// Package restic wraps the restic CLI: locate the binary, run it
// with --json, parse streamed events. The agent calls this; the
// control-plane never invokes restic.
package restic

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"strings"
	"time"
)

// Locate resolves the path to the restic binary. Honour an explicit
// override if provided, else fall back to PATH.
func Locate(override string) (string, error) {
	if override != "" {
		if _, err := exec.LookPath(override); err == nil {
			return override, nil
		}
		return "", fmt.Errorf("restic: configured path %q not executable", override)
	}
	bin, err := exec.LookPath("restic")
	if err != nil {
		return "", fmt.Errorf("restic: not on PATH: %w", err)
	}
	return bin, nil
}

// Env is the per-invocation context for a restic command.
//
// RepoURL is the bare URL as the operator typed it — no embedded
// credentials. RepoUsername (optional) carries the HTTP basic-auth
// user for `rest:` repos. The merged URL (with `user:pass@host`
// embedded) is built once inside envSlice() at the moment of exec
// and fed straight to the subprocess via RESTIC_REPOSITORY; we
// never assign it back to Env, never pass it to slog. If anything
// in this package ever needs to *log* a URL, use RedactURL.
type Env struct {
	Bin           string            // path to restic binary
	RepoURL       string            // RESTIC_REPOSITORY (no embedded creds)
	RepoUsername  string            // optional HTTP basic-auth user for rest: URLs
	RepoPassword  string            // doubles as RESTIC_PASSWORD and (for rest:) HTTP basic-auth password
	ExtraEnv      map[string]string // any other RESTIC_* / passthrough
	WorkDir       string            // CWD; default = current
}

// EventKind enumerates what we care about in restic's --json output
// for `backup`. Restic's other commands emit different shapes; we
// switch on message_type.
type EventKind string

const (
	EventStatus     EventKind = "status"      // periodic progress
	EventVerbose    EventKind = "verbose_status"
	EventSummary    EventKind = "summary"     // emitted once at end of backup
	EventErrorEvent EventKind = "error"
)

// BackupStatus mirrors the JSON status emitted by `restic backup`.
type BackupStatus struct {
	MessageType    string  `json:"message_type"`
	PercentDone    float64 `json:"percent_done"`
	TotalFiles     int64   `json:"total_files"`
	FilesDone      int64   `json:"files_done"`
	TotalBytes     int64   `json:"total_bytes"`
	BytesDone      int64   `json:"bytes_done"`
	SecondsElapsed int64   `json:"seconds_elapsed"`
	SecondsRem     int64   `json:"seconds_remaining"`
}

// BackupSummary mirrors the JSON summary block.
type BackupSummary struct {
	MessageType         string  `json:"message_type"`
	FilesNew            int64   `json:"files_new"`
	FilesChanged        int64   `json:"files_changed"`
	FilesUnmodified     int64   `json:"files_unmodified"`
	DirsNew             int64   `json:"dirs_new"`
	DirsChanged         int64   `json:"dirs_changed"`
	DirsUnmodified      int64   `json:"dirs_unmodified"`
	DataAdded           int64   `json:"data_added"`
	TotalFilesProcessed int64   `json:"total_files_processed"`
	TotalBytesProcessed int64   `json:"total_bytes_processed"`
	TotalDuration       float64 `json:"total_duration"`
	SnapshotID          string  `json:"snapshot_id"`
}

// LineHandler receives every stdout/stderr line. event is non-nil
// when the line is a recognised JSON status; raw always carries the
// original text (so we can also tee to job_logs as `stdout`).
type LineHandler func(stream string, raw string, event any)

// RunBackup executes `restic backup [paths...]` with --json and pumps
// status/summary into handle. Returns nil on success (exit code 0
// or 3 — 3 means "completed but had issues"; restic considers it a
// success). Other exit codes propagate as an error.
func (e Env) RunBackup(ctx context.Context, paths, excludes, tags []string, handle LineHandler) (*BackupSummary, error) {
	args := []string{"backup", "--json"}
	for _, ex := range excludes {
		args = append(args, "--exclude", ex)
	}
	for _, tag := range tags {
		args = append(args, "--tag", tag)
	}
	args = append(args, paths...)

	cmd := exec.CommandContext(ctx, e.Bin, args...)
	cmd.Env = e.envSlice()
	cmd.Dir = e.WorkDir

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, fmt.Errorf("restic backup: stdout pipe: %w", err)
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return nil, fmt.Errorf("restic backup: stderr pipe: %w", err)
	}

	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("restic backup: start: %w", err)
	}

	var summary *BackupSummary
	done := make(chan error, 2)
	go func() { done <- pumpStdout(stdout, handle, &summary) }()
	go func() { done <- pumpStderr(stderr, handle) }()

	// Wait for both pumps + the process.
	for i := 0; i < 2; i++ {
		if err := <-done; err != nil && handle != nil {
			handle("event", fmt.Sprintf("pump error: %v", err), nil)
		}
	}
	werr := cmd.Wait()
	if werr != nil {
		var ee *exec.ExitError
		if errors.As(werr, &ee) && ee.ExitCode() == 3 {
			// "incomplete backup" — restic still produced a snapshot.
			return summary, nil
		}
		return summary, fmt.Errorf("restic backup: %w", werr)
	}
	return summary, nil
}

// RunInit executes `restic init` against the configured repo. Returns
// nil on success. Restic init's output is small and not JSON-rich;
// we tee stdout/stderr verbatim through handle so the operator sees
// the same lines they'd see at the CLI ("created restic repository
// <id> at <url>" on success, "config file already exists" on a
// re-init attempt, etc.).
func (e Env) RunInit(ctx context.Context, handle LineHandler) error {
	cmd := exec.CommandContext(ctx, e.Bin, "init")
	cmd.Env = e.envSlice()
	cmd.Dir = e.WorkDir

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return fmt.Errorf("restic init: stdout pipe: %w", err)
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return fmt.Errorf("restic init: stderr pipe: %w", err)
	}

	if err := cmd.Start(); err != nil {
		return fmt.Errorf("restic init: start: %w", err)
	}

	// Sniff for "config file already exists" on stderr; if we see it
	// we'll treat the non-zero exit as a soft success — running init
	// against an already-initialised repo is a no-op semantically,
	// not a failure. Wraps the caller's handle so the line still
	// gets streamed verbatim to the operator-facing log.
	alreadyInited := false
	sniff := func(stream, line string, ev any) {
		if stream == "stderr" && strings.Contains(line, "config file already exists") {
			alreadyInited = true
		}
		if handle != nil {
			handle(stream, line, ev)
		}
	}

	done := make(chan error, 2)
	go func() { done <- pumpPlain(stdout, "stdout", sniff) }()
	go func() { done <- pumpPlain(stderr, "stderr", sniff) }()
	for i := 0; i < 2; i++ {
		if err := <-done; err != nil && handle != nil {
			handle("event", fmt.Sprintf("pump error: %v", err), nil)
		}
	}
	if werr := cmd.Wait(); werr != nil {
		if alreadyInited {
			if handle != nil {
				handle("event", "repo already initialised — treating as success", nil)
			}
			return nil
		}
		return fmt.Errorf("restic init: %w", werr)
	}
	return nil
}

func pumpPlain(r io.Reader, stream string, handle LineHandler) error {
	scanner := bufio.NewScanner(r)
	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for scanner.Scan() {
		if handle != nil {
			handle(stream, scanner.Text(), nil)
		}
	}
	return scanner.Err()
}

// envSlice converts Env's typed fields into the os/exec env shape.
//
// Deliberately does NOT inherit the parent process's environment:
// any RESTIC_* / AWS_* / B2_* vars in the operator's shell or the
// systemd unit's Environment= clause are filtered out so the
// control-plane is the unambiguous source of truth.
//
// HOME / XDG_CACHE_HOME are set explicitly because restic insists
// on one or the other for its cache dir; without it the command
// fails before ever talking to the repo.
func (e Env) envSlice() []string {
	home := "/var/lib/restic-manager"
	if h, ok := e.ExtraEnv["HOME"]; ok && h != "" {
		home = h
	} else if h := os.Getenv("HOME"); h != "" {
		home = h
	}
	xdg := home + "/.cache"
	if x, ok := e.ExtraEnv["XDG_CACHE_HOME"]; ok && x != "" {
		xdg = x
	} else if x := os.Getenv("XDG_CACHE_HOME"); x != "" {
		xdg = x
	}
	out := []string{
		"RESTIC_REPOSITORY=" + mergeRestCreds(e.RepoURL, e.RepoUsername, e.RepoPassword),
		"RESTIC_PASSWORD=" + e.RepoPassword,
		// Feed restic via env-only — keeps creds off ps(1).
		"PATH=/usr/local/bin:/usr/bin:/bin",
		"HOME=" + home,
		"XDG_CACHE_HOME=" + xdg,
	}
	for k, v := range e.ExtraEnv {
		// HOME / XDG_CACHE_HOME already merged in above.
		if k == "HOME" || k == "XDG_CACHE_HOME" {
			continue
		}
		out = append(out, k+"="+v)
	}
	return out
}

func pumpStdout(r io.Reader, handle LineHandler, summary **BackupSummary) error {
	scanner := bufio.NewScanner(r)
	scanner.Buffer(make([]byte, 0, 64*1024), 4*1024*1024) // status lines can get long
	for scanner.Scan() {
		line := scanner.Text()
		if handle == nil {
			continue
		}
		// Sniff message_type without a full Unmarshal so non-JSON
		// lines (very rare on stdout, but possible) survive.
		if !strings.HasPrefix(line, "{") {
			handle("stdout", line, nil)
			continue
		}
		var probe struct {
			MessageType string `json:"message_type"`
		}
		if err := json.Unmarshal([]byte(line), &probe); err != nil {
			handle("stdout", line, nil)
			continue
		}
		switch EventKind(probe.MessageType) {
		case EventStatus, EventVerbose:
			var ev BackupStatus
			if json.Unmarshal([]byte(line), &ev) == nil {
				handle("event", line, ev)
				continue
			}
		case EventSummary:
			var ev BackupSummary
			if json.Unmarshal([]byte(line), &ev) == nil {
				if summary != nil {
					s := ev
					*summary = &s
				}
				handle("event", line, ev)
				continue
			}
		case EventErrorEvent:
			handle("event", line, nil)
			continue
		}
		handle("stdout", line, nil)
	}
	return scanner.Err()
}

func pumpStderr(r io.Reader, handle LineHandler) error {
	scanner := bufio.NewScanner(r)
	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for scanner.Scan() {
		if handle != nil {
			handle("stderr", scanner.Text(), nil)
		}
	}
	return scanner.Err()
}

// suppress unused-time false-positive when nothing else in this file
// uses time but the file is part of a package that grows over time
var _ = time.Now