile, d.Name)); err == nil {
			out = append(out, d.Name)
		}
	}
	return out
}

// OpenRules reads the file of the included directory called name.
func OpenRules(e *engine.Engine, name string) (*Rules, error) {
	found := false
	for _, d := range e.Dirs {
		if d.Name == name {
			found = true
			break
		}
	}
	if !found {
		return nil, fmt.Errorf("model: %s is not an included directory", name)
	}
	file := config.DirFile(e.MainFile, name)
	text, err := os.ReadFile(file)
	if err != nil {
		return nil, err
	}
	r := &Rules{Name: name, File: file, Text: string(text), e: e,
		saved: string(text), stamp: sha256.Sum256(text)}
	return r, nil
}

// SetText replaces what the editor holds. Nothing is written until Save.
func (r *Rules) SetText(s string) { r.Text = s }

// Modified reports whether the text differs from what is on disk.
func (r *Rules) Modified() bool { return r.Text != r.saved }

// Revert throws the unsaved text away.
func (r *Rules) Revert() { r.Text = r.saved }

// Reload re-reads the file, dropping unsaved text - what to do when
// something else has edited it.
func (r *Rules) Reload() error {
	text, err := os.ReadFile(r.File)
	if err != nil {
		return err
	}
	r.Text, r.saved, r.stamp = string(text), string(text), sha256.Sum256(text)
	return nil
}

// Check loads the whole configuration with this file's unsaved text in
// place of what is on disk, and reports every problem it finds - in this
// file or in another, since one file's text can break another's include.
// Nothing is written.
func (r *Rules) Check() []*config.Diag {
	_, diags := r.load()
	r.Diags = diags
	return diags
}

// ErrorsHere is the subset of the last Check's diagnostics that belong to
// this file, for marking lines in the editor.
func (r *Rules) ErrorsHere() []*config.Diag {
	var out []*config.Diag
	for _, d := range r.Diags {
		if d.File == r.File {
			out = append(out, d)
		}
	}
	return out
}

// load builds an engine from the unsaved text.
func (r *Rules) load() (*engine.Engine, []*config.Diag) {
	over := map[string][]byte{r.File: []byte(r.Text)}
	e, diags := engine.LoadWith(r.e.MainFile, over)
	if e != nil {
		e.CacheDir = r.e.CacheDir
	}
	return e, diags
}

// Explain answers what the unsaved rules would do to one file - "Test on
// file" - as text. It can take seconds: content is extracted, so callers
// run it off the main loop. Nothing is written, and the file is not
// touched (GUI design §5.3).
func (r *Rules) Explain(ctx context.Context, path string) (string, error) {
	e, diags := r.load()
	if len(diags) > 0 {
		return "", fmt.Errorf("%s", diags[0])
	}
	x, err := e.ExplainWithChain(ctx, xdg.Expand(path))
	if err != nil {
		return "", err
	}
	return explainText(x), nil
}

// Save writes the text, keeping what was there as NAME.conf.bak. It
// refuses a file that will not load - a window must not leave krino unable
// to run - and refuses to overwrite an edit made elsewhere since the file
// was opened (GUI design §5.3).
func (r *Rules) Save() error {
	if diags := r.Check(); len(diags) > 0 {
		return fmt.Errorf("%s", diags[0])
	}
	on, err := os.ReadFile(r.File)
	if err != nil {
		return err
	}
	if sha256.Sum256(on) != r.stamp {
		return ErrChangedOnDisk
	}
	// The backup is the text being replaced, under the file's own
	// permissions: a rules file can hold real tax numbers, and a backup
	// readable by everyone would leak them.
	mode := os.FileMode(0o600)
	if fi, err := os.Stat(r.File); err == nil {
		mode = fi.Mode().Perm()
	}
	if err := os.WriteFile(r.File+".bak", on, mode); err != nil {
		return err
	}
	text := []byte(r.Text)
	if err := config.Replace(r.File, text); err != nil {
		return err
	}
	r.saved, r.stamp = r.Text, sha256.Sum256(text)
	return nil
}

// SaveOverwriting saves over an edit made elsewhere - the Overwrite the
// caller offers after ErrChangedOnDisk. The other edit is not lost: it
// becomes NAME.conf.bak, as any replaced text does.
func (r *Rules) SaveOverwriting() error {
	on, err := os.ReadFile(r.File)
	if err != nil {
		return err
	}
	r.stamp = sha256.Sum256(on)
	return r.Save()
}

// explainText renders an explanation for the Test on file pane: every
// exclude and rule with each test's answer, the captures a matching rule
// took, and the chain the file alone would get. It is the GUI's own
// rendering - krino explain(1) prints the same traces but no captures or
// chain.
func explainText(x *engine.Explanation) string {
	var b strings.Builder
	fmt.Fprintf(&b, "%s  (directory %s)\n", xdg.Abbrev(x.File.Path), x.Dir.Name)
	if x.Skip != "" {
		fmt.Fprintf(&b, "krino would not look at this file: %s\n", x.Skip)
	}
	if x.Excluded != "" {
		fmt.Fprintf(&b, "krino would set this file aside: %s\n", x.Excluded)
	}
	b.WriteString("\n")
	for _, xt := range x.Excludes {
		status := "no"
		if xt.Match {
			status = "MATCH"
		}
		fmt.Fprintf(&b, "%s: %s\n", xt.Text, status)
		writeTrace(&b, xt.Trace)
	}
	for _, rt := range x.Rules {
		if rt.Stopped != "" {
			fmt.Fprintf(&b, "rule %s: not evaluated, %s\n", rt.Rule.Name, rt.Stopped)
			continue
		}
		status := "no"
		switch {
		case rt.Match:
			status = "MATCH"
		case rt.Trace != nil && rt.Trace.Unknown:
			status = "undecided"
		}
		fmt.Fprintf(&b, "rule %s: %s\n", rt.Rule.Name, status)
		writeTrace(&b, rt.Trace)
		writeCaptures(&b, rt.Captures)
	}
	if x.NoDelete != "" {
		fmt.Fprintf(&b, "\nkrino would skip deleting this file: %s\n", x.NoDelete)
	}
	if len(x.Chain) > 0 {
		b.WriteString("\nthis file alone would get:\n")
		for _, s := range x.Chain {
			switch {
			case s.Skip != "":
				fmt.Fprintf(&b, "  %s skipped: %s\n", s.Kind, s.Skip)
			case s.Dst == "":
				fmt.Fprintf(&b, "  %s\n", s.Kind)
			default:
				fmt.Fprintf(&b, "  %s -> %s\n", s.Kind, xdg.Abbrev(s.Dst))
			}
		}
	}
	return b.String()
}

// writeTrace writes a condition's tree, indented two spaces.
func writeTrace(b *strings.Builder, t *cond.Trace) {
	if t == nil {
		return
	}
	var buf bytes.Buffer
	t.Format(&buf)
	for _, line := range strings.Split(strings.TrimRight(buf.String(), "\n"), "\n") {
		b.WriteString("  " + line + "\n")
	}
}

// writeCaptures lists what a matching rule's patterns captured, numbered as
// its actions' {1}, {2} ... see them.
func writeCaptures(b *strings.Builder, captures []string) {
	for i, c := range captures {
		fmt.Fprintf(b, "  {%d} = %s\n", i+1, c)
	}
}