package sources

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"sync"

	"gitea.maximumdirect.net/ejr/feedkit/config"
	"gitea.maximumdirect.net/ejr/feedkit/transport"
)

// HTTPSource is a reusable helper for polling HTTP-backed sources.
//
// It centralizes generic source config parsing (`params.url`,
// `params.user_agent`, and optional `params.conditional`), default HTTP client
// setup, and conditional GET validator handling. Concrete daemon sources remain
// responsible for decoding the response body and constructing events.
type HTTPSource struct {
	Driver                 string
	Name                   string
	URL                    string
	UserAgent              string
	Accept                 string
	Conditional            bool
	ResponseBodyLimitBytes int64
	Client                 *http.Client

	mu         sync.Mutex
	validators transport.HTTPValidators
}

// NewHTTPSource builds a generic HTTP polling helper from SourceConfig.
//
// Required params:
//   - params.url
//   - params.user_agent
//
// Optional params:
//   - params.conditional (default true): enable conditional GET using cached
//     ETag / Last-Modified validators
func NewHTTPSource(driver string, cfg config.SourceConfig, accept string) (*HTTPSource, error) {
	name := strings.TrimSpace(cfg.Name)
	if name == "" {
		return nil, fmt.Errorf("%s: name is required", driver)
	}
	if cfg.Params == nil {
		return nil, fmt.Errorf("%s %q: params are required (need params.url and params.user_agent)", driver, cfg.Name)
	}

	url, ok := cfg.ParamString("url", "URL")
	if !ok {
		return nil, fmt.Errorf("%s %q: params.url is required", driver, cfg.Name)
	}

	userAgent, ok := cfg.ParamString("user_agent", "userAgent")
	if !ok {
		return nil, fmt.Errorf("%s %q: params.user_agent is required", driver, cfg.Name)
	}

	conditional := true
	if _, exists := cfg.Params["conditional"]; exists {
		var ok bool
		conditional, ok = cfg.ParamBool("conditional")
		if !ok {
			return nil, fmt.Errorf("source %q: params.conditional must be a boolean", cfg.Name)
		}
	}

	timeout := transport.DefaultHTTPTimeout
	if _, exists := cfg.Params["http_timeout"]; exists {
		var ok bool
		timeout, ok = cfg.ParamDuration("http_timeout")
		if !ok || timeout <= 0 {
			return nil, fmt.Errorf("source %q: params.http_timeout must be a positive duration", cfg.Name)
		}
	}

	bodyLimit := transport.DefaultHTTPResponseBodyLimitBytes
	if _, exists := cfg.Params["http_response_body_limit_bytes"]; exists {
		rawLimit, ok := cfg.ParamInt("http_response_body_limit_bytes")
		if !ok || rawLimit <= 0 {
			return nil, fmt.Errorf("source %q: params.http_response_body_limit_bytes must be a positive integer", cfg.Name)
		}
		bodyLimit = int64(rawLimit)
	}

	return &HTTPSource{
		Driver:                 driver,
		Name:                   name,
		URL:                    url,
		UserAgent:              userAgent,
		Accept:                 accept,
		Conditional:            conditional,
		ResponseBodyLimitBytes: bodyLimit,
		Client:                 transport.NewHTTPClient(timeout),
	}, nil
}

// FetchBytesIfChanged fetches the configured URL and reports whether the
// upstream content changed. An unchanged 304 response returns changed=false
// with no body and no error.
func (s *HTTPSource) FetchBytesIfChanged(ctx context.Context) ([]byte, bool, error) {
	client := s.Client
	if client == nil {
		client = transport.NewHTTPClient(transport.DefaultHTTPTimeout)
	}

	s.mu.Lock()
	validators := s.validators
	s.mu.Unlock()

	bodyLimit := s.ResponseBodyLimitBytes
	if bodyLimit <= 0 {
		bodyLimit = transport.DefaultHTTPResponseBodyLimitBytes
	}

	body, changed, next, err := transport.FetchBodyIfChangedWithLimit(
		ctx,
		client,
		s.URL,
		s.UserAgent,
		s.Accept,
		s.Conditional,
		validators,
		bodyLimit,
	)
	if err != nil {
		return nil, false, fmt.Errorf("%s %q: %w", s.Driver, s.Name, err)
	}

	if s.Conditional {
		s.mu.Lock()
		s.validators = next
		s.mu.Unlock()
	}

	return body, changed, nil
}

// FetchJSONIfChanged fetches the configured URL and returns the raw response
// body as json.RawMessage when content changed. An unchanged 304 response
// returns changed=false with a nil body and no error.
func (s *HTTPSource) FetchJSONIfChanged(ctx context.Context) (json.RawMessage, bool, error) {
	body, changed, err := s.FetchBytesIfChanged(ctx)
	if err != nil || !changed {
		return nil, changed, err
	}
	return json.RawMessage(body), true, nil
}