// Package preset loads user-editable JSON files that describe how to
// launch agents and processes. SPEC §10: every spawnable thing is a
// preset; patterm has no hard-coded agent or process types.
package preset

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

// Kind is "agent" or "command". Process presets are SPEC §7's
// `command` kind (session-persistent). Terminal entries don't have
// presets — they're created freeform with `kind: terminal` via
// spawn_process.
type Kind string

const (
	KindAgent   Kind = "agent"
	KindCommand Kind = "command"
)

// Preset is one loaded preset file. Agent-only fields stay zero on
// process presets and vice versa.
type Preset struct {
	// Source path (informational; not serialized).
	Path string `json:"-"`
	Kind Kind   `json:"-"`

	Name       string            `json:"name"`
	Argv       []string          `json:"argv"`
	Env        map[string]string `json:"env,omitempty"`
	WorkingDir string            `json:"working_dir,omitempty"`

	// Process-only.
	Shell bool `json:"shell,omitempty"`

	// Agent-only. SPEC §10.
	MCPInjection     *MCPInjection `json:"mcp_injection,omitempty"`
	ReadySignal      *ReadySignal  `json:"ready_signal,omitempty"`
	ChromeTrimHints  []string      `json:"chrome_trim_hints,omitempty"`
}

// MCPInjection covers the strategies SPEC §10 enumerates plus
// `cli_override` for agents (like codex) that accept inline config
// overrides via repeated CLI flags, and `config_env` for agents (like
// opencode) that read their config from an env var. The fields used
// depend on Kind.
type MCPInjection struct {
	Kind       string `json:"kind"` // "flag" | "config_file" | "env_var" | "cli_override" | "config_env"
	Flag       string `json:"flag,omitempty"`
	ConfigPath string `json:"config_path,omitempty"`
	Var        string `json:"var,omitempty"`

	// config_file fields. patterm reads the file at Path, merges in a
	// `patterm` entry under MergeKey, writes the result inside a temp
	// directory laid out so HomeVar + HomePath points at the merged
	// file, and exports HomeVar to the child. Format is inferred from
	// Path's extension (toml or json) when blank.
	Path     string `json:"path,omitempty"`
	MergeKey string `json:"merge_key,omitempty"`
	Format   string `json:"format,omitempty"`
	HomeVar  string `json:"home_var,omitempty"`
	HomePath string `json:"home_path,omitempty"`

	// cli_override fields. patterm emits one `<Flag> <KeyPrefix>.<k>=<v>`
	// pair per MCP setting (command, args) so the agent merges them
	// into its in-memory config without touching any file on disk. Used
	// for codex's `-c key=value`.
	KeyPrefix string `json:"key_prefix,omitempty"`
}

// ReadySignal lets a preset override the default 1s-idle heuristic.
type ReadySignal struct {
	IdleMS  int    `json:"idle_ms,omitempty"`
	Pattern string `json:"pattern,omitempty"`
}

// Set is what the palette consumes.
type Set struct {
	Agents    []*Preset
	Processes []*Preset
}

// Load scans the standard locations under $XDG_CONFIG_HOME/patterm/
// presets/{agents,processes}/*.json. Unknown files are skipped with a
// warning to stderr; the spec is forgiving here.
func Load() (Set, error) {
	base, err := ConfigDir()
	if err != nil {
		return Set{}, err
	}
	if err := os.MkdirAll(base, 0o700); err != nil {
		return Set{}, fmt.Errorf("preset: mkdir %s: %w", base, err)
	}

	// Make sure the default-preset files exist on first run. Idempotent.
	if err := ensureDefaults(base); err != nil {
		return Set{}, err
	}

	agents, err := loadDir(filepath.Join(base, "presets", "agents"), KindAgent)
	if err != nil {
		return Set{}, err
	}
	procs, err := loadDir(filepath.Join(base, "presets", "processes"), KindCommand)
	if err != nil {
		return Set{}, err
	}
	return Set{Agents: agents, Processes: procs}, nil
}

// ConfigDir resolves $XDG_CONFIG_HOME/patterm (with the conventional
// fallback to ~/.config/patterm).
func ConfigDir() (string, error) {
	if h := os.Getenv("XDG_CONFIG_HOME"); h != "" {
		return filepath.Join(h, "patterm"), nil
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(home, ".config", "patterm"), nil
}

func loadDir(dir string, kind Kind) ([]*Preset, error) {
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return nil, fmt.Errorf("preset: mkdir %s: %w", dir, err)
	}
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, fmt.Errorf("preset: read %s: %w", dir, err)
	}
	var out []*Preset
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".json") {
			continue
		}
		path := filepath.Join(dir, e.Name())
		p, err := loadFile(path, kind)
		if err != nil {
			fmt.Fprintf(os.Stderr, "patterm: preset %s: %v\n", path, err)
			continue
		}
		out = append(out, p)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
	return out, nil
}

func loadFile(path string, kind Kind) (*Preset, error) {
	b, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	var p Preset
	if err := json.Unmarshal(b, &p); err != nil {
		return nil, err
	}
	if p.Name == "" {
		return nil, errors.New("missing 'name'")
	}
	if len(p.Argv) == 0 && !p.Shell {
		return nil, errors.New("missing 'argv'")
	}
	p.Path = path
	p.Kind = kind
	return &p, nil
}

// ResolvedArgv returns the argv to actually exec, handling the
// process-preset "shell: true" case (SPEC §10).
func (p *Preset) ResolvedArgv() []string {
	if p.Shell && len(p.Argv) > 0 {
		return []string{"sh", "-lc", strings.Join(p.Argv, " ")}
	}
	return p.Argv
}

// ensureDefaults writes default agent presets (claude/codex/opencode)
// and a sample process preset on first run. Never overwrites existing
// user files.
func ensureDefaults(base string) error {
	defaults := []struct {
		rel  string
		body string
	}{
		{
			"presets/agents/claude.json",
			`{
  "name": "claude",
  "argv": ["claude"],
  "mcp_injection": { "kind": "flag", "flag": "--mcp-config" },
  "ready_signal": { "idle_ms": 1000 },
  "chrome_trim_hints": [
    "^Welcome to Claude Code",
    "^/help for help",
    "^cwd:",
    "^\\s*│\\s*>",
    "^\\s*╭─+╮$",
    "^\\s*╰─+╯$",
    "^\\? for shortcuts"
  ]
}
`,
		},
		{
			"presets/agents/codex.json",
			`{
  "name": "codex",
  "argv": ["codex"],
  "mcp_injection": {
    "kind": "cli_override",
    "flag": "-c",
    "key_prefix": "mcp_servers.patterm",
    "format": "toml"
  },
  "ready_signal": { "idle_ms": 1000 },
  "chrome_trim_hints": [
    "^OpenAI Codex",
    "^\\s*model:",
    "^\\s*workdir:",
    "^>_$",
    "^\\s*▌"
  ]
}
`,
		},
		{
			"presets/agents/opencode.json",
			`{
  "name": "opencode",
  "argv": ["opencode"],
  "mcp_injection": {
    "kind": "config_env",
    "path": "~/.config/opencode/opencode.json",
    "merge_key": "mcp",
    "format": "json",
    "var": "OPENCODE_CONFIG_CONTENT"
  },
  "ready_signal": { "idle_ms": 1000 },
  "chrome_trim_hints": [
    "^\\s*█",
    "^\\s*opencode v",
    "^\\s*~/",
    "^\\s*>_"
  ]
}
`,
		},
		{
			"presets/processes/shell.json",
			`{
  "name": "shell",
  "argv": ["__SHELL__"]
}
`,
		},
	}
	for _, d := range defaults {
		full := filepath.Join(base, d.rel)
		if _, err := os.Stat(full); err == nil {
			continue
		}
		if err := os.MkdirAll(filepath.Dir(full), 0o700); err != nil {
			return err
		}
		body := d.body
		if strings.Contains(body, "__SHELL__") {
			shell := os.Getenv("SHELL")
			if shell == "" {
				shell = "/bin/sh"
			}
			body = strings.ReplaceAll(body, "__SHELL__", shell)
		}
		if err := os.WriteFile(full, []byte(body), 0o600); err != nil {
			return err
		}
	}
	return nil
}