package tentacle

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"syscall"
)

// LoadLocalSpecs reads an explicit development launch list, not a manifest or
// installation catalog. It does not execute code or discover directories.
func LoadLocalSpecs(path string) ([]Spec, error) {
	file, err := os.OpenFile(path, os.O_RDONLY|syscall.O_NONBLOCK, 0)
	if err != nil {
		return nil, err
	}
	defer file.Close()
	info, err := file.Stat()
	if err != nil {
		return nil, err
	}
	if !info.Mode().IsRegular() {
		return nil, fmt.Errorf("local tentacle list must be a regular file")
	}
	data, err := io.ReadAll(io.LimitReader(file, MaxFrameBytes+1))
	if err != nil {
		return nil, err
	}
	if len(data) > MaxFrameBytes {
		return nil, ErrLimit
	}
	if err := validate_json(data); err != nil {
		return nil, err
	}
	var specs []Spec
	decoder := json.NewDecoder(bytes.NewReader(data))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(&specs); err != nil {
		return nil, err
	}
	if len(specs) > DefaultLimits().Processes {
		return nil, ErrLimit
	}
	seen := make(map[string]bool)
	for _, spec := range specs {
		if err := validate_spec(spec); err != nil {
			return nil, err
		}
		if seen[spec.ID] {
			return nil, fmt.Errorf("duplicate local tentacle ID")
		}
		seen[spec.ID] = true
	}
	return specs, nil
}

// DelegatedParent enables controllers only within the launcher's explicitly
// delegated unit. The reader already lives in its own leaf; it is never moved
// here. Other launchers can supply an already configured absolute parent.
func DelegatedParent() (string, error) {
	data, err := os.ReadFile("/proc/self/cgroup")
	if err != nil {
		return "", err
	}
	parent, err := delegated_parent(string(data))
	if err != nil {
		return "", err
	}
	if err := write_control(parent, "cgroup.subtree_control", "+cpu +memory +pids"); err != nil {
		return "", err
	}
	return parent, nil
}

func delegated_parent(membership string) (string, error) {
	for _, line := range strings.Split(membership, "\n") {
		if !strings.HasPrefix(line, "0::/") {
			continue
		}
		path := strings.TrimPrefix(line, "0::")
		if filepath.Clean(path) != path || filepath.Base(path) != "reader" ||
			!strings.HasSuffix(filepath.Dir(path), ".service") {
			break
		}
		return filepath.Join("/sys/fs/cgroup", filepath.Dir(path)), nil
	}
	return "", fmt.Errorf("%w: reader requires a delegated service with DelegateSubgroup=reader", ErrContainment)
}