package execenv

import (
	"fmt"
	"io"
	"log/slog"
	"os"
	"path/filepath"
)

// Directories to symlink from the shared ~/.codex/ into the per-task CODEX_HOME.
// The shared directory is created if it doesn't exist, ensuring Codex session
// logs are always written to the global home where users can find them.
var codexSymlinkedDirs = []string{
	"sessions",
}

// Files to symlink from the shared ~/.codex/ into the per-task CODEX_HOME.
// Symlinks share state (e.g. auth tokens) so changes propagate automatically.
var codexSymlinkedFiles = []string{
	"auth.json",
}

// Files to copy from the shared ~/.codex/ into the per-task CODEX_HOME.
// Copies are isolated — changes don't affect the shared home.
var codexCopiedFiles = []string{
	"config.json",
	"config.toml",
	"instructions.md",
}

// CodexHomeOptions carries optional inputs for prepareCodexHomeWithOpts that
// affect the generated per-task config.toml.
type CodexHomeOptions struct {
	// CodexVersion is the detected Codex CLI version (e.g. "0.121.0"). Empty
	// means unknown; on macOS, unknown is treated as "probably broken" so the
	// daemon falls back to danger-full-access for network access. See
	// codex_sandbox.go for details.
	CodexVersion string
	// GOOS overrides the target platform when deciding the sandbox policy.
	// Empty means use runtime.GOOS. Primarily exists so tests can exercise
	// both macOS and Linux paths deterministically.
	GOOS string
}

// prepareCodexHome is a thin wrapper around prepareCodexHomeWithOpts kept for
// tests that don't care about platform-aware sandbox configuration. It
// assumes a Linux-like environment where workspace-write + network_access
// works correctly.
func prepareCodexHome(codexHome string, logger *slog.Logger) error {
	return prepareCodexHomeWithOpts(codexHome, CodexHomeOptions{GOOS: "linux"}, logger)
}

// prepareCodexHomeWithOpts creates a per-task CODEX_HOME directory and seeds
// it with config from the shared ~/.codex/ home. Auth is symlinked (shared),
// config files are copied (isolated). The per-task config.toml gets a
// daemon-managed sandbox block picked by codexSandboxPolicyFor.
func prepareCodexHomeWithOpts(codexHome string, opts CodexHomeOptions, logger *slog.Logger) error {
	sharedHome := resolveSharedCodexHome()

	if err := os.MkdirAll(codexHome, 0o755); err != nil {
		return fmt.Errorf("create codex-home dir: %w", err)
	}

	// Symlink shared directories (sessions) so logs stay in the global home.
	for _, name := range codexSymlinkedDirs {
		src := filepath.Join(sharedHome, name)
		dst := filepath.Join(codexHome, name)
		if err := ensureDirSymlink(src, dst); err != nil {
			logger.Warn("execenv: codex-home dir symlink failed", "dir", name, "error", err)
		}
	}

	// Symlink shared files (auth).
	for _, name := range codexSymlinkedFiles {
		src := filepath.Join(sharedHome, name)
		dst := filepath.Join(codexHome, name)
		if err := ensureSymlink(src, dst); err != nil {
			logger.Warn("execenv: codex-home symlink failed", "file", name, "error", err)
		}
	}

	// Copy config files (isolated per task).
	for _, name := range codexCopiedFiles {
		src := filepath.Join(sharedHome, name)
		dst := filepath.Join(codexHome, name)
		if err := copyFileIfExists(src, dst); err != nil {
			logger.Warn("execenv: codex-home copy failed", "file", name, "error", err)
		}
	}

	// Drop `[[skills.config]]` entries inherited from the user's
	// ~/.codex/config.toml. Codex Desktop writes plugin-backed skills with a
	// `name` and no `path`, which the CLI's stricter TOML parser rejects with
	// `missing field path` and bails out of `thread/start`. Multica writes the
	// agent's active skills directly to `codex-home/skills/`, so the
	// user-level registry is redundant here. See codex_skill_strip.go.
	if err := sanitizeCopiedCodexConfig(filepath.Join(codexHome, "config.toml")); err != nil {
		logger.Warn("execenv: codex-home sanitize config failed", "error", err)
	}

	if err := exposeSharedCodexPluginCache(codexHome, sharedHome); err != nil {
		logger.Warn("execenv: codex-home plugin cache exposure failed", "error", err)
	}

	// Write a daemon-managed sandbox block into config.toml. On macOS we may
	// need to fall back to danger-full-access because of openai/codex#10390;
	// see codex_sandbox.go for the full rationale.
	policy := codexSandboxPolicyFor(opts.GOOS, opts.CodexVersion)
	if err := ensureCodexSandboxConfig(filepath.Join(codexHome, "config.toml"), policy, opts.CodexVersion, logger); err != nil {
		logger.Warn("execenv: codex-home ensure sandbox config failed", "error", err)
	}

	// Disable Codex native multi-agent inside daemon-managed task sessions
	// so the parent thread's `turn/completed` is not interpreted as task
	// completion while spawned subagents are still running. See
	// codex_multi_agent.go for the full rationale and escape hatch.
	if err := ensureCodexMultiAgentConfig(filepath.Join(codexHome, "config.toml"), logger); err != nil {
		logger.Warn("execenv: codex-home ensure multi-agent config failed", "error", err)
	}

	return nil
}

// resolveSharedCodexHome returns the path to the user's shared Codex home.
// Checks $CODEX_HOME first, falls back to ~/.codex.
func resolveSharedCodexHome() string {
	if v := os.Getenv("CODEX_HOME"); v != "" {
		abs, err := filepath.Abs(v)
		if err == nil {
			return abs
		}
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return filepath.Join(os.TempDir(), ".codex") // last resort fallback
	}
	return filepath.Join(home, ".codex")
}

func exposeSharedCodexPluginCache(codexHome, sharedHome string) error {
	src := filepath.Join(sharedHome, "plugins", "cache")
	dst := filepath.Join(codexHome, "plugins", "cache")
	if err := os.MkdirAll(src, 0o755); err != nil {
		return fmt.Errorf("create shared plugin cache dir: %w", err)
	}
	if err := os.MkdirAll(filepath.Dir(dst), 0o755); err != nil {
		return fmt.Errorf("create codex plugin dir: %w", err)
	}

	if fi, err := os.Lstat(dst); err == nil {
		isLink := fi.Mode()&os.ModeSymlink != 0
		if isLink {
			if target, readlinkErr := os.Readlink(dst); readlinkErr == nil && target == src {
				return nil
			}
			if err := os.Remove(dst); err != nil {
				return fmt.Errorf("remove stale plugin cache link: %w", err)
			}
		} else {
			if err := os.RemoveAll(dst); err != nil {
				return fmt.Errorf("remove stale plugin cache path: %w", err)
			}
		}
	}

	if err := createDirLink(src, dst); err != nil {
		return fmt.Errorf("expose shared plugin cache: %w", err)
	}
	return nil
}

// ensureDirSymlink creates a symlink dst → src for a directory.
// Unlike ensureSymlink, it creates the source directory if it doesn't exist,
// so Codex can write to it immediately.
func ensureDirSymlink(src, dst string) error {
	if err := os.MkdirAll(src, 0o755); err != nil {
		return fmt.Errorf("create shared dir %s: %w", src, err)
	}

	// Check if dst already exists.
	if fi, err := os.Lstat(dst); err == nil {
		if fi.Mode()&os.ModeSymlink != 0 {
			target, err := os.Readlink(dst)
			if err == nil && target == src {
				return nil // already correct
			}
			os.Remove(dst)
		} else {
			// Regular file/dir exists — don't overwrite.
			return nil
		}
	}

	return createDirLink(src, dst)
}

// ensureSymlink creates a symlink dst → src. If src doesn't exist, it's a no-op.
// If dst already exists as a correct symlink, it's a no-op. If dst is a broken
// symlink, it's replaced.
func ensureSymlink(src, dst string) error {
	if _, err := os.Stat(src); os.IsNotExist(err) {
		return nil // source doesn't exist — skip
	}

	// Check if dst already exists.
	if fi, err := os.Lstat(dst); err == nil {
		if fi.Mode()&os.ModeSymlink != 0 {
			// It's a symlink — check if it points to the right place.
			target, err := os.Readlink(dst)
			if err == nil && target == src {
				return nil // already correct
			}
			// Wrong target — remove and recreate.
			os.Remove(dst)
		} else {
			// Regular file exists — don't overwrite.
			return nil
		}
	}

	return createFileLink(src, dst)
}

// (The daemon used to write a minimal inline config here; the authoritative
// sandbox/network directives now live in a managed block rendered by
// codex_sandbox.go's ensureCodexSandboxConfig so they can be updated
// idempotently without touching user-managed keys.)

// copyFileIfExists copies src to dst. If src doesn't exist, it's a no-op.
// If dst already exists, it's not overwritten.
func copyFileIfExists(src, dst string) error {
	if _, err := os.Stat(src); os.IsNotExist(err) {
		return nil
	}

	// Don't overwrite existing file.
	if _, err := os.Stat(dst); err == nil {
		return nil
	}

	return copyFile(src, dst)
}

// copyFile copies src to dst unconditionally.
func copyFile(src, dst string) error {
	in, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("open %s: %w", src, err)
	}
	defer in.Close()

	out, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o644)
	if err != nil {
		return fmt.Errorf("create %s: %w", dst, err)
	}
	defer out.Close()

	if _, err := io.Copy(out, in); err != nil {
		return fmt.Errorf("copy %s → %s: %w", src, dst, err)
	}
	return nil
}