package agent

import (
	"fmt"

	"github.com/warrenronsiek/ctask/internal/workspace"
)

// Profile describes a built-in agent. The Default command is what ctask
// invokes when AgentSpec.Command is empty; Type is the canonical name.
type Profile struct {
	Type    string
	Default string
}

// BuiltinProfiles enumerates the v0.6 built-in agents. "custom" is NOT
// in this map — it is the escape hatch with no defaults. Keep this in
// sync with workspace.knownAgentTypes AND workspace.IsBuiltinAgentType
// (update all three together when a new built-in lands).
var BuiltinProfiles = map[string]Profile{
	"claude":   {Type: "claude", Default: "claude"},
	"opencode": {Type: "opencode", Default: "opencode"},
}

// IsKnownType reports whether t is "claude", "opencode", or "custom".
func IsKnownType(t string) bool {
	if t == "custom" {
		return true
	}
	_, ok := BuiltinProfiles[t]
	return ok
}

// Resolved is the launch-ready agent value: a single executable name or
// path, optional arguments, and an env-var map merged AFTER ctask's own
// exported vars at launch time.
type Resolved struct {
	Type    string
	Command string
	Args    []string
	Env     map[string]string
}

// Resolve combines a workspace's AgentSpec with the user-level
// default_agent into a launch-ready Resolved. Resolution rules (per
// v0.6 spec §5):
//
//  1. If spec.Type is empty, fall through to defaultAgent.
//  2. If the resolved type is "custom", spec.Command is required.
//  3. Otherwise, the resolved command is spec.Command if set,
//     else BuiltinProfiles[type].Default.
//  4. Args and Env are carried verbatim from the spec.
//
// Resolve does NOT call exec.LookPath. PATH validation is the launch
// path's job (shell.ExecAgent fails fast with a diagnostic) and
// `ctask agents check`'s job. Keeping Resolve I/O-free makes it
// trivially testable and reusable.
func Resolve(spec workspace.AgentSpec, defaultAgent string) (*Resolved, error) {
	typ := spec.Type
	if typ == "" {
		typ = defaultAgent
	}
	if !IsKnownType(typ) {
		return nil, fmt.Errorf("agent: unknown type %q (must be claude, opencode, or custom)", typ)
	}

	cmd := spec.Command
	if cmd == "" {
		if typ == "custom" {
			return nil, fmt.Errorf("agent: type \"custom\" requires command field")
		}
		cmd = BuiltinProfiles[typ].Default
	}

	return &Resolved{
		Type:    typ,
		Command: cmd,
		Args:    spec.Args,
		Env:     spec.Env,
	}, nil
}