// Package config is the handful of preferences the setup wizard writes down.
//
// It holds defaults, never facts: every field is something a flag or an
// environment variable may override for a given run. Nothing here is required
// for the harness to start, which is what lets a missing file mean "first
// run" rather than "broken install".
package config

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
)

// Filename is the config's name inside the harness config directory.
const Filename = "config.json"

// Version is stamped on every write. It exists so a future change of shape
// has something to branch on rather than guessing from which keys are present.
const Version = 1

// Approval modes, as written to the file. They are spelled out rather than
// stored as a bool, because "approvals: false" reads as if approvals were
// broken rather than as if they were turned off deliberately.
const (
	ApprovalsAsk       = "ask"
	ApprovalsAcceptAll = "accept-all"
)

// Efforts are the values the API's output_config.effort accepts, in the order
// the wizard offers them.
var Efforts = []string{"low", "medium", "high", "xhigh", "max"}

// Themes are the TUI palettes, in the order the wizard offers them. The names
// live here rather than in the tui package so that reading a config never
// depends on a terminal front end being linked in — the eval runner has none.
// The tui package maps each name to actual colours.
var Themes = []string{"ember", "mint", "iris", "mono"}

// Config is what the wizard saves. Every field is optional: an empty one means
// "no preference", which falls through to the flag, the environment, or the
// built-in default, in that order.
type Config struct {
	Version int `json:"version"`
	// Model is an API model id, not a display name.
	Model string `json:"model,omitempty"`
	// Effort is one of Efforts.
	Effort string `json:"effort,omitempty"`
	// Approvals is ApprovalsAsk or ApprovalsAcceptAll.
	Approvals string `json:"approvals,omitempty"`
	// Theme is one of Themes.
	Theme string `json:"theme,omitempty"`
}

// Path is where the config lives: $XDG_CONFIG_HOME/harness/config.json, or
// ~/.config/harness/config.json when XDG_CONFIG_HOME is unset.
func Path() (string, error) {
	dir, err := os.UserConfigDir()
	if err != nil {
		return "", fmt.Errorf("config: no config directory: %w", err)
	}
	return filepath.Join(dir, "harness", Filename), nil
}

// Load reads the config. The boolean reports whether a usable one was found;
// a missing file is not an error, because that is exactly what the first run
// looks like and the wizard is the answer to it.
//
// A file that exists but cannot be read or parsed comes back as an error with
// found=false. The caller is expected to carry on with defaults and say so:
// what it must not do is treat the file as absent, because the next Save would
// then overwrite settings the user still has.
func Load() (Config, bool, error) {
	path, err := Path()
	if err != nil {
		return Config{}, false, err
	}
	raw, err := os.ReadFile(path)
	if errors.Is(err, fs.ErrNotExist) {
		return Config{}, false, nil
	}
	if err != nil {
		return Config{}, false, fmt.Errorf("config: reading %s: %w", path, err)
	}

	var cfg Config
	if err := json.Unmarshal(raw, &cfg); err != nil {
		return Config{}, false, fmt.Errorf("config: %s is not valid JSON: %w", path, err)
	}
	return sanitize(cfg), true, nil
}

// sanitize drops values this build does not recognise. A config written by a
// newer harness, or edited by hand, should degrade to the default for that
// field rather than be forwarded to the API, which would reject the request
// with an error pointing at nothing the user can see.
func sanitize(c Config) Config {
	if !ValidEffort(c.Effort) {
		c.Effort = ""
	}
	if c.Approvals != ApprovalsAsk && c.Approvals != ApprovalsAcceptAll {
		c.Approvals = ""
	}
	if !ValidTheme(c.Theme) {
		c.Theme = ""
	}
	return c
}

// ValidEffort reports whether e is one of the levels the API accepts.
func ValidEffort(e string) bool { return contains(Efforts, e) }

// ValidTheme reports whether name is a palette this build knows.
func ValidTheme(name string) bool { return contains(Themes, name) }

func contains(set []string, v string) bool {
	for _, s := range set {
		if s == v {
			return true
		}
	}
	return false
}

// Save writes the config, creating the directory if it is not there yet.
//
// The write goes to a temporary file that is then renamed over the target, so
// an interrupted or failed write leaves the previous config intact instead of
// truncating it to nothing.
func Save(c Config) error {
	path, err := Path()
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return fmt.Errorf("config: creating %s: %w", filepath.Dir(path), err)
	}

	c.Version = Version
	body, err := json.MarshalIndent(c, "", "  ")
	if err != nil {
		return fmt.Errorf("config: encoding: %w", err)
	}
	body = append(body, '\n')

	tmp, err := os.CreateTemp(filepath.Dir(path), Filename+".*")
	if err != nil {
		return fmt.Errorf("config: %w", err)
	}
	defer os.Remove(tmp.Name()) // no-op once the rename below succeeds
	if _, err := tmp.Write(body); err != nil {
		tmp.Close()
		return fmt.Errorf("config: writing %s: %w", tmp.Name(), err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("config: writing %s: %w", tmp.Name(), err)
	}
	if err := os.Rename(tmp.Name(), path); err != nil {
		return fmt.Errorf("config: replacing %s: %w", path, err)
	}
	return nil
}

// Or returns the first non-empty of its arguments. It is how precedence is
// spelled at the call sites: Or(flag, cfg.Model) is "the flag, else what was
// configured, else whatever the client defaults to".
func Or(vals ...string) string {
	for _, v := range vals {
		if v != "" {
			return v
		}
	}
	return ""
}