package main

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"time"

	stdio "git.novox.be/novox/mesh-sdk/go"
)

// The values other modules keep on the bus for a block they contributed (novox/hq ADR 0260).
//
// A block that `shows` a state is rendered as a custom block running `i3status-value <state> <key>`.
// i3status-rs cannot reach the bus, and this bundle can: the node's runtime launched it, and the mesh
// granted this module a read of every state the modules on its machine offer the bar. So it watches each
// state its bars name and leaves the value's text in this module's own directory, where the block's
// command reads it. No file of another module is read, and nothing but the bus passes between them.

// valueCall is how a bar names a value: the command the template renders.
var valueCall = regexp.MustCompile(`i3status-value ([a-z0-9][a-z0-9-]*\.[a-z0-9][a-z0-9-]*) ([^\s"]+)`)

// Wanted is one state and key a bar shows.
type Wanted struct{ State, Key string }

func (w Wanted) file() string { return w.State + "@" + w.Key }

// wantedIn is every value the bars' files name, each once, in order.
func wantedIn(files []string) []Wanted {
	seen := map[Wanted]bool{}
	for _, f := range files {
		raw, err := os.ReadFile(f)
		if err != nil {
			continue
		}
		for _, m := range valueCall.FindAllStringSubmatch(string(raw), -1) {
			seen[Wanted{State: m[1], Key: m[2]}] = true
		}
	}
	out := make([]Wanted, 0, len(seen))
	for w := range seen {
		out = append(out, w)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].file() < out[j].file() })
	return out
}

// valuesDir is where the values are left: the account's runtime directory, gone at logout.
func valuesDir() string {
	return filepath.Join(runUserDir, strconv.Itoa(os.Getuid()), "i3status-rust", "values")
}

// keep writes one change of a value to its file: the value's `text`, or no file once it is deleted.
func keep(dir string, w Wanted, c stdio.StateChange) error {
	path := filepath.Join(dir, w.file())
	if c.Op == "delete" || c.Op == "purge" {
		if err := os.Remove(path); err != nil && !os.IsNotExist(err) {
			return err
		}
		return nil
	}
	var v struct {
		Text string `json:"text"`
	}
	if err := json.Unmarshal(c.Value, &v); err != nil {
		return fmt.Errorf("%s's value for %s has no text: %w", w.State, w.Key, err)
	}
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return err
	}
	tmp := path + ".new"
	if err := os.WriteFile(tmp, []byte(v.Text+"\n"), 0o600); err != nil {
		return err
	}
	return os.Rename(tmp, path)
}

// Watcher is a function that watches one key of one state; the SDK's in the bundle, a fake in a test.
type Watcher func(state, key string, handle func(stdio.StateChange) error) error

// followValues watches every value the bars name, starting the ones not yet watched each time it is
// called; one the runtime refuses — a read not granted yet — is tried again the next time.
func followValues(files []string, dir string, watching map[Wanted]bool, watch Watcher) []string {
	var said []string
	for _, w := range wantedIn(files) {
		if watching[w] {
			continue
		}
		w := w
		err := watch(w.State, w.Key, func(c stdio.StateChange) error { return keep(dir, w, c) })
		if err != nil {
			said = append(said, fmt.Sprintf("cannot watch %s %s: %v", w.State, w.Key, err))
			continue
		}
		watching[w] = true
	}
	return said
}

// FollowValues runs followValues every half minute for as long as the bundle runs, so a block a push
// adds is followed without a restart.
func FollowValues() {
	watching := map[Wanted]bool{}
	watch := func(state, key string, handle func(stdio.StateChange) error) error {
		return stdio.State(state).Watch(key, handle)
	}
	for {
		files, _ := filepath.Glob(filepath.Join(configDir(), "*.toml"))
		for _, s := range followValues(files, valuesDir(), watching, watch) {
			fmt.Fprintln(os.Stderr, "i3status-rust:", s)
		}
		time.Sleep(30 * time.Second)
	}
}