package core

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

func readPipe(
	f io.ReadCloser,
	send chan []byte,
	done chan int,
) {
	defer func() {
		done <- 0
	}()
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		data := scanner.Bytes()
		send <- data
	}
}

func Execute(
	source string,
	argv []string,
	env []string,
	state []byte,
	input string,
	timeout time.Duration,
	postProcess func(item Item) Item,
) (
	items []Item,
	newState []byte,
	err error,
) {
	log.Printf("executing %v", argv)

	if len(argv) == 0 {
		return nil, nil, errors.New("empty argv")
	}
	if source == "" {
		return nil, nil, errors.New("empty source")
	}

	stateFile, err := os.CreateTemp("", "intake_state_*")
	if err != nil {
		return nil, nil, fmt.Errorf("error: failed to create temp state file: %v", err)
	}
	defer func() {
		if err := os.Remove(stateFile.Name()); err != nil {
			log.Printf("error: failed to delete %s", stateFile.Name())
		}
	}()

	_, err = stateFile.Write(state)
	if err != nil {
		return nil, nil, fmt.Errorf("error: failed to write state file: %v", err)
	}

	env = append(env, "STATE_PATH="+stateFile.Name())

	ctx, cancel := context.WithTimeout(context.Background(), timeout)
	defer cancel()
	cmd := exec.CommandContext(ctx, argv[0], argv[1:]...)
	cmd.Env = append(os.Environ(), env...)
	cmd.WaitDelay = time.Second * 5

	// Open pipes to the command
	stdin, err := cmd.StdinPipe()
	if err != nil {
		return nil, nil, err
	}
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, nil, err
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return nil, nil, err
	}

	cout := make(chan []byte)
	cerr := make(chan []byte)
	coutDone := make(chan int)
	cerrDone := make(chan int)

	// Routines handling the process i/o
	go readPipe(stdout, cout, coutDone)
	go readPipe(stderr, cerr, cerrDone)

	// Kick off the command
	err = cmd.Start()
	if err != nil {
		return nil, nil, err
	}

	// Write any input to stdin and close it
	io.WriteString(stdin, input)
	stdin.Close()

	// Collect outputs until std{out,err} close
	parseError := false
	stdoutDone := false
	stderrDone := false
monitor:
	for {
		select {
		case data := <-cout:
			var item Item
			err := json.Unmarshal(data, &item)
			if err != nil || item.Id == "" {
				log.Printf("[%s: stdout] %s", source, strings.TrimSpace(string(data)))
				parseError = true
			} else {
				if postProcess != nil {
					item = postProcess(item)
				}
				item.Active = true   // These fields aren't up to
				item.Created = 0     // the action to set and
				item.Source = source // shouldn't be overrideable
				log.Printf("[%s:   item] %s\n", source, item.Id)
				items = append(items, item)
			}

		case data := <-cerr:
			log.Printf("[%s: stderr] %s\n", source, data)

		case <-coutDone:
			stdoutDone = true
			if stdoutDone && stderrDone {
				break monitor
			}

		case <-cerrDone:
			stderrDone = true
			if stdoutDone && stderrDone {
				break monitor
			}
		}
	}

	err = cmd.Wait()
	if ctx.Err() == context.DeadlineExceeded {
		log.Printf("Timed out after %v\n", timeout)
		return nil, nil, err
	} else if exiterr, ok := err.(*exec.ExitError); ok {
		log.Printf("error: %s failed with exit code %d\n", argv[0], exiterr.ExitCode())
		return nil, nil, err
	} else if err != nil {
		log.Printf("error: %s failed with error: %s\n", argv[0], err)
		return nil, nil, err
	}

	if parseError {
		log.Printf("error: could not parse item\n")
		return nil, nil, errors.New("invalid JSON")
	}

	newState, err = os.ReadFile(stateFile.Name())
	if err != nil {
		return nil, nil, fmt.Errorf("error: failed to read state file: %v", err)
	}

	return
}

// Execute an action that takes an item as input and returns the item modified.
// This is basically just a wrapper over [Execute] that handles the input and backfilling.
func ExecuteItemAction(
	item Item,
	argv []string,
	env []string,
	state []byte,
	timeout time.Duration,
	postProcess func(item Item) Item,
) (Item, []byte, error) {
	itemJson, err := json.Marshal(item)
	if err != nil {
		return Item{}, nil, fmt.Errorf("failed to serialize item: %v", err)
	}

	res, newState, err := Execute(item.Source, argv, env, state, string(itemJson), timeout, postProcess)
	if err != nil {
		return Item{}, nil, fmt.Errorf("failed to execute action for %s/%s: %v", item.Source, item.Id, err)
	}
	if len(res) != 1 {
		return Item{}, nil, fmt.Errorf("expected action to produce exactly one item, got %d", len(res))
	}
	newItem := res[0]
	BackfillItem(&newItem, &item)

	return newItem, newState, nil
}