// Package lockfile defines agent-lib lockfile schema v2: the deterministic
// JSON document pinning vendored sources, their selection and renames.
package lockfile

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"sort"
)

const (
	// Version is the schema version of lockfile v2.
	Version = 2
	// FileName is the lockfile name inside the work repository root.
	FileName = "agent-lib.lock.json"
)

// ErrNotExist reports that no lockfile exists yet.
var ErrNotExist = errors.New("no lockfile found")

// Content type names used across discovery, lockfile and the external area.
const (
	TypeSkill   = "skills"
	TypeCommand = "commands"
	TypeAgent   = "agents"
	TypeMcp     = "mcp"
)

// Types lists all content types in canonical order.
var Types = []string{TypeSkill, TypeCommand, TypeAgent, TypeMcp}

// Discovery configures where items are found inside a source repository.
// Empty values select the standard layouts (skills/, commands/, agents/, mcp/
// relative to Root).
type Discovery struct {
	Root        string `json:"root,omitempty"`
	SkillsDir   string `json:"skills_dir,omitempty"`
	CommandsDir string `json:"commands_dir,omitempty"`
	AgentsDir   string `json:"agents_dir,omitempty"`
	McpDir      string `json:"mcp_dir,omitempty"`
}

func (d Discovery) Resolve() Discovery {
	r := d
	if r.SkillsDir == "" {
		r.SkillsDir = TypeSkill
	}
	if r.CommandsDir == "" {
		r.CommandsDir = TypeCommand
	}
	if r.AgentsDir == "" {
		r.AgentsDir = TypeAgent
	}
	if r.McpDir == "" {
		r.McpDir = TypeMcp
	}
	return r
}

// SelectionMode is either "all" or "include".
type SelectionMode string

const (
	ModeAll     SelectionMode = "all"
	ModeInclude SelectionMode = "include"
)

// Selection expresses what enters the work repository: everything minus
// Exclude (mode all), or exactly Include (mode include).
type Selection struct {
	Mode    SelectionMode `json:"mode"`
	Exclude []string      `json:"exclude,omitempty"`
	Include []string      `json:"include,omitempty"`
}

// Source pins one vendored git source.
type Source struct {
	URL       string              `json:"url"`
	Ref       string              `json:"ref"`
	Rev       string              `json:"rev"`
	Discovery *Discovery          `json:"discovery,omitempty"`
	Selection Selection           `json:"selection"`
	Renames   map[string]string   `json:"renames,omitempty"`
	Inventory map[string][]string `json:"inventory,omitempty"`
	Warnings  []string            `json:"warnings,omitempty"`
}

// Lockfile is the root document of schema v2.
type Lockfile struct {
	Version int                `json:"version"`
	Sources map[string]*Source `json:"sources"`
}

// New returns an empty lockfile v2.
func New() *Lockfile {
	return &Lockfile{Version: Version, Sources: map[string]*Source{}}
}

// Load reads the lockfile at path. A missing file yields ErrNotExist.
func Load(path string) (*Lockfile, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil, ErrNotExist
		}
		return nil, err
	}
	var l Lockfile
	if err := json.Unmarshal(data, &l); err != nil {
		return nil, fmt.Errorf("lockfile %s is not valid JSON: %w", path, err)
	}
	if l.Version != Version {
		return nil, fmt.Errorf("lockfile %s has schema version %d, want %d", path, l.Version, Version)
	}
	if l.Sources == nil {
		l.Sources = map[string]*Source{}
	}
	return &l, nil
}

// Save canonically orders all slices and maps, then writes deterministic JSON.
func (l *Lockfile) Save(path string) error {
	for _, src := range l.Sources {
		sort.Strings(src.Selection.Exclude)
		sort.Strings(src.Selection.Include)
		sort.Strings(src.Warnings)
		for _, items := range src.Inventory {
			sort.Strings(items)
		}
	}
	data, err := Marshal(l)
	if err != nil {
		return err
	}
	return os.WriteFile(path, data, 0o644)
}

// Marshal renders the lockfile as deterministic bytes: fixed field order via
// struct layout, sorted map keys, two-space indent, trailing newline.
func Marshal(l *Lockfile) ([]byte, error) {
	data, err := json.MarshalIndent(l, "", "  ")
	if err != nil {
		return nil, err
	}
	return append(data, '\n'), nil
}